The Earth is buffered from the ferocious onslaught of the solar wind by a thin layer of matter known as the atmosphere and geospace.This layer absorbs energy from irradiance and outburst from the Sun,as well as from d...The Earth is buffered from the ferocious onslaught of the solar wind by a thin layer of matter known as the atmosphere and geospace.This layer absorbs energy from irradiance and outburst from the Sun,as well as from disasters,transient phenomena and anthropogenic emissions originated from Earth.Through complicated physics,the absorbed energy changes the atmospheric and geospace state and sometimes gets re-released to power extreme events such as space weather.Taking place globally,these complicated processes cannot be understood unless they are studied globally.The Chinese scientists have proposed the International Meridian Circle Program(IMCP)to meet this demand.By operating nearly 1000 instruments encompassing all latitudes along with the 120°E–60°W longitudes,IMCP aims,for the first time,to construct comprehensive 3D data representation of the atmosphere and geospace on a global scale and empower interdisciplinary research to tackle key questions related to Earth’s environment and climate change.展开更多
Energetic electron measurement is of great significance to theoretical space physics research and space weather applications.Current energetic electron detectors must cooperate with a spin-stabilized satellite platfor...Energetic electron measurement is of great significance to theoretical space physics research and space weather applications.Current energetic electron detectors must cooperate with a spin-stabilized satellite platform to achieve high angular resolution in pitch angle distribution and three-dimensional(3D)imaging measurement of energetic electrons.This article introduces a cross-type quasi-3D imaging electron spectrometer(IES)based on pinhole imaging technology developed in the laboratory.The imager is composed of five imaging units,including a nine-pixel area array Si-PIN detector imaging unit in the middle and four three-pixel linear array Si-PIN detector imaging units placed in a cross-shape around it.The combination of five imaging units forms two orthogonal nine-pixel linear array detectors(with a common pixel in the middle).There are four pixels with a view angle of 20°×20°in the 45°oblique directions of the cross-type detection array.There are 21 imaging pixels in the entire crosstype sensor head,corresponding to 21 directions.Two multichannel integrated preamplifier ASICs are integrated in the sensor head to realize particle signal readout from 21 pixels.With a back-end electronics system,each pixel can achieve high energy resolution detection of 50–600 keV electrons.Radioactive sources and electron accelerators are used to calibrate the cross-type imaging sensor head,and the results demonstrate its good energy and directional detection characteristics(the energy resolution reaches 6.9 keV for the incident 200 keV electron beam).We performed simulations on the imaging sensor head’s ability to measure the electron pitch angle distribution on the three-axis stabilized platform,and the results show that the sensor head can perform quasi-three-dimensional detection of electrons incident within 2πsolid angles on the three-axis stabilized satellite platform,with an average angular resolution of the electron pitch angle distribution of less than 6°.展开更多
A three-dimensional numerical model is employed to investigate ULF waves ex-cited by the sudden impulse (SI) of the solar wind dynamic pressure interacting with a dipole magnetosphere. We focus on the solar wind-magne...A three-dimensional numerical model is employed to investigate ULF waves ex-cited by the sudden impulse (SI) of the solar wind dynamic pressure interacting with a dipole magnetosphere. We focus on the solar wind-magnetosphere energy coupling through ULF waves, and the influences of the SI spectrum on the cavity mode structure and the energy deposition due to field line resonances (FLRs) in the magnetosphere. The numerical results show that for a given SI lasting for 1 min with amplitude of 50 mV/m impinging on the subsolar magnetopause, the total ULF energy transported from the solar wind to the magnetosphere is about the magni-tude of 1014 J. The efficiency of the solar wind energy input is around 1%, which depends little on the location of the magnetopause in the model. It is also found that the energy of the cavity mode is confined in the region near the magnetopause, whereas, the energy of the toroidal mode may be distributed among a few specific L-shells. With a given size of the model magnetosphere and plasma density distri-bution, it is shown that the fundamental eigenfrequency of the cavity mode and the central locations of the FLRs do not vary noticeably with the power spectrum of the SI. It is worth noting that the spectrum of the SI affects the excitation of higher harmonics of the global cavity mode. The broader the bandwidth of the SI is, the higher harmonics of cavity mode could be excited. Meanwhile, the corresponding FLRs regions are broadened at the same time, which implies that the global cavity modes and toroidal modes can resonate on more magnetic L-shells when more harmonics of the global cavity modes appear.展开更多
A research topic of great interest to the space physics community is the observation of plasmas flowing at hundreds of kilometers per second in the Earth’s plasma sheet. Although considerable effort has been made to ...A research topic of great interest to the space physics community is the observation of plasmas flowing at hundreds of kilometers per second in the Earth’s plasma sheet. Although considerable effort has been made to understand the source of fast-flowing plasmas, many questions remain unanswered about the mechanisms that produce high-speed flows and the effects they have on magnetospheric disturbances, especially their contributions to magnetospheric convection and substorms. In this paper, we discuss briefly the history of high-speed flows and review the proposed mechanisms, signatures of high-speed flows in auroras and their interaction with the background plasma. We then summarize the relationships between high-speed flows and magnetic structures, discuss questions associated with substorms, and finally pose several important scientific questions that need to be addressed.展开更多
