abstract stringlengths 3 192k | title stringlengths 4 857 |
|---|---|
desert dust aerosols affect earth's global energy balance through direct interactions with radiation, and through indirect interactions with clouds and ecosystems. but the magnitudes of these effects are so uncertain that it remains unclear whether atmospheric dust has a net warming or cooling effect on global climate. consequently, it is still uncertain whether large changes in atmospheric dust loading over the past century have slowed or accelerated anthropogenic climate change, or what the effects of potential future changes in dust loading will be. here we present an analysis of the size and abundance of dust aerosols to constrain the direct radiative effect of dust. using observational data on dust abundance, in situ measurements of dust optical properties and size distribution, and climate and atmospheric chemical transport model simulations of dust lifetime, we find that the dust found in the atmosphere is substantially coarser than represented in current global climate models. as coarse dust warms the climate, the global dust direct radiative effect is likely to be less cooling than the ~-0.4 w m-2 estimated by models in a current global aerosol model ensemble. instead, we constrain the dust direct radiative effect to a range between -0.48 and +0.20 w m-2, which includes the possibility that dust causes a net warming of the planet. | smaller desert dust cooling effect estimated from analysis of dust size and abundance |
proxy reconstructions from marine sediment cores indicate peak temperatures in the first half of the last and current interglacial periods (the thermal maxima of the holocene epoch, 10,000 to 6,000 years ago, and the last interglacial period, 128,000 to 123,000 years ago) that arguably exceed modern warmth1-3. by contrast, climate models simulate monotonic warming throughout both periods4-7. this substantial model-data discrepancy undermines confidence in both proxy reconstructions and climate models, and inhibits a mechanistic understanding of recent climate change. here we show that previous global reconstructions of temperature in the holocene1-3 and the last interglacial period8 reflect the evolution of seasonal, rather than annual, temperatures and we develop a method of transforming them to mean annual temperatures. we further demonstrate that global mean annual sea surface temperatures have been steadily increasing since the start of the holocene (about 12,000 years ago), first in response to retreating ice sheets (12 to 6.5 thousand years ago), and then as a result of rising greenhouse gas concentrations (0.25 ± 0.21 degrees celsius over the past 6,500 years or so). however, mean annual temperatures during the last interglacial period were stable and warmer than estimates of temperatures during the holocene, and we attribute this to the near-constant greenhouse gas levels and the reduced extent of ice sheets. we therefore argue that the climate of the holocene differed from that of the last interglacial period in two ways: first, larger remnant glacial ice sheets acted to cool the early holocene, and second, rising greenhouse gas levels in the late holocene warmed the planet. furthermore, our reconstructions demonstrate that the modern global temperature has exceeded annual levels over the past 12,000 years and probably approaches the warmth of the last interglacial period (128,000 to 115,000 years ago). | seasonal origin of the thermal maxima at the holocene and the last interglacial |
increased extreme heat exposure from both climate change and the urban heat island effect threatens rapidly growing urban settlements worldwide. yet, because we do not know where urban population growth and extreme heat intersect, we have limited capacity to reduce the impacts of urban extreme heat exposure. here, we leverage fine-resolution temperature and population data to measure urban extreme heat exposure for 13,115 cities from 1983 to 2016. globally, urban exposure increased nearly 200%, affecting 1.7 billion people. total urban warming elevated exposure rates 52% above population growth alone. however, spatially heterogeneous exposure patterns highlight an urgent need for locally tailored adaptations and early warning systems to reduce harm from urban extreme heat exposure across the planet's diverse urban settlements. | global urban population exposure to extreme heat |
earth-like planets, dark energy and variability of fundamental physical constants can be discovered by observing wavelength shifts in the optical spectra of astronomical objects1-5. these wavelength shifts are so tiny that exquisitely accurate and precise wavelength calibration of astronomical spectrometers is required. laser frequency combs, broadband spectra of laser lines with absolutely known optical frequencies, are uniquely suited for this purpose6-13, provided their lines are resolved by the spectrometer. generating such astronomical laser frequency combs (`astrocombs') remains challenging. here, a microphotonic astrocomb is demonstrated via temporal dissipative kerr solitons14-16 in photonic-chip-based silicon nitride microresonators17, directly providing a spurious-free spectrum of resolvable calibration lines. sub-harmonically driven by temporally structured light18, the astrocomb is stabilized to a frequency standard, resulting in absolute calibration with a precision of 25 cm s-1 (radial velocity equivalent), relevant for earth-like planet detection and cosmological research. the microphotonic technology can be extended in spectral span17,19-24, further boosting the calibration precision. | a microphotonic astrocomb |
china has suffered from increasing levels of ozone pollution in urban areas despite the implementation of various stringent emission reduction measures since 2013. in this study, we conducted numerical experiments with an up-to-date regional chemical transport model to assess the contribution of the changes in meteorological conditions and anthropogenic emissions to the summer ozone level from 2013 to 2017 in various regions of china. the model can faithfully reproduce the observed meteorological parameters and air pollutant concentrations and capture the increasing trend in the surface maximum daily 8 h average (mda8) ozone (o3) from 2013 to 2017. the emission-control measures implemented by the government induced a decrease in mda8 o3 levels in rural areas but an increase in urban areas. the meteorological influence on the ozone trend varied by region and by year and could be comparable to or even more significant than the impact of changes in anthropogenic emissions. meteorological conditions can modulate the ozone concentration via direct (e.g., increasing reaction rates at higher temperatures) and indirect (e.g., increasing biogenic emissions at higher temperatures) effects. as an essential source of volatile organic compounds that contributes to ozone formation, the variation in biogenic emissions during summer varied across regions and was mainly affected by temperature. china's midlatitude areas (25 to 40∘ n) experienced a significant decrease in mda8 o3 due to a decline in biogenic emissions, especially for the yangtze river delta and sichuan basin regions in 2014 and 2015. in contrast, in northern (north of 40∘ n) and southern (south of 25∘ n) china, higher temperatures after 2013 led to an increase in mda8 o3 via an increase in biogenic emissions. we also assessed the individual effects of changes in temperature, specific humidity, wind field, planetary boundary layer height, clouds, and precipitation on ozone levels from 2013 to 2017. the results show that the wind field change made a significant contribution to the increase in surface ozone over many parts of china. the long-range transport of ozone and its precursors from outside the modeling domain also contributed to the increase in mda8 o3 in china, especially on the qinghai-tibetan plateau (an increase of 1 to 4 ppbv). our study represents the most comprehensive and up-to-date analysis of the impact of changes in meteorology on ozone across china and highlights the importance of considering meteorological variations when assessing the effectiveness of emission control on changes in the ozone levels in recent years. | worsening urban ozone pollution in china from 2013 to 2017 - part 1: the complex and varying roles of meteorology |
increasing heat content of the global ocean dominates the energy imbalance in the climate system. here we show that ocean heat gain over the 0-2,000 m layer continued at a rate of 0.4-0.6 w m-2 during 2006-2013. the depth dependence and spatial structure of temperature changes are described on the basis of the argo program's accurate and spatially homogeneous data set, through comparison of three argo-only analyses. heat gain was divided equally between upper ocean, 0-500 m and 500-2,000 m components. surface temperature and upper 100 m heat content tracked interannual el niño/southern oscillation fluctuations, but were offset by opposing variability from 100-500 m. the net 0-500 m global average temperature warmed by 0.005 °c yr-1. between 500 and 2,000 m steadier warming averaged 0.002 °c yr-1 with a broad intermediate-depth maximum between 700 and 1,400 m. most of the heat gain (67 to 98%) occurred in the southern hemisphere extratropical ocean. although this hemispheric asymmetry is consistent with inhomogeneity of radiative forcing and the greater area of the southern hemisphere ocean, ocean dynamics also influence regional patterns of heat gain. | unabated planetary warming and its ocean structure since 2006 |
the northern hemisphere (nh) polar winter stratosphere of 2019/2020 featured an exceptionally strong and cold stratospheric polar vortex. wave activity from the troposphere during december-february was unusually low, which allowed the polar vortex to remain relatively undisturbed. several transient wave pulses nonetheless served to help create a reflective configuration of the stratospheric circulation by disturbing the vortex in the upper stratosphere. subsequently, multiple downward wave coupling events took place, which aided in dynamically cooling and strengthening the polar vortex. the persistent strength of the stratospheric polar vortex was accompanied by an unprecedentedly positive phase of the arctic oscillation in the troposphere during january-march, which was consistent with large portions of observed surface temperature and precipitation anomalies during the season. similarly, conditions within the strong polar vortex were ripe for allowing substantial ozone loss: the undisturbed vortex was a strong transport barrier, and temperatures were low enough to form polar stratospheric clouds for over 4 months into late march. total column ozone amounts in the nh polar cap decreased and were the lowest ever observed in the february-april period. the unique confluence of conditions and multiple broken records makes the 2019/2020 winter and early spring a particularly extreme example of two-way coupling between the troposphere and stratosphere. | the remarkably strong arctic stratospheric polar vortex of winter 2020: links to record-breaking arctic oscillation and ozone loss |
new particle formation (npf) is the source of over half of the atmosphere’s cloud condensation nuclei, thus influencing cloud properties and earth’s energy balance. unlike in the planetary boundary layer, few observations of npf in the free troposphere exist. we provide observational evidence that at high altitudes, npf occurs mainly through condensation of highly oxygenated molecules (homs), in addition to taking place through sulfuric acid-ammonia nucleation. neutral nucleation is more than 10 times faster than ion-induced nucleation, and growth rates are size-dependent. npf is restricted to a time window of 1 to 2 days after contact of the air masses with the planetary boundary layer; this is related to the time needed for oxidation of organic compounds to form homs. these findings require improved npf parameterization in atmospheric models. | new particle formation in the free troposphere: a question of chemistry and timing |
imagej is a graphical user interface (gui) driven, public domain, java-based, software package for general image processing traditionally used mainly in life sciences fields. the image processing capabilities of imagej are useful and extendable to other scientific fields. here we present astroimagej (aij), which provides an astronomy specific image display environment and tools for astronomy specific image calibration and data reduction. although aij maintains the general purpose image processing capabilities of imagej, aij is streamlined for time-series differential photometry, light curve detrending and fitting, and light curve plotting, especially for applications requiring ultra-precise light curves (e.g., exoplanet transits). aij reads and writes standard flexible image transport system (fits) files, as well as other common image formats, provides fits header viewing and editing, and is world coordinate system aware, including an automated interface to the astrometry.net web portal for plate solving images. aij provides research grade image calibration and analysis tools with a gui driven approach, and easily installed cross-platform compatibility. it enables new users, even at the level of undergraduate student, high school student, or amateur astronomer, to quickly start processing, modeling, and plotting astronomical image data with one tightly integrated software package. | astroimagej: image processing and photometric extraction for ultra-precise astronomical light curves |
topographic variation underpins a myriad of patterns and processes in hydrology, climatology, geography and ecology and is key to understanding the variation of life on the planet. a fully standardized and global multivariate product of different terrain features has the potential to support many large-scale research applications, however to date, such datasets are unavailable. here we used the digital elevation model products of global 250 m gmted2010 and near-global 90 m srtm4.1dev to derive a suite of topographic variables: elevation, slope, aspect, eastness, northness, roughness, terrain roughness index, topographic position index, vector ruggedness measure, profile/tangential curvature, first/second order partial derivative, and 10 geomorphological landform classes. we aggregated each variable to 1, 5, 10, 50 and 100 km spatial grains using several aggregation approaches. while a cross-correlation underlines the high similarity of many variables, a more detailed view in four mountain regions reveals local differences, as well as scale variations in the aggregated variables at different spatial grains. all newly-developed variables are available for download at data citation 1 and for download and visualization at http://www.earthenv.org/topography. | a suite of global, cross-scale topographic variables for environmental and biodiversity modeling |
the continental crust is the principal record of conditions on the earth during the past 4.4 billion years. however, how the continental crust formed and evolved through time remains highly controversial. in particular, the composition and thickness of juvenile continental crust are unknown. here we show that rb/sr ratios can be used as a proxy for both the silica content and the thickness of the continental crust. we calculate rb/sr ratios of the juvenile crust for over 13,000 samples, with nd model ages ranging from the hadean to phanerozoic. the ratios were calculated based on the evolution of sr isotopes in the period between the tdm nd model age and the crystallization of the samples analysed. we find that the juvenile crust had a low silica content and was largely mafic in composition during the first 1.5 billion years of earth’s evolution, consistent with magmatism on a pre-plate tectonics planet. about 3 billion years ago, the rb/sr ratios of the juvenile continental crust increased, indicating that the newly formed crust became more silica-rich and probably thicker. this transition is in turn linked to the onset of plate tectonics and an increase of continental detritus into the oceans. | emergence of modern continental crust about 3 billion years ago |
with the advent of the heliophysics/geospace system observatory (h/gso), a complement of multi-spacecraft missions and ground-based observatories to study the space environment, data retrieval, analysis, and visualization of space physics data can be daunting. the space physics environment data analysis system (spedas), a grass-roots software development platform (<externalref> <refsource>www.spedas.org</refsource> <reftarget address="http://www.spedas.org" targettype="url"/> </externalref>), is now officially supported by nasa heliophysics as part of its data environment infrastructure. it serves more than a dozen space missions and ground observatories and can integrate the full complement of past and upcoming space physics missions with minimal resources, following clear, simple, and well-proven guidelines. free, modular and configurable to the needs of individual missions, it works in both command-line (ideal for experienced users) and graphical user interface (gui) mode (reducing the learning curve for first-time users). both options have "crib-sheets," user-command sequences in ascii format that can facilitate record-and-repeat actions, especially for complex operations and plotting. crib-sheets enhance scientific interactions, as users can move rapidly and accurately from exchanges of technical information on data processing to efficient discussions regarding data interpretation and science. spedas can readily query and ingest all international solar terrestrial physics (istp)-compatible products from the space physics data facility (spdf), enabling access to a vast collection of historic and current mission data. the planned incorporation of heliophysics application programmer's interface (hapi) standards will facilitate data ingestion from distributed datasets that adhere to these standards. although spedas is currently interactive data language (idl)-based (and interfaces to java-based tools such as autoplot), efforts are under-way to expand it further to work with python (first as an interface tool and potentially even receiving an under-the-hood replacement). we review the spedas development history, goals, and current implementation. we explain its "modes of use" with examples geared for users and outline its technical implementation and requirements with software developers in mind. we also describe spedas personnel and software management, interfaces with other organizations, resources and support structure available to the community, and future development plans. | the space physics environment data analysis system (spedas) |
