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These species are subdivisions of genus types that can occur in partly unstable air with limited convection. The species castellanus appears when a mostly stable stratocumuliform or cirriform layer becomes disturbed by localized areas of airmass instability, usually in the morning or afternoon. This results in the formation of embedded cumuliform buildups arising from a common stratiform base. Castellanus resembles the turrets of a castle when viewed from the side, and can be found with stratocumuliform genera at any tropospheric altitude level and with limited-convective patches of high-level cirrus. Tufted clouds of the more detached floccus species are subdivisions of genus-types which may be cirriform or stratocumuliform in overall structure. They are sometimes seen with cirrus, cirrocumulus, altocumulus, and stratocumulus.
A newly recognized species of stratocumulus or altocumulus has been given the name volutus, a roll cloud that can occur ahead of a cumulonimbus formation. There are some volutus clouds that form as a consequence of interactions with specific geographical features rather than with a parent cloud. Perhaps the strangest geographically specific cloud of this type is the Morning Glory, a rolling cylindrical cloud that appears unpredictably over the Gulf of Carpentaria in Northern Australia. Associated with a powerful "ripple" in the atmosphere, the cloud may be "surfed" in glider aircraft.
Unstable or mostly unstable
More general airmass instability in the troposphere tends to produce clouds of the more freely convective cumulus genus type, whose species are mainly indicators of degrees of atmospheric instability and resultant vertical development of the clouds. A cumulus cloud initially forms in the low level of the troposphere as a cloudlet of the species humilis that shows only slight vertical development. If the air becomes more unstable, the cloud tends to grow vertically into the species mediocris, then strongly convective congestus, the tallest cumulus species which is the same type that the International Civil Aviation Organization refers to as 'towering cumulus'. | Cloud | Wikipedia | 445 | 47515 | https://en.wikipedia.org/wiki/Cloud | Physical sciences | Earth science | null |
With highly unstable atmospheric conditions, large cumulus may continue to grow into even more strongly convective cumulonimbus calvus (essentially a very tall congestus cloud that produces thunder), then ultimately into the species capillatus when supercooled water droplets at the top of the cloud turn into ice crystals giving it a cirriform appearance.
Varieties
Genus and species types are further subdivided into varieties whose names can appear after the species name to provide a fuller description of a cloud. Some cloud varieties are not restricted to a specific altitude level or form, and can therefore be common to more than one genus or species.
Opacity-based
All cloud varieties fall into one of two main groups. One group identifies the opacities of particular low and mid-level cloud structures and comprises the varieties translucidus (thin translucent), perlucidus (thick opaque with translucent or very small clear breaks), and opacus (thick opaque). These varieties are always identifiable for cloud genera and species with variable opacity. All three are associated with the stratiformis species of altocumulus and stratocumulus. However, only two varieties are seen with altostratus and stratus nebulosus whose uniform structures prevent the formation of a perlucidus variety. Opacity-based varieties are not applied to high clouds because they are always translucent, or in the case of cirrus spissatus, always opaque.
Pattern-based
A second group describes the occasional arrangements of cloud structures into particular patterns that are discernible by a surface-based observer (cloud fields usually being visible only from a significant altitude above the formations). These varieties are not always present with the genera and species with which they are otherwise associated, but only appear when atmospheric conditions favor their formation. Intortus and vertebratus varieties occur on occasion with cirrus fibratus. They are respectively filaments twisted into irregular shapes, and those that are arranged in fishbone patterns, usually by uneven wind currents that favor the formation of these varieties. The variety radiatus is associated with cloud rows of a particular type that appear to converge at the horizon. It is sometimes seen with the fibratus and uncinus species of cirrus, the stratiformis species of altocumulus and stratocumulus, the mediocris and sometimes humilis species of cumulus, and with the genus altostratus. | Cloud | Wikipedia | 507 | 47515 | https://en.wikipedia.org/wiki/Cloud | Physical sciences | Earth science | null |
Another variety, duplicatus (closely spaced layers of the same type, one above the other), is sometimes found with cirrus of both the fibratus and uncinus species, and with altocumulus and stratocumulus of the species stratiformis and lenticularis. The variety undulatus (having a wavy undulating base) can occur with any clouds of the species stratiformis or lenticularis, and with altostratus. It is only rarely observed with stratus nebulosus. The variety lacunosus is caused by localized downdrafts that create circular holes in the form of a honeycomb or net. It is occasionally seen with cirrocumulus and altocumulus of the species stratiformis, castellanus, and floccus, and with stratocumulus of the species stratiformis and castellanus.
Combinations
It is possible for some species to show combined varieties at one time, especially if one variety is opacity-based and the other is pattern-based. An example of this would be a layer of altocumulus stratiformis arranged in seemingly converging rows separated by small breaks. The full technical name of a cloud in this configuration would be altocumulus stratiformis radiatus perlucidus, which would identify respectively its genus, species, and two combined varieties.
Other types
Supplementary features and accessory clouds are not further subdivisions of cloud types below the species and variety level. Rather, they are either hydrometeors or special cloud types with their own Latin names that form in association with certain cloud genera, species, and varieties. Supplementary features, whether in the form of clouds or precipitation, are directly attached to the main genus-cloud. Accessory clouds, by contrast, are generally detached from the main cloud.
Precipitation-based supplementary features
One group of supplementary features are not actual cloud formations, but precipitation that falls when water droplets or ice crystals that make up visible clouds have grown too heavy to remain aloft. Virga is a feature seen with clouds producing precipitation that evaporates before reaching the ground, these being of the genera cirrocumulus, altocumulus, altostratus, nimbostratus, stratocumulus, cumulus, and cumulonimbus. | Cloud | Wikipedia | 479 | 47515 | https://en.wikipedia.org/wiki/Cloud | Physical sciences | Earth science | null |
When the precipitation reaches the ground without completely evaporating, it is designated as the feature praecipitatio. This normally occurs with altostratus opacus, which can produce widespread but usually light precipitation, and with thicker clouds that show significant vertical development. Of the latter, upward-growing cumulus mediocris produces only isolated light showers, while downward growing nimbostratus is capable of heavier, more extensive precipitation. Towering vertical clouds have the greatest ability to produce intense precipitation events, but these tend to be localized unless organized along fast-moving cold fronts. Showers of moderate to heavy intensity can fall from cumulus congestus clouds. Cumulonimbus, the largest of all cloud genera, has the capacity to produce very heavy showers. Low stratus clouds usually produce only light precipitation, but this always occurs as the feature praecipitatio due to the fact this cloud genus lies too close to the ground to allow for the formation of virga.
Cloud-based supplementary features
Incus is the most type-specific supplementary feature, seen only with cumulonimbus of the species capillatus. A cumulonimbus incus cloud top is one that has spread out into a clear anvil shape as a result of rising air currents hitting the stability layer at the tropopause where the air no longer continues to get colder with increasing altitude.
The mamma feature forms on the bases of clouds as downward-facing bubble-like protuberances caused by localized downdrafts within the cloud. It is also sometimes called mammatus, an earlier version of the term used before a standardization of Latin nomenclature brought about by the World Meteorological Organization during the 20th century. The best-known is cumulonimbus with mammatus, but the mamma feature is also seen occasionally with cirrus, cirrocumulus, altocumulus, altostratus, and stratocumulus.
A tuba feature is a cloud column that may hang from the bottom of a cumulus or cumulonimbus. A newly formed or poorly organized column might be comparatively benign, but can quickly intensify into a funnel cloud or tornado.
An arcus feature is a roll cloud with ragged edges attached to the lower front part of cumulus congestus or cumulonimbus that forms along the leading edge of a squall line or thunderstorm outflow. A large arcus formation can have the appearance of a dark menacing arch. | Cloud | Wikipedia | 511 | 47515 | https://en.wikipedia.org/wiki/Cloud | Physical sciences | Earth science | null |
Several new supplementary features have been formally recognized by the World Meteorological Organization (WMO). The feature fluctus can form under conditions of strong atmospheric wind shear when a stratocumulus, altocumulus, or cirrus cloud breaks into regularly spaced crests. This variant is sometimes known informally as a Kelvin–Helmholtz (wave) cloud. This phenomenon has also been observed in cloud formations over other planets and even in the Sun's atmosphere. Another highly disturbed but more chaotic wave-like cloud feature associated with stratocumulus or altocumulus cloud has been given the Latin name asperitas. The supplementary feature cavum is a circular fall-streak hole that occasionally forms in a thin layer of supercooled altocumulus or cirrocumulus. Fall streaks consisting of virga or wisps of cirrus are usually seen beneath the hole as ice crystals fall out to a lower altitude. This type of hole is usually larger than typical lacunosus holes. A murus feature is a cumulonimbus wall cloud with a lowering, rotating cloud base than can lead to the development of tornadoes. A cauda feature is a tail cloud that extends horizontally away from the murus cloud and is the result of air feeding into the storm.
Accessory clouds
Supplementary cloud formations detached from the main cloud are known as accessory clouds. The heavier precipitating clouds, nimbostratus, towering cumulus (cumulus congestus), and cumulonimbus typically see the formation in precipitation of the pannus feature, low ragged clouds of the genera and species cumulus fractus or stratus fractus.
A group of accessory clouds comprise formations that are associated mainly with upward-growing cumuliform and cumulonimbiform clouds of free convection. Pileus is a cap cloud that can form over a cumulonimbus or large cumulus cloud, whereas a velum feature is a thin horizontal sheet that sometimes forms like an apron around the middle or in front of the parent cloud. An accessory cloud recently officially recognized by the World meteorological Organization is the flumen, also known more informally as the beaver's tail. It is formed by the warm, humid inflow of a super-cell thunderstorm, and can be mistaken for a tornado. Although the flumen can indicate a tornado risk, it is similar in appearance to pannus or scud clouds and does not rotate.
Mother clouds | Cloud | Wikipedia | 499 | 47515 | https://en.wikipedia.org/wiki/Cloud | Physical sciences | Earth science | null |
Clouds initially form in clear air or become clouds when fog rises above surface level. The genus of a newly formed cloud is determined mainly by air mass characteristics such as stability and moisture content. If these characteristics change over time, the genus tends to change accordingly. When this happens, the original genus is called a mother cloud. If the mother cloud retains much of its original form after the appearance of the new genus, it is termed a genitus cloud. One example of this is stratocumulus cumulogenitus, a stratocumulus cloud formed by the partial spreading of a cumulus type when there is a loss of convective lift. If the mother cloud undergoes a complete change in genus, it is considered to be a mutatus cloud.
Other genitus and mutatus clouds
The genitus and mutatus categories have been expanded to include certain types that do not originate from pre-existing clouds. The term flammagenitus (Latin for 'fire-made') applies to cumulus congestus or cumulonimbus that are formed by large scale fires or volcanic eruptions. Smaller low-level "pyrocumulus" or "fumulus" clouds formed by contained industrial activity are now classified as cumulus homogenitus (Latin for 'man-made'). Contrails formed from the exhaust of aircraft flying in the upper level of the troposphere can persist and spread into formations resembling cirrus which are designated cirrus homogenitus. If a cirrus homogenitus cloud changes fully to any of the high-level genera, they are termed cirrus, cirrostratus, or cirrocumulus homomutatus. Stratus cataractagenitus (Latin for 'cataract-made') are generated by the spray from waterfalls. Silvagenitus (Latin for 'forest-made') is a stratus cloud that forms as water vapor is added to the air above a forest canopy.
Large scale patterns
Sometimes certain atmospheric processes cause clouds to become organized into patterns that can cover large areas. These patterns are usually difficult to identify from surface level and are best seen from an aircraft or spacecraft.
Stratocumulus fields | Cloud | Wikipedia | 464 | 47515 | https://en.wikipedia.org/wiki/Cloud | Physical sciences | Earth science | null |
Stratocumulus clouds can be organized into "fields" that take on certain specially classified shapes and characteristics. In general, these fields are more discernible from high altitudes than from ground level. They can often be found in the following forms:
Actinoform, which resembles a leaf or a spoked wheel.
Closed cell, which is cloudy in the center and clear on the edges, similar to a filled honeycomb.
Open cell, which resembles an empty honeycomb, with clouds around the edges and clear, open space in the middle.
Vortex streets
These patterns are formed from a phenomenon known as a Kármán vortex which is named after the engineer and fluid dynamicist Theodore von Kármán. Wind driven clouds, usually mid level altocumulus or high level cirrus, can form into parallel rows that follow the wind direction. When the wind and clouds encounter high elevation land features such as a vertically prominent islands, they can form eddies around the high land masses that give the clouds a twisted appearance.
Distribution
Convergence along low-pressure zones
Although the local distribution of clouds can be significantly influenced by topography, the global prevalence of cloud cover in the troposphere tends to vary more by latitude. It is most prevalent in and along low pressure zones of surface tropospheric convergence which encircle the Earth close to the equator and near the 50th parallels of latitude in the northern and southern hemispheres. The adiabatic cooling processes that lead to the creation of clouds by way of lifting agents are all associated with convergence; a process that involves the horizontal inflow and accumulation of air at a given location, as well as the rate at which this happens. Near the equator, increased cloudiness is due to the presence of the low-pressure Intertropical Convergence Zone (ITCZ) where very warm and unstable air promotes mostly cumuliform and cumulonimbiform clouds. Clouds of virtually any type can form along the mid-latitude convergence zones depending on the stability and moisture content of the air. These extratropical convergence zones are occupied by the polar fronts where air masses of polar origin meet and clash with those of tropical or subtropical origin. This leads to the formation of weather-making extratropical cyclones composed of cloud systems that may be stable or unstable to varying degrees according to the stability characteristics of the various airmasses that are in conflict.
Divergence along high pressure zones | Cloud | Wikipedia | 480 | 47515 | https://en.wikipedia.org/wiki/Cloud | Physical sciences | Earth science | null |
Divergence is the opposite of convergence. In the Earth's troposphere, it involves the horizontal outflow of air from the upper part of a rising column of air, or from the lower part of a subsiding column often associated with an area or ridge of high pressure. Cloudiness tends to be least prevalent near the poles and in the subtropics close to the 30th parallels, north and south. The latter are sometimes referred to as the horse latitudes. The presence of a large-scale high-pressure subtropical ridge on each side of the equator reduces cloudiness at these low latitudes. Similar patterns also occur at higher latitudes in both hemispheres.
Luminance, reflectivity, and coloration
The luminance or brightness of a cloud is determined by how light is reflected, scattered, and transmitted by the cloud's particles. Its brightness may also be affected by the presence of haze or photometeors such as halos and rainbows. In the troposphere, dense, deep clouds exhibit a high reflectance (70–95%) throughout the visible spectrum. Tiny particles of water are densely packed and sunlight cannot penetrate far into the cloud before it is reflected out, giving a cloud its characteristic white color, especially when viewed from the top. Cloud droplets tend to scatter light efficiently, so that the intensity of the solar radiation decreases with depth into the gases. As a result, the cloud base can vary from a very light to very-dark-gray depending on the cloud's thickness and how much light is being reflected or transmitted back to the observer. High thin tropospheric clouds reflect less light because of the comparatively low concentration of constituent ice crystals or supercooled water droplets which results in a slightly off-white appearance. However, a thick dense ice-crystal cloud appears brilliant white with pronounced gray shading because of its greater reflectivity. | Cloud | Wikipedia | 386 | 47515 | https://en.wikipedia.org/wiki/Cloud | Physical sciences | Earth science | null |
As a tropospheric cloud matures, the dense water droplets may combine to produce larger droplets. If the droplets become too large and heavy to be kept aloft by the air circulation, they will fall from the cloud as rain. By this process of accumulation, the space between droplets becomes increasingly larger, permitting light to penetrate farther into the cloud. If the cloud is sufficiently large and the droplets within are spaced far enough apart, a percentage of the light that enters the cloud is not reflected back out but is absorbed giving the cloud a darker look. A simple example of this is one's being able to see farther in heavy rain than in heavy fog. This process of reflection/absorption is what causes the range of cloud color from white to black.
Striking cloud colorations can be seen at any altitude, with the color of a cloud usually being the same as the incident light. During daytime when the sun is relatively high in the sky, tropospheric clouds generally appear bright white on top with varying shades of gray underneath. Thin clouds may look white or appear to have acquired the color of their environment or background. Red, orange, and pink clouds occur almost entirely at sunrise/sunset and are the result of the scattering of sunlight by the atmosphere. When the Sun is just below the horizon, low-level clouds are gray, middle clouds appear rose-colored, and high clouds are white or off-white. Clouds at night are black or dark gray in a moonless sky, or whitish when illuminated by the Moon. They may also reflect the colors of large fires, city lights, or auroras that might be present. | Cloud | Wikipedia | 331 | 47515 | https://en.wikipedia.org/wiki/Cloud | Physical sciences | Earth science | null |
A cumulonimbus cloud that appears to have a greenish or bluish tint is a sign that it contains extremely high amounts of water; hail or rain which scatter light in a way that gives the cloud a blue color. A green colorization occurs mostly late in the day when the sun is comparatively low in the sky and the incident sunlight has a reddish tinge that appears green when illuminating a very tall bluish cloud. Supercell type storms are more likely to be characterized by this but any storm can appear this way. Coloration such as this does not directly indicate that it is a severe thunderstorm, it only confirms its potential. Since a green/blue tint signifies copious amounts of water, a strong updraft to support it, high winds from the storm raining out, and wet hail; all elements that improve the chance for it to become severe, can all be inferred from this. In addition, the stronger the updraft is, the more likely the storm is to undergo tornadogenesis and to produce large hail and high winds.
Yellowish clouds may be seen in the troposphere in the late spring through early fall months during forest fire season. The yellow color is due to the presence of pollutants in the smoke. Yellowish clouds are caused by the presence of nitrogen dioxide and are sometimes seen in urban areas with high air pollution levels.
Effects
Tropospheric clouds exert numerous influences on Earth's troposphere and climate. First and foremost, they are the source of precipitation, thereby greatly influencing the distribution and amount of precipitation. Because of their differential buoyancy relative to surrounding cloud-free air, clouds can be associated with vertical motions of the air that may be convective, frontal, or cyclonic. The motion is upward if the clouds are less dense because condensation of water vapor releases heat, warming the air and thereby decreasing its density. This can lead to downward motion because lifting of the air results in cooling that increases its density. All of these effects are subtly dependent on the vertical temperature and moisture structure of the atmosphere and result in major redistribution of heat that affect the Earth's climate. | Cloud | Wikipedia | 440 | 47515 | https://en.wikipedia.org/wiki/Cloud | Physical sciences | Earth science | null |
The complexity and diversity of clouds in the troposphere is a major reason for difficulty in quantifying the effects of clouds on climate and climate change. On the one hand, white cloud tops promote cooling of Earth's surface by reflecting shortwave radiation (visible and near infrared) from the Sun, diminishing the amount of solar radiation that is absorbed at the surface, enhancing the Earth's albedo. Most of the sunlight that reaches the ground is absorbed, warming the surface, which emits radiation upward at longer, infrared, wavelengths. At these wavelengths, however, water in the clouds acts as an efficient absorber. The water reacts by radiating, also in the infrared, both upward and downward, and the downward longwave radiation results in increased warming at the surface. This is analogous to the greenhouse effect of greenhouse gases and water vapor.
High-level genus-types particularly show this duality with both short-wave albedo cooling and long-wave greenhouse warming effects. On the whole, ice-crystal clouds in the upper troposphere (cirrus) tend to favor net warming. However, the cooling effect is dominant with mid-level and low clouds, especially when they form in extensive sheets. Measurements by NASA indicate that on the whole, the effects of low and mid-level clouds that tend to promote cooling outweigh the warming effects of high layers and the variable outcomes associated with vertically developed clouds. | Cloud | Wikipedia | 289 | 47515 | https://en.wikipedia.org/wiki/Cloud | Physical sciences | Earth science | null |
As difficult as it is to evaluate the influences of current clouds on current climate, it is even more problematic to predict changes in cloud patterns and properties in a future, warmer climate, and the resultant cloud influences on future climate. In a warmer climate more water would enter the atmosphere by evaporation at the surface; as clouds are formed from water vapor, cloudiness would be expected to increase. But in a warmer climate, higher temperatures would tend to evaporate clouds. Both of these statements are considered accurate, and both phenomena, known as cloud feedbacks, are found in climate model calculations. Broadly speaking, if clouds, especially low clouds, increase in a warmer climate, the resultant cooling effect leads to a negative feedback in climate response to increased greenhouse gases. But if low clouds decrease, or if high clouds increase, the feedback is positive. Differing amounts of these feedbacks are the principal reason for differences in climate sensitivities of current global climate models. As a consequence, much research has focused on the response of low and vertical clouds to a changing climate. Leading global models produce quite different results, however, with some showing increasing low clouds and others showing decreases. For these reasons the role of tropospheric clouds in regulating weather and climate remains a leading source of uncertainty in global warming projections.
Stratospheric classification and distribution
Polar stratospheric clouds (PSC's) are found in the lowest part of the stratosphere. Moisture is scarce above the troposphere, so nacreous and non-nacreous clouds at this altitude range are restricted to polar regions in the winter where and when the air is coldest.
PSC's show some variation in structure according to their chemical makeup and atmospheric conditions, but are limited to a single very high range of altitude of about Accordingly, they are classified as a singular type with no differentiated altitude levels, genus types, species, or varieties. There is no Latin nomenclature in the manner of tropospheric clouds, but rather descriptive names of several general forms using common English. | Cloud | Wikipedia | 420 | 47515 | https://en.wikipedia.org/wiki/Cloud | Physical sciences | Earth science | null |
Supercooled nitric acid and water PSC's, sometimes known as type 1, typically have a stratiform appearance resembling cirrostratus or haze, but because they are not frozen into crystals, do not show the pastel colors of the nacreous types. This type of PSC has been identified as a cause of ozone depletion in the stratosphere. The frozen nacreous types are typically very thin with mother-of-pearl colorations and an undulating cirriform or lenticular (stratocumuliform) appearance. These are sometimes known as type 2.
