Multi-Scale Physical Process in the Magnetosphere

0254-6124/2008/28(5)-454-14Chin. J. Space Sci.Cao Jinbin, Liu Zhenxing. Multi-scale physical proces in the magnetoephere. Chin. J. Space Sei, 2008, 28(6): 454~467Multi-Scale Physical Process in the Magnetosphere*CAO JinbinLIU Zhenxing(State Key Labonatory for Space Weather, Center for Space Sciences and Applied Reseanch,Chinese Academy of Sciences, Beijing 100190)Abstract The brief report presents a part of the research results of the magnetospheric pbysicsresearches in China during the period of 2006- -2008. During the past two years, China-ESA cooperation DSP (Double Star Program) satellites were basically operating normally in its extendedlifetime. The DSP and Cluster missions provide Chinese space physicists high quality data to studymulti-scale physical process in the magnetosphere. The work made based on the data of DSP ispresented in the paper of“Progress of Double Star Program" of this issue.Key words Magnetosphere, Progres1 Geomagnetic Stormsnightside had the nearly same waveforms a8 those ob-served on the ground in the H (northward) compo-Wang et al[1 make a statistical survey of Interplane-ent. We suggest that the SCs observed by Oerstedtary (IP) shocks and Storm Sudden Commencements on the nightside were dominantly c8used by the en-(SSCs) observed between 1995 and 2004. We find hanced magnetopause currents, which were transmit-that 75% of sSCs are associated with shocks, consis-ted by the compressional bydromagnetic waves, andtent with previous work. We use this survey to inves the efectst of the lonospheric Current (IC) were neg-tigate the efect of the interplanetary shock strength ligible on the nightside. The SC waveforms observedand orientation on the SSC rise time. We find that by Oersted on the dayside were apparently diferentthe higher the speed of an IP shock, the less timefrom those observed on the ground. Near the Day-it takes to sweep by the magnetosphere, and thus side Dip Equator (DDE), corresponding to Prelimi-the shorter the rise time of the corresponding SsC.nary Reverse Impulses (PRIs) observed in the groundThe orientation of an IP shock also efectse the SsC H component, Oersted always observed positive im-rise time. Generally speaking, a highly oblique shock pulses in the B11 component, which suggest that thecauses asymmetric compression of the magnetosphere PRIs at the DDE are generated by westward IC8. Onwith respect to the noon -midnight meridian, takes the dayside, corresponding to positive Main Impulsesmore time to sweep by magnetosphere, and thus re(MIs) of SCs observed in the ground H component,sults in a longer rise time of the SSC.the Oersted B11 component always presented clearOersted is a low-altitude (638~849km) polar-decreases, which implies that an eastward IC was ex-orbiting setllite. Using vector magnetic field mea- cited after the PRI. The generation mechanism forsurements obtained from Oersted, Han et al[2the westward and eastward ICs are discussed accord-identified more than 20 geomagnetic Sudden Com-ing to previously proposed models. On the dayside,mencement (SC) events on both dayside (06:00- we suggest that the waveforms observed both on the18:00MLT) and nightside (18:00- -06:00MLT). The ground and at Oersted during the time period of PRIunique properties reflected by these events have never and Nincident compres-been reported before. The SC& observed by Oer-sional中国煤化工d caused by thested in the B11 (compressional) component on the IC8. 1YHCNMHGedjustabovethe* Supported by the National Natural Science Foundation of China (40390153, 40523006) and 973 Program (2006CB806305)Received 2008-05-10Cao Jinbin et al: Multi- Scale Physical Proce8s in the Magnetophere455ionosphere are significant complementary to our em- by the LANL-97A satllite on 14 June 1998 is 7.1 Re,pirical knowledge for SCs.and the injection time agrees well with the substormonset time identified by the Polar Utraviolet Imager.The method has been applied to an event happened at2 Magnetospheric Substorms22:54 UT on 11 March 1998, when both the satellitesThe properties of proton (0eV < E < 40keV) in the(1991-080 and LANL-97A) observed the dispersion-less character. The results indicate that the radialplasma sheet are examined by He et al3] by meansdistance of injection source locates