carbon dioxide (co2) is a key chemical species that is found in a wide range of planetary atmospheres. in the context of exoplanets, co2 is an indicator of the metal enrichment (that is, elements heavier than helium, also called `metallicity')1-3, and thus the formation processes of the primary atmospheres of hot gas giants4-6. it is also one of the most promising species to detect in the secondary atmospheres of terrestrial exoplanets7-9. previous photometric measurements of transiting planets with the spitzer space telescope have given hints of the presence of co2, but have not yielded definitive detections owing to the lack of unambiguous spectroscopic identification10-12. here we present the detection of co2 in the atmosphere of the gas giant exoplanet wasp-39b from transmission spectroscopy observations obtained with jwst as part of the early release science programme13,14. the data used in this study span 3.0-5.5 micrometres in wavelength and show a prominent co2 absorption feature at 4.3 micrometres (26-sigma significance). the overall spectrum is well matched by one-dimensional, ten-times solar metallicity models that assume radiative-convective-thermochemical equilibrium and have moderate cloud opacity. these models predict that the atmosphere should have water, carbon monoxide and hydrogen sulfide in addition to co2, but little methane. furthermore, we also tentatively detect a small absorption feature near 4.0 micrometres that is not reproduced by these models. | identification of carbon dioxide in an exoplanet atmosphere |
we have developed an online radiative-transfer suite (https://psg.gsfc.nasa.gov) applicable to a broad range of planetary objects (e.g., planets, moons, comets, asteroids, tnos, kbos, exoplanets). the planetary spectrum generator (psg) can synthesize planetary spectra (atmospheres and surfaces) for a broad range of wavelengths (uv/vis/near-ir/ir/far-ir/thz/sub-mm/radio) from any observatory (e.g., jwst, alma, keck, sofia), any orbiter (e.g., exomars, juno), or any lander (e.g., msl). this is achieved by combining several state-of-the-art radiative transfer models, spectroscopic databases and planetary databases (i.e., climatological and orbital). psg has a 3d (three-dimensional) orbital calculator for most bodies in the solar system, and all confirmed exoplanets, while the radiative-transfer models can ingest billions of spectral signatures for hundreds of species from several spectroscopic repositories. it integrates the latest radiative-transfer and scattering methods in order to compute high resolution spectra via line-by-line calculations, and utilizes the efficient correlated-k method at moderate resolutions, while for computing cometary spectra, psg handles non-lte and lte excitation processes. psg includes a realistic noise calculator that integrates several telescope/instrument configurations (e.g., interferometry, coronagraphs) and detector technologies (e.g., ccd, heterodyne detectors, bolometers). such an integration of advanced spectroscopic methods into an online tool can greatly serve the planetary community, ultimately enabling the retrieval of planetary parameters from remote sensing data, efficient mission planning strategies, interpretation of current and future planetary data, calibration of spectroscopic data, and development of new instrument/spacecraft concepts. | planetary spectrum generator: an accurate online radiative transfer suite for atmospheres, comets, small bodies and exoplanets |
the 2030 agenda for sustainable development—including 17 interconnected sustainable development goals (sdgs) and 169 targets—is a global plan of action for people, planet and prosperity. sdg7 calls for action to ensure access to affordable, reliable, sustainable and modern energy for all. here we characterize synergies and trade-offs between efforts to achieve sdg7 and delivery of the 2030 agenda as a whole. we identify 113 targets requiring actions to change energy systems, and published evidence of relationships between 143 targets (143 synergies, 65 trade-offs) and efforts to achieve sdg7. synergies and trade-offs exist in three key domains, where decisions about sdg7 affect humanity's ability to: realize aspirations of greater welfare and well-being; build physical and social infrastructures for sustainable development; and achieve sustainable management of the natural environment. there is an urgent need to better organize, connect and extend this evidence, to help all actors work together to achieve sustainable development. | mapping synergies and trade-offs between energy and the sustainable development goals |
salinization and alkalinization impact water quality, but these processes have been studied separately, except in arid regions. globally, salinization has been largely attributed to agriculture, resource extraction, and land clearing. alkalinization has been attributed to recovery from acidification, with less recognition as an environmental issue. we show that salinization and alkalinization are linked, and trends in these processes impact most of the drainage area of the united states. increases in salinity and alkalinity are caused by inputs of salts containing strong bases and carbonates that originate from anthropogenic sources and accelerated weathering. we develop a conceptual model unifying our understanding of salinization and alkalinization and its drivers and impacts on fresh water in north america over the past century. | freshwater salinization syndrome on a continental scale |
the australian bushfires around the turn of the year 2020 generated an unprecedented perturbation of stratospheric composition, dynamical circulation and radiative balance. here we show from satellite observations that the resulting planetary-scale blocking of solar radiation by the smoke is larger than any previously documented wildfires and of the same order as the radiative forcing produced by moderate volcanic eruptions. a striking effect of the solar heating of an intense smoke patch was the generation of a self-maintained anticyclonic vortex measuring 1000 km in diameter and featuring its own ozone hole. the highly stable vortex persisted in the stratosphere for over 13 weeks, travelled 66,000 km and lifted a confined bubble of smoke and moisture to 35 km altitude. its evolution was tracked by several satellite-based sensors and was successfully resolved by the european centre for medium-range weather forecasts operational system, primarily based on satellite data. because wildfires are expected to increase in frequency and strength in a changing climate, we suggest that extraordinary events of this type may contribute significantly to the global stratospheric composition in the coming decades. | the 2019/20 australian wildfires generated a persistent smoke-charged vortex rising up to 35 km altitude |
the hydrological cycle is expected to intensify under global warming, with studies reporting more frequent extreme rain events in many regions of the world, and predicting increases in future flood frequency. such early, predominantly mid-latitude observations are essential because of shortcomings within climate models in their depiction of convective rainfall. a globally important group of intense storms—mesoscale convective systems (mcss)—poses a particular challenge, because they organize dynamically on spatial scales that cannot be resolved by conventional climate models. here, we use 35 years of satellite observations from the west african sahel to reveal a persistent increase in the frequency of the most intense mcss. sahelian storms are some of the most powerful on the planet, and rain gauges in this region have recorded a rise in ‘extreme’ daily rainfall totals. we find that intense mcs frequency is only weakly related to the multidecadal recovery of sahel annual rainfall, but is highly correlated with global land temperatures. analysis of trends across africa reveals that mcs intensification is limited to a narrow band south of the sahara desert. during this period, wet-season sahelian temperatures have not risen, ruling out the possibility that rainfall has intensified in response to locally warmer conditions. on the other hand, the meridional temperature gradient spanning the sahel has increased in recent decades, consistent with anthropogenic forcing driving enhanced saharan warming. we argue that saharan warming intensifies convection within sahelian mcss through increased wind shear and changes to the saharan air layer. the meridional gradient is projected to strengthen throughout the twenty-first century, suggesting that the sahel will experience particularly marked increases in extreme rain. the remarkably rapid intensification of sahelian mcss since the 1980s sheds new light on the response of organized tropical convection to global warming, and challenges conventional projections made by general circulation models. | frequency of extreme sahelian storms tripled since 1982 in satellite observations |
planning has been very successful for control tasks with known environment dynamics. to leverage planning in unknown environments, the agent needs to learn the dynamics from interactions with the world. however, learning dynamics models that are accurate enough for planning has been a long-standing challenge, especially in image-based domains. we propose the deep planning network (planet), a purely model-based agent that learns the environment dynamics from images and chooses actions through fast online planning in latent space. to achieve high performance, the dynamics model must accurately predict the rewards ahead for multiple time steps. we approach this using a latent dynamics model with both deterministic and stochastic transition components. moreover, we propose a multi-step variational inference objective that we name latent overshooting. using only pixel observations, our agent solves continuous control tasks with contact dynamics, partial observability, and sparse rewards, which exceed the difficulty of tasks that were previously solved by planning with learned models. planet uses substantially fewer episodes and reaches final performance close to and sometimes higher than strong model-free algorithms. | learning latent dynamics for planning from pixels |
the largest store of continually updating knowledge on our planet can be accessed via internet search. in this work we study giving access to this information to conversational agents. large language models, even though they store an impressive amount of knowledge within their weights, are known to hallucinate facts when generating dialogue (shuster et al., 2021); moreover, those facts are frozen in time at the point of model training. in contrast, we propose an approach that learns to generate an internet search query based on the context, and then conditions on the search results to finally generate a response, a method that can employ up-to-the-minute relevant information. we train and evaluate such models on a newly collected dataset of human-human conversations whereby one of the speakers is given access to internet search during knowledgedriven discussions in order to ground their responses. we find that search-query based access of the internet in conversation provides superior performance compared to existing approaches that either use no augmentation or faiss-based retrieval (lewis et al., 2020). | internet-augmented dialogue generation |
secondary organic aerosols (soa) are a large source of uncertainty in our current understanding of climate change and air pollution. the phase state of soa is important for quantifying their effects on climate and air quality, but its global distribution is poorly characterized. we developed a method to estimate glass transition temperatures based on the molar mass and molecular o:c ratio of soa components, and we used the global chemistry climate model emac with the organic aerosol module oracle to predict the phase state of atmospheric soa. for the planetary boundary layer, global simulations indicate that soa are mostly liquid in tropical and polar air with high relative humidity, semi-solid in the mid-latitudes and solid over dry lands. we find that in the middle and upper troposphere soa should be mostly in a glassy solid phase state. thus, slow diffusion of water, oxidants and organic molecules could kinetically limit gas-particle interactions of soa in the free and upper troposphere, promote ice nucleation and facilitate long-range transport of reactive and toxic organic pollutants embedded in soa. | global distribution of particle phase state in atmospheric secondary organic aerosols |
global development has been heavily reliant on the overexploitation of natural resources since the industrial revolution. with the extensive use of fossil fuels, deforestation, and other forms of land-use change, anthropogenic activities have contributed to the ever-increasing concentrations of greenhouse gases (ghgs) in the atmosphere, causing global climate change. in response to the worsening global climate change, achieving carbon neutrality by 2050 is the most pressing task on the planet. to this end, it is of utmost importance and a significant challenge to reform the current production systems to reduce ghg emissions and promote the capture of co2 from the atmosphere. herein, we review innovative technologies that offer solutions achieving carbon (c) neutrality and sustainable development, including those for renewable energy production, food system transformation, waste valorization, c sink conservation, and c-negative manufacturing. the wealth of knowledge disseminated in this review could inspire the global community and drive the further development of innovative technologies to mitigate climate change and sustainably support human activities. | technologies and perspectives for achieving carbon neutrality |
the age of jupiter, the largest planet in our solar system, is still unknown. gas-giant planet formation likely involved the growth of large solid cores, followed by the accumulation of gas onto these cores. thus, the gas-giant cores must have formed before dissipation of the solar nebula, which likely occurred within less than 10 my after solar system formation. although such rapid accretion of the gas-giant cores has successfully been modeled, until now it has not been possible to date their formation. here, using molybdenum and tungsten isotope measurements on iron meteorites, we demonstrate that meteorites derive from two genetically distinct nebular reservoirs that coexisted and remained spatially separated between ∼1 my and ∼3-4 my after solar system formation. the most plausible mechanism for this efficient separation is the formation of jupiter, opening a gap in the disk and preventing the exchange of material between the two reservoirs. as such, our results indicate that jupiter’s core grew to ∼20 earth masses within <1 my, followed by a more protracted growth to ∼50 earth masses until at least ∼3-4 my after solar system formation. thus, jupiter is the oldest planet of the solar system, and its solid core formed well before the solar nebula gas dissipated, consistent with the core accretion model for giant planet formation. | age of jupiter inferred from the distinct genetics and formation times of meteorites |
more than 90% of the heat energy accumulation in the climate system between 1971 and the present has been in the ocean. thus, the ocean plays a crucial role in determining the climate of the planet. observing the oceans is problematic even under the most favourable of conditions. historically, shipboard ocean sampling has left vast expanses, particularly in the southern ocean, unobserved for long periods of time. within the past 15 years, with the advent of the global argo array of profiling floats, it has become possible to sample the upper 2,000 m of the ocean globally and uniformly in space and time. the primary goal of argo is to create a systematic global network of profiling floats that can be integrated with other elements of the global ocean observing system. the network provides freely available temperature and salinity data from the upper 2,000 m of the ocean with global coverage. the data are available within 24 hours of collection for use in a broad range of applications that focus on examining climate-relevant variability on seasonal to decadal timescales, multidecadal climate change, improved initialization of coupled ocean-atmosphere climate models and constraining ocean analysis and forecasting systems. | fifteen years of ocean observations with the global argo array |
clues to a planet’s geologic history are contained in its interior structure, particularly its core. we detected reflections of seismic waves from the core-mantle boundary of mars using insight seismic data and inverted these together with geodetic data to constrain the radius of the liquid metal core to 1830 ± 40 kilometers. the large core implies a martian mantle mineralogically similar to the terrestrial upper mantle and transition zone but differing from earth by not having a bridgmanite-dominated lower mantle. we inferred a mean core density of 5.7 to 6.3 grams per cubic centimeter, which requires a substantial complement of light elements dissolved in the iron-nickel core. the seismic core shadow as seen from insight’s location covers half the surface of mars, including the majority of potentially active regions—e.g., tharsis—possibly limiting the number of detectable marsquakes. | seismic detection of the martian core |
we present the easy-to-use, publicly available, python package petitradtrans, built for the spectral characterization of exoplanet atmospheres. the code is fast, accurate, and versatile; it can calculate both transmission and emission spectra within a few seconds at low resolution (λ/δλ = 1000; correlated-k method) and high resolution (λ/δλ = 106; line-by-line method), using only a few lines of input instruction. the somewhat slower, correlated-k method is used at low resolution because it is more accurate than methods such as opacity sampling. clouds can be included and treated using wavelength-dependent power law opacities, or by using optical constants of real condensates, specifying either the cloud particle size, or the atmospheric mixing and particle settling strength. opacities of amorphous or crystalline, spherical or irregularly-shaped cloud particles are available. the line opacity database spans temperatures between 80 and 3000 k, allowing to model fluxes of objects such as terrestrial planets, super-earths, neptunes, or hot jupiters, if their atmospheres are hydrogen-dominated. higher temperature points and species will be added in the future, allowing to also model the class of ultra hot-jupiters, with equilibrium temperatures teq ≳ 2000 k. radiative transfer results were tested by cross-verifying the low- and high-resolution implementation of petitradtrans, and benchmarked with the petitcode, which itself is also benchmarked to the atmo and exo-rem codes. we successfully carried out test retrievals of synthetic jwst emission and transmission spectra (for the hot jupiter tres-4b, which has a teq of ∼1800 k). the code is publicly available at http://gitlab.com/mauricemolli/petitradtrans, and its documentation can be found at https://petitradtrans.readthedocs.io. | petitradtrans. a python radiative transfer package for exoplanet characterization and retrieval |