It is believed that a southward interplanetary magnetic field (IMF) is mainly responsible for the energy input from solar wind into the magnetosphere.This paper presents an unusual case of strong anti-sunward plasma f...It is believed that a southward interplanetary magnetic field (IMF) is mainly responsible for the energy input from solar wind into the magnetosphere.This paper presents an unusual case of strong anti-sunward plasma flow (up to 2 km/s) in the polar cap ionosphere and large cross-polar cap potential (CPCP) during a period of horizontal IMF (|BZ| < 2 nT) observed by both ACE (at the L1 point) and Geotail (on the dusk flank of the magnetosheath).The CPCP is even higher than that under preceding BZ ≈-23 nT.Furthermore,GOES8 observed that the magnetosheath field turns northward as the anti-sunward plasma flow and CPCP start to increase,which implies that the magnetosheath field interacting with the Earth's magnetopause has significantly rotated and differs from the IMF observed by ACE and Geotail.In accordance with previous theoretical work,we suggest that the magnetic field line draping produces a southward magnetosheath field and enhances anti-sunward plasma flow and the CPCP.展开更多
The characteristic and properties of ULF waves in the plasmasphere boundary layer during two very quiet periods are present. The ULF waves were detected by Double Star TC-1 when the spacecraft passed through the plasm...The characteristic and properties of ULF waves in the plasmasphere boundary layer during two very quiet periods are present. The ULF waves were detected by Double Star TC-1 when the spacecraft passed through the plasmasphere in an outbound and inbound trajectories, respectively. A clear association between the ULF waves and periodic variations of energetic ions fluxes was observed. The ob-servations showed that the wave frequency was higher inside the plasmasphere than outside. The mechanism generating these ULF waves and possible diagnos-ing of the "classical plasmapause" location with the ULF wave were discussed.展开更多
Three earthward flowing magnetic flux ropes observed in the duskside plasma sheet at geocentric solar magnetospheric coordinate X~–55 Re by P1 and P2 of acceleration,reconnection,turbulence and electrodynamics of moo...Three earthward flowing magnetic flux ropes observed in the duskside plasma sheet at geocentric solar magnetospheric coordinate X~–55 Re by P1 and P2 of acceleration,reconnection,turbulence and electrodynamics of moon’s interaction with the sun mission during 13:00–15:00 UT on July 3,2012,were studied.The morphologies of the flux ropes were studied in detail based on Grad-Shfranov reconstruction method and electronic pitch angle distribution data.It is found that(1)the flux rope cross-sectional dimensions are 1.0 Re×0.78 Re,1.3 Re×0.78 Re,and 2.5 Re×1.25 Re,respectively.The magnetic field lines were asymmetric about the center with field line compression on both sides of the current sheet at the leading region;(2)the electron energy flux data presented asymmetry with larger electron flux and lower temperature in the precursor region.The flux ropes were blocked by the resistance of compressed particle density in the front central plasma sheet and the enhanced magnetic field on its sides;and(3)it is found that the flux rope has a layered structure.From inside out,event 1 can be divided into three regions,namely electronic depletion core region,closed field line region,and the caudal area possible with fields connected with the ionosphere.It suggests that the flux ropes cannot merge with the tail magnetic field lines near the lunar orbit.Especially,the flux rope asymmetrical shape reflects the different reconnection processes that caused it on both sides of the magnetic structure.The events shown in this paper support the multiple X-line magnetic reconnection model for flux ropes with in situ observations.展开更多
Two substorms occurred at ～04:05 and ～04:55 UT on February 26,2008 are studied with the in-situ observations of THEMIS satellites and ground-based aurora and magnetic field measurements.Angelopoulos et al.have made ...Two substorms occurred at ～04:05 and ～04:55 UT on February 26,2008 are studied with the in-situ observations of THEMIS satellites and ground-based aurora and magnetic field measurements.Angelopoulos et al.have made a comprehensive study of the 04:55 UT event.We showed detailed features of the two substorms with much attention to the first event and to the rela-tionship between mid-tail magnetic reconnection(MR) and substorm activities.It was found that in the earlier stage of each substorm,a first auroral intensification occurred 2-3 min soon after the start of mid-tail MR,followed by a slow and very lim-ited expansion.The auroral arcs were weak,short-lived,and localized,characterizing all features of a pseudobreakup.We re-garded the first auroral brightening as the initial onset of the substorms.A few minutes later,a second stronger auroral intensification appeared,followed by quick and extensive expansions.It was interesting to note that the second brightening and related poleward expansion happened almost simultaneously(within a couple of minutes) with the onset of earthward flow and dipolarization in the near-Earth tail and other phenomenon of the substorm expansion phase.We thus regarded the second auroral brightening as the major onset of the substorms.Furthermore,it was seen that during the growth phase of the two substorms,the polar cap open flux Ψ kept increasing,while it quickly reduced during the substorm expansion and recovery phase.These variations of Ψ implied that the evolution of the two substorm expansion phases were closely related to MR of tail lobe open field lines.Analysis of substorm activities revealed that the two events studied were small substorms;while estimate of MR rate indicated that the MR processes in the two substorms were weak.The aforementioned observations suggested that mid-tail MR initiated the pseudobreakup first;the earthward flow generated by MR transported magnetic flux and energy to the near-Earth tail to cause the formation of SCW and CD,which induced near-Earth dipolarization and major auroral brightening,and eventually led to the onset of the substorm expansion phase.These results were clearly consistent with the picture of NENL and RCS models and supported the two step initiation scenario of substorms.展开更多