Mesospheric classification and distribution
Noctilucent clouds are the highest in the atmosphere and are found near the top of the mesosphere at about or roughly ten times the altitude of tropospheric high clouds. They are given this Latin derived name because of their illumination well after sunset and before sunrise. They typically have a bluish or silvery white coloration that can resemble brightly illuminated cirrus. Noctilucent clouds may occasionally take on more of a red or orange hue. They are not common or widespread enough to have a significant effect on climate. However, an increasing frequency of occurrence of noctilucent clouds since the 19th century may be the result of climate change.
Ongoing research indicates that convective lift in the mesosphere is strong enough during the polar summer to cause adiabatic cooling of small amount of water vapor to the point of saturation. This tends to produce the coldest temperatures in the entire atmosphere just below the mesopause. There is evidence that smoke particles from burnt-up meteors provide much of the condensation nuclei required for the formation of noctilucent cloud.
Noctilucent clouds have four major types based on physical structure and appearance. Type I veils are very tenuous and lack well-defined structure, somewhat like cirrostratus fibratus or poorly defined cirrus. Type II bands are long streaks that often occur in groups arranged roughly parallel to each other. They are usually more widely spaced than the bands or elements seen with cirrocumulus clouds. Type III billows are arrangements of closely spaced, roughly parallel short streaks that mostly resemble cirrus. Type IV whirls are partial or, more rarely, complete rings of cloud with dark centers. | Cloud | Wikipedia | 488 | 47515 | https://en.wikipedia.org/wiki/Cloud | Physical sciences | Earth science | null |
Distribution in the mesosphere is similar to the stratosphere except at much higher altitudes. Because of the need for maximum cooling of the water vapor to produce noctilucent clouds, their distribution tends to be restricted to polar regions of Earth. Sightings are rare more than 45 degrees south of the north pole or north of the south pole.
Extraterrestrial
Cloud cover has been seen on most other planets in the Solar System. Venus's thick clouds are composed of sulfur dioxide (due to volcanic activity) and appear to be almost entirely stratiform. They are arranged in three main layers at altitudes of 45 to 65 km that obscure the planet's surface and can produce virga. No embedded cumuliform types have been identified, but broken stratocumuliform wave formations are sometimes seen in the top layer that reveal more continuous layer clouds underneath. On Mars, noctilucent, cirrus, cirrocumulus and stratocumulus composed of water-ice have been detected mostly near the poles. Water-ice fogs have also been detected on Mars.
Both Jupiter and Saturn have an outer cirriform cloud deck composed of ammonia, an intermediate stratiform haze-cloud layer made of ammonium hydrosulfide, and an inner deck of cumulus water clouds. Embedded cumulonimbus are known to exist near the Great Red Spot on Jupiter. The same category-types can be found covering Uranus and Neptune, but are all composed of methane. Saturn's moon Titan has cirrus clouds believed to be composed largely of methane. The Cassini–Huygens Saturn mission uncovered evidence of polar stratospheric clouds and a methane cycle on Titan, including lakes near the poles and fluvial channels on the surface of the moon.
Some planets outside the Solar System are known to have atmospheric clouds. In October 2013, the detection of high altitude optically thick clouds in the atmosphere of exoplanet Kepler-7b was announced, and, in December 2013, in the atmospheres of GJ 436 b and GJ 1214 b.
In culture and religion | Cloud | Wikipedia | 436 | 47515 | https://en.wikipedia.org/wiki/Cloud | Physical sciences | Earth science | null |
Clouds play an important mythical or non-scientific role in various cultures and religious traditions. The ancient Akkadians believed that the clouds (in meteorology, probably the supplementary feature mamma) were the breasts of the sky goddess Antu and that rain was milk from her breasts. In , Yahweh is described as guiding the Israelites through the desert in the form of a "pillar of cloud" by day and a "pillar of fire" by night. In Mandaeism, uthras (celestial beings) are also occasionally mentioned as being in anana ("clouds"; e.g., in Right Ginza Book 17, Chapter 1), which can also be interpreted as female consorts.
The Cloud of Unknowing is a 14th-century work of Christian mysticism that advises a contemplative practice focused on experiencing God through love and "unknowing."
In the ancient Greek comedy The Clouds, written by Aristophanes and first performed at the City Dionysia in 423 BC, the philosopher Socrates declares that the Clouds are the only true deities and tells the main character Strepsiades not to worship any deities other than the Clouds, but to pay homage to them alone. In the play, the Clouds change shape to reveal the true nature of whoever is looking at them, turning into centaurs at the sight of a long-haired politician, wolves at the sight of the embezzler Simon, deer at the sight of the coward Cleonymus, and mortal women at the sight of the effeminate informer Cleisthenes. They are hailed the source of inspiration to comic poets and philosophers; they are masters of rhetoric, regarding eloquence and sophistry alike as their "friends".
In China, clouds are symbols of luck and happiness. Overlapping clouds (in meteorology, probably duplicatus clouds) are thought to imply eternal happiness and clouds of different colors are said to indicate "multiplied blessings".
Informal cloud watching or cloud gazing is a popular activity involving watching the clouds and looking for shapes in them, a form of pareidolia. | Cloud | Wikipedia | 441 | 47515 | https://en.wikipedia.org/wiki/Cloud | Physical sciences | Earth science | null |
Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most often refers to the water cycle. It can also be defined as the change in the state of water vapor to liquid water when in contact with a liquid or solid surface or cloud condensation nuclei within the atmosphere. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition.
Initiation
Condensation is initiated by the formation of atomic/molecular clusters of that species within its gaseous volume—like rain drop or snow flake formation within clouds—or at the contact between such gaseous phase and a liquid or solid surface. In clouds, this can be catalyzed by water-nucleating proteins, produced by atmospheric microbes, which are capable of binding gaseous or liquid water molecules.
Reversibility scenarios
A few distinct reversibility scenarios emerge here with respect to the nature of the surface.
absorption into the surface of a liquid (either of the same substance or one of its solvents)—is reversible as evaporation.
adsorption (as dew droplets) onto solid surface at pressures and temperatures higher than the species' triple point—also reversible as evaporation.
adsorption onto solid surface (as supplemental layers of solid) at pressures and temperatures lower than the species' triple point—is reversible as sublimation.
Most common scenarios
Condensation commonly occurs when a vapor is cooled and/or compressed to its saturation limit when the molecular density in the gas phase reaches its maximal threshold. Vapor cooling and compressing equipment that collects condensed liquids is called a "condenser".
Measurement
Psychrometry measures the rates of condensation through evaporation into the air moisture at various atmospheric pressures and temperatures. Water is the product of its vapor condensation—condensation is the process of such phase conversion.
Applications of condensation
Condensation is a crucial component of distillation, an important laboratory and industrial chemistry application. | Condensation | Wikipedia | 427 | 47521 | https://en.wikipedia.org/wiki/Condensation | Physical sciences | Phase transitions | null |
Because condensation is a naturally occurring phenomenon, it can often be used to generate water in large quantities for human use. Many structures are made solely for the purpose of collecting water from condensation, such as air wells and fog fences. Such systems can often be used to retain soil moisture in areas where active desertification is occurring—so much so that some organizations educate people living in affected areas about water condensers to help them deal effectively with the situation.
It is also a crucial process in forming particle tracks in a cloud chamber. In this case, ions produced by an incident particle act as nucleation centers for the condensation of the vapor producing the visible "cloud" trails.
Commercial applications of condensation, by consumers as well as industry, include power generation, water desalination, thermal management, refrigeration, and air conditioning.
Biological adaptation
Numerous living beings use water made accessible by condensation. A few examples of these are the Australian thorny devil, the darkling beetles of the Namibian coast, and the coast redwoods of the West Coast of the United States.
Condensation in building construction
Condensation in building construction is an unwanted phenomenon as it may cause dampness, mold health issues, wood rot, corrosion, weakening of mortar and masonry walls, and energy penalties due to increased heat transfer. To alleviate these issues, the indoor air humidity needs to be lowered, or air ventilation in the building needs to be improved. This can be done in a number of ways, for example opening windows, turning on extractor fans, using dehumidifiers, drying clothes outside and covering pots and pans whilst cooking. Air conditioning or ventilation systems can be installed that help remove moisture from the air, and move air throughout a building. The amount of water vapor that can be stored in the air can be increased simply by increasing the temperature. However, this can be a double edged sword as most condensation in the home occurs when warm, moisture heavy air comes into contact with a cool surface. As the air is cooled, it can no longer hold as much water vapor. This leads to deposition of water on the cool surface. This is very apparent when central heating is used in combination with single glazed windows in winter.
Interstructure condensation may be caused by thermal bridges, insufficient or lacking insulation, damp proofing or insulated glazing.
Table | Condensation | Wikipedia | 490 | 47521 | https://en.wikipedia.org/wiki/Condensation | Physical sciences | Phase transitions | null |
Convection is single or multiphase fluid flow that occurs spontaneously through the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convection is unspecified, convection due to the effects of thermal expansion and buoyancy can be assumed. Convection may also take place in soft solids or mixtures where particles can flow.
Convective flow may be transient (such as when a multiphase mixture of oil and water separates) or steady state (see convection cell). The convection may be due to gravitational, electromagnetic or fictitious body forces. Heat transfer by natural convection plays a role in the structure of Earth's atmosphere, its oceans, and its mantle. Discrete convective cells in the atmosphere can be identified by clouds, with stronger convection resulting in thunderstorms. Natural convection also plays a role in stellar physics. Convection is often categorised or described by the main effect causing the convective flow; for example, thermal convection.
Convection cannot take place in most solids because neither bulk current flows nor significant diffusion of matter can take place.
Granular convection is a similar phenomenon in granular material instead of fluids.
Advection is fluid motion created by velocity instead of thermal gradients.
Convective heat transfer is the intentional use of convection as a method for heat transfer. Convection is a process in which heat is carried from place to place by the bulk movement of a fluid and gases.
History
In the 1830s, in The Bridgewater Treatises, the term convection is attested in a scientific sense. In treatise VIII by William Prout, in the book on chemistry, it says: | Convection | Wikipedia | 343 | 47526 | https://en.wikipedia.org/wiki/Convection | Physical sciences | Fluid mechanics | null |
[...] This motion of heat takes place in three ways, which a common fire-place very well illustrates. If, for instance, we place a thermometer directly before a fire, it soon begins to rise, indicating an increase of temperature. In this case the heat has made its way through the space between the fire and the thermometer, by the process termed radiation. If we place a second thermometer in contact with any part of the grate, and away from the direct influence of the fire, we shall find that this thermometer also denotes an increase of temperature; but here the heat must have travelled through the metal of the grate, by what is termed conduction. Lastly, a third thermometer placed in the chimney, away from the direct influence of the fire, will also indicate a considerable increase of temperature; in this case a portion of the air, passing through and near the fire, has become heated, and has carried up the chimney the temperature acquired from the fire. There is at present no single term in our language employed to denote this third mode of the propagation of heat; but we venture to propose for that purpose, the term convection, [in footnote: [Latin] Convectio, a carrying or conveying] which not only expresses the leading fact, but also accords very well with the two other terms.
Later, in the same treatise VIII, in the book on meteorology, the concept of convection is also applied to "the process by which heat is communicated through water".
Terminology
Today, the word convection has different but related usages in different scientific or engineering contexts or applications.
In fluid mechanics, convection has a broader sense: it refers to the motion of fluid driven by density (or other property) difference.
In thermodynamics, convection often refers to heat transfer by convection, where the prefixed variant Natural Convection is used to distinguish the fluid mechanics concept of Convection (covered in this article) from convective heat transfer.
Some phenomena which result in an effect superficially similar to that of a convective cell may also be (inaccurately) referred to as a form of convection; for example, thermo-capillary convection and granular convection. | Convection | Wikipedia | 460 | 47526 | https://en.wikipedia.org/wiki/Convection | Physical sciences | Fluid mechanics | null |
Mechanisms
Convection may happen in fluids at all scales larger than a few atoms. There are a variety of circumstances in which the forces required for convection arise, leading to different types of convection, described below. In broad terms, convection arises because of body forces acting within the fluid, such as gravity.
Natural convection
Natural convection is a flow whose motion is caused by some parts of a fluid being heavier than other parts. In most cases this leads to natural circulation: the ability of a fluid in a system to circulate continuously under gravity, with transfer of heat energy.
The driving force for natural convection is gravity. In a column of fluid, pressure increases with depth from the weight of the overlying fluid. The pressure at the bottom of a submerged object then exceeds that at the top, resulting in a net upward buoyancy force equal to the weight of the displaced fluid. Objects of higher density than that of the displaced fluid then sink. For example, regions of warmer low-density air rise, while those of colder high-density air sink. This creates a circulating flow: convection.
Gravity drives natural convection. Without gravity, convection does not occur, so there is no convection in free-fall (inertial) environments, such as that of the orbiting International Space Station. Natural convection can occur when there are hot and cold regions of either air or water, because both water and air become less dense as they are heated. But, for example, in the world's oceans it also occurs due to salt water being heavier than fresh water, so a layer of salt water on top of a layer of fresher water will also cause convection.
Natural convection has attracted a great deal of attention from researchers because of its presence both in nature and engineering applications. In nature, convection cells formed from air raising above sunlight-warmed land or water are a major feature of all weather systems. Convection is also seen in the rising plume of hot air from fire, plate tectonics, oceanic currents (thermohaline circulation) and sea-wind formation (where upward convection is also modified by Coriolis forces). In engineering applications, convection is commonly visualized in the formation of microstructures during the cooling of molten metals, and fluid flows around shrouded heat-dissipation fins, and solar ponds. A very common industrial application of natural convection is free air cooling without the aid of fans: this can happen on small scales (computer chips) to large scale process equipment. | Convection | Wikipedia | 504 | 47526 | https://en.wikipedia.org/wiki/Convection | Physical sciences | Fluid mechanics | null |
Natural convection will be more likely and more rapid with a greater variation in density between the two fluids, a larger acceleration due to gravity that drives the convection or a larger distance through the convecting medium. Natural convection will be less likely and less rapid with more rapid diffusion (thereby diffusing away the thermal gradient that is causing the convection) or a more viscous (sticky) fluid.
The onset of natural convection can be determined by the Rayleigh number (Ra).
Differences in buoyancy within a fluid can arise for reasons other than temperature variations, in which case the fluid motion is called gravitational convection (see below). However, all types of buoyant convection, including natural convection, do not occur in microgravity environments. All require the presence of an environment which experiences g-force (proper acceleration).
The difference of density in the fluid is the key driving mechanism. If the differences of density are caused by heat, this force is called as "thermal head" or "thermal driving head." A fluid system designed for natural circulation will have a heat source and a heat sink. Each of these is in contact with some of the fluid in the system, but not all of it. The heat source is positioned lower than the heat sink.
Most fluids expand when heated, becoming less dense, and contract when cooled, becoming denser. At the heat source of a system of natural circulation, the heated fluid becomes lighter than the fluid surrounding it, and thus rises. At the heat sink, the nearby fluid becomes denser as it cools, and is drawn downward by gravity. Together, these effects create a flow of fluid from the heat source to the heat sink and back again.
Gravitational or buoyant convection
Gravitational convection is a type of natural convection induced by buoyancy variations resulting from material properties other than temperature. Typically this is caused by a variable composition of the fluid. If the varying property is a concentration gradient, it is known as solutal convection. For example, gravitational convection can be seen in the diffusion of a source of dry salt downward into wet soil due to the buoyancy of fresh water in saline. | Convection | Wikipedia | 436 | 47526 | https://en.wikipedia.org/wiki/Convection | Physical sciences | Fluid mechanics | null |
Variable salinity in water and variable water content in air masses are frequent causes of convection in the oceans and atmosphere which do not involve heat, or else involve additional compositional density factors other than the density changes from thermal expansion (see thermohaline circulation). Similarly, variable composition within the Earth's interior which has not yet achieved maximal stability and minimal energy (in other words, with densest parts deepest) continues to cause a fraction of the convection of fluid rock and molten metal within the Earth's interior (see below).
Gravitational convection, like natural thermal convection, also requires a g-force environment in order to occur.
Solid-state convection in ice
Ice convection on Pluto is believed to occur in a soft mixture of nitrogen ice and carbon monoxide ice. It has also been proposed for Europa, and other bodies in the outer Solar System.
Thermomagnetic convection
Thermomagnetic convection can occur when an external magnetic field is imposed on a ferrofluid with varying magnetic susceptibility. In the presence of a temperature gradient this results in a nonuniform magnetic body force, which leads to fluid movement. A ferrofluid is a liquid which becomes strongly magnetized in the presence of a magnetic field.
Combustion
In a zero-gravity environment, there can be no buoyancy forces, and thus no convection possible, so flames in many circumstances without gravity smother in their own waste gases. Thermal expansion and chemical reactions resulting in expansion and contraction gases allows for ventilation of the flame, as waste gases are displaced by cool, fresh, oxygen-rich gas. moves in to take up the low pressure zones created when flame-exhaust water condenses.
Examples and applications
Systems of natural circulation include tornadoes and other weather systems, ocean currents, and household ventilation. Some solar water heaters use natural circulation. The Gulf Stream circulates as a result of the evaporation of water. In this process, the water increases in salinity and density. In the North Atlantic Ocean, the water becomes so dense that it begins to sink down. | Convection | Wikipedia | 425 | 47526 | https://en.wikipedia.org/wiki/Convection | Physical sciences | Fluid mechanics | null |
Convection occurs on a large scale in atmospheres, oceans, planetary mantles, and it provides the mechanism of heat transfer for a large fraction of the outermost interiors of the Sun and all stars. Fluid movement during convection may be invisibly slow, or it may be obvious and rapid, as in a hurricane. On astronomical scales, convection of gas and dust is thought to occur in the accretion disks of black holes, at speeds which may closely approach that of light.
Demonstration experiments
Thermal convection in liquids can be demonstrated by placing a heat source (for example, a Bunsen burner) at the side of a container with a liquid. Adding a dye to the water (such as food colouring) will enable visualisation of the flow.
Another common experiment to demonstrate thermal convection in liquids involves submerging open containers of hot and cold liquid coloured with dye into a large container of the same liquid without dye at an intermediate temperature (for example, a jar of hot tap water coloured red, a jar of water chilled in a fridge coloured blue, lowered into a clear tank of water at room temperature).
A third approach is to use two identical jars, one filled with hot water dyed one colour, and cold water of another colour. One jar is then temporarily sealed (for example, with a piece of card), inverted and placed on top of the other. When the card is removed, if the jar containing the warmer liquid is placed on top no convection will occur. If the jar containing colder liquid is placed on top, a convection current will form spontaneously.
Convection in gases can be demonstrated using a candle in a sealed space with an inlet and exhaust port. The heat from the candle will cause a strong convection current which can be demonstrated with a flow indicator, such as smoke from another candle, being released near the inlet and exhaust areas respectively.
Double diffusive convection
Convection cells | Convection | Wikipedia | 382 | 47526 | https://en.wikipedia.org/wiki/Convection | Physical sciences | Fluid mechanics | null |
A convection cell, also known as a Bénard cell, is a characteristic fluid flow pattern in many convection systems. A rising body of fluid typically loses heat because it encounters a colder surface. In liquid, this occurs because it exchanges heat with colder liquid through direct exchange. In the example of the Earth's atmosphere, this occurs because it radiates heat. Because of this heat loss the fluid becomes denser than the fluid underneath it, which is still rising. Since it cannot descend through the rising fluid, it moves to one side. At some distance, its downward force overcomes the rising force beneath it, and the fluid begins to descend. As it descends, it warms again and the cycle repeats itself. Additionally, convection cells can arise due to density variations resulting from differences in the composition of electrolytes.
Atmospheric convection
Atmospheric circulation
Atmospheric circulation is the large-scale movement of air, and is a means by which thermal energy is distributed on the surface of the Earth, together with the much slower (lagged) ocean circulation system. The large-scale structure of the atmospheric circulation varies from year to year, but the basic climatological structure remains fairly constant.
Latitudinal circulation occurs because incident solar radiation per unit area is highest at the heat equator, and decreases as the latitude increases, reaching minima at the poles. It consists of two primary convection cells, the Hadley cell and the polar vortex, with the Hadley cell experiencing stronger convection due to the release of latent heat energy by condensation of water vapor at higher altitudes during cloud formation.
Longitudinal circulation, on the other hand, comes about because the ocean has a higher specific heat capacity than land (and also thermal conductivity, allowing the heat to penetrate further beneath the surface ) and thereby absorbs and releases more heat, but the temperature changes less than land. This brings the sea breeze, air cooled by the water, ashore in the day, and carries the land breeze, air cooled by contact with the ground, out to sea during the night. Longitudinal circulation consists of two cells, the Walker circulation and El Niño / Southern Oscillation.
Weather | Convection | Wikipedia | 432 | 47526 | https://en.wikipedia.org/wiki/Convection | Physical sciences | Fluid mechanics | null |
Some more localized phenomena than global atmospheric movement are also due to convection, including wind and some of the hydrologic cycle. For example, a foehn wind is a down-slope wind which occurs on the downwind side of a mountain range. It results from the adiabatic warming of air which has dropped most of its moisture on windward slopes. Because of the different adiabatic lapse rates of moist and dry air, the air on the leeward slopes becomes warmer than at the same height on the windward slopes.
A thermal column (or thermal) is a vertical section of rising air in the lower altitudes of the Earth's atmosphere. Thermals are created by the uneven heating of the Earth's surface from solar radiation. The Sun warms the ground, which in turn warms the air directly above it. The warmer air expands, becoming less dense than the surrounding air mass, and creating a thermal low. The mass of lighter air rises, and as it does, it cools by expansion at lower air pressures. It stops rising when it has cooled to the same temperature as the surrounding air. Associated with a thermal is a downward flow surrounding the thermal column. The downward moving exterior is caused by colder air being displaced at the top of the thermal. Another convection-driven weather effect is the sea breeze.
