A sharp dipolarization front(DF)has recently been detected in the Earth's magnetotail and is associated with complex kinetic effects.We present one event where a tailward propagating negative DF(with Bz decreasing...A sharp dipolarization front(DF)has recently been detected in the Earth's magnetotail and is associated with complex kinetic effects.We present one event where a tailward propagating negative DF(with Bz decreasing sharply to negative value)was observed near a reconnection region.The thickness of the negative DF is comparable with the local ion gyro-radius/inertial length.There is a strong field-aligned current at the front.Electromagnetic whistler wave enhancements are observed around the front,associated with counter-streaming electron beams.We further compare the features of the observed negative DF with the recent kinetic simulation results,as well as the Earthward propagating DFs observed by the THEMIS spacecraft.展开更多
A three-dimensional(3-D)global hybrid simulation is carried out for the generation and structure of magnetic reconnection in the magnetosheath due to interaction of an interplanetary Tangential Discontinuity(TD)with t...A three-dimensional(3-D)global hybrid simulation is carried out for the generation and structure of magnetic reconnection in the magnetosheath due to interaction of an interplanetary Tangential Discontinuity(TD)with the bow shock and magnetosphere.Runs are performed for solar wind TDs possessing diFFerent initial half-widths.As the TD propagates through the bow shock toward the magnetopause,it is greatly narrowed by a two-step compression processes,a "shock compression" followed by a subsequent "convective compression".In cases with a relatively thin solar wind TD,3-D patchy reconnection is initiated in the transmitted TD,forming magnetosheath flux ropes.Multiple components of ion particles are present in the velocity distribution in the magnetosheath merging,accompanied by ion heating.For cases with a relatively wide initial TD,a dominant single X-line appears in the subsolar magnetosheath after the transmitted TD is narrowed.A shock analysis is performed for the detailed structure of magnetic reconnection in the magnetosheath.Rotational Discontinuity(RD)/TimeDependent Intermediate Shock(TDIS)are found to dominate the reconnection layer,which and some weak slow shocks are responsible for the ion heating and acceleration.展开更多
With coordinated observations of the NOAA 15 satellite and OUL magnetometer station in Finland, we report that the elec- tromagnetic ion cyclotron （EMIC） waves which were stimulated by the compression of the magneto...With coordinated observations of the NOAA 15 satellite and OUL magnetometer station in Finland, we report that the elec- tromagnetic ion cyclotron （EMIC） waves which were stimulated by the compression of the magnetosphere drive relativistic electron precipitation in geoquiescence on 1 Jan 2007. After an enhancement of solar wind dynamic pressure （SWDP）, a day- side Pcl pulsation was observed by the OUL station. Such a Pcl pulsation is caused by an EMIC wave which propagates from the generation source to lower altitudes. Simultaneously, the NOAA 15 satellite registered an enhancement of precipitating electron count rates with energies 〉3 MeV within the anisotropic zone of protons. This phenomenon is coincident with the quasi-linear theoretical calculation presented in this paper. Our observations suggest that after a positive impulse of solar wind, the compression-related EMIC waves can drive relativistic electrons precipitation and play a pivotal role in the dynamic of ra- diation belts.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos.41004060 and 40890163the Open Research Fund Program of the Key Laboratory of Space Weather,Chinese Academy of Sciencesthe Fundamental Research Funds for the Central Universities.
文摘A sharp dipolarization front(DF)has recently been detected in the Earth's magnetotail and is associated with complex kinetic effects.We present one event where a tailward propagating negative DF(with Bz decreasing sharply to negative value)was observed near a reconnection region.The thickness of the negative DF is comparable with the local ion gyro-radius/inertial length.There is a strong field-aligned current at the front.Electromagnetic whistler wave enhancements are observed around the front,associated with counter-streaming electron beams.We further compare the features of the observed negative DF with the recent kinetic simulation results,as well as the Earthward propagating DFs observed by the THEMIS spacecraft.
基金Supported by NSF grant ATM-0646442 to Auburn University and the National Natural Science Foundation of China(NSFC) grant 40640420563 to Wuhan University
文摘A three-dimensional(3-D)global hybrid simulation is carried out for the generation and structure of magnetic reconnection in the magnetosheath due to interaction of an interplanetary Tangential Discontinuity(TD)with the bow shock and magnetosphere.Runs are performed for solar wind TDs possessing diFFerent initial half-widths.As the TD propagates through the bow shock toward the magnetopause,it is greatly narrowed by a two-step compression processes,a "shock compression" followed by a subsequent "convective compression".In cases with a relatively thin solar wind TD,3-D patchy reconnection is initiated in the transmitted TD,forming magnetosheath flux ropes.Multiple components of ion particles are present in the velocity distribution in the magnetosheath merging,accompanied by ion heating.For cases with a relatively wide initial TD,a dominant single X-line appears in the subsolar magnetosheath after the transmitted TD is narrowed.A shock analysis is performed for the detailed structure of magnetic reconnection in the magnetosheath.Rotational Discontinuity(RD)/TimeDependent Intermediate Shock(TDIS)are found to dominate the reconnection layer,which and some weak slow shocks are responsible for the ion heating and acceleration.
基金supported by the National Natural Science Foundation of China(Grant Nos.41374168,41174140,41174147 and 41004060)the Research Fund for the Doctoral Program of Higher Education of China(Grant No.20110141110043)the Fundamental Research Funds for the Central Universities of China(Grant No.2012212020204)
文摘With coordinated observations of the NOAA 15 satellite and OUL magnetometer station in Finland, we report that the elec- tromagnetic ion cyclotron （EMIC） waves which were stimulated by the compression of the magnetosphere drive relativistic electron precipitation in geoquiescence on 1 Jan 2007. After an enhancement of solar wind dynamic pressure （SWDP）, a day- side Pcl pulsation was observed by the OUL station. Such a Pcl pulsation is caused by an EMIC wave which propagates from the generation source to lower altitudes. Simultaneously, the NOAA 15 satellite registered an enhancement of precipitating electron count rates with energies 〉3 MeV within the anisotropic zone of protons. This phenomenon is coincident with the quasi-linear theoretical calculation presented in this paper. Our observations suggest that after a positive impulse of solar wind, the compression-related EMIC waves can drive relativistic electrons precipitation and play a pivotal role in the dynamic of ra- diation belts.