Earth's bow shock is the result of interaction between the supersonic solar wind and Earth's magnetopause. However, data limitations mean the model of the shape and position of the bow shock are based largely ...Earth's bow shock is the result of interaction between the supersonic solar wind and Earth's magnetopause. However, data limitations mean the model of the shape and position of the bow shock are based largely on near-Earth satellite data. The model of the bow shock in the distant magnetotail and other factors that affect the bow shock, such as the interplanetary magnetic field(IMF) B_y, remain unclear. Here, based on the bow shock crossings of ARTEMIS from January 2011 to January 2015, new coefficients of the tail-flaring angle a of the Chao model(one of the most accurate models currently available) were obtained by fitting data from the middle-distance magnetotail(near-lunar orbit, geocentric distance -20R_E>X>-50R_E). In addition, the effects of the IMF B_y on the flaring angle a were analyzed. Our results showed that:(1) the new fitting coefficients of the Chao model in the middle-distance magnetotail are more consistent with the observed results;(2) the tail-flaring angle a of the bow shock increases as the absolute value of the IMF B_y increases. Moreover, positive IMF B_y has a greater effect than negative IMF B_y on flaring angle. These results provide a reference for bow shock modeling that includes the IMF B_y.展开更多
Although much has been done on the hemispheric asymmetry (or seasonal variations) of auroral hemispheric power (HP), the dependence of HP hemispheric asymmetry on solar cycle has not yet been studied. We have analyzed...Although much has been done on the hemispheric asymmetry (or seasonal variations) of auroral hemispheric power (HP), the dependence of HP hemispheric asymmetry on solar cycle has not yet been studied. We have analyzed data during 1979-2010 and investigated the dependence of HP hemispheric asymmetry/seasonal variation for the whole solar cycle. Here we show that (1) the hemispheric asymmetry of HP is positively correlated to the value of solar F10.7 with some time delay; (2) it is closely related to the coupling function between the solar wind and magnetosphere; and (3) the winter hemisphere receives more auroral power than the summer hemisphere for Kp ~0 to 6. The statistic results can be partly understood in the framework of the ionospheric conductivity feedback model. The similarity and differences between our results and previous results are discussed in the paper.展开更多
When the IMF turns southward, a great amount of magnetic energy is stored in the magnetotail, and the electric field across the magnetotail substantially en-hances. As long as magnetic reconnection (MR) in the mag-net...When the IMF turns southward, a great amount of magnetic energy is stored in the magnetotail, and the electric field across the magnetotail substantially en-hances. As long as magnetic reconnection (MR) in the mag-netotail initiates and continues, the magnetic field and plasma in the central plasma sheet are carried away to the near-Earth and down to the tail, the magnetic field and plasma in the lobe region enter the CPS and are involved in MR. We call this process “Continuous Lobe Reconnection (CLR)”. In this paper a detailed analysis of Cluster observa-tion of MR through 2001―2003 is made. Plenty of CLR events are found that led to considerable changes of tail con-figuration, appearance of BBF, as well as large-scale bubbles in which both plasma temperature and number density sub-stantially decrease. It is shown that in general CLR events last for dozens of minutes and have good correspondence to substorm initiation under the condition of continuous southward IMF.展开更多
We present evidence of geomagnetic storms in Mercury’s magnetosphere based on MESSENGER magnetic field observations made just before the probe impacted the planet.Our findings answer the question of whether geomagnet...We present evidence of geomagnetic storms in Mercury’s magnetosphere based on MESSENGER magnetic field observations made just before the probe impacted the planet.Our findings answer the question of whether geomagnetic storms can occur in other planetary magnetospheres.The interaction of the solar wind with Mercury’s magnetosphere is known to involve flux transfer events in the dayside magnetosphere,plasmoids and flux ropes in the magnetotail,and substorm-like processes,all of which occur morphologically similar to Earth but with significant differences.The significantly weaker magnetic field,smaller magnetosphere,and much faster timescale of processes around Mercury,when compared with Earth,enable charged particles to escape its magnetosphere more efficiently through magnetopause shadowing and direct bombard of the surface.Our analysis of MESSENGER’s data during a coronal mass ejection(CME)proves that,despite these substantial differences,a bifurcated ring current can form in Mercury’s magnetosphere that initiates magnetic storms under strong solar wind driving.展开更多
In cases where substorm injections can be observed simultaneously by multiple spacecraft,they can help elucidate the potential mechanisms of particle transport and energization,of great importance to understanding and...In cases where substorm injections can be observed simultaneously by multiple spacecraft,they can help elucidate the potential mechanisms of particle transport and energization,of great importance to understanding and modeling the magnetosphere.In this paper,using data returned from the BeiDa-IES（BD-IES） instrument onboard a satellite in an inclined（55°） geosynchronous orbit（IGSO）,in combination with two geo-transfer orbiting（GTO） satellite Van Allen Probes（A and B）,we analyze a substorm injection event that occurred on the 16 th of October 2015.During this substorm injection,the IGSO onboard BD-IES was outbound,while both Van Allen Probe satellites（A and B） were inbound,a configuration of multiple trajectories that provides a unique opportunity to simultaneously investigate both the inward and outward radial propagation of substorm injection.Indicated by AE/AL indices,this substorm was closely related to an IMF/solar wind discontinuity that showed a sharp change in IMF Bz direction to the north.The innermost signature of this substorm injection was detected by Van Allen Probes A and B at L-3.7,while the outermost signature was observed by the onboard BD-IES instrument at L-10.These data indicate that the substorm had a global,rather than just local,effect.Finally,we suggest that electric fields carried by fast-mode compressional waves around the substorm injection are the most likely candidate mechanism for the electron injection signatures observed in the inner- and outermost inner magnetosphere.展开更多