at 8.1 Re at mag-of a superposed epoch analysis, using 115 magneto-netotail, and particles move earthward from magnetail plasma injection events which are identifed fromtotail into inner magnetosphere at 22:30UT.Cluster magnetotail orbit time in between 2001 andBasing on the data from three stllites of Clus-2004. All events distribute in magnetic local timefrom 20:00UT to 04:00UT. Five clases of magneto-ter (C1, C3 and C4) in the year of 2001 and 2002, Matail injection events are found to be similar with theet al5 examine the relationship between the Rapidgeosynchronous observation: (1) pure ion injections;Convection Event (RCE) and substorm. The observa-(2) ion injections followed a few minutes later by antion of RCE measured by single satellite is not exactlyelectron injection; (3) simultaneous ion and electronwhat happened in the magnetotail. Both C1 and C3injections; (4) electron injections followed a few min-observed the event occurring on July 25, 2002, bututes later by an ion injection; (5) pure electron in-C4 did not. Among the 306 RCEs jointly measuredjections. Proton shows a significant increase in tem-by three satellites, 215 ones were obeerved by C1.perature and density at the onset, and injects earth-C3 and C4 obtained 266 and 227 ones respectively.ward with an increasing velocity more than the pre-The average duration of RCE in the magnetosphereinjection average one. Superposed epoch analysis oncan't be really represented by the outcome surveyedthe simultaneous observation data of dusk -dawn elec-by single satellite. So our analysis has shown thattric field from the EFW (Electric Field and Waves)RCE transports more fractions of energy and mag-instrument, we found two diferent electric field con-netic fAux 'than what had calculated by single satellitefigurations: (1) electric field increases suddenly atin the central plasma sbeet. Relationship betweenthe onset and the value is positive; (2) electric fieldBursty Bulk Flow (BBF) termed by the velocity andchanges the direction at the onset, and turns intosubstorm is more close than that of RCE defined bya negative value. The simulation results of veloc-the magnetic fux.ity vector after injection in equatorial plain, calcu-lated in static magnetic (T89c) and electric (olland- 3 Magnetic ReconnectionStern) field models, agree with the statistical resultsmostly, and that suggests the electric drift caused byWei et al6] present Cluster observations of wavesdawn-dusk convection electric field is one of the me-in the whistler frequency range during magnetic rechanisms of the particles injected earthward in mag-connection in the Earth's magnetotail. On 21 Au-netotail(-18Re< R< - 10Ra).gust 2002 the Cluster spacecraft encountered a quasi-Measurements of energetic particles obtainedcollisionless magnetic reconnection event when itby the two geosynchronous satellites (1991-080 andcrossed the plasma sheet. Prior to the southwardLANL-97A) are performed to investigate the plasmaturning of magnetic field in the tailward fow, theinjection boundary and source region during the mag-weak whistler waves were first observed. The burstnetospheric substorms by He et al4. The mea-of whistler waves appeared about 30s earlier thansurement method is developed to allow remote se the southward turning. During magnetic reconnec-nsing of the plasma injection time and the radial dis-tion event, the waves in the whistler frequency rangetance of injection boundaries by using measured en- were g中国煤化工i the reonergy dispersion and modeling particle drifts withintion plFjuency range arethe Volland-Stern electric field and the dipole mag-mainlyMHC N M H Gright-band polanetic field model. The radial distance of the injectionrized whistler waves, while those in the lower freboundary deduced from a dispersion event observedquency range are quasi-perpendicular propagating456Chin. J. Space Sci.2008, 28(5)linear polarized waves, which may be a superposition larger than the transpolar potential, and the ratioof several linearly polarized waves. The combined between them increases with increasing ionosphericobservations of energetic electrons and waves show conductance. The fact that method 2 also gives rea-that after the southward turning of magnetic field, sonable answers means that the appearance of par-the waves in the