Theoretical analysis has demonstrated that the dispersion relation of chorus waves plays an essential role in the resonant interaction and energy transformation between the waves and magnetospheric electrons.Previous ...Theoretical analysis has demonstrated that the dispersion relation of chorus waves plays an essential role in the resonant interaction and energy transformation between the waves and magnetospheric electrons.Previous quantitative analyses often simplified the chorus dispersion relation by using the cold plasma assumption.However,the applicability of the cold plasma assumption is doubtful,especially during geomagnetic disturbances.We here present a systematic statistical analysis on the validity of the cold plasma dispersion relation of chorus waves based on observations from the Van Allen Probes over the period from 2012 to 2018.The statistical results show that the observed magnetic field intensities deviate substantially from those calculated from the cold plasma dispersion relation and that they become more pronounced with an increase in geomagnetic activity or a decrease in background plasma density.The region with large deviations is mainly concentrated in the nightside and expands in both the radial and azimuthal directions as the geomagnetic activity increases or the background plasma density decreases.In addition,the bounce-averaged electron scattering rates are computed by using the observed and cold plasma dispersion relation of chorus waves.Compared with usage of the cold plasma dispersion relation,usage of the observed dispersion relation considerably lowers the minimum resonant energy of electrons and lowers the scattering rates of electrons above tens of kiloelectronvolts but enhances those below.Furthermore,these differences are more pronounced with the enhancement of geomagnetic activity or the decrease in background plasma density.展开更多
This paper studies inter-annual variations of 6.5-Day Waves(6.5 DWs) observed at altitudes 20-110 km between 52°S-52°N latitudes during March 2002-January 2021, and how these variations were related to the e...This paper studies inter-annual variations of 6.5-Day Waves(6.5 DWs) observed at altitudes 20-110 km between 52°S-52°N latitudes during March 2002-January 2021, and how these variations were related to the equatorial stratospheric Quasi-Biennial Oscillation(QBO). Temperature amplitudes of the 6.5 DWs are calculated based on SABER/TIMED observations. QBO zonal winds are obtained from an ERA5 reanalysis dataset. QBO phases are derived using an Empirical Orthogonal Functions(EOF) method. Wavelet analysis of the observed 6.5 DW variations demonstrates obvious spectral maximums around 28-38 months at 32°N-52°N, and around 26-30 months at 32°S-52°S. In the Northern Hemisphere, peak periods lengthened poleward;in the Southern Hemisphere, however,they were unchanged with latitude. Residual 6.5 DWs amplitudes have been determined by removing composite amplitudes from 6.5 DWs amplitudes. Comparisons between QBO and monthly maximum residual 6.5 DWs amplitudes(AMmax) show clear correlations between the QBO and 6.5 DWs in both hemispheres, but the observed relationship is stronger in the NH. When AMmax NH, the mean QBO profile was easterly at all levels from 70 to 5 hPa;when the AMmax below 30 hPa. Linear Pearson correlation coefficients between QBO phases and AMmax 20°N-52°N in April and around 64 km at 24°S in February, and large negative values from 80 to 110 km between 20°N-50°N in August and at 96-106 km between 20°S-44°S in February. These results indicate quantitative correlations between QBO and 6.5 DWs and provide credible evidences for further studies of QBO modulations on long-term variations of 6.5 DWs.展开更多
In this study, we provide a detailed case study of the X-pattern of equatorial ionization anomaly(EIA) observed on the night of September 12, 2021 by the Global-scale Observations of the Limb and Disk(GOLD) mission. U...In this study, we provide a detailed case study of the X-pattern of equatorial ionization anomaly(EIA) observed on the night of September 12, 2021 by the Global-scale Observations of the Limb and Disk(GOLD) mission. Unlike most previous studies about the X-pattern observed under the severely disturbed background ionosphere, this event is observed under geomagnetically quiet and low solar activity conditions. GOLD's continuous observations reveal that the X-pattern intensity evolves with local time, while its center's longitude remains constant. The total electron content(TEC) data derived from the ground-based Global Navigation Satellite System(GNSS) network aligns well with GOLD observations in capturing the formation of the X-pattern, extending coverage to areas beyond GOLD's observational reach. Additionally, the ESA's Swarm mission show that both sides of the X-pattern can coincide with the occurrence of small-scale equatorial plasma bubbles(EPBs). To further analyze the possible drivers of the X-pattern, observations from the Ionospheric Connection Explorer(ICON) satellite were used. It shows that the latitudinal expansion(or width) between the EIA crests in two hemispheres is proportional(or inversely proportional) to the upward(or downward) plasma drift velocity, which suggests that the zonal electric field should have a notable influence on the formation of EIA X-pattern. Further simulations using the SAMI2 model support this mechanism, as the X-pattern of EIA is successfully reproduced by setting the vertical plasma drift to different values at different longitudes.展开更多
This paper report paleomagnetic data from late Cretaceous diorite dykes that sub-vertically intrude granodiorites in the eastern Gangdese belt near the city of Lhasa.Our research goals are to provide further constrain...This paper report paleomagnetic data from late Cretaceous diorite dykes that sub-vertically intrude granodiorites in the eastern Gangdese belt near the city of Lhasa.Our research goals are to provide further constraints on pre-collisional structure of the southern margin of Asia and the onset of the India-Asia collision.Magnetite is identified as the main magnetic carrier in our study.The magnetite shows no evidence of metamorphism or alteration as determined from optical and scanning electron microscope observations.A strong mineral orientation is revealed by anisotropy of magnetic susceptibility analysis both for the intruded dykes and the country rocks.The authors interpret this AMS fabric to have formed during intrusion rather than deformation.Fifteen of 23 sites yield acceptable site mean characteristic remanences with dual polarities.A scatter analysis of the virtual geomagnetic poles suggests that the mean result adequately averaged paleosecular variation.The paleomagnetic pole from the Gangdese dykes yields a paleolatitude of 14.3°N±5.8°N for the southern margin of Asia near Lhasa.The paleolatitude corresponds to an in-between position of the Lhasa terrane during about 130‒60 Ma.Furthermore,the mean declination of the characteristic remanent magnetization reveals a significant counterclockwise rotation of 18°±9°for the sampling location since about 83 Ma.In the light of tectonic setting of the dykes,the strike of the southern margin of Asia near Lhasa is restored to trend approximately about 310°,which is compatible with the hypothesis that the southern margin of Eurasia had a quasi-linear structure prior to its collision with India.展开更多