The strong field-aligned pitch angle distribution of electrons is observed right at the dipolarization front (DF) before the arriving of a high speed flow when the four Cluster satellites are traveling in the magnetot...The strong field-aligned pitch angle distribution of electrons is observed right at the dipolarization front (DF) before the arriving of a high speed flow when the four Cluster satellites are traveling in the magnetotail around 15 R E on July 22, 2001. The increased electron fluxes only last for a short time period at the DF, corresponding to just a few bouncing periods for 1 keV electrons. The field-aligned current contributed by these electrons agrees well with that calculated by the magnetic field observations by four satellites at the front. These electron streams are found in the energy range of 0.2-2 keV, peak around 1 keV. It is suggested that these downward current electrons may be originated near the aurora region by some kinds of potential structure. The occurrence of these electrons implies that the formation of the dipolarization front and the associated field-aligned current play an important role in the magnetosphere-ionosphere coupling.展开更多
The plasmasphere is a region of relatively dense （-10-10000 cm^-3） plasma, surrounding the Earth and ex- tending to distances of about five Earth radii （RE）. It is filled with large amount of cold （-1 eV） plasma...The plasmasphere is a region of relatively dense （-10-10000 cm^-3） plasma, surrounding the Earth and ex- tending to distances of about five Earth radii （RE）. It is filled with large amount of cold （-1 eV） plasma originated from the Earth＇s ionosphere and co-rotating with the Earth due to the large scale co-rotation electric field. The outermost boundary of the plasmashere is called the plasmapause.展开更多
Foreshock cavitons are transient phenomena observed in the terrestrial foreshock region.They are characterized by a simultaneous depression of magnetic field magnitude and plasma density,which are bounded with enhance...Foreshock cavitons are transient phenomena observed in the terrestrial foreshock region.They are characterized by a simultaneous depression of magnetic field magnitude and plasma density,which are bounded with enhancements of these two parameters and surrounded by ultralow frequency(ULF)waves.Previous studies focused on the interplanetary magnetic field(IMF)conditions,solar wind(SW)conditions,and the growth of the foreshock waves related to the generation of foreshock cavitons.Previously,a multipoint spacecraft analysis method using Cluster data was applied to analyze only two foreshock cavitons,and this method did not consider uncertainties.In this study,multipoint spacecraft analysis methods,including the timing method,the minimum directional derivative(MDD)method,and the spatiotemporal difference(STD)method are applied to determine the velocity in both spacecraft and solar wind frames.The propagation properties show good agreement with previous results from simulations and observations that most cavitons move sunward in the solar wind frame,with the velocities larger than the Alfvén speed.The propagation properties of foreshock cavitons support the formation mechanism of cavitons in previous simulations,which suggested that cavitons are formed due to the nonlinear evolution of compressive ULF waves.We find that there is clear decreasing trend between the size of cavitons and their velocity in the solar wind frame.In addition,the timing method considering errors has been applied to study the evolution properties by comparing the velocities with errors of the leading and trailing edges,and we identify three stable cavitons and one contracting caviton,which has not been studied before.Most cavitons should remain stable when they travel toward the Earth’s bow shock.The relationship between the size of foreshock cavitons and their distance from the bow shock is also discussed.展开更多
Outflowing ion beams forming four successive inverted-V structures in the energy-time spectrograms of H+, He+, and O+ were observed at an altitude of 3.4 RE by Cluster satellites travelling above the auroral accelerat...Outflowing ion beams forming four successive inverted-V structures in the energy-time spectrograms of H+, He+, and O+ were observed at an altitude of 3.4 RE by Cluster satellites travelling above the auroral acceleration region (AAR) in the southern hemisphere on February 14, 2001. Energization by negative U-shaped potential structures in the AAR is believed to be responsible for the formation of these outflowing ion inverted-V structures. Thus, utilizing the different motion properties of the three ion species, the altitude of the upper boundary of the AAR is estimated to be ~11100 km. Moreover, based on multi-satellite observations, each of these U-shaped potential structures involved in this event crosses the latitudinal direction at ~0.4°–1° invariantlatitude (ILAT), moving poleward at an average speed of ~0.2° ILAT per minute, before disappearing at ~71.5° ILAT.展开更多
基金Supported by Beijing Municipal Science and Technology Commission(Z181100002918001)。
文摘The Earth is buffered from the ferocious onslaught of the solar wind by a thin layer of matter known as the atmosphere and geospace.This layer absorbs energy from irradiance and outburst from the Sun,as well as from disasters,transient phenomena and anthropogenic emissions originated from Earth.Through complicated physics,the absorbed energy changes the atmospheric and geospace state and sometimes gets re-released to power extreme events such as space weather.Taking place globally,these complicated processes cannot be understood unless they are studied globally.The Chinese scientists have proposed the International Meridian Circle Program(IMCP)to meet this demand.By operating nearly 1000 instruments encompassing all latitudes along with the 120°E–60°W longitudes,IMCP aims,for the first time,to construct comprehensive 3D data representation of the atmosphere and geospace on a global scale and empower interdisciplinary research to tackle key questions related to Earth’s environment and climate change.
