Magnetospheric Physics in China*

CAO Jinbin YANG Junying

Magnetospheric Physics in China*

CAO Jinbin YANG Junying

(100191) (100191)

In the past two years, many progresses were made in Magnetospheric Physics by using the data of SuperMAG, Double Star Program, Cluster, THEMIS, RBSP, DMSP, DEMETER, NOAA, Van Allen probe, Swarm, MMS, ARTEMIS, MESSENGER, Fengyun, BeiDa., or by computer simulations. This paper briefly reviews these works based on papers selected from the 248 publications from January 2018 to December 2019. The subjects covered various sub-branches of Magnetospheric Physics, including geomagnetic storm, magnetospheric substorm, magnetic reconnection, solar wind-magnetosphere-ionosphere interaction, radiation belt, ring current, whistler waves, plasmasphere, outer magnetosphere, magnetotail, planetary magnetosphere, and technique.

Magnetospheric physics, Data, Computer simulations

1 Geomagnetic Storms

In Ref[1], the occurrence probability of extreme geomagnetic storms is estimated by applying Extreme Value Theory (EVT) to the geomagnetic activityindex. Theindex has 172 years’ observation time span, which is much longer than other geomagnetic indices, and thus is more suitable for analysis for rarely occurred extreme geomagnetic storms. They use two newly developed EVT methods, Block Maxima Method (BMM) and Peak Over Threshold (POT), and find that the extreme geomagnetic storm happened in March 1989 may happen once per century. This result implies that they should pay more attention to such extreme geomagnetic storms that can cause Space Weather hazards.

从广州出发飞 行了16个小时，再坐上2小时的大巴，穿越一片片平坦开阔的葡萄园、橄榄园，路过一栋栋白色或浅黄色的石屋，终于抵达普利亚产区的中心城市：曼杜里亚。此时接近正午，阳光正好，清劲的海风扑面而来，一下子驱散了长途旅行的不适。空气中弥漫着橄榄香、泥土香，暖暖的，非常惬意。放眼望去，都是狭窄的石头街道、古老的石头房子和教堂，街上行人寥寥。

Based on the data from the SuperMAG collaboration in 2000–2014, the Magnetic Latitude (MLAT) location of the Ring Current (RC) denoted by the MLAT of the maximum horizontal magnetic disturbance during the main phase of 67 intense geomagnetic storms (≤–100 nT) are derived. The results of Liu[2]show that the maximum horizontal magnetic disturbance does not always occur in the magnetic equator, indicating that the RC might be tilted in the latitudinal direction during these storms. Specifically, the tilt of the RC near the day-night line is affected by the direction of solar wind. When the solar wind flows southward against the magnetic equatorial plane, the RC is more likely to show a dayside-lifted tilt. When the solar wind flows northward, the pattern is opposite. Tilts of the RC near the dawn-dusk line are also found in most of these storms. The location of the RC is mainly lifted in the dusk side and declined in the dawn side for positive IMFB, while the tilt is reversed for negative IMFB. A possible interpretation might be the IMFB-related twisting of the geomagnetic field. Besides, the monthly averaged MLAT of the fitted RC also varies with seasons. It is shifted to the southern hemisphere in the northern summer and to the northern hemisphere in the northern winter, which might indicate that the RC is not centered on a single plane. Such a seasonal variation might be related to the angle between the solar wind and the magnetic equatorial plane.

The temporal and spatial evolution of Electromagnetic Ion Cyclotron (EMIC) waves during the magnetic storm of 21–29 June 2015 is investigated by Wang[3]using high-resolution magnetic field observations from Swarm constellation in the ionosphere and Van Allen Probes in the magnetosphere. Magnetospheric EMIC waves had a maximum occurrence frequency in the afternoon sector and shifted equatorward during the expansion phase and poleward during the recovery phase. However, ionospheric waves in subauroral regions occurred more frequently in the nighttime than during the day and exhibited less obvious latitudinal movements. During the main phase, dayside EMIC waves occurred in both the ionosphere and magnetosphere in response to the dramatic increase in the solar wind dynamic pressure. Waves were absent in the magnetosphere and ionosphere around the minimum Sym-. During the early recovery phase, He+band EMIC waves were observed in the ionosphere and magnetosphere. During the late recovery phase, H+band EMIC waves emerged in response to enhanced earthward convection during substorms in the pre-midnight sector. The occurrence of EMIC waves in the noon sector was affected by the intensity of substorm activity. Both ionospheric wave frequency and power were higher in the summer hemisphere than in the winter hemisphere. Waves were confined to an MLT interval of less than 5 h with a duration of less than 186 min from coordinated observations. The results could provide additional insights into the spatial characteristics and propagation features of EMIC waves during storm periods.

During periods of storm activity and enhanced convection, the plasma density in the afternoon sector of the magnetosphere is highly dynamic due to the development of Plasmaspheric Drainage Plume (PDP) structure. This significantly affects the local Alfvén speed and alters the propagation of ULF waves launched from the magnetopause. Therefore, it can be expected that the accessibility of ULF wave power for radiation belt energization is sensitively dependent on the recent history of magnetospheric convection and the stage of development of the PDP. This is investigated using a 3D model for ULF waves within the magnetosphere in which the plasma density distribution is evolved using an advection model for cold plasma, driven by a (VollandStern) convection electrostatic field (resulting in PDP structure). The wave model includes magnetic field day/night asymmetry and extends to a paraboloid dayside magnetopause, from which ULF waves are launched at various stages during the PDP development. Degeling[4]find that the plume structure significantly alters the field line resonance location, and the turning point for MHD fast waves, introducing strong asymmetry in the ULF wave distribution across the noon meridian. Moreover, the density enhancement within the PDP creates a waveguide or local cavity for MHD fast waves, such that eigenmodes formed allow the penetration of ULF wave power to much lowerwithin the plume than outside, providing an avenue for electron energization.

Based on a calculated open×convection passage of a flux tube with Subauroral Polarization Streams (SAPS) electric field involved, Qiao[5]use the Dynamic Fluid-Kinetic model to simulate the transport of major ion species (H+, He+, and O+) along magnetic field line (field-aligned) within the flux tube during the 2015 St. Patrick’s Day storm. The drift trajectory is confirmed to be quite realistic based on observations and empirical models, mean­while, the foot print of flux tube is initiated from subauroral latitudes toward polar latitudes along this drift pass. The Dynamic Fluid-Kinetic simulation displays interesting temporal evolution of the field- aligned plasma distribution at subauroral latitudes: The storm enhanced density region continuously provides upward ion flux filling into plasmasphere, but the equatorial mass loading in plasmaspheric plume increases at first and then decreases. Further analyses found that the SAPS particularly impact the field-aligned transport of O+particles from ionosphere to plasmasphere but have much less effect on H+and He+particles at subauroral latitudes, which causes significant enhancements of equatorial O+density. The results show that the SAPS have significant effects on both drifting trajectory of the flux tube and associated field-aligned ion dynamics. This work reveals intimate storm time interaction between the inner magnetosphere and ionosphere which may affect the dynamics in outer magnetosphere or even at magnetopause with flux tube convection.

Three different episodes of Prompt Penetration Electric Field (PPEF) disturbances are observed during the main phase of the St. Patrick’s Day storm on 17 March 2015 under steady southward Interplanetary Magnetic Field (IMF)Bconditions unlike the conventional PPEF associated with southward or northward turnings of IMFB. As reported by Tulasi[6], these PPEF events took place during the period when strong disturbance dynamo fields are prevailing in the background. The first event is triggered by a solar wind dynamic pressure pulse that caused a sharp eastward PPEF and strong enhancement of equatorial electrojet current in Brazilian dayside. The second event caused another short but strong westward PPEF on dayside due to the reversal of IMFBfrom duskward to dawnward under steady IMFB. The third event caused a longer eastward PPEF in association with a solar wind dynamic pressure pulse followed by the onset of a substorm, which has led to strong enhancement of equatorial electrojet, quick rejuvenation and symmetric redistribution of equatorial ionization anomaly in the Brazilian sector. The signatures of the PPEF with opposite polarity and smaller magnitudes are also observed in the Asian sector on the nightside. The possible mechanisms for the observed PPEF events under steady IMFBare discussed in terms of changes in the high-latitude field-aligned currents and reconfiguration of high-latitude convection fields using Active Magnetosphere and Planetary Electro­dynamics Response Experiment and Super Dual Auroral Radar Network high-frequency radar observations.

我们发现，Painless DPN组较Non-DPN组左侧丘脑局部一致性减低。丘脑是除嗅觉外所有感觉传至大脑皮层的集中部位，是皮质下感觉的最后中继站，起到重要的感觉加工和信号调制功能［21］。有研究表明［22］，维持丘脑神经元功能可能是糖尿病患者感知神经性疼痛症状的先决条件。本研究中，Painless DPN组丘脑局部神经元活动降低，提示丘脑神经功能受损，这也许可以解释为何部分DPN患者不出现神经性疼痛症状。

He[9]report multi-satellite observations of the oscillations in the Subauroral Polarization Strea­m (SAPS) during a severe magnetic storm on 20 November 2003. The SAPS oscillations (SAPSOs) occurred during the main phase of the magnetic storm when thecomponent of the southward interplanetary magnetic field (IMFB) turned from positive to negative. The SAPSOs were first observed in the pre-midnight sector and propagated toward the dusk sector. The formation and evolution of SAPSO corresponded well with the plasma sheet ions injection and precipitation, indicating that the SAPSOs are possibly generated by the interaction between the hot plasma sheet and the cold plasmasphere under particular conditions (., change of the polarity of IMFBaccompanied with a sudden enhancement of plasma sheet ion density). The hemispheric asymmetry of the SAPS channels is suggested to be related to the hemispheric differences in the ionospheric plasma condition and the ionospheric convection.

He[12]present multisatellite observations of the large-scale structures of Subauroral Polarization Streams (SAPS) during the main phase of a severe geomagnetic storm that occurred on 31 March 2001. Observations by the Defense Meteorological Satellite Program F12 to F15 satellites indicate that the SAPS were first generated around the dusk sector at the beginning of the main phase. The SAPS channel then expanded toward the midnight sector and moved to lower latitudes as the main phase progressed. The peak velocity, latitudinal width, latitudinal alignment, and longitudinal span of the SAPS channel were highly dynamic during the storm main phase. The large westward velocities of the SAPS were located in the region of low electron densities, associated with low ionospheric conductivity. The large-scale structures of the SAPS also corresponded closely to those of the Region-2 field- aligned currents, which were mainly determined by the azimuthal pressure gradient of the ring current.

Spacecraft surface charging during geomagnetically disturbed times is one of the most important causes of satellite anomalies. Predicting the surface charging environment is one prevalent task of the geospace environment models. Therefore, the Geospace Environment Modeling (GEM) Focus Group “Inner Magnetosphere Cross-energy/Popu­lation Interactions” initiated a community-wide challenge study to assess the capability of several inner magnetosphere ring current models in determining surface charging environment for the Van Allen Probes orbits during the 17 March 2013 storm event. The integrated electron flux between 10 and 50 keV is used as the metrics. Various skill scores are applied to quantitatively measure the modeling performance against observations. Results indicate that no model consistently performs the best in all of the skill scores or for both satellites. Yu[13]find that from these simulations the ring current model with observational f­lux boundary condition and Weimer electric potential driver generally reproduces the most realistic flux level around the spacecraft. A simple and weaker Volland-Stern electric field is not capable of effectively transporting the same plasma at the boundary toward the Earth. On the other hand, if the ring current model solves the electric field self-consistently and obtains similar strength and pattern in the equatorial plane as the Weimer model, the boundary condition plays another crucial role in determining the electron flux level in the inner region. When the boundary flux spectra based on Magnetohydrodynamics (MHD) model/empirical model deviate from the shape or magnitude of the observed distribution function, the simulation produces poor skill scores along Van Allen Probes orbits.