Wavelike perturbations in the ionosphere of Titan,the largest satellite of Saturn,are explored based on the Cassini Ion Neutral Mass Spectrometer(INMS)measurements.Strong wavelike perturbations are identified for more...Wavelike perturbations in the ionosphere of Titan,the largest satellite of Saturn,are explored based on the Cassini Ion Neutral Mass Spectrometer(INMS)measurements.Strong wavelike perturbations are identified for more than twenty ion species,from simple ones such as N^(+)and CH_(4)^(+)to complex ones such as C_(2)H_(3)CNH^(+)and C_(4)H_(7)^(+).Simultaneous wavelike perturbations in background N_(2),indicative of atmospheric gravity waves,are also observed,motivating us to speculate that the INMS-derived ion perturbations are wave-driven.The amplitudes of the ion perturbations are found to be larger than that of the N_(2)perturbations.Clear compositional variation is revealed by the data:heavier ion species exhibit greater amplitudes.Such observations might be understood based on considerations either of force balance or chemical loss in Titan’s ionosphere.展开更多
Solar active regions(ARs)are formed by the emergence of current-carrying magnetic flux tubes from below the photosphere.Although for an isolated flux tube the direct and return currents flowing along the tube should b...Solar active regions(ARs)are formed by the emergence of current-carrying magnetic flux tubes from below the photosphere.Although for an isolated flux tube the direct and return currents flowing along the tube should balance with each other,it remains controversial whether such a neutralization of currents is also maintained during the emergence process.Here we present a systematic survey of the degrees of the current neutralization in a large sample of flux-emerging ARs which appeared on the solar disk around the central meridian from 2010 to 2022.The vector magnetograms taken by Helioseismic and Magnetic Imager onboard Solar Dynamic Observatory are employed to calculate the distributions of the vertical current density at the photosphere.Focusing on the main phase of flux emergence,i.e.,the phase in which the total unsigned magnetic flux is continuously increased,we statistically examined the ratios of direct to return currents in all the ARs.Such a large-sample statistical study suggests that most of the ARs were born with currents close to neutralization.The degree of current neutralization seems to be not affected by the active-region size,the active-region growing rate,and the total unsigned current.The only correlation of significance as found is that the stronger the magnetic field nonpotentiality is,the further the AR deviates from current neutrality,which supports previous event studies that eruption-productive ARs often have non-neutralized currents.展开更多
Suprathermal electrons are an important population of the Martian ionosphere, either produced by photoionization of atmospheric neutrals or supplied from the Solar Wind (SW). This study is dedicated to an in-depth inv...Suprathermal electrons are an important population of the Martian ionosphere, either produced by photoionization of atmospheric neutrals or supplied from the Solar Wind (SW). This study is dedicated to an in-depth investigation of the pitch angle distribution of suprathermal electrons at two representative energies, 19−55 eV and 124−356 eV, using the extensive measurements made by the Solar Wind Electron Analyzer on board the Mars Atmosphere and Volatile Evolution. Throughout the study, we focus on the overall degree of anisotropy, defined as the standard deviation of suprathermal electron intensity among different directions which is normalized by the mean omni-directional intensity. The available data reveal the following characteristics: (1) In general, low energy electrons are more isotropic than high energy electrons, and dayside electrons are more isotropic than nightside electrons;(2) On the dayside, the anisotropy increases with increasing altitude at low energies but remains roughly constant at high energies, whereas on the nightside, the anisotropy decreases with increasing altitude at all energies;(3) Electrons tend to be more isotropic in strongly magnetized regions than in weakly magnetized regions, especially on the nightside. These observations indicate that the anisotropy is a useful diagnostic of suprathermal electron transport, for which the conversion between the parallel and perpendicular momenta as required by the conservation of the first adiabatic invariant, along with the atmospheric absorption at low altitudes, are two crucial factors modulating the observed variation of the anisotropy. Our analysis also highlights the different roles on the observed anisotropy exerted by suprathermal electrons of different origins.展开更多
An important population of the dayside Martian ionosphere are photoelectrons that are produced by solar Extreme Ultraviolet and X-ray ionization of atmospheric neutrals.A typical photoelectron energy spectrum is chara...An important population of the dayside Martian ionosphere are photoelectrons that are produced by solar Extreme Ultraviolet and X-ray ionization of atmospheric neutrals.A typical photoelectron energy spectrum is characterized by a distinctive peak near 27 eV related to the strong solar HeⅡ emission line at 30.4 nm,and an additional peak near 500 eV related to O Auger ionization.In this study,the extensive measurements made by the Solar Wind Electron Analyzer on board the recent Mars Atmosphere and Volatile Evolution spacecraft are analyzed and found to verify the scenario that Martian ionosphere photoelectrons are driven by solar radiation.We report that the photoelectron intensities at the centers of both peaks increase steadily with increasing solar ionizing flux below 90 nm and that the observed solar cycle variation is substantially more prominent near the O Auger peak than near the HeⅡ peak.The latter observation is clearly driven by a larger variability in solar irradiance at shorter wavelengths.When the solar ionizing flux increases from 1 mW·m^-2 to 2.5 mW·m^-2,the photoelectron intensity increases by a factor of 3.2 at the HeⅡ peak and by a much larger factor of 10.5 at the O Auger peak,both within the optically thin regions of the Martian atmosphere.展开更多
