Geomagnetic substorms release plasma and energy from the magnetotail to the inner magnetosphere and high latitude ionosphere.In this study,we investigate substorms of different time duration,observed during the years ...Geomagnetic substorms release plasma and energy from the magnetotail to the inner magnetosphere and high latitude ionosphere.In this study,we investigate substorms of different time duration,observed during the years 1982 to 2012.We measure substorm duration by a method based on the SME index.Our results demonstrate that longer-duration substorms occur more frequently during solar maximum years,and more frequently between the months of May and July,likely due to the higher polar ionospheric conductivity and more sunward geomagnetic pole directions during summer in the northern hemisphere.Additionally,longer substorms occur more frequently under stronger,longer-lasting southward IMF,and are accompanied by slower solar winds,suggesting that extended magnetic reconnection is required to drive longer substorms.Substorm durations are not significantly related to the minimum SML index,but longer substorms usually have higher SMU and continuously rising PC indices.The SME indices of long-duration substorms show a bimodal MLT distribution located near midnight and dusk after substorm onset,with the peak originally at midnight moving eastward to the morning side during the late recovery phase.Longer duration substorms have a stronger effect on the overall ring current at all MLT sectors except dawnside.Our results provide new insights into the development process and influencing factors of substorms,from the expansion phase to the recovery phase.展开更多
The plasmapause locations determined from the Chang'e-3(CE-3) Extreme Ultraviolet Camera(EUVC) images and the auroral boundaries determined from the Defense Meteorological Satellite Program(DMSP) Special Sensor Ul...The plasmapause locations determined from the Chang'e-3(CE-3) Extreme Ultraviolet Camera(EUVC) images and the auroral boundaries determined from the Defense Meteorological Satellite Program(DMSP) Special Sensor Ultraviolet Spectrographic Imager(SSUSI) images are used to investigate the plasmaspheric evolutions during substorms. The most important finding is a nightside pointing plasmaspheric plume observed at 23:05 UT on 21 April 2014 under quiet solar wind and geomagnetic conditions, which drifted from the dusk sector. High correlations between the plasmapause evolutions and the auroral signatures exist during substorms. After substorm onset, the plasmapause erosion and the equatorward expansion of the auroral oval occur almost simultaneously in both MLT and UT, and then both the erosion and the expansion propagate westward and eastward. It is suggested that the plasmaspheric erosion and its MLT propagations are induced by the enhanced earthward plasma convection during substorm period, and the substorm dipolarization causes pitch-angle scattering of plasma sheet electrons and the resulting precipitation excites aurora emissions at the same time.展开更多
With conjunction observations of electromagnetic fields and plasma from Time History of Events and Macroscale Interactions during Substorm(THEMIS)in the near-Earth magnetotail,we investigate the spatial and temporal p...With conjunction observations of electromagnetic fields and plasma from Time History of Events and Macroscale Interactions during Substorm(THEMIS)in the near-Earth magnetotail,we investigate the spatial and temporal properties of substorm dipolarizations in the near-Earth plasma sheet(NEPS)during a substorm at 03:23 UT on 12 February 2008.Substorm dipolarizations with different features are detected by three near-Earth THEMIS probes(THA(P5),THD(P3)and THE(P4))in the magnetotail.In the current sheet with a large plasma beta value(β>2,whereβis the ratio of the plasma thermal pressure to the magnetic pressure),the dipolarization within the substorm onset region,(−10.4,2.8,−2.6)RE_gsm,has a large initial magnetic field elevation angle,θ>60°,θ=arctan(Bz/(Bx2+By2)1/2),and is accompanied by energetic ion(tens to hundred keV)dispersionless injection detected by THD(P3).This substorm onset dipolarization is characterized by Bx and By components around 0 nT with significant fluctuations.The Bz component increases sharply and its subsequent magnitude approaches the total magnetic field,Bt.The maximum value of the elevation angle approaches 85°during the later substorm expansion phase.In the NEPS withβ~1,the dipolarization outside the substorm onset region is characterized by a magnetic elevation angle with a small beginning value ofθ<45°and following multi-step enhancements during the substorm expansion phase.The maximum value of the elevation angle approaches to 70°during the later substorm expansion phase.Our observation results indicate that characteristics of dipolarization with a large beginning elevation angle within the substorm onset region provide a new indicator to identify substorm onset location.展开更多
