Geomagnetic storms can result in large magnetic field disturbances and intense currents in the magnetosphere and even on the ground.As an important medium of momentum and energy transport among the solar wind,magnetos...Geomagnetic storms can result in large magnetic field disturbances and intense currents in the magnetosphere and even on the ground.As an important medium of momentum and energy transport among the solar wind,magnetosphere,and ionosphere,field-aligned currents(FACs)can also be strengthened in storm times.This study shows the responses of FACs in the plasma sheet boundary layer(PSBL)observed by the Magnetospheric Multiscale(MMS)spacecraft in different phases of a large storm that lasted from May 27,2017,to May 29,2017.Most of the FACs were carried by electrons,and several FACs in the storm time also contained sufficient ion FACs.The FAC magnitudes were larger in the storm than in the quiet period,and those in the main phase were the strongest.In this case,the direction of the FACs in the main phase showed no preference for tailward or earthward,whereas the direction of the FACs in the recovery phase was mostly tailward.The results suggest that the FACs in the PSBL are closely related to the storm and could be driven by activities in the tail region,where the energy transported from the solar wind to the magnetosphere is stored and released as the storm is evolving.Thus,the FACs are an important medium of energy transport between the tail and the ionosphere,and the PSBL is a significant magnetosphere–ionosphere coupling region in the nightside.展开更多
In this investigation effort, we eventually infer that the overall quadrapole pattern of B<sub>y</sub> deflections, in the vicinity of a source in the Earth’s magnetotail, is most likely due to field alig...In this investigation effort, we eventually infer that the overall quadrapole pattern of B<sub>y</sub> deflections, in the vicinity of a source in the Earth’s magnetotail, is most likely due to field aligned currents (FACs) and not to Hall currents associated with an X-type collisionless reconnection. This categorically expressed statement is based upon sufficient observational evidence tightly associated with our own suggested model and the preceded works of the same author. Using representative events measured by satellite, our main aim is to describe the nature of the fundamental mechanism determining the polarity of the B<sub>y</sub> deflections associated with intense earthward ionplasma flows. A major finding is that we either observe magnetic flux rope (MFR) like structures (that is, entities having all the morphological features of ropes; i.e., a dipolar signature of B<sub>z</sub> occurring simultaneously with peaked B<sub>y</sub> and B<sub>total</sub> deflections) or mere B<sub>y</sub> deflections, however, the sign for all these (B<sub>y</sub>deflections) is always determined by the satellite placement in north (positive) or south (negative) plasma sheet. Therefore, the MFR-like structures located earthward of the source are most likely pseudo-MFRs;there is neither a tubular topology nor an axial magnetic field, the B<sub>y</sub> deflections are produced by FACs. According to the presented model, a fundamental concept is that both ions and electrons are simultaneously accelerated at the source site;in turn, the earthward streaming electrons (ions) form a bifurcated electron (ion) FAC just outside the electron diffusion region-EDR (IDR). In this way, inside the IDR (and earthward of the source) positive (negative) B<sub>y</sub> deflections in north (south) plasma sheet (PS) are produced due to FACs, and not to (inward) Hall currents as in the context of an X-line. Moreover, the ions form an “ion jet” within the IDR, while just outside this region they produce positive (negative) B<sub>y</sub> deflections in north (south) PS caused by ion FACs. The ion jet in the IDR is enveloped by the bifurcated electron FAC. Eventually, although the resulting pattern of B<sub>y</sub> deflections, due to both electron and ion FACs, is apparently the same with that resulting from Hall currents (in the X-line model), the underlying natural processes are, however, radically different. Certainly, the dominant “spatial entity” within the IDR is the ion jet-current (and not the Hall-electron current). Additional implications of the ion jets are also discussed.展开更多