The solar flare is a sudden eruptive solar phenomenon with significant enhancements in solar X-ray and Extreme Ultraviolet radiations,resulting in large amounts of energy being injected into the planetary atmosphere.C...The solar flare is a sudden eruptive solar phenomenon with significant enhancements in solar X-ray and Extreme Ultraviolet radiations,resulting in large amounts of energy being injected into the planetary atmosphere.Case studies have been extensively presented to analyze the effect of extremely large flares on the Martian upper atmosphere,but the general features of the Martian thermospheric response to flares are still poorly understood.In this work,we select 12 intense solar flares that occurred between 2015 and 2017 and investigate the densities and compositional variations of the dayside Martian thermosphere to these flares with the aid of the measurements made by the Mars Atmosphere and Volatile EvolutioN.The statistical studies indicate that the responses of the Martian thermosphere to flares are complicated that both the class of the flare and the wavelength of the enhanced radiation may have prominent influences on the thermal expansion of the atmosphere and the atmospheric photochemical reactions.展开更多
Solar Wind(SW)electron precipitation is able to deposit a substantial amount of energy in the nightside Martian upper atmosphere,potentially exerting an influence on its thermal structure.This study serves as the firs...Solar Wind(SW)electron precipitation is able to deposit a substantial amount of energy in the nightside Martian upper atmosphere,potentially exerting an influence on its thermal structure.This study serves as the first investigation of such an issue,with the aid of the simultaneous measurements of both neutral density and energetic electron intensity made on board the recent Mars Atmosphere and Volatile Evolution(MAVEN)spacecraft.We report that,from a statistical point of view,the existing measurements do not support a scenario of noticeable neutral heating via SW electron precipitation.However,during 3%−4%of the MAVEN orbits for which data are available,strong correlation between nightside temperature and electron intensity is observed,manifested as collocated enhancements in both parameters,as compared to the surrounding regions.In addition,our analysis also indicates that neutral heating via SW electron precipitation tends to be more effective at altitudes below 160 km for integrated electron intensities above 0.01 ergs·cm^−2·s^−1 over the energy range of 3−450 eV.The results reported here highlight the necessity of incorporating SW electron precipitation as a heat source in the nightside Martian upper atmosphere under extreme circumstances such as during interplanetary coronal mass ejections.展开更多
The CO2^+;ultraviolet doublet(UVD)emission near 289 nm is an important feature of dayside airglow emission from planetaryupper atmospheres.In this study,we analyzed the brightness profiles of CO2^+;UVDemission on Mars...The CO2^+;ultraviolet doublet(UVD)emission near 289 nm is an important feature of dayside airglow emission from planetaryupper atmospheres.In this study,we analyzed the brightness profiles of CO2^+;UVDemission on Mars by using the extensive observationsmade by the lmaging Ultraviolet Spectrograph on board the recent Mars Atmosphere and Volatle Evolution spacecraft.Strong solar cycleand solar zenith angle variations in peak emission intensity and altitude were revealed by the data:(1)Both the peak intensity and altitude increase with increasing solar activity,and(2)the peak intensity decreases,whereas the peak altitude increases,with increasingsolar zenith angle.These observations can be favorably interpreted by the solar-driven scenario combined with the fact that photoionization and photoelectron impact ionization are the two most important processes responsible for the production of excited-state cotand consequently the intensity of CO2^+;UVDemission.Despite this,we propose that an extra driver,presumably related to thecomplicated variation in the background atmosphere,such as the occurrence of globaldust storms is required to fuly interpret theobservations.In general,our analysis suggests that the CO2^+;UVD emission is a useful diagnostic of the variability of the dayside Martianatmosphere under the influences of both internal and external drivers.展开更多
A mechanism for energy transfer from the solar wind to the Martian ionosphere through open magnetic flux rope is proposed based on the observations by Mars Atmosphere and Volatile EvolutioN(MAVEN).The satellite was lo...A mechanism for energy transfer from the solar wind to the Martian ionosphere through open magnetic flux rope is proposed based on the observations by Mars Atmosphere and Volatile EvolutioN(MAVEN).The satellite was located in the dayside magnetosheath at an altitude of about 70o km above the northern hemisphere.Collisions between the hot solar wind protons and the cold heavy ions/neutrals in the subsolar region can cool the protons and heat the heavy ions.As a result,the magnetosheath protons are siphoned into the ionosphere due to the thermal pressure gradient of protons and the heated heavy ions escape along the open magnetic field lines.Although direct collisions in the lower-altitude region were not detected,this physical process is demonstrated by MAVEN measurements of enhanced proton density,decreased proton temperature and oppositely directed motions of hot and cool protons within the flux rope,which are very different from the observational features of the flux transfer events near the Earth's magnetopause.This mechanism could universally exist in many contexts where a collisionless plasma region is connected to a collisional plasma region.By reconstructing the magnetic geometry and the cross-section of the flux rope using the Grad-Shafranov technique,the ion loss rates are quantitatively estimated to be on the order of 1023 s-l,which is much higher than previously estimated.展开更多
Recent studies revealed that the long-lasting daytime ionospheric enhancements of Total Electron Content(TEC)were sometimes observed in the Asian sector during the recovery phase of geomagnetic storms e.g.,Lei(J Geoph...Recent studies revealed that the long-lasting daytime ionospheric enhancements of Total Electron Content(TEC)were sometimes observed in the Asian sector during the recovery phase of geomagnetic storms e.g.,Lei(J Geophys Res Space Phys 123:3217-3232,2018),Li(J Geophys Res Space Phys 125:e2020JA028238,2020).However,they focused only on the dayside ionosphere,and no dedicated studies have been performed to investigate the nighttime ionospheric behavior during such kinds of storm recovery phases.In this study,we focused on two geomagnetic storms that happened on 7-8 September 2017 and 25-26 August 2018,which showed the prominent daytime TEC enhancements in the Asian sector during their recovery phases,to explore the nighttime large-scale ionospheric responses as well as the small-scale Equatorial Plasma Irregularities(EPIs).It is found that during the September 2017 storm recovery phase,the nighttime ionosphere in the American sector is largely depressed,which is similar to the daytime ionospheric response in the same longitude sector;while in the Asian sector,only a small TEC increase is observed at nighttime,which is much weaker than the prominent daytime TEC enhancement in this longitude sector.During the recovery phase of the August 2018 storm,a slight TEC increase is observed on the night side at all longitudes,which is also weaker than the prominent daytime TEC enhancement.For the small-scale EPIs,they are enhanced and extended to higher latitudes during the main phase of both storms.However,during the recovery phases of the first storm,the EPIs are largely enhanced and suppressed in the Asian and American sectors,respectively,while no prominent nighttime EPIs are observed during the second storm recovery phase.The clear north-south asymmetry of equatorial ionization anomaly crests during the second storm should be responsible for the suppression of EPIs during this storm.In addition,our results also suggest that the dusk side ionospheric response could be affected by the daytime ionospheric plasma density/TEC variations during the recovery phase of geomagnetic storms,which further modulates the vertical plasma drift and plasma gradient.As a result,the growth rate of post-sunset EPIs will be enhanced or inhibited.展开更多