Exohiss is a low-frequency structureless whistler-mode emission potentially contributing to the precipitation loss of radiation belt electrons outside the plasmasphere. Exohiss is usually considered the plasmaspheric ...Exohiss is a low-frequency structureless whistler-mode emission potentially contributing to the precipitation loss of radiation belt electrons outside the plasmasphere. Exohiss is usually considered the plasmaspheric hiss leaked out of the dayside plasmapause.However, the evolution of exohiss after the leakage has not been fully understood. Here we report the prompt enhancements of exohiss waves following substorm injections observed by Van Allen Probes. Within several minutes, the energetic electron fluxes around 100 keV were enhanced by up to 5 times, accompanied by an up to 10-time increase of the exohiss wave power. These substorm-injected electrons are shown to produce a new peak of linear growth rate in the exohiss band(< 0.1 f_(ce)). The corresponding path-integrated growth rate of wave power within 10° latitude of the magnetic equatorial plane can reach 13.4, approximately explaining the observed enhancement of exohiss waves. These observations and simulations suggest that the substorm-injected energetic electrons could amplify the preexisting exohiss waves.展开更多
This is a concise review of physics of the substorm in the magnetotail.It consists of two parts. The first part summarizes historical developments in the early days of the space age(1960-1975)when the basic concepts s...This is a concise review of physics of the substorm in the magnetotail.It consists of two parts. The first part summarizes historical developments in the early days of the space age(1960-1975)when the basic concepts such as magnetotail and reconnection were established and the leading model of the substorm was introduced.The second part is an overview of the research conducted in recent years(1995-2010)when very significant advances have been achieved in understanding the substorm physics by virtue of several major satellites missions that addressed the magnetotail physics intensively.展开更多
The Substorm Current Wedge （SCW） occurrence in the late growth and onset phases of substorms was proposed as the current system which disrupts cross-tail current by diverting it to the ionosphere. The closure curren...The Substorm Current Wedge （SCW） occurrence in the late growth and onset phases of substorms was proposed as the current system which disrupts cross-tail current by diverting it to the ionosphere. The closure current for the SCW originally was suggested to be the strong westward auroral electrojet （WEJ）. However, the SCW-WEJ system has no viable generator current. Similarly, the asymmetric or Partial Ring Current （PRC） increases in strength during the growth phase, and is sometimes associated with an enhanced Region 2 field-aligned current （FAC） closing to the ionosphere, but specifics of that closure have been lacking. Here we present a tmifying picture which includes the SCW post- and pre-midnight （AM and PM, respectively） currents and a generator current in the midnight portion of the PRC system, with these currents based upon a model of the nightside magnetotail magnetic geometry. That geometry consists of open north and south lobe regions surrounding a plasmasheet with two types of closed field line regions-stretched lines in the central part of the plasmasheet （SPS） and dipolar lines （DPS） between the low lati- tude boundary layer （LLBL） regions and the SPS. There is also an important plasmasheet transition region （TPS） in which the dipolar field near the plasmapause gradually transforms to stretched lines near the earthward edge of the SPS, and in which the midnight part of the PRC flows. We propose that our proposed near-onset current system consists of a central current which be- comes part of the midnight sector PRC and which is the generator, to which are linked two three-part current systems, one on the dawnside and one on the duskside. The three-part systems consist of up and down FACs closing as Pedersen currents in the iono- sphere. These 3-part systems are not activated until near-onset is reached, because of a lack of ionospheric conductivity in the appropriate locations where the Pedersen current closure occurs. The initial downward FAC of the 3-part dawnside system and the final upward FAC of the 3-part duskside system correspond to the AM and PM current segments, respectively, of the originally proposed SCW.展开更多
Both theory and simulation have played important roles in defining and illuminating the key mechanisms involved in substorms.Basic theories of magnetic reconnection and of interchange and ballooning instabilities were...Both theory and simulation have played important roles in defining and illuminating the key mechanisms involved in substorms.Basic theories of magnetic reconnection and of interchange and ballooning instabilities were developed more than 50 years ago,and these plasma physical concepts have been central in discussions of substorm physics.A vast amount of research on reconnection,including both theoretical and computational studies,has helped provide a picture of how reconnection operates in the collisionless environment of the magnetosphere.Still,however,we do not fully understand how key microscale processes and large-scale dynamics work together to determine the location and rate of reconnection.While in the last twenty