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we evaluate the performance of the latest version of international reference ionosphere (iri-2016) by comparing the estimated total electron content (tec) with the observed values from four geodetic global positioning system (gps) receivers, latitudinally aligned from the equator to low latitudes (-5° to 20° geomagneti... | evaluation of long-term variability of ionospheric total electron content from iri-2016 model over the indian sub-continent with a latitudinal chain of dual-frequency geodetic gps observations during 2002 to 2019 |
the k index is one of the oldest universal indices of geomagnetic activity, introduced in 1938 by julius bartels, that is still being widely used. up to the present day, long-term time series of homogeneous k index records have been accumulated at data repositories all over the world. the multidecadal practice of its a... | historical k index data collection of soviet magnetic observatories, 1957-1992 |
the sun is variable in activity with changes on time-scales as short as minutes to as long as a solar cycle. although the most accurate measurements are limited to the satellite era, the past four decades, looking at the solar variability over this period provides a possible link between complex dynamics of the sun and... | solar x-ray variability in terms of a fractional heteroskedastic time series model |
based on the omni database, the influence of the solar activity decrease in solar cycles (scs) 23–24 on the behavior of the relative helium ions abundance nα/np inside interplanetary coronal mass ejections (icmes) is investigated. the dependences of the helium abundance on the plasma and interplanetary magnetic field p... | helium abundance decrease in icmes in 23–24 solar cycles |
the origin of nonradial solar wind flows and their effect on space weather are poorly understood. here we present a detailed investigation of 12 nonradial solar wind events during solar cycles 23-24, covering the period 1995-2017. in all these events the azimuthal flow angles of the solar wind exceed 6° as measured at ... | the origin of extremely nonradial solar wind outflows |
we present a statistical study of electromagnetic ion cyclotron (emic) waves observed at antarctic station (geographic 70.7°s, 11.8°e, l =5 ) on quiet and disturbed days during 2011-2017. the data span a fairly good period of both ascending and descending phases of the solar cycle 24, which has witnessed extremely low ... | occurrence characteristics of electromagnetic ion cyclotron waves at sub-auroral antarctic station maitri during solar cycle 24 |
this paper reports the statistical analysis of zonal drift velocity of equatorial plasma bubbles (epbs) inferred from advanced optical technique (all-sky imager) with oi 630.0-nm airglow emission from january to april of 2011 to 2013. over 143 nights of observations have been carried out using all-sky imager over low-l... | zonal drift velocity of equatorial plasma bubbles during ascending phase of 24th solar cycle using all-sky imager over kolhapur, india |
the solar magnetic activity cycle provides energy input that is released in intense bursts of radiation known as solar flares. as such, the dynamics of the activity cycle is embedded in the sequence of times between the flare events. recent analysis shows that solar flares exhibit memory on different timescales. these ... | clustering behavior in solar flare dynamics |
from observations of the solar white-light corona at 65 eclipses from 1851 to 2015 we confirm earlier findings that the flattening index of the white-light corona depends on the phase, rather than the magnitude of solar cycles, which is in contrast with behavior of other major solar activity indices like the sunspot nu... | the flattening index of the eclipse white-light corona and magnetic fields |
we examine the density structure of equatorial depletions referred to here as equatorial plasma bubbles (epbs). data recorded by the ion velocity meter as part of the coupled ion neutral dynamics investigation (cindi) aboard the communication/navigation outage forecasting system (c/nofs) satellite are used to study epb... | the plasma environment associated with equatorial ionospheric irregularities |
coronal holes (chs) play a significant role in making the earth geo-magnetically active during the declining and minimum phases of the solar cycle. in this study, we analysed the evolutionary characteristics of the recurring chs from the year 1992 to 2016. the extended minimum of solar cycle 23 shows unusual characteri... | recurring coronal holes and their rotation rates during the solar cycles 22-24 |
solar flares observed during the 24th solar-activity cycle and accompanied by fluxes of particles detected at the earth's orbit with intensities exceeding 10 particles cm-2 s-1 and energies of more than 10 mev per particle mainly occurred in activity complexes (82% of cases), with 80% of these occurring no more than 20... | proton flares in solar activity complexes: possible origins and consequences |
