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
A particle-in-cell simulation of symmetric reconnection with zero guide field is carried out to understand the dynamics of ions along the separatrices.Through the investigation of ion velocity distributions at differe...A particle-in-cell simulation of symmetric reconnection with zero guide field is carried out to understand the dynamics of ions along the separatrices.Through the investigation of ion velocity distributions at different moments and locations along the separatrices,a typical distribution is found:two counter-streaming populations in the perpendicular direction,with another two populations accelerated into distinct energy levels in the parallel direction.Backward tracing of ions reveals that the counter-streaming cores are mostly composed of ions initially located at the same side of the separatrix,while the other two accelerated populations in the parallel direction are composed of ions crossing through the neutral sheet.Through analysis of energy conversion of these populations,it is found that the ion energization along the separatrix is attributable primarily to the Hall electric field,while that in the region between the two separatrices is caused primarily by the induced reconnection electric field.For the counter-streaming population,the low-energy ions that cross the separatrix twice are affected by both Hall and reconnection electric fields,while the high-energy ions that directly enter the separatrix from the unperturbed plasma are energized mainly by the Hall electric field.For the two energized populations in the parallel direction,the ions with lower-energy are accelerated mainly by the in-plane electric field and the Hall electric field on the opposite side of the separatrix,whereas the ions with higher-energy not only experience the same energization process but also are constantly accelerated by the reconnection electric field.展开更多
A new combined Fermi, betatron, and turbulent electron acceleration mechanism is proposed in interaction of magnetic islands during turbulent magnetic reconnection evolution in explosive astrophysical phenomena at lar...A new combined Fermi, betatron, and turbulent electron acceleration mechanism is proposed in interaction of magnetic islands during turbulent magnetic reconnection evolution in explosive astrophysical phenomena at large temporal-spatial scale(LTSTMR), the ratio of observed current sheets thickness to electron characteristic length, electron Larmor radius for low-β and electron inertial length for high-β, is on the order of 10^(10)–10^(11); the ratio of observed evolution time to electron gyroperiod is on the order of 10~7–10~9).The original combined acceleration model is known to be one of greatest importance in the interaction of magnetic islands; it assumes that the continuous kinetic-dynamic temporal-spatial scale evolution occurs as two separate independent processes.In this paper, we reconsider the combined acceleration mechanism by introducing a kinetic-dynamic-hydro full-coupled model instead of the original micro-kinetic or macro-dynamic model.We investigate different acceleration mechanisms in the vicinity of neutral points in magnetic islands evolution, from the stage of shrink and breakup into smaller islands(kinetic scale), to the stage of coalescence and growth into larger islands(dynamic scale), to the stages of constant and quasi-constant(contracting-expanding) islands(hydro scale).As a result, we give for the first time the acceleration efficiencies of different types of acceleration mechanisms in magnetic islands' interactions in solar atmosphere LTSTMR activities(pico-, 10^(–2)–10~5 m; nano-, 10~5–10~6 m; micro-, 10~6–10~7 m; macro-, 10~7–10~8 m; large-,10~8–10~9 m).展开更多
Two-dimensional particle-in-cell (PIC) simulation is used to investigate electron dynamics in colli- sionless magnetic reconnection, and the proton/electron mass ratio is taken to be mi /me = 256. The results show tha...Two-dimensional particle-in-cell (PIC) simulation is used to investigate electron dynamics in colli- sionless magnetic reconnection, and the proton/electron mass ratio is taken to be mi /me = 256. The results show that the presence of a strong initial guide field will change the direction of the electron flow. The electron density cavities and the parallel electric field can be found in the electron inflow re- gion along the separatrix, and the electron inflow and density cavities only appear in the second and fourth quadrants. What is different from the results with a smaller mass ratio is that new structures appear in the diffusion region near the X line: (1) Narrow regions of density enhancement and density cavities can be found synchronously in this region; and (2) corresponding to the electron density changes near the X line, the strong parallel electric fields are found to occur in the first and third quadrants. These electric fields perhaps play a more important role in acceleration and heating electrons than those fields located in the density cavities.展开更多
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 NSFC grants 41821003 and 41974192,by the B-type Strategic Priority Program of the Chinese Academy of Sciences(Grant No.XDB41000000)by the pre-research projects on Civil Aerospace Technologies No.D020103 funded by China’s National Space Administration(CNSA).