years,it has become clear that interchange processes are important for transporting plasma through the plasma sheet in the form of bursty bulk flows and substorm expansions,we still have not reached the point where simulations are able to realistically and defensibly represent all of the important aspects of the phenomenon.More than two decades ago it was suggested that the ballooning instability,the basic theory for which dates from the 1950s,may play an important role in substorms.Now the majority of experts agree that regions of the plasma sheet are often linearly unstable to ideal-MHD ballooning.However,it is also clear that kinetic effects introduce important modifications to the MHD stability criterion.It is still uncertain whether ballooning plays a leading role in substorms or has just a minor part.Among the different types of simulations that have been applied to the substorm problem,global MHD codes are unique in that,in a sense, they represent the entire global substorm phenomenon,including coupling to the solar wind and ionosphere, and the important mechanisms of reconnection,interchange,and ballooning.However,they have not yet progressed to the point where they can accurately represent the whole phenomenon,because grid-resolution problems limit the accuracy with which they can solve the equations of ideal MHD and the couphng to the ionosphere,and they cannot accurately represent small-scale processes that violate ideal MHD.展开更多
Geomagnetic storms and substorms play a central role in both the daily life of mankind and in academic space physics.The profiles of storms,especially their initial phase morphology and the intensity of their substorm...Geomagnetic storms and substorms play a central role in both the daily life of mankind and in academic space physics.The profiles of storms,especially their initial phase morphology and the intensity of their substorms under different interplanetary conditions,have usually been ignored in previous studies.In this study,97 intense geomagnetic storms(Dstmin≤–100 nT)between 1998 and 2018 were studied statistically using the double superposed epoch analysis(DSEA)and normalized superposed epoch analysis(NSEA)methods.These storms are categorized into two types according to different interplanetary magnetic field(IMF)Bz orientations:geomagnetic storms whose IMF is northward,both upstream and downstream relative to the interplanetary shock,and geomagnetic storms whose upstream and downstream IMF is consistently southward.We further divide these two types into two subsets,by different geomagnetic storm profiles:Type Ⅰ/Type Ⅱ—one/two-step geomagnetic storms with northward IMF both upstream and downstream of the interplanetary shock;Type Ⅲ/TypeⅣ—one/two-step geomagnetic storms with southward IMF both upstream and downstream of the interplanetary shock.The results show that:(1)geomagnetic storms with northward IMF both upstream and downstream of the interplanetary shock have a clear initial phase;geomagnetic storms with southward IMF in both upstream and downstream of the interplanetary shock do not;(2)the IMF is an important controlling factor in affecting the intensity characteristics of substorms.When Bz is positive before and after the interplanetary shock arrival,the Auroral Electrojet(AE)index changes gently during the initial phase of geomagnetic storms,the median value of AE index is maintained at 500–1000 nT;(3)when Bz is negative before and after the interplanetary shock arrival,the AE index rises rapidly and reaches its maxmum value about one hour after storm sudden commencements(SSC),although the time is scaled between reference points and the maximum value of AE is usually greater than 1,000 nT,representing intense substorms;(4)for most cases,the Dst0 usually reaches its minimum at least one hour after Bz.These results are useful in improving contemporary space weather models,especially for those that address geomagnetic storms and substorms.展开更多
The characteristics of a strong aurora substorm observed at Antarctic Zhongshan station (magnetic latitude=74.5°) on 8 April, 1999, were discussed and analyzed. The developing steps of the aurora substorm that ha...The characteristics of a strong aurora substorm observed at Antarctic Zhongshan station (magnetic latitude=74.5°) on 8 April, 1999, were discussed and analyzed. The developing steps of the aurora substorm that happened in dusk time were almost the same with that of midnight aurora substorm. The averaged moving speed of the aurora arc toward pole area during the substorm expansion phase was about 3.0 km/s, westward-traveling surge speed was about 2.0 km/s. The extension from south to north in the substorm can cover 1100 km in distance.展开更多
Magnetic reconnection is one of the most important,dynamic phenomena in the magnetotail in terms of magnetic field line configuration change and energy release.It is believed to occur in the distant magnetotail mainly...Magnetic reconnection is one of the most important,dynamic phenomena in the magnetotail in terms of magnetic field line configuration change and energy release.It is believed to occur in the distant magnetotail mainly during southward interplanetary magnetic field periods and in the near-Earth magnetotail in association with substorms.In the present paper,we discuss several important issues concerning magnetic reconnection in the magnetotail associated with substorms,such as reconnection signatures,location,timing,spatial scale,and behavior,from the macroscopic,observational point of view.展开更多