reconnection process are greatly en-allel electric field along the last closed magnetic fieldhanced by energetic electron beams.lines is responsible for the diference between the iono-The effect of guiding field to low frequency elec~ spheric and the reconnection potentials and betweentromagnetic instabilities in the collisionless current the transpolar potential and the reconnection volt-sheet was studied by Wei et al1 with the disper- age as well. We suggest that similar methods may besion relation obtained by cllisionless and compres- applicable to general cases with arbitrary IMF orien-ible magnetohydrodynamic model. The result show tations.the guiding field affects on the three-dimensional dis-Based on the simultaneous FGM observations ofturbed propagation waves strongly. (1) On the mid- 4 Cluster stllites, Zhang et al9 calculated and 8n8-dle plane of current sheet (z = 0), if there is notlyzed the current density of FTEs occurred betweenguiding field, no instability observed, but if there is 12:24UT and 12:54 UT on April 1, 2004 by using theguiding field, instabilities take place. (2) Near the Curlometer analyzer. It showed that intense currentmiddle of current sheet (z = 0.2), the current sheet flows inside the fAux tubes with the current densityis instable. With increasing of guiding field, the grow reaching as high as about 10 A/m2. By Minimumrate increased obviously. The wave mode may be Directional Derivative (or Difference) (MDD) analyz-whistler or low-hybrid wave. (3) Near the edge of ing, it was also found that the FTEs were of the quasicurrent sheet (z = 0.8), the efect of guiding field be-2D structure, the direction of the current was almostcome not clearly. The instability wave mode is quasi- parallel to the plasma fAows and the axis of the fuxparallel propagation whistler.tubes.Hu et al8] studied the ionospheric and recon-Zhang et al1o] analyzed the observations ofnection potentials of the earth: Results from globalthe FGM and PEACE on Cluster Spacecrafts, andMHD simulations. The reconnection potential along the CUTLASS Finland radar between 11:00UT andthe reconnection line provides a quantitative de-11:40UT on 11 February 2004. In this interval,scription of magnetic reconnection that dominatesthe Cluster spacecraft array was encountering thethe solar wind- magnetosphere coupling. To prop- northern hemisphere, high altitude cusp, and crossingerly determine the reconnection potential is a firstthe magnetopause into the magnetosheath at aboutand crucial step in deeply understanding magneto 11:18UT. A large number of Flux Transfer Eventsspberic processes. This paper proposes three meth-(FTEs) were observed by all 4 Cluster spacecrafts. Itods to calculate the reconnection potential based on is found that these FTEs appeared quasi-periodicallydata obtained by global magnetohydrodynamic simu-with a period of about 130s. Since all 4 Clusterlations of the Earth's magnetosphere-ionosphere sy- spacecrafts observed these FTEs, we applied the four-tem. The simulations are limited to the due south- spacecraft techniques“Minimum Directional Deriva-ward Interplanetary Magnetic Field (IMF) case for tive (or Difference)”(MDD) and "Spatio-Temporalsimplicity. The three methods are all based on the Diference" (STD) to calculate the dimension, motionline integration of electric field and differ in the choiceand scale of these FTEs. The inferred northwardlyof integration path, radial rays in the equatorial plane reconnected fAux tubes for these FTEs are shown tofor method 1, last closed magnetic field lines formove northward or north-east and tailward with amethod 2, and IMF lines nearby the reconnection linequasi-2-D structure and a scale of 0.87~1.81 Re Thefor method 3. The effect of numerical difusion of theionospheric footprint of the Cluster spacecrafts du-algorithm is included approximately by an equivalentring the boundary passage is shown to map centrallyuniform resistivity. For a properly selected numeri-withil中国煤化工UTLASS Finlandcal resistivity, the three methods give answers of theradarCNMH(ter power of CUT-reconnection potential, which are reasonably close to LASS uara ennulceu川sy ucuruy with the magneto-each other. The reconnection voltage is found to bespheric FTEs at the latitude of the Cluster footprint.Cao Jinbin et al: Multi Scale