it is widely accepted that astrophysical magnetic fields are generated by dynamo action. in many cases, these fields exhibit organisation on a scale larger than that of the underlying turbulent flow (e.g. the 11-year solar cycle). the mechanism for the generation of so-called large-scale fields remains an open problem.... | convection-driven kinematic dynamos with a self-consistent shear flow |
aims: we estimate the injection of relative magnetic helicity into the solar atmosphere by surface flux transport over 27 solar cycles (1700-2009).methods: we determine the radial magnetic field evolution using two separate surface flux transport models: one driven by magnetogram inputs and another by statistical activ... | hemispheric injection of magnetic helicity by surface flux transport |
we consider a perfect electrically conducting rotating fluid in the presence of an ambient toroidal magnetic field, governed by the shallow water magnetohydrodynamic (mhd) equations in a modified equatorial beta plane approximation. using a multiple scale asymptotic technique, previously developed by boyd (1980) for eq... | solitary waves in shallow water magnetohydrodynamics |
since venus has no substantial planetary magnetic field, the fast-flowing solar wind plasma interacts directly with its ionosphere, upper atmosphere, and corona. the thermal atmosphere and hot oxygen corona of venus are expected to play essential roles in the interaction process. to quantify their effects, we combine t... | the effects of the upper atmosphere and corona on the solar wind interaction with venus |
we have being studying the zonal and vertical e region electric field components inferred from the doppler shifts of type 2 echoes (gradient drift irregularities) detected with the 50 mhz backscatter coherent radar set at são luis, brazil (slz, 2.3°s, 44.2°w) during the solar cycle 24. in this report we present the dep... | e region electric field dependence of the solar activity |
a model capable of reproducing a set of solar wind parameters along the virtual spacecraft orbit out of an ecliptic plane has been developed. in the framework of a quasi-stationary axisymmetric self-consistent mhd model the spatial distributions of magnetic field and plasma characteristics at distances from 20 to 1200 ... | ulysses flyby in the heliosphere: comparison of the solar wind model with observational data |
we apply the kuramoto model with four coupled oscillators to the description of the phase evolution of solar magnetic field proxies at different latitudes. we show that a ring of four coupled oscillators does represent the frequency synchronization of the meridional circulation and the phase evolution of solar proxies.... | north-south asymmetry of solar meridional circulation and synchronization: two rings of four coupled oscillators |
in this paper, we study solar magnetic activity by means of a complex network approach. a complex network was built based on information on the space and time evolution of sunspots provided by image recognition algorithms on solar magnetograms taken during the complete 23rd solar cycle. both directed and undirected net... | complex network study of solar magnetograms |
reconstructions of past solar activity based on cosmogenic radioisotopes have reavealed that the sun spends a significant fraction (≈20 %) of its time in aperiodically recurring states of so-called grand minima or grand maxima, namely epochs of strongly supressed and markedly above-average levels of magnetic activity, ... | grand activity minima and maxima via dual dynamos |
near-earth solar winds are separated into two groups: slow solar wind (ssw) with plasma speed [vsw] <500 km s−1 and high-speed solar wind (hsw) with vsw>700 km s−1. a comparative study is performed on the plasma and interplanetary magnetic field (imf) properties of the near-earth ssw and hsw, using solar wind mea... | near-earth high-speed and slow solar winds: a statistical study on their characteristics and geomagnetic impacts |
all sky imager (asi) data of over 351 nights with oi 630.0 nm emission recorded during 2011 to 2015 (increasing phase of 24th solar cycle) are analyzed to study the percentage occurrence of epbs. the asi is installed at low latitude station kolhapur (16.8 °n, 74.2 °e, 10.6° dip. lat.) which has 140° field of view (fov)... | variation in occurrence of equatorial plasma bubbles (epbs) using all sky imager from low latitude station kolhapur (16.8 °n, 74.2 °e, 10.6° dip. lat.) |
a spectral radiometer located at the south pole has obtained a long-term record of ground-level solar irradiance at wavelengths from 315 to 600 nm. data acquired during the sunlit periods from 1992 to 2016 provide information on the scattering properties of the atmosphere and their variation covering more than two sola... | an analysis of couplings between solar activity and atmospheric opacity at the south pole |
using the hilbert-huang transform and the lomb-scargle method, we investigate periodicities in the daily solar radius data during the time interval from february 1978 to october 1999 derived from calern observatory. the following prominent periods are found: (1) the rotation cycle signal; (2) several mid-term periods i... | periodicity of the solar radius revisited by using empirical mode decomposition and the lomb-scargle method |