Warm air has a lower density than cool air, so warm air rises within cooler air, similar to hot air balloons. Clouds form as relatively warmer air carrying moisture rises within cooler air. As the moist air rises, it cools, causing some of the water vapor in the rising packet of air to condense. When the moisture condenses, it releases energy known as latent heat of condensation which allows the rising packet of air to cool less than its surrounding air, continuing the cloud's ascension. If enough instability is present in the atmosphere, this process will continue long enough for cumulonimbus clouds to form, which support lightning and thunder. Generally, thunderstorms require three conditions to form: moisture, an unstable airmass, and a lifting force (heat).
All thunderstorms, regardless of type, go through three stages: the developing stage, the mature stage, and the dissipation stage. The average thunderstorm has a diameter. Depending on the conditions present in the atmosphere, these three stages take an average of 30 minutes to go through.
Oceanic circulation | Convection | Wikipedia | 492 | 47526 | https://en.wikipedia.org/wiki/Convection | Physical sciences | Fluid mechanics | null |
Solar radiation affects the oceans: warm water from the Equator tends to circulate toward the poles, while cold polar water heads towards the Equator. The surface currents are initially dictated by surface wind conditions. The trade winds blow westward in the tropics, and the westerlies blow eastward at mid-latitudes. This wind pattern applies a stress to the subtropical ocean surface with negative curl across the Northern Hemisphere, and the reverse across the Southern Hemisphere. The resulting Sverdrup transport is equatorward. Because of conservation of potential vorticity caused by the poleward-moving winds on the subtropical ridge's western periphery and the increased relative vorticity of poleward moving water, transport is balanced by a narrow, accelerating poleward current, which flows along the western boundary of the ocean basin, outweighing the effects of friction with the cold western boundary current which originates from high latitudes. The overall process, known as western intensification, causes currents on the western boundary of an ocean basin to be stronger than those on the eastern boundary.
As it travels poleward, warm water transported by strong warm water current undergoes evaporative cooling. The cooling is wind driven: wind moving over water cools the water and also causes evaporation, leaving a saltier brine. In this process, the water becomes saltier and denser and decreases in temperature. Once sea ice forms, salts are left out of the ice, a process known as brine exclusion. These two processes produce water that is denser and colder. The water across the northern Atlantic Ocean becomes so dense that it begins to sink down through less salty and less dense water. (This open ocean convection is not unlike that of a lava lamp.) This downdraft of heavy, cold and dense water becomes a part of the North Atlantic Deep Water, a south-going stream.
Mantle convection
Mantle convection is the slow creeping motion of Earth's rocky mantle caused by convection currents carrying heat from the interior of the Earth to the surface. It is one of 3 driving forces that causes tectonic plates to move around the Earth's surface. | Convection | Wikipedia | 430 | 47526 | https://en.wikipedia.org/wiki/Convection | Physical sciences | Fluid mechanics | null |
The Earth's surface is divided into a number of tectonic plates that are continuously being created and consumed at their opposite plate boundaries. Creation (accretion) occurs as mantle is added to the growing edges of a plate. This hot added material cools down by conduction and convection of heat. At the consumption edges of the plate, the material has thermally contracted to become dense, and it sinks under its own weight in the process of subduction at an ocean trench. This subducted material sinks to some depth in the Earth's interior where it is prohibited from sinking further. The subducted oceanic crust triggers volcanism.
Convection within Earth's mantle is the driving force for plate tectonics. Mantle convection is the result of a thermal gradient: the lower mantle is hotter than the upper mantle, and is therefore less dense. This sets up two primary types of instabilities. In the first type, plumes rise from the lower mantle, and corresponding unstable regions of lithosphere drip back into the mantle. In the second type, subducting oceanic plates (which largely constitute the upper thermal boundary layer of the mantle) plunge back into the mantle and move downwards towards the core-mantle boundary. Mantle convection occurs at rates of centimeters per year, and it takes on the order of hundreds of millions of years to complete a cycle of convection.
Neutrino flux measurements from the Earth's core (see kamLAND) show the source of about two-thirds of the heat in the inner core is the radioactive decay of 40K, uranium and thorium. This has allowed plate tectonics on Earth to continue far longer than it would have if it were simply driven by heat left over from Earth's formation; or with heat produced from gravitational potential energy, as a result of physical rearrangement of denser portions of the Earth's interior toward the center of the planet (that is, a type of prolonged falling and settling).
Stack effect | Convection | Wikipedia | 402 | 47526 | https://en.wikipedia.org/wiki/Convection | Physical sciences | Fluid mechanics | null |
The Stack effect or chimney effect is the movement of air into and out of buildings, chimneys, flue gas stacks, or other containers due to buoyancy. Buoyancy occurs due to a difference in indoor-to-outdoor air density resulting from temperature and moisture differences. The greater the thermal difference and the height of the structure, the greater the buoyancy force, and thus the stack effect. The stack effect helps drive natural ventilation and infiltration. Some cooling towers operate on this principle; similarly the solar updraft tower is a proposed device to generate electricity based on the stack effect.
Stellar physics
The convection zone of a star is the range of radii in which energy is transported outward from the core region primarily by convection rather than radiation. This occurs at radii which are sufficiently opaque that convection is more efficient than radiation at transporting energy.
Granules on the photosphere of the Sun are the visible tops of convection cells in the photosphere, caused by convection of plasma in the photosphere. The rising part of the granules is located in the center where the plasma is hotter. The outer edge of the granules is darker due to the cooler descending plasma. A typical granule has a diameter on the order of 1,000 kilometers and each lasts 8 to 20 minutes before dissipating. Below the photosphere is a layer of much larger "supergranules" up to 30,000 kilometers in diameter, with lifespans of up to 24 hours.
Water convection at freezing temperatures
Water is a fluid that does not obey the Boussinesq approximation. This is because its density varies nonlinearly with temperature, which causes its thermal expansion coefficient to be inconsistent near freezing temperatures. The density of water reaches a maximum at 4 °C and decreases as the temperature deviates. This phenomenon is investigated by experiment and numerical methods. Water is initially stagnant at 10 °C within a square cavity. It is differentially heated between the two vertical walls, where the left and right walls are held at 10 °C and 0 °C, respectively. The density anomaly manifests in its flow pattern. As the water is cooled at the right wall, the density increases, which accelerates the flow downward. As the flow develops and the water cools further, the decrease in density causes a recirculation current at the bottom right corner of the cavity. | Convection | Wikipedia | 481 | 47526 | https://en.wikipedia.org/wiki/Convection | Physical sciences | Fluid mechanics | null |
Another case of this phenomenon is the event of super-cooling, where the water is cooled to below freezing temperatures but does not immediately begin to freeze. Under the same conditions as before, the flow is developed. Afterward, the temperature of the right wall is decreased to −10 °C. This causes the water at that wall to become supercooled, create a counter-clockwise flow, and initially overpower the warm current. This plume is caused by a delay in the nucleation of the ice. Once ice begins to form, the flow returns to a similar pattern as before and the solidification propagates gradually until the flow is redeveloped.
Nuclear reactors
In a nuclear reactor, natural circulation can be a design criterion. It is achieved by reducing turbulence and friction in the fluid flow (that is, minimizing head loss), and by providing a way to remove any inoperative pumps from the fluid path. Also, the reactor (as the heat source) must be physically lower than the steam generators or turbines (the heat sink). In this way, natural circulation will ensure that the fluid will continue to flow as long as the reactor is hotter than the heat sink, even when power cannot be supplied to the pumps. Notable examples are the S5G
and S8G United States Naval reactors, which were designed to operate at a significant fraction of full power under natural circulation, quieting those propulsion plants. The S6G reactor cannot operate at power under natural circulation, but can use it to maintain emergency cooling while shut down.
By the nature of natural circulation, fluids do not typically move very fast, but this is not necessarily bad, as high flow rates are not essential to safe and effective reactor operation. In modern design nuclear reactors, flow reversal is almost impossible. All nuclear reactors, even ones designed to primarily use natural circulation as the main method of fluid circulation, have pumps that can circulate the fluid in the case that natural circulation is not sufficient.
Mathematical models of convection
A number of dimensionless terms have been derived to describe and predict convection, including the Archimedes number, Grashof number, Richardson number, and the Rayleigh number.
In cases of mixed convection (natural and forced occurring together) one would often like to know how much of the convection is due to external constraints, such as the fluid velocity in the pump, and how much is due to natural convection occurring in the system. | Convection | Wikipedia | 490 | 47526 | https://en.wikipedia.org/wiki/Convection | Physical sciences | Fluid mechanics | null |
The relative magnitudes of the Grashof number and the square of the Reynolds number determine which form of convection dominates. If , forced convection may be neglected, whereas if , natural convection may be neglected. If the ratio, known as the Richardson number, is approximately one, then both forced and natural convection need to be taken into account.
Onset
The onset of natural convection is determined by the Rayleigh number (Ra). This dimensionless number is given by
where
is the difference in density between the two parcels of material that are mixing
is the local gravitational acceleration
is the characteristic length-scale of convection: the depth of the boiling pot, for example
is the diffusivity of the characteristic that is causing the convection, and
is the dynamic viscosity.
Natural convection will be more likely and/or more rapid with a greater variation in density between the two fluids, a larger acceleration due to gravity that drives the convection, and/or a larger distance through the convecting medium. Convection will be less likely and/or less rapid with more rapid diffusion (thereby diffusing away the gradient that is causing the convection) and/or a more viscous (sticky) fluid.
For thermal convection due to heating from below, as described in the boiling pot above, the equation is modified for thermal expansion and thermal diffusivity. Density variations due to thermal expansion are given by:
where
is the reference density, typically picked to be the average density of the medium,
is the coefficient of thermal expansion, and
is the temperature difference across the medium.
The general diffusivity, , is redefined as a thermal diffusivity, .
Inserting these substitutions produces a Rayleigh number that can be used to predict thermal convection.
Turbulence
The tendency of a particular naturally convective system towards turbulence relies on the Grashof number (Gr).
In very sticky, viscous fluids (large ν), fluid motion is restricted, and natural convection will be non-turbulent.
Following the treatment of the previous subsection, the typical fluid velocity is of the order of , up to a numerical factor depending on the geometry of the system. Therefore, Grashof number can be thought of as Reynolds number with the velocity of natural convection replacing the velocity in Reynolds number's formula. However In practice, when referring to the Reynolds number, it is understood that one is considering forced convection, and the velocity is taken as the velocity dictated by external constraints (see below). | Convection | Wikipedia | 501 | 47526 | https://en.wikipedia.org/wiki/Convection | Physical sciences | Fluid mechanics | null |
Behavior
The Grashof number can be formulated for natural convection occurring due to a concentration gradient, sometimes termed thermo-solutal convection. In this case, a concentration of hot fluid diffuses into a cold fluid, in much the same way that ink poured into a container of water diffuses to dye the entire space. Then:
Natural convection is highly dependent on the geometry of the hot surface, various correlations exist in order to determine the heat transfer coefficient.
A general correlation that applies for a variety of geometries is
The value of f4(Pr) is calculated using the following formula
Nu is the Nusselt number and the values of Nu0 and the characteristic length used to calculate Re are listed below (see also Discussion):
Warning: The values indicated for the Horizontal cylinder are wrong; see discussion.
Natural convection from a vertical plate
One example of natural convection is heat transfer from an isothermal vertical plate immersed in a fluid, causing the fluid to move parallel to the plate. This will occur in any system wherein the density of the moving fluid varies with position. These phenomena will only be of significance when the moving fluid is minimally affected by forced convection.
When considering the flow of fluid is a result of heating, the following correlations can be used, assuming the fluid is an ideal diatomic, has adjacent to a vertical plate at constant temperature and the flow of the fluid is completely laminar.
Num = 0.478(Gr0.25)
Mean Nusselt number = Num = hmL/k
where
hm = mean coefficient applicable between the lower edge of the plate and any point in a distance L (W/m2. K)
L = height of the vertical surface (m)
k = thermal conductivity (W/m. K)
Grashof number = Gr =
where
g = gravitational acceleration (m/s2)
L = distance above the lower edge (m)
ts = temperature of the wall (K)
t∞ = fluid temperature outside the thermal boundary layer (K)
v = kinematic viscosity of the fluid (m2/s)
T = absolute temperature (K)
When the flow is turbulent different correlations involving the Rayleigh Number (a function of both the Grashof number and the Prandtl number) must be used. | Convection | Wikipedia | 471 | 47526 | https://en.wikipedia.org/wiki/Convection | Physical sciences | Fluid mechanics | null |
Note that the above equation differs from the usual expression for Grashof number because the value has been replaced by its approximation , which applies for ideal gases only (a reasonable approximation for air at ambient pressure).
Pattern formation
Convection, especially Rayleigh–Bénard convection, where the convecting fluid is contained by two rigid horizontal plates, is a convenient example of a pattern-forming system.
When heat is fed into the system from one direction (usually below), at small values it merely diffuses (conducts) from below upward, without causing fluid flow. As the heat flow is increased, above a critical value of the Rayleigh number, the system undergoes a bifurcation from the stable conducting state to the convecting state, where bulk motion of the fluid due to heat begins. If fluid parameters other than density do not depend significantly on temperature, the flow profile is symmetric, with the same volume of fluid rising as falling. This is known as Boussinesq convection.
As the temperature difference between the top and bottom of the fluid becomes higher, significant differences in fluid parameters other than density may develop in the fluid due to temperature. An example of such a parameter is viscosity, which may begin to significantly vary horizontally across layers of fluid. This breaks the symmetry of the system, and generally changes the pattern of up- and down-moving fluid from stripes to hexagons, as seen at right. Such hexagons are one example of a convection cell.
As the Rayleigh number is increased even further above the value where convection cells first appear, the system may undergo other bifurcations, and other more complex patterns, such as spirals, may begin to appear. | Convection | Wikipedia | 345 | 47526 | https://en.wikipedia.org/wiki/Convection | Physical sciences | Fluid mechanics | null |
The cryosphere is an umbrella term for those portions of Earth's surface where water is in solid form. This includes sea ice, ice on lakes or rivers, snow, glaciers, ice caps, ice sheets, and frozen ground (which includes permafrost). Thus, there is a overlap with the hydrosphere. The cryosphere is an integral part of the global climate system. It also has important feedbacks on the climate system. These feedbacks come from the cryosphere's influence on surface energy and moisture fluxes, clouds, the water cycle, atmospheric and oceanic circulation.
Through these feedback processes, the cryosphere plays a significant role in the global climate and in climate model response to global changes. Approximately 10% of the Earth's surface is covered by ice, but this is rapidly decreasing. Current reductions in the cryosphere (caused by climate change) are measurable in ice sheet melt, glaciers decline, sea ice decline, permafrost thaw and snow cover decrease.
Definition and terminology
The cryosphere describes those portions of Earth's surface where water is in solid form. Frozen water is found on the Earth's surface primarily as snow cover, freshwater ice in lakes and rivers, sea ice, glaciers, ice sheets, and frozen ground and permafrost (permanently frozen ground).
The cryosphere is one of five components of the climate system. The others are the atmosphere, the hydrosphere, the lithosphere and the biosphere.
The term cryosphere comes from the Greek word kryos, meaning cold, frost or ice and the Greek word sphaira, meaning globe or ball.
Cryospheric sciences is an umbrella term for the study of the cryosphere. As an interdisciplinary Earth science, many disciplines contribute to it, most notably geology, hydrology, and meteorology and climatology; in this sense, it is comparable to glaciology.
The term deglaciation describes the retreat of cryospheric features. | Cryosphere | Wikipedia | 406 | 47527 | https://en.wikipedia.org/wiki/Cryosphere | Physical sciences | Water: General | null |
Properties and interactions
There are several fundamental physical properties of snow and ice that modulate energy exchanges between the surface and the atmosphere. The most important properties are the surface reflectance (albedo), the ability to transfer heat (thermal diffusivity), and the ability to change state (latent heat). These physical properties, together with surface roughness, emissivity, and dielectric characteristics, have important implications for observing snow and ice from space. For example, surface roughness is often the dominant factor determining the strength of radar backscatter. Physical properties such as crystal structure, density, length, and liquid water content are important factors affecting the transfers of heat and water and the scattering of microwave energy.
Residence time and extent
The residence time of water in each of the cryospheric sub-systems varies widely. Snow cover and freshwater ice are essentially seasonal, and most sea ice, except for ice in the central Arctic, lasts only a few years if it is not seasonal. A given water particle in glaciers, ice sheets, or ground ice, however, may remain frozen for 10–100,000 years or longer, and deep ice in parts of East Antarctica may have an age approaching 1 million years.
Most of the world's ice volume is in Antarctica, principally in the East Antarctic Ice Sheet. In terms of areal extent, however, Northern Hemisphere winter snow and ice extent comprise the largest area, amounting to an average 23% of hemispheric surface area in January. The large areal extent and the important climatic roles of snow and ice is related to their unique physical properties. This also indicates that the ability to observe and model snow and ice-cover extent, thickness, and physical properties (radiative and thermal properties) is of particular significance for climate research.
Surface reflectance
The surface reflectance of incoming solar radiation is important for the surface energy balance (SEB). It is the ratio of reflected to incident solar radiation, commonly referred to as albedo. Climatologists are primarily interested in albedo integrated over the shortwave portion of the electromagnetic spectrum (~300 to 3500 nm), which coincides with the main solar energy input. Typically, albedo values for non-melting snow-covered surfaces are high (~80–90%) except in the case of forests. | Cryosphere | Wikipedia | 476 | 47527 | https://en.wikipedia.org/wiki/Cryosphere | Physical sciences | Water: General | null |
The higher albedos for snow and ice cause rapid shifts in surface reflectivity in autumn and spring in high latitudes, but the overall climatic significance of this increase is spatially and temporally modulated by cloud cover. (Planetary albedo is determined principally by cloud cover, and by the small amount of total solar radiation received in high latitudes during winter months.) Summer and autumn are times of high-average cloudiness over the Arctic Ocean so the albedo feedback associated with the large seasonal changes in sea-ice extent is greatly reduced. It was found that snow cover exhibited the greatest influence on Earth's radiative balance in the spring (April to May) period when incoming solar radiation was greatest over snow-covered areas.
Thermal properties of cryospheric elements
The thermal properties of cryospheric elements also have important climatic consequences. Snow and ice have much lower thermal diffusivities than air. Thermal diffusivity is a measure of the speed at which temperature waves can penetrate a substance. Snow and ice are many orders of magnitude less efficient at diffusing heat than air. Snow cover insulates the ground surface, and sea ice insulates the underlying ocean, decoupling the surface-atmosphere interface with respect to both heat and moisture fluxes. The flux of moisture from a water surface is eliminated by even a thin skin of ice, whereas the flux of heat through thin ice continues to be substantial until it attains a thickness in excess of 30 to 40 cm. However, even a small amount of snow on top of the ice will dramatically reduce the heat flux and slow down the rate of ice growth. The insulating effect of snow also has major implications for the hydrological cycle. In non-permafrost regions, the insulating effect of snow is such that only near-surface ground freezes and deep-water drainage is uninterrupted. | Cryosphere | Wikipedia | 385 | 47527 | https://en.wikipedia.org/wiki/Cryosphere | Physical sciences | Water: General | null |
While snow and ice act to insulate the surface from large energy losses in winter, they also act to retard warming in the spring and summer because of the large amount of energy required to melt ice (the latent heat of fusion, 3.34 x 105 J/kg at 0 °C). However, the strong static stability of the atmosphere over areas of extensive snow or ice tends to confine the immediate cooling effect to a relatively shallow layer, so that associated atmospheric anomalies are usually short-lived and local to regional in scale. In some areas of the world such as Eurasia, however, the cooling associated with a heavy snowpack and moist spring soils is known to play a role in modulating the summer monsoon circulation.
Climate change feedback mechanisms
There are numerous cryosphere-climate feedbacks in the global climate system. These operate over a wide range of spatial and temporal scales from local seasonal cooling of air temperatures to hemispheric-scale variations in ice sheets over time scales of thousands of years. The feedback mechanisms involved are often complex and incompletely understood. For example, Curry et al. (1995) showed that the so-called "simple" sea ice-albedo feedback involved complex interactions with lead fraction, melt ponds, ice thickness, snow cover, and sea-ice extent.
The role of snow cover in modulating the monsoon is just one example of a short-term cryosphere-climate feedback involving the land surface and the atmosphere.
Components
Glaciers and ice sheets
Ice sheets and glaciers are flowing ice masses that rest on solid land. They are controlled by snow accumulation, surface and basal melt, calving into surrounding oceans or lakes and internal dynamics. The latter results from gravity-driven creep flow ("glacial flow") within the ice body and sliding on the underlying land, which leads to thinning and horizontal spreading. Any imbalance of this dynamic equilibrium between mass gain, loss and transport due to flow results in either growing or shrinking ice bodies.Relationships between global climate and changes in ice extent are complex. The mass balance of land-based glaciers and ice sheets is determined by the accumulation of snow, mostly in winter, and warm-season ablation due primarily to net radiation and turbulent heat fluxes to melting ice and snow from warm-air advection Where ice masses terminate in the ocean, iceberg calving is the major contributor to mass loss. In this situation, the ice margin may extend out into deep water as a floating ice shelf, such as that in the Ross Sea.