The auroral electrojet index is an important index in monitoring and predicting substorms.A substorms usually includes auroral breakup,auroral electrojet event marked by AE increase,energetic particle injection at geo...The auroral electrojet index is an important index in monitoring and predicting substorms.A substorms usually includes auroral breakup,auroral electrojet event marked by AE increase,energetic particle injection at geosynchronous orbit,mid-low latitude Pi2,etc.However the question whether an auroral electrojet event corresponds to a substorms remains unanswered.Using the auroral electrojet index in 2004,we analyzed five auroral electrojet events and studied their relation with substorms.The results show that there are three kinds of auroral electrojet events:(1) simultaneous rapid increase of westward auroral electrojet and eastward auroral electrojet;(2) rapid increase of westward auroral electrojet and almost unchangeable eastward auroral electrojet;(3) rapid increase of eastward auroral electrojet and almost unchangeable westward auroral electrojet.Most of auroral electrojet events correspond to substorms.However a few auroral electrojet events are not accompanied by substorms.This situation most often occurs for the auroral electrojet event in which eastward auroral electrojet dominates.展开更多
The cause of substorm onset is not yet understood. Chen CX(2016) proposed an entropy switch model, in which substorm onset results from the development of interchange instability. In this study, we sought observationa...The cause of substorm onset is not yet understood. Chen CX(2016) proposed an entropy switch model, in which substorm onset results from the development of interchange instability. In this study, we sought observational evidence for this model by using Time History of Events and Macroscale Interactions during Substorms(THEMIS) data. We examined two events, one with and the other without a streamer before substorm onset. In contrast to the stable magnetosphere, where the total magnetic field strength is a decreasing function and entropy is an increasing function of the downtail distance, in both events the total magnetic field strength and entropy were reversed before substorm onset. After onset, the total magnetic field strength, entropy, and other plasma quantities fluctuated. In addition, a statistical study was performed. By confining the events with THEMIS satellites located in the downtail region between ~8 and ~12 Earth radii, and 3 hours before and after midnight, we found the occurrence rate of the total magnetic field strength reversal to be 69% and the occurrence rate of entropy reversal to be 77% of the total 205 events.展开更多
This paper gives a brief account of substorm modeling with different key elements or factors. The progress of our understanding of substorms consists of three chief stages during this century. Nine previous substorm m...This paper gives a brief account of substorm modeling with different key elements or factors. The progress of our understanding of substorms consists of three chief stages during this century. Nine previous substorm models are briefly recapitulated, and then a recent two neutral-points model by Prof. C.T. Russell is introduced. In order to test or to strengthen this new model, several correlated examples of meaningful data are duly given in this short paper.展开更多
This paper discusses the problems we confront in the study of magnetospheric substorms. This includes the global processes of magnetospheric substorms, the origin of the southern-northern component of interplanetary m...This paper discusses the problems we confront in the study of magnetospheric substorms. This includes the global processes of magnetospheric substorms, the origin of the southern-northern component of interplanetary magnetic field, quantitative effects of the interplanetary conditions, driving processes of the solar wind, location of the triggering of the expansion phase, and relationship between magnetospheric storms and substorms. Moreover, the research directions in the future have also been discussed.展开更多
对NOAA的POES系列极轨卫星观测得到的1978年以来近30年的极光沉降粒子半球能量的估算值EPI(Estimated Power Input)数据进行了分析,结果表明,极光沉降粒子有显著的春秋分峰值的年变化特征,并且有冬季半球沉降能量较大的南北半球不对称性...对NOAA的POES系列极轨卫星观测得到的1978年以来近30年的极光沉降粒子半球能量的估算值EPI(Estimated Power Input)数据进行了分析,结果表明,极光沉降粒子有显著的春秋分峰值的年变化特征,并且有冬季半球沉降能量较大的南北半球不对称性.对EPI的时均值Pa与地磁指数AE、D_(st)的相关分析得到.Pa与AE的相关系数为0.76,Pa与D_(st)的相关系数为-0.55.把南北半球的时均值SPa,NPa数据分别与AE,D_(st)指数做相关,发现SPa与AE的相关性稍高于NPa的,SPa和NPa与D_(st)的相关性近似.当时延τ=0时,AE与Pa的相关最好,表明全球极光沉降粒子和极光电集流的变化同步;当D_(st)滞后于Pa,时延τ=1～2 h,Pa与D_(st)的相关最好,并且时延τ为6～8 h,Pa与D_(st)的相关都好于无时延的水平.展开更多
基金supported by NSFC research Grant 42274200National Key R&D Program of China 2023YFC2808900the International Space Science Institute(ISSI)in Bern,through ISSI International Team project#24-628-Precipitation of Energetic Particles from Magnetosphere and Their Effects on the Atmosphere.