A combined action of plasma convection and pitch-angle diffusion of electrons and protons leads to the formation of plasma pressure distribution in the magnetosphere on the night side, and, as it is known, steady elec...A combined action of plasma convection and pitch-angle diffusion of electrons and protons leads to the formation of plasma pressure distribution in the magnetosphere on the night side, and, as it is known, steady electric bulk currents are connected to distribution of gas pressure. The divergence of these bulk currents brings about a spatial distribution of field-aligned currents, i.e. magnetospheric sources of ionospheric current. The projection (mapping) of the plasma pressure relief onto the ionosphere corresponds to the form and position of the auroral oval. This projection, like the real oval, executes a motion with a change of the convection electric field, and expands with an enhancement of the field. Knowing the distribution (3D) of the plasma pressure we can determine the places of MHD-compressor and MHD-generators location in the magnetosphere. Unfortunately, direct observations of plasma distribution in the magnetosphere are faced with large difficulties, because pressure must be known everywhere in the plasma sheet at high resolution, which in situ satellites have been unable to provide. Modeling of distribution of plasma pressure (on ~ 3-12 Re) is very important, because the data from multisatellite magnetospheric missions for these purposes would be a very expensive project.展开更多
A 3-dimensional resistive MHD simulation was carried out to study the effect of the upward ions on the field-aligned currents (FACs) in the near-earth magnetotail. The simulation results show that the up-flow ions ori...A 3-dimensional resistive MHD simulation was carried out to study the effect of the upward ions on the field-aligned currents (FACs) in the near-earth magnetotail. The simulation results show that the up-flow ions originating from the nightside auroral oval would drift into the center plasma sheet along the magnetic field lines in the plasma sheet boundary, and have an important effect on the field-aligned currents. The main conclusions include that: 1) the upward-ions mainly affect the field- aligned currents in the near-earth magnetotail (inside 15 Re); 2) the generated FACs in the near-earth region have two types, i.e., Region 1 FAC in the high-latitude and Region 2 FAC in the low-latitude; 3) FACs increase with the enhancement of the upward ion flux; 4) with the same flux of the upward ions, FACs enhance with the increase of the velocity of the up-flow ions; 5) the intensification of FACs is also closely related with the latitude of the upward ions, and the ions from the closed field line region generate larger FACs; 6) the generation of FACs is closely related with By created by the upward ions.展开更多
A long-standing mystery in the study of Field-Aligned Currents(FACs) has been that: how the currents are generated and why they appear to be much stronger at high altitudes than in the ionosphere. Here we present two ...A long-standing mystery in the study of Field-Aligned Currents(FACs) has been that: how the currents are generated and why they appear to be much stronger at high altitudes than in the ionosphere. Here we present two events of magnetotail FACs observed by the Magnetospheric Multiscale Spacecraft(MMS) on 1 st July and 14 th July 2016, to show how the Substorm Current Wedges(SCW) were formed. The results show that particles were transferred heading towards the Earth during the expansion phase of substorms.The azimuthal flow formed clockwise(counter-clockwise) vortex-like motion, and then generated downward(upward) FACs on the tailward/poleward side of the distorted field with opposite vorticity on their Earthward/equatorward side. We also analyzed the Region 1 FACs observed by the Earth Explorer Swarm spacecraft on 1 st July 2016 and found that they were associated with FACs observed by MMS, although differing by a factor of 10. This difference suggests that either there was the closure of the currents at altitudes above 500 km or the currents were not strictly parallel to B and closed at longitudes away from where they were generated.展开更多
Field-aligned currents in the inner magnetosphere arc studied by using ISEE-2 magnetometer da-la, A method is proposed to calculate ×B with single-satellite data. From the morphology of ×B in time (or L). a ...Field-aligned currents in the inner magnetosphere arc studied by using ISEE-2 magnetometer da-la, A method is proposed to calculate ×B with single-satellite data. From the morphology of ×B in time (or L). a lot of large fluctuations are found in ×B near L = 5.5RE corresponding to the field-aligned currents. Statistical study shows that the field-aligned current in the inner magnetosphere is a function of B, L, MLT and AL. The region of the projections of ×B along the magnetic field line onto the ionosphere is not symmetrical for the geomagnetic pole. The inner boundary is independent of the geomagnetic disturbance, but during substorms the outer boundary shifts equatorward. The spatial distribution of the in- and out-flowing currents is complicated. The region-1-and-2 system is hardly distinguishable.展开更多