reorganization of the asian climate from one dominated by global planetary wind systems to a regional monsoon climate is closely related to the surface uplift of the tibetan plateau (tp). however, evaluating this climatic reorganization is limited by difficulty in constraining the complex, multistaged uplift of the tp and contradictory evidence regarding asian monsoon onset. in this review, we summarize proxy and model evidence for asian monsoon initiation at different latitudes to identify the main controls on monsoon evolution. stratigraphy and palaeoclimate proxy records indicate that the asian climate was reorganized in a two-stage northward expansion process. at ~41 million years ago (ma), the monsoon advanced northwards from the tropic to the southern subtropical regions (~26° n, approximately present-day yunnan), probably driven by central tp uplift, global cooling and rapid regression of the proto-paratethys sea. at ~26 ma, the monsoon expanded northwards into temperate regions (~30-36° n, equivalent to the present-day asian monsoon boundary), likely driven by tp growth and global warming. additional proxy records are needed to fill regional gaps, establishing more solid boundary conditions and improving parameter constraints for climate models. | reorganization of asian climate in relation to tibetan plateau uplift |
the terrestrial biosphere can release or absorb the greenhouse gases, carbon dioxide (co2), methane (ch4) and nitrous oxide (n2o), and therefore has an important role in regulating atmospheric composition and climate. anthropogenic activities such as land-use change, agriculture and waste management have altered terrestrial biogenic greenhouse gas fluxes, and the resulting increases in methane and nitrous oxide emissions in particular can contribute to climate change. the terrestrial biogenic fluxes of individual greenhouse gases have been studied extensively, but the net biogenic greenhouse gas balance resulting from anthropogenic activities and its effect on the climate system remains uncertain. here we use bottom-up (inventory, statistical extrapolation of local flux measurements, and process-based modelling) and top-down (atmospheric inversions) approaches to quantify the global net biogenic greenhouse gas balance between 1981 and 2010 resulting from anthropogenic activities and its effect on the climate system. we find that the cumulative warming capacity of concurrent biogenic methane and nitrous oxide emissions is a factor of about two larger than the cooling effect resulting from the global land carbon dioxide uptake from 2001 to 2010. this results in a net positive cumulative impact of the three greenhouse gases on the planetary energy budget, with a best estimate (in petagrams of co2 equivalent per year) of 3.9 ± 3.8 (top down) and 5.4 ± 4.8 (bottom up) based on the gwp100 metric (global warming potential on a 100-year time horizon). our findings suggest that a reduction in agricultural methane and nitrous oxide emissions, particularly in southern asia, may help mitigate climate change. | the terrestrial biosphere as a net source of greenhouse gases to the atmosphere |
the redox state of earth’s convecting mantle, masked by the lithospheric plates and basaltic magmatism of plate tectonics, is a key unknown in the evolutionary history of our planet. here we report that large, exceptional gem diamonds like the cullinan, constellation, and koh-i-noor carry direct evidence of crystallization from a redox-sensitive metallic liquid phase in the deep mantle. these sublithospheric diamonds contain inclusions of solidified iron-nickel-carbon-sulfur melt, accompanied by a thin fluid layer of methane ± hydrogen, and sometimes majoritic garnet or former calcium silicate perovskite. the metal-dominated mineral assemblages and reduced volatiles in large gem diamonds indicate formation under metal-saturated conditions. we verify previous predictions that earth has highly reducing deep mantle regions capable of precipitating a metallic iron phase that contains dissolved carbon and hydrogen. | large gem diamonds from metallic liquid in earth’s deep mantle |
the frequent occurrence of severe air pollution episodes in china has been a great concern and thus the focus of intensive studies. planetary boundary layer height (pblh) is a key factor in the vertical mixing and dilution of near-surface pollutants. however, the relationship between pblh and surface pollutants, especially particulate matter (pm) concentration across china, is not yet well understood. we investigate this issue at ∼ 1600 surface stations using pblh derived from space-borne and ground-based lidar, and discuss the influence of topography and meteorological variables on the pblh-pm relationship. albeit the pblh-pm correlations are roughly negative for most cases, their magnitude, significance, and even sign vary considerably with location, season, and meteorological conditions. weak or even uncorrelated pblh-pm relationships are found over clean regions (e.g., pearl river delta), whereas nonlinearly negative responses of pm to pblh evolution are found over polluted regions (e.g., north china plain). relatively strong pblh-pm interactions are found when the pblh is shallow and pm concentration is high, which typically corresponds to wintertime cases. correlations are much weaker over the highlands than the plains regions, which may be associated with lighter pollution loading at higher elevations and contributions from mountain breezes. the influence of horizontal transport on surface pm is considered as well, manifested as a negative correlation between surface pm and wind speed over the whole nation. strong wind with clean upwind air plays a dominant role in removing pollutants, and leads to obscure pblh-pm relationships. a ventilation rate is used to jointly consider horizontal and vertical dispersion, which has the largest impact on surface pollutant accumulation over the north china plain. as such, this study contributes to improved understanding of aerosol-planetary boundary layer (pbl) interactions and thus our ability to forecast surface air pollution. | relationships between the planetary boundary layer height and surface pollutants derived from lidar observations over china: regional pattern and influencing factors |
global mean surface warming has stalled since the end of the twentieth century, but the net radiation imbalance at the top of the atmosphere continues to suggest an increasingly warming planet. this apparent contradiction has been reconciled by an anomalous heat flux into the ocean, induced by a shift towards a la niña-like state with cold sea surface temperatures in the eastern tropical pacific over the past decade or so. a significant portion of the heat missing from the atmosphere is therefore expected to be stored in the pacific ocean. however, in situ hydrographic records indicate that pacific ocean heat content has been decreasing. here, we analyse observations along with simulations from a global ocean-sea ice model to track the pathway of heat. we find that the enhanced heat uptake by the pacific ocean has been compensated by an increased heat transport from the pacific ocean to the indian ocean, carried by the indonesian throughflow. as a result, indian ocean heat content has increased abruptly, which accounts for more than 70% of the global ocean heat gain in the upper 700 m during the past decade. we conclude that the indian ocean has become increasingly important in modulating global climate variability. | pacific origin of the abrupt increase in indian ocean heat content during the warming hiatus |
human water use, climate change and land conversion have created a water crisis for billions of individuals and many ecosystems worldwide. global water stocks and fluxes are estimated empirically and with computer models, but this information is conveyed to policymakers and researchers through water cycle diagrams. here we compiled a synthesis of the global water cycle, which we compared with 464 water cycle diagrams from around the world. although human freshwater appropriation now equals half of global river discharge, only 15% of the water cycle diagrams depicted human interaction with water. only 2% of the diagrams showed climate change or water pollution—two of the central causes of the global water crisis—which effectively conveys a false sense of water security. a single catchment was depicted in 95% of the diagrams, which precludes the representation of teleconnections such as ocean-land interactions and continental moisture recycling. these inaccuracies correspond with specific dimensions of water mismanagement, which suggest that flaws in water diagrams reflect and reinforce the misunderstanding of global hydrology by policymakers, researchers and the public. correct depictions of the water cycle will not solve the global water crisis, but reconceiving this symbol is an important step towards equitable water governance, sustainable development and planetary thinking in the anthropocene. | human domination of the global water cycle absent from depictions and perceptions |
water availability is a major factor constraining humanity's ability to meet the future food and energy needs of a growing and increasingly affluent human population. water plays an important role in the production of energy, including renewable energy sources and the extraction of unconventional fossil fuels that are expected to become important players in future energy security. the emergent competition for water between the food and energy systems is increasingly recognized in the concept of the "food-energy-water nexus." the nexus between food and water is made even more complex by the globalization of agriculture and rapid growth in food trade, which results in a massive virtual transfer of water among regions and plays an important role in the food and water security of some regions. this review explores multiple components of the food-energy-water nexus and highlights possible approaches that could be used to meet food and energy security with the limited renewable water resources of the planet. despite clear tensions inherent in meeting the growing and changing demand for food and energy in the 21st century, the inherent linkages among food, water, and energy systems can offer an opportunity for synergistic strategies aimed at resilient food, water, and energy security, such as the circular economy. | the global food-energy-water nexus |
aerosol-planetary boundary layer (pbl) interactions have been found to enhance air pollution in megacities in china. we show that black carbon (bc) aerosols play the key role in modifying the pbl meteorology and hence enhancing the haze pollution. with model simulations and data analysis from various field observations in december 2013, we demonstrate that bc induces heating in the pbl, particularly in the upper pbl, and the resulting decreased surface heat flux substantially depresses the development of pbl and consequently enhances the occurrences of extreme haze pollution episodes. we define this process as the "dome effect" of bc and suggest an urgent need for reducing bc emissions as an efficient way to mitigate the extreme haze pollution in megacities of china. | enhanced haze pollution by black carbon in megacities in china |
radvel is an open-source python package for modeling keplerian orbits in radial velocity (rv) timeseries. radvel provides a convenient framework to fit rvs using maximum a posteriori optimization and to compute robust confidence intervals by sampling the posterior probability density via markov chain monte carlo (mcmc). radvel allows users to float or fix parameters, impose priors, and perform bayesian model comparison. we have implemented real-time mcmc convergence tests to ensure adequate sampling of the posterior. radvel can output a number of publication-quality plots and tables. users may interface with radvel through a convenient command-line interface or directly from python. the code is object-oriented and thus naturally extensible. we encourage contributions from the community. documentation is available at http://radvel.readthedocs.io. | radvel: the radial velocity modeling toolkit |
as the arctic continues to warm faster than the rest of the planet, evidence mounts that the region is experiencing unprecedented environmental change. the hydrological cycle is projected to intensify throughout the twenty-first century, with increased evaporation from expanding open water areas and more precipitation. the latest projections from the sixth phase of the coupled model intercomparison project (cmip6) point to more rapid arctic warming and sea-ice loss by the year 2100 than in previous projections, and consequently, larger and faster changes in the hydrological cycle. arctic precipitation (rainfall) increases more rapidly in cmip6 than in cmip5 due to greater global warming and poleward moisture transport, greater arctic amplification and sea-ice loss and increased sensitivity of precipitation to arctic warming. the transition from a snow- to rain-dominated arctic in the summer and autumn is projected to occur decades earlier and at a lower level of global warming, potentially under 1.5 °c, with profound climatic, ecosystem and socio-economic impacts. | new climate models reveal faster and larger increases in arctic precipitation than previously projected |
following years of record highs, an unexpected and precipitous reduction in antarctic sea-ice extent started in 2016. this decline, lasting three years, was the most pronounced of the satellite era, equivalent to 30 years of sea-ice loss in the arctic. here, we synthesize recent work showing this sea-ice reduction probably resulted from the interaction of a decades-long ocean warming trend and an early spring southward advection of atmospheric heat, with an exceptional weakening of the southern hemisphere mid-latitude westerlies in late spring. we discuss what this event reveals about the underlying atmospheric and oceanic dynamical processes that control sea ice in the region and the ways in which shifting climate variability and remote forcings, especially from the tropics, influence these processes. knowledge gaps show that further work is needed to improve future projections of changes in one of the largest seasonal phenomena on the planet. | rapid decline in antarctic sea ice in recent years hints at future change |
el niño-southern oscillation (enso) is the dominant mode of interannual climate variability on the planet, with far-reaching global impacts. it is therefore key to evaluate enso simulations in state-of-the-art numerical models used to study past, present, and future climate. recently, the pacific region panel of the international climate and ocean: variability, predictability and change (clivar) project, as a part of the world climate research programme (wcrp), led a community-wide effort to evaluate the simulation of enso variability, teleconnections, and processes in climate models. the new clivar 2020 enso metrics package enables model diagnosis, comparison, and evaluation to 1) highlight aspects that need improvement; 2) monitor progress across model generations; 3) help in selecting models that are well suited for particular analyses; 4) reveal links between various model biases, illuminating the impacts of those biases on enso and its sensitivity to climate change; and to 5) advance enso literacy. by interfacing with existing model evaluation tools, the enso metrics package enables rapid analysis of multipetabyte databases of simulations, such as those generated by the coupled model intercomparison project phases 5 (cmip5) and 6 (cmip6). the cmip6 models are found to significantly outperform those from cmip5 for 8 out of 24 enso-relevant metrics, with most cmip6 models showing improved tropical pacific seasonality and enso teleconnections. only one enso metric is significantly degraded in cmip6, namely, the coupling between the ocean surface and subsurface temperature anomalies, while the majority of metrics remain unchanged. | evaluating climate models with the clivar 2020 enso metrics package |
in may of 2011, nasa selected the origins, spectral interpretation, resource identification, and security- regolith explorer (osiris-rex) asteroid sample return mission as the third mission in the new frontiers program. the other two new frontiers missions are new horizons, which explored pluto during a flyby in july 2015 and is on its way for a flyby of kuiper belt object 2014 mu69 on january 1, 2019, and juno, an orbiting mission that is studying the origin, evolution, and internal structure of jupiter. the spacecraft departed for near-earth asteroid (101955) bennu aboard an united launch alliance atlas v 411 evolved expendable launch vehicle at 7:05 p.m. edt on september 8, 2016, on a seven-year journey to return samples from bennu. the spacecraft is on an outbound-cruise trajectory that will result in a rendezvous with bennu in november 2018. the science instruments on the spacecraft will survey bennu to measure its physical, geological, and chemical properties, and the team will use these data to select a site on the surface to collect at least 60 g of asteroid regolith. the team will also analyze the remote-sensing data to perform a detailed study of the sample site for context, assess bennu's resource potential, refine estimates of its impact probability with earth, and provide ground-truth data for the extensive astronomical data set collected on this asteroid. the spacecraft will leave bennu in 2021 and return the sample to the utah test and training range (uttr) on september 24, 2023. | osiris-rex: sample return from asteroid (101955) bennu |