文摘Geomagnetic substorms release plasma and energy from the magnetotail to the inner magnetosphere and high latitude ionosphere.In this study,we investigate substorms of different time duration,observed during the years 1982 to 2012.We measure substorm duration by a method based on the SME index.Our results demonstrate that longer-duration substorms occur more frequently during solar maximum years,and more frequently between the months of May and July,likely due to the higher polar ionospheric conductivity and more sunward geomagnetic pole directions during summer in the northern hemisphere.Additionally,longer substorms occur more frequently under stronger,longer-lasting southward IMF,and are accompanied by slower solar winds,suggesting that extended magnetic reconnection is required to drive longer substorms.Substorm durations are not significantly related to the minimum SML index,but longer substorms usually have higher SMU and continuously rising PC indices.The SME indices of long-duration substorms show a bimodal MLT distribution located near midnight and dusk after substorm onset,with the peak originally at midnight moving eastward to the morning side during the late recovery phase.Longer duration substorms have a stronger effect on the overall ring current at all MLT sectors except dawnside.Our results provide new insights into the development process and influencing factors of substorms,from the expansion phase to the recovery phase.
基金supported by National Natural Science Foundation of China (41674155 and 41274147)Youth Innovation Promotion Association of Chinese Academy of Sciences (No.2017258)Key Research Project of Chinese Academy of Sciences:Application Research on the Scientific Data from Chang’E-3 Mission (KGZD-EW-603)
文摘The plasmapause locations determined from the Chang'e-3(CE-3) Extreme Ultraviolet Camera(EUVC) images and the auroral boundaries determined from the Defense Meteorological Satellite Program(DMSP) Special Sensor Ultraviolet Spectrographic Imager(SSUSI) images are used to investigate the plasmaspheric evolutions during substorms. The most important finding is a nightside pointing plasmaspheric plume observed at 23:05 UT on 21 April 2014 under quiet solar wind and geomagnetic conditions, which drifted from the dusk sector. High correlations between the plasmapause evolutions and the auroral signatures exist during substorms. After substorm onset, the plasmapause erosion and the equatorward expansion of the auroral oval occur almost simultaneously in both MLT and UT, and then both the erosion and the expansion propagate westward and eastward. It is suggested that the plasmaspheric erosion and its MLT propagations are induced by the enhanced earthward plasma convection during substorm period, and the substorm dipolarization causes pitch-angle scattering of plasma sheet electrons and the resulting precipitation excites aurora emissions at the same time.
基金supported by the National Natural Science Foundation of China(NSFC)under grants 41731070,41674167,41574161the Strategic Pioneer Program on Space Science,Chinese Academy of Sciences,grants XDA15052500,XDA15350201 and XDA15011401the Specialized Research Fund for State Key Laboratories of China.
文摘With conjunction observations of electromagnetic fields and plasma from Time History of Events and Macroscale Interactions during Substorm(THEMIS)in the near-Earth magnetotail,we investigate the spatial and temporal properties of substorm dipolarizations in the near-Earth plasma sheet(NEPS)during a substorm at 03:23 UT on 12 February 2008.Substorm dipolarizations with different features are detected by three near-Earth THEMIS probes(THA(P5),THD(P3)and THE(P4))in the magnetotail.In the current sheet with a large plasma beta value(β>2,whereβis the ratio of the plasma thermal pressure to the magnetic pressure),the dipolarization within the substorm onset region,(−10.4,2.8,−2.6)RE_gsm,has a large initial magnetic field elevation angle,θ>60°,θ=arctan(Bz/(Bx2+By2)1/2),and is accompanied by energetic ion(tens to hundred keV)dispersionless injection detected by THD(P3).This substorm onset dipolarization is characterized by Bx and By components around 0 nT with significant fluctuations.The Bz component increases sharply and its subsequent magnitude approaches the total magnetic field,Bt.The maximum value of the elevation angle approaches 85°during the later substorm expansion phase.In the NEPS withβ~1,the dipolarization outside the substorm onset region is characterized by a magnetic elevation angle with a small beginning value ofθ<45°and following multi-step enhancements during the substorm expansion phase.The maximum value of the elevation angle approaches to 70°during the later substorm expansion phase.Our observation results indicate that characteristics of dipolarization with a large beginning elevation angle within the substorm onset region provide a new indicator to identify substorm onset location.