Sea ice | Cryosphere | Wikipedia | 512 | 47527 | https://en.wikipedia.org/wiki/Cryosphere | Physical sciences | Water: General | null |
Sea ice covers much of the polar oceans and forms by freezing of sea water. Satellite data since the early 1970s reveal considerable seasonal, regional, and interannual variability in the sea ice covers of both hemispheres. Seasonally, sea-ice extent in the Southern Hemisphere varies by a factor of 5, from a minimum of 3–4 million km2 in February to a maximum of 17–20 million km2 in September. The seasonal variation is much less in the Northern Hemisphere where the confined nature and high latitudes of the Arctic Ocean result in a much larger perennial ice cover, and the surrounding land limits the equatorward extent of wintertime ice. Thus, the seasonal variability in Northern Hemisphere ice extent varies by only a factor of 2, from a minimum of 7–9 million km2 in September to a maximum of 14–16 million km2 in March.
The ice cover exhibits much greater regional-scale interannual variability than it does hemispherical. For instance, in the region of the Sea of Okhotsk and Japan, maximum ice extent decreased from 1.3 million km2 in 1983 to 0.85 million km2 in 1984, a decrease of 35%, before rebounding the following year to 1.2 million km2. The regional fluctuations in both hemispheres are such that for any several-year period of the satellite record some regions exhibit decreasing ice coverage while others exhibit increasing ice cover.
Frozen ground and permafrost
Snow cover
Most of the Earth's snow-covered area is located in the Northern Hemisphere, and varies seasonally from 46.5 million km2 in January to 3.8 million km2 in August.
Snow cover is an extremely important storage component in the water balance, especially seasonal snowpacks in mountainous areas of the world. Though limited in extent, seasonal snowpacks in the Earth's mountain ranges account for the major source of the runoff for stream flow and groundwater recharge over wide areas of the midlatitudes. For example, over 85% of the annual runoff from the Colorado River basin originates as snowmelt. Snowmelt runoff from the Earth's mountains fills the rivers and recharges the aquifers that over a billion people depend on for their water resources.
Furthermore, over 40% of the world's protected areas are in mountains, attesting to their value both as unique ecosystems needing protection and as recreation areas for humans.
Ice on lakes and rivers | Cryosphere | Wikipedia | 497 | 47527 | https://en.wikipedia.org/wiki/Cryosphere | Physical sciences | Water: General | null |
Ice forms on rivers and lakes in response to seasonal cooling. The sizes of the ice bodies involved are too small to exert anything other than localized climatic effects. However, the freeze-up/break-up processes respond to large-scale and local weather factors, such that considerable interannual variability exists in the dates of appearance and disappearance of the ice. Long series of lake-ice observations can serve as a proxy climate record, and the monitoring of freeze-up and break-up trends may provide a convenient integrated and seasonally-specific index of climatic perturbations. Information on river-ice conditions is less useful as a climatic proxy because ice formation is strongly dependent on river-flow regime, which is affected by precipitation, snow melt, and watershed runoff as well as being subject to human interference that directly modifies channel flow, or that indirectly affects the runoff via land-use practices.
Lake freeze-up depends on the heat storage in the lake and therefore on its depth, the rate and temperature of any inflow, and water-air energy fluxes. Information on lake depth is often unavailable, although some indication of the depth of shallow lakes in the Arctic can be obtained from airborne radar imagery during late winter (Sellman et al. 1975) and spaceborne optical imagery during summer (Duguay and Lafleur 1997). The timing of breakup is modified by snow depth on the ice as well as by ice thickness and freshwater inflow.
Changes caused by climate change
Ice sheet melt
Decline of glaciers
Sea ice decline
Permafrost thaw
Snow cover decrease
Studies in 2021 found that Northern Hemisphere snow cover has been decreasing since 1978, along with snow depth. Paleoclimate observations show that such changes are unprecedented over the last millennia in Western North America.
North American winter snow cover increased during the 20th century, largely in response to an increase in precipitation.
Because of its close relationship with hemispheric air temperature, snow cover is an important indicator of climate change. | Cryosphere | Wikipedia | 401 | 47527 | https://en.wikipedia.org/wiki/Cryosphere | Physical sciences | Water: General | null |
Global warming is expected to result in major changes to the partitioning of snow and rainfall, and to the timing of snowmelt, which will have important implications for water use and management. These changes also involve potentially important decadal and longer time-scale feedbacks to the climate system through temporal and spatial changes in soil moisture and runoff to the oceans.(Walsh 1995). Freshwater fluxes from the snow cover into the marine environment may be important, as the total flux is probably of the same magnitude as desalinated ridging and rubble areas of sea ice. In addition, there is an associated pulse of precipitated pollutants which accumulate over the Arctic winter in snowfall and are released into the ocean upon ablation of the sea ice. | Cryosphere | Wikipedia | 153 | 47527 | https://en.wikipedia.org/wiki/Cryosphere | Physical sciences | Water: General | null |
Cumulonimbus () is a dense, towering, vertical cloud, typically forming from water vapor condensing in the lower troposphere that builds upward carried by powerful buoyant air currents. Above the lower portions of the cumulonimbus the water vapor becomes ice crystals, such as snow and graupel, the interaction of which can lead to hail and to lightning formation, respectively.
When causing thunderstorms, these clouds may be called thunderheads. Cumulonimbus can form alone, in clusters, or along squall lines. These clouds are capable of producing lightning and other dangerous severe weather, such as tornadoes, hazardous winds, and large hailstones. Cumulonimbus progress from overdeveloped cumulus congestus clouds and may further develop as part of a supercell. Cumulonimbus is abbreviated as Cb.
Appearance
Towering cumulonimbus clouds are typically accompanied by smaller cumulus clouds. The cumulonimbus base may extend several kilometres (miles) across, or be as small as several tens of metres (yards) across, and occupy low to upper altitudes within the troposphere - formed at altitude from approximately . Normal peaks usually reach to as much as , with unusually high ones typically topping out around and extreme instances claimed to be as high as or more. Well-developed cumulonimbus clouds are characterized by a flat, anvil shaped top (anvil dome), caused by wind shear or inversion at the equilibrium level near the tropopause. The shelf of the anvil may precede the main cloud's vertical component for many kilometres (miles), and be accompanied by lightning. Occasionally, rising air parcels surpass the equilibrium level (due to momentum) and form an overshooting top culminating at the maximum parcel level. When vertically developed, this largest of all clouds usually extends through all three cloud regions. Even the smallest cumulonimbus cloud dwarfs its neighbors in comparison.
Species
Cumulonimbus calvus: cloud with puffy top, similar to cumulus congestus which it develops from; under the correct conditions it can become a cumulonimbus capillatus.
Cumulonimbus capillatus: cloud with cirrus-like, fibrous-edged top. | Cumulonimbus cloud | Wikipedia | 474 | 47530 | https://en.wikipedia.org/wiki/Cumulonimbus%20cloud | Physical sciences | Clouds | null |
Types
Cumulonimbus flammagenitus (pyrocumulonimbus): rapidly growing cloud forming from non-atmospheric heat and condensation nuclei sources such as wildfires and volcanic eruptions.
Supplementary features
Accessory clouds
Arcus (including roll and shelf clouds): low, horizontal cloud formation associated with the leading edge of thunderstorm outflow.
Pannus: accompanied by a lower layer of fractus species cloud forming in precipitation.
Pileus (species calvus only): small cap-like cloud over parent cumulonimbus.
Velum: a thin horizontal sheet that forms around the middle of a cumulonimbus.
Supplementary features
Incus (species capillatus only): cumulonimbus with flat anvil-like cirriform top caused by wind shear where the rising air currents hit the inversion layer at the tropopause.
Mamma or mammatus: consisting of bubble-like protrusions on the underside.
Tuba: column hanging from the cloud base which can develop into a funnel cloud or tornado. They are known to drop very low, sometimes just above ground level.
Flanking line is a line of small cumulonimbus or cumulus generally associated with severe thunderstorms.
An overshooting top is a dome that rises above the thunderstorm; it is associated with severe weather.
Precipitation-based supplementary features
Rain: precipitation that reaches the ground as liquid, often in a precipitation shaft.
Virga: precipitation that evaporates before reaching the ground.
Effects | Cumulonimbus cloud | Wikipedia | 312 | 47530 | https://en.wikipedia.org/wiki/Cumulonimbus%20cloud | Physical sciences | Clouds | null |
Cumulonimbus storm cells can produce torrential rain of a convective nature (often in the form of a rain shaft) and flash flooding, as well as straight-line winds. Most storm cells die after about 20 minutes, when the precipitation causes more downdraft than updraft, causing the energy to dissipate. If there is sufficient instability and moisture in the atmosphere, however (on a hot summer day, for example), the outflowing moisture and gusts from one storm cell can lead to new cells forming just a few kilometres (miles) from the former one a few tens of minutes later or in some cases hundreds of kilometres (miles) away many hours later. This process cause thunderstorm formation (and decay) to last for several hours or even over multiple days. Cumulonimbus clouds can also occur as dangerous winter storms called "thundersnow" which are associated with particularly intense snowfall rates and with blizzard conditions when accompanied by strong winds that further reduce visibility. However, cumulonimbus clouds are most common in tropical regions and are also frequent in moist environments during the warm season in the middle latitudes. A dust storm caused by a cumulonimbus downburst is a haboob.
Hazards to aviation
Cumulonimbus are a notable hazard to aviation due most importantly to potent wind currents but also reduced visibility and lightning, as well as icing and hail if flying inside the cloud. Within and in the vicinity of thunderstorms there is significant turbulence and clear-air turbulence (particularly downwind), respectively. Wind shear within and under a cumulonimbus is often intense with downbursts being responsible for many accidents in earlier decades before training and technological detection and nowcasting measures were implemented. A small form of downburst, the microburst, is the most often implicated in crashes because of their rapid onset and swift changes in wind and aerodynamic conditions over short distances. Most downbursts are associated with visible precipitation shafts, however, dry microbursts are generally invisible to the naked eye. At least one fatal commercial airline accident was associated with flying through a tornado.
Life cycle or stages | Cumulonimbus cloud | Wikipedia | 446 | 47530 | https://en.wikipedia.org/wiki/Cumulonimbus%20cloud | Physical sciences | Clouds | null |
In general, cumulonimbus require moisture, an unstable air mass, and a lifting force in order to form. Cumulonimbus typically go through three stages: the developing stage, the mature stage (where the main cloud may reach supercell status in favorable conditions), and the dissipation stage. The average thunderstorm has a diameter and a height of approximately . Depending on the conditions present in the atmosphere, these three stages take an average of 30 minutes to go through.
Cloud types
Clouds form when the dew point temperature of water is reached in the presence of condensation nuclei in the troposphere. The atmosphere is a dynamic system, and the local conditions of turbulence, uplift, and other parameters give rise to many types of clouds. Various types of cloud occur frequently enough to have been categorized. Furthermore, some atmospheric processes can make the clouds organize in distinct patterns such as wave clouds or actinoform clouds. These are large-scale structures and are not always readily identifiable from a single point of view. | Cumulonimbus cloud | Wikipedia | 211 | 47530 | https://en.wikipedia.org/wiki/Cumulonimbus%20cloud | Physical sciences | Clouds | null |
Cumulus clouds are clouds that have flat bases and are often described as puffy, cotton-like, or fluffy in appearance. Their name derives from the Latin , meaning "heap" or "pile". Cumulus clouds are low-level clouds, generally less than in altitude unless they are the more vertical cumulus congestus form. Cumulus clouds may appear by themselves, in lines, or in clusters.
Cumulus clouds are often precursors of other types of clouds, such as cumulonimbus, when influenced by weather factors such as instability, humidity, and temperature gradient. Normally, cumulus clouds produce little or no precipitation, but they can grow into the precipitation-bearing cumulus congestus or cumulonimbus clouds. Cumulus clouds can be formed from water vapour, supercooled water droplets, or ice crystals, depending upon the ambient temperature. They come in many distinct subforms and generally cool the earth by reflecting the incoming solar radiation.
Cumulus clouds are part of the larger category of free-convective cumuliform clouds, which include cumulonimbus clouds. The latter genus-type is sometimes categorized separately as cumulonimbiform due to its more complex structure that often includes a cirriform or anvil top. There are also cumuliform clouds of limited convection that comprise stratocumulus (low-étage), altocumulus (middle-étage) and cirrocumulus (high-étage). These last three genus-types are sometimes classified separately as stratocumuliform.
Formation
Cumulus clouds form via atmospheric convection as air warmed by the surface begins to rise. As the air rises, the temperature drops (following the lapse rate), causing the relative humidity (RH) to rise. If convection reaches a certain level the RH reaches one hundred percent, and the "wet-adiabatic" phase begins. At this point a positive feedback ensues: since the RH is above 100%, water vapor condenses, releasing latent heat, warming the air and spurring further convection. | Cumulus cloud | Wikipedia | 435 | 47532 | https://en.wikipedia.org/wiki/Cumulus%20cloud | Physical sciences | Clouds | null |
In this phase, water vapor condenses on various nuclei present in the air, forming the cumulus cloud. This creates the characteristic flat-bottomed puffy shape associated with cumulus clouds. The height of the cloud (from its bottom to its top) depends on the temperature profile of the atmosphere and of the presence of any inversions. During the convection, surrounding air is entrained (mixed) with the thermal and the total mass of the ascending air increases.
Rain forms in a cumulus cloud via a process involving two non-discrete stages. The first stage occurs after the droplets coalesce onto the various nuclei. Langmuir writes that surface tension in the water droplets provides a slightly higher pressure on the droplet, raising the vapor pressure by a small amount. The increased pressure results in those droplets evaporating and the resulting water vapor condensing on the larger droplets. Due to the extremely small size of the evaporating water droplets, this process becomes largely meaningless after the larger droplets have grown to around 20 to 30 micrometres, and the second stage takes over. In the accretion phase, the raindrop begins to fall, and other droplets collide and combine with it to increase the size of the raindrop. Langmuir was able to develop a formula which predicted that the droplet radius would grow unboundedly within a discrete time period.
Description
The liquid water density within a cumulus cloud has been found to change with height above the cloud base rather than being approximately constant throughout the cloud. In one particular study, the concentration was found to be zero at cloud base. As altitude increased, the concentration rapidly increased to the maximum concentration near the middle of the cloud. The maximum concentration was found to be anything up to 1.25 grams of water per kilogram of air. The concentration slowly dropped off as altitude increased to the height of the top of the cloud, where it immediately dropped to zero again.
Cumulus clouds can form in lines stretching over long called cloud streets. These cloud streets cover vast areas and may be broken or continuous. They form when wind shear causes horizontal circulation in the atmosphere, producing the long, tubular cloud streets. They generally form during high-pressure systems, such as after a cold front. | Cumulus cloud | Wikipedia | 457 | 47532 | https://en.wikipedia.org/wiki/Cumulus%20cloud | Physical sciences | Clouds | null |
The height at which the cloud forms depends on the amount of moisture in the thermal that forms the cloud. Humid air will generally result in a lower cloud base. In temperate areas, the base of the cumulus clouds is usually below above ground level, but it can range up to in altitude. In arid and mountainous areas, the cloud base can be in excess of .
Cumulus clouds can be composed of ice crystals, water droplets, supercooled water droplets, or a mixture of them.
One study found that in temperate regions, the cloud bases studied ranged from above ground level. These clouds were normally above , and the concentration of droplets ranged from . This data was taken from growing isolated cumulus clouds that were not precipitating. The droplets were very small, ranging down to around 5 micrometres in diameter. Although smaller droplets may have been present, the measurements were not sensitive enough to detect them. The smallest droplets were found in the lower portions of the clouds, with the percentage of large droplets (around 20 to 30 micrometres) rising dramatically in the upper regions of the cloud. The droplet size distribution was slightly bimodal in nature, with peaks at the small and large droplet sizes and a slight trough in the intermediate size range. The skew was roughly neutral. Furthermore, large droplet size is roughly inversely proportional to the droplet concentration per unit volume of air.
In places, cumulus clouds can have "holes" where there are no water droplets. These can occur when winds tear the cloud and incorporate the environmental air or when strong downdrafts evaporate the water.
Subforms
Cumulus clouds come in four distinct species, cumulus humilis, mediocris, congestus, and fractus. These species may be arranged into the variety, cumulus radiatus; and may be accompanied by up to seven supplementary features, cumulus pileus, velum, virga, praecipitatio, arcus, pannus, and tuba. | Cumulus cloud | Wikipedia | 411 | 47532 | https://en.wikipedia.org/wiki/Cumulus%20cloud | Physical sciences | Clouds | null |
The species Cumulus fractus is ragged in appearance and can form in clear air as a precursor to cumulus humilis and larger cumulus species-types; or it can form in precipitation as the supplementary feature pannus (also called scud) which can also include stratus fractus of bad weather. Cumulus humilis clouds look like puffy, flattened shapes. Cumulus mediocris clouds look similar, except that they have some vertical development. Cumulus congestus clouds have a cauliflower-like structure and tower high into the atmosphere, hence their alternate name "towering cumulus". The variety Cumulus radiatus forms in radial bands called cloud streets and can comprise any of the four species of cumulus.
Cumulus supplementary features are most commonly seen with the species congestus. Cumulus virga clouds are cumulus clouds producing virga (precipitation that evaporates while aloft), and cumulus praecipitatio produce precipitation that reaches the Earth's surface. Cumulus pannus comprise shredded clouds that normally appear beneath the parent cumulus cloud during precipitation. Cumulus arcus clouds have a gust front, and cumulus tuba clouds have funnel clouds or tornadoes. Cumulus pileus clouds refer to cumulus clouds that have grown so rapidly as to force the formation of pileus over the top of the cloud. Cumulus velum clouds have an ice crystal veil over the growing top of the cloud.
There are also cumulus cataractagenitus, which are formed by waterfalls.
Forecast
Cumulus humilis clouds usually indicate fair weather. Cumulus mediocris clouds are similar, except that they have some vertical development, which implies that they can grow into cumulus congestus or even cumulonimbus clouds, which can produce heavy rain, lightning, severe winds, hail, and even tornadoes. Cumulus congestus clouds, which appear as towers, will often grow into cumulonimbus storm clouds. They can produce precipitation. Glider pilots often pay close attention to cumulus clouds, as they can be indicators of rising air drafts or thermals underneath that can suck the plane high into the sky—a phenomenon known as cloud suck.
Effects on climate | Cumulus cloud | Wikipedia | 454 | 47532 | https://en.wikipedia.org/wiki/Cumulus%20cloud | Physical sciences | Clouds | null |
Due to reflectivity, clouds cool the earth by around , an effect largely caused by stratocumulus clouds. However, at the same time, they heat the earth by around by reflecting emitted radiation, an effect largely caused by cirrus clouds. This averages out to a net loss of . Cumulus clouds, on the other hand, have a variable effect on heating the Earth's surface. The more vertical cumulus congestus species and cumulonimbus genus of clouds grow high into the atmosphere, carrying moisture with them, which can lead to the formation of cirrus clouds. The researchers speculated that this might even produce a positive feedback, where the increasing upper atmospheric moisture further warms the earth, resulting in an increasing number of cumulus congestus clouds carrying more moisture into the upper atmosphere.
Relation to other clouds
Cumulus clouds are a genus of free-convective low-level cloud along with the related limited-convective cloud stratocumulus. These clouds form from ground level to at all latitudes. Stratus clouds are also low-level. In the middle level are the alto- clouds, which consist of the limited-convective stratocumuliform cloud altocumulus and the stratiform cloud altostratus. Mid-level clouds form from to in polar areas, in temperate areas, and in tropical areas. The high-level cloud, cirrocumulus, is a stratocumuliform cloud of limited convection. The other clouds in this level are cirrus and cirrostratus. High clouds form in high latitudes, in temperate latitudes, and in low, tropical latitudes. Cumulonimbus clouds, like cumulus congestus, extend vertically rather than remaining confined to one level.
Cirrocumulus clouds | Cumulus cloud | Wikipedia | 374 | 47532 | https://en.wikipedia.org/wiki/Cumulus%20cloud | Physical sciences | Clouds | null |
Cirrocumulus clouds form in patches and cannot cast shadows. They commonly appear in regular, rippling patterns or in rows of clouds with clear areas between. Cirrocumulus are, like other members of the cumuliform and stratocumuliform categories, formed via convective processes. Significant growth of these patches indicates high-altitude instability and can signal the approach of poorer weather. The ice crystals in the bottoms of cirrocumulus clouds tend to be in the form of hexagonal cylinders. They are not solid, but instead tend to have stepped funnels coming in from the ends. Towards the top of the cloud, these crystals have a tendency to clump together. These clouds do not last long, and they tend to change into cirrus because as the water vapor continues to deposit on the ice crystals, they eventually begin to fall, destroying the upward convection. The cloud then dissipates into cirrus. Cirrocumulus clouds come in four species which are common to all three genus-types that have limited-convective or stratocumuliform characteristics: stratiformis, lenticularis, castellanus, and floccus. They are iridescent when the constituent supercooled water droplets are all about the same size.
Altocumulus clouds
Altocumulus clouds are a mid-level cloud that forms from high to in polar areas, in temperate areas, and in tropical areas. They can have precipitation and are commonly composed of a mixture of ice crystals, supercooled water droplets, and water droplets in temperate latitudes. However, the liquid water concentration was almost always significantly greater than the concentration of ice crystals, and the maximum concentration of liquid water tended to be at the top of the cloud while the ice concentrated itself at the bottom. The ice crystals in the base of the altocumulus clouds and in the virga were found to be dendrites or conglomerations of dendrites while needles and plates resided more towards the top. Altocumulus clouds can form via convection or via the forced uplift caused by a warm front.
Stratocumulus clouds | Cumulus cloud | Wikipedia | 440 | 47532 | https://en.wikipedia.org/wiki/Cumulus%20cloud | Physical sciences | Clouds | null |
A stratocumulus cloud is another type of stratocumuliform cloud. Like cumulus clouds, they form at low levels and via convection. However, unlike cumulus clouds, their growth is almost completely retarded by a strong inversion. As a result, they flatten out like stratus clouds, giving them a layered appearance. These clouds are extremely common, covering on average around twenty-three percent of the Earth's oceans and twelve percent of the Earth's continents. They are less common in tropical areas and commonly form after cold fronts. Additionally, stratocumulus clouds reflect a large amount of the incoming sunlight, producing a net cooling effect. Stratocumulus clouds can produce drizzle, which stabilizes the cloud by warming it and reducing turbulent mixing.
