2008年4月24日行星际激波事件相关联的超热电子90°投掷角的增强
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摘要
利用测试粒子数值模拟的方法研究了与STEREO-A卫星观测到的2008年4月24日行星际激波事件相关联的超热电子90°投掷角的增强.根据激波到达前给定时刻超热电子的观测分布,拟合得到不同投掷角的初始分布函数;在给定的激波参数下,采用时间向后的方法计算特定能道上激波下游超热电子的投掷角分布.由于超热电子具有较高的共振频率,模拟采用的磁场湍流谱包含了低能电子发生共振的耗散区.对以215.76, 151.67,106.63 eV为中心的三个能道进行了模拟.结果表明,不同能道上超热电子在激波下游的投掷角分布均在90°投掷角附近出现峰值,呈现出明显的90°投掷角增强,这与观测结果符合得很好.可以认为在激波对电子的加速过程中,电子与湍流耗散区的共振对90°投掷角的增强具有重要作用.
Using test particle simulations, the 90° pitch angle enhancements of suprathermal electrons associated with the interplanetary shock on 24 April 2008 observed by STEREO-A spacecraft have been studied. Firstly, the initial distribution function for each pitch angle channel is obtained by fitting the observed distribution at a given time before the shock arrival, and then the time-backward method is used to calculate the pitch angle distributions of suprathermal electrons downstream of the shock for a given energy channel. Due to the higher resonance frequency of suprathermal electrons, the turbulence spectrum includes the dissipation range in which low-energy electrons resonate.Three energy channels with central energies of 215.76 eV, 151.67 eV, and 106.63 eV are simulated.The results show that a peak of the pitch angle distributions downstream of the shock obtained for these energy channels appears near the 90° pitch angle. The enhancement at the 90° pitch angle is in good agreement with the observations. The resonance between suprathermal electrons and the turbulence dissipation range in the process of shock acceleration is suggested to play a crucial role in this phenomenon. A thorough study of the electric and magnetic field fluctuations at interplanetary shocks can provide a better understanding of the nature of 90° pitch angle enhancements of suprathemal electrons.
Using test particle simulations, the 90° pitch angle enhancements of suprathermal electrons associated with the interplanetary shock on 24 April 2008 observed by STEREO-A spacecraft have been studied. Firstly, the initial distribution function for each pitch angle channel is obtained by fitting the observed distribution at a given time before the shock arrival, and then the time-backward method is used to calculate the pitch angle distributions of suprathermal electrons downstream of the shock for a given energy channel. Due to the higher resonance frequency of suprathermal electrons, the turbulence spectrum includes the dissipation range in which low-energy electrons resonate.Three energy channels with central energies of 215.76 eV, 151.67 eV, and 106.63 eV are simulated.The results show that a peak of the pitch angle distributions downstream of the shock obtained for these energy channels appears near the 90° pitch angle. The enhancement at the 90° pitch angle is in good agreement with the observations. The resonance between suprathermal electrons and the turbulence dissipation range in the process of shock acceleration is suggested to play a crucial role in this phenomenon. A thorough study of the electric and magnetic field fluctuations at interplanetary shocks can provide a better understanding of the nature of 90° pitch angle enhancements of suprathemal electrons.
引文
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[13] MATTHAEUS W H, GOLDSTEIN M L, ROBERTS D A. Evidence for the presence of quasi-two-dimensional nearly incompressible fluctuations in the solar wind[J].J. Geophys. Res., 1990, 95(A12):20673-20683
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[15] BIEBER J W, WANNER W, MATTHAEUS W H. Dominant two-dimensional solar wind turbulence with implications for cosmic ray transport[J]. J. Geophys. Res., 1996,101(A2):2511-2522
[16] GRAY P C, PONTIUS D H JR, MATTHAEUS W H.Scaling of field-line random walk in model solar wind fluctuations[J]. Geophys. Res. Lett., 1996, 23(9):965-968
[17] ZANK G P, LI G, FLORINSKI V, et al. Particle acceleration at perpendicular shock waves:Model and observations[J]. J. Geophys. Res., 2006, 111(A6):A06108
[18] QIN G, KONG F J, ZHANG L H. Effects of shock and turbulence properties on electron acceleration[J]. Astrophys. J., 2018, 860(1):3-11
[19] LI G, KONG X, ZANK G, et al. On the spectral hardening at≥300 keV in solar flares[J]. Astrophys. J., 2013,769(1):22
[20] QIN G, MATTHAEUS W H, BIEBER J W. Subdiffusive transport of charged particles perpendicular to the large scale magnetic field[J]. Geophys. Res. Lett., 2002,29(4):1048
[21] QIN G, MATTHAEUS W H, BIEBER J W. Perpendicular transport of charged particles in composite model turbulence:Recovery of diffusion[J]. Astrophys. J. Lett.,2002, 578(2):L117-L120
[22] KONG F J, QIN G, ZHANG L H. Numerical simulations of particle acceleration at interplanetary quasiperpendicular shocks[J]. Astrophys. J.,2017,845(1):43