in this paper we use wavelets and lomb-scargle spectral analysis techniques to investigate the changing pattern of the different harmonics of the 27-day solar rotation period of the ae (auroral electrojet) index during various phases of different solar cycles between 1960 and 2014. previous investigations have revealed... | spectral analysis of auroral geomagnetic activity during various solar cycles between 1960 and 2014 |
we statistically investigate the solar cycle dependence of the magnetic field fluctuations in the frequency range 30-300 mhz based on venus express data. we present the spatial distributions of fluctuation properties during three typical periods of the solar cycle, and a comparative study is also performed. with the in... | statistical study of low-frequency magnetic field fluctuations near venus during the solar cycle |
the magnetic plage strength index (mpsi) and themountwilson sunspot index (mwsi), which have been measured at mount wilson observatory (mwo) since the 1970s and which indicate weak and strong magnetic field activity on the solar full disk, respectively, are used to systematically investigate midterm periodicities in th... | systematic investigation of mid-term periodicity of the solar full-disk magnetic fields |
in the present work, we evaluate the accuracy of the solar quiet reference field (sqrf) model for estimating and predicting the geomagnetic solar quiet (sq) daily field variation in the south america magnetic anomaly (sama) region. this model is based on the data set of fluxgate magnetometers from 12 magnetic stations ... | evaluation of the solar quiet reference field (sqrf) model for space weather applications in the south america magnetic anomaly |
in this paper, 106 active regions (ars) in the visible solar hemisphere in solar cycle 24 whose maximum sunspot groups' areas were larger than 400 µh were selected. the association of their flare index (iflare), largest flare magnitude (mflare), and fastest coronal mass ejection (cme) velocity (vcme) with the vector ma... | on the possibility of predicting flare index and cme velocity using vector magnetograms |
vhf and gps-scinda receivers located both at nairobi (36.8°e, 1.3°s) in kenya and at kampala (32.57°e, 0.335°n) in uganda were used to investigate ionospheric scintillation and forecast scintillations of a few hundred meter-scale irregularities associated with equatorial ionospheric irregularities for the period 2011 a... | prediction of ionospheric scintillation using neural network over east african region during ascending phase of sunspot cycle 24 |
we study the solar-cycle variation of the divergence and vorticity of subsurface horizontal flows from the surface to a depth of 16 mm. the flows were derived with ring-diagram analysis applied to michelson doppler imager (mdi) dynamics program, global oscillation network group (gong), and helioseismic and magnetic ima... | divergence and vorticity of subsurface flows during solar cycles 23 and 24 |
the solar eruptive events and their origin are important in the context of forecasting their occurrence and their effects on the space and the earth. in this paper, a set of 45 x-class flare-associated coronal mass ejections (cmes) and their source region characteristics are analysed. the x-ray flares and white light c... | active region and flare ribbon properties associated with x-class flares and cmes of solar cycle 24 |
interplanetary magnetic field (imf) magnitude, plasma and solar parameters recorded at 1 au over a period of 50 years have been studied according to imf polarity sense. our results indicated that there is a symmetric in toward and away days which may depend slightly upon the magnetic state of the heliosphere. statistic... | the occurrence of non-uniformity of solar and plasma features throughout five solar cycles |
comparing with solar cycles 21-23, the level of solar activity in the current cycle is very low. so far, there have been only five sars and 45 x class flares. the monthly smoothed total solar irradiance decreased sharply by 0.09% from the maximum of cycle 23 to the minima between cycles 23 and 24. in this contribution,... | super-active regions in solar cycle 24 |
the distribution of mass density along the field lines affects the ratios of toroidal (azimuthally oscillating) alfvén frequencies, and given the ratios of these frequencies, we can get information about that distribution. here we assume the commonly used power law form for the field line distribution, ρm = ρm,eq(lre/r... | field line distribution of mass density at geostationary orbit |
solar cycle 25 began in 2019 december and has been progressing nominally since. however, a closely associated pair of strong active regions, noaa 12786 and 12785, emerged in 2020 november. the greater, northern component, 12786, attained a maximum sunspot area of 1000 μhemi. the sudden, uncharacteristic emergence of su... | what is exceptional about solar activity in the early phase of cycle 25? |