A climatological survey of Martian ionospheric plasma density irregularities was conducted by exploring the in-situ measurements of the Mars Atmosphere and Volatile EvolutioN(MAVEN) spacecraft. The irregularities were...A climatological survey of Martian ionospheric plasma density irregularities was conducted by exploring the in-situ measurements of the Mars Atmosphere and Volatile EvolutioN(MAVEN) spacecraft. The irregularities were first classified as enhancement, depletion, and oscillation. By checking the simultaneous magnetic field fluctuation, the irregularities have been classified into two types: with or without magnetic signatures. The classified irregularities exhibit diverse global occurrence patterns, as those with magnetic signatures tend to appear near the periphery of the crustal magnetic anomaly(MA), and those without magnetic signatures prefer to appear either inside of the MA or outside of the MA, depending on the type and solar zenith angle. Under most circumstances, the irregularities have a considerable occurrence rate at altitudes above the ionospheric dynamo height(above 200 km), and the magnetization state of the ions seems irrelevant to their occurrence. In addition, the irregularities do not show dependence on magnetic field geometry, except that the enhancement without magnetic signatures favors the vertical field line, implying its equivalence to the localized bulge. Other similarities and discrepancies exist in reference to previous studies. We believe this global survey complements previous research and provides crucial research clues for future efforts to clarify the nature of the Martian ionospheric irregularities.展开更多
Extensive research efforts have revealed that the Martian dust storms can perturb the upper atmospheric condition and as a consequence,enhance plasma density and photoelectron flux in the ionosphere.However,previous o...Extensive research efforts have revealed that the Martian dust storms can perturb the upper atmospheric condition and as a consequence,enhance plasma density and photoelectron flux in the ionosphere.However,previous observational studies of the Martian dust storm impacts have been restricted to regions below 400 km,which limits our understanding of the Martian dust storm effects in the upper ionosphere and magnetosphere.Here,based on the suprathermal electron measurements made by the Solar Wind Electron Analyzer onboard the Mars Atmosphere and Volatile Evolution,we identify with an automatic procedure the occurrences of all photoelectron boundary(PEB)crossings at solar zenith angle below 120°(with a dust-free median altitude of about 600 km).Using the dayside PEB as a proxy of the upper ionospheric and magnetospheric condition,we analyze the variations of the PEB altitude during the 2018 global dust storm(GDS)of Mars Year 34(MY34)and compare them with the period in MY33 when there was no global dust storm.We conclude that the column dust optical depth(CDOD)emerges as one of the main driving factors for PEB altitude variations during the GDS.Our analysis implies that the GDS can affect the Martian upper atmosphere and ionosphere over considerable distances and extended time scales.展开更多
Electromagnetic ion cyclotron(EMIC)emission is an efficient mechanism for scattering loss of energetic protons.Here,we report an event that provides both in-situ observation of energetic proton differential fluxes in ...Electromagnetic ion cyclotron(EMIC)emission is an efficient mechanism for scattering loss of energetic protons.Here,we report an event that provides both in-situ observation of energetic proton differential fluxes in the inner magnetosphere and precipitation of protons at ionospheric altitudes.During the 7-8 September 2015 geomagnetic storm the Van Allen Probes observed strong EMIC waves around L=5 and a distinct decrement in fluxes of tens of keV protons around pitch angles 0°-45°.Meanwhile,precipitating protons at ionospheric altitudes were found to significantly enhanced(by several orders of magnitude),measured by NOAA 18 and 19 when they magnetically linked to the Van Allen Probe-A.By solving the Fokker-Planck diffusion equation,we show that EMIC waves can efficiently produce loss of energetic protons within about 2 h in the pitch angle range of~0°-45°,comparable to the satellite observations.展开更多
基金supported by the National Natural Science Foundation of China (NSFC) through Grant Number 42074193
文摘Theoretical analysis has demonstrated that the dispersion relation of chorus waves plays an essential role in the resonant interaction and energy transformation between the waves and magnetospheric electrons.Previous quantitative analyses often simplified the chorus dispersion relation by using the cold plasma assumption.However,the applicability of the cold plasma assumption is doubtful,especially during geomagnetic disturbances.We here present a systematic statistical analysis on the validity of the cold plasma dispersion relation of chorus waves based on observations from the Van Allen Probes over the period from 2012 to 2018.The statistical results show that the observed magnetic field intensities deviate substantially from those calculated from the cold plasma dispersion relation and that they become more pronounced with an increase in geomagnetic activity or a decrease in background plasma density.The region with large deviations is mainly concentrated in the nightside and expands in both the radial and azimuthal directions as the geomagnetic activity increases or the background plasma density decreases.In addition,the bounce-averaged electron scattering rates are computed by using the observed and cold plasma dispersion relation of chorus waves.Compared with usage of the cold plasma dispersion relation,usage of the observed dispersion relation considerably lowers the minimum resonant energy of electrons and lowers the scattering rates of electrons above tens of kiloelectronvolts but enhances those below.Furthermore,these differences are more pronounced with the enhancement of geomagnetic activity or the decrease in background plasma density.