2 Magnetospheric Substorms

Substorm injections are one of the most dynamic processes in Earth’s magnetosphere and have global consequences and broad implications for Space Weather modeling. They can be monitored using energetical electron detectors on geosynchronous satellites. The Imaging Electron Spectrometer (IES) onboard a Chinese navigation satellite, launched on 16 October 2015 into an Inclined Geosynchronous Satellite Orbit (IGSO), provides the first energetic electron measurement in IGSO orbit to the best of our knowledge. The IES was developed by Peking University and is named hereafter as BD-IES. Using a pinhole technique, the BD-IES instrument measures 50~600 keV incident electrons in eight energy channels from nine directions covering a range of 180° in polar angle. Data collection by the BD-IES instrument have passed the 1-year mark by the time of issue of Zong[14], which reflects a successful milestone for the mission. The innermost and outermost signatures of substorm injection at≈6 and 12 have been observed by the BD-IES with a highshell spatial coverage, complementary to the existing missions such as the Van Allen Probes that covers the range below≈6. There are other two BD-IES instruments to be installed in the coming Chinese Sun-synchronous and geosynchronous satellites, respectively. Such a configuration will provide a unique opportunity to investigate inward and outward radial propagation of the substorm injection region simultaneously at high and low L shells. It will further elucidate potential mechanisms for the particle energization and transport, two of the most important topics in magnetospheric dynamics.

The interaction between Interplanetary (IP) shocks and the Earth’s magnetosphere would gene­rate/excite various types of geomagnetic phenomena. In order to analyze what kind of IP shock is more likely to trigger intense substorms (/>1000 nT) and how the energetic electrons respond to intense substorms at geosynchronous orbit, Ma[15]perform a systematic survey of 246 IP shock events using SuperMag and LANL observations between 2001 and 2013. The statistical analysis shows that intense substorms (>1000 nT) triggered by IP shocks are most likely to occur under the southward Interplanetary Magnetic Field (IMF) and fast solar wind preconditions. Besides, intense substorms after the IP shock arrival are much more likely to occur when IMF points toward (away from) the Sun around spring (autumn) equinox, which can be ascribed to the Russell-McPherron effect. Thus, the IMFs precondition of an IP shock and the Russell-McPherron effect can be considered as precursors of an intense substorm. Furthermore, after the shock arrival associated with intense substorms, low-energy (<200 keV) electron fluxes increase significantly at geosynchronous orbit, and high-energy (>200 keV) electron fluxes decrease. The spectral index becomes softer with intense substorms and remains almost unchanged with moderate substorms no matter whether the IMF precondition is southward or northward.

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 as the plasmaspheric hiss leaked out of the dayside plasmapause. However, the evolution of exohiss after the leakage has not been fully understood. Gao[16]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 (<0.1ce). 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.

Tang and Wang[17]investigate the large-scale substorm current systems developed from its onset in an idealized substorm event simulated by global Magnetohydrodynamic (MHD) models. Mainly three current systems (loops) are revealed: (i) the classical substorm current wedge, which is composed by the disputed cross-tail current in the magnetotail, the nightside westward electrojet in the high-latitude ionosphere and a pair of Region 1 Field-Aligned Currents (FAC); (ii) the partial-ring current system, which is braced by two Region 2 FACs; and (iii) the meridional current system, which is formed by an equatorial radial current (outward/inward in the morning/evening sector), and Region 1 and Region 2 FACs at its two ends. The Region 2 FAC connects with Region 1 FAC by a latitudinal horizontal current at each morning/evening ionosphere to complete Loops 2 and 3. A quantitative study shows the significant enhancement of these current systems during the substorm expansion phase, while Loop 1 dominates, which can reach a magnitude of about 1. Empirical relations among the ionospheric currents and the related magnetotail currents are established based on the simulation results, implying that the substorm current systems are not evolved locally or separately, but must be viewed from a global perspective. This knowledge of large-scale substorm current system would deepen our understanding of the substorm development and could be validated by observations in the future.

The Polar Cap Boundary (PCB) is a fundamental indicator of magnetospheric activities especially during a substorm cycle. Taking a period on 8 March 2008 as an example, Wang[18]investigate the location of PCB and its dynamics during a substorm event. The PCB location is determined from the Piecewise Parabolic Method with a Lagrangian Remap (PPMLR) Magnetohydrodynamic (MHD) simulation data and Defense Meteorological Satellite Program (DMSP) observations, respectively. Model- observation comparison indicates that the PPMLR- MHD model gives a reliable estimate of PCB location during a complex substorm sequence. They further analyze the evolution of PCB in that period. The polar cap expands under southward Interplanetary Magnetic Field (IMF), since the low-latitude dayside reconnection produces new open magnetic flux. Meanwhile, more solar wind energy enters and stores in the magnetosphere with the decreasing SML (SuperMAG Auroral Lower) index. After the substorm expansion onset, the polar cap contracts for a while due to the explosive increase of nightside reconnection. When the IMF direction turns northward, the polar cap contracts continuously, since the dayside reconnection ceases and no more open ma­gnetic flux are supplied, and the stored energy in the magnetosphere releases with the increasing SML index. The model results are in good accord with the features from observations.

Electromagnetic field and plasma data from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) near-Earth probes are used by Sun[19]to investigate magnetic dipolarizations inside geosynchronous orbit on 27 August 2014 during an intense substorm withmax≈1000 nT. THEMIS-D (TH-D) was located inside geosynchronous orbit around midnight in the interval from 09:25 UT to 09:55 UT. During this period, two distinct magnetic dipolarizations with tailward ion flows are observed by TH-D. The first one is indicated by the magnetic elevation angle increase from 15 to 250 around 09:30:40 UT. The tailward perpendicular velocity is⊥≈–50 km·s–1. The second one is pre­sented by the elevation angle increase from 25 to 450 around 09:36 UT, and the tailward perpendicular velocity is⊥x≈–70 km·s–1. These two significant dipolarizations are accompanied with the sharp increase in the energy flux of energetic electron inside geosynchronous orbit. After a 5 min expansion of the Near-Earth Plasma Sheet (NEPS), THEMISE (TH-E) located outside geosynchronous orbit also detected this tailward expanding plasma sheet with ion flows of –150 km·s–1. The dipolarization propagates tailward with a speed of –47 km·s–1along a 2.2e distance in thedirection between TH-D and TH-E within 5 min. These dipolarizations with tailward ion flows observed inside geosynchronous orbit indicate a new energy transfer path in the inner magnetosphere during substorms.

Electron flux measurements outside Geosynchronous Orbit (GSO) obtained by the BeiDa Imaging Electron Spectrometer instrument onboard a 55° inclined GSO satellite and inside GSO obtained by the Van Allen Probes are analyzed to investigate the temporal and spatial evolutions of the substorm injection region. In 1 year data started from October 2015, 63 injection events are identified. First, Liu[20]show that the injection signatures can be detected in a large radial extent in one single event, for example, from≈4.1 to≈9.3. Second, injection onset times are derived from the energy dispersion of particle injection signatures of each satellite. The difference of the onset times among satellites reveals that the injection boundary, termed as “injection front” in this paper, can propagate both earthward and tailward with a speed varying from a few km·s–1to 100 km·s–1. Third, evolutions of the upper-cutoff magnetic moments (uc) of injected electrons are analyzed, upon which the injection events are classified into two categories. In one category, theucobserved by two radially separated satellites are equal taking into account the error caused by the finite width of energy channels, whereas in the other category,ucat lowershells are smaller than those at highershells.

根据临安区各镇、街雷竹林分布面积，随机选择90户竹农进行问卷调查，获得有效问卷85份。调查内容包括雷竹种植户的年龄、家庭人口、劳动力状况、竹林覆盖面积、成本状况、产出效益、流转愿意、希望的竹林面积等。

As reported by Li and Wang[21], after the passage of an Interplanetary (IP) shock at 06:13 UT on 24 August 2005, the enhancement (>6 nPa) of solar wind dynamic pressure and the southward turning of IMF cause the earthward movement of dayside magnetopause and the drift loss of energetic particles near geosynchronous orbit. The persistent electron drift loss makes the geosynchronous satellites cannot observe the substorm electron injection phenomenon during the two substorm expansion phases (06:57 UT–07:39 UT) on that day. Behind the IP shock, the fluctuations (0.5~3 nPa) of solar wind dynamic pre­ssure not only alter the dayside auroral brightness but also cause the entire auroral oval to swing in the day-night direction. However, there is no Pi2 pulsation in the nightside auroral oval during the substorm growth phase from 06:13 UT to 06:57 UT. During the subsequent two substorm expansion phases, the substorm expansion activities cause the nightside aurora oval brightening from substorm onset site to higher latitudes, and meanwhile, the enhancement (decline) of solar wind dynamic pressure makes the nightside auroral oval move toward the magnetic equator (the magnetic pole). These observations demonstrate that solar wind dynamic pressure changes and substorm expansion activities can jointly control the luminosity and location of the nightside auroral oval when the internal and external disturbances occur simultaneously. During the impact of a strong IP shock, the earthward movement of dayside magnetopause probably causes the disappearance of the substorm electron injections near geosynchronous orbit.

目前，网络和物流已经成为野生动物非法贸易的主要渠道。2018年，全省森林公安机关侦办的野生动物非法贸易案件中，涉及网络和物流的重特大案件达到90%以上。以珍贵、濒危野生动物制品为原材料制作的小型工艺品成为网络野生动物非法贸易的主要种类，购买受法律保护的野生动物为宠物、网购野生动物及其制品等行为依然大量存在。

Yu[22]report a new modeling capability that self-consistently couples physics-based magnetospheric electron precipitation with its impact on the ionosphere. Specifically, the ring current model RAM-SCBE is two-way coupled to an ionospheric electron transport model GLOW (GLobal airglOW), representing a significant improvement over previous models, in which the ionosphere is either treated as a 2D spherical boundary of the magnetosphere or is driven by empirical precipitation models that are incapable of capturing small-scale, transient variations. The new model enables us to study the impact of substorm-associated, spectrum-resolved electron precipitation on the 3D ionosphere. They found that after each substorm injection, a high-energy tail of precipitation is produced in the dawn sector outside the plasmapause, by energetic electrons (10<< 100 keV) scattered by whistler-mode chorus waves. Consequently, an ionospheric sublayer characterized by enhanced Pedersen conductivity arises at unusually low altitude (about 85 km), with its latitudinal width of about 5°~10° in the auroral zone. The sublayer structure appears intermittently, in correlation with recurrent substorm injections. It propagates eastward from the nightside to the dayside in the same drift direction of source electrons injected from the plasma sheet, resulting in a global impact within the ionosphere. This study demonstrates the model’s capability of revealing complex cross-scale interactions in the geospace environment.

3 Magnetic Reconnection

The magnetic structure and topology of the three- dimensional (3D) magnetic reconnection region are significantly dynamic and complex. Small-scale flux ropes and magnetic null points are frequently detected in the reconnection outflow region and diffusion region due to the increased in-situ measurements at high temporal cadences. Previous studies have demonstrated that X-line and small-scale flux ropes are both related to null points. By applying a fitting-reconstruction method with the input of the Cluster dataset, Guo[23]reveal three types of spiral null pairs that serve as the skeleton of the flux ropes. Two spiral nulls can be connected by a spine, or by a separator, or by both spine and separator. A theoretical model is proposed to explain these spiral null pairs. The observational results and the model indicate that the number of magnetic loops of the flux rope is restricted by the linkage pattern of two nulls, while the flux rope is confined by the two nulls and their fan surfaces. The model predicts that the magnetic perturbations in the reconnection region can transform the linkage types of the nulls and eventually lead to the evolution of flux ropes.

Using the in situ measurements of ROCSAT-1 satellite during 181 geomagnetic storms happened from July 1999 to June 2004, a superposed epoch analysis of the Equatorial Plasma Depletions (EPDs) occurrence is conducted by Wan[70]. At postsunset hours (18:00UT – 22:00LT), the EPDs occurrence is enhanced shortly at the storm onset, but afterward, a long-last suppression dominates. The EPDs occurrence at Midnight (22:00 LT–02:00 LT) generally shares a similar pattern to that at postsunset hours. The occurrence at predawn (02:00 LT–04:00 LT) gradual increases near storm onset and reach its maximum at 6~9 h and decays until 18 h. For a given longitude at postsunset/midnight, the EPDs occurrence tends to be suppressed or promoted when the EPDs do or do not prevail. The disturbed vertical plasma drift generally determines the inhibition/promotion of the EPDs occurrence at postsunset/predawn. However, for predawn EPDs occurrence, the plasma vertical drift cannot well explain the longitudinal variation. The continuous observations from consecutive orbits of ROCSAT-1 are carefully compared and the result suggests that the geomagnetic storm-induced additional predawn EPDs are preferred to be the longer-lived developed EPDs rather than fresh EPDs. In addition, a possible mechanism concerning the background plasma density enhancement which might be related with the energetic electrons induced nighttime ionization is proposed.