the prediction of an extended solar minimum is extremely important because of the severity of its impact on the near-earth space. here, we present a new method for predicting the descent time of the forthcoming solar cycle (sc); the method is based on the estimation of the shannon entropy. we use the daily and monthly ... | a new method for forecasting the solar cycle descent time |
aims: we aim to characterise the solar cycle progression simultaneously at different latitudes in each solar hemisphere using solar magnetic field data provided by the wilcox solar observatory (wso). we also investigate whether the features observed in the wso data are best explained by the babcock-leighton (bl) mechan... | hemispheric progression of solar cycles in solar magnetic field data and its relation to the solar dynamo models |
quite often powerful flares occur during a decrease of solar activity. in this work, we make an attempt to consider x-class flares at the minima of solar activity cycles as a separate group of events. out of nine x-class flares we selected three such events that occurred at the minima of solar cycles 22-24: sol1996-07-... | energetics of x-class flares at the minima of 22, 23, and 24 solar cycles |
a solar rotational period of approximately 27 days has been detected in cloud and lightning activities, although the mechanism of the sun-climate connection remains unclear. in previous studies, lightning activity in japan showed a significant signal of the solar rotational period, especially around the maxima of the d... | searching for the 27-day solar rotational cycle in lightning events recorded in old diaries in kyoto from the 17th to 18th century |
since the field-line mixing model of giacalone et al. suggests that ion dropouts cannot happen in the “gradual” solar energetic particle (sep) event because of the large size of the particle source region in the event, the observational evidence of ion dropouts in the gradual sep event should challenge the model. we ha... | electron-ion intensity dropouts in gradual solar energetic particle events during solar cycle 23 |
the point of view is substantiated that during periods of low sunspot activity many heliospheric characteristics (the solar wind velocity, the form of the heliospheric current sheet, the strength of the heliospheric magnetic field) can be considered as the manifestations in the heliosphere of the poloidal branch of sol... | on contribution of poloidal branch of solar activity to heliosphere and gcr modulation |
modelling with high accuracy the open magnetic field and the fast solar wind in the heliosphere is essential for space weather forecasting purposes. primary sources of open magnetic field flux are coronal holes (ch), uni-polar regions that appear as dark patches in the solar corona when observed in x-ray and extreme-ul... | the impact of coronal hole characteristics and solar cycle activity in reconstructing coronal holes with euhforia |
this paper deals with extreme conditions of the global magnetosphere disturbance: very quiet and greatly disturbed, and their relationship with interplanetary medium parameters. the degree of global magnetosphere disturbance was estimated from the monthly and annual number of magnetically quiet and magnetically disturb... | global disturbance of earth's magnetosphere and its connection with space weather |
to explain the observed phenomenon of 11-year sunspot cycle with two peaks, we draw attention to the possible role of the turbulent magnetic pumping effects in the solar convection zone (scz) at the reconstructing of the toroidal magnetic field that generates the sunspots. turbulent radial pumping of magnetic field has... | role of rotational radial magnetic advection in possible explaining a cycle with two peaks |
the sun's magnetic field exhibits coherence in space and time on much larger scales than the turbulent convection that ultimately powers the dynamo. in the past the α-effect (mean-field) concept has been used to model the solar cycle, but recent work has cast doubt on the validity of the mean-field ansatz under solar c... | destruction of large-scale magnetic field in non-linear simulations of the shear dynamo |
understanding the transport and deposition of the cosmogenic isotope10be is vital for the application of the isotope data to infer past changes of solar activity, to reconstruct past earth's magnetic field intensity and climate change. here, we use data of the cosmogenic isotope10be from the greenland ice cores, namely... | the influence of orbital forcing on 10be deposition in greenland over the glacial period |
synoptic telescopes are fundamental tools in solar physics. they are tipically used for high cadence full-disk observations of the sun at different wavelengths, in order to study the solar activity across the solar cycle. the tsst (tor vergata synoptic solar telescope) is a new synoptic telescope composed of a ha filte... | tor vergata synoptic solar telescope: preliminary optical design and spectral characterization |
the correlation scale and taylor scale, which characterize the turbulence and dissipation levels, of the solar wind upstream of mars are determined using the mars atmosphere and volatile evolution magnetic field data from 2015 to 2020, which covers half of a solar cycle from the solar maximum to the solar minimum. our ... | the variation of the solar wind correlation scale and taylor scale upstream of mars observed by maven |