Physical Proce8s in the Magmetosphere457These radar auroral features subsequently propagatedexistence of the shear fows modifies the structure andpoleward, forming classic‘ 'poleward-moving radarstrength of the time dependent intermediate shocksauroral form”structures at higher latitudes. Whilst,significantly. (1) The perpendicular shear flow Vyothe FTE motions are shown to be consistent with thecan lead to the reversal of the rotation sense of theexpected motion of reconnected magnetic fux tubestangential magnetic field in time -dependent interme-over the surface of the magnetopause, arising from adiate shocks. The critical shear flow speeds, Uc andpredominantly sub-solar reconnection site during theV0e, for the reversal of field rotations in TDIS andprevailing upstream conditions.TDISO, respectively, are calculated. (2) For shearHu et al] studied Dayside flow bursts and highfAow speed Uyo = Ue, the strong TDIS is replaced by alatitude reconnection when the IMF is strongly north-steady Intermediate Shock (IS), whereas at VyO = Ucward. The characteristics of dayside ionospheric con-an Alfven wave pulse is present in the reconnectionvection are studied using Northern emispheric Super-layer. (3) The presence of tangential shear fow Uz0DARN data and DMSP particle and flow observa-alters not only the strength of TDIS and TDISO buttions when the Interplanetary Magnetic Field (IMF)also the critical speeds ve and Voe. The critical shearwas strongly northward during 13:00- -15:00UT onflow speeds obtained from our simulation are found2 March 2002. Although IMF Bx was positive,to agree very well with those from the ideal Magneto-which is believed to favour Southern Hemispherehydrodynamics (MHD), in which the time dependenthigh-latitude reconnection at equinox, a four-cell con-intermediate shocks are replaced by rotational discon-vection pattern was observed and lasted for more thantinuities.1.5h in the Northern Hemisphere. The reconnectionXiao et al13) present in situ evidence for therate derived from an analysis of the Northern Hemi-structure of the magnetic null in a 3D reconnectionsphere Super-DARN data ilustrates that the high-event in the Earth's magnetotail. Magnetic reconne~latitude reconnection was quasi-periodic, with a petion is one of the most important processes in astro-riod between 4~16 min. A sawtooth-like and reversephysical, space and laboratory plasmas. Identifyingdispersed ion signature was observed by DMSP-F14the structure around the point at which the magneticin the sunward cusp convection at around 14:41 UT,field lines break and subsequently reform, known asconfirming that the high-latitude reconnection wasthe magnetic null point, is crucial to improving ourpulsed accompanying the pulsed reconnection, strongunderstanding reconnection. But owing to the inhe-antisunward ionospheric flow bursts were observed inrently three-dimensional nature of this process, mag-the post- noon LLBL region on closed field lines, pro-netic nulls are only detectable through measurementspagating with the same speed as8 the plasma convec- obtained simultaneously ftom at least four points intion. DMSP flow data show that a similar fow pat-space. Using data collected by the four spacecraft oftern and particle precipitation occurred in the conju-the Cluster consellation as they traversed a difusiongate southern bemisphere.region in the Earth's magnetotail on 15 September,Sun et al12) investigate the efects of sbear fows2001, we report here the first in situ evidence for theon the so-called“component reconnection" , in which structure of an isolated magnetic null. The resultsthe guide field By≠0, by solving a one-dimensionalindicate that it has a positive-spiral structure whoseRiemann problem for magnetopause reconnection 18-spatial extent is of the same order as the local ioning a resistive MHD simulation. Specifically, we con-inertial length scale, suggesting that the Hall effectsider the existence of a shear flow perpendicular tocould play an important role in 3D reconnection dy-the antiparallel magnetic field Bz, while a finite shearnamics.fow tangential to B, may also be present. In theScalings of Hall magnetohydrodynamics recon-cases without a magnetosheath flow and having thus a nection in higb-β plasmas has been studied in steadysbeared flow across