基金supported by the National Natural Science Foundation of China(Grant Nos.42274225,41374167 and 41674175)。
文摘Energetic electron measurement is of great significance to theoretical space physics research and space weather applications.Current energetic electron detectors must cooperate with a spin-stabilized satellite platform to achieve high angular resolution in pitch angle distribution and three-dimensional(3D)imaging measurement of energetic electrons.This article introduces a cross-type quasi-3D imaging electron spectrometer(IES)based on pinhole imaging technology developed in the laboratory.The imager is composed of five imaging units,including a nine-pixel area array Si-PIN detector imaging unit in the middle and four three-pixel linear array Si-PIN detector imaging units placed in a cross-shape around it.The combination of five imaging units forms two orthogonal nine-pixel linear array detectors(with a common pixel in the middle).There are four pixels with a view angle of 20°×20°in the 45°oblique directions of the cross-type detection array.There are 21 imaging pixels in the entire crosstype sensor head,corresponding to 21 directions.Two multichannel integrated preamplifier ASICs are integrated in the sensor head to realize particle signal readout from 21 pixels.With a back-end electronics system,each pixel can achieve high energy resolution detection of 50–600 keV electrons.Radioactive sources and electron accelerators are used to calibrate the cross-type imaging sensor head,and the results demonstrate its good energy and directional detection characteristics(the energy resolution reaches 6.9 keV for the incident 200 keV electron beam).We performed simulations on the imaging sensor head’s ability to measure the electron pitch angle distribution on the three-axis stabilized platform,and the results show that the sensor head can perform quasi-three-dimensional detection of electrons incident within 2πsolid angles on the three-axis stabilized satellite platform,with an average angular resolution of the electron pitch angle distribution of less than 6°.
基金the National Natural Science Foundation of China (Grant Nos. 40425004 and 40528005)the Major State Basic Research De-velopment Program of China (973 Program) (Grant No. 2006CB806305)
文摘A three-dimensional numerical model is employed to investigate ULF waves ex-cited by the sudden impulse (SI) of the solar wind dynamic pressure interacting with a dipole magnetosphere. We focus on the solar wind-magnetosphere energy coupling through ULF waves, and the influences of the SI spectrum on the cavity mode structure and the energy deposition due to field line resonances (FLRs) in the magnetosphere. The numerical results show that for a given SI lasting for 1 min with amplitude of 50 mV/m impinging on the subsolar magnetopause, the total ULF energy transported from the solar wind to the magnetosphere is about the magni-tude of 1014 J. The efficiency of the solar wind energy input is around 1%, which depends little on the location of the magnetopause in the model. It is also found that the energy of the cavity mode is confined in the region near the magnetopause, whereas, the energy of the toroidal mode may be distributed among a few specific L-shells. With a given size of the model magnetosphere and plasma density distri-bution, it is shown that the fundamental eigenfrequency of the cavity mode and the central locations of the FLRs do not vary noticeably with the power spectrum of the SI. It is worth noting that the spectrum of the SI affects the excitation of higher harmonics of the global cavity mode. The broader the bandwidth of the SI is, the higher harmonics of cavity mode could be excited. Meanwhile, the corresponding FLRs regions are broadened at the same time, which implies that the global cavity modes and toroidal modes can resonate on more magnetic L-shells when more harmonics of the global cavity modes appear.
基金supported by the National Natural Science Foundation of China (40874086 and 41031065)the Specialized Research Fund for State Key Laboratories (08262DAA4S)
文摘A research topic of great interest to the space physics community is the observation of plasmas flowing at hundreds of kilometers per second in the Earth’s plasma sheet. Although considerable effort has been made to understand the source of fast-flowing plasmas, many questions remain unanswered about the mechanisms that produce high-speed flows and the effects they have on magnetospheric disturbances, especially their contributions to magnetospheric convection and substorms. In this paper, we discuss briefly the history of high-speed flows and review the proposed mechanisms, signatures of high-speed flows in auroras and their interaction with the background plasma. We then summarize the relationships between high-speed flows and magnetic structures, discuss questions associated with substorms, and finally pose several important scientific questions that need to be addressed.