it is generally believed that solar activities are closely linked with magnetic fields on the solar surface. to learn more about how solar flares are produced in relation to solar magnetic configurations, we examined a total of 37,741 soft-x ray solar flare events observed by a series of goes satellites. the flare and ... | investigating the associations between solar flares and magnetic complexity of active regions |
the photospheric magnetic field is the source of the coronal and heliospheric magnetic fields (hmf), but their mutual correspondence is non-trivial and depends on the phase of the solar cycle. the photospheric field during the hmf sector crossings observed at 1 au has been found to contain enhanced field intensities an... | structure of the photospheric magnetic field during sector crossings of the heliospheric magnetic field |
we investigate long-term variation of the very slow solar wind (vssw), whose speed is less than 350 km/s, during the period between 1997 and 2015, that is, cycles 23 and 24, using interplanetary scintillation measurements, which enable determination of the global distribution of the flow speed and the electron density ... | rarefaction of the very slow (<350 km/s) solar wind in cycle 24 compared with cycle 23 |
a sporadic e layer with dense ionization blocks the upper ionospheric layers in ionosonde observations and it is called, blanketing sporadic e (esb). although earlier studies have demonstrated that esb occurrence is dependent on solar activity, seasons, local time, and equatorial electrojet/counter equatorial electroje... | quiet and disturbed time characteristics of blanketing es (esb) during solar cycle 23 |
we have examined the ne/o and fe/o characteristics of large solar energetic particle (sep) events at the ion energy range of 3-40 mev nucleon-1 during solar cycles 23 and 24. in each cycle, the solar activity displays an ~3 yr rising phase and a longer declining phase. while fe-poor events only appeared in the declinin... | ne/o and fe/o characteristics of large solar energetic particle events during solar cycles 23 and 24 |
solar oblateness is a fundamental parameter of the sun, which provides indirect information on the inner rotation profile and on the distribution of matter. it also puts constraints on general relativity. but this quantity is difficult to measure due to its very small value where the solar equator-to-pole radius differ... | on hmi solar oblateness during solar cycle 24 and impact of the space environment on results |
waiting time distributions (wtds) of solar flares are investigated all through the solar cycle. the same approach applied to coronal mass ejections (cmes) in a previous work is considered here for flare occurrence. our analysis reveals that flares and cmes share some common statistical properties, which result dependen... | statistical properties of solar flares and coronal mass ejections through the solar cycle |
correlations between solar, interplanetary-medium parameters, and geomagnetic-activity proxies in 27-day averages (a bartels rotation) were analyzed for the 2009 - 2016 time interval. in this analysis, two new proxies were considered: i) bz s gsm (geocentric solar magnetic), calculated as the daily percentage of the im... | relating 27-day averages of solar, interplanetary medium parameters, and geomagnetic activity proxies in solar cycle 24 |
recent solar cycles (scs) 21-24 have experienced a gradual decrease in their activity with considerable weakening during current sc 24. this is a unique opportunity to examine the long-term response of earth's low-latitude ring-current and high latitude auroral electrojet current systems during such systematically decr... | characteristics of probability distribution functions of low- and high-latitude current systems during solar cycle 24 |
one of the most important input fields for an ionospheric model is the horizontal neutral wind. the primary mechanism by which the neutral wind affects ionospheric densities is the inducement of an upward or downward ion drift along the magnetic field lines; this affects the rate at which ions are lost through recombin... | how uncertainty in the neutral wind limits the accuracy of ionospheric modeling and forecasting |
methods of localizing coronal sources of the solar wind (sw), such as coronal holes, quasi-stationary fluxes from active regions, and transient sources associated with small-scale active phenomena are considered based on vacuum-ultraviolet (euv) images of the corona at low solar activity during the initial period of th... | identification of coronal sources of the solar wind from solar images in the euv spectral range |
historical solar irradiance is a critical input to climate models. as no direct measurements are available before 1978, reconstructions of past irradiance changes are employed instead. such reconstructions are based on the knowledge that solar irradiance on time scales of interest to climate studies is modulated by the... | accounting for small bipolar magnetic regions in solar irradiance reconstructions |