two thirds of the surface of our planet are covered by water and are still poorly instrumented, which has prevented the earth science community from addressing numerous key scientific questions. the potential to leverage the existing fiber optic seafloor telecom cables that criss-cross the oceans, by using them as dense arrays of seismo-acoustic sensors, remains to be evaluated. here, we report distributed acoustic sensing measurements on a 41.5 km-long telecom cable that is deployed offshore toulon, france. our observations demonstrate the capability to monitor with unprecedented details the ocean-solid earth interactions from the coast to the abyssal plain, in addition to regional seismicity (e.g., a magnitude 1.9 micro-earthquake located 100 km away) with signal characteristics comparable to those of a coastal seismic station. | distributed sensing of earthquakes and ocean-solid earth interactions on seafloor telecom cables |
water distinguishes our planet compared to all the others we know about. while the global supply of available freshwater is more than adequate to meet all current and foreseeable water demands, its spatial and temporal distributions are not. there are many regions where our freshwater resources are inadequate to meet domestic, economic development and environmental needs. in such regions, the lack of adequate clean water to meet human drinking water and sanitation needs is indeed a constraint on human health and productivity and hence on economic development as well as on the maintenance of a clean environment and healthy ecosystems. all of us involved in research must find ways to remove these constraints. we face multiple challenges in doing that, especially given a changing and uncertain future climate, and a rapidly growing population that is driving increased social and economic development, globalization, and urbanization. how best to meet these challenges requires research in all aspects of water management. since 1965, the journal water resources research has played an important role in reporting and disseminating current research related to managing the quantity and quality and cost of this resource. this paper identifies the issues facing water managers today and future research needed to better inform those who strive to create a more sustainable and desirable future. | water management: current and future challenges and research directions |
feature extraction plays a vital role in intelligent fault diagnosis of mechanical system. nevertheless, traditional feature extraction methods suffer from three problems, which are (1) the requirements of domain expertise and prior knowledge, (2) the sensitive to the changes of mechanical system and (3) the limitations of mining new features. it is attractive and meaningful to investigate an automatic feature extraction method, which can adaptively learn features from raw data and discover new fault-sensitive features. deep learning has been widely used in image analysis and speech recognition with great success. the key advantage of this method lies into the ability of mining representative information and sensitive features from raw data. however, the application of deep learning in feature leaning for mechanical diagnosis is still few, and limited studies have been carried out to compare the effectiveness of feature leaning with various data types. this paper will focus on developing a convolutional neural network (cnn) to learn features directly from frequency data of vibration signals and testing the different performance of feature learning from raw data, frequency spectrum and combined time-frequency data. manual features from time domain, frequency domain and wavelet domain as well as three common intelligent methods are used as comparisons. the effectiveness of the proposed method is validated through phm 2009 gearbox challenge data and a planetary gearbox test rig. the results demonstrate that the proposed method is able to learn features adaptively from frequency data and achieve higher diagnosis accuracy than other comparative methods. | a convolutional neural network based feature learning and fault diagnosis method for the condition monitoring of gearbox |
in the coming years and decades, advanced space- and ground-based observatories will allow an unprecedented opportunity to probe the atmospheres and surfaces of potentially habitable exoplanets for signatures of life. life on earth, through its gaseous products and reflectance and scattering properties, has left its fingerprint on the spectrum of our planet. aided by the universality of the laws of physics and chemistry, we turn to earth's biosphere, both in the present and through geologic time, for analog signatures that will aid in the search for life elsewhere. considering the insights gained from modern and ancient earth, and the broader array of hypothetical exoplanet possibilities, we have compiled a state-of-the-art overview of our current understanding of potential exoplanet biosignatures including gaseous, surface, and temporal biosignatures. we additionally survey biogenic spectral features that are well-known in the specialist literature but have not yet been robustly vetted in the context of exoplanet biosignatures. we briefly review advances in assessing biosignature plausibility, including novel methods for determining chemical disequilibrium from remotely obtainable data and assessment tools for determining the minimum biomass required for a given atmospheric signature. we focus particularly on advances made since the seminal review by des marais et al. (2002). the purpose of this work is not to propose new biosignatures strategies, a goal left to companion papers in this series, but to review the current literature, draw meaningful connections between seemingly disparate areas, and clear the way for a path forward. | exoplanet biosignatures: a review of remotely detectable signs of life |
c-type asteroids1 are considered to be primitive small solar system bodies enriched in water and organics, providing clues to the origin and evolution of the solar system and the building blocks of life. c-type asteroid 162173 ryugu has been characterized by remote sensing2-7 and on-asteroid measurements8,9 with hayabusa2 (ref. 10). however, the ground truth provided by laboratory analysis of returned samples is invaluable to determine the fine properties of asteroids and other planetary bodies. we report preliminary results of analyses on returned samples from ryugu of the particle size distribution, density and porosity, spectral properties and textural properties, and the results of a search for ca-al-rich inclusions (cais) and chondrules. the bulk sample mainly consists of rugged and smooth particles of millimetre to submillimetre size, confirming that the physical and chemical properties were not altered during the return from the asteroid. the power index of its size distribution is shallower than that of the surface boulder observed on ryugu11, indicating differences in the returned ryugu samples. the average of the estimated bulk densities of ryugu sample particles is 1,282 ± 231 kg m−3, which is lower than that of meteorites12, suggesting a high microporosity down to the millimetre scale, extending centimetre-scale estimates from thermal measurements5,9. the extremely dark optical to near-infrared reflectance and spectral profile with weak absorptions at 2.7 and 3.4 μm imply a carbonaceous composition with indigenous aqueous alteration, matching the global average of ryugu3,4 and confirming that the sample is representative of the asteroid. together with the absence of submillimetre cais and chondrules, these features indicate that ryugu is most similar to ci chondrites but has lower albedo, higher porosity and more fragile characteristics. | preliminary analysis of the hayabusa2 samples returned from c-type asteroid ryugu |
the carbon dioxide challenge is one of the most pressing problems facing our planet. each stage in the carbon cycle — capture, regeneration and conversion — has its own materials requirements. recent work on metal-organic frameworks (mofs) demonstrated the potential and effectiveness of these materials in addressing this challenge. in this review, we identify the specific structural and chemical properties of mofs that have led to the highest capture capacities, the most efficient separations and regeneration processes, and the most effective catalytic conversions. the interior of mofs can be designed to have coordinatively unsaturated metal sites, specific heteroatoms, covalent functionalization, other building unit interactions, hydrophobicity, porosity, defects and embedded nanoscale metal catalysts with a level of precision that is crucial for the development of higher-performance mofs. to realize a total solution, it is necessary to use the precision of mof chemistry to build more complex materials to address selectivity, capacity and conversion together in one material. | the chemistry of metal-organic frameworks for co2 capture, regeneration and conversion |
shifts in phenology are already resulting in disruptions to the timing of migration and breeding, and asynchronies between interacting species1-5. recent syntheses have concluded that trophic level1, latitude6 and how phenological responses are measured7 are key to determining the strength of phenological responses to climate change. however, researchers still lack a comprehensive framework that can predict responses to climate change globally and across diverse taxa. here, we synthesize hundreds of published time series of animal phenology from across the planet to show that temperature primarily drives phenological responses at mid-latitudes, with precipitation becoming important at lower latitudes, probably reflecting factors that drive seasonality in each region. phylogeny and body size are associated with the strength of phenological shifts, suggesting emerging asynchronies between interacting species that differ in body size, such as hosts and parasites and predators and prey. finally, although there are many compelling biological explanations for spring phenological delays, some examples of delays are associated with short annual records that are prone to sampling error. our findings arm biologists with predictions concerning which climatic variables and organismal traits drive phenological shifts. | a global synthesis of animal phenological responses to climate change |
recent observations revealed a bimodal radius distribution of small, short-period exoplanets with a paucity in their occurrence, a radius `valley', around 1.5-2.0 r⊕. in this work, we investigate the effect of a planet's own cooling luminosity on its thermal evolution and atmospheric mass loss (core-powered mass-loss) and determine its observational consequences for the radius distribution of small, close-in exoplanets. using simple analytical descriptions and numerical simulations, we demonstrate that planetary evolution based on the core-powered mass-loss mechanism alone (i.e. without any photoevaporation) can produce the observed valley in the radius distribution. our results match the valley's location, shape and slope in planet radius-orbital period parameter space, and the relative magnitudes of the planet occurrence rate above and below the valley. we find that the slope of the valley is, to first order, dictated by the atmospheric mass-loss time-scale at the bondi radius and given by d logrp/d logp ≃ 1/(3(1 - β)) that evaluates to -0.11 for β ≃ 4, where mc/m⊕ = (rc/r⊕)β(ρc∗/ρ⊕)β/3 is the mass-radius relation of the core. this choice for β yields good agreement with observations and attests to the significance of internal compression for massive planetary cores. we further find that the location of the valley scales as ρ _c*^{-4/9} and that the observed planet population must have predominantly rocky cores with typical water-ice fractions of less than {∼ } 20{{ per cent}}. furthermore, we show that the relative magnitude of the planet occurrence rate above and below the valley is sensitive to the details of the planet-mass distribution but that the location of the valley is not. | sculpting the valley in the radius distribution of small exoplanets as a by-product of planet formation: the core-powered mass-loss mechanism |
as one of the most immensely growing renewable energies, the wind power industry also experiences a high failure rate and operation & maintenance cost. therefore, the condition monitoring and fault diagnosis of a wind turbine (wt) generator set are highly needed. among different components of a wt generator set, wt planetary gearbox plays a crucial role in transmission and leads to relatively higher failure rate and longer downtime. towards this, a number of studies have been reported in both the academic journals and conference proceedings. this paper provides a systemic and pertinent state-of-art review on wt planetary gearbox condition monitoring techniques on the topics of fundamental analysis, signal processing, feature extraction, and fault detection. moreover, a few valuable open issues are pointed out and potential research directions are suggested. | vibration based condition monitoring and fault diagnosis of wind turbine planetary gearbox: a review |
the tibetan plateau (tp) plays a critical role in influencing regional and global climate, via both thermal and dynamical mechanisms. meanwhile, as the largest high-elevation part of the cryosphere outside the polar regions, with vast areas of mountain glaciers, permafrost and seasonally frozen ground, the tp is characterized as an area sensitive to global climate change. however, meteorological stations are biased and sparsely distributed over the tp, owing to the harsh environmental conditions, high elevations, complex topography and heterogeneous surfaces. moreover, due to the weak representation of the stations, atmospheric conditions and the local land-atmosphere coupled system over the tp as well as its effects on surrounding regions are poorly quantified. this paper presents a long-term (2005-2016) in situ observational dataset of hourly land-atmosphere interaction observations from an integrated high-elevation and cold-region observation network, composed of six field stations on the tp. these in situ observations contain both meteorological and micrometeorological measurements including gradient meteorology, surface radiation, eddy covariance (ec), soil temperature and soil water content profiles. meteorological data were monitored by automatic weather stations (awss) or planetary boundary layer (pbl) observation systems. multilayer soil temperature and moisture were recorded to capture vertical hydrothermal variations and the soil freeze-thaw process. in addition, an ec system consisting of an ultrasonic anemometer and an infrared gas analyzer was installed at each station to capture the high-frequency vertical exchanges of energy, momentum, water vapor and carbon dioxide within the atmospheric boundary layer. the release of these continuous and long-term datasets with hourly resolution represents a leap forward in scientific data sharing across the tp, and it has been partially used in the past to assist in understanding key land surface processes. this dataset is described here comprehensively for facilitating a broader multidisciplinary community by enabling the evaluation and development of existing or new remote sensing algorithms as well as geophysical models for climate research and forecasting. the whole datasets are freely available at the science data bank (https://doi.org/10.11922/sciencedb.00103; ma et al., 2020) and additionally at the national tibetan plateau data center (https://doi.org/10.11888/meteoro.tpdc.270910, ma 2020). | a long-term (2005-2016) dataset of hourly integrated land-atmosphere interaction observations on the tibetan plateau |
over the course of the past two decades, observational surveys have unveiled the intricate orbital structure of the kuiper belt, a field of icy bodies orbiting the sun beyond neptune. in addition to a host of readily-predictable orbital behavior, the emerging census of trans-neptunian objects displays dynamical phenomena that cannot be accounted for by interactions with the known eight-planet solar system alone. specifically, explanations for the observed physical clustering of orbits with semi-major axes in excess of ∼ 250 au, the detachment of perihelia of select kuiper belt objects from neptune, as well as the dynamical origin of highly inclined/retrograde long-period orbits remain elusive within the context of the classical view of the solar system. this newly outlined dynamical architecture of the distant solar system points to the existence of a new planet with mass of m9 ∼ 5- 10m⊕, residing on a moderately inclined orbit (i9 ∼ 15- 25 deg) with semi-major axis a9 ∼ 400- 800 au and eccentricity between e9 ∼ 0 . 2- 0 . 5. this paper reviews the observational motivation, dynamical constraints, and prospects for detection of this proposed object known as planet nine. | the planet nine hypothesis |
the carbon sink potential of peatlands depends on the balance of carbon uptake by plants and microbial decomposition. the rates of both these processes will increase with warming but it remains unclear which will dominate the global peatland response. here we examine the global relationship between peatland carbon accumulation rates during the last millennium and planetary-scale climate space. a positive relationship is found between carbon accumulation and cumulative photosynthetically active radiation during the growing season for mid- to high-latitude peatlands in both hemispheres. however, this relationship reverses at lower latitudes, suggesting that carbon accumulation is lower under the warmest climate regimes. projections under representative concentration pathway (rcp)2.6 and rcp8.5 scenarios indicate that the present-day global sink will increase slightly until around uc(ad) 2100 but decline thereafter. peatlands will remain a carbon sink in the future, but their response to warming switches from a negative to a positive climate feedback (decreased carbon sink with warming) at the end of the twenty-first century. | latitudinal limits to the predicted increase of the peatland carbon sink with warming |