Cumulonimbus clouds
Cumulonimbus clouds are the final form of growing cumulus clouds. They form when cumulus congestus clouds develop a strong updraft that propels their tops higher and higher into the atmosphere until they reach the tropopause at in altitude. Cumulonimbus clouds, commonly called thunderheads, can produce high winds, torrential rain, lightning, gust fronts, waterspouts, funnel clouds, and tornadoes. They commonly have anvil clouds.
Horseshoe clouds
A short-lived horseshoe cloud may occur when a horseshoe vortex deforms a cumulus cloud.
Extraterrestrial
Some cumuliform and stratocumuliform clouds have been discovered on most other planets in the Solar System. On Mars, the Viking Orbiter detected cirrocumulus and stratocumulus clouds forming via convection primarily near the polar icecaps. The Galileo space probe detected massive cumulonimbus clouds near the Great Red Spot on Jupiter. Cumuliform clouds have also been detected on Saturn. In 2008, the Cassini spacecraft determined that cumulus clouds near Saturn's south pole were part of a cyclone over in diameter. The Keck Observatory detected whitish cumulus clouds on Uranus. Like Uranus, Neptune has methane cumulus clouds. Venus, however, does not appear to have cumulus clouds. | Cumulus cloud | Wikipedia | 443 | 47532 | https://en.wikipedia.org/wiki/Cumulus%20cloud | Physical sciences | Clouds | null |
The haptophytes, classified either as the Haptophyta, Haptophytina or Prymnesiophyta (named for Prymnesium), are a clade of algae.
The names Haptophyceae or Prymnesiophyceae are sometimes used instead. This ending implies classification at the class rank rather than as a division. Although the phylogenetics of this group has become much better understood in recent years, there remains some dispute over which rank is most appropriate.
Characteristics
The chloroplasts are pigmented similarly to those of the heterokonts, but the structure of the rest of the cell is different, so it may be that they are a separate line whose chloroplasts are derived from similar red algal endosymbionts. Haptophyte chloroplasts contain chlorophylls a, c1, and c2 but lack chlorophyll b. For carotenoids, they have beta-, alpha-, and gamma- carotenes. Like diatoms and brown algae, they have also fucoxanthin, an oxidized isoprenoid derivative that is likely the most important driver of their brownish-yellow color.
The cells typically have two slightly unequal flagella, both of which are smooth, and a unique organelle called a haptonema, which is superficially similar to a flagellum but differs in the arrangement of microtubules and in its use. The name comes from the Greek hapsis, touch, and nema, round thread. The mitochondria have tubular cristae.
Most haptophytes reportedly produce chrysolaminarin rather than starch as their major storage polysaccharide, but some Pavlovaceae produce paramylon. The chain length of the chrysolaminarin is reportedly short (polymers of 20–50 glycosides, unlike the 300+ of comparable amylose), and it is located in cytoplasmic membrane-bound vacuoles.
Significance | Haptophyte | Wikipedia | 428 | 47535 | https://en.wikipedia.org/wiki/Haptophyte | Biology and health sciences | Other organisms | null |
The best-known haptophytes are coccolithophores, which make up 673 of the 762 described haptophyte species, and have an exoskeleton of calcareous plates called coccoliths. Coccolithophores are some of the most abundant marine phytoplankton, especially in the open ocean, and are extremely abundant as microfossils, forming chalk deposits. Other planktonic haptophytes of note include Chrysochromulina and Prymnesium, which periodically form toxic marine algal blooms, and Phaeocystis, blooms of which can produce unpleasant foam which often accumulates on beaches.
Haptophytes are economically important, as species such as Pavlova lutheri and Isochrysis sp. are widely used in the aquaculture industry to feed oyster and shrimp larvae. They contain a large amount of polyunsaturated fatty acids such as docosahexaenoic acid (DHA), stearidonic acid and alpha-linolenic acid. Tisochrysis lutea contains betain lipids and phospholipids.
Classification
The haptophytes were first placed in the class Chrysophyceae (golden algae), but ultrastructural data have provided evidence to classify them separately. Both molecular and morphological evidence supports their division into five orders; coccolithophores make up the Isochrysidales and Coccolithales. Very small (2-3μm) uncultured pico-prymnesiophytes are ecologically important.
Haptophytes was discussed to be closely related to cryptomonads.
Haptophytes are closely related to the SAR clade. | Haptophyte | Wikipedia | 372 | 47535 | https://en.wikipedia.org/wiki/Haptophyte | Biology and health sciences | Other organisms | null |
Subphylum Haptophytina Cavalier-Smith 2015 [Haptophyta Hibberd 1976 sensu Ruggerio et al. 2015]
Clade Rappemonada Kim et al. 2011
Class Rappephyceae Cavalier-Smith 2015
Order Rappemonadales
Family Rappemonadaceae
Clade Haptomonada (Margulis & Schwartz 1998) [Haptophyta Hibberd 1976 emend. Edvardsen & Eikrem 2000; Prymnesiophyta Green & Jordan, 1994; Prymnesiomonada; Prymnesiida Hibberd 1976; Haptophyceae Christensen 1962 ex Silva 1980; Haptomonadida; Patelliferea Cavalier-Smith 1993]
Class Pavlovophyceae Cavalier-Smith 1986 [Pavlovophycidae Cavalier-Smith 1986]
Order Pavlovales Green 1976
Family Pavlovaceae Green 1976
Class Prymnesiophyceae Christensen 1962 emend. Cavalier-Smith 1996 [Haptophyceae s.s.; Prymnesiophycidae Cavalier-Smith 1986; Coccolithophyceae Casper 1972 ex Rothmaler 1951]
Family †Eoconusphaeraceae Kristan-Tollmann 1988 [Conusphaeraceae]
Family †Goniolithaceae Deflandre 1957
Family †Lapideacassaceae Black, 1971
Family †Microrhabdulaceae Deflandre 1963
Family †Nannoconaceae Deflandre 1959
Family †Polycyclolithaceae Forchheimer 1972 emend Varol, 1992
Family †Lithostromationaceae Deflandre 1959
Family †Rhomboasteraceae Bown, 2005
Family Braarudosphaeraceae Deflandre 1947
Family Ceratolithaceae Norris 1965 emend Young & Bown 2014 [Triquetrorhabdulaceae Lipps 1969 - cf Young & Bown 2014]
Family Alisphaeraceae Young et al., 2003
Family Papposphaeraceae Jordan & Young 1990 emend Andruleit & Young 2010
Family Umbellosphaeraceae Young et al., 2003 [Umbellosphaeroideae]
Order †Discoasterales Hay 1977
Family †Discoasteraceae Tan 1927
Family †Heliolithaceae Hay & Mohler 1967
Family †Sphenolithaceae Deflandre 1952
Family †Fasciculithaceae Hay & Mohler 1967
Order Phaeocystales Medlin 2000 | Haptophyte | Wikipedia | 506 | 47535 | https://en.wikipedia.org/wiki/Haptophyte | Biology and health sciences | Other organisms | null |
Family Phaeocystaceae Lagerheim 1896
Order Prymnesiales Papenfuss 1955 emend. Edvardsen and Eikrem 2000
Family Chrysochromulinaceae Edvardsen, Eikrem & Medlin 2011
Family Prymnesiaceae Conrad 1926 ex Schmidt 1931
Subclass Calcihaptophycidae
Order Isochrysidales Pascher 1910 [Prinsiales Young & Bown 1997]
Family †Prinsiaceae Hay & Mohler 1967 emend. Young & Bown, 1997
Family Isochrysidaceae Parke 1949 [Chrysotilaceae; Marthasteraceae Hay 1977]
Family Noëlaerhabdaceae Jerkovic 1970 emend. Young & Bown, 1997 [Gephyrocapsaceae Black 1971]
Order †Eiffellithales Rood, Hay & Barnard 1971 (loxolith; imbricating murolith)
Family †Chiastozygaceae Rood, Hay & Barnard 1973 [Ahmuellerellaceae Reinhardt, 1965]
Family †Eiffellithaceae Reinhardt 1965
Family †Rhagodiscaceae Hay 1977
Order Stephanolithiales Bown & Young 1997 (protolith; non-imbrication murolith)
Family Parhabdolithaceae Bown 1987
Family †Stephanolithiaceae Black 1968 emend. Black 1973
Order Zygodiscales Young & Bown 1997 [Crepidolithales]
Family Helicosphaeraceae Black 1971
Family Pontosphaeraceae Lemmermann 1908
Family †Zygodiscaceae Hay & Mohler 1967
Order Syracosphaerales Ostenfeld 1899 emend. Young et al., 2003 [Rhabdosphaerales Ostenfeld 1899]
Family Calciosoleniaceae Kamptner 1927
Family Syracosphaeraceae Lohmann, 1902 [Halopappiaceae Kamptner 1928] (caneolith & cyrtolith; murolith)
Family Rhabdosphaeraceae Haeckel, 1894 (planolith)
Order †Watznaueriales Bown 1987 (imbricating placolith)
Family †Watznaueriaceae Rood, Hay & Barnard 1971
Order †Arkhangelskiales Bown & Hampton 1997
Family †Arkhangelskiellaceae Bukry 1969
Family †Kamptneriaceae Bown & Hampton 1997 | Haptophyte | Wikipedia | 494 | 47535 | https://en.wikipedia.org/wiki/Haptophyte | Biology and health sciences | Other organisms | null |
Order †Podorhabdales Rood 1971 [Biscutales Aubry 2009; Prediscosphaerales Aubry 2009] (non-imbricating or radial placolith)
Family †Axopodorhabdaceae Wind & Wise 1977 [Podorhabdaceae Noel 1965]
Family †Biscutaceae Black, 1971
Family †Calyculaceae Noel 1973
Family †Cretarhabdaceae Thierstein 1973
Family †Mazaganellaceae Bown 1987
Family †Prediscosphaeraceae Rood et al., 1971 [Deflandriaceae Black 1968]
Family †Tubodiscaceae Bown & Rutledge 1997
Order Coccolithales Schwartz 1932 [Coccolithophorales]
Family Reticulosphaeraceae Cavalier-Smith 1996 [Reticulosphaeridae]
Family Calcidiscaceae Young & Bown 1997
Family Coccolithaceae Poche 1913 emend. Young & Bown, 1997 [Coccolithophoraceae]
Family Pleurochrysidaceae Fresnel & Billard 1991
Family Hymenomonadaceae Senn 1900 [Ochrosphaeraceae Schussnig 1930] | Haptophyte | Wikipedia | 248 | 47535 | https://en.wikipedia.org/wiki/Haptophyte | Biology and health sciences | Other organisms | null |
The carrying capacity of an environment is the maximum population size of a biological species that can be sustained by that specific environment, given the food, habitat, water, and other resources available. The carrying capacity is defined as the environment's maximal load, which in population ecology corresponds to the population equilibrium, when the number of deaths in a population equals the number of births (as well as immigration and emigration). Carrying capacity of the environment implies that the resources extraction is not above the rate of regeneration of the resources and the wastes generated are within the assimilating capacity of the environment. The effect of carrying capacity on population dynamics is modelled with a logistic function. Carrying capacity is applied to the maximum population an environment can support in ecology, agriculture and fisheries. The term carrying capacity has been applied to a few different processes in the past before finally being applied to population limits in the 1950s. The notion of carrying capacity for humans is covered by the notion of sustainable population.
An early detailed examination of global limits was published in the 1972 book Limits to Growth, which has prompted follow-up commentary and analysis, including much criticism. A 2012 review in Nature by 22 international researchers expressed concerns that the Earth may be "approaching a state shift" in which the biosphere may become less hospitable to human life and in which human carrying capacity may diminish. This concern that humanity may be passing beyond "tipping points" for safe use of the biosphere has increased in subsequent years. Recent estimates of Earth's carrying capacity run between two billion and four billion people, depending on how optimistic researchers are about international cooperation to solve collective action problems.
Origins
In terms of population dynamics, the term 'carrying capacity' was not explicitly used in 1838 by the Belgian mathematician Pierre François Verhulst when he first published his equations based on research on modelling population growth.
The origins of the term "carrying capacity" are uncertain, with sources variously stating that it was originally used "in the context of international shipping" in the 1840s, or that it was first used during 19th-century laboratory experiments with micro-organisms. A 2008 review finds the first use of the term in English was an 1845 report by the US Secretary of State to the US Senate. It then became a term used generally in biology in the 1870s, being most developed in wildlife and livestock management in the early 1900s. It had become a staple term in ecology used to define the biological limits of a natural system related to population size in the 1950s. | Carrying capacity | Wikipedia | 503 | 47544 | https://en.wikipedia.org/wiki/Carrying%20capacity | Biology and health sciences | Ecology | Biology |
Neo-Malthusians and eugenicists popularised the use of the words to describe the number of people the Earth can support in the 1950s, although American biostatisticians Raymond Pearl and Lowell Reed had already applied it in these terms to human populations in the 1920s.
Hadwen and Palmer (1923) defined carrying capacity as the density of stock that could be grazed for a definite period without damage to the range.
It was first used in the context of wildlife management by the American Aldo Leopold in 1933, and a year later by the American Paul Lester Errington, a wetlands specialist. They used the term in different ways, Leopold largely in the sense of grazing animals (differentiating between a 'saturation level', an intrinsic level of density a species would live in, and carrying capacity, the most animals which could be in the field) and Errington defining 'carrying capacity' as the number of animals above which predation would become 'heavy' (this definition has largely been rejected, including by Errington himself). The important and popular 1953 textbook on ecology by Eugene Odum, Fundamentals of Ecology, popularised the term in its modern meaning as the equilibrium value of the logistic model of population growth.
Mathematics
The specific reason why a population stops growing is known as a limiting or regulating factor.
The difference between the birth rate and the death rate is the natural increase. If the population of a given organism is below the carrying capacity of a given environment, this environment could support a positive natural increase; should it find itself above that threshold the population typically decreases. Thus, the carrying capacity is the maximum number of individuals of a species that an environment can support in long run.
Population size decreases above carrying capacity due to a range of factors depending on the species concerned, but can include insufficient space, food supply, or sunlight. The carrying capacity of an environment varies for different species.
In the standard ecological algebra as illustrated in the simplified Verhulst model of population dynamics, carrying capacity is represented by the constant K:
where
is the population size,
is the intrinsic rate of natural increase
is the carrying capacity of the local environment, and
, the derivative of with respect to time , is the rate of change in population with time.
Thus, the equation relates the growth rate of the population to the current population size, incorporating the effect of the two constant parameters and . (Note that decrease is negative growth.) The choice of the letter came from the German Kapazitätsgrenze (capacity limit). | Carrying capacity | Wikipedia | 510 | 47544 | https://en.wikipedia.org/wiki/Carrying%20capacity | Biology and health sciences | Ecology | Biology |
This equation is a modification of the original Verhulst model:
In this equation, the carrying capacity , , is
When the Verhulst model is plotted into a graph, the population change over time takes the form of a sigmoid curve, reaching its highest level at . This is the logistic growth curve and it is calculated with:
where
is the natural logarithm base (also known as Euler's number),
is the value of the sigmoid's midpoint,
is the curve's maximum value,
is the logistic growth rate or steepness of the curve and
The logistic growth curve depicts how population growth rate and carrying capacity are inter-connected. As illustrated in the logistic growth curve model, when the population size is small, the population increases exponentially. However, as population size nears carrying capacity, the growth decreases and reaches zero at .
What determines a specific system's carrying capacity involves a limiting factor; this may be available supplies of food or water, nesting areas, space, or the amount of waste that can be absorbed without degrading the environment and decreasing carrying capacity.
Population ecology
Carrying capacity is a commonly used concept for biologists when trying to better understand biological populations and the factors which affect them. When addressing biological populations, carrying capacity can be seen as a stable dynamic equilibrium, taking into account extinction and colonization rates. In population biology, logistic growth assumes that population size fluctuates above and below an equilibrium value.
Numerous authors have questioned the usefulness of the term when applied to actual wild populations. Although useful in theory and in laboratory experiments, carrying capacity as a method of measuring population limits in the environment is less useful as it sometimes oversimplifies the interactions between species. | Carrying capacity | Wikipedia | 358 | 47544 | https://en.wikipedia.org/wiki/Carrying%20capacity | Biology and health sciences | Ecology | Biology |
Agriculture
It is important for farmers to calculate the carrying capacity of their land so they can establish a sustainable stocking rate. For example, calculating the carrying capacity of a paddock in Australia is done in Dry Sheep Equivalents (DSEs). A single DSE is 50 kg Merino wether, dry ewe or non-pregnant ewe, which is maintained in a stable condition. Not only sheep are calculated in DSEs, the carrying capacity for other livestock is also calculated using this measure. A 200 kg weaned calf of a British style breed gaining 0.25 kg/day is 5.5DSE, but if the same weight of the same type of calf were gaining 0.75 kg/day, it would be measured at 8DSE. Cattle are not all the same, their DSEs can vary depending on breed, growth rates, weights, if it is a cow ('dam'), steer or ox ('bullock' in Australia), and if it weaning, pregnant or 'wet' (i.e. lactating).
In other parts of the world different units are used for calculating carrying capacities. In the United Kingdom the paddock is measured in LU, livestock units, although different schemes exist for this. New Zealand uses either LU, EE (ewe equivalents) or SU (stock units). In the US and Canada the traditional system uses animal units (AU). A French/Swiss unit is Unité de Gros Bétail (UGB).
In some European countries such as Switzerland the pasture (alm or alp) is traditionally measured in Stoß, with one Stoß equaling four Füße (feet). A more modern European system is Großvieheinheit (GV or GVE), corresponding to 500 kg in liveweight of cattle. In extensive agriculture 2 GV/ha is a common stocking rate, in intensive agriculture, when grazing is supplemented with extra fodder, rates can be 5 to 10 GV/ha. In Europe average stocking rates vary depending on the country, in 2000 the Netherlands and Belgium had a very high rate of 3.82 GV/ha and 3.19 GV/ha respectively, surrounding countries have rates of around 1 to 1.5 GV/ha, and more southern European countries have lower rates, with Spain having the lowest rate of 0.44 GV/ha. | Carrying capacity | Wikipedia | 500 | 47544 | https://en.wikipedia.org/wiki/Carrying%20capacity | Biology and health sciences | Ecology | Biology |
This system can also be applied to natural areas. Grazing megaherbivores at roughly 1 GV/ha is considered sustainable in central European grasslands, although this varies widely depending on many factors. In ecology it is theoretically (i.e. cyclic succession, patch dynamics, Megaherbivorenhypothese) taken that a grazing pressure of 0.3 GV/ha by wildlife is enough to hinder afforestation in a natural area. Because different species have different ecological niches, with horses for example grazing short grass, cattle longer grass, and goats or deer preferring to browse shrubs, niche differentiation allows a terrain to have slightly higher carrying capacity for a mixed group of species, than it would if there were only one species involved.
Some niche market schemes mandate lower stocking rates than can maximally be grazed on a pasture. In order to market ones' meat products as 'biodynamic', a lower Großvieheinheit of 1 to 1.5 (2.0) GV/ha is mandated, with some farms having an operating structure using only 0.5 to 0.8 GV/ha.
The Food and Agriculture Organization has introduced three international units to measure carrying capacity: FAO Livestock Units for North America, FAO Livestock Units for sub-Saharan Africa, and Tropical Livestock Units.
Another rougher and less precise method of determining the carrying capacity of a paddock is simply by looking objectively at the condition of the herd. In Australia, the national standardized system for rating livestock conditions is done by body condition scoring (BCS). An animal in a very poor condition is scored with a BCS of 0, and an animal which is extremely healthy is scored at 5: animals may be scored between these two numbers in increments of 0.25. At least 25 animals of the same type must be scored to provide a statistically representative number, and scoring must take place monthly -if the average falls, this may be due to a stocking rate above the paddock's carrying capacity or too little fodder. This method is less direct for determining stocking rates than looking at the pasture itself, because the changes in the condition of the stock may lag behind changes in the condition of the pasture.
Fisheries | Carrying capacity | Wikipedia | 466 | 47544 | https://en.wikipedia.org/wiki/Carrying%20capacity | Biology and health sciences | Ecology | Biology |
In fisheries, carrying capacity is used in the formulae to calculate sustainable yields for fisheries management. The maximum sustainable yield (MSY) is defined as "the highest average catch that can be continuously taken from an exploited population (=stock) under average environmental conditions". MSY was originally calculated as half of the carrying capacity, but has been refined over the years, now being seen as roughly 30% of the population, depending on the species or population. Because the population of a species which is brought below its carrying capacity due to fishing will find itself in the exponential phase of growth, as seen in the Verhulst model, the harvesting of an amount of fish at or below MSY is a surplus yield which can be sustainably harvested without reducing population size at equilibrium, keeping the population at its maximum recruitment. However, annual fishing can be seen as a modification of r in the equation -i.e. the environment has been modified, which means that the population size at equilibrium with annual fishing is slightly below what K would be without it.
Note that mathematically and in practical terms, MSY is problematic. If mistakes are made and even a tiny amount of fish are harvested each year above the MSY, populations dynamics imply that the total population will eventually decrease to zero. The actual carrying capacity of the environment may fluctuate in the real world, which means that practically, MSY may actually vary from year to year (annual sustainable yields and maximum average yield attempt to take this into account). Other similar concepts are optimum sustainable yield and maximum economic yield; these are both harvest rates below MSY.
These calculations are used to determine fishing quotas.