Huang[25]report in-situ observations of an electron jet generated by secondary reconnection within the outflow region of primary reconnection in the terrestrial magnetotail by the Magnetospheric Multiscale (MMS) mission. The MMS spacecraft first passed through the primary X-line and then crossed the electron jet in the outflow of primary reconnection. There are a series of small-scale flux ropes in the secondary reconnection region. Decoupling from the magnetic field for both ions and electrons, an intense out-of-plane current, unambiguous Hall currents, and a Hall electromagnetic field appear in the electron jet. Strong electron dissipation (·′>0), a nonzero electric field in the electron frame, and electron crescent-like shaped distributions are detected in the center of the electron jet, implying that MMS spacecraft were likely passing through the electron diffusion region. The significant electron dissipation indicates that the electrons can be accelerated in the electron jet and the electron jet may be another important electron acceleration channel along with the electron diffusion region.

The separatrix region is the region between the separatrix and the reconnection jet. Due to the×drift and velocity filter effect in which high-energy particles with high parallel speed can be seen prior to low-energy particles along the field line, electrons are separated from ions. The electron dynamics in this region is of interest; however it has not been studied in detail, because of the insufficient resolution of plasma data. Bai[26]present a slow separatrix crossing event observed by Magnetospheric Multi- scale (MMS) satellite constellation on 1 January 2016, from the magnetosheath side with high-resolution burst mode data. The electron edge and ion edge are clearly distinguished in the separatrix region. Two types of electron dispersion, one with a short duration (about 0.3 s) and the other with a longer duration (about 13 s) were detected between the electron and ion edges. The rapid dispersion (with a small time scale) is mainly in the parallel direction, which might originate from a thin layer with non-frozen-in electrons close to the separatrix. The gradual (long time scale) dispersion is seen from parallel to perpendicular directions, which comes from the×drift of a curved D-shape distribution of electrons. The width of the electron diffusion region on the magnetosheath side is estimated based on MMS observation. The observation also reveals an unexpected parallel electron beam outside of the electron edge. Wave-particle interaction or parallel potential in the inflow region may be responsible for the generation of this electron population.

Unlike a quadrupolar Hall magnetic field in symmetric magnetic reconnection, a bipolar or qua­d- rupolar Hall magnetic field occurs in asymmetric reconnection as indicated by recent observations from the Magnetospheric Multiscale (MMS) mission. Dai[27]presents analytic calculations of the structures of Hall magnetic fields in asymmetric reconnection. The Hall magnetic fields are analyzed in terms of kinetic Alfvén wave eigenmodes of the reconnection layer. The bipolar and quadrupolar patterns of Hall magnetic fields correspond to a dominance of the=0 and=1 kinetic Alfvén wave eigenmode, respectively. The asymmetry of Hall fields is linked to the asymmetry of the Alfvén speed profile. The Hall magnetic fields are shifted toward and enhanced on the low Alfvén speed side of the reconnection layer. The asymmetry in the magnetic field strength of the reconnection layer has a major effect on the structures of Hall magnetic fields.

Secondary flux ropes are suggested to play important roles in energy dissipation and particle acceleration during magnetic reconnection. However, their generation mechanism is not fully understood. Zhong[28]present the first direct evidence that a secondary flux rope was generated due to the evolution of an electron vortex, which was driven by the electron Kelvin-Helmholtz instability in an ion diffusion region as observed by the Magnetospheric Multiscale mission. The sub-ion scale (less than the ion inertial length) flux rope was embedded within the electron vortex, which contained a secondary electron diffusion region at the trailing edge of the flux rope. They propose that intense electron shear flow produced by reconnection generated the electron Kelvin-Helmholtz vortex, which induced a secondary reconnection in the exhaust of the primary X line and then led to the formation of the flux rope. This result strongly suggests that secondary electron Kelvin- Helmholtz instability is important for reconnection dynamics.

Dynamical nightside auroral structures are often observed by the All Sky Imagers (ASI) at the Chinese Yellow River Station (CYRS) at Ny-Ålesund, Svalbard, located in the polar cap near the poleward edge of the nightside auroral oval. The boundaries of the nightside auroral oval are stable during quiet geomagnetic conditions, while they often expand poleward and pass through the overhead area of CYRS during the substorm expansion phase. The motions of these boundaries often give rise to strong disturbances of satellite navigations and communications. Two cases of these auroral boundary motions have been introduced to investigate their associated ionospheric scintillations: one is Fixed Boundary Auroral Emissions (FBAE) with stable and fixed auroral boundaries, and another is Bouncing Boundary Auroral Emissions (BBAE) with dynamical and largely expanding auroral boundaries. Observations of Shishir[58]show that the auroral boundaries, identified from the sharp gradient of the auroral emission intensity from the ASI images, were clearly associated with ionospheric scintillations observed by Global Navigation Satellite System (GNSS) scintillation receiver at the CYRS. However, amplitude scintillation (4) and phase scintillation () respond in an entirely different way in these two cases due to the different generation mechanisms as well as different IMF (Interplanetary Magnetic Field) condition.4andhave similar levels around the FBAE, whilewas much stronger than4around BBAE. The BBAE were associated with stronger particle precipitation during the substorm expansion phase. IU/IL, appeared to be a good indicator of the poleward moving auroral structures during the BBAE as well as FBAE.

It has been proposed that, in the near-Earth magnetotail, earthward propagating flux ropes can merge with the Earth’s dipole magnetic field and dissipate its magnetic energy. However, the reconnection diffusion region related to this process has not been identified. Man[29]report the first in situ observation of magnetic reconnection between an earthward propagating flux rope and the closed magnetic field lines connecting to Earth. Magnetospheric Multiscale (MMS) spacecraft crossed a vertical current sheet between the leading edge of the flux rope (negativeB) and the geomagnetic field (positiveB). The sub-ion-scale current sheet, super- Alfvénic electron outflow, Hall magnetic and electric field, conversion of magnetic energy to plasma energy (·> 0), and magnetic null were observed during the crossing. All the above signatures indicate that MMS detected the reconnection diffusion region. This result is also relevant to other planets with intrinsic magnetosphere.

Magnetic reconnection efficiently converts mag­netic energy into kinetic and thermal energy of plasmas. The electric field at the X-line, which represents the reconnection rate, is commonly used to measure how fast the reconnection proceeds. However, the Energy Conversion Rate (ECR) has rarely been investigated. Using a 2.5D particle-in-cell simulation, Yi[30]examined the temporal evolution of the ECR in collisionless reconnection. It is found that the ECR reaches peak significantly later than the reconnection rate does. This is because the energy conversion primarily occurs at the reconnection fronts rather than at the X-line. With the increase of the inflow density, both the reconnection rate and the conversion rate decrease. The presence of a guide field leads to the reduction of both the reconnection rate and the conversion rate, though reconnection remains fast. They further find that ECR does not depend on the mass ratio but is sensitive to the length of the simulation domain.

Reconnection Front (RF) has frequently been observed in the magnetotail and is well known as the depolarization front in the near-Earth tail. Whether the RF exists in reconnection with distinct plasma/ field properties across the reconnecting current sheet (asymmetric reconnection) is unknown yet. Song[31]use 2.5D particle-in-cell simulations to investigate the properties of RF in asymmetric reconnection and compare it to RFs in symmetric reconnection. They find that RF is a robust structure in asymmetric reconnection. Its moving speed and thickness are smaller than those in symmetric reco­nnection. Its properties, such as the current density, electromagnetic field structure, are examined. Some features of RF in asymmetric reconnection are drastically different than those in symmetric reconnection. These results are of great help for studying RF in plasma environments with asymmetric reconnection, such as Earth’s magnetopause.

Magnetic holes have been widely observed in various space plasma systems. The origin of magnetic holes and their influence on background plasma are under debate. Zhong[32]show a kinetic-scale electron vortex magnetic hole in a non-ideal region of an active X line, which was observed by the Magnetospheric Multiscale mission at the dayside magn­etopause. Intense current and non-ideal electric field in the electron frame were observed within the mag- netic hole, which led to strong energy dissipation. Thus, the electron vortex magnetic hole probably provided an additional energy dissipation channel besides the electron diffusion region adjacent to the hole. They suggest that magnetic reconnection provided favorable conditions for the formation of this kinetic-scale magnetic hole and is an important source of magnetic holes in space plasma.

卧式窗选落地帘；观景窗使用带有拉绳等机械装置的重型帘轨；高大的凸窗可采用由几幅单独的帘布组成的落地窗帘，窗户之间，各帘布单独系好，使用连续的帘盒将各幅帘布连为一个整体；凸窗较小或成弧形，可以当作一个整体来装饰，采用一个双幅帘，每幅都能完全地拉至窗户的两边；双窗，一般说来，装饰时最好把它们当作一个整体来处理。

Studies on Sun-climate connection have been carried out for several decades, and almost all of them focused on the effects of solar total irradiation energy. As the second major terrestrial energy source from outer space, the solar wind energy flux exhibits more significant long-term variations. However, its link to global climate change is rarely concerned and remains a mystery. As a fundamental and important aspect of the Earth’s weather and climate system, tropical cyclone activity has been causing more and more attentions. Li[65]investigated the possible modulation of the total energy flux input from the solar wind into the Earth’s magnetosphere on the global tropical cyclone activity during 1963–2012. From a global perspective, the accumulated cyclone energy increases gradually since 1963 and starts to decrease after 1994. Compare to the previously frequently used parameters,., the sunspot number, the total solar irradiation, the solar10.7irradiation, the tropical sea surface temperature, and the south oscillation index, the total solar wind energy flux input exhibits a better correlation with the global tropical cyclone activity. Furthermore, the tropical cyclones seem to be stronger with more intense geom­agnetic activities. A plausible modulation mechanism is thus proposed to link the terrestrial weather phenomenon to the seemingly-unrelated solar wind energy input.

除此之外，浦东开发整个面上也采用了多渠道筹资开发的办法，用足用好浦东开发优惠政策，通过招商引资、土地批租、证券市场和金融融资。到2000年，浦东开发的第一个10年，通过土地批租、股票市场、外资、内资及金融机构融资贷款筹集了至少5000亿元以上的开发资金。

Cold ions of plasmaspheric origin have been observed to abundantly appear in the magnetospheric side of the Earth’s magnetopause. These cold ions could affect the magnetic reconnection processes at the magnetopause by changing the Alfven velocity and the reconnection rate, while they could also be heated in the reconnection layer during the ongoing reconnections. Zhang[34]report in-situ observations from a partially crossing of a reconnection layer near the subsolar magnetopause. During this crossing, step-like accelerating processes of the cold ions were clearly observed, suggesting that the inflow cold ions may be separately accelerated by the rotation discontinuity and slow shock inside the reconnection layer.

从图7可以看出，随着贮藏时间的延长，异丁醇和异戊醇的含量均成下降趋势，且近乎平行。高级醇含量降低可能是在贮藏过程中，溶解氧与高级醇发生了氧化反应转化为醛或酸，或是高级醇与酸类物质发生了酯化反应。

Magnetic reconnection is essentially a multi- scale phenomenon, driven by kinetic processes in microscopic region and enabling explosive energy conversion from magnetic field energy to plasma kinetic energy in large areas. It has been poorly understood how the kinetic process around the X-line connects to the Magnetohydrodynamics (MHD) scale process in the reconnection downstream region. Fujimoto[37]investigated the energy conversion process in the region far downstream of the X-line, by means of the Particle-in-Cell (PIC) simulation with the Adaptive Mesh Refinement (AMR). The AMR-PIC model enables efficient kinetic simulation of multi- scale phenomena using dynamically adaptive meshes. It is found that the ion energy gain dominates in the reconnection region and is carried out mainly in the exhaust center rather than the exhaust boundaries. The simulation results suggest that the energy conversion process in collisionless magnetic reconnection is significantly different from that in the MHD reconnection model in which most energy conversion occurs at slow mode shocks formed at the exhaust boundaries.

Suprathermal electrons with energy from tens to hundreds of keV are frequently observed in the Earth’s magnetotail. The generation of such electrons is typically attributed to magnetic reconnection, Dipolarization Fronts (DFs), or flux transport. How- ever, which of these contributes more to this gene- ration remains unclear. Xu[38]quantitatively compared the electron acceleration by these processes, using the Cluster data. They analyze an event detected in the mid-tail and find that the suprathermal electrons there are first accelerated by magnetic reconnection and transported earthward, and then further accelerated locally at the DF. The acceleration process by reconnection and transport, resulting in an isotropic pitch angle distribution, contributes about 70% to the total flux enhancement, while the acceleration process by the DF, resulting in a pancake distribution, contributes about 30% to the flux enhancement. The electron acceleration at the DF is primarily attributed to a local betatron process that is successfully reproduced using an analytic model. In order to better understand this phenomenon, they examine an additional 16 similar events and find that the DFs and magnetic reconnection statistically contribute 11%~38% and 62%~ 89% to the total flux enhancement, respectively. This study greatly improves our understanding of the electron energization process in the magnetotail.