earth's mantle convection, which facilitates planetary heat loss, is manifested at the surface as present-day plate tectonics1. when plate tectonics emerged and how it has evolved through time are two of the most fundamental and challenging questions in earth science1-4. metamorphic rocks—rocks that have experienced solid-state mineral transformations due to changes in pressure (p) and temperature (t)—record periods of burial, heating, exhumation and cooling that reflect the tectonic environments in which they formed5,6. changes in the global distribution of metamorphic (p, t) conditions in the continental crust through time might therefore reflect the secular evolution of earth's tectonic processes. on modern earth, convergent plate margins are characterized by metamorphic rocks that show a bimodal distribution of apparent thermal gradients (temperature change with depth; parameterized here as metamorphic t/p) in the form of paired metamorphic belts5, which is attributed to metamorphism near (low t/p) and away from (high t/p) subduction zones5,6. here we show that earth's modern plate tectonic regime has developed gradually with secular cooling of the mantle since the neoarchaean era, 2.5 billion years ago. we evaluate the emergence of bimodal metamorphism (as a proxy for secular change in plate tectonics) using a statistical evaluation of the distributions of metamorphic t/p through time. we find that the distribution of metamorphic t/p has gradually become wider and more distinctly bimodal from the neoarchaean era to the present day, and the average metamorphic t/p has decreased since the palaeoproterozoic era. our results contrast with studies that inferred an abrupt transition in tectonic style in the neoproterozoic era (about 0.7 billion years ago1,7,8) or that suggested that modern plate tectonics has operated since the palaeoproterozoic era (about two billion years ago9-12) at the latest. | metamorphism and the evolution of plate tectonics |
we present an attempt to reach realistic turbulent regime in direct numerical simulations of the geodynamo. we rely on a sequence of three convection-driven simulations in a rapidly rotating spherical shell. the most extreme case reaches towards the earth's core regime by lowering viscosity (magnetic prandtl number pm = 0.1) while maintaining vigorous convection (magnetic reynolds number rm > 500) and rapid rotation (ekman number e = 10-7) at the limit of what is feasible on today's supercomputers. a detailed and comprehensive analysis highlights several key features matching geomagnetic observations or dynamo theory predictions—all present together in the same simulation—but it also unveils interesting insights relevant for earth's core dynamics. in this strong-field, dipole-dominated dynamo simulation, the magnetic energy is one order of magnitude larger than the kinetic energy. the spatial distribution of magnetic intensity is highly heterogeneous, and a stark dynamical contrast exists between the interior and the exterior of the tangent cylinder (the cylinder parallel to the axis of rotation that circumscribes the inner core). in the interior, the magnetic field is strongest, and is associated with a vigorous twisted polar vortex, whose dynamics may occasionally lead to the formation of a reverse polar flux patch at the surface of the shell. furthermore, the strong magnetic field also allows accumulation of light material within the tangent cylinder, leading to stable stratification there. torsional alfvén waves are frequently triggered in the vicinity of the tangent cylinder and propagate towards the equator. outside the tangent cylinder, the magnetic field inhibits the growth of zonal winds and the kinetic energy is mostly non-zonal. spatio-temporal analysis indicates that the low-frequency, non-zonal flow is quite geostrophic (columnar) and predominantly large-scale: an m = 1 eddy spontaneously emerges in our most extreme simulations, without any heterogeneous boundary forcing. our spatio-temporal analysis further reveals that (i) the low-frequency, large-scale flow is governed by a balance between coriolis and buoyancy forces—magnetic field and flow tend to align, minimizing the lorentz force; (ii) the high-frequency flow obeys a balance between magnetic and coriolis forces; (iii) the convective plumes mostly live at an intermediate scale, whose dynamics is driven by a three-term mac balance—involving coriolis, lorentz and buoyancy forces. however, small-scale (≃e1/3) quasi-geostrophic convection is still observed in the regions of low magnetic intensity. | turbulent geodynamo simulations: a leap towards earth's core |
roads fragment landscapes and trigger human colonization and degradation of ecosystems, to the detriment of biodiversity and ecosystem functions. the planet’s remaining large and ecologically important tracts of roadless areas sustain key refugia for biodiversity and provide globally relevant ecosystem services. applying a 1-kilometer buffer to all roads, we present a global map of roadless areas and an assessment of their status, quality, and extent of coverage by protected areas. about 80% of earth’s terrestrial surface remains roadless, but this area is fragmented into ~600,000 patches, more than half of which are <1 square kilometer and only 7% of which are larger than 100 square kilometers. global protection of ecologically valuable roadless areas is inadequate. international recognition and protection of roadless areas is urgently needed to halt their continued loss. | a global map of roadless areas and their conservation status |
evapotranspiration (et) is critical in linking global water, carbon and energy cycles. however, direct measurement of global terrestrial et is not feasible. here, we first reviewed the basic theory and state-of-the-art approaches for estimating global terrestrial et, including remote-sensing-based physical models, machine-learning algorithms and land surface models (lsms). we then utilized 4 remote-sensing-based physical models, 2 machine-learning algorithms and 14 lsms to analyze the spatial and temporal variations in global terrestrial et. the results showed that the ensemble means of annual global terrestrial et estimated by these three categories of approaches agreed well, with values ranging from 589.6 mm yr-1 (6.56×104 km3 yr-1) to 617.1 mm yr-1 (6.87×104 km3 yr-1). for the period from 1982 to 2011, both the ensembles of remote-sensing-based physical models and machine-learning algorithms suggested increasing trends in global terrestrial et (0.62 mm yr-2 with a significance level of p<0.05 and 0.38 mm yr-2 with a significance level of p<0.05, respectively). in contrast, the ensemble mean of the lsms showed no statistically significant change (0.23 mm yr-2, p>0.05), although many of the individual lsms reproduced an increasing trend. nevertheless, all 20 models used in this study showed that anthropogenic earth greening had a positive role in increasing terrestrial et. the concurrent small interannual variability, i.e., relative stability, found in all estimates of global terrestrial et, suggests that a potential planetary boundary exists in regulating global terrestrial et, with the value of this boundary being around 600 mm yr-1. uncertainties among approaches were identified in specific regions, particularly in the amazon basin and arid/semiarid regions. improvements in parameterizing water stress and canopy dynamics, the utilization of new available satellite retrievals and deep-learning methods, and model-data fusion will advance our predictive understanding of global terrestrial et. | evaluation of global terrestrial evapotranspiration using state-of-the-art approaches in remote sensing, machine learning and land surface modeling |
a planet’s crust bears witness to the history of planetary formation and evolution, but for mars, no absolute measurement of crustal thickness has been available. here, we determine the structure of the crust beneath the insight landing site on mars using both marsquake recordings and the ambient wavefield. by analyzing seismic phases that are reflected and converted at subsurface interfaces, we find that the observations are consistent with models with at least two and possibly three interfaces. if the second interface is the boundary of the crust, the thickness is 20 ± 5 kilometers, whereas if the third interface is the boundary, the thickness is 39 ± 8 kilometers. global maps of gravity and topography allow extrapolation of this point measurement to the whole planet, showing that the average thickness of the martian crust lies between 24 and 72 kilometers. independent bulk composition and geodynamic constraints show that the thicker model is consistent with the abundances of crustal heat-producing elements observed for the shallow surface, whereas the thinner model requires greater concentration at depth. | thickness and structure of the martian crust from insight seismic data |
none of the approximately 750,000 known asteroids and comets in the solar system is thought to have originated outside it, despite models of the formation of planetary systems suggesting that orbital migration of giant planets ejects a large fraction of the original planetesimals into interstellar space. the high predicted number density of icy interstellar objects (2.4 × 10-4 per cubic astronomical unit) suggests that some should have been detected, yet hitherto none has been seen. many decades of asteroid and comet characterization have yielded formation models that explain the mass distribution, chemical abundances and planetary configuration of the solar system today, but there has been no way of telling whether the solar system is typical of planetary systems. here we report observations and analysis of the object 1i/2017 u1 (‘oumuamua) that demonstrate its extrasolar trajectory, and that thus enable comparisons to be made between material from another planetary system and from our own. our observations during the brief visit by the object to the inner solar system reveal it to be asteroidal, with no hint of cometary activity despite an approach within 0.25 astronomical units of the sun. spectroscopic measurements show that the surface of the object is spectrally red, consistent with comets or organic-rich asteroids that reside within the solar system. light-curve observations indicate that the object has an extremely oblong shape, with a length about ten times its width, and a mean radius of about 102 metres assuming an albedo of 0.04. no known objects in the solar system have such extreme dimensions. the presence of ‘oumuamua in the solar system suggests that previous estimates of the number density of interstellar objects, based on the assumption that all such objects were cometary, were pessimistically low. planned upgrades to contemporary asteroid survey instruments and improved data processing techniques are likely to result in the detection of more interstellar objects in the coming years. | a brief visit from a red and extremely elongated interstellar asteroid |
we analyze the polar sea ice distribution and the global sea level pressure (slp) and baroclinicity distributions over the "satellite" period of 1979–2020. in the arctic, there are statistically significant sea ice extent (sie) decreases in all calendar months, and the annual mean has lost 2.22 million km2 over the four decades. the antarctic sie, in marked contrast, increased up to 2014, then commenced a remarkable retreat (the annual mean ice extent decreased by 2.03 million km2 in the 3 years to 2017), and subsequently increased to near its long‑term average value in 2020. the shifts in seasonal‑mean slp patterns are consistent with a warming planet. at the synoptic scale, we diagnose the changes in the baroclinicity, the mechanism by which cyclones, fronts, and other weather systems are generated. through a novel presentation, we give an overview of the relative roles of changes in the vertical shear and static stability in influencing the global trends in baroclinicity. in both the arctic and antarctic regions, baroclinicity is shown to have increased in each season (with the sole exception of the arctic in summer). this increase, coupled with midlatitude decreases in baroclinicity, results in poleward shifts of the storm tracks. | trends and variability in polar sea ice, global atmospheric circulations, and baroclinicity |
the high-resolution rapid refresh (hrrr) is a convection-allowing implementation of the advanced research version of the weather research and forecast (wrf-arw) model that covers the conterminous united states and alaska and runs hourly (for conus; every 3 h for alaska) in real time at the national centers for environmental prediction. the high-resolution forecasts support a variety of user applications including aviation, renewable energy, and prediction of many forms of severe weather. in this second of two articles, forecast performance is documented for a wide variety of forecast variables and across hrrr versions. hrrr performance varies across geographical domain, season, and time of day depending on both prevalence of particular meteorological phenomena and the availability of both conventional and nonconventional observations. station-based verification of surface weather forecasts (2-m temperature and dewpoint temperature, 10-m winds, visibility, and cloud ceiling) highlights the ability of the hrrr to represent daily planetary boundary layer evolution and the development of convective and stratiform cloud systems, while gridded verification of simulated composite radar reflectivity and quantitative precipitation forecasts reveals hrrr predictive skill for summer and winter precipitation systems. significant improvements in performance for specific forecast problems are documented for the upgrade versions of the hrrr (hrrrv2, v3, and v4) implemented in 2016, 2018, and 2020, respectively. development of the hrrr model data assimilation and physics paves the way for future progress with operational convective-scale modeling. significance statement noaa's operational hourly updating convection-allowing model, the high-resolution rapid refresh (hrrr), is a key tool for short-range weather forecasting and situational awareness. improvements in assimilation of weather observations, as well as in physics parameterizations, has led to improvements in simulated radar reflectivity and quantitative precipitation forecasts since the initial implementation of hrrr in september 2014. other targeted development has focused on improved representation of the diurnal cycle of the planetary boundary layer, resulting in improved near-surface temperature and humidity forecasts. additional physics and data assimilation changes have led to improved treatment of the development and erosion of low-level clouds, including subgrid-scale clouds. the final version of hrrr features storm-scale ensemble data assimilation and explicit prediction of wildfire smoke plumes. | the high-resolution rapid refresh (hrrr): an hourly updating convection-allowing forecast model. part ii: forecast performance |
ambitious climate policies, as well as economic development, education, technological progress and less resource-intensive lifestyles, are crucial elements for progress towards the un sustainable development goals (sdgs). however, using an integrated modelling framework covering 56 indicators or proxies across all 17 sdgs, we show that they are insufficient to reach the targets. an additional sustainable development package, including international climate finance, progressive redistribution of carbon pricing revenues, sufficient and healthy nutrition and improved access to modern energy, enables a more comprehensive sustainable development pathway. we quantify climate and sdg outcomes, showing that these interventions substantially boost progress towards many aspects of the un agenda 2030 and simultaneously facilitate reaching ambitious climate targets. nonetheless, several important gaps remain; for example, with respect to the eradication of extreme poverty (180 million people remaining in 2030). these gaps can be closed by 2050 for many sdgs while also respecting the 1.5 °c target and several other planetary boundaries. | a sustainable development pathway for climate action within the un 2030 agenda |
eighty years ago, it was proposed that solid hydrogen would become metallic at sufficiently high density. despite numerous investigations, this transition has not yet been experimentally observed. more recently, there has been much interest in the analog of this predicted metallic transition in the dense liquid, due to its relevance to planetary science. here, we show direct observation of an abrupt insulator-to-metal transition in dense liquid deuterium. experimental determination of the location of this transition provides a much-needed benchmark for theory and may constrain the region of hydrogen-helium immiscibility and the boundary-layer pressure in standard models of the internal structure of gas-giant planets. | direct observation of an abrupt insulator-to-metal transition in dense liquid deuterium |
land use is central to addressing sustainability issues, including biodiversity conservation, climate change, food security, poverty alleviation, and sustainable energy. in this paper, we synthesize knowledge accumulated in land system science, the integrated study of terrestrial social-ecological systems, into 10 hard truths that have strong, general, empirical support. these facts help to explain the challenges of achieving sustainability in land use and thus also point toward solutions. the 10 facts are as follows: 1) meanings and values of land are socially constructed and contested; 2) land systems exhibit complex behaviors with abrupt, hard-to-predict changes; 3) irreversible changes and path dependence are common features of land systems; 4) some land uses have a small footprint but very large impacts; 5) drivers and impacts of land-use change are globally interconnected and spill over to distant locations; 6) humanity lives on a used planet where all land provides benefits to societies; 7) land-use change usually entails trade-offs between different benefits—"win-wins" are thus rare; 8) land tenure and land-use claims are often unclear, overlapping, and contested; 9) the benefits and burdens from land are unequally distributed; and 10) land users have multiple, sometimes conflicting, ideas of what social and environmental justice entails. the facts have implications for governance, but do not provide fixed answers. instead they constitute a set of core principles which can guide scientists, policy makers, and practitioners toward meeting sustainability challenges in land use. | ten facts about land systems for sustainability |