基金supported by the KIP Pilot Project of the Chinese Academy of Scineces(KZCX2-YW-123)the National Natural Science Foundation of China (41004072,41031065,41074106,41074117,40974090,40874088 and 40831061)the National Basic Research Program of China(2011CB811405)
文摘It is believed that a southward interplanetary magnetic field (IMF) is mainly responsible for the energy input from solar wind into the magnetosphere.This paper presents an unusual case of strong anti-sunward plasma flow (up to 2 km/s) in the polar cap ionosphere and large cross-polar cap potential (CPCP) during a period of horizontal IMF (|BZ| < 2 nT) observed by both ACE (at the L1 point) and Geotail (on the dusk flank of the magnetosheath).The CPCP is even higher than that under preceding BZ ≈-23 nT.Furthermore,GOES8 observed that the magnetosheath field turns northward as the anti-sunward plasma flow and CPCP start to increase,which implies that the magnetosheath field interacting with the Earth's magnetopause has significantly rotated and differs from the IMF observed by ACE and Geotail.In accordance with previous theoretical work,we suggest that the magnetic field line draping produces a southward magnetosheath field and enhances anti-sunward plasma flow and the CPCP.
基金the National Natural Science Foundation of China (Grant Nos. 40504017, 40636031)
文摘The characteristic and properties of ULF waves in the plasmasphere boundary layer during two very quiet periods are present. The ULF waves were detected by Double Star TC-1 when the spacecraft passed through the plasmasphere in an outbound and inbound trajectories, respectively. A clear association between the ULF waves and periodic variations of energetic ions fluxes was observed. The ob-servations showed that the wave frequency was higher inside the plasmasphere than outside. The mechanism generating these ULF waves and possible diagnos-ing of the "classical plasmapause" location with the ULF wave were discussed.
基金supported by the Specialized Research Fund for State Key Laboratoriesthe scientific research foundation of Shandong province Outstanding Young Scientist Award(Grant No.2013BSE27132)+2 种基金the National Natural Science Foundation of China(Grant Nos.4103106541322031)the Shandong Natural Science Foundation(Grant No.JQ201112)
文摘Three earthward flowing magnetic flux ropes observed in the duskside plasma sheet at geocentric solar magnetospheric coordinate X~–55 Re by P1 and P2 of acceleration,reconnection,turbulence and electrodynamics of moon’s interaction with the sun mission during 13:00–15:00 UT on July 3,2012,were studied.The morphologies of the flux ropes were studied in detail based on Grad-Shfranov reconstruction method and electronic pitch angle distribution data.It is found that(1)the flux rope cross-sectional dimensions are 1.0 Re×0.78 Re,1.3 Re×0.78 Re,and 2.5 Re×1.25 Re,respectively.The magnetic field lines were asymmetric about the center with field line compression on both sides of the current sheet at the leading region;(2)the electron energy flux data presented asymmetry with larger electron flux and lower temperature in the precursor region.The flux ropes were blocked by the resistance of compressed particle density in the front central plasma sheet and the enhanced magnetic field on its sides;and(3)it is found that the flux rope has a layered structure.From inside out,event 1 can be divided into three regions,namely electronic depletion core region,closed field line region,and the caudal area possible with fields connected with the ionosphere.It suggests that the flux ropes cannot merge with the tail magnetic field lines near the lunar orbit.Especially,the flux rope asymmetrical shape reflects the different reconnection processes that caused it on both sides of the magnetic structure.The events shown in this paper support the multiple X-line magnetic reconnection model for flux ropes with in situ observations.
基金supported by the National Natural Science Foundation of China (Grant No.40731056)the National Basic Research Program of China ("973" Project) (Grant No.2006CB806305)+1 种基金the NASA NAS5-02099 of USAthe für Luftund Raumfahrt 50QP0402 of Germany
文摘Two substorms occurred at ～04:05 and ～04:55 UT on February 26,2008 are studied with the in-situ observations of THEMIS satellites and ground-based aurora and magnetic field measurements.Angelopoulos et al.have made a comprehensive study of the 04:55 UT event.We showed detailed features of the two substorms with much attention to the first event and to the rela-tionship between mid-tail magnetic reconnection(MR) and substorm activities.It was found that in the earlier stage of each substorm,a first auroral intensification occurred 2-3 min soon after the start of mid-tail MR,followed by a slow and very lim-ited expansion.The auroral arcs were weak,short-lived,and localized,characterizing all features of a pseudobreakup.We re-garded the first auroral brightening as the initial onset of the substorms.A few minutes later,a second stronger auroral intensification appeared,followed by quick and extensive expansions.It was interesting to note that the second brightening and related poleward expansion happened almost simultaneously(within a couple of minutes) with the onset of earthward flow and dipolarization in the near-Earth tail and other phenomenon of the substorm expansion phase.We thus regarded the second auroral brightening as the major onset of the substorms.Furthermore,it was seen that during the growth phase of the two substorms,the polar cap open flux Ψ kept increasing,while it quickly reduced during the substorm expansion and recovery phase.These variations of Ψ implied that the evolution of the two substorm expansion phases were closely related to MR of tail lobe open field lines.Analysis of substorm activities revealed that the two events studied were small substorms;while estimate of MR rate indicated that the MR processes in the two substorms were weak.The aforementioned observations suggested that mid-tail MR initiated the pseudobreakup first;the earthward flow generated by MR transported magnetic flux and energy to the near-Earth tail to cause the formation of SCW and CD,which induced near-Earth dipolarization and major auroral brightening,and eventually led to the onset of the substorm expansion phase.These results were clearly consistent with the picture of NENL and RCS models and supported the two step initiation scenario of substorms.