基金jointly supported by the National Basic Research Program of China through grant 2012CB825606the National Natural Science Foundation of China through grants 41504118,41375045,41525015,and 41774186+1 种基金the Natural Science Foundation of Jiangsu Province through grants BK20150709 and BK20161531Projects Supported by the Specialized Research Fund for State Key Laboratories。
文摘This paper studies inter-annual variations of 6.5-Day Waves(6.5 DWs) observed at altitudes 20-110 km between 52°S-52°N latitudes during March 2002-January 2021, and how these variations were related to the equatorial stratospheric Quasi-Biennial Oscillation(QBO). Temperature amplitudes of the 6.5 DWs are calculated based on SABER/TIMED observations. QBO zonal winds are obtained from an ERA5 reanalysis dataset. QBO phases are derived using an Empirical Orthogonal Functions(EOF) method. Wavelet analysis of the observed 6.5 DW variations demonstrates obvious spectral maximums around 28-38 months at 32°N-52°N, and around 26-30 months at 32°S-52°S. In the Northern Hemisphere, peak periods lengthened poleward;in the Southern Hemisphere, however,they were unchanged with latitude. Residual 6.5 DWs amplitudes have been determined by removing composite amplitudes from 6.5 DWs amplitudes. Comparisons between QBO and monthly maximum residual 6.5 DWs amplitudes(AMmax) show clear correlations between the QBO and 6.5 DWs in both hemispheres, but the observed relationship is stronger in the NH. When AMmax NH, the mean QBO profile was easterly at all levels from 70 to 5 hPa;when the AMmax below 30 hPa. Linear Pearson correlation coefficients between QBO phases and AMmax 20°N-52°N in April and around 64 km at 24°S in February, and large negative values from 80 to 110 km between 20°N-50°N in August and at 96-106 km between 20°S-44°S in February. These results indicate quantitative correlations between QBO and 6.5 DWs and provide credible evidences for further studies of QBO modulations on long-term variations of 6.5 DWs.
基金supported by the National Key R&D Program of China (Grant No. 2022YFF0503700)the special funds of Hubei Luojia Laboratory (220100011)+1 种基金Chao Xiong is supported by the ISSI-BJ project, “the electromagnetic data validation and scientific application research based on CSES satellite”ISSI/ISSI-BJ project “Multi-Scale Magnetosphere–Ionosphere–Thermosphere Interaction”。
文摘In this study, we provide a detailed case study of the X-pattern of equatorial ionization anomaly(EIA) observed on the night of September 12, 2021 by the Global-scale Observations of the Limb and Disk(GOLD) mission. Unlike most previous studies about the X-pattern observed under the severely disturbed background ionosphere, this event is observed under geomagnetically quiet and low solar activity conditions. GOLD's continuous observations reveal that the X-pattern intensity evolves with local time, while its center's longitude remains constant. The total electron content(TEC) data derived from the ground-based Global Navigation Satellite System(GNSS) network aligns well with GOLD observations in capturing the formation of the X-pattern, extending coverage to areas beyond GOLD's observational reach. Additionally, the ESA's Swarm mission show that both sides of the X-pattern can coincide with the occurrence of small-scale equatorial plasma bubbles(EPBs). To further analyze the possible drivers of the X-pattern, observations from the Ionospheric Connection Explorer(ICON) satellite were used. It shows that the latitudinal expansion(or width) between the EIA crests in two hemispheres is proportional(or inversely proportional) to the upward(or downward) plasma drift velocity, which suggests that the zonal electric field should have a notable influence on the formation of EIA X-pattern. Further simulations using the SAMI2 model support this mechanism, as the X-pattern of EIA is successfully reproduced by setting the vertical plasma drift to different values at different longitudes.
基金financially supported by the National Science Foundation of China(92055205,41672223)the start-up funding from Sun Yat-sen University(74110-18841244).
文摘This paper report paleomagnetic data from late Cretaceous diorite dykes that sub-vertically intrude granodiorites in the eastern Gangdese belt near the city of Lhasa.Our research goals are to provide further constraints on pre-collisional structure of the southern margin of Asia and the onset of the India-Asia collision.Magnetite is identified as the main magnetic carrier in our study.The magnetite shows no evidence of metamorphism or alteration as determined from optical and scanning electron microscope observations.A strong mineral orientation is revealed by anisotropy of magnetic susceptibility analysis both for the intruded dykes and the country rocks.The authors interpret this AMS fabric to have formed during intrusion rather than deformation.Fifteen of 23 sites yield acceptable site mean characteristic remanences with dual polarities.A scatter analysis of the virtual geomagnetic poles suggests that the mean result adequately averaged paleosecular variation.The paleomagnetic pole from the Gangdese dykes yields a paleolatitude of 14.3°N±5.8°N for the southern margin of Asia near Lhasa.The paleolatitude corresponds to an in-between position of the Lhasa terrane during about 130‒60 Ma.Furthermore,the mean declination of the characteristic remanent magnetization reveals a significant counterclockwise rotation of 18°±9°for the sampling location since about 83 Ma.In the light of tectonic setting of the dykes,the strike of the southern margin of Asia near Lhasa is restored to trend approximately about 310°,which is compatible with the hypothesis that the southern margin of Eurasia had a quasi-linear structure prior to its collision with India.
