数值研究太阳调制引发的银河宇宙线正电子的各向异性  

A numerical study of the galactic cosmic positron anisotropy induced by solar modulation

作　　者：刘新铭 宋小健 耿泽坤 罗熙 LIU XinMing;SONG XiaoJian;GENG ZeKun;LUO Xi(School of Physics and Technology,University of Jinan,Jinan 250022,China;Shandong Institute of Advanced Technology,Jinan 250100,China)

机构地区：[1]济南大学物理科学与技术学院,济南250022 [2]山东高等技术研究院,济南250100

出　　处：《地球物理学报》2024年第4期1299-1313,共15页Chinese Journal of Geophysics

基　　金：国家自然科学基金(U2106201,42150105);山东高等技术研究院自主项目(2020106R01);山东省“泰山学者青年专家”人才项目共同资助

摘　　要：能量低于30 GeV的银河宇宙线正电子进入日球层时会与太阳风以及冻结在其中的日球层磁场发生相互作用,太阳风对流、扩散、漂移的综合调制效应会导致银河宇宙线正电子通量出现各向异性.本研究利用帕克(Parker)传输方程描述正电子在日球层中的传输过程,将日球层顶(120 AU)的局地星际能谱作为边界条件,利用交替方向隐式方法(ADI)求解传输方程,计算银河宇宙线正电子的通量,接着计算银河宇宙线正电子的梯度,最后计算出0.01 GeV,0.1 GeV,1 GeV能量的正电子的极向各向异性和径向各向异性.研究发现:(1)由于低能量正电子的漂移几乎为0,因此极向各向异性仅由扩散决定,它的绝对值在日球层南北半球相同纬度上相等并且在黄道面处的值为0;高能量的正电子受到了漂移作用的影响,导致极向各向异性在黄道面处的值不为0,南北半球相同纬度上的绝对值也不相等.(2)低能量正电子的径向各向异性仅由扩散和对流决定;高能量正电子的径向各向异性由扩散、对流、漂移三者共同决定.另外,黄道面处正电子的极向梯度为0,因此任何能量的正电子在此处的径向各向异性也只由扩散和对流决定;正电子在日球层高纬度地区由于扩散和漂移较大,从而具有较大的径向各向异性.As the galactic cosmic ray positrons with energies below 30 GeV enter the heliosphere, they interact with the solar wind and the heliospheric magnetic field which get frozen inside. The overall modulation effects, including the solar wind convection, diffusion and drift, lead to galactic cosmic ray positrons anisotropy. In this study, Parker's transport equation is used to study the transport process of positrons in the heliosphere. The local interstellar spectrum of positrons at the heliosphere boundary (120 AU) is used as the simulation boundary. Using the alternating direction implicit (ADI) method, the flux of galactic cosmic ray positrons in the heliosphere is calculated, as well as the gradient of galactic cosmic ray positrons. Based on these numerical results, the polar and radial components of the anisotropy with energies of 0.01 GeV, 0.1 GeV, 1 GeV are obtained. It has been found that: (1) For low energy positrons, Since their drift of low energy positrons is almost negligible, the polar anisotropy component is only determined by diffusion. Its magnitude is equivalent at the same latitude in the northern and southern heliosphere, and it is vanishing at the equator. On the other hand, the positrons with high energy are affected by drift process, resulting in non-zero polar anisotropy component at the equator and different magnitude at the same latitude in the northern and southern heliosphere. (2) The radial anisotropy component of low-energy positrons are only determined by diffusion and convection. On the other hand, the positrons with high energy are affected by drift process, the radial anisotropy component is determined by diffusion, convection and drift. In addition, the polar gradient of positrons is almost negligible, so the radial anisotropy of any energy positrons here is only determined by diffusion and convection;Positrons exhibit significant radial anisotropy in high latitude regions of the heliosphere due to their large diffusion and drift.

关 键 词：宇宙线正电子 太阳调制 数值模拟 扩散系数 梯度 各向异性 

分 类 号：P352[天文地球—空间物理学]