[23] LIU Y D, LUHMANN J G, KAJDIC P, et al. Observations of an extreme storm in interplanetary space caused by successive coronal mass ejections[J]. Nat. Commun.,2014, 5:3481
[24] LIU Y, RICHARDSON J D, BELCHER J W, et al. Plasma depletion and mirror waves ahead of interplanetary coronal mass ejections[J]. J. Geophys. Res., 2006,111(A9):A09108
[25] LIU Y, RICHARDSON J D, BELCHER J W, et al. Temperature anisotropy in a shocked plasma:Mirror-mode instabilities in the heliosheath[J]. Astrophys. J. Lett., 2007,659(1):L65-L68
*http://cdaweb.sci.gsfc.nasa.gov/index.html
**http://www-ssc.igpp.ucla.edu/~jlan/STEREO/Level3/STEREO_Level3_Shock.pdf
*http://stereo.irap.omp.eu/CEF/PAD/ahead/
[2] FELDMAN W C, ASBRIDGE J R, BAME S J, et al. Characteristic electron variations across simple highspeed solar wind streams[J]. J. Geophys. Res., 1978,83(A11):5285-5295
[3] PILIPP W G, MIGGENRIEDER H, MONTGOMERY M D, et al. Characteristics of electron velocity distribution functions in the solar wind derived from the Helios plasma experiment[J]. J. Geophys. Res., 1987, 92(A2):1075-1092
[4] MAKSIMOVIC M, ZOUGANELIS I, CHAUFRAY J Y,et al. Radial evolution of the electron distribution functions in the fast solar wind between 0.3 and 1.5 AU[J]. J.Geophys. Res., 2005, 110(A9):A09104
[5] LIN R P. Wind observations of suprathermal electrons in the interplanetary medium[J]. Space Sci. Rev., 1998,86(1/2/3/4):61-78
[6] LEMONS D S, FELDMAN W C. Collisional modification to the exospheric theory of solar wind halo electron pitch angle distributions[J]. J. Geophys. Res., 1983,88(A9):6881-6887
[7] PAGEL C, GARY S P, DE KONING C A, et al. Scattering of suprathermal electrons in the solar wind:ACE observations[J]. J. Geophys. Res., 2007, 112(A4):A04103
[8] VOCKS C, MANN G. Generation of suprathermal electrons by resonant wave-particle interaction in the solar corona and wind[J].Astrophys. J., 2003, 593(2):1134-1145
[9] VOCKS C, SALEM C, LIN R P, et al. Electron halo and strahl formation in the solar wind by resonant interaction with whistler waves[J].Astrophys. J., 2005, 627(1):540-549
[10] SAITO S, GARY S P. Whistler scattering of suprathermal electrons in the solar wind:particle-in-cell simulations[J].J. Geophys. Res., 2007, 112(A6):A06116
[11] GOSLING J T, SKOUG R M, FELDMAN W C. Solar wind electron halo depletions at pitch angle[J]. Geophys.Res. Lett., 2001, 28(22):4155-4158
[12] KAJDIC P, LAVRAUD B, ZASLAVSKY A, et al. Ninety degrees pitch angle enhancements of suprathermal electrons associated with interplanetary shocks[J]. J. Geophys. Res., 2014, 119(9):7038-7060
[13] MATTHAEUS W H, GOLDSTEIN M L, ROBERTS D A. Evidence for the presence of quasi-two-dimensional nearly incompressible fluctuations in the solar wind[J].J. Geophys. Res., 1990, 95(A12):20673-20683
[14] ZANK G P, MATTHAEUS W H. Waves and turbulence in the solar wind[J]. J. Geophys. Res., 1992,97(A11):17189-17194
[15] BIEBER J W, WANNER W, MATTHAEUS W H. Dominant two-dimensional solar wind turbulence with implications for cosmic ray transport[J]. J. Geophys. Res., 1996,101(A2):2511-2522
[16] GRAY P C, PONTIUS D H JR, MATTHAEUS W H.Scaling of field-line random walk in model solar wind fluctuations[J]. Geophys. Res. Lett., 1996, 23(9):965-968
[17] ZANK G P, LI G, FLORINSKI V, et al. Particle acceleration at perpendicular shock waves:Model and observations[J]. J. Geophys. Res., 2006, 111(A6):A06108
[18] QIN G, KONG F J, ZHANG L H. Effects of shock and turbulence properties on electron acceleration[J]. Astrophys. J., 2018, 860(1):3-11
[19] LI G, KONG X, ZANK G, et al. On the spectral hardening at≥300 keV in solar flares[J]. Astrophys. J., 2013,769(1):22
[20] QIN G, MATTHAEUS W H, BIEBER J W. Subdiffusive transport of charged particles perpendicular to the large scale magnetic field[J]. Geophys. Res. Lett., 2002,29(4):1048
[21] QIN G, MATTHAEUS W H, BIEBER J W. Perpendicular transport of charged particles in composite model turbulence:Recovery of diffusion[J]. Astrophys. J. Lett.,2002, 578(2):L117-L120
[22] KONG F J, QIN G, ZHANG L H. Numerical simulations of particle acceleration at interplanetary quasiperpendicular shocks[J]. Astrophys. J.,2017,845(1):43
[23] LIU Y D, LUHMANN J G, KAJDIC P, et al. Observations of an extreme storm in interplanetary space caused by successive coronal mass ejections[J]. Nat. Commun.,2014, 5:3481
[24] LIU Y, RICHARDSON J D, BELCHER J W, et al. Plasma depletion and mirror waves ahead of interplanetary coronal mass ejections[J]. J. Geophys. Res., 2006,111(A9):A09108
[25] LIU Y, RICHARDSON J D, BELCHER J W, et al. Temperature anisotropy in a shocked plasma:Mirror-mode instabilities in the heliosheath[J]. Astrophys. J. Lett., 2007,659(1):L65-L68
*http://cdaweb.sci.gsfc.nasa.gov/index.html
**http://www-ssc.igpp.ucla.edu/~jlan/STEREO/Level3/STEREO_Level3_Shock.pdf
*http://stereo.irap.omp.eu/CEF/PAD/ahead/