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 ...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. Here we present 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 hydromagnetic waves, which were excited by a pulse in the solar wind dynamic pressure. Multi-spacecraft measurements from THEMIS also suggest higher wave frequencies at lower L shells (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.展开更多
With geomagnetic measurements on board of CHAMP satellite, the characteristics of global large-scale field-aligned currents (FACs) in the topside ionosphere are investigated along with their responses to interplanetar...With geomagnetic measurements on board of CHAMP satellite, the characteristics of global large-scale field-aligned currents (FACs) in the topside ionosphere are investigated along with their responses to interplanetary conditions for the superstorm of November, 2003. It is found that (1) The storm-time FAC densities enhanced greatly in comparison with quiet period and the enhancements show hemispheric asymmetry of both summer-winter and sunlit-dark. (2) For the first time, it is revealed that the lati-tude-integrated FAC density is controlled mainly by solar wind dynamic pressure rather than IMF. (3) FACs expanded equatorward dramatically, with the lowest latitude being 45° MLat or more; on the day-side this expansion was controlled directly by IMF Bz, showing an interaction time scale of about 25 min in the solar wind-magnetosphere-ionosphere coupling system, and a nonlinear saturation of the equatorward expansion when IMF Bz < -30 nT; while on the nightside, the expansion and recovery lagged about 3 h behind the IMF changes but nearly in phase with changes of SYM-H index. (4) During the storm main phase, the nightside FAC latitude coverage extended to 25° or wider, appearing multi-sheet current structure with more than 10 sheets.展开更多
太阳风向磁层-电离层(Magnetosphere and Ionosphere,MI)系统输入能量,而输入的能量随后在MI系统中消耗.本文从能量守恒原理出发,讨论太阳风-磁层-电离层(SMI)耦合过程中的能流路径和能量收支的定量关系.主要讨论9个问题:(1)太阳风向MI...太阳风向磁层-电离层(Magnetosphere and Ionosphere,MI)系统输入能量,而输入的能量随后在MI系统中消耗.本文从能量守恒原理出发,讨论太阳风-磁层-电离层(SMI)耦合过程中的能流路径和能量收支的定量关系.主要讨论9个问题:(1)太阳风向MI系统的能量输入,(2)MI系统对能量输入的响应,(3)环电流的能量消耗,(4)极区电离层焦耳加热的能量消耗,(5)极光粒子沉降的能量消耗,(6)磁尾能量的消耗、储存以及返回下游太阳风,(7)平静期间的能量积累与释放,(8)能量在不同能汇中的分配,(9)评价能量函数的准则和方法.展开更多
基金funded by the National Natural Science Foundation of China(NSFCGrant Nos.42204177,42274219,41974205,42130204,42241155,and 42241133)+5 种基金the Guangdong Basic and Applied Basic Research Foundation-Natural Science Foundation of Guangdong(Grant Nos.2022A1515010257,2022A1515011698,and 2023A1515030132)the Shenzhen Science and Technology Research Program(Grant Nos.JCYJ20210324121403009 and JCYJ20210324121412034)the Macao foundation,the Fundamental Research Funds for the Central Universities(Grant No.HIT.OCEF.2022041)the Shenzhen Key Laboratory Launching Project(Grant No.ZDSYS20210702140800001)the pre-research project on Civil Aerospace Technologies(Grant No.D020103)funded by the China National Space Administration.YuanQiang Chen was also funded by China Postdoctoral Science Foundation(Grant No.2022M720944)supported by the Chinese Academy of Sciences Center for Excellence in Comparative Planetology.
文摘Geomagnetic storms can result in large magnetic field disturbances and intense currents in the magnetosphere and even on the ground.As an important medium of momentum and energy transport among the solar wind,magnetosphere,and ionosphere,field-aligned currents(FACs)can also be strengthened in storm times.This study shows the responses of FACs in the plasma sheet boundary layer(PSBL)observed by the Magnetospheric Multiscale(MMS)spacecraft in different phases of a large storm that lasted from May 27,2017,to May 29,2017.Most of the FACs were carried by electrons,and several FACs in the storm time also contained sufficient ion FACs.The FAC magnitudes were larger in the storm than in the quiet period,and those in the main phase were the strongest.In this case,the direction of the FACs in the main phase showed no preference for tailward or earthward,whereas the direction of the FACs in the recovery phase was mostly tailward.The results suggest that the FACs in the PSBL are closely related to the storm and could be driven by activities in the tail region,where the energy transported from the solar wind to the magnetosphere is stored and released as the storm is evolving.Thus,the FACs are an important medium of energy transport between the tail and the ionosphere,and the PSBL is a significant magnetosphere–ionosphere coupling region in the nightside.