基金supported by the B-type Strategic Priority Program No. XDB41000000funded by the Chinese Academy of Sciences and the pre-research projects on Civil Aerospace Technologies No.s D020105 and D020103+1 种基金funded by China’s National Space Administrationsupport from the National Science Foundation of China through grants 42030201, 41904154 and 42104170
文摘Wavelike perturbations in the ionosphere of Titan,the largest satellite of Saturn,are explored based on the Cassini Ion Neutral Mass Spectrometer(INMS)measurements.Strong wavelike perturbations are identified for more than twenty ion species,from simple ones such as N^(+)and CH_(4)^(+)to complex ones such as C_(2)H_(3)CNH^(+)and C_(4)H_(7)^(+).Simultaneous wavelike perturbations in background N_(2),indicative of atmospheric gravity waves,are also observed,motivating us to speculate that the INMS-derived ion perturbations are wave-driven.The amplitudes of the ion perturbations are found to be larger than that of the N_(2)perturbations.Clear compositional variation is revealed by the data:heavier ion species exhibit greater amplitudes.Such observations might be understood based on considerations either of force balance or chemical loss in Titan’s ionosphere.
基金supported by the National Natural Science Foundation of China(NSFC)U2031108Yunnan Key Laboratory of Solar Physics and Space Science under the number YNSPCC202213。
文摘Solar active regions(ARs)are formed by the emergence of current-carrying magnetic flux tubes from below the photosphere.Although for an isolated flux tube the direct and return currents flowing along the tube should balance with each other,it remains controversial whether such a neutralization of currents is also maintained during the emergence process.Here we present a systematic survey of the degrees of the current neutralization in a large sample of flux-emerging ARs which appeared on the solar disk around the central meridian from 2010 to 2022.The vector magnetograms taken by Helioseismic and Magnetic Imager onboard Solar Dynamic Observatory are employed to calculate the distributions of the vertical current density at the photosphere.Focusing on the main phase of flux emergence,i.e.,the phase in which the total unsigned magnetic flux is continuously increased,we statistically examined the ratios of direct to return currents in all the ARs.Such a large-sample statistical study suggests that most of the ARs were born with currents close to neutralization.The degree of current neutralization seems to be not affected by the active-region size,the active-region growing rate,and the total unsigned current.The only correlation of significance as found is that the stronger the magnetic field nonpotentiality is,the further the AR deviates from current neutrality,which supports previous event studies that eruption-productive ARs often have non-neutralized currents.
基金the National Natural Science Foundation of China through grants 42241114,42274218 and 42304166the B-type Strategic Priority Program No.XDB41000000 funded by the Chinese Academy of Sciences+1 种基金the pre-research project on Civil Aerospace Technologies No.D020105 funded by China’s National Space Administration,the Guangdong Basic and Applied Research Foundation Project 2021A1515110271the Key Laboratory of Geospace Environment,Chinese Academy of Sciences,University of Science&Technology of China.
文摘Suprathermal electrons are an important population of the Martian ionosphere, either produced by photoionization of atmospheric neutrals or supplied from the Solar Wind (SW). This study is dedicated to an in-depth investigation of the pitch angle distribution of suprathermal electrons at two representative energies, 19−55 eV and 124−356 eV, using the extensive measurements made by the Solar Wind Electron Analyzer on board the Mars Atmosphere and Volatile Evolution. Throughout the study, we focus on the overall degree of anisotropy, defined as the standard deviation of suprathermal electron intensity among different directions which is normalized by the mean omni-directional intensity. The available data reveal the following characteristics: (1) In general, low energy electrons are more isotropic than high energy electrons, and dayside electrons are more isotropic than nightside electrons;(2) On the dayside, the anisotropy increases with increasing altitude at low energies but remains roughly constant at high energies, whereas on the nightside, the anisotropy decreases with increasing altitude at all energies;(3) Electrons tend to be more isotropic in strongly magnetized regions than in weakly magnetized regions, especially on the nightside. These observations indicate that the anisotropy is a useful diagnostic of suprathermal electron transport, for which the conversion between the parallel and perpendicular momenta as required by the conservation of the first adiabatic invariant, along with the atmospheric absorption at low altitudes, are two crucial factors modulating the observed variation of the anisotropy. Our analysis also highlights the different roles on the observed anisotropy exerted by suprathermal electrons of different origins.
基金supported by the B-type Strategic Priority Program No.XDB41000000funded by the Chinese Academy of Sciences and the pre-research project on Civil Aerospace Technologies No.D020105funded by China's National Space Administration(CNSA).The authors also acknowledge support from the National Natural Science Foundation of China(NSFC)through grants 41904154,41525015,and 41774186.
文摘An important population of the dayside Martian ionosphere are photoelectrons that are produced by solar Extreme Ultraviolet and X-ray ionization of atmospheric neutrals.A typical photoelectron energy spectrum is characterized by a distinctive peak near 27 eV related to the strong solar HeⅡ emission line at 30.4 nm,and an additional peak near 500 eV related to O Auger ionization.In this study,the extensive measurements made by the Solar Wind Electron Analyzer on board the recent Mars Atmosphere and Volatile Evolution spacecraft are analyzed and found to verify the scenario that Martian ionosphere photoelectrons are driven by solar radiation.We report that the photoelectron intensities at the centers of both peaks increase steadily with increasing solar ionizing flux below 90 nm and that the observed solar cycle variation is substantially more prominent near the O Auger peak than near the HeⅡ peak.The latter observation is clearly driven by a larger variability in solar irradiance at shorter wavelengths.When the solar ionizing flux increases from 1 mW·m^-2 to 2.5 mW·m^-2,the photoelectron intensity increases by a factor of 3.2 at the HeⅡ peak and by a much larger factor of 10.5 at the O Auger peak,both within the optically thin regions of the Martian atmosphere.