基金supported by the National Natural Science Foundation of China(Grant Nos.41322031,41404131,41574157,41031065&41304129)the Specialized Research Fund for State Key Laboratoriesthe Shandong Natural Science Foundation(Grant Nos.2013BSE27132,BS2013HZ001)
文摘Earth's bow shock is the result of interaction between the supersonic solar wind and Earth's magnetopause. However, data limitations mean the model of the shape and position of the bow shock are based largely on near-Earth satellite data. The model of the bow shock in the distant magnetotail and other factors that affect the bow shock, such as the interplanetary magnetic field(IMF) B_y, remain unclear. Here, based on the bow shock crossings of ARTEMIS from January 2011 to January 2015, new coefficients of the tail-flaring angle a of the Chao model(one of the most accurate models currently available) were obtained by fitting data from the middle-distance magnetotail(near-lunar orbit, geocentric distance -20R_E>X>-50R_E). In addition, the effects of the IMF B_y on the flaring angle a were analyzed. Our results showed that:(1) the new fitting coefficients of the Chao model in the middle-distance magnetotail are more consistent with the observed results;(2) the tail-flaring angle a of the bow shock increases as the absolute value of the IMF B_y increases. Moreover, positive IMF B_y has a greater effect than negative IMF B_y on flaring angle. These results provide a reference for bow shock modeling that includes the IMF B_y.
基金supported by Ocean Public Welfare Scientific Research Project, State Oceanic Administration People’s Republic of China (201005017)the National Basic Research Program of China(2011CB811404)
文摘Although much has been done on the hemispheric asymmetry (or seasonal variations) of auroral hemispheric power (HP), the dependence of HP hemispheric asymmetry on solar cycle has not yet been studied. We have analyzed data during 1979-2010 and investigated the dependence of HP hemispheric asymmetry/seasonal variation for the whole solar cycle. Here we show that (1) the hemispheric asymmetry of HP is positively correlated to the value of solar F10.7 with some time delay; (2) it is closely related to the coupling function between the solar wind and magnetosphere; and (3) the winter hemisphere receives more auroral power than the summer hemisphere for Kp ~0 to 6. The statistic results can be partly understood in the framework of the ionospheric conductivity feedback model. The similarity and differences between our results and previous results are discussed in the paper.
基金supported by the N ational Natural Science Foundation of China major program(Grant No.40390152)the State Key Basic Research Program(Grant No.G200000784)+2 种基金the XK 100010404 of Beijing Citythe Space Weather LaboratoryCenter for Space Science and Applied Research.CAS.
文摘When the IMF turns southward, a great amount of magnetic energy is stored in the magnetotail, and the electric field across the magnetotail substantially en-hances. As long as magnetic reconnection (MR) in the mag-netotail initiates and continues, the magnetic field and plasma in the central plasma sheet are carried away to the near-Earth and down to the tail, the magnetic field and plasma in the lobe region enter the CPS and are involved in MR. We call this process “Continuous Lobe Reconnection (CLR)”. In this paper a detailed analysis of Cluster observa-tion of MR through 2001―2003 is made. Plenty of CLR events are found that led to considerable changes of tail con-figuration, appearance of BBF, as well as large-scale bubbles in which both plasma temperature and number density sub-stantially decrease. It is shown that in general CLR events last for dozens of minutes and have good correspondence to substorm initiation under the condition of continuous southward IMF.
基金supported by Major Project of Chinese National Programs for Fundamental Research and Development(Grant No.2021YFA0718600)China Space Agency Project(Grant No.D020301)+2 种基金the National Natural Science Foundation of China(Grant No.42011530080)financial support from the Canadian Space Agency and NSERCpartially supported by National Science Foundation(Grant No.AGS-1352669)。
文摘We present evidence of geomagnetic storms in Mercury’s magnetosphere based on MESSENGER magnetic field observations made just before the probe impacted the planet.Our findings answer the question of whether geomagnetic storms can occur in other planetary magnetospheres.The interaction of the solar wind with Mercury’s magnetosphere is known to involve flux transfer events in the dayside magnetosphere,plasmoids and flux ropes in the magnetotail,and substorm-like processes,all of which occur morphologically similar to Earth but with significant differences.The significantly weaker magnetic field,smaller magnetosphere,and much faster timescale of processes around Mercury,when compared with Earth,enable charged particles to escape its magnetosphere more efficiently through magnetopause shadowing and direct bombard of the surface.Our analysis of MESSENGER’s data during a coronal mass ejection(CME)proves that,despite these substantial differences,a bifurcated ring current can form in Mercury’s magnetosphere that initiates magnetic storms under strong solar wind driving.