Magnetic nulls, where magnetic field strength becomes zero, play a crucial role in energy conversion and particle acceleration during magnetic reconnection. Recent simulations have suggested that Recon­nection Fronts (RFs) inside the reconnection jet can be host to magnetic nulls. However, observational ev­idence for the RF-associated magnetic nulls remains absent so far. In this study, Liu[39]presents such evidence by using the First-Order Taylor Expansion (FOTE) method and Cluster measurements. They confirm for the first time the existence of magnetic nulls around RFs, and find that the dip region ahead of RFs and the nearby magnetic flux ropes around RFs can be host to magnetic nulls. The observed magnetic nulls are all spiral types, and the recon­structed topologies are consistent with theoretical models. Their results verify the existence of magnetic nulls around RFs and may shed new lights on the study of magnetic reconnection and RF dynamics.

Using MMS high-resolution measurements, Liu[40]present the first observation of fast electron jet (e ≈2000 km·s–1) at a Dipolarization Front (DF) in the magnetotail plasma sheet. This jet, with a scale comparable to the DF thickness (about 0.9i), is primarily in the tangential plane to the DF current sheet and mainly undergoes the×drift motion; it contributes significantly to the current system at the DF, including a localized ring-current that can modify the DF topology. Associated with this fast jet, they observed a persistent normal electric field, strong lower hybrid drift waves, and strong energy conversion at the DF. Such strong energy conversion is primarily attributed to the electron-jet-driven current (e≈2i), rather than the ion current suggested in previous studies.

利用超高速打击侵彻深度与地冲击效应等效计算理论，可建立防护工程中抗超高速武器打击的最小安全防护层厚度的估算公式为[19]

Kinetic Alfvén Waves (KAWs) are believed to be capable of efficiently transporting energy and play an important role in facilitating magnetic reconnection. KAW eigenmode theory suggests that Hall fields can be considered as the components of KAW, providing a mechanism for the generation and dissipation of KAW in magnetic reconnection. Using particle-in-cell simulations, Huang[41]examined Hall fields in the magnetic reconnection region and found that (i) hall electric filed is balanced by the ion pressure gradient and (ii) the ratio of Hall electric field to Hall magnetic field is on the order of Alfvén speed. These results are consistent with KAW physics. Simulation results also indicate that KAWs are excited in the reconnection site and then transmitted along the separatrices. The wave Poynting flux propagates parallel to the magnetic field lines, carrying substantial energy. It is further found that a thinner current sheet provides a favorable condition for the excitation of KAW and results in a higher ratio of the Hall fields.

Theoretically, magnetic reconnection, the process responsible for solar flares and magnetospheric substorms, occurs at the X-line or radial null in the Electron Diffusion Region (EDR). However, whether this theory is correct is unknown, because the radial null (X-line) has never been observed inside the EDR due to the lack of efficient techniques and the scarcity of EDR measurements. Fu[42]report such evidence, using data from the recent MMS mission and the newly developed First-Order Taylor Expansion (FOTE) Expansion technique. They investigate 12 EDR candidates at the Earth’s magnetopause and find radial nulls (X-lines) in all of them. In some events, spacecraft are only 3 km (one electron inertial length) away from the null. They reconstruct the magnetic topology of these nulls and find it agrees well with theoretical models. These nulls, as reconstructed for the first time inside the EDR by the FOTE technique, indicate that the EDR is active and the reconnection process is ongoing.

“西湖山水还依旧……看到断桥桥未断，我寸肠断，一片深情付东流！”白衣女子一挥水袖，哀怨的歌声隐隐传来。

Magnetic reconnection, the process typically lasting for a few seconds in space, is able to accelerate electrons. However, the efficiency of the acceleration during such a short period is still a puzzle. Previous analyses, based on spacecraft measurements in the Earth’s magnetotail, indicate that magnetic reconnection can enhance electron fluxes up to 100 times. This efficiency is very low, creating an impression that magnetic reconnection is not good at particle acceleration. By analyzing Cluster data, Fu[43]report here a remarkable magnetic reconnection event during which electron fluxes are enhanced by 10000 times. Such acceleration, 100 times more efficient than those in previous studies, is caused by the betatron mechanism. Both reconnection fronts and magnetic islands contribute to the acceleration, with the former being more prominent.

Using data from the MMS mission and the First-Order Taylor Expansion (FOTE) method, Wang[44]revealed electron distribution functions around a reconnection X-line at the Earths mag­netopause. They find cigar distribution of electrons in both the magnetosphere-side and magneto- sheath-side inflow regions, isotropic distribution of electrons at the separatrix, and loss of high-energy electrons in the antiparallel direction in the magneto- sheath-side inflow region. They interpret the formation of cigar distribution in the inflow regions using the Fermi mechanism, as suggested in previous simulations, the loss of high-energy electrons in the magnetosheath side using the parallel electric fields, which evacuate electrons to escape the diffusion region along the antiparallel direction, and the isotropic distribution at the separatrix using the pitch angle scattering by whistler waves, which exist frequently at the separatrix. They also find that the electron distribution functions can change rapidly (within 60 ms) from isotropic to cigar as the spacecraft moves slightly away from the separatrix.

Complex magnetic structures are ubiquitous in turbulent astrophysical plasmas. Such structures can be host to many dynamic processes, such as magnetic reconnection and energy dissipation. Thus, revealing the 3D topologies of these structures is necessary. Liu[45]propose a new method to reconstruct complex magnetic topologies in quasi-steady space plasmas, by utilizing eight-point measurements of magnetic fields and particles. Such a method, based on the Second-Order Taylor Expansion (SOTE) of a magnetic field, is nonlinear; it is constrained byÑ×= 0 andÑ´=0, where=e(i –e) is from particle moments. A benchmark test of this method, using the simulation data, shows that the method can give accurate reconstruction results within an area about three times the size of a spacecraft tetrahedron. By comparing to the previous First-Order Taylor Expansion (FOTE) method, this method (SOTE) gives similar results for reconstructing quasilinear structures but exhibits better accuracy in reconstructing nonlinear structures. Such a method will be useful to the multi-scale missions, such as the future European Space Agency’s “cross-scale” mission and China’s “self-adaptive” mission. Also, it can be applied to four-point missions, such as Cluster and the Magnetospheric Multiscale Mission. They demonstrated how to apply this method to the four-point missions. In principle, this method will be useful to study shocks, magnetic holes, dipolarization fronts, and other nonlinear structures in space plasmas.

With high-resolution data of the Magnetospheric Multiscale (MMS) mission, Chen[46]observed a Magnetic Flux Rope (MFR) in the Earth’s magnetosheath. This MFR, showing a clear bipolar variation of the magnetic field in the normal component to local current sheet, contains a strong core field. They use the FOTE method to reconstruct the topology of this MFR and find it is consistent with previous expectation. For the first time, the spiral field and core field of the MFR are both revealed from the FOTE method. Comparing topologies reconstructed at different times, they suggest that the axis of the MFR rotates about 88° at different spatial location. Shape and size of the normal projection to axis vary with the spatial location as well. Inside the MFR, a significant increase of plasma density from 40 to 80 cm–3, a sharp decrease of ion temperature from 200 to 50 eV, an enhancement of cold ions and a series of filamentary currents are found.

Electrostatic Solitary Waves (ESWs) have been reported inside reconnection jets, but their source and role remain unclear hitherto. Liu[47]present the first observational evidence of ESWs generation by cold ion beams inside the jet, by using high- cadence measurements from the Magnetospheric Multiscale spacecraft in the Earth’s magnetotail. Inside the jet, intense ESWs with amplitude up to 30 mV·m–1and potential up to about 7% of the electron temperature are observed in association with accelerated cold ion beams. Instability analysis shows that the ion beams are unstable, providing free energy for the ESWs. The waves are observed to thermalize the beams, thus providing a new channel for ion heating inside the jet. Their study suggests that electrostatic turbulence can play an important role in the jet dynamics.

Radial nulls, where magnetic field strength becomes zero and the magnetic field lines point radially in the fan plane, are believed to be crucial for particle acceleration and energy dissipation during magnetic reconnection. Recent simulations have suggested that Reconnection Fronts (RFs) embedded in the reconnection jet can be host to radial nulls. However, observational evidence for radial nulls near the RFs remains elusive hitherto, owing to the absence of an efficient null-detection method and high- resolution measurements. Liu[48]present such evidence by using the newly developed First-Order Taylor Expansion method and the high-resolution measurements from the recent MMS mission. For the first time, they confirm the existence of radial nulls near the RFs and find that the upstream region ahead of the RFs can preferentially host the radial nulls. The reconstructed topologies of the observed radial nulls are consistent with theoretical models. Associated with these radial nulls, no clear particle and wave activities were found, meaning that they were inactive during the observations.

4 Solar Wind-magnetosphere- ion­osphere Interaction

By using 10-year of Challenging Mini-satellite Payload satellite observations, Wang[49]investigated the average conditions of the Interplanetary Magnetic Field (IMF) prevailing during the westward Counter Equatorial Electrojet (CEJ). Equally, they compared the average IMF conditions accompanying high-latitude field-aligned currents of the Region 1 (R1) and Region 2 (R2). It shows that both CEJ and high-latitude field-aligned currents events when R2 is greater than R1 tend to happen preferably during the northward turning of the IMFBand the substorm recovery phase. Sunlight has an important influence on the longitudinal distribution of the Equatorial Electrojet (EEJ), and the effect is opposite to the tidal electric field at E region. The anti-correlation between cos0.5(SZA) (Solar Zenith Angle effect) average values during CEJ events and EEJ intensity is most prominent around June solstice. By using combined measurements from Challenging Minisatellite Payload and DMSP satellites, it is found that before the occurrence and in the initial phase of a subauroral polarization stream the EEJ gets enhanced, and after about 30 min it reduces in intensity. The CEJ occurrence rate more than doubles during subauroral polarization stream periods compared to normal conditions.

The polar outflows, as an important plasma source of the Earth’s magnetosphere, usually exhibit significant north-south asymmetries, which can strongly affect the plasma distributions in the magnetotail lobe and perhaps contribute to the substorm triggering. But the mechanism of the asymmetric transport of these outflows is still unclear. In this Letter, 3D global Magnetohydrodynamic (MHD) simulations are performed to investigate the deve­lopment of the polar outflows after their escapes from the inner boundary under influences of the IMFB. It is found that the velocity of northern polar outflows is much stronger than the south. Wang[50]suggest that the IMFBcauses the north-south asymmetries in the magnetospheric configuration, and subsequently, great differences of the force and mass distributions appear between the two hemispheres, which lead to the significant north-south asymmetries in the transport of the polar outflows. They also discuss the differences in the acceleration mechanisms of the polar outflows between the northward and southward IMF cases.

In Ref[51], the Space Weather Modeling Framework (SWMF) is used to simulate the real- time response of the magnetosphere to a solar wind event on 5 June 1998, in which the interplanetary magnetic field shifted its direction from north to south. Since most current models do not take into account convective effects of the inner magneto­sphere, they first study the importance of Rice Convection Model (RCM) in the global model. They then focus on the following four aspects of the mag­netosphere’s response: the magnetosphere’s density distribution, the structure of its magnetic field lines, the area of the polar cap boundary, and the corre­­­sponding ionospheric current change. They find that (i) when the IMF changes from north to south in this event, high magnetosheath density is observed to flow downstream along the magnetopause with the solar wind, low-latitude reconnection at dayside occurs under the southward IMF, while the magnetic field lines in the tail lobe caudal, caused by the nightside high latitude reconnection, extend into the interplanetary space, open magnetic field lines exist simultaneously at both high and low latitudes at the magnetopause; (ii) the area of the polar cap is obviously increased if the IMF turns from the north to the south, this observation is highly consistent with empirical observations; (iii) the ionospheric field align current in the northern hemisphere is stronger than in the southern hemisphere and also increases as the IMF changes from north to south. SWMF with the Rice Convection effect provides reliable modeling of the magnetospheric and ionospheric response to this solar wind variation.