an mhd shell model is used to describe the dissipative events that take place in magnetized plasmas. we analyze the activity of the time series of the magnetic energy dissipation rate obtained in the mhd shell model, which evolves under two forcing regimes: quiet and active states. to this purpose, we use solar wind da... | study of the fractality of magnetized plasma using an mhd shell model driven by solar wind data |
we investigate the nature of monthly sunspot numbers and solar flux f10.7 by employing the linear and multiple regression techniques. we observed a brilliant correlation between monthly mean sunspot number and f10.7. we observed that even in deep solar minimum there exist some magnetic activities. we obtained the coeff... | the solar flux and sunspot number; a long-trend analysis |
this paper investigates the dependence of the occurrence frequency of ionospheric upflowing oxygen (o+) ions on the sunspot cycle and geomagnetic activity. we examine the upflows response to the geomagnetic disturbances as well as the influence of the ion energy factor in controlling the magnitude of the occurrence fre... | geomagnetic and solar activity dependence of ionospheric upflowing o+: fast observations |
we investigate the sizes of 86 non-flaring solar active regions with respect to the brightness temperature at 8 mm and active region magnetic field strength. the data were collected in aprilűseptember, 2014, and aprilűjuly, 2015 at aalto university, metsähovi radio observatory with the 14-m radio telescope. the observa... | sizes of solar active regions at 8 mm |
a new reconstruction of the number of sunspots (sn) in 1000-1700, along with possible errors, has been obtained based on an analysis of auroral observations at middle and low latitudes and data on the earth's magnetic field at that time. the intensity and configuration of the main magnetic field of the earth affect the... | reconstruction of the solar activity in 1000-1700 based on auroral data with allowance for the contribution of the main magnetic field of the earth |
context. during solar minima the spatial power spectrum of the photospheric magnetic field is dominated by the low-degree zonal (axisymmetric; m = 0) harmonic components, reflecting the large polar coronal holes of unipolar magnetic field. however, measuring polar fields is difficult because of the unequal visibility o... | spatial power spectrum of the photospheric magnetic field during solar minimum |
we provide a long epoch study of a set of solar and plasma parameters (sunspot number rz, total solar irradiance tsi, solar radio flux sf, solar wind speed v, ion density n, dynamic pressure nv 2, and ion temperature t) covering a temporal range of several decades corresponding to almost four solar cycles. such data ha... | a study of north-south asymmetry of interplanetary magnetic field plasma and some solar indices throughout four solar cycles |
the energy dispersion of magnetic rossby waves has been investigated by applying the two-dimensional incompressible magnetohydrodynamic (mhd) equations in both uniform basic flow and basic magnetic field. the dispersion relation suggests that the magnetic rossby waves can be divided into fast- and slow-propagating mode... | on the energy dispersion of magnetic rossby waves |
this study aims at investigating surface magnetic flux participation among different types of magnetic features during solar cycle 24. state-of-the-art observations from sdo/hmi and hinode/sot are combined to form a unique database in the interval from april 2010 to october 2015. unlike previous studies, the statistics... | magnetic flux participation in solar surface magnetism during solar cycle 24 |
sunspot pairs develop in connection with cell networks at or near the boundaries of positive and negative unipolar magnetic (um) field regions. in this paper, we confirm his findings by recent data. in this connection, svalgaard and wilcox (1976) found also that solar activities occur only at one side of um boundaries,... | single spots, unipolar magnetic regions, and pairs of spots: 2. the development of sunspot pairs and the hale boundary |
flares and coronal mass ejections should follow a pattern of build-up and release, with the build-up phase understood as the gradual addition of stress to the coronal magnetic field. recently hudson (mon. not. roy. astron. soc.491, 4435, 2020) presented observational evidence for this pattern in two isolated active reg... | solar flare build-up and release |
we present composite white-light images of the 2019 july 2, total solar eclipse, from the minimum of the solar-activity cycle. we exhibit high-resolution high dynamic range composites from three observation sites in chile, including one made of 646 individual ground-based images and with such a wide field it exceeds th... | compositing eclipse images from the ground and from space |
magnetic flux rope (mfr) is closely connected with solar eruptions, such as flares and coronal mass ejections. the classical scenario assumes a single mfr for each eruption, but it is reasonable to expect multiple mfrs in a complex active region (ar). statistically investigating ar 11897, we verify the existence of mul... | multi-flux-rope system in solar active regions |