基金supported by the Guangdong Basic and Applied Research Foundation through Grant 2021A1515110271。
文摘The solar flare is a sudden eruptive solar phenomenon with significant enhancements in solar X-ray and Extreme Ultraviolet radiations,resulting in large amounts of energy being injected into the planetary atmosphere.Case studies have been extensively presented to analyze the effect of extremely large flares on the Martian upper atmosphere,but the general features of the Martian thermospheric response to flares are still poorly understood.In this work,we select 12 intense solar flares that occurred between 2015 and 2017 and investigate the densities and compositional variations of the dayside Martian thermosphere to these flares with the aid of the measurements made by the Mars Atmosphere and Volatile EvolutioN.The statistical studies indicate that the responses of the Martian thermosphere to flares are complicated that both the class of the flare and the wavelength of the enhanced radiation may have prominent influences on the thermal expansion of the atmosphere and the atmospheric photochemical reactions.
基金the B-type Strategic Priority Program No.XDB41000000 funded by the Chinese Academy of Sciencesthe pre-research project on Civil Aerospace Technologies No.D020105 funded by China’s National Space Administrationthe National Natural Science Foundation of China through grants 41525015,41774186,41904154,and 42030201.
文摘Solar Wind(SW)electron precipitation is able to deposit a substantial amount of energy in the nightside Martian upper atmosphere,potentially exerting an influence on its thermal structure.This study serves as the first investigation of such an issue,with the aid of the simultaneous measurements of both neutral density and energetic electron intensity made on board the recent Mars Atmosphere and Volatile Evolution(MAVEN)spacecraft.We report that,from a statistical point of view,the existing measurements do not support a scenario of noticeable neutral heating via SW electron precipitation.However,during 3%−4%of the MAVEN orbits for which data are available,strong correlation between nightside temperature and electron intensity is observed,manifested as collocated enhancements in both parameters,as compared to the surrounding regions.In addition,our analysis also indicates that neutral heating via SW electron precipitation tends to be more effective at altitudes below 160 km for integrated electron intensities above 0.01 ergs·cm^−2·s^−1 over the energy range of 3−450 eV.The results reported here highlight the necessity of incorporating SW electron precipitation as a heat source in the nightside Martian upper atmosphere under extreme circumstances such as during interplanetary coronal mass ejections.
基金This work is supported by the B-type Strategic Priority Program(no.XDB41000000)the Chinese Academy of Sciences and the pre-research project on Civil Aerospace Technologies(no.D020105)the China National Space Administration.The authors also acknowledge support from the National Science Foundation of China(NSFC)through grants 41525015 and 41774186.The data used in this work are publicly available at the MAVEN Science Data Center(http://lasp.colorado.edu/maven/sdc/public/).
文摘The CO2^+;ultraviolet doublet(UVD)emission near 289 nm is an important feature of dayside airglow emission from planetaryupper atmospheres.In this study,we analyzed the brightness profiles of CO2^+;UVDemission on Mars by using the extensive observationsmade by the lmaging Ultraviolet Spectrograph on board the recent Mars Atmosphere and Volatle Evolution spacecraft.Strong solar cycleand solar zenith angle variations in peak emission intensity and altitude were revealed by the data:(1)Both the peak intensity and altitude increase with increasing solar activity,and(2)the peak intensity decreases,whereas the peak altitude increases,with increasingsolar zenith angle.These observations can be favorably interpreted by the solar-driven scenario combined with the fact that photoionization and photoelectron impact ionization are the two most important processes responsible for the production of excited-state cotand consequently the intensity of CO2^+;UVDemission.Despite this,we propose that an extra driver,presumably related to thecomplicated variation in the background atmosphere,such as the occurrence of globaldust storms is required to fuly interpret theobservations.In general,our analysis suggests that the CO2^+;UVD emission is a useful diagnostic of the variability of the dayside Martianatmosphere under the influences of both internal and external drivers.
基金National Natural Science Foundation of China(42122061)the Science and Technology Development Fund of Macao SAR(0002/2019/A1)Macao Foundation,and the pre-research project on Civil Aerospace Technologies No.D020308 and D020104 funded by China National Space Administration.C.M.thanks the Austrian Science Fund(FWF):P31521-N27.C.J.F.thanks NASA grant:80NSSC19K1293.A basic version of the Grad-Shafranov reconstruction method in Matlab is available at https://github.com/cmoestl/interplanetarygrad-shafranov.We acknowledge the MAVEN contract for support.All MAVEN data are available on the Planetary Data System(https://pds.nasa.gov).
文摘A mechanism for energy transfer from the solar wind to the Martian ionosphere through open magnetic flux rope is proposed based on the observations by Mars Atmosphere and Volatile EvolutioN(MAVEN).The satellite was located in the dayside magnetosheath at an altitude of about 70o km above the northern hemisphere.Collisions between the hot solar wind protons and the cold heavy ions/neutrals in the subsolar region can cool the protons and heat the heavy ions.As a result,the magnetosheath protons are siphoned into the ionosphere due to the thermal pressure gradient of protons and the heated heavy ions escape along the open magnetic field lines.Although direct collisions in the lower-altitude region were not detected,this physical process is demonstrated by MAVEN measurements of enhanced proton density,decreased proton temperature and oppositely directed motions of hot and cool protons within the flux rope,which are very different from the observational features of the flux transfer events near the Earth's magnetopause.This mechanism could universally exist in many contexts where a collisionless plasma region is connected to a collisional plasma region.By reconstructing the magnetic geometry and the cross-section of the flux rope using the Grad-Shafranov technique,the ion loss rates are quantitatively estimated to be on the order of 1023 s-l,which is much higher than previously estimated.
基金the National Natural Science Foundation of China(42174191)the start-up program of Wuhan University(600460020)+2 种基金Xin Wan is supported by the China Postdoctoral Science Foundation(2020M683025)Fan Yin is supported by the National Key Research and Development Program of China(Grants 2018YFC1503501-01)the Dragon 5 cooperation 2020-2024(project no.59236)and Chinese Meridian Project.
