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
We analyze observations of three bow shock crossings which occurred during 2007.using upstream data from STEREO A/B.ACE and WIND,combined with multi-point THEMIS and Cluster data,and TC-1 data located near noon.During...We analyze observations of three bow shock crossings which occurred during 2007.using upstream data from STEREO A/B.ACE and WIND,combined with multi-point THEMIS and Cluster data,and TC-1 data located near noon.During the crossing of 7 May 2007.we find that following a rapid reduction in solar wind ram pressure and subsequent pressure pulse seen by ACE and WIND upstream,the bow shock responds asymmetrically from dawn to dusk.Cluster data on the dawn-side suggest the bow shock is significantly flared and responds rapidly to the pulse arrival,while TC-1 at noon,and THEMIS on the dusk-side,are well matched to the model bow shock,but show a delayed response.The crossings observed on 21 May and 2 June show contrasting response matching the model boundary for northward Interplanetary Magnetic Field(IMF).The IMF and solar wind plasma data suggest that,the bow shock crossing at dawn-dusk side and subsolar point were mainly caused by large and smaller scale features of the solar wind ram pressure rise rather than the influence of IMF.展开更多
Using coordinated observations from the Cluster,DMSP and ESR radar,high-altitude cusp was investigated for a time period characterized by four fast reversals of the IMF BZ.On February 12,2003,Cluster was flying sunwar...Using coordinated observations from the Cluster,DMSP and ESR radar,high-altitude cusp was investigated for a time period characterized by four fast reversals of the IMF BZ.On February 12,2003,Cluster was flying sunward at duskside over the Northern Hemisphere,across the high-altitude northern cusp twice.Both the two crossings are during steady northward IMF interval,whereas ion fluxes detected during the time period are quite different.The cusp in the first crossing is a "typical" northward-IMF one,with short-lived ion injections of evident "reversed" dispersion signatures.In the second crossing,however,the cusp appears to be a region reminiscent of the Stagnant Exterior Cusp (SEC).In addition,evident upward-flowing O+ ion bursts,possibly original from polar ionosphere,are also detected during the second cusp crossing,together with enhancement of trapped magnetospheric-like electron fluxes.We suggest that the SEC-like cusp is likely on newly closed field lines,which were first reconnected (being opened) at low latitudes and later reconnected again (being closed) poleward of the northern cusp.展开更多
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Supported by STFC in-house research grant and by NSFC grants(D041003,41431071)
文摘We analyze observations of three bow shock crossings which occurred during 2007.using upstream data from STEREO A/B.ACE and WIND,combined with multi-point THEMIS and Cluster data,and TC-1 data located near noon.During the crossing of 7 May 2007.we find that following a rapid reduction in solar wind ram pressure and subsequent pressure pulse seen by ACE and WIND upstream,the bow shock responds asymmetrically from dawn to dusk.Cluster data on the dawn-side suggest the bow shock is significantly flared and responds rapidly to the pulse arrival,while TC-1 at noon,and THEMIS on the dusk-side,are well matched to the model bow shock,but show a delayed response.The crossings observed on 21 May and 2 June show contrasting response matching the model boundary for northward Interplanetary Magnetic Field(IMF).The IMF and solar wind plasma data suggest that,the bow shock crossing at dawn-dusk side and subsolar point were mainly caused by large and smaller scale features of the solar wind ram pressure rise rather than the influence of IMF.
基金supported by the National Natural Science Foundation of China (Grant Nos. 40874079)the Ministry of Science and Technology of China (Grant No. 2006BAB18B06)
文摘Using coordinated observations from the Cluster,DMSP and ESR radar,high-altitude cusp was investigated for a time period characterized by four fast reversals of the IMF BZ.On February 12,2003,Cluster was flying sunward at duskside over the Northern Hemisphere,across the high-altitude northern cusp twice.Both the two crossings are during steady northward IMF interval,whereas ion fluxes detected during the time period are quite different.The cusp in the first crossing is a "typical" northward-IMF one,with short-lived ion injections of evident "reversed" dispersion signatures.In the second crossing,however,the cusp appears to be a region reminiscent of the Stagnant Exterior Cusp (SEC).In addition,evident upward-flowing O+ ion bursts,possibly original from polar ionosphere,are also detected during the second cusp crossing,together with enhancement of trapped magnetospheric-like electron fluxes.We suggest that the SEC-like cusp is likely on newly closed field lines,which were first reconnected (being opened) at low latitudes and later reconnected again (being closed) poleward of the northern cusp.