A Transpolar Arc (TPA), which extended from postmidnight to prenoon, was seen on 16 September 2001 in the Northern Hemisphere under northward IMF-Band weakly dawnward IMF-Bconditions. Super Dual Auroral Radar Network detected significant westward plasma flows just equatorward of the poleward edge of the midnight sector auroral oval. These plasma flows were confined to closed field lines and are identified as the ionospheric plasma flow signature of Tail Reconnection during IMF Northward Nonsubstorm Intervals (TRINNIs). These TRINNI flows persisted for 53 min from prior to the TPA appearance to the cessation of TPA growth. They are usually observed before (and during) intervals when TPAs are present, but in this case, subsided after the TPA was completely connected to the dayside. Additional slower flows across the open/closed polar cap boundary were seen at the TPA onset time in the same magnetic local time sector as the nightside end of the TPA. These ionospheric flows suggest that magnetotail reconnection significantly contributed to the TPA formation, as proposed by Milan(https://doi.org/ 10.1029/2004JA010835)Nowada[53]proposed a possible scenario for an absence of the TRINNI flows during the TPA brightening by considering the relation between the extent of the magnetotail reconnection line mapped onto nightside auroral oval and the TPA width; TRINNI flows would subside when the extent of X-line is comparable to the TPA width. Therefore, our results suggest that the fate (absence or presence) of TRINNI flows on closed field lines during the TPA formation would be closely related with magnetotail reconnection extent.

Pitkänen[54]investigated THEMIS satellite measurements made in a tail-aligned constellation during a time interval on 1–2 January 2009, which has previously been attributed to an interval of an interplanetary magnetic fieldB-driven magnetotail twisting. They find evidence for that the orientation of the convection electric field in the tail is twist-mode dependent. For earthward flow and a negative twist (induced tailB< 0), the electric field is found to have northwardEand tailwardEcomponents. During a positive twist (induced tailB> 0), the directions ofEandEare reversed. TheEcomponent shows the expected dawn-to-dusk direction for earthward flow. The electric field components preserve their orientation across the neutral sheet, and a quasi-collinear field is observed irrespective of the tail distance. The electric field associated with the tailward flow has an opposite direction compared to the earthward flow for the negative twist. For the positive twist, the results are less clear. The corresponding plasma convection and thus the magnetic flux transport have an opposite dawn-dusk direction above and below the neutral sheet. The directions depend on the tail twist mode. The hemi- spherically asymmetric earthward plasma flows are suggested to be a manifestation of an asymmetric Dungey cycle in a twisted magnetotail. The role of tailward flows deserves further investigation.

Using results from a new drift kinetic model in the topside ionosphere, Shi[55]captured the mode conversion from kinetic Alfven waves to electron acoustic waves. When the kinetic Alfven waves propagate into the transition region, where the electron density of ionospheric origin becomes comparable to that of magnetospheric origin, the steep temperature gradient leads to the mode conversion. The electron acoustic waves are short-lived by dissipating their energy into the electron energization, thus revealing a new type of electron acceleration in the topside ionosphere.

Polar cap patches are common irregularities in the polar ionosphere, where their formation and evolution can directly affect satellite navigations and communications as well as over-the-horizon radar observations,. However, affected by the various dynamic processes during the solar wind-magnetos­phere-ionosphere coupling, there is no fully accepted formation mechanism of polar cap patches. A statistical analysis of 345 patches at the dayside sectors during 09:00 MLT–15:00 MLT (Magnetic Local Time), observed by EISCAT Svalbard Radar (ESR) 42 m antenna from 2010 to 2013, has been performed by Jin[56]. The dependence of their occurrence on solar wind and IMF conditions as well as their MLT distribution has been statistically investigated. The results show that the polar cap patches are preferentially formed during southward IMF conditions. In particular, the MLT dependence of the patches presents a clear IMFB-related prenoon- postnoon asymmetry, suggesting the patch formation is clearly modulated by the IMFBpolarity. Moreover, their statistical results indicate that the patches should not be caused by the variations of the solar wind dynamic pressure or the solar wind velocity. All the results indicate that the pulsed dayside magnetic reconnection is possibly a significant formation mechanism of polar cap patches.

Geomagnetic crochet is believed to be directly related to solar flares. Relevant studies are important to understand the influence of solar eruptions on near-earth space environment, and to develop Space Weather forecasting techniques. Using the data from the geomagnetic station of Shandong University (Weihai), the Intermagnet Geomagnetic chain and the Meridian Space Weather Monitoring Project, the GOES satellite and the digital ionosonde system, Lei.[57]investigated a geomagnetic crochet associated with an M5.6 solar flare. Their conclusions are listed as follows. The characteristics of geomagnetic crochet are different between the northern and southern hemispheres and prenoon/postnoon, and the geomagnetic response has about 3 minutes’ delay in comparison to the peak time of the solar flare. Geomagnetic disturbance is not obvious at night. They use the data of more than 50 magnetic stations located in the dayside hemisphere and found that the amplitude of geomagnetic crochet had a normal distribution, with the maximum being near noon. At last, they use geomagnetic data to get the crochet current systems during the event and the quiet current systemq during quiet days. Their statistical study on the geomagnetic crochets and solar flares from 1996 to 2015 shows that the-class flare is most likely the cause of magnetic crochets, and the possibility is about 42%; most magnetic crochets are caused by M-class flares; smaller flares, like A-, B-, C-class flares are hardly associated with magnetic crochets.

地理信息数据仓库实施环境部署主要采用了图3的方式，具体的配置信息如表1所示。首先，可以将ORACLE系统安装在地理信息数据库服务器一点，利用其构建数据库环境，存储地理信息、注册信息等[3]。

Xing[59]report results from the analysis of a case of conjugate Polar Cap Arcs (PCAs) observed on 5 February 2006 in the Northern Hemisphere by the ground-based Yellow River Station all-sky imager (Svalbard) and in both hemispheres by the space- based DMSP/SSUSI and TIMED/GUVI instruments. The PCA’s motion in dawn-dusk direction shows a clear dependence on the IMFBcomponent and presents a clear asymmetry between Southern and Northern Hemispheres, that is, formed on the dusk side and moving from dusk to dawn in the Northern Hemisphere and vice versa in the other hemisphere. The already existing PCAs’ motion is influenced by the changes in the IMF By with a time delay of similar to 70 min. They also observed strong flow shears/reversals around the PCAs in both hemispheres. The precipitating particles observed in the ionosphere associated with PCAs showed properties of boundary layer plasma. Based on these observations, they might reasonably expect that the topological changes in the magnetotail can produce a strip of closed field lines and local processes would set up conditions for the formation and evolution of PCAs.

成立于1945年的伏能士焊接技术国际有限公司是来自奥地利的高端焊接设备制造商，其在华唯一全资子公司——伏能士（上海）商贸有限公司的焊接业务部成立于2013年1月。伏能士拥有442名研发专家、1000多项有效发明专利，产品涉及电弧焊设备、自动化焊接设备、激光焊接设备、电阻点焊设备等，遍布70多个国家，广泛应用于汽车、轨道、航天、工程建设等高质量要求的行业。

By analyzing a five-year period (2010–2014) of Defense Meteorological Satellite Program (DMSP) plasma data, Ma[61]investigated ion upflow occurrence, speed, density, and flux above the polar cap in the northern hemisphere under different Solar Zenith Angle (SZA), solar activity (10.7), and convection speed. Higher upflow occurrence rates in the dawn sector are associated with regions of higher convection speed, while higher upflow flux in the dusk sector is associated with higher density. The upflow occurrence increases with convection speed and solar activity but decreases with SZA. Upflow occurrence is the lowest when the SZA > 100º and the convection speeds are low. While, the upflow velocity and flux show a clear seasonal dependence with higher speed in the winter and higher flux in the summer during low convection conditions. However, they are detected for the first time to be both higher in summer during high convection conditions. These results suggest that ion upflow in the polar cap is controlled by the combination of convection, solar activity, and solar illumination.

The 616 mid and high altitude cusp crossings, collected from Cluster observation for the time interval from 1 February 2001 to 31 December 2010, are used to study IMF effect on cusp locations. Although the statistical errors in their study are quite significant, Xu[63]show that with the increasing of the negativeB, the invariant latitude of the cusp moves to poleward for northward IMF, while it slightly shifts to equatorward for southward IMF. For the increasing positiveB, the invariant latitude of the cusp doesn’t change too much. This phenomenon is observed obviously for the southern hemisphere, but no apparent phenomenon merges on the northern hemisphere. Moreover, when the negativeBis enhanced, the magnetic local time of cusp turns to dawnward (duskward) for northern (southern) hemisphere under southward IMF. Consistent with previous study, they also find that with the increasing of southwardB, the invariant latitude of the cusp moves equatorward for both northern and southern hemisphere, while it keeps almost unchanged for northwardB.

The Cold-Dense Plasma Sheet (CDPS) plays an important role in the entry process of the solar wind plasma into the magnetosphere. Investigating the seasonal variation of CDPS occurrences will help us better understand the long-term variation of plasma exchange between the solar wind and magnetosphere, but any seasonal variation of CDPS occurrences has not yet been reported in the literature. Bai[64]investigated the seasonal variation of the occurrence rate of CDPS using Geotail data from 1996 to 2015 and find a semiannual variation of the CDPS occurrences. Given the higher probability of solar wind entry under stronger northward IMF conditions, 20 years of IMF data (1996–2015) are used to investigate the seasonal variation of IMFBunder northward IMF conditions. They find a semiannual variation of IMFB, which is consistent with the Russell- McPherron (R-M) effect. They therefore suggest that the semiannual variation of CDPS may be related to the R-M effect.

It has been shown that the guide field substantially modifies the structure of the reconnection layer. For instance, the Hall magnetic and electric fields are distorted in guide field reconnection compared to reconnection without guide fields (. anti-parallel reconnection). Fu[33]performed 2.5D electromagnetic full particle simulation to study the electric field structures in magnetic reconnection under different initial guide fields (g). Once the amplitude of a guide field exceeds 0.3 times the asymptotic magnetic field0, the traditional bipolar Hall electric field is clearly replaced by a tripolar electric field, which consists of a newly emerged electric field and the bipolar Hall electric field. The newly emerged electric field is a convective electric field about one ion inertial length away from the neutral sheet. It arises from the disappearance of the Hall electric field due to the substantial modification of the magnetic field and electric current by the imposed guide field. The peak magnitude of this new electric field increases linearly with the increment of guide field strength. Possible applications of these results to space observations are also discussed.

Galactic Cosmic Rays (GCRs), modulated by the Heliospheric Magnetic Field (HMF), are speculated to provide a possible link between solar activities and the Earth’s lightning variation. To test this hypothesis, Wu[66]investigated the correlation between the sudden decrease of GCR in a few hours to one day, known as Forbush Decrease (FD), and the lightning incidence in the tropics and subtropics. During the operating period of the TRMM Satellite, 28 FD events are identified with their Decrease Amplitudes (DAs) greater than 4%. For a typical FD event occurred on 10 January 2002, the daily Cosmic Ray (CR) intensity presents an intense counts decline from 5830.33 min–1to 5675.96min–1in one day. Correspondingly, the daily lightning count decreases right after the FD’s onset without any obvious time delay, specifically from 3474 d–1to 672 d–1in one day, and reaches its minimum of 355 d–1another day later. Based on the Superposed Epoch Analysis (SEA), a similar statistical correlation is further confirmed. On average, the adjusted daily lightning anomaly decreases from 0.33 to – 0.31 in three days after the FD’s onset. The result of the Monte Carlo test indicates that such positive relevance between the CR intensity and the lightning incidence during an FD event is statistically significant.

Ionospheric outflow from the polar cap through the polar wind plays an important role in the evolution of the atmosphere and magnetospheric dynamics. Both solar illumination and solar wind energy input are known to be energy sources of the polar wind. However, observational studies of the energy transfer from these two energy sources to the polar wind are difficult. Because of their low energy, polar wind ions are invisible to regular ion detectors onboard a positively charged spacecraft. Using a new technique that indirectly measures these low-energy ions, Li[67]are able to estimate the energy budget of the polar wind. Their results show that solar illumination provides about 107W of the kinetic energy of the polar wind, in addition to the energy transferred from the solar wind with a maximum rate of about 108W. The energy transfer efficiency of solar illumination to the kinetic energy of the polar wind is about 6 to 7 orders of magnitude lower than that of the solar wind. Moreover, daily and seasonal changes in the orientation of the geomagnetic dipole axis control solar illumination over the polar cap, modulating both energies of the polar wind and energy transfer efficiencies from the two energy sources.