文摘In this investigation effort, we eventually infer that the overall quadrapole pattern of B<sub>y</sub> deflections, in the vicinity of a source in the Earth’s magnetotail, is most likely due to field aligned currents (FACs) and not to Hall currents associated with an X-type collisionless reconnection. This categorically expressed statement is based upon sufficient observational evidence tightly associated with our own suggested model and the preceded works of the same author. Using representative events measured by satellite, our main aim is to describe the nature of the fundamental mechanism determining the polarity of the B<sub>y</sub> deflections associated with intense earthward ionplasma flows. A major finding is that we either observe magnetic flux rope (MFR) like structures (that is, entities having all the morphological features of ropes; i.e., a dipolar signature of B<sub>z</sub> occurring simultaneously with peaked B<sub>y</sub> and B<sub>total</sub> deflections) or mere B<sub>y</sub> deflections, however, the sign for all these (B<sub>y</sub>deflections) is always determined by the satellite placement in north (positive) or south (negative) plasma sheet. Therefore, the MFR-like structures located earthward of the source are most likely pseudo-MFRs;there is neither a tubular topology nor an axial magnetic field, the B<sub>y</sub> deflections are produced by FACs. According to the presented model, a fundamental concept is that both ions and electrons are simultaneously accelerated at the source site;in turn, the earthward streaming electrons (ions) form a bifurcated electron (ion) FAC just outside the electron diffusion region-EDR (IDR). In this way, inside the IDR (and earthward of the source) positive (negative) B<sub>y</sub> deflections in north (south) plasma sheet (PS) are produced due to FACs, and not to (inward) Hall currents as in the context of an X-line. Moreover, the ions form an “ion jet” within the IDR, while just outside this region they produce positive (negative) B<sub>y</sub> deflections in north (south) PS caused by ion FACs. The ion jet in the IDR is enveloped by the bifurcated electron FAC. Eventually, although the resulting pattern of B<sub>y</sub> deflections, due to both electron and ion FACs, is apparently the same with that resulting from Hall currents (in the X-line model), the underlying natural processes are, however, radically different. Certainly, the dominant “spatial entity” within the IDR is the ion jet-current (and not the Hall-electron current). Additional implications of the ion jets are also discussed.
文摘A combined action of plasma convection and pitch-angle diffusion of electrons and protons leads to the formation of plasma pressure distribution in the magnetosphere on the night side, and, as it is known, steady electric bulk currents are connected to distribution of gas pressure. The divergence of these bulk currents brings about a spatial distribution of field-aligned currents, i.e. magnetospheric sources of ionospheric current. The projection (mapping) of the plasma pressure relief onto the ionosphere corresponds to the form and position of the auroral oval. This projection, like the real oval, executes a motion with a change of the convection electric field, and expands with an enhancement of the field. Knowing the distribution (3D) of the plasma pressure we can determine the places of MHD-compressor and MHD-generators location in the magnetosphere. Unfortunately, direct observations of plasma distribution in the magnetosphere are faced with large difficulties, because pressure must be known everywhere in the plasma sheet at high resolution, which in situ satellites have been unable to provide. Modeling of distribution of plasma pressure (on ~ 3-12 Re) is very important, because the data from multisatellite magnetospheric missions for these purposes would be a very expensive project.
基金Supported by the National Natural Science Foundation of China (Grant Nos. CNSF-40474058 and CNSF-40536030)
文摘A 3-dimensional resistive MHD simulation was carried out to study the effect of the upward ions on the field-aligned currents (FACs) in the near-earth magnetotail. The simulation results show that the up-flow ions originating from the nightside auroral oval would drift into the center plasma sheet along the magnetic field lines in the plasma sheet boundary, and have an important effect on the field-aligned currents. The main conclusions include that: 1) the upward-ions mainly affect the field- aligned currents in the near-earth magnetotail (inside 15 Re); 2) the generated FACs in the near-earth region have two types, i.e., Region 1 FAC in the high-latitude and Region 2 FAC in the low-latitude; 3) FACs increase with the enhancement of the upward ion flux; 4) with the same flux of the upward ions, FACs enhance with the increase of the velocity of the up-flow ions; 5) the intensification of FACs is also closely related with the latitude of the upward ions, and the ions from the closed field line region generate larger FACs; 6) the generation of FACs is closely related with By created by the upward ions.