the heating of the chromosphere is a long-lived puzzle in modern astronomy. solar synoptic maps of he i 10830 å intensity, which are observed at national solar observatory/kitt peak from jul. 2005 to mar. 2013 are utilized to investigate the phase relation of long-term evolution of the quiet chromosphere represented by... | phase relation of the quiet chromosphere in the he i line with the solar cycle |
ground-based observations of the solar wind using interplanetary scintillation (ips) have been regularly performed since 1980s at the solar-terrestrial environment laboratory of nagoya university using the 327-mhz multi-station system. it has been revealed from the ips observations that the global distribution of the s... | global distribution of the solar wind and its evolution during cycles 22-24 |
the unusual low solar wind density and weak magnetic field observed at the near-earth orbit during the 2007-2009 solar minimum years has been an actively studied subject. our previous numerical simulation suggested that an inflation of the heliosphere current/plasma sheet (hcs/hps) could be the cause of the density and... | heliospheric plasma sheet inflation as a cause of solar wind anomaly during the solar cycle 23-24 minimum |
we have studied the effect of the β solar wind parameter (equal to the ratio of the plasma pressure to the magnetic pressure) on statistical characteristics of the ap index reflecting the triggering behavior of the activity of earth's magnetosphere. the trigger effect of the dynamics of magnetospheric activity consists... | influence of the ß solar wind parameter on statistical characteristics of the ap index in the solar activity cycle |
sunspot numbers and sunspot areas are the most fundamental indices of long-term solar activity levels and the solar magnetic dynamo. this paper presents a deep-learning method for segmenting the components of sunspots in the purple mountain astronomical observatory (pmo) historical hand drawings spanning from 1954 to 2... | sunspots extraction in pmo sunspot drawings based on deep learning |
rapid magnetic fluctuations are known to be closely linked to the high-latitude geomagnetic activity, in particular, to geomagnetic pulsations and subtorms. increasing amount of commercial activity in the arctic regions requires better monitoring capability and improved understanding on the effects of geomagnetic hazar... | high-frequency geomagnetic fluctuations at auroral oval and polar cap |
we present an analysis of observations of the indices of the sunspot numbers (ssn from the national oceanic and atmospheric administration (noaa)), the radio-emission flux at a wavelength of 10.7 cm ( f 10.7), and the total solar irradiance (tsi) in cycles 22-24. we have found that the ratio of the observed values ssno... | general trends in the change in solar activity indices in the period from the late xx to early xxi century |
in 2008, international center for space weather science and education, kyushu university (icswse) proposed the ee-index, which is an index to monitor the equatorial geomagnetic phenomena. ee-index has been improved with the development of the magnetic data acquisition system and the circum-pan pacific magnetometer netw... | long-term eej variations by using the improved ee-index |
the large-scale configuration of the uv solar corona at the minimum activity between solar cycles 22 and 23 is explored in this paper. exploiting a large sample of spectroscopic observations acquired by the ultraviolet coronagraph spectrometer aboard the solar and heliospheric observatory in the two-year period of 1996... | the dipolar solar minimum corona |
we study solar wind anomalies and their associations with solar wind structures using the stereo solar wind and suprathermal electron (ste) data from impact and plastic. we define solar wind anomalies as temporary and local excursions from the average solar wind state, regardless of their origins, for six anomalies: su... | solar wind anomalies at 1 au and their associations with large-scale structures |
ingredients of the total unsigned flux from all active regions (ars) on the solar disc during cycle 24 (july 2010 to december 2017) were explored using line-of-sight magne- tograms acquired by the helioseismic and magnetic imager (hmi) onboard the solar dynamics observatory (sdo). we classified ars into three categorie... | time variations of the total unsigned magnetic flux of active regions during the solar cycle 24 |
various approaches to forecasting the solar cycle based on solar dynamo models are considered. the importance of separating predictions of catastrophic events such as the maunder minimum, predictions of general trends in solar activity between grand minima, and forecasts of the next cycle, based on current knowledge of... | dynamo theory and perspectives of forecasting solar cycles |