Previous studies mostly focused on ionosphere and thermosphere responses to strong southward IMFBconditions. However, it is not clear how the Ionosphere and Thermosphere (IT) system responds to Alfvénic quasi-periodic oscillating IMFBconditions. In Ref[68], simulations by the Coupled Magnetosphere Ionosphere Thermosphere model have been used to investigate the effects of IMFBtemporal variations with 10, 30, and 60 min oscillation periods on the coupled IT system. The simulation results show that the cross polar cap potential and auroral peak electron energy flux are stronger when the IMFBoscillation frequency is lower. The relatively small periodic wind responses in the 10 min IMF oscillation case indicate a low-pass filter nature of the magnetosphere-ionosphere-thermosphere system. Two different thermospheric wind (n) responses are revealed. One is the almost simultaneous responses at all latitudes, and the other shows a typical traveling atmospheric disturbances signature with a time delay with respect to the latitude for all UTs. The simultaneousn responses at all latitudes appear in the daytime Northern Hemisphere, which are mainly caused by the ion drag force in association with penetration electric fields induced plasma density and ion drifts changes. The short-period traveling atmospheric disturbances occurring in the nighttime of both hemispheres and the daytime of the Southern Hemisphere propagate from high to low latitudes showing latitudinal dependence. Both responses oscillate with the same frequencies as those of IMFBoscillations.

根据西安市教育局发布的《“名校+”工程行动计划（2018—2021年）》，该市将通过实施“名校+”工程，运用一长多校（一所名校校长兼多所薄弱学校校长）、委托管理、兼并融合、结对提升等4种管理模式，做到6个统筹，即统筹组建“名校+”，统筹改善办学条件，统筹配备管理团队，统筹配置教师队伍，统筹开展教育教学，统筹施行质量监测。

The term “polar cap hot patch” is a newly identified high-density plasma irregularity at high latitudes, which is associated with high electron temperature and particle precipitation, while a classical polar cap patch has lower electron temperature. To investigate characteristics of hot patches versus classical patches, five years of in situ database of plasma observations from the DMSP satellites was analyzed. For the first time, Ma[60]show how the ion/electron temperature ratio (or temperature difference) can be used to distinguish between classical and hot patches. For classical patches (i/e> 0.8 orei+ 600 K), the vertical ion flux is generally upward. The highest upflow occurrence was found near the polar cap boundary, associated with hot patches, particle precipitation, strong convection speed, and localized field-aligned currents. This result shows that the polar cap hot patches may play a very important role in solar wind-magnetosphere-ionosphere coupling processes.

With the advantage of fast plasma measurements of the Magnetospheric Multiscale (MMS) mission in the magnetotail, Chen[72]first investigated the particle carriers of Field-Aligned Currents (FACs) in the plasma sheet boundary layer for three cases. In all cases, electrons are the main carriers of FACs, while the contribution of ions can be neglected. The analysis of these cases indicates that thermal electrons (energy range from 0.5e to 5e, wheree is the electron parallel temperature) are the main carrier of the FACs. However, cold electrons (energy less than 0.5e) can also significantly contribute to the FACs. In one of three cases, suprathermal electrons (energy greater than 5e) contribute but a small portion to the total current. The difference between the cases may depend on the local dynamics in the magnetotail. Then a statistical analysis was performed, which also shows that the thermal electrons are dominant in most of the FACs, while the cold electrons can be dominant in some cases. However, the suprathermal electrons cannot support the FACs solely, and they and the cold electrons are more often supporting the FACs together with the thermal electrons.

Field-aligned currents play a significant role in the magnetosphere-ionosphere coupling. With the multipoint measurements and the advanced instruments of the four Magnetosphere Multiscale spacecraft, Chen[73]estimated the fine structure of field-aligned currents in the Plasma Sheet Boundary Layer (PSBL) by using the plasma moment data from the Fast Plasma Investigation. Those fine field-aligned currents under higher temporal resolutions could be quite different from that under the lower temporal resolution: Bipolar current signals can be observed under higher resolutions, while no current signal appears under the lower resolution; higher current density magnitude and shorter time scale of the current layer under higher resolutions are observed than that under the lower resolution. The essential reason could be that the spatial scale of some field-aligned current layers in the PSBL is too small to be found by low temporal measurements; thus, their results demonstrate the necessity of high data resolutions in resolving the subproton-scale structure of the field-aligned current and dynamics in the PSBL.

Observations of vertical ion drift velocities (V) at the topside of the ionosphere by Defense Meteorological Satellite Program (DMSP) satellites have been accumulated over decades and provide us a unique opportunity to study the vertical ion drifts through the ionosphere on different temporal and spatial scales. In Ref[74],Vdata of F13, which are of high quality, are taken as the reference to rescale the measurements of DMSP F11, F12, F14, F15, and F16 at high latitudes from 50°N/S to 90°N/S, which show significant differences from each other in magnitudes. Through rescaling, allVdata of F11~F16 are in a similar order of magnitudes. Moreover, their spatial and temporal distributions resemble each other on average and are consistent with the excepted averaged behaviors reported in previous studies. Thus, the rescaling is basically effective, which provides an opportunity to construct a data set ofVfrom 1995 to 2014 that covers nearly two solar cycles for further statistical analysis. Meanwhile, it should be noted that the rescaling results are qualitative/semiqualitative with some uncertainty, which needs more detailed discussion and analysis in future studies.

但作为一辆大型豪华轿车，XJ应该如何演绎捷豹品牌一直以来在运动方面的造诣，同时展现英国人对于豪华轿车的独到见解呢？在上世纪60年代，完成这样的挑战绝非是易事。

Ionospheric outflow has been shown to be a dominant ion source of Earth’s magnetosphere. However, most studies in the literature are about ionospheric outflow injected into the nightside magnetosphere. We still know little about ionospheric outflow injected into the dayside magnetosphere and its further energization after it enters the magnetosphere. With data from Magnetospheric Multiscale mission, Liu[76]reports direct observations of the modulation of dayside ionospheric outflow ions by Ultralow Frequency (ULF) waves. The observations indicate that the modulation is mass dependent, which demonstrates the possibility of using ULF waves as a mass spectrometer to identify ion species. Moreover, the measurement suggests that polarization drift may play a role in O+modulation, which may lead to a true acceleration and even nonadiabatic behavior of O+. This interaction scenario can work throughout the whole magnetosphere and impact upon the plasma environment and dynamics.

In Earth’s high-latitude ionosphere, the poleward motion of east–west elongated auroral arcs has been attributed to standing hydromagnetic waves, especially when the auroral arcs appear quasi- periodically with a recurrence time of a few minutes. The validation of this scenario requires spacecraft observations of ultra-low-frequency hydromagnetic waves in the magnetosphere and simultaneous observations of poleward-moving auroral arcs near the spacecraft footprints. Zhao[77]presented the first observational evidence from the multi-spacecraft THEMIS (Time History of Events and Macroscale Interactions during Substorms) mission and the conjugated all-sky imager to support the scenario that standing hydromagnetic waves can generate the quasi-periodic appearance of poleward-moving auro­ral arcs. In this specific event, the observed waves were toroidal branches of the standing hydroma­g- netic waves, which were excited by a pulse in the solar wind dynamic pressure. Multi-spacecraft mea­surements from THEMIS also suggest higher wave frequencies at lowershells (consistent with the distribution of magnetic field line eigenfrequencies), which indicates that the phase difference across latitudes would increase with time. As time proceeds, the enlarged phase difference corresponds to a lower propagation speed of the auroral arcs, which agrees very well with the ground-based optical data.

The flux variations of energetic electrons are one of the most important topics to understand dynamic processes in the space environment and the forecast for high-energy electron burst. BeiDa Image Electron Spectrometer (BD-IES), an imaging energetic electron spectrometer onboard a Chinese navigation satellite at an inclined geosynchronous orbit, can provide 50~600 keV electron flux data, which is used to investigate electron flux variations at GEO orbit during Co-rotating Interaction Region events (CIRs). The superposed epoch analysis is applied to study the electron flux variations in different energy cha­nnels of BD-IES during CIRs and the results support previous works. Yin[78]revealed that electron fluxes in different channels all have a dropout before or at CIR interface and then the recovery of electrons with low energy reaches maximum earlier than that of electrons with high energy, with longer time differences for larger energy gap, which is consistent with two major mechanisms for energizing particles: inward radial diffusion and local acceleration. In addition, they investigate the relationship between electron flux enhancement in each energy channel and magnetic local time and the extent of enhancement for electron flux peak value compared with average value before the interface. These results can contribute to our understanding of electron flux variations at GEO during CIRs, and thus lay foundations for forecast research on high-energy electron enhancement during CIRs.

Previous observations indicate that there are mainly unstructured plasmaspheric hiss in the high- density plasmasphere, whereas structured whistler mode chorus waves with the lowest frequency of 0.1ce (ce is the electron gyrofrequency) are observed mostly outside the plasmapause. Yu[79]observed ultrawide band rising-tone chorus waves with frequencies extending to lower hybrid resonance frequency (LHR≈ 101 Hz) in a dawnside high-density region (07:00 MLT ande ≈75 cm–3) inside the oscillating plasmapause. The ultrawideband chorus waves have also typical two-band structures separated by a power gap at 0.5ce, but their lowest frequency (LHR≈ 0.023ce) in the high-density region is much smaller than that of the normal chorus waves (> 0.1ce) in the low-density trough (e< 40 cm–3). The Poynting fluxes of the waves indicate that the ultrawideband chorus waves are excited near the magnetic equator. By comparing the linear wave growth rate to the nonlinear growth rate, they found that the ultrawideband chorus waves are probably amplified through the nonlinear excitation mechanism.

Samanes[80]studied the dynamics of the nighttime lower ionosphere height through continuous monitoring of the VLF modal interference distance (so-called distance). Since the distanceis related to the nighttime propagation modes within the Earth-Ionosphere waveguide, it provides information of the nighttime reflection height (N). They have used a long-term VLF narrowband database of almost 8 years (2006–2014) from a long transequatorial VLF propagation path between the transmitter NPM (Hawaii, 21.4 kHz) and the receiver ATI (Atibaia, Brazil). Their results show thatNassumes lower values during northern hemisphere wintertime as compared with summertime. By using the Lomb- Scargle periodogram, periodicities around 180 (SAO), 365 (AO) and 800 (QBO) days have been found, being the periodicity around 180 days stronger than all other oscillations. Since these large-scale oscillations are commonly observed in several measurable parameters of the Mesosphere-Lower Thermosphere (MLT) region, their results suggest that the night­time lower ionosphere can be strongly influenced by the dynamics of the MLT region. The effect of the long-term solar activity onNis also studied, resulting in a high negative correlation (=–0.91). This effect makesNdecrease around 1.2 km from low to high solar activity. This result suggests a control of the solar radiation on the nighttime lower ionosphere, and hence, on the electron density at night.

While Subauroral Polarization Streams (SAPS) are well recognized as representatively one of the most important features of magnetosphere-ionosphere (M-I) coupling processes in the subauroral region, the Double-Peak Subauroral Ion Drifts (DSAIDs) is a newly recognized ionospheric phenomenon, categorized as a subset of Subauroral Ion Drifts (SAIDs). Wei[81]investigated both SAPS and DSAIDs that appear during the storm main phase of the 17 March 2015 event through a combination of multi- point observations and numerical simulations. They find that when SAPS/DSAIDs are observed by the DMSP spacecraft near the dusk subauroral region, strong electric fields are detected minutes later by the Van Allen Probes almost in the same conjugate region near the equatorial plane. Numerical simulations are carried out not only to reveal the global context and dynamic evolution of the SAPS in both the magnetospheric and ionospheric systems, but also to aid the understanding of the effect of conductance on the DSAIDs. Their results confirm that SAPS are indeed associated with Region 2 Field- Aligned Currents (FACs) flowing into the low conductance region. On the other hand, the DSAIDs may be related to the double-conductance-trough in the subauroral region.

Double-peak Subauroral Ion Drifts (DSAIDs), characterized by two high-speed flow channels, is a newly identified flow structure in the subauroral ionosphere. Two Region 2 field-aligned currents (R2 FACs) might cause the DSAIDs. However, the underlying physical process that drives the double R2 FACs is unknown. Wei[82]report a DSAIDs event and reveal its magnetospheric drivers. Defense Meteorological Satellite Program F18 satellite observed DSAIDs in the dusk side subauroral region, which corresponded well to two low-density troughs and two R2 FACs. The Van Allen Probe B demonstrated that intense substorm ion injections recurrently occurred prior to the formation of DSAIDs, suggesting a potential magnetospheric driver of DSAIDs. Simulation confirms that recurrent ion injections intensify the partial ring current and create double pressure peaks in the near-Earth dusk- to-midnight region, leading two R2 FACs to flow into the ionosphere. The two R2 FACs are thus responsible for the DSAIDs formation. This study unveils the generation mechanism of DSAIDs and deepens the knowledge of the complex magnetosphere-iono- sphere system.