基金supported by National Natural Science Foundation of China grants 41631071, 41774170, 41274174, 41174125, 41131065, 41421063, 41231066 and 41304134Chinese Academy of Sciences grants KZCX2-EW-QN510 and KZZD-EW-01-4+2 种基金CAS Key Research Program of Frontier Sciences grant QYZDB-SSWDQC015National Key Basic Research Special Foundation of China Grant No. 2011CB811403Fundamental Research Funds for the Central Universities WK2080000077
文摘Exohiss is a low-frequency structureless whistler-mode emission potentially contributing to the precipitation loss of radiation belt electrons outside the plasmasphere. Exohiss is usually considered the plasmaspheric hiss leaked out of the dayside plasmapause.However, the evolution of exohiss after the leakage has not been fully understood. Here we report the prompt enhancements of exohiss waves following substorm injections observed by Van Allen Probes. Within several minutes, the energetic electron fluxes around 100 keV were enhanced by up to 5 times, accompanied by an up to 10-time increase of the exohiss wave power. These substorm-injected electrons are shown to produce a new peak of linear growth rate in the exohiss band(< 0.1 f_(ce)). The corresponding path-integrated growth rate of wave power within 10° latitude of the magnetic equatorial plane can reach 13.4, approximately explaining the observed enhancement of exohiss waves. These observations and simulations suggest that the substorm-injected energetic electrons could amplify the preexisting exohiss waves.
文摘This is a concise review of physics of the substorm in the magnetotail.It consists of two parts. The first part summarizes historical developments in the early days of the space age(1960-1975)when the basic concepts such as magnetotail and reconnection were established and the leading model of the substorm was introduced.The second part is an overview of the research conducted in recent years(1995-2010)when very significant advances have been achieved in understanding the substorm physics by virtue of several major satellites missions that addressed the magnetotail physics intensively.
文摘The Substorm Current Wedge （SCW） occurrence in the late growth and onset phases of substorms was proposed as the current system which disrupts cross-tail current by diverting it to the ionosphere. The closure current for the SCW originally was suggested to be the strong westward auroral electrojet （WEJ）. However, the SCW-WEJ system has no viable generator current. Similarly, the asymmetric or Partial Ring Current （PRC） increases in strength during the growth phase, and is sometimes associated with an enhanced Region 2 field-aligned current （FAC） closing to the ionosphere, but specifics of that closure have been lacking. Here we present a tmifying picture which includes the SCW post- and pre-midnight （AM and PM, respectively） currents and a generator current in the midnight portion of the PRC system, with these currents based upon a model of the nightside magnetotail magnetic geometry. That geometry consists of open north and south lobe regions surrounding a plasmasheet with two types of closed field line regions-stretched lines in the central part of the plasmasheet （SPS） and dipolar lines （DPS） between the low lati- tude boundary layer （LLBL） regions and the SPS. There is also an important plasmasheet transition region （TPS） in which the dipolar field near the plasmapause gradually transforms to stretched lines near the earthward edge of the SPS, and in which the midnight part of the PRC flows. We propose that our proposed near-onset current system consists of a central current which be- comes part of the midnight sector PRC and which is the generator, to which are linked two three-part current systems, one on the dawnside and one on the duskside. The three-part systems consist of up and down FACs closing as Pedersen currents in the iono- sphere. These 3-part systems are not activated until near-onset is reached, because of a lack of ionospheric conductivity in the appropriate locations where the Pedersen current closure occurs. The initial downward FAC of the 3-part dawnside system and the final upward FAC of the 3-part duskside system correspond to the AM and PM current segments, respectively, of the originally proposed SCW.