the reconnection layer, two timestates by Wane. et al(14l. It azain confirms predependent intermediate shocks TDIS and TDIS0 arevious中国煤化工:tion results that .present on the magnetosheath side and the magneto-whileMCNMHGlayerisscaledbyspheric side, respectively, and the strength of TDIS isWA/SLei = q/Le, where wA 18 the Alfven frequency,much stronger than that of TDISO. Nevertheless, theSei is the ion gyrofrequency, Lc is the typical 8y-458Chin. J. Space Sci.2008, 28(5)tem length scale, and dh = c/Wpi is the ion inertial type of field and particle configuration has not beenlength, the length of the layer should be scaled by directly observed in space plasmas. Xiao et al17](wA/S2i)1/2Lc = (d;Lc)2/2, to yield the fast recon-report the identification of a pair of nulls, the null-nection rate of (d/Lc)2/2vA with UA 88 the Alfven null line that connects them, and associated fans andvelocity. It is also shown that the reconnection rate spines in the magnetotail of the Earth using data fromis proportional to the perturbed boundary flow. Fur- the four Cluster spacecraft. With d; and de designat-thermoreit is found that in the high-B plasmas, the ing the ion and electron inertial lengths, respectively,reconnection keeps constant in the regime β < 2, andthe separation between the nulls is found to be aboutdecays a8 β-1/2 for β≥2.0.7+0.3du and an associated ocilltion is identifed asXiao et al3), Magnetic reconnection is a major8 lower-hybrid wave with wavelength about de. Thisenergy transfer process in plasmas, and plays a crucial in situ evidence of the full 3D reconnection geometryrole in space plasma physics and space weather pro-and associated dynamics provides an important stepcesses such as solar Aare, CME, and magnetosphere towards establishing an observational frarmework ofsubstorms, a8 well as in MHD instabilities in mag-3D reconnection.netic confinement fusion. It is therefore a fundamen-Density depletions were detected by Wind, Clus-tal problem in plasma physics. Except for a system ter, and Polar spacecrafts in the observations of diffu-such as toroidal magnetic confinement devices with asion region encounters at the Earth's magnetotail andperiodic boundary condition, three dimensional (3D)magnetopause. Yang et al8] investigate the layersmagnetic reconnection in general occurs on magneticof density depletion in magnetic reconnection usingseparatrix generated by magnetic nulls. Xiao et al15] a 2.5-dimensional Hall MHD code developed from ahere briefly review the 3D magnetic reconnection the-multistep implicit scheme. The numerical results atory and progresses of related satellite observations.the quasi-steady state of the Hall MHD reconnectionXiao et al[16] studied fast magnetic reconnec-with d:/Lc≥1.0, where di is the ion inertial lengthtion in the magnetotail. Fast reconnection is crucial and Le is the half thickness of the initial current sheet,to magnetospheric substorms, solar and stellar fares show not only the density depletions along the mag-and fusion plamas. UItimate confirmation of fastnetic separatrices but also a density dip in the x di-reconnection must be achieved by multi-spacecraft rection near the X neutral line. The comparativedetections of the reconnection rate itself and 880-tests with various Hall terms demonstrate that theciated dimensions of the difusion region. Here we density depletion in the magnetic reconnection is 8report a multi spacecraft measurement of fast recon-peculiar feature of the case with a strong Hall effectnection rate 7rec≈Vin≈(0.07 ~ 0.15)uA based on (d;/Lc ≥1.0). The layers of low density following thedirectly measurements of the plasma flow into the dif-shape of separatrices are in coincidence with the refusion region, where uhn is the speed of reconnecting gions of high magnetic pressure. In the spatial profileAux and VA the characteristic Alfven speed. It falls of density ρ along z, which is in quantitative agree-in the range of about (0.03 ~ 0.2)UA predicted inment with Cluster observation, the obvious dips lo-steady state reconnection simulation. The characte- cated at the separatrices coincide with the peak andristic sizes for the difusion region of the width Lz≈valley in tbe profle of Kr(J x B)z/p for the case with0.9d; (= 460km) and the length Lx≈(3.3 ~ 5.1)ddh/Lc = 2.0. It indicates the