Yang[83]investigated the statistical, dual- spacecraft correlations of Field-Aligned Current (FAC) signatures between two Swarm spacecraft. For the first time, they infer the orientations of the current sheets of FACs by directly using the maximum correlations obtained from sliding data segments. The current sheet orientations are shown to broadly follow the mean shape of the auroral boundary for the lower latitudes and that these are best ordered on the dusk side. Orientations at higher latitudes are less well ordered. In addition, the maximum correlation coefficients are explored as a function of magnetic local time and in terms of either the time shift (t) or the shift in longitude (lon) between Swarms A and C for various filtering levels and choice of auroral region. They find that the low-latitude FACs show the strongest correlations for a broad range of magnetic local time centered on dawn and dusk, with a higher correlation coefficient on the dusk side and lower correlations near noon and midnight. The positions of maximum correlation are sensitive to the level of low-pass filter applied to the data, implying temporal influence in the data. This study clearly reflects the two different domains of FACs: small-scale (some tens of kilometers), which are time variable, and large-scale (>50 km), which are rather stationary. The methodology is deliberately chosen to highlight the locations of small-scale influences that are generally variable in both time and space. They may fortuitously find a potential new way to recognize bursts of the 1st type of irregular pulsations of(Pi1B) using low-Earth orbit satellites.

5 Radiation Belt, Ring Current and Whistler Waves

Wave number vectorsand minimum cyclotron resonant electron energiesminof Electromagnetic Ion Cyclotron (EMIC) waves are analyzed via the phase differencing technique by using Magnetospheric Multiscale Mission data. It is demonstrated that the phase differencing method provides an estimate of the dominant wave number when finitespectrum broadenings occur. A case study is conducted for the EMIC event on 20 November 2015, showing remarkable agreements with spectral analysis in wave propagation directions. Liu[84]find that obtained wave vectors, roughly agreeing with the validity of cold plasma theory, might significantly vary from wave packet to wave packet. Numerical calculations indicate thatmincan range from 0.5 to tens of MeV, suggesting that EMIC waves can effectively interact with those relativistic electrons. This study enriches our understanding of the applicability of phase differencing. It further supports that EMIC waves can be responsible for the loss of electrons with an extremely broad energy range in the magnetosphere.

Sudden changes of the solar wind dynamic pressure have significant impacts on the dynamics of the magnetosphere-ionosphere system. As reported by Zhao[85], on 18 February 2011, a sudden decrease in solar wind dynamic pressure was observed by the Wind satellite, which drove the entire magnetosphere-ionosphere system as recorded in many ground-based and space-based measurements. In the magnetosphere, Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft observed a counterclockwise plasma flow vortex propagating tailward. Near the magnetic footprints of the THEMIS spacecraft, the ground magnetometers observed magnetic field variations that corresponded to a counterclockwise vortex in the equivalent ionospheric currents, which in turn indicated the presence of upward field-aligned currents. The all-sky imager at RANK station near the THEMIS footprints also observed a simultaneous enhancement of the auroral brightness. Therefore, this comprehensive case study demonstrates a causal chain that links the solar wind dynamic pressure variations to magnetospheric, ionospheric, and auroral activities.

High-energy trapped particles in the radiation belts constitute potential threats to the functionality of satellites as they enter into those regions. In the inner radiation belt, the characteristics of high- ener­- gy (>20 MeV) protons variations during geomag­netic activity times have been studied by implementing 4-year (2013–2016) observations of the Van Allen probes. An empirical formula has been used by Xu[87]to remove the satellite orbit effect, by which proton fluxes have been normalized to the geomagnetic equator. Case studies show that the region of<1.7 is relatively stable, while>1.7 is more dynamic and the most significant variation of proton fluxes occurs at=2.0. The 4-year survey at=2.0 indicates that for every geomagnetic storm, sharp descent in proton fluxes is accompanied by the corresponding depression of Sym-index, with a one-to-one correspondence, regardless of the storm intensity. Proton flux dropouts are synchronous with Sym-reduction with similar short timescales. Their observational results reveal that high-energy protons in the inner radiation belt are very dynamic, especially for the outer zone of the inner belt, which is beyond our previous knowledge.

Whistler mode chorus waves play a key role in controlling electron dynamics in Earth’s inner magnetosphere. A criterion has been previously suggested whereby if the maximum value of the linear growth rate of whistler mode waves exceeds a certain critical bound, then fully nonlinear wave growth occurs and chorus waves are generated. This criterion corresponds to a boundary curve in (h/0,T) space wherehis the hot electron number density,0is the cold electron number density, andTis the thermal anisotropy. Chorus waves are generated in the region above the boundary curve, while no chorus waves are generated below the boundary curve. Tang and Summers[88]make use of a recently published set of 36 particle simulations of chorus, and they thereby are able to confirm the validity of the criterion. It is expected that this simple concept of the theoretical boundary curve based on linear theory will be useful in guiding the choice of parameters in future simulations of the chorus and also of practical use in interpreting experimental chorus wave data.

Strong electrostatic Electron Cyclotron Harmonic (ECH) waves on the dayside magnetosphere have been reported based on observations of the Magnetospheric Multiscale (MMS) spacecraft. Lou[89]analyzes high-quality wave data from the four MMS satellites between 1 September 2015 and 30 August 2018 to investigate the statistical properties of dayside ECH emissions. The results show that dayside ECH waves are preferentially observed on the prenoon side in the outer magnetosphere (= 8~12), with average wave amplitudew> 0.1 mV·m–1. In addition, besides the typical near-equatorial (|MLAT|≤15°) region, dayside ECH waves exhibit moderate occurrence rate and wave amplitude in higher latitudinal regions (, 15 < |MLAT|≤40°), possibly due to the off-equatorial geomagnetic field minimum. Their reported double peaks of dayside ECH wave occurrence zone and considerable occurrence rates of pre-noonside ECH waves suggest that dayside ECH waves can be a potentially important contributor to the formation of dayside diffuse aurora.

VLF (Very Low Frequency) electromagnetic waves at 3~30 kHz have the characteristics of long wavelength and long propagation distance. They can propagate along the Earth-lower ionosphere waveguide, and are widely used in many fields including com­munication and navigation. The Long Wavelength Propagation Capability (LWPC) model based on the waveguide mode theory provides a useful tool to evaluate the propagation path and amplitude of VLF waves, which can be analyzed to investigate ionospheric disturbances caused by solar flares, magnetic storms, earthquakes and other extreme events. In Ref.[90], the very simple electron density and collision frequency modules originally embedded in LWPC are updated by the International Reference Ionosphere (IRI) model for simulation improvements. The obtained numerical results are then compared to the observed amplitude of NWC VLF transmitter signals by Wuhan University VLF receiver at the Wuhan station. It is found that the amplitude variations of NWC VLF transmitter signals modeled using the LWPC and IRI models are much closer to the observations, which mainly results from the improved nighttime electron density profile from the IRI model and justifies the importance of electron density of the lower ionosphere to the VLF signal propagation properties. In addition, the dawn-dusk electron density variation on the wave propagation path largely modulates the NWC VLF signal amplitude, and forms an obvious transition region during the sunrise and sunset periods. Therefore, incorp­oration of the IRI model into LWPC improves quantitative analyses and prediction performance of the propagation processes of VLF transmitter signals, and provides an evaluation method of long wave navigation and communication quality.

As an important loss mechanism of radiation belt electrons, Electromagnetic Ion Cyclotron (EMIC) waves show up as three distinct frequency bands below the hydrogen (H+), helium (He+), and oxygen (O+) ion gyro frequencies. Compared to O+-band EMIC waves, H+- and He+-band emissions generally occur more frequently and result in more efficient scattering removal of < 5 MeV relativistic electrons. Therefore, knowledge about the occurrence of these two bands is important for understanding the evolution of the relativistic electron population. To evaluate the occurrence pattern and wave properties of H+- and He+-band EMIC waves when they occur concurrently, Fu[91]investigated 64 events of multi-band EMIC emissions identified from high quality Van Allen Probes wave data. Their quantitative results demonstrate a strong occurrence dependence of the multi-band EMIC emissions on Magnetic Local Time (MLT) and-shell to mainly concentrate on the dayside region of=4~6. They also find that the average magnetic field amplitude of H+-band waves is larger than that of He+-band waves only when<4.5 andʹ<300 nT and He+-band emissions are more intense under all other conditions. In contrast to 5 events that have average H+-band amplitude over 2 nT, 19 events exhibit >2 nT He+-band amplitude, indicating that the He+-band waves can be more easily amplified than the H+-band waves under the same circumstances. For simultaneous occurrences of the two EMIC wave bands, their frequencies vary with-shell and geomagnetic activity: the peak wave frequency of H+-band emissions varies between 0.25cp and 0.8cp with the average between 0.25cp and 0.6cp, while that of He+-band emissions varies between 0.03 and 0.23cp with the average between 0.05cp and 0.15cp. These newly observed occurrence features of simult­aneous H+- and He+-band EMIC emissions provide improved information to quantify the overall contribution of multi-band EMIC waves to the loss processes of radiation belt electrons.

Wang[92]present a detailed investigation of bounce-resonant pitch angle scattering of ring current electrons caused by Electromagnetic Ion Cyclotron (EMIC) waves. It is found that H+band EMIC waves can resonate with near-equatorially mirroring electrons over a wide range of-shells (3≤≤6) and energies and lead to the efficient transport of ring current electrons (, 10 keV to 100 keV) from near 90° pitch angles to lower pitch angles. Computations of the bounce-resonant pitch angle scattering rates show a strong dependence on theshell, electron energy, and resonance harmonics. When the-shell increases, the orders of bounce resonance contributing to the whole scattering coe­fficient decrease, and meanwhile, it becomes difficult for the bounce resonance of higher orders to occur. Furthermore, when the electron energy increases, the bounce resonance orders decrease. Their results demonstrate that bounce-resonant scattering by H+band EMIC waves can be an important loss mechanism for 10~100 keV electrons because of the absence of cyclotron resonance for ring current electrons interacting with EMIC waves. They conclude that bounce resonant scattering by H+band EMIC waves should be incorporated into future modeling efforts of the ring current electron dynamics.

A statistical analysis on the radiation belt dropouts is performed based on 4 years of electron phase space density data from the Van Allen Probes. The,, andʹ dependence of dropouts and their driving mechanisms and geomagnetic and solar wind conditions are investigated using electron phase space density data sets for the first time. Results of Xiang[93]suggest that Electromagnetic Ion Cyclotron (EMIC) wave scattering is the dominant dropout mechanism at lowʹ region, which requires the most active geomagnetic and solar wind conditions. In contrast, dropouts at highʹ have a higher occurrence and are due to a combination of EMIC wave scattering and outward radial diffusion associated with magnetopause shadowing. In addition, outward radial diffusion at highʹ is found to cause larger dropouts than EMIC wave scattering and is accompanied with active geomagnetic and solar wind drivers.

Hua[94]analyzed an energetic electron flux enhancement event in the inner radiation belt observed by Van Allen Probes during an intense geomagnetic storm. The energetic electron flux at≈1.5 increased by a factor of 3 with pronounced butterfly Pitch Angle Distributions (PADs). Using a three-dimensional radiation belt model, they simulate the electron evolution under the impact of radial diffusion, local wave-particle interactions including hiss, very low frequency transmitters, and magnetosonic waves, as well as Coulomb scattering. Consistency between observation and simulation suggests that inward radial diffusion plays a dominant role in accelerating electrons up to 900 keV and transporting the butterfly PADs from higher-shells to form the butterfly PADs at≈1.5. However, local wave-particle interactions also contribute to driving butterfly PADs at≥1.9. Their study provides a feasible mechanism to explain the electron flux enhancement in the inner belt and the persistent presence of the butterfly PADs at≈1.5.

Recently, Cosmic Ray Albedo Neutron Decay (CRAND) has been identified as the main source of relativistic electrons measured at the inner edge of inner radiation belt. Xiang[95]introduced a drift-source model that includes azimuthal drift and a CRAND electron source to simulate the quasi- trapped electron distribution measured by the DEMETER satellite during 20–30 April 2010. The simulated longitude distribution of quasi-trapped electron fluxes at the inner edge of inner radiation belt successfully reproduces the DEMETER observations, confirming CRAND as the main source for these electrons. Furthermore, a comparison of the energy spectrum and thedistribution of the quasi-trapped relativistic electrons between simulations and observations further suggests that CRAND is likely the dominant source for 300~700 keV quasi-trapped electrons at<2 and≈3.