基金supported by the NASA Heliospheric Theory Program under grant NNX08AI55G
文摘Both theory and simulation have played important roles in defining and illuminating the key mechanisms involved in substorms.Basic theories of magnetic reconnection and of interchange and ballooning instabilities were developed more than 50 years ago,and these plasma physical concepts have been central in discussions of substorm physics.A vast amount of research on reconnection,including both theoretical and computational studies,has helped provide a picture of how reconnection operates in the collisionless environment of the magnetosphere.Still,however,we do not fully understand how key microscale processes and large-scale dynamics work together to determine the location and rate of reconnection.While in the last twenty years,it has become clear that interchange processes are important for transporting plasma through the plasma sheet in the form of bursty bulk flows and substorm expansions,we still have not reached the point where simulations are able to realistically and defensibly represent all of the important aspects of the phenomenon.More than two decades ago it was suggested that the ballooning instability,the basic theory for which dates from the 1950s,may play an important role in substorms.Now the majority of experts agree that regions of the plasma sheet are often linearly unstable to ideal-MHD ballooning.However,it is also clear that kinetic effects introduce important modifications to the MHD stability criterion.It is still uncertain whether ballooning plays a leading role in substorms or has just a minor part.Among the different types of simulations that have been applied to the substorm problem,global MHD codes are unique in that,in a sense, they represent the entire global substorm phenomenon,including coupling to the solar wind and ionosphere, and the important mechanisms of reconnection,interchange,and ballooning.However,they have not yet progressed to the point where they can accurately represent the whole phenomenon,because grid-resolution problems limit the accuracy with which they can solve the equations of ideal MHD and the couphng to the ionosphere,and they cannot accurately represent small-scale processes that violate ideal MHD.
文摘Geomagnetic storms and substorms play a central role in both the daily life of mankind and in academic space physics.The profiles of storms,especially their initial phase morphology and the intensity of their substorms under different interplanetary conditions,have usually been ignored in previous studies.In this study,97 intense geomagnetic storms(Dstmin≤–100 nT)between 1998 and 2018 were studied statistically using the double superposed epoch analysis(DSEA)and normalized superposed epoch analysis(NSEA)methods.These storms are categorized into two types according to different interplanetary magnetic field(IMF)Bz orientations:geomagnetic storms whose IMF is northward,both upstream and downstream relative to the interplanetary shock,and geomagnetic storms whose upstream and downstream IMF is consistently southward.We further divide these two types into two subsets,by different geomagnetic storm profiles:Type Ⅰ/Type Ⅱ—one/two-step geomagnetic storms with northward IMF both upstream and downstream of the interplanetary shock;Type Ⅲ/TypeⅣ—one/two-step geomagnetic storms with southward IMF both upstream and downstream of the interplanetary shock.The results show that:(1)geomagnetic storms with northward IMF both upstream and downstream of the interplanetary shock have a clear initial phase;geomagnetic storms with southward IMF in both upstream and downstream of the interplanetary shock do not;(2)the IMF is an important controlling factor in affecting the intensity characteristics of substorms.When Bz is positive before and after the interplanetary shock arrival,the Auroral Electrojet(AE)index changes gently during the initial phase of geomagnetic storms,the median value of AE index is maintained at 500–1000 nT;(3)when Bz is negative before and after the interplanetary shock arrival,the AE index rises rapidly and reaches its maxmum value about one hour after storm sudden commencements(SSC),although the time is scaled between reference points and the maximum value of AE is usually greater than 1,000 nT,representing intense substorms;(4)for most cases,the Dst0 usually reaches its minimum at least one hour after Bz.These results are useful in improving contemporary space weather models,especially for those that address geomagnetic storms and substorms.
基金Sup POrted by the National Natural Science FOundation of China(4 96 3416 0 )
文摘The characteristics of a strong aurora substorm observed at Antarctic Zhongshan station (magnetic latitude=74.5°) on 8 April, 1999, were discussed and analyzed. The developing steps of the aurora substorm that happened in dusk time were almost the same with that of midnight aurora substorm. The averaged moving speed of the aurora arc toward pole area during the substorm expansion phase was about 3.0 km/s, westward-traveling surge speed was about 2.0 km/s. The extension from south to north in the substorm can cover 1100 km in distance.