major role of the Hall(= 1680 ~ 2597 km) are measured as well. The lengthterm in the formation of the density depletion layersof the diffusion region Lx is determined for the firstnear the separatrices. On the basis of the comparisontime based on the in situ observations. Furthermore,between Wind observation and simulation results, weother features detected during the event also matchargue that the density dip observed by Wind wouldthe previous observation and simulation results.be distributed around the reconnection X-line, ratherDetection of a separator line that connects mag-than along the magnetic senaratrix. In the case withnetic nulls and the determination of the dynamics a stron中国煤化工fows go aroundand plasma environment of such a structure canthe difCNMHGnsinthisregionimprove our understanding of the three-dimensional are signncantly reaucea aue to tne action of the in-(3D) magnetic reconnection process. However, this plane Lorentz force. A density dip in the vicinity ofCao Jinbin et al: Multi-Scale Physical Process in the Magnetosphere459the X-line is attributed to the hard entry of in-planeconnection events. Simultaneously, Cluster observedion flow and might be related to an increase of the electromagnetic wave associated with reconnectionion drift velocity in the y direction.events. There are three kinds of reconnection eventsLi et al make a numerical study of the Hall in these 14 events. There are 8 events in the first kindMHD reconnection proces with various values of the of reconnection event, in this kind of reconnectionplasma parameter β (the ratio of plasma pressure events wave activity were observed prior to the recon-to magnetic pressure) ranging from 0.5 to 6.5. The nection event and simultaneously Hall magnetic feldreconnection rate 8A/Ht|et in quasi-steady state iswas observed. The wave activity included right handfound to be in the range of 0.15≥8A/Htlet≥0.095. polarized Whistler. The second kind of reconnec-The time series of the normal magnetic field By andtion events had two events. Whistler waves and Hallthe velocity components Ux and Uz at selected points magnetic field were observed in this kind of events,are transformed into power spectra via Fast Fourier but the wave activity was not prior to reconnectionTransform (FFT). The results show that the fre-events. The third kind of events had two events. Thequencies of the power spectra are in the range of Whistler waves and Hall magnetic were not observedSei < w < 8Sci, hei being the proton cyclotron fre-in this kind of reconnection event. In these 14 events,quency. With the increase of B, the peak amplitude the strong Whistler waves corresponded to Hall mag-decreases and the peak frequency gets lower. Usingnetic field. Whistler waves may mainly be excited inthe Minimum Variance Analysis (MVA) the direction Hall magnetic field regions.of propagation of the wave is determined. Th anglea between the wave vector K and the local magnetic4 Solar Wind Magnetospherefield B increases with increasing B. The hodographInteractionof the electric field E is plotted for selected pointsin the three calculated examples. The results of thisWang et a[22] did a statistical survey of solar windwork might provide a possible link between the fastdynamic pressure (Pa) pulses and geosynchronousreconnection rate and the whistler wave.The magnetic fux ropes observed by Clustermagnetic fields observed between 1998 and 2005. Infrom 2001 to 2005 in the magnetotail are surveyedgeomagnetic quiet times with Dst>- -50nT, we findpy Zhang et al(20]. We have performed a statistic111 solar wind dynamic pressure pulses which pro-study on the relationship between the formation ofduce geosynchronous magnetic field response8. Thesethe magnetic fux ropes and Interplanetary Magneticresponses are often observed by two or three GOESField (IMF). Considering the IMF condition when thespacecraft at different local times in geosynchronousfux ropes are observed, For the 80% of the total 73orbit. The magnitudes of the geosynchronous mag-fux ropes cases, there are dominant By in IMF 8C-netic field changes (dB,) have a peak near thecordingly, while in the 78% of all cases there are corenoon meridian, similar to the results obtained in thefields with the same direction as the IMF By. It isstudy of the response of the