Wei[96]report multi-spacecraft observations of ULF waves from Van Allen Probes (RBSP), Magnetospheric Multiscale (MMS), Time History of Events and Macroscale Interactions during Substorm (THEMIS), and Geostationary Operational Environmental Satellites (GOES). On 31 August 2015, global-scale poloidal waves were observed in data from RBSP-B, GOES, and THEMIS from= 4 to= 8 over a wide range of Magnetic Local Time (MLT). The polarization states varied towards purely poloidal polarity. In two consecutive orbits over 18 h, RBSP-A and RBSP-B recorded gradual variation of the polarization states of the poloidal waves; the ratio (|a|/|r|) decreased from 0.82 to 0.13. After the variation of polarization states, the poloidal ULF waves became very purely poloidal waves, localized in both L and MLT. They identify the poloidal wave as second harmonic mode with a large azimuthal wave number () of –232. From RBSP particle mea- surements they find evidence that the high-m poloidal waves during the polarization variations were powered by inward radial gradients and bump-on-tail ion distributions through the=1 drift-bounce resonance. Most of the time, the dominant free energy source was inward radial gradients, compared with the positive gradient in the energy distribution of the bump-on-tail ion distributions.

By investigating the resonant energy and latitudinal resonance region of Landau resonance between H+band Electromagnetic Ion Cyclotron (EMIC) waves and radiation belt electrons and performing calculations of quasi-linear diffusion coefficients, Fu[97]find that Landau resonance with EMIC waves, characterized by a very broad range of resonant energies from below 1 eV to above 10 MeV and the strikingly small extent of the latitudinal resonance region well below 0.1°, can be a feasible candidate accounting for the pitch angle scattering of near-equatorially mirroring electrons. Compared to the dominant pitch angle scattering caused by the cyclotron resonance for greater than about 2 MeV electrons at equatorial pitch angles less than about 80° with the rates well above 10–4s–1, Landau resonance with H+band EMIC waves has the potential to drive more efficient pitch angle scattering of radiation belt electrons from about 10 MeV down to tens of kiloelectron volts at equatorial pitch angles greater than about 85°.

Both Magnetosonic (MS) waves and plasmaspheric hiss can resonantly scatter outer radiation belt electrons, leading to various electron pitch angle distribution. Based on electron diffusion coefficients calculations and 2D Fokker-Planck diffusion simulations, Hua[98]performed a parametric study to quantitatively investigate the net electron scattering effect and the relative contributions of simultaneous-

ly occurring hiss and MS waves with groups of different wave amplitude combinations. It is found that the combined scattering effects are dominated by pitch angle scattering due to hiss emissions at=4, when their amplitude is comparable to or stronger than that of MS waves, thereby producing the butterfly, top-hat, flat-top, and pancake pitch angle distributions, while the butterfly distributions can evolve over a broader energy range when MS waves join the combined scattering effects. Their results demonstrate that the relative intensities of various plasma waves play an essential role in controlling the radiation belt electron dynamics.

Electromagnetic ion cyclotron waves have long been recognized to play a crucial role in the dynamic loss of ring current protons. While the field-aligned propagation approximation of electromagnetic ion cyclotron waves was widely used to quantify the scattering loss of ring current protons, in this study, Cao[99]find that the wave normal distribution strongly affects the pitch angle scattering efficiency of protons. Increase of peak normal angle or angular width can considerably reduce the scattering rates of ≤10 keV protons. For >10 keV protons, the field- aligned propagation approximation results in a pronounced underestimate of the scattering of intermediate equatorial pitch angle protons and overestimates the scattering of high equatorial pitch angle protons by orders of magnitude. Their results suggest that the wave normal distribution of electromagnetic ion cyclotron waves plays an important role in the pitch angle evolution and scattering loss of ring current protons and should be incorporated in future global modeling of ring current dynamics.

Fu[100]developed a general 3D relativistic Test Particle (TP) simulation code to examine the trajectories and pitch angle variations of test electrons. They investigate the conditions when the electrons transit broadband, parallel propagating H+band Electromagnetic Ion Cyclotron (EMIC) waves to find whether the classical Quasilinear Theory (QLT) can be applied to interactions between H+band EMIC waves and radiation belt relativistic (and ultra-relativistic) electrons. They find that to reach good consistency between TP scattering coefficients and QLT calculations, the wave-particle resonant interaction time (which indicates the time of particles traveling in the wave fields and being resonant with the wave fields) must be carefully calculated to ensure the validity of the linear diffusion process. This wave-particle resonant interaction time depends largely on the wave amplitude, the bandwidth, and the initial parameters of electrons for TP simulations; once the time of electrons traveling in the wave fields becomes large enough when the pitch angles of electrons scattered by wave fields reach the maximal value limited by the resonance condition and cannot be diffused any longer, the linear diffusion process of particles defined by QLT will not be valid any longer. When the resonant electrons start to travel through the wave field, they undergo the linear diffusion process resulting from the pitch angle scattering by the H+band EMIC wave field. As the time of trave­ling in the wave fields increases, the test electrons will suffer effective pitch angle scattering and the pitch angles of these electrons will reach the maximum value limited by the resonance condition, which is determined by the wave and electron parameters. These electrons are then reflected by the wave fields and the linear wave-particle interactions defined by QLT will not be valid anymore. This kind of wave- particle interaction subsequently introduces considerable deviation of TP diffusion coefficients from those predicted by QLT calculations. Their results demonstrate that the general validity of QLT in describing how broadband EMIC waves affect radia- tion belt relativistic electrons is highly related to the time of electron traveling in the wave fields, which tends to increase for smaller wave power and broader wave frequency spectra.

Hua[102]report a typical event that fast Magnetosonic (MS) waves, exohiss, and two-band chorus waves occurred simultaneously on the dayside observed by Van Allen Probes on 25 December 2013. By combining calculations of electron diffusion coefficients and 2D Fokker-Planck diffusion simulations, they quantitatively analyze the combined scattering effect of multiple waves to demonstrate that the net impact of combined scattering does not simply depend on the wave intensity dominance of various plasma waves. Although the observed MS waves are most intense, the electron butterfly distribution is inhibited by exohiss and chorus, and electrons are considerably accelerated by combined scattering of MS and chorus waves. The simulated electron pitch angle distributions exhibit the variation trend consistent with the observations. Their results strongly suggest that competition and cooperation between resonant interactions with concurrently occurring magnetospheric waves need to be carefully treated in modeling and comprehending the radiation belt electron dynamics.

Fu[103]develop a full relativistic test particle code to model the combined electron scattering effect of Landau and bounce resonances with magnetosonic waves. Test particle simulations of magnetosonic wave-electron interactions indicate that the two resonances coexist to affect radiation belt electrons at different energies and pitch angles, and the resultant combined pitch angle scattering and energy diffusion can reach the rates of about 10–4and 10–5s, respectively, for electrons 40~500 keV at pitch angles 70°~80° for the given wave model (about 200 pT) inside the plasmapause at=4.5. Comparisons with the quasi-linear theory results show that the test particle combined scattering rates are generally an order of magnitude weaker, possibly because the electrons are moved out of the Landau resonance by the advective effect of the bounce resonance. Their investigation demonstrates that the Landau and bounce resonances with magnetosonic waves cannot be treated independently or additively in terms of quasi-linear theory to simulate the associated radiation belt electron dynamics.

Fast Magnetosonic (MS) waves are commonly regarded as electromagnetic waves that are characteristically confined within ±3° of the geomagnetic equator. Ni[104]report two typical off-equatorial MS events observed by Van Allen Probes, that is, the 8 May 2014 event that occurred at the geomagnetic latitudes of 7.5°– 9.2° both inside and outside the plasmasphere with the wave amplitude up to 590 pT and the 9 January 2014 event that occurred at the latitudes of – (15.7°–17.5°) outside the plasmasphere with a smaller amplitude about 81 pT. Detailed test particle simulations quantify the electron resonant scattering rates by the off-equatorial MS waves to find that they can cause the pitch angle scattering and momentum diffusion of radiation belt electrons with equatorial pitch angles < 75° or < 58° (depending on the wave latitudinal coverage) on timescales of a day. Subsequent two-dimensional Fokker-Planck diffusion simulations indicate that the strong off-equatorial MS waves are capable of efficiently transporting high pitch angle electrons to lower pitch angles to facilitate the formation of radiation belt electron butterfly distributions for a broad energy range from 100 keV to >1 MeV within an hour. Their study clearly demonstrates that the presence of off-equatorial MS waves, in addition to equatorial MS waves, can contribute importantly to the dynamical variations of radiation belt electron fluxes and their pitch angle distribution.

To investigate the hot plasma effects on the cyclotron-resonant interactions between Electromagnetic Ion Cyclotron (EMIC) waves and radiation belt electrons in a realistic magnetospheric environment, calculations of the wave-induced bounce- averaged pitch angle diffusion coefficients are performed by Ni[105]using both the cold and hot plasma dispersion relations. The results demonstrate that the hot plasma effects have a pronounced influence on the electron pitch angle scattering rates due to all three EMIC emission bands (H+, He+, and O+) when the hot plasma dispersion relation deviates significantly from the cold plasma approximation. For a given wave spectrum, the modification of the dispersion relation by hot anisotropic protons can strongly increase the minimum resonant energy for electrons interacting with O+band EMIC waves, while the minimum resonant energies for H+and He+bands are not greatly affected. For H+band EMIC waves, inclusion of hot protons tends to weaken the pitch angle scattering efficiency of >5 MeV electrons. The most crucial differences introduced by the hot plasma effects occur for >3 MeV electron scattering rates by He+band EMIC waves. Mainly due to the changes of resonant frequency and wave group velocity when the hot protons are included, the difference in scattering rates can be up to an order of magnitude, showing a strong dependence on both electron energy and equatorial pitch angle. Their study confirms the importance of including hot plasma effects in modeling the scattering of ultra-relativistic radiation belt electrons by EMIC waves.

Currently, the generation mechanism for the lower-shell dayside chorus has still remained an open question. He[106]report two storm events: 6–7 March 2016 and 20–21 January 2016, when Van Allen Probes observed enhanced dayside chorus with lower and higher wave normal angles (the angles between the wave vector and the geomagnetic field) in the region of=3.5~6.3 and MLT=5.6~13.5. Hot and energetic (1~100 keV) electrons displayed enh­ancements in fluxes and anisotropy when they were injected from the plasma sheet and drifted from midnight through dawn toward the dayside. Calculations of chorus local growth rates under different wave normal angles show that the upper cutoff and peak wave frequencies display similar patterns to the observations. Chorus growth rates maximize for the parallel propagation and drop with increasing wave normal angles. The current results confirm that the observed lower-shell dayside chorus can be excited by anisotropic electrons originating from the plasma sheet in drifting from the nightside to the dayside.

Previous theoretical studies have shown that dayside chorus can produce butterfly distribution of energetic electrons in the Earth’s radiation belts by preferentially accelerating medium pitch angle electrons, but this requires the further confirmation from high resolution satellite observation. Jin[107]report correlated Van Allen Probes data on wave and particle during the 11–13 April 2014 geomagnetic storm. They find that a butterfly pitch angle distribution of relativistic electrons is formed around the location=4.52, corresponding to the presence of enhanced dayside chorus. Using a Gaussian distribution fit to the observed chorus spectra, they calculate the bounce-averaged diffusion rates and solve two-dimensional Fokker-Planck equation. Numerical results demonstrate that acceleration by dayside chorus can yield the electron flux evolution both in the energy and butterfly pitch angle distribution comparable to the observation, providing a further evidence for the formation of butterfly distribution of relativistic electrons driven by Very Low Frequency (VLF) plasma waves.

To better understand rapid enhancements of the seed populations (hundreds of keV electrons) in the heart of the Earth’s outer radiation belt (ʹ≈3.5~5.0) during different geomagnetic activities, Tang[109]investigated three enhancement events measured by Van Allen Probes in detail. Observations of the fluxes and the pitch angle distributions of energetic electrons are analyzed to determine rapid enhancements of the seed populations. They show that three specified processes associated with substorm electron injections can lead to rapid enhancements of the seed populations, and the electron energy increases up to 342 keV. In the first process, substorm electron injections accompanied by the