基金Supported in part by the Global COE Program of Nagoya University "Quest for Fundamental Principles in the Universe(QFPU)" from JSPS and MEXT of Japan
文摘Magnetic reconnection is one of the most important,dynamic phenomena in the magnetotail in terms of magnetic field line configuration change and energy release.It is believed to occur in the distant magnetotail mainly during southward interplanetary magnetic field periods and in the near-Earth magnetotail in association with substorms.In the present paper,we discuss several important issues concerning magnetic reconnection in the magnetotail associated with substorms,such as reconnection signatures,location,timing,spatial scale,and behavior,from the macroscopic,observational point of view.
基金Supported by the Pilot Project of the Knowledge Innovation Program of Chinese Academy of Sciences
文摘The auroral electrojet index is an important index in monitoring and predicting substorms.A substorms usually includes auroral breakup,auroral electrojet event marked by AE increase,energetic particle injection at geosynchronous orbit,mid-low latitude Pi2,etc.However the question whether an auroral electrojet event corresponds to a substorms remains unanswered.Using the auroral electrojet index in 2004,we analyzed five auroral electrojet events and studied their relation with substorms.The results show that there are three kinds of auroral electrojet events:(1) simultaneous rapid increase of westward auroral electrojet and eastward auroral electrojet;(2) rapid increase of westward auroral electrojet and almost unchangeable eastward auroral electrojet;(3) rapid increase of eastward auroral electrojet and almost unchangeable westward auroral electrojet.Most of auroral electrojet events correspond to substorms.However a few auroral electrojet events are not accompanied by substorms.This situation most often occurs for the auroral electrojet event in which eastward auroral electrojet dominates.
基金supported by the National Natural Science Foundation of China(Grant No.NSFC41974204)。
文摘The cause of substorm onset is not yet understood. Chen CX(2016) proposed an entropy switch model, in which substorm onset results from the development of interchange instability. In this study, we sought observational evidence for this model by using Time History of Events and Macroscale Interactions during Substorms(THEMIS) data. We examined two events, one with and the other without a streamer before substorm onset. In contrast to the stable magnetosphere, where the total magnetic field strength is a decreasing function and entropy is an increasing function of the downtail distance, in both events the total magnetic field strength and entropy were reversed before substorm onset. After onset, the total magnetic field strength, entropy, and other plasma quantities fluctuated. In addition, a statistical study was performed. By confining the events with THEMIS satellites located in the downtail region between ~8 and ~12 Earth radii, and 3 hours before and after midnight, we found the occurrence rate of the total magnetic field strength reversal to be 69% and the occurrence rate of entropy reversal to be 77% of the total 205 events.
文摘This paper gives a brief account of substorm modeling with different key elements or factors. The progress of our understanding of substorms consists of three chief stages during this century. Nine previous substorm models are briefly recapitulated, and then a recent two neutral-points model by Prof. C.T. Russell is introduced. In order to test or to strengthen this new model, several correlated examples of meaningful data are duly given in this short paper.
文摘This paper discusses the problems we confront in the study of magnetospheric substorms. This includes the global processes of magnetospheric substorms, the origin of the southern-northern component of interplanetary magnetic field, quantitative effects of the interplanetary conditions, driving processes of the solar wind, location of the triggering of the expansion phase, and relationship between magnetospheric storms and substorms. Moreover, the research directions in the future have also been discussed.
文摘对NOAA的POES系列极轨卫星观测得到的1978年以来近30年的极光沉降粒子半球能量的估算值EPI(Estimated Power Input)数据进行了分析,结果表明,极光沉降粒子有显著的春秋分峰值的年变化特征,并且有冬季半球沉降能量较大的南北半球不对称性.对EPI的时均值Pa与地磁指数AE、D_(st)的相关分析得到.Pa与AE的相关系数为0.76,Pa与D_(st)的相关系数为-0.55.把南北半球的时均值SPa,NPa数据分别与AE,D_(st)指数做相关,发现SPa与AE的相关性稍高于NPa的,SPa和NPa与D_(st)的相关性近似.当时延τ=0时,AE与Pa的相关最好,表明全球极光沉降粒子和极光电集流的变化同步;当D_(st)滞后于Pa,时延τ=1～2 h,Pa与D_(st)的相关最好,并且时延τ为6～8 h,Pa与D_(st)的相关都好于无时延的水平.