we explore the evolution of solar activity for next several sunspot cycles beyond 2016 using data for the geomagnetic indices aa/ap and the solar polar magnetic field intensity for shorter time intervals; the indices are related to the solar wind and do not depend on earth's climate. we find that the baseline of the ge... | evolution of sunspot number timeline for next several cycles beyond 2016 |
the temporal and spatial variations of solar magnetic activity indices in the various atmospheric layers are important for understanding and revealing the dynamic processes of magnetic field of the sun. in this paper, the midrange periodicities (located at 50-500 days) of the solar hα flare index during solar cycles 21... | the midrange periodicities of solar hα flare index during solar cycles 21-24 |
throat aurora is believed to be associated with magnetopause indentations and has direct implications on magnetopause reconnection. in this study, for the first time, we use defense meteorological satellite program/special sensor ultraviolet spectrographic imager observations over ∼14 years to characterize the throat a... | statistical analysis of throat aurora using long term dmsp/ssusi observation |
in this paper initiative has been taken to search the periodicities of linear speed of coronal mass ejection in solar cycle 23. double exponential smoothing and discrete wavelet transform are being used for detrending and filtering of the cme linear speed time series. to choose the appropriate statistical methodology f... | stationarity and periodicities of linear speed of coronal mass ejection: a statistical signal processing approach |
strong solar radio brightenings have been extensively studied in the past, and their correlation to the sunspots and active regions are already well known. but even when the sun is ostensibly quiet, there is practically always some activity that can be detected in the radio domain. in this article we investigate these ... | identifying 8 mm radio brightenings during the solar activity minimum |
the date compensated discrete fourier transform and cleanest algorithm are used to study the temporal variations of the solar radius observed at rio de janeiro observatory from 1998 march 2 to 2009 november 6. the cleanest spectra show several significant periodicities around 400, 312, 93.5, 86.2, 79.4, 70.9, 53.2, and... | on the variation of solar radius in rotation cycles |
the monitoring program of long-term variation of selected fraunhofer lines is described. the aim of the program is to study how the physical parameters of the quiet solar atmosphere change over the solar cycle no. 24. the research is based on high spectral resolution observations of the quiet sun using the horizontal s... | kyiv monitoring program of fraunhofer lines variation with 11-year cycle of solar activity |
the potential to diagnose the beginning of the solar cycle based on the detection of small-scale magnetic formations, the magnetic nodes of ephemeral active regions in the zone of mid-heliolatitudes from 40° to 60°, has been studied. magnetic nodes were detected at the stage of their emergence by the multifractal segme... | possibility of diagnostics of the beginning of solar cycle 25 based on its precursors at mid-heliolatitudes |
evidence from 40 years of magnetic field measurements, 110 years of polar faculae counts, and 150 years of geomagnetic field measurements, strongly indicates that the strength of the magnetic field at the sun's poles near the time of a sunspot cycle minimum determines the strength of the following solar activity cycle.... | predicting the amplitude and hemispheric asymmetry of solar cycle 25 with surface flux transport |
the development of the solar magnetic activity in cycle 24 has been analyzed. it has been shown that the significant north-south asymmetry of magnetic activity was accompanied by the asynchronous reorganization of solar magnetic fields in the northern and southern hemispheres. the formation of unipolar magnetic regions... | restructuring of the solar magnetic fields and flare activity centers in cycle 24 |
due to the dynamo mechanism of the sun, the magnetic activity of its atmosphere presents a periodic cycle about 11 years long. the last three solar cycles have shown a systematic decrease of activity, with the last minimum (2008/2009) being considerably more quiet than the previous one (1996), as well as magnetically w... | comparative analysis of solar minima with euv tomography |
coronal holes (chs) are regions in the solar corona characterized by plasma density lower than in the surrounding quiet sun. therefore they appear dark in images of the solar atmosphere made, e.g., in extreme ultraviolet (euv). identifying chs on solar images is difficult since ch boundaries are not sharp, but typicall... | a uniform series of low-latitude coronal holes in 1973-2018 |
under this study we considered active region 09415 of the 23-rd cycle of solar activity which was observed with the 2d spatial resolution at three frequencies: 17 and 34 ghz with the nobeyama radioheliograph (norh) and 17 ghz with the solar siberian radiotelescope (ssrt). we detected rapid development of a compact micr... | evolution of the compact microwave inter-sunspot source before strong flare |
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