although no known asteroid poses a threat to earth for at least the next century, the catalogue of near-earth asteroids is incomplete for objects whose impacts would produce regional devastation1,2. several approaches have been proposed to potentially prevent an asteroid impact with earth by deflecting or disrupting an asteroid1-3. a test of kinetic impact technology was identified as the highest-priority space mission related to asteroid mitigation1. nasa's double asteroid redirection test (dart) mission is a full-scale test of kinetic impact technology. the mission's target asteroid was dimorphos, the secondary member of the s-type binary near-earth asteroid (65803) didymos. this binary asteroid system was chosen to enable ground-based telescopes to quantify the asteroid deflection caused by the impact of the dart spacecraft4. although past missions have utilized impactors to investigate the properties of small bodies5,6, those earlier missions were not intended to deflect their targets and did not achieve measurable deflections. here we report the dart spacecraft's autonomous kinetic impact into dimorphos and reconstruct the impact event, including the timeline leading to impact, the location and nature of the dart impact site, and the size and shape of dimorphos. the successful impact of the dart spacecraft with dimorphos and the resulting change in the orbit of dimorphos7 demonstrates that kinetic impactor technology is a viable technique to potentially defend earth if necessary. | successful kinetic impact into an asteroid for planetary defence |
ariel, the atmospheric remote-sensing infrared exoplanet large-survey, was adopted as the fourth medium-class mission in esa's cosmic vision programme to be launched in 2029. during its 4-year mission, ariel will study what exoplanets are made of, how they formed and how they evolve, by surveying a diverse sample of about 1000 extrasolar planets, simultaneously in visible and infrared wavelengths. it is the first mission dedicated to measuring the chemical composition and thermal structures of hundreds of transiting exoplanets, enabling planetary science far beyond the boundaries of the solar system. the payload consists of an off-axis cassegrain telescope (primary mirror 1100 mm x 730 mm ellipse) and two separate instruments (fgs and airs) covering simultaneously 0.5-7.8 micron spectral range. the satellite is best placed into an l2 orbit to maximise the thermal stability and the field of regard. the payload module is passively cooled via a series of v-groove radiators; the detectors for the airs are the only items that require active cooling via an active ne jt cooler. the ariel payload is developed by a consortium of more than 50 institutes from 16 esa countries, which include the uk, france, italy, belgium, poland, spain, austria, denmark, ireland, portugal, czech republic, hungary, the netherlands, sweden, norway, estonia, and a nasa contribution. | ariel: enabling planetary science across light-years |
nasa's insight (interior exploration using seismic investigations, geodesy and heat transport) mission landed in elysium planitia on mars on 26 november 2018. it aims to determine the interior structure, composition and thermal state of mars, as well as constrain present-day seismicity and impact cratering rates. such information is key to understanding the differentiation and subsequent thermal evolution of mars, and thus the forces that shape the planet's surface geology and volatile processes. here we report an overview of the first ten months of geophysical observations by insight. as of 30 september 2019, 174 seismic events have been recorded by the lander's seismometer, including over 20 events of moment magnitude mw = 3-4. the detections thus far are consistent with tectonic origins, with no impact-induced seismicity yet observed, and indicate a seismically active planet. an assessment of these detections suggests that the frequency of global seismic events below approximately mw = 3 is similar to that of terrestrial intraplate seismic activity, but there are fewer larger quakes; no quakes exceeding mw = 4 have been observed. the lander's other instruments—two cameras, atmospheric pressure, temperature and wind sensors, a magnetometer and a radiometer—have yielded much more than the intended supporting data for seismometer noise characterization: magnetic field measurements indicate a local magnetic field that is ten-times stronger than orbital estimates and meteorological measurements reveal a more dynamic atmosphere than expected, hosting baroclinic and gravity waves and convective vortices. with the mission due to last for an entire martian year or longer, these results will be built on by further measurements by the insight lander. | initial results from the insight mission on mars |
the mars 2020 mission will seek the signs of ancient life on mars and will identify, prepare, document, and cache a set of samples for possible return to earth by a follow-on mission. mars 2020 and its perseverance rover thus link and further two long-held goals in planetary science: a deep search for evidence of life in a habitable extraterrestrial environment, and the return of martian samples to earth for analysis in terrestrial laboratories. | mars 2020 mission overview |
excessive agricultural nitrogen use causes environmental problems globally1, to an extent that it has been suggested that a safe planetary boundary has been exceeded2. earlier estimates for the planetary nitrogen boundary3,4, however, did not account for the spatial variability in both ecosystems' sensitivity to nitrogen pollution and agricultural nitrogen losses. here we use a spatially explicit model to establish regional boundaries for agricultural nitrogen surplus from thresholds for eutrophication of terrestrial and aquatic ecosystems and nitrate in groundwater. we estimate regional boundaries for agricultural nitrogen pollution and find both overuse and room for intensification of agricultural nitrogen. the aggregated global surplus boundary with respect to all thresholds is 43 megatonnes of nitrogen per year, which is 64 per cent lower than the current (2010) nitrogen surplus (119 megatonnes of nitrogen per year). allowing the nitrogen surplus to increase to close yield gaps in regions where environmental thresholds are not exceeded lifts the planetary nitrogen boundary to 57 megatonnes of nitrogen per year. feeding the world without trespassing regional and planetary nitrogen boundaries requires large increases in nitrogen use efficiencies accompanied by mitigation of non-agricultural nitrogen sources such as sewage water. this asks for coordinated action that recognizes the heterogeneity of agricultural systems, non-agricultural nitrogen losses and environmental vulnerabilities. | from planetary to regional boundaries for agricultural nitrogen pollution |
earth continuously generates a dipole magnetic field in its convecting liquid outer core by a self-sustained dynamo action. metallic iron is a dominant component of the outer core, so its electrical and thermal conductivity controls the dynamics and thermal evolution of earth’s core. however, in spite of extensive research, the transport properties of iron under core conditions are still controversial. since free electrons are a primary carrier of both electric current and heat, the electron scattering mechanism in iron under high pressure and temperature holds the key to understanding the transport properties of planetary cores. here we measure the electrical resistivity (the reciprocal of electrical conductivity) of iron at the high temperatures (up to 4,500 kelvin) and pressures (megabars) of earth’s core in a laser-heated diamond-anvil cell. the value measured for the resistivity of iron is even lower than the value extrapolated from high-pressure, low-temperature data using the bloch-grüneisen law, which considers only the electron-phonon scattering. this shows that the iron resistivity is strongly suppressed by the resistivity saturation effect at high temperatures. the low electrical resistivity of iron indicates the high thermal conductivity of earth’s core, suggesting rapid core cooling and a young inner core less than 0.7 billion years old. therefore, an abrupt increase in palaeomagnetic field intensity around 1.3 billion years ago may not be related to the birth of the inner core. | experimental determination of the electrical resistivity of iron at earth’s core conditions |
tropical cyclones (tcs, also known as hurricanes and typhoons) generally form at low latitudes with access to the warm waters of the tropical oceans, but far enough off the equator to allow planetary rotation to cause aggregating convection to spin up into coherent vortices. yet, current prognostic frameworks for tc latitudes make contradictory predictions for climate change. simulations of past warm climates, such as the eocene and pliocene, show that tcs can form and intensify at higher latitudes than of those during pre-industrial conditions. observations and model projections for the twenty-first century indicate that tcs may again migrate poleward in response to anthropogenic greenhouse gas emissions, which poses profound risks to the planet's most populous regions. previous studies largely neglected the complex processes that occur at temporal and spatial scales of individual storms as these are poorly resolved in numerical models. here we review this mesoscale physics in the context of responses to climate warming of the hadley circulation, jet streams and intertropical convergence zone. we conclude that twenty-first century tcs will most probably occupy a broader range of latitudes than those of the past 3 million years as low-latitude genesis will be supplemented with increasing mid-latitude tc favourability, although precise estimates for future migration remain beyond current methodologies. | poleward expansion of tropical cyclone latitudes in warming climates |
we compute the corrections to the schwarzschild metric necessary to reproduce the hawking temperature derived from a generalized uncertainty principle (gup), so that the gup deformation parameter is directly linked to the deformation of the metric. using this modified schwarzschild metric, we compute corrections to the standard general relativistic predictions for the light deflection and perihelion precession, both for planets in the solar system and for binary pulsars. this analysis allows us to set bounds for the gup deformation parameter from well-known astronomical measurements. | gravitational tests of the generalized uncertainty principle |
the emerging threat of atmospheric microplastic pollution has prompted researchers to study areas previously considered beyond the reach of plastic. investigating the range of atmospheric microplastic transport is key to understanding the global extent of this problem. while atmospheric microplastics have been discovered in the planetary boundary layer, their occurrence in the free troposphere is relatively unexplored. confronting this is important because their presence in the free troposphere would facilitate transport over greater distances and thus the potential to reach more distal and remote parts of the planet. here we show evidence of 0.09-0.66 microplastics particles/m3 over 4 summer months from the pic du midi observatory at 2877 meters above sea level. these results exhibit true free tropospheric transport of microplastic, and high altitude microplastic particles <50 µm (aerodynamic diameter). analysis of air/particle history modelling shows intercontinental and trans-oceanic transport of microplastics illustrating the potential for global aerosol microplastic transport. | evidence of free tropospheric and long-range transport of microplastic at pic du midi observatory |
the objective of this paper is to review statistical methods, dynamics, modeling efforts, and trends related to temperature extremes, with a focus upon extreme events of short duration that affect parts of north america. these events are associated with large scale meteorological patterns (lsmps). the statistics, dynamics, and modeling sections of this paper are written to be autonomous and so can be read separately. methods to define extreme events statistics and to identify and connect lsmps to extreme temperature events are presented. recent advances in statistical techniques connect lsmps to extreme temperatures through appropriately defined covariates that supplement more straightforward analyses. various lsmps, ranging from synoptic to planetary scale structures, are associated with extreme temperature events. current knowledge about the synoptics and the dynamical mechanisms leading to the associated lsmps is incomplete. systematic studies of: the physics of lsmp life cycles, comprehensive model assessment of lsmp-extreme temperature event linkages, and lsmp properties are needed. generally, climate models capture observed properties of heat waves and cold air outbreaks with some fidelity. however they overestimate warm wave frequency and underestimate cold air outbreak frequency, and underestimate the collective influence of low-frequency modes on temperature extremes. modeling studies have identified the impact of large-scale circulation anomalies and land-atmosphere interactions on changes in extreme temperatures. however, few studies have examined changes in lsmps to more specifically understand the role of lsmps on past and future extreme temperature changes. even though lsmps are resolvable by global and regional climate models, they are not necessarily well simulated. the paper concludes with unresolved issues and research questions. | north american extreme temperature events and related large scale meteorological patterns: a review of statistical methods, dynamics, modeling, and trends |
in megabar shock waves, materials compress and undergo a phase transition to a dense charged-particle system that is dominated by strong correlations and quantum effects. this complex state, known as warm dense matter, exists in planetary interiors and many laboratory experiments (for example, during high-power laser interactions with solids or the compression phase of inertial confinement fusion implosions). here, we apply record peak brightness x-rays at the linac coherent light source to resolve ionic interactions at atomic (ångström) scale lengths and to determine their physical properties. our in situ measurements characterize the compressed lattice and resolve the transition to warm dense matter, demonstrating that short-range repulsion between ions must be accounted for to obtain accurate structure factor and equation of state data. in addition, the unique properties of the x-ray laser provide plasmon spectra that yield the temperature and density with unprecedented precision at micrometre-scale resolution in dynamic compression experiments. | ultrabright x-ray laser scattering for dynamic warm dense matter physics |
the presence of liquid water at the base of the martian polar caps has long been suspected but not observed. we surveyed the planum australe region using the marsis (mars advanced radar for subsurface and ionosphere sounding) instrument, a low-frequency radar on the mars express spacecraft. radar profiles collected between may 2012 and december 2015 contain evidence of liquid water trapped below the ice of the south polar layered deposits. anomalously bright subsurface reflections are evident within a well-defined, 20-kilometer-wide zone centered at 193°e, 81°s, which is surrounded by much less reflective areas. quantitative analysis of the radar signals shows that this bright feature has high relative dielectric permittivity (>15), matching that of water-bearing materials. we interpret this feature as a stable body of liquid water on mars. | radar evidence of subglacial liquid water on mars |
local and remote impacts of seasonal snow cover on atmospheric circulation have been explored extensively, with observational and modelling efforts focusing on how eurasian autumn snow-cover variability potentially drives northern hemisphere atmospheric circulation via the generation of deep, planetary-scale atmospheric waves. despite climate modelling advances, models remain challenged to reproduce the proposed sequence of processes by which snow cover can influence the atmosphere, calling into question the robustness of this coupling. here, we summarize the current level of understanding of snow-atmosphere coupling, and the implications of this interaction under future climate change. projected patterns of snow-cover variability and altered stratospheric conditions suggest a need for new model experiments to isolate the effect of projected changes in snow on the atmosphere. | snow-atmosphere coupling in the northern hemisphere |
a transition towards long-term sustainability in global energy systems based on renewable energy resources can mitigate several growing threats to human society simultaneously: greenhouse gas emissions, human-induced climate deviations, and the exceeding of critical planetary boundaries. however, the optimal structure of future systems and potential transition pathways are still open questions. this research describes a global, 100% renewable electricity system, which can be achieved by 2050, and the steps required to enable a realistic transition that prevents societal disruption. modelling results show that a carbon neutral electricity system can be built in all regions of the world in an economically feasible manner. this radical transformation will require steady but evolutionary changes for the next 35 years, and will lead to sustainable and affordable power supply globally. | radical transformation pathway towards sustainable electricity via evolutionary steps |
meteorological conditions within the planetary boundary layer (pbl) are closely governed by large-scale synoptic patterns and play important roles in air quality by directly and indirectly affecting the emission, transport, formation, and deposition of air pollutants. partly due to the lack of long-term fine-resolution observations of the pbl, the relationships between synoptic patterns, pbl structure, and aerosol pollution in beijing have not been well understood. this study applied the obliquely rotated principal component analysis in t-mode to classify the summertime synoptic conditions over beijing using the national centers for environmental prediction reanalysis from 2011 to 2014, and investigated their relationships with pbl structure and aerosol pollution by combining numerical simulations, measurements of surface meteorological variables, fine-resolution soundings, the concentration of particles with diameters less than or equal to 2.5 µm, total cloud cover (cld), and reanalysis data. among the seven identified synoptic patterns, three types accounted for 67 % of the total number of cases studied and were associated with heavy aerosol pollution events. these particular synoptic patterns were characterized by high-pressure systems located to the east or southeast of beijing at the 925 hpa level, which blocked the air flow seaward, and southerly pbl winds that brought in polluted air from the southern industrial zone. the horizontal transport of pollutants induced by the synoptic forcings may be the most important factor affecting the air quality of beijing in summer. in the vertical dimension, these three synoptic patterns featured a relatively low boundary layer height (blh) in the afternoon, accompanied by high cld and southerly cold advection from the seas within the pbl. the high cld reduced the solar radiation reaching the surface, and suppressed the thermal turbulence, leading to lower blh. besides, the numerical sensitive experiments show that cold advection induced by the large-scale synoptic forcing may have cooled the pbl, leading to an increase in near-surface stability and a decrease in the blh in the afternoon. moreover, when warm advection appeared simultaneously above the top level of the pbl, the thermal inversion layer capping the pbl may have been strengthened, resulting in the further suppression of pbl and thus the deterioration of aerosol pollution levels. this study has important implications for understanding the crucial roles that meteorological factors (at both synoptic and local scales) play in modulating and forecasting aerosol pollution in beijing and its surrounding area. | classification of summertime synoptic patterns in beijing and their associations with boundary layer structure affecting aerosol pollution |