Humans
Human carrying capacity is a function of how people live and the technology at their disposal. The two great economic revolutions that marked human history up to 1900—the agricultural and industrial revolutions—greatly increased the Earth's human carrying capacity, allowing human population to grow from 5 to 10 million people in 10,000 BCE to 1.5 billion in 1900. The immense technological improvements of the past 100 years—in applied chemistry, physics, computing, genetic engineering, and more—have further increased Earth's human carrying capacity, at least in the short term. Without the Haber-Bosch process for fixing nitrogen, modern agriculture could not support 8 billion people. Without the Green Revolution of the 1950s and 60s, famine might have culled large numbers of people in poorer countries during the last three decades of the twentieth century. | Carrying capacity | Wikipedia | 501 | 47544 | https://en.wikipedia.org/wiki/Carrying%20capacity | Biology and health sciences | Ecology | Biology |
Recent technological successes, however, have come at grave environmental costs. Climate change, ocean acidification, and the huge dead zones at the mouths of many of world's great rivers, are a function of the scale of contemporary agriculture and the many other demands 8 billion people make on the planet. Scientists now speak of humanity exceeding or threatening to exceed 9 planetary boundaries for safe use of the biosphere. Humanity's unprecedented ecological impacts threaten to degrade the ecosystem services that people and the rest of life depend on—potentially decreasing Earth's human carrying capacity. The signs that we have crossed this threshold are increasing.
The fact that degrading Earth's essential services is obviously possible, and happening in some cases, suggests that 8 billion people may be above Earth's human carrying capacity. But human carrying capacity is always a function of a certain number of people living a certain way. This was encapsulated by Paul Ehrlich and James Holdren's (1972) IPAT equation: environmental impact (I) = population (P) x affluence (A) x the technologies used to accommodate human demands (T). IPAT has found spectacular confirmation in recent decades within climate science, where the Kaya identity for explaining changes in emissions is essentially IPAT with two technology factors broken out for ease of use.
This suggests to technological optimists that new technological discoveries (or the deployment of existing ones) could continue to increase Earth's human carrying capacity, as it has in the past. Yet technology has unexpected side effects, as we have seen with stratospheric ozone depletion, excessive nitrogen deposition in the world's rivers and bays, and global climate change. This suggests that 8 billion people may be sustainable for a few generations, but not over the long term, and the term ‘carrying capacity’ implies a population that is sustainable indefinitely. It is possible, too, that efforts to anticipate and manage the impacts of powerful new technologies, or to divide up the efforts needed to keep global ecological impacts within sustainable bounds among more than 200 nations all pursuing their own self-interest, may prove too complicated to achieve over the long haul. | Carrying capacity | Wikipedia | 442 | 47544 | https://en.wikipedia.org/wiki/Carrying%20capacity | Biology and health sciences | Ecology | Biology |
One issue with applying carrying capacity to any species is that ecosystems are not constant and change over time, therefore changing the resources available. Research has shown that sometimes the presence of human populations can increase local biodiversity, demonstrating that human habitation does not always lead to deforestation and decreased biodiversity. Another issue to consider when applying carrying capacity, especially to humans, is that measuring food resources is arbitrary. This is due to choosing what to consider (e.g., whether or not to include plants that are not available every year), how to classify what is considered (e.g., classifying edible plants that are not usually eaten as food resources or not), and determining if caloric values or nutritional values are privileged. Additional layers to this for humans are their cultural differences in taste (e.g., some consume flying termites) and individual choices on what to invest their labor into (e.g., fishing vs. farming), both of which vary over time. This leads to the need to determine whether or not to include all food resources or only those the population considered will consume. Carrying capacity measurements over large areas also assumes homogeneity in the resources available but this does not account for how resources and access to them can greatly vary within regions and populations. They also assume that the populations in the region only rely on that region’s resources even though humans exchange resources with others from other regions and there are few, if any, isolated populations. Variations in standards of living which directly impact resource consumption are also not taken into account. These issues show that while there are limits to resources, a more complex model of how humans interact with their ecosystem needs to be used to understand them.
Recent warnings that humanity may have exceeded Earth's carrying capacity
Between 1900 and 2020, Earth's human population increased from 1.6 billion to 7.8 billion (a 390% increase). These successes greatly increased human resource demands, generating significant environmental degradation. | Carrying capacity | Wikipedia | 397 | 47544 | https://en.wikipedia.org/wiki/Carrying%20capacity | Biology and health sciences | Ecology | Biology |
Millennium ecosystem assessment
The Millennium Ecosystem Assessment (MEA) of 2005 was a massive, collaborative effort to assess the state of Earth's ecosystems, involving more than 1,300 experts worldwide. Their first two of four main findings were the following. The first finding is:Over the past 50 years, humans have changed ecosystems more rapidly and extensively than in any comparable period of time in human history, largely to meet rapidly growing demands for food, fresh water, timber, fiber, and fuel. This has resulted in a substantial and largely irreversible loss in the diversity of life on Earth.The second of the four main findings is:The changes that have been made to ecosystems have contributed to substantial net gains in human well-being and economic development, but these gains have been achieved at growing costs in the form of the degradation of many ecosystem services, increased risks of nonlinear changes, and the exacerbation of poverty for some groups of people. These problems, unless addressed, will substantially diminish the benefits that future generations obtain from ecosystems.According to the MEA, these unprecedented environmental changes threaten to reduce the Earth's long-term human carrying capacity. “The degradation of ecosystem services could grow significantly worse during the first half of this [21st] century,” they write, serving as a barrier to improving the lives of poor people around the world. | Carrying capacity | Wikipedia | 275 | 47544 | https://en.wikipedia.org/wiki/Carrying%20capacity | Biology and health sciences | Ecology | Biology |
Critiques of Carrying Capacity with Relation to Humans
Humans and human culture itself are highly adaptable things that have overcome issues that seemed incomprehensible at the time before. It is not to say that carrying capacity is not something that should be considered and thought about, but it should be taken with some skepticism when presented as a concretely evidenced proof of something. Many biologists, ecologists, and social scientists have disposed of the term altogether due to the generalizations that are made that gloss over the complexity of interactions that take place on the micro and macro level. Carrying capacity in a human environment is subject to change at any time due to the highly adaptable nature of human society and culture. If resources, time, and energy are put into an issue, there very well may be a solution that exposes itself. This also should not be used as an excuse to overexploit or take advantage of the land or resources that are available. Nonetheless, it is possible to not be pessimistic as technological, social, and institutional adaptions could be accelerated, especially in a time of need, to solve problems, or in this case, increase carrying capacity. There are also of course resources on this Earth that are limited that most certainly will run out if overused or used without proper oversight/checks and balances. If things are left without remaining checked then overconsumption and exploitation of land and resources is likely to occur. | Carrying capacity | Wikipedia | 291 | 47544 | https://en.wikipedia.org/wiki/Carrying%20capacity | Biology and health sciences | Ecology | Biology |
Ecological Footprint accounting measures the demands people make on nature and compares them to available supplies, for both individual countries and the world as a whole. Developed originally by Mathis Wackernagel and William Rees, it has been refined and applied in a variety of contexts over the years by Global Footprint Network (GFN). On the demand side, the Ecological Footprint measures how fast a population uses resources and generates wastes, with a focus on five main areas: carbon emissions (or carbon footprint), land devoted to direct settlement, timber and paper use, food and fiber use, and seafood consumption. It converts these into per capita or total hectares used. On the supply side, national or global biocapacity represents the productivity of ecological assets in a particular nation or the world as a whole; this includes “cropland, grazing land, forest land, fishing grounds, and built-up land.” Again the various metrics to capture biocapacity are translated into the single term of hectares of available land. As Global Footprint Network (GFN) states:Each city, state or nation’s Ecological Footprint can be compared to its biocapacity, or that of the world. If a population’s Ecological Footprint exceeds the region’s biocapacity, that region runs a biocapacity deficit. Its demand for the goods and services that its land and seas can provide—fruits and vegetables, meat, fish, wood, cotton for clothing, and carbon dioxide absorption—exceeds what the region’s ecosystems can regenerate. In more popular communications, this is called “an ecological deficit.” A region in ecological deficit meets demand by importing, liquidating its own ecological assets (such as overfishing), and/or emitting carbon dioxide into the atmosphere. If a region’s biocapacity exceeds its Ecological Footprint, it has a biocapacity reserve.According to the GFN's calculations, humanity has been using resources and generating wastes in excess of sustainability since approximately 1970: currently humanity use Earth's resources at approximately 170% of capacity. This implies that humanity is well over Earth's human carrying capacity for our current levels of affluence and technology use. According to Global Footprint Network:In 2024, [Earth Overshoot Day] fell on August 1. Earth Overshoot Day marks the date when humanity has exhausted nature’s budget for the year | Carrying capacity | Wikipedia | 495 | 47544 | https://en.wikipedia.org/wiki/Carrying%20capacity | Biology and health sciences | Ecology | Biology |
For the rest of the year, we are maintaining our ecological deficit by drawing down local resource stocks and accumulating carbon dioxide in the atmosphere. We are operating in overshoot.The concept of ‘ecological overshoot’ can be seen as equivalent to exceeding human carrying capacity. According to the most recent calculations from Global Footprint Network, most of the world's residents live in countries in ecological overshoot (see the map on the right). | Carrying capacity | Wikipedia | 89 | 47544 | https://en.wikipedia.org/wiki/Carrying%20capacity | Biology and health sciences | Ecology | Biology |
This includes countries with dense populations (such as China, India, and the Philippines), countries with high per capita consumption and resource use (France, Germany, and Saudi Arabia), and countries with both high per capita consumption and large numbers of people (Japan, the United Kingdom, and the United States). | Carrying capacity | Wikipedia | 63 | 47544 | https://en.wikipedia.org/wiki/Carrying%20capacity | Biology and health sciences | Ecology | Biology |
Planetary Boundaries Framework
According to its developers, the planetary boundaries framework defines “a safe operating space for humanity based on the intrinsic biophysical processes that regulate the stability of the Earth system.” Human civilization has evolved in the relative stability of the Holocene epoch; crossing planetary boundaries for safe levels of atmospheric carbon, ocean acidity, or one of the other stated boundaries could send the global ecosystem spiraling into novel conditions that are less hospitable to life—possibly reducing global human carrying capacity. This framework, developed in an article published in 2009 in Nature and then updated in two articles published in 2015 in Science and in 2018 in PNAS, identifies nine stressors of planetary support systems that need to stay within critical limits to preserve stable and safe biospheric conditions (see figure below). Climate change and biodiversity loss are seen as especially crucial, since on their own, they could push the Earth system out of the Holocene state: “transitions between time periods in Earth history have often been delineated by substantial shifts in climate, the biosphere, or both.”
The scientific consensus is that humanity has exceeded three to five of the nine planetary boundaries for safe use of the biosphere and is pressing hard on several more. By itself, crossing one of the planetary boundaries does not prove humanity has exceeded Earth's human carrying capacity; perhaps technological improvements or clever management might reduce this stressor and bring us back within the biosphere's safe operating space. But when several boundaries are crossed, it becomes harder to argue that carrying capacity has not been breached. Because fewer people helps reduce all nine planetary stressors, the more boundaries are crossed, the clearer it appears that reducing human numbers is part of what is needed to get back within a safe operating space. Population growth regularly tops the list of causes of humanity's increasing impact on the natural environment in Earth system science literature. Recently, planetary boundaries developer Will Steffen and co-authors ranked global population change as the leading indicator of the influence of socio-economic trends on the functioning of the Earth system in the modern era, post-1750. | Carrying capacity | Wikipedia | 425 | 47544 | https://en.wikipedia.org/wiki/Carrying%20capacity | Biology and health sciences | Ecology | Biology |
Daylight saving time (DST), also referred to as daylight saving(s), daylight savings time, daylight time (United States and Canada), or summer time (United Kingdom, European Union, and others), is the practice of advancing clocks to make better use of the longer daylight available during summer so that darkness falls at a later clock time. The typical implementation of DST is to set clocks forward by one hour in spring or late winter, and to set clocks back by one hour to standard time in the autumn (or fall in North American English, hence the mnemonic: "spring forward and fall back").
Overview
Around 34 percent of the world's countries use DST. Some countries observe it only in some regions. In Canada, all of Yukon, most of Saskatchewan, and parts of Nunavut, Ontario, British Columbia and Quebec do not observe DST. It is observed by four Australian states and one territory. In the United States, it is observed by all states except Hawaii and Arizona (within the latter, however, the Navajo Nation does observe it).
Historically, several ancient societies adopted seasonal changes to their timekeeping to make better use of daylight; Roman timekeeping even included changes to water clocks to accommodate this. However, these were changes to the time divisions of the day rather than setting the whole clock forward. In a satirical letter to the editor of the Journal de Paris in 1784, Benjamin Franklin suggested that if Parisians could only wake up earlier in the summer they would economize on candle and oil usage, but he did not propose changing the clocks. In 1895, New Zealand entomologist and astronomer George Hudson made the first realistic proposal to change clocks by two hours every spring to the Wellington Philosophical Society, but this was not implemented until 1928 and in another form. In 1907, William Willett proposed the adoption of British Summer Time as a way to save energy; although seriously considered by Parliament, it was not implemented until 1916.
The first implementation of DST was by Port Arthur (today merged into Thunder Bay), in Ontario, Canada, in 1908, but only locally, not nationally. The first nation-wide implementations were by the German and Austro-Hungarian Empires, both starting on 30 April 1916. Since then, many countries have adopted DST at various times, particularly since the 1970s energy crisis.
Rationale | Daylight saving time | Wikipedia | 480 | 47548 | https://en.wikipedia.org/wiki/Daylight%20saving%20time | Technology | Timekeeping | null |
Industrialized societies usually follow a clock-based schedule for daily activities that do not change throughout the course of the year. The time of day that individuals begin and end work or school, and the coordination of mass transit, for example, usually remain constant year-round. In contrast, an agrarian society's daily routines for work and personal conduct are more likely governed by the length of daylight hours and by solar time, which change seasonally because of the Earth's axial tilt. North and south of the tropics, daylight lasts longer in that hemisphere's summer and is shorter in that hemisphere's winter, with the effect becoming greater the farther one moves away from the equator. DST is of little use for locations near the Equator, because these regions see only a small variation in daylight over the course of the year.
After synchronously resetting all clocks in a region to one hour ahead of standard time in spring in anticipation of longer daylight hours, individuals following a clock-based schedule will be awakened an hour earlier in the solar day than they would have otherwise. They will begin and complete daily work routines an hour earlier; in most cases, they will have an extra hour of daylight available to them after their workday activities.
The clock shift is partly motivated by practicality. At the summer solstice, in American temperate latitudes, for example, the sun rises around 4:30 standard time and sets around 19:30. Since most people are asleep at 04:30, it is seen as practical to treat 04:30 as if it were 05:30, thereby allowing people to wake closer to the sunrise and be active in the evening light, as the sun under DST sets an hour later (20:30). The longer evening daylight hours are attractive to golfers, for example, while farmers traditionally expressed dislike for having to be out working while dew is still heavy.
Proponents of daylight saving time argue that most people prefer more daylight hours after the typical "nine to five" workday. Supporters have also argued that DST decreases energy consumption by reducing the need for lighting and heating, but the actual effect on overall energy use is heavily disputed. For evaluation, it is required to go beyond considering only energy demand for lighting and also consider the energy used for heating or cooling buildings. | Daylight saving time | Wikipedia | 468 | 47548 | https://en.wikipedia.org/wiki/Daylight%20saving%20time | Technology | Timekeeping | null |
Variation within a time zone
The effect of daylight saving time also varies according to how far east or west the location is within its time zone, with locations farther east inside the time zone benefiting more from DST than locations farther west in the same time zone. In spite of a width spanning thousands of kilometers, all of China is located within a single time zone per government mandate, minimizing any potential benefit of daylight saving time there.
History
Ancient civilizations adjusted daily schedules to the sun more flexibly than DST does, often dividing daylight into 12 hours regardless of daytime, so that each daylight hour became progressively longer during spring and shorter during autumn. For example, the Romans kept time with water clocks that had different scales for different months of the year; at Rome's latitude, the third hour from sunrise (hora tertia) started at 09:02 solar time and lasted 44 minutes at the winter solstice, but at the summer solstice it started at 06:58 and lasted 75 minutes. From the 14th century onward, equal-length civil hours supplanted unequal ones, so civil time no longer varied by season. Unequal hours are still used in a few traditional settings, such as monasteries of Mount Athos and in Jewish ceremonies.
Benjamin Franklin published the proverb "early to bed and early to rise makes a man healthy, wealthy, and wise", and published a letter in the Journal de Paris when he was an American envoy to France (1776–1785) suggesting that Parisians economize on candles by rising earlier to use morning sunlight. This 1784 satire proposed taxing window shutters, rationing candles, and waking the public by ringing church bells and firing cannons at sunrise. Despite common misconception, Franklin did not actually propose DST; 18th-century Europe did not even keep precise schedules. However, this changed as rail transport and communication networks required a standardization of clocks unknown in Franklin's day.
In 1810, the Spanish National Assembly Cortes of Cádiz issued a regulation that moved certain meeting times forward by one hour from 1 May to 30 September in recognition of seasonal changes, but it did not change the clocks. It also acknowledged that private businesses were in the practice of changing their opening hours to suit daylight conditions, but they did so of their volition. | Daylight saving time | Wikipedia | 467 | 47548 | https://en.wikipedia.org/wiki/Daylight%20saving%20time | Technology | Timekeeping | null |
New Zealand entomologist George Hudson first proposed modern DST. His shift-work job gave him spare time to collect insects and led him to value after-hours daylight. In 1895, he presented a paper to the Wellington Philosophical Society proposing a two-hour daylight-saving shift, and considerable interest was expressed in Christchurch; he followed up with an 1898 paper. Many publications credit the DST proposal to prominent English builder and outdoorsman William Willett, who independently conceived DST in 1907 during a pre-breakfast ride when he observed how many Londoners slept through a large part of a summer day. Willett also was an avid golfer who disliked cutting short his round at dusk. His solution was to advance the clock during the summer, and he published the proposal two years later. Liberal Party member of parliament Robert Pearce took up the proposal, introducing the first Daylight Saving Bill to the British House of Commons on 12 February 1908. A select committee was set up to examine the issue, but Pearce's bill did not become law and several other bills failed in the following years. Willett lobbied for the proposal in the UK until his death in 1915.
Port Arthur, Ontario, Canada, was the first city in the world to enact DST, on 1 July 1908. This was followed by Orillia, Ontario, introduced by William Sword Frost while mayor from 1911 to 1912. The first states to adopt DST () nationally were those of the German Empire and its World War I ally Austria-Hungary commencing on 30 April 1916, as a way to conserve coal during wartime. Britain, most of its allies, and many European neutrals soon followed. Russia and a few other countries waited until the next year, and the United States adopted daylight saving in 1918. Most jurisdictions abandoned DST in the years after the war ended in 1918, with exceptions including Canada, the United Kingdom, France, Ireland, and the United States. It became common during World War II (some countries adopted double summer time), and was standardized in the US by federal law in 1966, and widely adopted in Europe from the 1970s as a result of the 1970s energy crisis. Since then, the world has seen many enactments, adjustments, and repeals. | Daylight saving time | Wikipedia | 450 | 47548 | https://en.wikipedia.org/wiki/Daylight%20saving%20time | Technology | Timekeeping | null |
It is a common myth in the United States that DST was first implemented for the benefit of farmers. In reality, farmers have been one of the strongest lobbying groups against DST since it was first implemented. The factors that influence farming schedules, such as morning dew and dairy cattle's readiness to be milked, are ultimately dictated by the sun, so the clock change introduces unnecessary challenges.
DST was first implemented in the US with the Standard Time Act of 1918, a wartime measure for seven months during World War I in the interest of adding more daylight hours to conserve energy resources. Year-round DST, or "War Time", was implemented again during World War II. After the war, local jurisdictions were free to choose if and when to observe DST until the Uniform Time Act which standardized DST in 1966. Permanent daylight saving time was enacted for the winter of 1974, but there were complaints of children going to school in the dark and working people commuting and starting their work day in pitch darkness during the winter, and it was repealed a year later.
Year-round daylight time has been adopted by the Canadian province of Saskatchewan, except Lloydminster and area.
Procedure
The relevant authorities usually schedule clock changes to occur at (or soon after) midnight and on a weekend, in order to lessen disruption to weekday schedules. A one-hour change is usual, but twenty-minute and two-hour changes have been used in the past. Notable exceptions today include Lord Howe Island with a thirty-minute change, and Troll (research station) that shifts two hours directly between CEST and GMT since 2016.
In all countries that observe daylight saving time seasonally (i.e., during summer and not winter), the clock is advanced from standard time to daylight saving time in the spring, and it is turned back from daylight saving time to standard time in the autumn.
For a midnight change in spring, a digital display of local time would appear to jump from 23:59:59.9 to 01:00:00.0. For the same clock in autumn, the local time would appear to repeat the hour preceding midnight, i.e. it would jump from 23:59:59.9 to 23:00:00.0. | Daylight saving time | Wikipedia | 459 | 47548 | https://en.wikipedia.org/wiki/Daylight%20saving%20time | Technology | Timekeeping | null |
In most countries that observe seasonal daylight saving time, clocks revert in winter to "standard time". An exception exists in Ireland, where its winter clock has the same offset (UTC+00:00) and legal name as that in Britain (Greenwich Mean Time)—but while its summer clock also has the same offset as Britain's (UTC+01:00), its legal name is confusingly called Irish Standard Time as opposed to British Summer Time.
Since 2019, Morocco observes daylight saving time every month but Ramadan. During the holy month (the date of which is determined by the lunar calendar and thus moves annually with regard to the Gregorian calendar), the country's civil clocks observe Western European Time (UTC+00:00, which geographically overlaps most of the nation). At the close of that month, its clocks are turned forward to Western European Summer Time (UTC+01:00).