文摘Recent studies revealed that the long-lasting daytime ionospheric enhancements of Total Electron Content(TEC)were sometimes observed in the Asian sector during the recovery phase of geomagnetic storms e.g.,Lei(J Geophys Res Space Phys 123:3217-3232,2018),Li(J Geophys Res Space Phys 125:e2020JA028238,2020).However,they focused only on the dayside ionosphere,and no dedicated studies have been performed to investigate the nighttime ionospheric behavior during such kinds of storm recovery phases.In this study,we focused on two geomagnetic storms that happened on 7-8 September 2017 and 25-26 August 2018,which showed the prominent daytime TEC enhancements in the Asian sector during their recovery phases,to explore the nighttime large-scale ionospheric responses as well as the small-scale Equatorial Plasma Irregularities(EPIs).It is found that during the September 2017 storm recovery phase,the nighttime ionosphere in the American sector is largely depressed,which is similar to the daytime ionospheric response in the same longitude sector;while in the Asian sector,only a small TEC increase is observed at nighttime,which is much weaker than the prominent daytime TEC enhancement in this longitude sector.During the recovery phase of the August 2018 storm,a slight TEC increase is observed on the night side at all longitudes,which is also weaker than the prominent daytime TEC enhancement.For the small-scale EPIs,they are enhanced and extended to higher latitudes during the main phase of both storms.However,during the recovery phases of the first storm,the EPIs are largely enhanced and suppressed in the Asian and American sectors,respectively,while no prominent nighttime EPIs are observed during the second storm recovery phase.The clear north-south asymmetry of equatorial ionization anomaly crests during the second storm should be responsible for the suppression of EPIs during this storm.In addition,our results also suggest that the dusk side ionospheric response could be affected by the daytime ionospheric plasma density/TEC variations during the recovery phase of geomagnetic storms,which further modulates the vertical plasma drift and plasma gradient.As a result,the growth rate of post-sunset EPIs will be enhanced or inhibited.
基金supported by the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No.XDB41000000)the National Natural Science Foundation of China (Grant Nos.42374181,42374186,42104169,42104147,41804150,41804153)+6 种基金the Guangdong Basic and Applied Basic Research Foundation (Grant Nos.2021A1515011216,2022A1515011580,2020A1515110242)the Natural Science Foundation of Jiangsu Province (Grant No.BK20180445)the Joint Open Fund of Mengcheng National Geophysical Observatory (Grant No.MENGO-202217)the Science and Technology Project of Shangrao City (Grant No.2021F002)the Key Laboratory of Tropical Atmosphere-Ocean System (Sun Yat-sen University),Ministry of Education,the Fundamental Research Funds for the Central Universitiesthe Opening Funding of Chinese Academy of Sciences dedicated for the Chinese Meridian Projectthe Open Research Project of Large Research Infrastructures of CAS —“Study on the interaction between low/mid-latitude atmosphere and ionosphere based on the Chinese Meridian Project”。
文摘A climatological survey of Martian ionospheric plasma density irregularities was conducted by exploring the in-situ measurements of the Mars Atmosphere and Volatile EvolutioN(MAVEN) spacecraft. The irregularities were first classified as enhancement, depletion, and oscillation. By checking the simultaneous magnetic field fluctuation, the irregularities have been classified into two types: with or without magnetic signatures. The classified irregularities exhibit diverse global occurrence patterns, as those with magnetic signatures tend to appear near the periphery of the crustal magnetic anomaly(MA), and those without magnetic signatures prefer to appear either inside of the MA or outside of the MA, depending on the type and solar zenith angle. Under most circumstances, the irregularities have a considerable occurrence rate at altitudes above the ionospheric dynamo height(above 200 km), and the magnetization state of the ions seems irrelevant to their occurrence. In addition, the irregularities do not show dependence on magnetic field geometry, except that the enhancement without magnetic signatures favors the vertical field line, implying its equivalence to the localized bulge. Other similarities and discrepancies exist in reference to previous studies. We believe this global survey complements previous research and provides crucial research clues for future efforts to clarify the nature of the Martian ionospheric irregularities.
基金supported by the National Natural Science Foundation of China(Grant No.42241106)。
文摘Extensive research efforts have revealed that the Martian dust storms can perturb the upper atmospheric condition and as a consequence,enhance plasma density and photoelectron flux in the ionosphere.However,previous observational studies of the Martian dust storm impacts have been restricted to regions below 400 km,which limits our understanding of the Martian dust storm effects in the upper ionosphere and magnetosphere.Here,based on the suprathermal electron measurements made by the Solar Wind Electron Analyzer onboard the Mars Atmosphere and Volatile Evolution,we identify with an automatic procedure the occurrences of all photoelectron boundary(PEB)crossings at solar zenith angle below 120°(with a dust-free median altitude of about 600 km).Using the dayside PEB as a proxy of the upper ionospheric and magnetospheric condition,we analyze the variations of the PEB altitude during the 2018 global dust storm(GDS)of Mars Year 34(MY34)and compare them with the period in MY33 when there was no global dust storm.We conclude that the column dust optical depth(CDOD)emerges as one of the main driving factors for PEB altitude variations during the GDS.Our analysis implies that the GDS can affect the Martian upper atmosphere and ionosphere over considerable distances and extended time scales.
基金supported by the National Natural Science Foundation of China(Grant Nos.41774194,41974212 and 42074198)the Specialized Research Fund for State Key Laboratories。
文摘Electromagnetic ion cyclotron(EMIC)emission is an efficient mechanism for scattering loss of energetic protons.Here,we report an event that provides both in-situ observation of energetic proton differential fluxes in the inner magnetosphere and precipitation of protons at ionospheric altitudes.During the 7-8 September 2015 geomagnetic storm the Van Allen Probes observed strong EMIC waves around L=5 and a distinct decrement in fluxes of tens of keV protons around pitch angles 0°-45°.Meanwhile,precipitating protons at ionospheric altitudes were found to significantly enhanced(by several orders of magnitude),measured by NOAA 18 and 19 when they magnetically linked to the Van Allen Probe-A.By solving the Fokker-Planck diffusion equation,we show that EMIC waves can efficiently produce loss of energetic protons within about 2 h in the pitch angle range of~0°-45°,comparable to the satellite observations.