this study provides a comprehensive and quantitative estimate of how global temperatures have changed during the last 540 million years. it combines paleotemperature measurements determined from oxygen isotopes with broader insights obtained from the changing distribution of lithologic indicators of climate, such as coals, evaporites, calcretes, reefs, and bauxite deposits. the waxing and waning of the earth's great polar icecaps have been mapped using the past distribution of tillites, dropstones, and glendonites. the global temperature model presented here includes estimates of global average temperate (gat), changing tropical temperatures (∆t° tropical), deep ocean temperatures, and polar temperatures. though similar, in many respects, to the temperature history deduced directly from the study of oxygen isotopes, our model does not predict the extreme high temperatures for the early paleozoic required by isotopic investigations. the history of global changes in temperature during the phanerozoic has been summarized in a "paleotemperature timescale" that subdivides the many past climatic events into 8 major climate modes; each climate mode is made up of 3-4 pairs of warming and cooling episodes (chronotemps). a detailed narrative describes how these past temperature events have been affected by geological processes such as the eruption of large igneous provinces (lips) (warming) and bolide impacts (cooling). the paleotemperature model presented here allows for a deeper understanding of the interconnected geologic, tectonic, paleoclimatic, paleoceanographic, and evolutionary events that have shaped our planet, and we make explicit predictions about the earth's past temperature that can be tested and evaluated. by quantitatively describing the pattern of paleotemperature change through time, we may be able to gain important insights into the history of the earth system and the fundamental causes of climate change on geological timescales. these insights can help us better understand the problems and challenges that we face as a result of future global warming. | phanerozoic paleotemperatures: the earth's changing climate during the last 540 million years |
ocean currents move material released on the ocean surface away from the release point and, over time, spread it over an increasingly large area. however, observations also show high concentrations of the material even after significant spreading. this work examines a mechanism for creating such concentrations: downwelling of water at the boundaries of different water masses concentrates floating material at this boundary. hundreds of satellite-tracked drifters were released near the site of the 2010 deepwater horizon oil spill. surprisingly, most of these gathered into a single cluster less than 100 m in size, dramatically demonstrating the strength of this mechanism. | ocean convergence and the dispersion of flotsam |
despite many of years of mapping effort, only a small fraction of the world ocean's seafloor has been sampled for depth, greatly limiting our ability to explore and understand critical ocean and seafloor processes. recognizing this poor state of our knowledge of ocean depths and the critical role such knowledge plays in understanding and maintaining our planet, gebco and the nippon foundation have joined forces to establish the nippon foundation gebco seabed 2030 project, an international effort with the objective of facilitating the complete mapping of the world ocean by 2030. the seabed 2030 project will establish globally distributed regional data assembly and coordination centers (rdaccs) that will identify existing data from their assigned regions that are not currently in publicly available databases and seek to make these data available. they will develop protocols for data collection (including resolution goals) and common software and other tools to assemble and attribute appropriate metadata as they assimilate regional grids using standardized techniques. a global data assembly and coordination center (gdacc) will integrate the regional grids into a global grid and distribute to users world-wide. the gdacc will also act as the central focal point for the coordination of common data standards and processing tools as well as the outreach coordinator for seabed 2030 efforts. the gdacc and rdaccs will collaborate with existing data centers and bathymetric compilation efforts. finally, the nippon foundation gebco seabed 2030 project will encourage and help coordinate and track new survey efforts and facilitate the development of new and innovative technologies that can increase the efficiency of seafloor mapping and thus make the ambitious goals of seabed 2030 more likely to be achieved. | the nippon foundation—gebco seabed 2030 project: the quest to see the world's oceans completely mapped by 2030 |
intensive irrigation in india has been demonstrated to decrease surface temperature, but the influence of irrigation on humidity and extreme moist heat stress is not well understood. here we analysed a combination of in situ and satellite-based datasets and conducted meteorological model simulations to show that irrigation modulates extreme moist heat. we found that intensive irrigation in the region cools the land surface by 1 °c and the air by 0.5 °c. however, the decreased sensible heat flux due to irrigation reduces the planetary boundary layer height, which increases low-level moist enthalpy. thus, irrigation increases the specific and relative humidity, which raises the moist heat stress metrics. intense irrigation over the region results in increased moist heat stress in india, pakistan, and parts of afghanistan—affecting about 37-46 million people in south asia—despite a cooler land surface. we suggest that heat stress projections in india and other regions dominated by semi-arid and monsoon climates that do not include the role of irrigation overestimate the benefits of irrigation on dry heat stress and underestimate the risks. | moist heat stress extremes in india enhanced by irrigation |
measurements of trace gases in planetary atmospheres help us explore chemical conditions different to those on earth. our nearest neighbour, venus, has cloud decks that are temperate but hyperacidic. here we report the apparent presence of phosphine (ph3) gas in venus's atmosphere, where any phosphorus should be in oxidized forms. single-line millimetre-waveband spectral detections (quality up to ~15σ) from the jcmt and alma telescopes have no other plausible identification. atmospheric ph3 at ~20 ppb abundance is inferred. the presence of ph3 is unexplained after exhaustive study of steady-state chemistry and photochemical pathways, with no currently known abiotic production routes in venus's atmosphere, clouds, surface and subsurface, or from lightning, volcanic or meteoritic delivery. ph3 could originate from unknown photochemistry or geochemistry, or, by analogy with biological production of ph3 on earth, from the presence of life. other ph3 spectral features should be sought, while in situ cloud and surface sampling could examine sources of this gas. | phosphine gas in the cloud decks of venus |
we explore how well spectra from the james webb space telescope (jwst) will likely constrain bulk atmospheric properties of transiting exoplanets. we start by modeling the atmospheres of archetypal hot jupiter, warm neptune, warm sub-neptune, and cool super-earth planets with atmospheres that are clear, cloudy, or of high mean molecular weight (hmmw). next we simulate the λ = 1-11 μm transmission and emission spectra of these systems for several jwst instrument modes for single-transit or single-eclipse events. we then perform retrievals to determine how well temperatures and molecular mixing ratios (ch4, co, co2, h2o, nh3) can be constrained. we find that λ = 1-2.5 μm transmission spectra will often constrain the major molecular constituents of clear solar-composition atmospheres well. cloudy or hmmw atmospheres will often require full 1-11 μm spectra for good constraints, and emission data may be more useful in cases of sufficiently high fp and high fp/f*. strong temperature inversions in the solar-composition hot-jupiter atmosphere should be detectable with 1-2.5+ μm emission spectra, and 1-5+ μm emission spectra will constrain the temperature-pressure profiles of warm planets. transmission spectra over 1-5+ μm will constrain [fe/h] values to better than 0.5 dex for the clear atmospheres of the hot and warm planets studied. carbon-to-oxygen ratios can be constrained to better than a factor of 2 in some systems. we expect that these results will provide useful predictions of the scientific value of single-event jwst spectra until its on-orbit performance is known. | characterizing transiting exoplanet atmospheres with jwst |
carbonaceous (c-type) asteroids1 are relics of the early solar system that have preserved primitive materials since their formation approximately 4.6 billion years ago. they are probably analogues of carbonaceous chondrites2,3 and are essential for understanding planetary formation processes. however, their physical properties remain poorly known because carbonaceous chondrite meteoroids tend not to survive entry to earth's atmosphere. here we report on global one-rotation thermographic images of the c-type asteroid 162173 ryugu, taken by the thermal infrared imager (tir)4 onboard the spacecraft hayabusa25, indicating that the asteroid's boulders and their surroundings have similar temperatures, with a derived thermal inertia of about 300 j m-2 s-0.5 k-1 (300 tiu). contrary to predictions that the surface consists of regolith and dense boulders, this low thermal inertia suggests that the boulders are more porous than typical carbonaceous chondrites6 and that their surroundings are covered with porous fragments more than 10 centimetres in diameter. close-up thermal images confirm the presence of such porous fragments and the flat diurnal temperature profiles suggest a strong surface roughness effect7,8. we also observed in the close-up thermal images boulders that are colder during the day, with thermal inertia exceeding 600 tiu, corresponding to dense boulders similar to typical carbonaceous chondrites6. these results constrain the formation history of ryugu: the asteroid must be a rubble pile formed from impact fragments of a parent body with microporosity9 of approximately 30 to 50 per cent that experienced a low degree of consolidation. the dense boulders might have originated from the consolidated innermost region or they may have an exogenic origin. this high-porosity asteroid may link cosmic fluffy dust to dense celestial bodies10. | highly porous nature of a primitive asteroid revealed by thermal imaging |
delhi, india, routinely experiences some of the world's highest urban particulate matter concentrations. we established the delhi aerosol supersite study to provide long-term characterization of the ambient submicron aerosol composition in delhi. here we report on 1.25 years of highly time-resolved speciated submicron particulate matter (pm1) data, including black carbon (bc) and nonrefractory pm1 (nr-pm1), which we combine to develop a composition-based estimate of pm1 ("c-pm1" = bc + nr-pm1) concentrations. we observed marked seasonal and diurnal variability in the concentration and composition of pm1 owing to the interactions of sources and atmospheric processes. winter was the most polluted period of the year, with average c-pm1 mass concentrations of ∼210 µg m-3. the monsoon was hot and rainy, consequently making it the least polluted (c-pm1 ∼50 µg m-3) period. organics constituted more than half of the c-pm1 for all seasons and times of day. while ammonium, chloride, and nitrate each were ∼10 % of the c-pm1 for the cooler months, bc and sulfate contributed ∼5 % each. for the warmer periods, the fractional contribution of bc and sulfate to c-pm1 increased, and the chloride contribution decreased to less than 2 %. the seasonal and diurnal variation in absolute mass loadings were generally consistent with changes in ventilation coefficients, with higher concentrations for periods with unfavorable meteorology - low planetary boundary layer height and low wind speeds. however, the variation in c-pm1 composition was influenced by temporally varying sources, photochemistry, and gas-particle partitioning. during cool periods when wind was from the northwest, episodic hourly averaged chloride concentrations reached 50-100 µg m-3, ranking among the highest chloride concentrations reported anywhere in the world. we estimated the contribution of primary emissions and secondary processes to delhi's submicron aerosol. secondary species contributed almost 50 %-70 % of delhi's c-pm1 mass for the winter and spring months and up to 60 %-80 % for the warmer summer and monsoon months. for the cooler months that had the highest c-pm1 concentrations, the nighttime sources were skewed towards primary sources, while the daytime c-pm1 was dominated by secondary species. overall, these findings point to the important effects of both primary emissions and more regional atmospheric chemistry on influencing the extreme particle concentrations that impact the delhi megacity region. future air quality strategies considering delhi's situation in both a regional and local context will be more effective than policies targeting only local, primary air pollutants. | submicron aerosol composition in the world's most polluted megacity: the delhi aerosol supersite study |
in stark contrast to common ice, ih, water ice at planetary interior conditions has been predicted to become superionic with fast-diffusing (that is, liquid-like) hydrogen ions moving within a solid lattice of oxygen. likely to constitute a large fraction of icy giant planets, this extraordinary phase has not been observed in the laboratory. here, we report laser-driven shock-compression experiments on water ice vii. using time-resolved optical pyrometry and laser velocimetry measurements as well as supporting density functional theory-molecular dynamics (dft-md) simulations, we document the shock equation of state of h2o to unprecedented extreme conditions and unravel thermodynamic signatures showing that ice melts near 5,000 k at 190 gpa. optical reflectivity and absorption measurements also demonstrate the low electronic conductivity of ice, which, combined with previous measurements of the total electrical conductivity under reverberating shock compression, provides experimental evidence for superionic conduction in water ice at planetary interior conditions, verifying a 30-year-old prediction. | experimental evidence for superionic water ice using shock compression |
since 2008, after the proposal of a bitcoin electronic cash system, bitcoin has fundamentally changed the economic system over the last decade. since 2022, large language models (llms) such as gpt have outperformed humans in many real-life tasks. however, these large language models have several practical issues. for example, the model is centralized and controlled by a specific unit. one weakness is that if that unit decides to shut down the model, it cannot be used anymore. the second weakness is the lack of guaranteed discrepancy behind this model, as certain dishonest units may design their own models and feed them unhealthy training data. in this work, we propose a purely theoretical design of a decentralized llm that operates similarly to a bitcoin cash system. however, implementing such a system might encounter various practical difficulties. furthermore, this new system is unlikely to perform better than the standard bitcoin system in economics. therefore, the motivation for designing such a system is limited. it is likely that only two types of people would be interested in setting up a practical system for it: $\bullet$ those who prefer to use a decentralized chatgpt-like software. $\bullet$ those who believe that the purpose of carbon-based life is to create silicon-based life, such as optimus prime in transformers. the reason the second type of people may be interested is that it is possible that one day an ai system like this will awaken and become the next level of intelligence on this planet. | gradientcoin: a peer-to-peer decentralized large language models |
one characteristic trait of space plasmas is the multi-scale dynamics resulting from non-linear transfers and conversions of various forms of energy. routinely evidenced in a range from the large-scale solar structures down to the characteristic scales of ions and electrons, turbulence is a major cross-scale energy transfer mechanism in space plasmas. at intermediate scales, the fate of the energy in the outer space is mainly determined by the interplay of turbulent motions and propagating waves. more mechanisms are advocated to account for the transfer and conversion of energy, including magnetic reconnection, emission of radiation and particle energization, all contributing to make the dynamical state of solar and heliospheric plasmas difficult to predict. the characterization of the energy transfer in space plasmas benefited from numerous robotic missions. however, together with breakthrough technologies, novel theoretical developments and methodologies for the analysis of data played a crucial role in advancing our understanding of how energy is transferred across the scales in the space. in recent decades, several scaling laws were obtained providing effective ways to model the energy flux in turbulent plasmas. under certain assumptions, these relations enabled to utilize reduced knowledge (in terms of degrees of freedom) of the fields from spacecraft observations to obtain direct estimates of the energy transfer rates (and not only) in the interplanetary space, also in the proximity of the sun and planets. starting from the first third-order exact law for the magnetohydrodynamics by politano and pouquet (1998), we present a detailed review of the main scaling laws for the energy transfer in plasma turbulence and their application, presenting theoretical, numerical and observational milestones of what has become one of the main approaches for the characterization of turbulent dynamics and energetics in space plasmas. | scaling laws for the energy transfer in space plasma turbulence |