文摘A particle-in-cell simulation of symmetric reconnection with zero guide field is carried out to understand the dynamics of ions along the separatrices.Through the investigation of ion velocity distributions at different moments and locations along the separatrices,a typical distribution is found:two counter-streaming populations in the perpendicular direction,with another two populations accelerated into distinct energy levels in the parallel direction.Backward tracing of ions reveals that the counter-streaming cores are mostly composed of ions initially located at the same side of the separatrix,while the other two accelerated populations in the parallel direction are composed of ions crossing through the neutral sheet.Through analysis of energy conversion of these populations,it is found that the ion energization along the separatrix is attributable primarily to the Hall electric field,while that in the region between the two separatrices is caused primarily by the induced reconnection electric field.For the counter-streaming population,the low-energy ions that cross the separatrix twice are affected by both Hall and reconnection electric fields,while the high-energy ions that directly enter the separatrix from the unperturbed plasma are energized mainly by the Hall electric field.For the two energized populations in the parallel direction,the ions with lower-energy are accelerated mainly by the in-plane electric field and the Hall electric field on the opposite side of the separatrix,whereas the ions with higher-energy not only experience the same energization process but also are constantly accelerated by the reconnection electric field.
基金supported by the strategic priority research program of CAS (XDA17040507, XDA15010900)the national basic research program of China (2013CBA01503)+5 种基金the key program of NSFC (11333007)joint funds of NSFC(U1631130)frontier science key programs of CAS (QYZDJ-SSWSLH012)the program for innovation team of Yunnan Provincethe program for Guangdong introducing Innovative and entrepreneurial teams (2016ZT06D211)the special program for applied research on super computation of the NSFC-Guangdong joint fund (second phase) under No.U1501501
文摘A new combined Fermi, betatron, and turbulent electron acceleration mechanism is proposed in interaction of magnetic islands during turbulent magnetic reconnection evolution in explosive astrophysical phenomena at large temporal-spatial scale(LTSTMR), the ratio of observed current sheets thickness to electron characteristic length, electron Larmor radius for low-β and electron inertial length for high-β, is on the order of 10^(10)–10^(11); the ratio of observed evolution time to electron gyroperiod is on the order of 10~7–10~9).The original combined acceleration model is known to be one of greatest importance in the interaction of magnetic islands; it assumes that the continuous kinetic-dynamic temporal-spatial scale evolution occurs as two separate independent processes.In this paper, we reconsider the combined acceleration mechanism by introducing a kinetic-dynamic-hydro full-coupled model instead of the original micro-kinetic or macro-dynamic model.We investigate different acceleration mechanisms in the vicinity of neutral points in magnetic islands evolution, from the stage of shrink and breakup into smaller islands(kinetic scale), to the stage of coalescence and growth into larger islands(dynamic scale), to the stages of constant and quasi-constant(contracting-expanding) islands(hydro scale).As a result, we give for the first time the acceleration efficiencies of different types of acceleration mechanisms in magnetic islands' interactions in solar atmosphere LTSTMR activities(pico-, 10^(–2)–10~5 m; nano-, 10~5–10~6 m; micro-, 10~6–10~7 m; macro-, 10~7–10~8 m; large-,10~8–10~9 m).
基金Supported by National Natural Science Foundation of China (Grant No. 40725013)Open Research Program Foundation of State Key Laboratory for Space Weather, Chinese Academy Sciences
文摘Two-dimensional particle-in-cell (PIC) simulation is used to investigate electron dynamics in colli- sionless magnetic reconnection, and the proton/electron mass ratio is taken to be mi /me = 256. The results show that the presence of a strong initial guide field will change the direction of the electron flow. The electron density cavities and the parallel electric field can be found in the electron inflow re- gion along the separatrix, and the electron inflow and density cavities only appear in the second and fourth quadrants. What is different from the results with a smaller mass ratio is that new structures appear in the diffusion region near the X line: (1) Narrow regions of density enhancement and density cavities can be found synchronously in this region; and (2) corresponding to the electron density changes near the X line, the strong parallel electric fields are found to occur in the first and third quadrants. These electric fields perhaps play a more important role in acceleration and heating electrons than those fields located in the density cavities.