基金Supported by National Natural Science Foundation of China(41874190,41231066)
文摘A long-standing mystery in the study of Field-Aligned Currents(FACs) has been that: how the currents are generated and why they appear to be much stronger at high altitudes than in the ionosphere. Here we present two events of magnetotail FACs observed by the Magnetospheric Multiscale Spacecraft(MMS) on 1 st July and 14 th July 2016, to show how the Substorm Current Wedges(SCW) were formed. The results show that particles were transferred heading towards the Earth during the expansion phase of substorms.The azimuthal flow formed clockwise(counter-clockwise) vortex-like motion, and then generated downward(upward) FACs on the tailward/poleward side of the distorted field with opposite vorticity on their Earthward/equatorward side. We also analyzed the Region 1 FACs observed by the Earth Explorer Swarm spacecraft on 1 st July 2016 and found that they were associated with FACs observed by MMS, although differing by a factor of 10. This difference suggests that either there was the closure of the currents at altitudes above 500 km or the currents were not strictly parallel to B and closed at longitudes away from where they were generated.
基金a grant from the National Natural Science Foundation of Chinathe Chinese Academy of Sciences
文摘Field-aligned currents in the inner magnetosphere arc studied by using ISEE-2 magnetometer da-la, A method is proposed to calculate ×B with single-satellite data. From the morphology of ×B in time (or L). a lot of large fluctuations are found in ×B near L = 5.5RE corresponding to the field-aligned currents. Statistical study shows that the field-aligned current in the inner magnetosphere is a function of B, L, MLT and AL. The region of the projections of ×B along the magnetic field line onto the ionosphere is not symmetrical for the geomagnetic pole. The inner boundary is independent of the geomagnetic disturbance, but during substorms the outer boundary shifts equatorward. The spatial distribution of the in- and out-flowing currents is complicated. The region-1-and-2 system is hardly distinguishable.
基金supported by the National Natural Science Foundation of China (grant numbers 41774168 and 41421003)
文摘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. Here we present 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 hydromagnetic waves, which were excited by a pulse in the solar wind dynamic pressure. Multi-spacecraft measurements from THEMIS also suggest higher wave frequencies at lower L shells (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.
基金DAAD Sandwich Scholarship and the National Natural Science Foun-dation of China (Grant No. 40390150)
文摘With geomagnetic measurements on board of CHAMP satellite, the characteristics of global large-scale field-aligned currents (FACs) in the topside ionosphere are investigated along with their responses to interplanetary conditions for the superstorm of November, 2003. It is found that (1) The storm-time FAC densities enhanced greatly in comparison with quiet period and the enhancements show hemispheric asymmetry of both summer-winter and sunlit-dark. (2) For the first time, it is revealed that the lati-tude-integrated FAC density is controlled mainly by solar wind dynamic pressure rather than IMF. (3) FACs expanded equatorward dramatically, with the lowest latitude being 45° MLat or more; on the day-side this expansion was controlled directly by IMF Bz, showing an interaction time scale of about 25 min in the solar wind-magnetosphere-ionosphere coupling system, and a nonlinear saturation of the equatorward expansion when IMF Bz < -30 nT; while on the nightside, the expansion and recovery lagged about 3 h behind the IMF changes but nearly in phase with changes of SYM-H index. (4) During the storm main phase, the nightside FAC latitude coverage extended to 25° or wider, appearing multi-sheet current structure with more than 10 sheets.
文摘太阳风向磁层-电离层(Magnetosphere and Ionosphere,MI)系统输入能量,而输入的能量随后在MI系统中消耗.本文从能量守恒原理出发,讨论太阳风-磁层-电离层(SMI)耦合过程中的能流路径和能量收支的定量关系.主要讨论9个问题:(1)太阳风向MI系统的能量输入,(2)MI系统对能量输入的响应,(3)环电流的能量消耗,(4)极区电离层焦耳加热的能量消耗,(5)极光粒子沉降的能量消耗,(6)磁尾能量的消耗、储存以及返回下游太阳风,(7)平静期间的能量积累与释放,(8)能量在不同能汇中的分配,(9)评价能量函数的准则和方法.