geosynchronous fieldpossible tbat IMF can change the relative directionto the large and sharp solar wind dynamic pres-of the magnetic fields in the northern and southernsure variations. However, the relative change ofplasma sheet to form the magnetic topology favoringthe geosynchronous magnetic field dBz/B: (wberethe formation of the magnetic fux rope. IMF also hasBz is the average of the geosynchronous magnetica decisive efect on the directions of the core field infield Bz observed during the response to the pres-sure pulse) depends weakly on the local time; thusthe fux ropes. As indicated in these statistic results,the change of Bz(dB2) is proportional to the av-the formation of the fux ropes in the magnetotailerage field (Bz). As the magnitude of the relativedoes not depend on the direction of the IMF Bz.Wei et al(2] present the Whistle waves and Hallchange of solar wind dynamic pressure (dPa/Pa) in-magnetic field associated with near-Earth magnetocrea中国煤化工u magnetic fieldtail reconnection observed by Cluster. During 2001-variatYHThese results im-2003, the Cluster spacecraft passed through the near-ply tC N M H Gsynchronous magnetic field response could be determined by Bz. InEarth magnetotail, and observed 14 magnetotail readdition, the interplanetary field orientation does not460Chin. J. Space Sci.2008, 28(5)affect the response significantly. Using an MHD code for electrons with certain energy, 8 their lo8s regionwhich models the global behavior of the solar wind- controlled by hiss disappears, the inner radiation beltmagnetosphere ionosphere system, we reproduce the may connect with the outer radiation belt togethermain characteristics of the observations.completely.Several mechanisms have been used to explainAn extensive study of ring current injection andsolar wind plasma entry into the plasma sheet in the intensifcation of the storm-time ring current is con-magnetotail by Zhou et al[23). In this paper, we fo- ducted with three dimensional (3D) test particle tra-cus on the Gradient Drift Entry (GDE) process in jectory calculations (TPTCs) by Xie et al25]. Thethe equatorial fanks of the magnetosphere, based on TPTCs reveal more accurately the process of ringthe magnetopause picture of a tangential discontinu- current injection with the main results being the fol-ity with a small tangential electric field as was sug- lowing.gested by Alfven (1968). We discuss the GDE ef-(1) An intense convection electric field can efe~ciency in different conditions using the adiabatic the tively energize and inject plasma sheet particles intoory. It can be clearly shown that the GDE eficiencythe ring current region within 1~3 hours.is much lower during southward Interplanetary Mag(2) Injection ions often follow chaotic trajecto-netic Field (IMF), with a strong energy filter effect forries in non-adiabatic regions, which may have impli-incoming solar wind particles. Given a typical condi- cations in storm and ring current physics.tion, a critical energy for particle entry is calculated(3) The shielding electric field, which arises a8to be several keV. Only those particles with higher a consequence of enhanced convection and co-exists.energy can penetrate the magnetopause, a condition with injection and convection electric field, leads thewhich can be also proved by test particle simulations. original open trajectories to change into closed ones,The lower eficiency than that during northward IMF thus may play an important role in the formation ofduring periods of southward IMF is in agreement with the symmetric ring currentthe diferent properties of the plasma sheet observed,i.e., hot and tenuous when the IMF is southward, cold6 Plasma Sheetand dense for northward IMF.Lei et al26) studied current Sheet Structure and Mo5 Radiation Belt and Ring Currenttion Observed by Cluster on September 15, 2001.Multiple crossings of the neutral sheet were observedLi et al24) established a global qusi-linear difu- by the FGM and CIS experiments onboard the Clus-sion model of electrons by using the whistler-mode ter at -19 Re from 04:30UT to 05:15 UT on Septem-wave amplitude distribution model, the electron den- ber 15, 2001. The high-speed proton fAow, which resity distribution model and the IGRF10 magnetic versed fom tailward to Earthward, was detected dur-field model in 1