The time at which to change clocks differs across jurisdictions. Members of the European Union conduct a coordinated change, changing all zones at the same instant, at 01:00 Coordinated Universal Time (UTC), which means that it changes at 02:00 Central European Time (CET), equivalent to 03:00 Eastern European Time (EET). As a result, the time differences across European time zones remain constant. North America coordination of the clock change differs, in that each jurisdiction changes at each local clock's 02:00, which temporarily creates an imbalance with the next time zone (until it adjusts its clock, one hour later, at 2 am there). For example, Mountain Time is for one hour in the spring two hours ahead of Pacific Time instead of the usual one hour ahead, and instead of one hour in the autumn, briefly zero hours ahead of Pacific Time. | Daylight saving time | Wikipedia | 367 | 47548 | https://en.wikipedia.org/wiki/Daylight%20saving%20time | Technology | Timekeeping | null |
The dates on which clocks change vary with location and year; consequently, the time differences between regions also vary throughout the year. For example, Central European Time is usually six hours ahead of North American Eastern Time, except for a few weeks in March and October/November, while the United Kingdom and mainland Chile could be five hours apart during the northern summer, three hours during the southern summer, and four hours for a few weeks per year. Since 1996, European Summer Time has been observed from the last Sunday in March to the last Sunday in October; previously the rules were not uniform across the European Union. Starting in 2007, most of the United States and Canada observed DST from the second Sunday in March to the first Sunday in November, almost two-thirds of the year. Moreover, the beginning and ending dates are roughly reversed between the northern and southern hemispheres because spring and autumn are displaced six months. For example, mainland Chile observes DST from the second Saturday in October to the second Saturday in March, with transitions at the local clock's 24:00. In some countries, clocks are governed by regional jurisdictions within the country such that some jurisdictions change and others do not; this is currently the case in Australia, Canada, and the United States.
From year to year, the dates on which to change clock may also move for political or social reasons. The Uniform Time Act of 1966 formalized the United States' period of daylight saving time observation as lasting six months (it was previously declared locally); this period was extended to seven months in 1986, and then to eight months in 2005. The 2005 extension was motivated in part by lobbyists from the candy industry, seeking to increase profits by including Halloween (31 October) within the daylight saving time period. In recent history, Australian state jurisdictions not only changed at different local times but sometimes on different dates. For example, in 2008 most states there that observed daylight saving time changed clocks forward on 5 October, but Western Australia changed on 26 October.
Politics, religion and sport
The concept of daylight saving has caused controversy since its early proposals. Winston Churchill argued that it enlarges "the opportunities for the pursuit of health and happiness among the millions of people who live in this country" and pundits have dubbed it "Daylight Slaving Time". Retailing, sports, and tourism interests have historically favored daylight saving, while agricultural and evening-entertainment interests (and some religious groups) have opposed it; energy crises and war prompted its initial adoption. | Daylight saving time | Wikipedia | 505 | 47548 | https://en.wikipedia.org/wiki/Daylight%20saving%20time | Technology | Timekeeping | null |
Willett's 1907 proposal illustrates several political issues. It attracted many supporters, including Arthur Balfour, Churchill, David Lloyd George, Ramsay MacDonald, King Edward VII (who used half-hour DST or "Sandringham time" at Sandringham), the managing director of Harrods, and the manager of the National Bank Ltd. However, the opposition proved stronger, including Prime Minister H. H. Asquith, William Christie (the Astronomer Royal), George Darwin, Napier Shaw (director of the Meteorological Office), many agricultural organizations, and theatre-owners. After many hearings, a parliamentary committee vote narrowly rejected the proposal in 1909. Willett's allies introduced similar bills every year from 1911 through 1914, to no avail. People in the US demonstrated even more skepticism; Andrew Peters introduced a DST bill to the House of Representatives in May 1909, but it soon died in committee.
Germany and its allies led the way in introducing DST during World War I on 30 April 1916, aiming to alleviate hardships due to wartime coal shortages and air-raid blackouts. The political equation changed in other countries; the United Kingdom used DST first on 21 May 1916. US retailing and manufacturing interests—led by Pittsburgh industrialist Robert Garland—soon began lobbying for DST, but railroads opposed the idea. The US' 1917 entry into the war overcame objections, and DST started in 1918. | Daylight saving time | Wikipedia | 286 | 47548 | https://en.wikipedia.org/wiki/Daylight%20saving%20time | Technology | Timekeeping | null |
The end of World War I brought a change in DST use. Farmers continued to dislike DST, and many countries repealed it—like Germany itself, which dropped DST from 1919 to 1939 and from 1950 to 1979. Britain proved an exception; it retained DST nationwide but adjusted transition dates over the years for several reasons, including special rules during the 1920s and 1930s to avoid clock shifts on Easter mornings. , summer time began annually on the last Sunday in March under a European Community directive, which may be Easter Sunday (as in 2016). In the US, Congress repealed DST after 1919. President Woodrow Wilson—an avid golfer like Willett—vetoed the repeal twice, but his second veto was overridden. Only a few US cities retained DST locally, including New York (so that its financial exchanges could maintain an hour of arbitrage trading with London), and Chicago and Cleveland (to keep pace with New York). Wilson's successor as president, Warren G. Harding, opposed DST as a "deception", reasoning that people should instead get up and go to work earlier in the summer. He ordered District of Columbia federal employees to start work at 8 am rather than 9 am during the summer of 1922. Some businesses followed suit, though many others did not; the experiment was not repeated.
Since Germany's adoption of DST in 1916, the world has seen many enactments, adjustments, and repeals of DST, with similar politics involved. The history of time in the United States features DST during both world wars, but no standardization of peacetime DST until 1966. St. Paul and Minneapolis, Minnesota, kept different clocks for two weeks in May 1965: the capital city decided to switch to daylight saving time, while Minneapolis opted to follow the later date set by state law. In the mid-1980s, Clorox and 7-Eleven provided the primary funding for the Daylight Saving Time Coalition behind the 1987 extension to US DST. Both senators from Idaho, Larry Craig and Mike Crapo, voted for it based on the premise that fast-food restaurants sell more French fries (made from Idaho potatoes) during DST.
A referendum on the introduction of daylight saving took place in Queensland, Australia, in 1992, after a three-year trial of daylight saving. It was defeated with a 54.5% "no" vote, with regional and rural areas strongly opposed, and those in the metropolitan southeast in favor. | Daylight saving time | Wikipedia | 500 | 47548 | https://en.wikipedia.org/wiki/Daylight%20saving%20time | Technology | Timekeeping | null |
In 2003, the United Kingdom's Royal Society for the Prevention of Accidents supported a proposal to observe year-round daylight saving time, but it has been opposed by some industries, by some postal workers and farmers, and particularly by those living in the northern regions of the UK.
In 2005, the Sporting Goods Manufacturers Association and the National Association of Convenience Stores successfully lobbied for the 2007 extension to US DST.
In December 2008, the Daylight Saving for South East Queensland (DS4SEQ) political party was officially registered in Queensland, advocating the implementation of a dual-time-zone arrangement for daylight saving in South East Queensland, while the rest of the state maintained standard time. DS4SEQ contested the March 2009 Queensland state election with 32 candidates and received one percent of the statewide primary vote, equating to around 2.5% across the 32 electorates contested. After a three-year trial, more than 55% of Western Australians voted against DST in 2009, with rural areas strongly opposed. Queensland Independent member Peter Wellington introduced the Daylight Saving for South East Queensland Referendum Bill 2010 into the Queensland parliament on 14 April 2010, after being approached by the DS4SEQ political party, calling for a referendum at the next state election on the introduction of daylight saving into South East Queensland under a dual-time-zone arrangement. The Queensland parliament rejected Wellington's bill on 15 June 2011.
Russia declared in 2011 that it would stay in DST all year long (UTC+4:00) and Belarus followed with a similar declaration. (The Soviet Union had operated under permanent "summer time" from 1930 to at least 1982.) Russia's plan generated widespread complaints due to the dark of winter-time mornings, and thus was abandoned in 2014. The country changed its clocks to standard time (UTC+3:00) on 26 October 2014, intending to stay there permanently.
In the United States, Arizona (with the exception of the Navajo Nation), Hawaii, and the five populated territories (American Samoa, Guam, Puerto Rico, the Northern Mariana Islands, and the US Virgin Islands) do not participate in daylight saving time. Indiana only began participating in daylight saving time as recently as 2006. Since 2018, Florida Republican Senator Marco Rubio has repeatedly filed bills to extend daylight saving time permanently into winter, without success.
Mexico observed summertime daylight saving time starting in 1996. In late 2022, the nation's clocks "fell back" for the last time, in restoration of permanent standard time. | Daylight saving time | Wikipedia | 506 | 47548 | https://en.wikipedia.org/wiki/Daylight%20saving%20time | Technology | Timekeeping | null |
Religion
Some religious groups and individuals have opposed DST on religious grounds. For religious Muslims and Jews it makes religious practices such as prayer and fasting more difficult or inconvenient.
Some Muslim countries, such as Morocco, have temporarily abandoned DST during Ramadan.
In Israel, DST has been a point of contention between the religious and secular, resulting in fluctuations over the years, and a shorter DST period than in the EU and US. Religious Jews prefer a shorter DST due to DST delaying scheduled morning prayers, thus conflicting with standard working and business hours. Additionally, DST is ended before Yom Kippur (a 25-hour fast day starting and ending at sunset, much of which is spent praying in synagogue until the fast ends at sunset) since DST would result in the day ending later, which many feel makes it more difficult.
In the US, Orthodox Jewish groups have opposed extensions to DST, as well as a 2022 bipartisan bill that would make DST permanent, saying it will "interfere with the ability of members of our community to engage in congregational prayers and get to their places of work on time."
Effects
Effects on electricity consumption
Proponents of DST generally argue that it saves energy, promotes outdoor leisure activity in the evening (in summer), and is therefore good for physical and psychological health, reduces traffic accidents, reduces crime or is good for business. Opponents argue the actual energy savings are inconclusive.
Although energy conservation goals still remain, energy usage patterns have greatly changed since then. Electricity use is greatly affected by geography, climate, and economics, so the results of a study conducted in one place may not be relevant to another country or climate.
A 2017 meta-analysis of 44 studies found that DST leads to electricity savings of 0.3% during the days when DST applies. Several studies have suggested that DST increases motor fuel consumption, but a 2008 United States Department of Energy report found no significant increase in motor gasoline consumption due to the 2007 United States extension of DST. An early goal of DST was to reduce evening usage of incandescent lighting, once a primary use of electricity.
Economic effects
It has been argued that clock shifts correlate with decreased economic efficiency and that in 2000, the daylight-saving effect implied an estimated one-day loss of $31 billion on US stock exchanges. Others have asserted that the observed results depend on methodology and disputed the findings, though the original authors have refuted points raised by disputers. | Daylight saving time | Wikipedia | 507 | 47548 | https://en.wikipedia.org/wiki/Daylight%20saving%20time | Technology | Timekeeping | null |
Effects on health
There are measurable adverse effects of clock-shifts on human health. It has been shown to disrupt human circadian rhythms, negatively affecting human health in the process, and that the yearly DST clock-shifts can increase health risks such as heart attacks and traffic accidents.
A 2017 study in the American Economic Journal: Applied Economics estimated that "the transition into DST caused over 30 deaths at a social cost of $275 million annually", primarily by increasing sleep deprivation.
A correlation between clock shifts and increase in traffic accidents has been observed in North America and the UK but not in Finland or Sweden. Four reports have found that this effect is smaller than the overall reduction in traffic fatalities. According to data shared by Titan Casket, hospitals see a 24% increase in heart attacks and a 6% increase in fatal crashes each year when the time changes. In 2018, the European Parliament, reviewing a possible abolition of DST, approved a more in-depth evaluation examining the disruption of the human body's circadian rhythms which provided evidence suggesting the existence of an association between DST clock-shifts and a modest increase of occurrence of acute myocardial infarction, especially in the first week after the spring shift. However a Netherlands study found, against the majority of investigations, contrary or minimal effect. Year-round standard time (not year-round DST) is proposed by some to be the preferred option for public health and safety. Clock shifts were found to increase the risk of heart attack by 10 percent, and to disrupt sleep and reduce its efficiency. Effects on seasonal adaptation of the circadian rhythm can be severe and last for weeks.
Effects on social relations
DST hurts prime-time television broadcast ratings, drive-ins and other theaters. Artificial outdoor lighting has a marginal and sometimes even contradictory influence on crime and fear of crime.
Later sunsets from DST are thought to affect behavior; for example, increasing participation in after-school sports programs or outdoor afternoon sports such as golf, and attendance at professional sporting events. Advocates of daylight saving time argue that having more hours of daylight between the end of a typical workday and evening induces people to consume other goods and services. | Daylight saving time | Wikipedia | 441 | 47548 | https://en.wikipedia.org/wiki/Daylight%20saving%20time | Technology | Timekeeping | null |
In 2022, a publication of three replicating studies of individuals, between individuals, and transecting societies, demonstrated that sleep loss affects the human motivation to help others, which in its fMRI findings is "associated with deactivation of key nodes within the social cognition brain network that facilitates prosociality." Furthermore, they detected, through analysis of over three million real-world charitable donations, that the loss of sleep inflicted by the transition to daylight saving time reduces altruistic giving compared to controls (being states not implementing DST). They conclude that the effects on civil society are "non-trivial".
Another study, which also examined sleep manipulation due to the shift to daylight saving time in the spring, analyzed archival data from judicial punishment imposed by US federal courts which showed sleep-deprived judges exact more severe penalties.
Inconvenience
DST's clock shifts have the disadvantage of complexity. People must remember to change their clocks; this can be time-consuming, particularly for mechanical clocks that cannot be moved backward safely. People who work across time zone boundaries need to keep track of multiple DST rules, as not all locations observe DST or observe it the same way. The length of the calendar day becomes variable; it is no longer always 24 hours. Disruption to meetings, travel, broadcasts, billing systems, and records management is common, and can be expensive. During an autumn transition from 02:00 to 01:00, a clock shows local times from 01:00:00 through 01:59:59 twice, possibly leading to confusion.
Many farmers oppose DST, particularly dairy farmers as the milking patterns of their cows do not change with the time, and others whose hours are set by the sun. There is concern for schoolchildren who are out in the darkness during the morning due to late sunrises.
Remediation
Some clock-shift problems could be avoided by adjusting clocks continuously or at least more gradually—for example, Willett at first suggested weekly 20-minute transitions—but this would add complexity and has never been implemented. DST inherits and can magnify the disadvantages of standard time. For example, when reading a sundial, one must compensate for it along with time zone and natural discrepancies. Also, sun-exposure guidelines such as avoiding the sun within two hours of noon become less accurate when DST is in effect. | Daylight saving time | Wikipedia | 487 | 47548 | https://en.wikipedia.org/wiki/Daylight%20saving%20time | Technology | Timekeeping | null |
Terminology
As explained by Richard Meade in the English Journal of the (American) National Council of Teachers of English, the form daylight savings time (with an "s") was already much more common than the older form daylight saving time in American English ("the change has been virtually accomplished") in 1978. Nevertheless, dictionaries such as Merriam-Webster's, American Heritage, and Oxford, which typically describe actual usage instead of prescribing outdated usage (and therefore also list the newer form), still list the older form first. This is because the older form is still very common in print and is preferred by many editors. ("Although daylight saving time is considered correct, daylight savings time (with an "s") is commonly used.") The first two words are sometimes hyphenated (daylight-saving(s) time). Merriam-Webster's also lists the forms daylight saving, daylight savings (both without "time"), and daylight time. The Oxford Dictionary of American Usage and Style explains the development and current situation as follows:Although the singular form daylight saving time is the original one, dating from the early 20th century—and is preferred by some usage critics—the plural form is now extremely common in AmE. [...] The rise of daylight savings time appears to have resulted from the avoidance of a miscue: when saving is used, readers might puzzle momentarily over whether saving is a gerund (the saving of daylight) or a participle (the time for saving). [...] Using savings as the adjective—as in savings account or savings bond—makes perfect sense. More than that, it ought to be accepted as the better form.In Britain, Willett's 1907 proposal used the term daylight saving, but by 1911, the term summer time replaced daylight saving time in draft legislation. The same or similar expressions are used in many other languages: Sommerzeit in German, zomertijd in Dutch, kesäaika in Finnish, horario de verano or hora de verano in Spanish, and heure d'été in French. | Daylight saving time | Wikipedia | 444 | 47548 | https://en.wikipedia.org/wiki/Daylight%20saving%20time | Technology | Timekeeping | null |
The name of local time typically changes when DST is observed. American English replaces standard with daylight: for example, Pacific Standard Time (PST) becomes Pacific Daylight Time (PDT). In the United Kingdom, the standard term for UK time when advanced by one hour is British Summer Time (BST), and British English typically inserts summer into other time zone names, e.g. Central European Time (CET) becomes Central European Summer Time (CEST).
In North American English, people use the mnemonic "spring forward, fall back" (also "spring ahead ...", "spring up ...", and "... fall behind") to remember the direction in which to shift the clocks.
Computing
Changes to DST rules cause problems in existing computer installations. For example, the 2007 change to DST rules in North America required that many computer systems be upgraded, with the greatest onus on e-mail and calendar programs. The upgrades required a significant effort by corporate information technologists.
Some applications standardize on UTC to avoid problems with clock shifts and time zone differences. Likewise, most modern operating systems internally handle and store all times as UTC and only convert to local time for display. However, even if UTC is used internally, the systems still require external leap second updates and time zone information to correctly calculate local time as needed. Many systems in use today base their date/time calculations from data derived from the tz database also known as zoneinfo. | Daylight saving time | Wikipedia | 308 | 47548 | https://en.wikipedia.org/wiki/Daylight%20saving%20time | Technology | Timekeeping | null |
IANA time zone database
The tz database maps a name to the named location's historical and predicted clock shifts. This database is used by many computer software systems, including most Unix-like operating systems, Java, and the Oracle RDBMS; HP's "tztab" database is similar but incompatible. When temporal authorities change DST rules, zoneinfo updates are installed as part of ordinary system maintenance. In Unix-like systems the TZ environment variable specifies the location name, as in TZ=':America/New_York'. In many of those systems there is also a system-wide setting that is applied if the TZ environment variable is not set: this setting is controlled by the contents of the /etc/localtime file, which is usually a symbolic link or hard link to one of the zoneinfo files. Internal time is stored in time-zone-independent Unix time; the TZ is used by each of potentially many simultaneous users and processes to independently localize time display.
Older or stripped-down systems may support only the TZ values required by POSIX, which specify at most one start and end rule explicitly in the value. For example, TZ='EST5EDT,M3.2.0/02:00,M11.1.0/02:00' specifies time for the eastern United States starting in 2007. Such a TZ value must be changed whenever DST rules change, and the new value applies to all years, mishandling some older timestamps.
Opposition to clock changes
A move to permanent daylight saving time (staying on summer hours all year with no clock shifts) is sometimes advocated and is currently implemented in some jurisdictions such as Argentina, Belarus, Iceland, Kyrgyzstan, Morocco, Namibia, Saskatchewan, Singapore, Syria, Turkey, Turkmenistan, Uzbekistan and Yukon. Although Saskatchewan follows Central Standard Time, its capital city Regina experiences solar noon close to 13:00, in effect putting the city on permanent daylight time. Similarly, Yukon is classified as being in the Mountain Time Zone, though in effect it observes permanent Pacific Daylight Time to align with the Pacific time zone in summer, but local solar noon in the capital Whitehorse occurs nearer to 14:00, in effect putting Whitehorse on "double daylight time". | Daylight saving time | Wikipedia | 470 | 47548 | https://en.wikipedia.org/wiki/Daylight%20saving%20time | Technology | Timekeeping | null |
The United Kingdom and Ireland put clocks forward by an extra hour during World War II and experimented with year-round summer time between 1968 and 1971. Russia switched to permanent DST from 2011 to 2014, but the move proved unpopular because of the extremely late winter sunrises; in 2014, Russia switched permanently back to standard time. However, the change to permanent DST has proven popular in Turkey, with the Minister of Energy and Natural Resources saying the practice saves "millions in energy costs and reduces depression and anxiety levels associated with short exposure to daylight".
In September 2018, the European Commission proposed to end seasonal clock changes as of 2019. Member states would have the option of observing either daylight saving time all year round or standard time all year round. In March 2019, the European Parliament approved the commission's proposal, while deferring implementation from 2019 until 2021. In response to this proposition, the European Sleep Research Society stated "installing permanent Central European Time (CET, standard time or 'wintertime') is the best option for public health." , the decision has not been confirmed by the Council of the European Union. The council has asked the commission to produce a detailed assessment of its effects, but the Commission considers that the onus is on the Member States to find a common position in Council. As a result, progress on the issue is effectively blocked.
In the United States, several states have enacted legislation to implement permanent DST, but the bills would require Congress to change federal law in order to take effect. The Uniform Time Act of 1966 permits states to opt out of DST and observe permanent standard time, but it does not permit permanent DST. Florida senator Marco Rubio in particular has promoted changing the federal law to implement permanent DST, with the support of the Florida Chamber of Commerce seeking to boost evening revenue. In 2022, Rubio's "Sunshine Protection Act" passed the United States Senate without committee review by way of voice consent, with many senators afterward stating they were unaware of the vote or its topic. The bill was stopped in the US House, where questions were raised as to whether permanent DST or standard time would be more beneficial.