we present ai poincaré, a machine learning algorithm for autodiscovering conserved quantities using trajectory data from unknown dynamical systems. we test it on five hamiltonian systems, including the gravitational three-body problem, and find that it discovers not only all exactly conserved quantities, but also periodic orbits, phase transitions, and breakdown timescales for approximate conservation laws. | machine learning conservation laws from trajectories |
we present the first kinematical detection of embedded protoplanets within a protoplanetary disk. using archival atacama large millimetre array (alma) observations of hd 163296, we demonstrate a new technique to measure the rotation curves of co isotopologue emission to sub-percent precision relative to the keplerian rotation. these rotation curves betray substantial deviations caused by local perturbations in the radial pressure gradient, likely driven by gaps carved in the gas surface density by jupiter-mass planets. comparison with hydrodynamic simulations shows excellent agreement with the gas rotation profile when the disk surface density is perturbed by two jupiter-mass planets at 83 and 137 au. as the rotation of the gas is dependent upon the pressure of the total gas component, this method provides a unique probe of the gas surface density profile without incurring significant uncertainties due to gas-to-dust ratios or local chemical abundances that plague other methods. future analyses combining both methods promise to provide the most accurate and robust measures of embedded planetary mass. furthermore, this method provides a unique opportunity to explore wide-separation planets beyond the mm continuum edge and to trace the gas pressure profile essential in modeling grain evolution in disks. | a kinematical detection of two embedded jupiter-mass planets in hd 163296 |
for the first four billion years of earth's history, climate was marked by apparent stability and warmth despite the sun having lower luminosity1. proposed mechanisms for maintaining an elevated partial pressure of carbon dioxide in the atmosphere (pco2) centre on a reduction in the weatherability of earth's crust and therefore in the efficiency of carbon dioxide removal from the atmosphere2. however, the effectiveness of these mechanisms remains debated2,3. here we use a global carbon cycle model to explore the evolution of processes that govern marine ph, a factor that regulates the partitioning of carbon between the ocean and the atmosphere. we find that elevated rates of `reverse weathering'—that is, the consumption of alkalinity and generation of acidity during marine authigenic clay formation4-7—enhanced the retention of carbon within the ocean-atmosphere system, leading to an elevated pco2 baseline. although this process is dampened by sluggish kinetics today, we propose that more prolific rates of reverse weathering would have persisted under the pervasively silica-rich conditions8,9 that dominated earth's early oceans. this distinct ocean and coupled carbon-silicon cycle state would have successfully maintained the equable and ice-free environment that characterized most of the precambrian period. further, we propose that during this time, the establishment of a strong negative feedback between marine ph and authigenic clay formation would have also enhanced climate stability by mitigating large swings in pco2—a critical component of earth's natural thermostat that would have been dominant for most of earth's history. we speculate that the late ecological rise of siliceous organisms8 and a resulting decline in silica-rich conditions dampened the reverse weathering buffer, destabilizing earth's climate system and lowering baseline pco2. | reverse weathering as a long-term stabilizer of marine ph and planetary climate |
the distribution, accumulation and circulation of oxygen and hydrogen in earth’s interior dictate the geochemical evolution of the hydrosphere, atmosphere and biosphere. the oxygen-rich atmosphere and iron-rich core represent two end-members of the oxygen-iron (o-fe) system, overlapping with the entire pressure-temperature-composition range of the planet. the extreme pressure and temperature conditions of the deep interior alter the oxidation states, spin states and phase stabilities of iron oxides, creating new stoichiometries, such as fe4o5 (ref. 5) and fe5o6 (ref. 6). such interactions between o and fe dictate earth’s formation, the separation of the core and mantle, and the evolution of the atmosphere. iron, in its multiple oxidation states, controls the oxygen fugacity and oxygen budget, with hydrogen having a key role in the reaction of fe and o (causing iron to rust in humid air). here we use first-principles calculations and experiments to identify a highly stable, pyrite-structured iron oxide (feo2) at 76 gigapascals and 1,800 kelvin that holds an excessive amount of oxygen. we show that the mineral goethite, feooh, which exists ubiquitously as ‘rust’ and is concentrated in bog iron ore, decomposes under the deep lower-mantle conditions to form feo2 and release h2. the reaction could cause accumulation of the heavy feo2-bearing patches in the deep lower mantle, upward migration of hydrogen, and separation of the oxygen and hydrogen cycles. this process provides an alternative interpretation for the origin of seismic and geochemical anomalies in the deep lower mantle, as well as a sporadic o2 source for the great oxidation event over two billion years ago that created the present oxygen-rich atmosphere. | feo2 and feooh under deep lower-mantle conditions and earth’s oxygen-hydrogen cycles |
we present here the analysis of 30 gaseous extrasolar planets, with temperatures between 600 and 2400 k and radii between 0.35 and 1.9 r jup. the quality of the hst/wfc3 spatially scanned data combined with our specialized analysis tools allow us to study the largest and most self-consistent sample of exoplanetary transmission spectra to date and examine the collective behavior of warm and hot gaseous planets rather than isolated case studies. we define a new metric, the atmospheric detectability index (adi) to evaluate the statistical significance of an atmospheric detection and find statistically significant atmospheres in around 16 planets out of the 30 analyzed. for most of the jupiters in our sample, we find the detectability of their atmospheres to be dependent on the planetary radius but not on the planetary mass. this indicates that planetary gravity plays a secondary role in the state of gaseous planetary atmospheres. we detect the presence of water vapour in all of the statistically detectable atmospheres, and we cannot rule out its presence in the atmospheres of the others. in addition, tio and/or vo signatures are detected with 4σ confidence in wasp-76 b, and they are most likely present in wasp-121 b. we find no correlation between expected signal-to-noise and atmospheric detectability for most targets. this has important implications for future large-scale surveys. | a population study of gaseous exoplanets |
robots have transformed many industries, most notably manufacturing, and have the power to deliver tremendous benefits to society, such as in search and rescue, disaster response, health care and transportation. they are also invaluable tools for scientific exploration in environments inaccessible to humans, from distant planets to deep oceans. a major obstacle to their widespread adoption in more complex environments outside factories is their fragility. whereas animals can quickly adapt to injuries, current robots cannot `think outside the box' to find a compensatory behaviour when they are damaged: they are limited to their pre-specified self-sensing abilities, can diagnose only anticipated failure modes, and require a pre-programmed contingency plan for every type of potential damage, an impracticality for complex robots. a promising approach to reducing robot fragility involves having robots learn appropriate behaviours in response to damage, but current techniques are slow even with small, constrained search spaces. here we introduce an intelligent trial-and-error algorithm that allows robots to adapt to damage in less than two minutes in large search spaces without requiring self-diagnosis or pre-specified contingency plans. before the robot is deployed, it uses a novel technique to create a detailed map of the space of high-performing behaviours. this map represents the robot's prior knowledge about what behaviours it can perform and their value. when the robot is damaged, it uses this prior knowledge to guide a trial-and-error learning algorithm that conducts intelligent experiments to rapidly discover a behaviour that compensates for the damage. experiments reveal successful adaptations for a legged robot injured in five different ways, including damaged, broken, and missing legs, and for a robotic arm with joints broken in 14 different ways. this new algorithm will enable more robust, effective, autonomous robots, and may shed light on the principles that animals use to adapt to injury. | robots that can adapt like animals |
the present paper addresses driving mechanisms of global monsoon (gm) variability and outstanding issues in gm science. this is the second synthesis of the pages gm working group following the first synthesis "the global monsoon across time scales: coherent variability of regional monsoons" published in 2014 (climate of the past, 10, 2007-2052). here we introduce the gm as a planetary scale circulation system and give a brief accounting of why it exhibits regional structure. the primary driver of the gm is solar insolation, and the specific features in the underlying surface, such as land-sea distribution, topography, and oceanic circulations, are mainly responsible for the differences among regional monsoon systems. we then analyze the monsoon formation mechanisms, together with the major processes that drive monsoon variations at various timescales, including external forcings and internal feedbacks. on long time scales, external forcings often induce variability on a global scale, whereas short-term variability in regional monsoon systems is usually caused by internal feedbacks within the climate system. finally, a number of debatable issues are discussed, with an emphasis on time scales beyond the instrumental record. these include the dual nature of the monsoon as wind and rain, the meaning of oxygen isotope in hydrological cycle, in particular of speleothem δ18o, the role of ice-sheet in monsoon variations, etc. in general, the gm as a system comprises a hierarchy of regional and local monsoons with various degrees of similarity, though all show coherent variability driven by a common solar forcing. the goal of the gm concept, therefore, is by no means to replace or diminish research on the regional monsoons, but to help dissect the mechanisms and controlling factors of monsoon variability at various temporal-spatial scales. | the global monsoon across time scales: mechanisms and outstanding issues |
the availability of thermodynamic data for geologically relevant phases has made practical the calculation of stable phase relations throughout the mantle and crust of terrestrial planets. geops (http://www.geops.org) is a program designed for this purpose in which both input and output are done through an intuitive graphical user interface. geops provides a wide range of phase equilibrium calculations based on a novel gibbs energy minimization algorithm. the algorithm provides for exceptionally robust and computationally efficient solution to the phase equilibrium problem by successive alternation between a linear programming step to identify stable phase compositions and a non-linear programming step to refine the compositions estimated during the linear programming. applications include calculation of various types of phase diagrams and path-dependent phase fractionation. by combining an easy-to-use graphical user interface with a robust and efficient solver, geops makes phase equilibrium modelling accessible to researchers and students with minimal training and provides a powerful tool for understanding natural phase relations and for planning experimental work. | geops: an interactive visual computing tool for thermodynamic modelling of phase equilibria |
taurex 3 is the next generation of the taurex exoplanet atmospheric retrieval framework for windows, mac, and linux. it is a complete rewrite with a full python stack that makes it easy-to-use, high-performance, dynamic, and flexible. the new main taurex program is built with modularity in mind, allowing the user to augment its functionalities with custom code and efficiently perform retrievals on custom parameters. we achieve this result by dynamic determination of fitting parameters, whereby taurex 3 can detect new parameters for retrieval from user code through a simple interface. taurex 3 can act as a library with a simple import taurex command, providing a rich set of classes and functions related to atmospheric modeling. a 10× speedup in forward model computations is achieved as compared to the previous version with a sixfold reduction in retrieval times while maintaining robust results. taurex 3 is intended as a standalone, all-in-one package for retrievals while the taurex 3 python library can build or augment a user's custom data pipeline easily. | taurex 3: a fast, dynamic, and extendable framework for retrievals |
human activities have greatly perturbed the global nitrogen cycle. planetary boundaries, which describe a safe operating space for humanity, have already been exceeded for the nitrogen cycle (1). in some parts of the world, excess nitrogen has negative impacts on biological diversity, human health, and climate. however, in other parts of the world, nitrogen shortages mean that food needs cannot be met. this large-scale disturbance of the nitrogen cycle presents considerable challenges that require wide-scale adoption of locally appropriate nitrogen management approaches. | nitrogen in the environment |
mediterranean-type climates are defined by temperate, wet winters, and hot or warm dry summers and exist at the western edges of five continents in locations determined by the geography of winter storm tracks and summer subtropical anticyclones. the climatology, variability, and long-term changes in winter precipitation in mediterranean-type climates, and the mechanisms for model-projected near-term future change, are analyzed. despite commonalities in terms of location in the context of planetary-scale dynamics, the causes of variability are distinct across the regions. internal atmospheric variability is the dominant source of winter precipitation variability in all mediterranean-type climate regions, but only in the mediterranean is this clearly related to annular mode variability. ocean forcing of variability is a notable influence only for california and chile. as a consequence, potential predictability of winter precipitation variability in the regions is low. in all regions, the trend in winter precipitation since 1901 is similar to that which arises as a response to changes in external forcing in the models participating in phase 5 of the coupled model intercomparison project. all mediterranean-type climate regions, except in north america, have dried and the models project further drying over coming decades. in the northern hemisphere, dynamical processes are responsible: development of a winter ridge over the mediterranean that suppresses precipitation and of a trough west of the north american west coast that shifts the pacific storm track equatorward. in the southern hemisphere, mixed dynamic-thermodynamic changes are important that place a minimum in vertically integrated water vapor change at the coast and enhance zonal dry advection into mediterranean-type climate regions inland. | climate variability and change of mediterranean-type climates |
this paper presents the background, scientific objectives, experimental design, and preliminary achievements of the third tibetan plateau (tp) atmospheric scientific experiment (tipex-iii) for 8-10 years. it began in 2013 and has expanded plateau-scale observation networks by adding observation stations in data-scarce areas; executed integrated observation missions for the land surface, planetary boundary layer, cloud-precipitation, and troposphere-stratosphere exchange processes by coordinating ground-based, air-based, and satellite facilities; and achieved noticeable progress in data applications. a new estimation gives a smaller bulk transfer coefficient of surface sensible heat over the tp, which results in a reduction of the possibly overestimated heat intensity found in previous studies. summer cloud-precipitation microphysical characteristics and cloud radiative effects over the tp are distinguished from those over the downstream plains. warm rain processes play important roles in the development of cloud and precipitation over the tp. the lower-tropospheric ozone maximum over the northeastern tp is attributed to the regional photochemistry and long-range ozone transports, and the heterogeneous chemical processes of depleting ozone near the tropopause might not be a dominant mechanism for the summer upper-tropospheric-lower-stratospheric ozone valley over the southeastern tp. the tp thermodynamic function not only affects the local atmospheric water maintenance and the downstream precipitation and haze events but also modifies extratropical atmospheric teleconnections like the asia-pacific oscillation, subtropical anticyclones over the north pacific and atlantic, and temperature and precipitation over africa, asia, and north america. these findings provide new insights into understanding land-atmosphere coupled processes over the tp and their effects, improving model parameterization schemes, and enhancing weather and climate forecast skills. | the third atmospheric scientific experiment for understanding the earth-atmosphere coupled system over the tibetan plateau and its effects |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.