基金supported by the National Natural Science Foundation of China(Grant No.41421003)Major Project of Chinese National Programs for Fundamental Research and Development(Grant No.2012CB825603)
文摘In cases where substorm injections can be observed simultaneously by multiple spacecraft,they can help elucidate the potential mechanisms of particle transport and energization,of great importance to understanding and modeling the magnetosphere.In this paper,using data returned from the BeiDa-IES（BD-IES） instrument onboard a satellite in an inclined（55°） geosynchronous orbit（IGSO）,in combination with two geo-transfer orbiting（GTO） satellite Van Allen Probes（A and B）,we analyze a substorm injection event that occurred on the 16 th of October 2015.During this substorm injection,the IGSO onboard BD-IES was outbound,while both Van Allen Probe satellites（A and B） were inbound,a configuration of multiple trajectories that provides a unique opportunity to simultaneously investigate both the inward and outward radial propagation of substorm injection.Indicated by AE/AL indices,this substorm was closely related to an IMF/solar wind discontinuity that showed a sharp change in IMF Bz direction to the north.The innermost signature of this substorm injection was detected by Van Allen Probes A and B at L-3.7,while the outermost signature was observed by the onboard BD-IES instrument at L-10.These data indicate that the substorm had a global,rather than just local,effect.Finally,we suggest that electric fields carried by fast-mode compressional waves around the substorm injection are the most likely candidate mechanism for the electron injection signatures observed in the inner- and outermost inner magnetosphere.
基金supported by the National Natural Science Foundation of China (40874086 and 41031065)the National Basic Research Program of China (2011CB811404)
文摘The strong field-aligned pitch angle distribution of electrons is observed right at the dipolarization front (DF) before the arriving of a high speed flow when the four Cluster satellites are traveling in the magnetotail around 15 R E on July 22, 2001. The increased electron fluxes only last for a short time period at the DF, corresponding to just a few bouncing periods for 1 keV electrons. The field-aligned current contributed by these electrons agrees well with that calculated by the magnetic field observations by four satellites at the front. These electron streams are found in the energy range of 0.2-2 keV, peak around 1 keV. It is suggested that these downward current electrons may be originated near the aurora region by some kinds of potential structure. The occurrence of these electrons implies that the formation of the dipolarization front and the associated field-aligned current play an important role in the magnetosphere-ionosphere coupling.
文摘The plasmasphere is a region of relatively dense （-10-10000 cm^-3） plasma, surrounding the Earth and ex- tending to distances of about five Earth radii （RE）. It is filled with large amount of cold （-1 eV） plasma originated from the Earth＇s ionosphere and co-rotating with the Earth due to the large scale co-rotation electric field. The outermost boundary of the plasmashere is called the plasmapause.
基金supported by the National Natural Science Foundation of China(Grant Nos.41574157,41628402&41774153)partially supported by National Science Foundation(Grant No.AGS-1352669)+1 种基金the International Space Science Institute-Beijing for supporting the international team “Dayside Transient Phenomena and Their Impact on the Magnetosphere-Ionosphere”supported by the specialized research fund for State Key Laboratories
文摘Foreshock cavitons are transient phenomena observed in the terrestrial foreshock region.They are characterized by a simultaneous depression of magnetic field magnitude and plasma density,which are bounded with enhancements of these two parameters and surrounded by ultralow frequency(ULF)waves.Previous studies focused on the interplanetary magnetic field(IMF)conditions,solar wind(SW)conditions,and the growth of the foreshock waves related to the generation of foreshock cavitons.Previously,a multipoint spacecraft analysis method using Cluster data was applied to analyze only two foreshock cavitons,and this method did not consider uncertainties.In this study,multipoint spacecraft analysis methods,including the timing method,the minimum directional derivative(MDD)method,and the spatiotemporal difference(STD)method are applied to determine the velocity in both spacecraft and solar wind frames.The propagation properties show good agreement with previous results from simulations and observations that most cavitons move sunward in the solar wind frame,with the velocities larger than the Alfvén speed.The propagation properties of foreshock cavitons support the formation mechanism of cavitons in previous simulations,which suggested that cavitons are formed due to the nonlinear evolution of compressive ULF waves.We find that there is clear decreasing trend between the size of cavitons and their velocity in the solar wind frame.In addition,the timing method considering errors has been applied to study the evolution properties by comparing the velocities with errors of the leading and trailing edges,and we identify three stable cavitons and one contracting caviton,which has not been studied before.Most cavitons should remain stable when they travel toward the Earth’s bow shock.The relationship between the size of foreshock cavitons and their distance from the bow shock is also discussed.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41031065, 41421003)by the Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences
文摘Outflowing ion beams forming four successive inverted-V structures in the energy-time spectrograms of H+, He+, and O+ were observed at an altitude of 3.4 RE by Cluster satellites travelling above the auroral acceleration region (AAR) in the southern hemisphere on February 14, 2001. Energization by negative U-shaped potential structures in the AAR is believed to be responsible for the formation of these outflowing ion inverted-V structures. Thus, utilizing the different motion properties of the three ion species, the altitude of the upper boundary of the AAR is estimated to be ~11100 km. Moreover, based on multi-satellite observations, each of these U-shaped potential structures involved in this event crosses the latitudinal direction at ~0.4°–1° invariantlatitude (ILAT), moving poleward at an average speed of ~0.2° ILAT per minute, before disappearing at ~71.5° ILAT.
基金The authors are grateful to Japanese WDC-C2 KY0T0 AE index service for presenting AU,AL and AE indices and to Goddard Space Flight Center,NASA for presenting data of the interpanaetary condition and auroradata.Thanks are also given to Cluster and Double-Star Data Center for providing data used in the study.This work was supported by the National Natural Science Foundation of China(Grant No.40390152)the State Key Basic Research Program(Grant No.G200000784)the XK100010404 of Beijing City,and the Space Weather Laboratory,Center for Space Science and Applied Research,CAS.