Advocates cite the same advantages as normal DST without the problems associated with the twice yearly clock shifts. Additional benefits have also been cited, including safer roadways, boosting the tourism industry, and energy savings. Detractors cite the relatively late sunrises, particularly in winter, that year-round DST entails. | Daylight saving time | Wikipedia | 504 | 47548 | https://en.wikipedia.org/wiki/Daylight%20saving%20time | Technology | Timekeeping | null |
Some experts in circadian rhythms and sleep health recommend year-round standard time as the preferred option for public health and safety. However, some experts state that permanent daylight saving time is still a better option when compared to annual clock changes. Several chronobiology societies have published position papers against adopting DST permanently. A paper by the Society for Research on Biological Rhythms states: "based on comparisons of large populations living in DST or ST or on western versus eastern edges of time zones, the advantages of permanent ST outweigh switching to DST annually or permanently." The World Federation of Societies for Chronobiology recommended "reassigning countries and regions to their actual sun-clock based time zones" and held the position of being "against the switching between DST and Standard Time and even more so against adopting DST permanently." The American Academy of Sleep Medicine (AASM) holds the position that "seasonal time changes should be abolished in favor of a fixed, national, year-round standard time," and that "standard time is a better option than daylight saving time for our health, mood and well-being." Their position was endorsed by 20 other organizations, including the American College of Chest Physicians, National Safety Council, and National PTA.
Current public opinion polls show mixed results. Surveys reported between 2021 and 2022 by the National Sleep Foundation, YouGov, CBS, and Monmouth University indicate more Americans would prefer permanent DST. A 2019 survey by the National Opinion Research Center and a 2021 survey by the Associated Press indicate more Americans would prefer permanent Standard Time. The National Sleep Foundation, YouGov, and Monmouth University polls leaned significantly in favor of seeing daylight saving time made permanent. The Monmouth University poll reported 44% preferring year-round DST and 13% preferring year-round standard time. The NORC at the University of Chicago found 79% of those interviewed to be in favor of permanent DST during the Oil Crisis in December 1973; 42% of poll takers supported it the following February. | Daylight saving time | Wikipedia | 412 | 47548 | https://en.wikipedia.org/wiki/Daylight%20saving%20time | Technology | Timekeeping | null |
A low Earth orbit (LEO) is an orbit around Earth with a period of 128 minutes or less (making at least 11.25 orbits per day) and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, peaking in number at an altitude around , while the farthest in LEO, before medium Earth orbit (MEO), have an altitude of 2,000 kilometers, about one-third of the radius of Earth and near the beginning of the inner Van Allen radiation belt.
The term LEO region is used for the area of space below an altitude of (about one-third of Earth's radius). Objects in orbits that pass through this zone, even if they have an apogee further out or are sub-orbital, are carefully tracked since they present a collision risk to the many LEO satellites.
No human spaceflights other than the lunar missions of the Apollo program (1968-1972) have taken place beyond LEO. All space stations to date have operated geocentric within LEO.
Defining characteristics
A wide variety of sources define LEO in terms of altitude. The altitude of an object in an elliptic orbit can vary significantly along the orbit. Even for circular orbits, the altitude above ground can vary by as much as (especially for polar orbits) due to the oblateness of Earth's spheroid figure and local topography. While definitions based on altitude are inherently ambiguous, most of them fall within the range specified by an orbit period of 128 minutes because, according to Kepler's third law, this corresponds to a semi-major axis of . For circular orbits, this in turn corresponds to an altitude of above the mean radius of Earth, which is consistent with some of the upper altitude limits in some LEO definitions.
The LEO region is defined by some sources as a region in space that LEO orbits occupy. Some highly elliptical orbits may pass through the LEO region near their lowest altitude (or perigee) but are not in a LEO orbit because their highest altitude (or apogee) exceeds . Sub-orbital objects can also reach the LEO region but are not in a LEO orbit because they re-enter the atmosphere. The distinction between LEO orbits and the LEO region is especially important for analysis of possible collisions between objects which may not themselves be in LEO but could collide with satellites or debris in LEO orbits. | Low Earth orbit | Wikipedia | 478 | 47568 | https://en.wikipedia.org/wiki/Low%20Earth%20orbit | Physical sciences | Orbital mechanics | null |
Orbital characteristics
The mean orbital velocity needed to maintain a stable low Earth orbit is about , which translates to . However, this depends on the exact altitude of the orbit. Calculated for a circular orbit of the orbital velocity is , but for a higher orbit the velocity is reduced to . The launch vehicle's delta-v needed to achieve low Earth orbit starts around .
The pull of gravity in LEO is only slightly less than on the Earth's surface. This is because the distance to LEO from the Earth's surface is much less than the Earth's radius. However, an object in orbit is in a permanent free fall around Earth, because in orbit the gravitational force and the centrifugal force balance each other out. As a result, spacecraft in orbit continue to stay in orbit, and people inside or outside such craft continuously experience weightlessness.
Objects in LEO orbit Earth between the denser part of the atmosphere and below the inner Van Allen radiation belt. They encounter atmospheric drag from gases in the thermosphere (approximately 80–600 km above the surface) or exosphere (approximately and higher), depending on orbit height. Satellites in orbits that reach altitudes below decay quickly due to atmospheric drag.
Equatorial low Earth orbits (ELEO) are a subset of LEO. These orbits, with low orbital inclination, allow rapid revisit times over low-latitude locations on Earth. Prograde equatorial LEOs also have lower delta-v launch requirements because they take advantage of the Earth's rotation. Other useful LEO orbits including polar orbits and Sun-synchronous orbits have a higher inclinations to the equator and provide coverage for higher latitudes on Earth. Some of the first generation of Starlink satellites used polar orbits which provide coverage everywhere on Earth. Later Starlink constellations orbit at a lower inclination and provide more coverage for populated areas.
Higher orbits include medium Earth orbit (MEO), sometimes called intermediate circular orbit (ICO), and further above, geostationary orbit (GEO). Orbits higher than low orbit can lead to early failure of electronic components due to intense radiation and charge accumulation.
In 2017, "very low Earth orbits" (VLEO) began to be seen in regulatory filings. These orbits, below about , require the use of novel technologies for orbit raising because they operate in orbits that would ordinarily decay too soon to be economically useful.
Use | Low Earth orbit | Wikipedia | 483 | 47568 | https://en.wikipedia.org/wiki/Low%20Earth%20orbit | Physical sciences | Orbital mechanics | null |
A low Earth orbit requires the lowest amount of energy for satellite placement. It provides high bandwidth and low communication latency. Satellites and space stations in LEO are more accessible for crew and servicing.
Since it requires less energy to place a satellite into a LEO, and a satellite there needs less powerful amplifiers for successful transmission, LEO is used for many communication applications, such as the Iridium phone system. Some communication satellites use much higher geostationary orbits and move at the same angular velocity as the Earth as to appear stationary above one location on the planet.
Disadvantages
Unlike geosynchronous satellites, satellites in low orbit have a small field of view and can only observe and communicate with a fraction of the Earth at a given time. This means that a large network (or constellation) of satellites is required to provide continuous coverage.
Satellites at lower altitudes of orbit are in the atmosphere and suffer from rapid orbital decay, requiring either periodic re-boosting to maintain stable orbits, or the launching of replacements for those that re-enter the atmosphere. The effects of adding such quantities of vaporized metals to Earth's stratosphere are potentially of concern but currently unknown.
Examples
The International Space Station is in LEO about above the Earth's surface. The station’s orbit decays by about and consequently needs re-boosting a few times a year.
The Iridium telecom satellites orbit at about .
Earth observation satellites, also known as remote sensing satellites, including spy satellites and other Earth imaging satellites, use LEO as they are able to see the surface of the Earth more clearly by being closer to it. A majority of artificial satellites are placed in LEO. Satellites can also take advantage of consistent lighting of the surface below via Sun-synchronous LEO orbits at an altitude of about and near polar inclination. Envisat (2002–2012) is one example.
The Hubble Space Telescope orbits at about above Earth.
Satellite internet constellations such as Starlink.
The Chinese Tiangong space station was launched in April 2021 and currently orbits between above the Earth's surface.
The gravimetry mission GRACE-FO orbits at about as did its predecessor, GRACE.
Former
GOCE (2009-2013), an ESA gravimetry mission, orbited at about 255 km (158 mi).
Super Low Altitude Test Satellite (2017-2019), nicknamed Tsubame, orbited at , the lowest altitude ever among Earth observation satellites. | Low Earth orbit | Wikipedia | 492 | 47568 | https://en.wikipedia.org/wiki/Low%20Earth%20orbit | Physical sciences | Orbital mechanics | null |
In fiction
In the film 2001: A Space Odyssey, Earth's transit station ("Space Station V") "orbited 300 km above Earth".
Space debris
The LEO environment is becoming congested with space debris because of the frequency of object launches. This has caused growing concern in recent years, since collisions at orbital velocities can be dangerous or deadly. Collisions can produce additional space debris, creating a domino effect known as Kessler syndrome. NASA's Orbital Debris Program tracks over 25,000 objects larger than 10 cm diameter in LEO, while the estimated number between 1 and 10 cm is 500,000, and the number of particles bigger than 1 mm exceeds 100 million. The particles travel at speeds up to , so even a small impact can severely damage a spacecraft. | Low Earth orbit | Wikipedia | 158 | 47568 | https://en.wikipedia.org/wiki/Low%20Earth%20orbit | Physical sciences | Orbital mechanics | null |
The American pickerel (Esox americanus) is a medium-sized species of North American freshwater predatory fish belonging to the pike family. The genus Esox is placed in family Esocidae in order Esociformes).
Two subspecies are sometimes recognised:
Redfin pickerel, sometimes called the brook pickerel, E. americanus americanus Gmelin, 1789;
Grass pickerel, E. americanus vermiculatus Lesueur, 1846.
Lesueur originally classified the grass pickerel as E. vermiculatus, but it is now considered a subspecies of E. americanus.
There is no widely accepted English common collective name for the two E. americanus subspecies; "American pickerel" is a translation of the French systematic name brochet d'Amérique.
Description
The two subspecies are very similar, but the grass pickerel lacks the redfin's distinctive orange to red fin coloration. The former's fins have dark leading edges and amber to dusky coloration. In addition, the light areas between the dark bands are generally wider on the grass pickerel and narrower on the redfin pickerel. Record size grass and redfin pickerels can weigh around and reach lengths of around . Redfin and grass pickerels are typically smaller than chain pickerels, which can be much larger.
Distribution and habitats
The redfin and grass pickerels occur primarily in sluggish, vegetated waters of pools, lakes and wetlands, and are carnivorous predators feeding on smaller fish. However, larger fishes, such as the striped bass (Morone saxatilis), bowfin (Amia calva) and gray weakfish (Cynoscion regalis), prey on the pickerels in turn when the latter venture into larger rivers or estuaries.
The pickerels reproduce by scattering spherical, sticky eggs in shallow, heavily vegetated waters. The eggs hatch in 11–15 days; the adult pickerels guard neither the eggs nor the young. | American pickerel | Wikipedia | 419 | 47571 | https://en.wikipedia.org/wiki/American%20pickerel | Biology and health sciences | Esociformes | Animals |
Both subspecies are native to the freshwater bodies of North America, and are not to be confused with their more aggressive big cousin, the northern pike. The redfin pickerel's range extends from the Saint Lawrence basin in Quebec down to the Gulf Coast, from Mississippi to Florida; while the grass pickerel's range is further west, extending from the Great Lakes Basin, from Ontario to Michigan, down to the western Gulf Coast, from eastern Texas to Mississippi.
Fishing
The E. americanus subspecies are not as highly prized as a game fish as their larger cousins, the northern pike and muskellunge, but they are nevertheless caught by anglers. McClane's Standard Fishing Encyclopedia describes ultralight tackle as a sporty if overlooked method to catch these small but voracious pikes. | American pickerel | Wikipedia | 164 | 47571 | https://en.wikipedia.org/wiki/American%20pickerel | Biology and health sciences | Esociformes | Animals |
The muskellunge (Esox masquinongy), often shortened to muskie, musky, ski, or lunge, is a species of large freshwater predatory fish native to North America. It is the largest member of the pike family, Esocidae.
Origin of name
The name "muskellunge" originates from the Ojibwe words maashkinoozhe meaning "great fish", mji-gnoozhe, maskinoše, or mashkinonge, meaning "bad pike", "big pike", or "ugly pike" respectively. The Algonquin word maskinunga is borrowed into the Canadian French words masquinongé or maskinongé. In English, before settling on the common name "muskellunge", there were at least 94 common names applied to this species, including but not limited to: muskelunge, muscallonge, muskallonge, milliganong, maskinonge, maskalonge, mascalonge, maskalung, muskinunge and masquenongez.
Description | Muskellunge | Wikipedia | 234 | 47578 | https://en.wikipedia.org/wiki/Muskellunge | Biology and health sciences | Esociformes | Animals |
Muskellunge closely resemble other esocids such as the northern pike (Esox lucius) and American pickerel (E. americanus) in both appearance and behavior. Like the northern pike and other aggressive pikes, the body plan is typical of ambush predators with an elongated body, flat head, and dorsal, pelvic, and anal fins set far back on the body. Muskellunge are typically long and weigh , though some have reached up to and almost . Martin Arthur Williamson caught a muskellunge with a weight of in November 2000 on Georgian Bay. The fish are a light silver, brown, or green, with dark vertical stripes on the flank, which may tend to break up into spots. In some cases, markings may be absent altogether, especially in fish from turbid waters. This is in contrast to northern pike, which have dark bodies with light markings. A reliable method to distinguish the two similar species is by counting the sensory pores on the underside of the mandible. A muskie will have seven or more per side, while the northern pike never has more than six. The lobes of the caudal (tail) fin in muskellunge come to a sharper point, while those of northern pike are more generally rounded. In addition, unlike pike, muskies have no scales on the lower half of their opercula.
Anglers seek large muskies as trophies or for sport. In places where muskie are not native, such as in Maine, anglers are encouraged not to release the fish back into the water because of their negative impact on native populations of trout and other smaller fish species. | Muskellunge | Wikipedia | 344 | 47578 | https://en.wikipedia.org/wiki/Muskellunge | Biology and health sciences | Esociformes | Animals |
Habitat
Muskellunge are found in oligotrophic and mesotrophic lakes and large rivers from northern Michigan, northern Wisconsin, and northern Minnesota through the Great Lakes region, Chautauqua Lake in western New York, north into Canada, throughout most of the St Lawrence River drainage, and northward throughout the upper Mississippi valley, although the species also extends as far south as Chattanooga in the Tennessee River valley. Also, a small population is found in the Broad River in South Carolina. Several North Georgia reservoirs also have healthy stocked populations of muskie. They are also found in the Red River drainage of the Hudson Bay basin. Muskie were introduced to western Saint John River in the late 1960s and have now spread to many connecting waterways in northern Maine. The Pineview Reservoir in Utah is one of three Utah locations where the hybrid Tiger muskellunge is found.
They prefer clear waters where they lurk along weed edges, rock outcrops, or other structures to rest. A fish forms two distinct home ranges in summer: a shallow range and a deeper one. The shallow range is generally much smaller than the deeper range due to shallow water heating up. A muskie continually patrols the ranges in search of available food in the appropriate conditions of water temperature.
Diet
Muskies are ambush predators who will swiftly bite their prey and then swallow it head first. Muskellunge are the top predator in any body of water where they occur and they will eat larger prey than most other freshwater fish. They eat all varieties of fish present in their ecosystem (including other muskellunge), along with the occasional insect, muskrat, rat, mouse, frog, or duck. They are capable of taking prey up to two-thirds of their body length due to their large stomachs. There have even been reports of large muskellunge attacking small dogs and even humans, although most of these reports are greatly exaggerated.
Length and weight
As muskellunge grow longer they increase in weight, but the relationship between length and weight is not linear. The relationship between them can be expressed by a power-law equation:
The exponent b is close to 3.0 for all species, and c is a constant for each species. For muskellunge, b = 3.325, higher than for many common species, and c = . | Muskellunge | Wikipedia | 482 | 47578 | https://en.wikipedia.org/wiki/Muskellunge | Biology and health sciences | Esociformes | Animals |
According to the International Game Fish Association (IGFA) the largest muskellunge on record was caught by Cal Johnson in Lac Courte Oreilles (recognized as Lake Courte Oreilles by the association), Hayward, Wisconsin, United States, on July 24, 1949. The fish weighed and was in length, and in girth.
Behavior
Muskellunge are sometimes gregarious, forming small schools in distinct territories. Muskellunge feeding behavior is directly synchronized with the lunar cycle. During both full and new moons, an increase in feeding activity can be attributed to the increase of moonlight, as it most similarly simulates daytime feeding. They spawn in mid- to late spring, somewhat later than northern pike, over shallow, vegetated areas. A rock or sand bottom is preferred for spawning so the eggs do not sink into the mud and suffocate. The males arrive first and attempt to establish dominance over a territory. Spawning may last from five to 10 days and occurs mainly at night. The eggs are negatively buoyant and slightly adhesive; they adhere to plants and the bottom of the lake. Soon afterward, they are abandoned by the adults. Those embryos which are not eaten by fish, insects, or crayfish hatch within two weeks. The larvae live on yolk until the mouth is fully developed, when they begin to feed on copepods and other zooplankton. They soon begin to prey upon fish. Juveniles generally attain a length of by November of their first year.
Predators
Adult muskellunge are apex predators where they occur naturally. Only humans and (rarely) large birds of prey such as bald eagles (Haliaeetus leucocephalus) pose a threat to an adult. But juveniles are consumed by other muskies, northern pike, bass, trout, and occasionally birds of prey. The muskellunge's low reproductive rate and slow growth render populations highly vulnerable to overfishing. This has prompted some jurisdictions to institute artificial propagation programs in an attempt to maintain otherwise unsustainably high rates of angling effort and habitat destruction. | Muskellunge | Wikipedia | 439 | 47578 | https://en.wikipedia.org/wiki/Muskellunge | Biology and health sciences | Esociformes | Animals |
Subspecies and hybrids
Though interbreeding with other pike species can complicate the classification of some individuals, zoologists usually recognize up to three subspecies of muskellunge.
The Great Lakes Muskellunge or Spotted Muskellunge (E. m. masquinongy) is the most common variety in the Great Lakes basin and surrounding area. The spots on the body form oblique rows.
The Chautauqua Muskellunge or Barred Muskellunge (E. m. ohioensis) is known from the Ohio River system, Chautauqua Lake, Lake Ontario, and the St Lawrence River.
The Clear Muskellunge (E. m. immaculatus) is most common in the inland lakes of Wisconsin, Minnesota, northwestern Ontario, and southeastern Manitoba.
The tiger muskellunge (E. masquinongy × lucius or E. lucius × masquinongy) is a hybrid of the muskie and northern pike. Hybrids are sterile, although females sometimes unsuccessfully engage in spawning motions. Some hybrids are artificially produced and planted for anglers to catch. Tiger muskies grow faster than pure muskies, but do not attain the ultimate size of their pure relatives, as the tiger muskie does not live as long.
Attacks on humans
Although very rare, muskie attacks on humans do occur on occasion. | Muskellunge | Wikipedia | 284 | 47578 | https://en.wikipedia.org/wiki/Muskellunge | Biology and health sciences | Esociformes | Animals |
Pollock or pollack (pronounced ) is the common name used for either of the two species of North Atlantic marine fish in the genus Pollachius. Pollachius pollachius is referred to as "pollock" in North America, Ireland and the United Kingdom, while Pollachius virens is usually known as saithe or coley in Great Britain and Ireland (derived from the older name coalfish). Other names for P. pollachius include the Atlantic pollock, European pollock, lieu jaune, and lythe or lithe; while P. virens is also known as Boston blue (distinct from bluefish), silver bill, or saithe.
Species
The recognized species in this genus are:
Pollachius pollachius (Linnaeus, 1758) (pollack)
Pollachius virens (Linnaeus, 1758) (coalfish)
Description
Both species can grow to . P. virens can weigh up to and P. pollachius can weigh up to . P. virens has a strongly defined, silvery lateral line running down the sides. Above the lateral line, the colour is a greenish black. The belly is white, while P. pollachius has a distinctly crooked lateral line, grayish to golden belly, and a dark brown back. P. pollachius also has a strong underbite. It can be found in water up to deep over rocks and anywhere in the water column.
As food
Atlantic pollock is largely considered to be a whitefish. Traditionally a popular source of food in some countries, such as Norway, in the United Kingdom it has previously been largely consumed as a cheaper and versatile alternative to cod and haddock. However, in recent years, pollock has become more popular due to overfishing of cod and haddock. It can now be found in most supermarkets as fresh fillets or prepared freezer items. For example, it is used minced in fish fingers or as an ingredient in imitation crab meat and is commonly used to make fish and chips. | Pollock | Wikipedia | 412 | 47579 | https://en.wikipedia.org/wiki/Pollock | Biology and health sciences | Acanthomorpha | Animals |
Because of its slightly grey colour, pollock is often prepared, as in Norway, as fried fish balls, or if juvenile-sized, breaded with oatmeal and fried, as in Shetland. Year-old fish are traditionally split, salted, and dried over a peat hearth in Orkney, where their texture becomes wooden. Coalfish can also be salted and smoked and achieve a salmon-like orange color (although it is not closely related to the salmon), as is the case in Germany, where the fish is commonly sold as Seelachs or sea salmon.
In 2009, UK supermarket Sainsbury's briefly renamed Atlantic pollock "colin" in a bid to boost ecofriendly sales of the fish as an alternative to cod. Sainsbury's, which said the new name was derived from the French for cooked pollock (colin), launched the product under the banner "Colin and chips can save British cod."
Pollock is regarded as a "low-mercury fish" – a woman weighing can safely eat up to per week, and a child weighing can safely eat up to .
Other fish called pollock
One member of the genus Gadus is also commonly referred to as pollock: the Alaska pollock or walleye pollock (Gadus chalcogrammus), including the form known as the Norway pollock. They are also members of the family Gadidae but not members of the genus Pollachius. | Pollock | Wikipedia | 290 | 47579 | https://en.wikipedia.org/wiki/Pollock | Biology and health sciences | Acanthomorpha | Animals |
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