地球环电流动力学过程研究  

Ring current dynamics in the Earth's inner magnetosphere

作　　者：庄雁 乐超[1] Zhuang Yan;Yue Chao(Institute of Space Physics and Applied Technology,Peking University,Beijing 100081,China)

机构地区：[1]北京大学空间物理与应用技术研究所,北京100871

出　　处：《地球与行星物理论评》2022年第5期556-566,共11页Reviews of Geophysics and Planetary Physics

基　　金：民用航天技术预先研究资助项目(D020303);国家重点研发计划资助项目(2020YFE0202100);国家自然科学基金资助项目(41974191)。

摘　　要：地球环电流主要分布在赤道附近约2~7个地球半径的区域,是地球磁层最重要的电流系统之一.高能离子(~1 keV到数百keV),例如质子和氧离子,被认为是环电流的主要载流子.地球磁暴期间环电流的增强被广泛认为是地球表面水平磁场扰动的主要原因.在磁暴主相之后,环电流通常需要几天(即磁暴恢复相)才能恢复到平静时期的水平.本文介绍了不同种类的粒子,特别是氧离子,对环电流的相对贡献以及环电流在磁暴恢复相期间的损失情况.在高极光电集流水平时,不同种类粒子的等离子体压强显著增加,其中H^(+)离子的压强主要分布在等离子体层内,并始终占主导地位.重离子和电子的压强在等离子体层外增加,形成强烈的晨昏不对称性,并分别在黄昏和黎明侧达到峰值.此外,无论是平静时期还是活跃时期,能量从50 keV到几百keV的氢离子贡献的压强是环电流等离子体压强的主要组成部分,而氦的贡献一般较小.在活跃时期,10 keV<E<50 keV的O^(+)离子和0.1 keV<E<40 keV的电子的贡献逐渐变得显著,它们在夜侧的贡献分别超过25%和20%.O^(+)离子对环电流的贡献与地磁活动密切相关.在sym-H值小于−60 nT的大磁暴中,无一例外的总是存在丰富的O^(+)离子,其相对压强贡献可以和H+离子相当(O^(+)离子压强与H+离子压强比R>0.8),在L小于3的情况下,其相对压强的贡献量有时甚至会大于H^(+)离子.与没有O^(+)离子贡献环电流的情况相比,当O^(+)离子对环电流有明显贡献时,O^(+)离子和等离子体总压强明显增大,随着sym-H的减小,压强峰值向低L值移动.此外,当sym-H小于−60 nT时,在大多数L壳层上没有O^(+)离子的概率都为0.这些观测特征都表明,在地磁活跃时期,O^(+)离子在环电流中起重要作用,可以说,没有O^(+)离子就没有磁暴.另一方面,在地磁相对平静的情况下,R值越小,O^(+)离子不出现的概率越高.这种强相关性表明,The terrestrial ring current,flowing near the equator at the altitude of 2 R_(E)~7 R_(E),is one of the most significant electric current systems of the Earth's magnetosphere.Energetic ions(~1 keV to hundreds of keV),such as protons and oxygen ions,are thought to be the main carriers of the ring current.The enhancement of ring current during geomagnetic storms is widely regarded as the main reason for the geomagnetic field disturbance.After the storm main phase,it usually takes several days(i.e.,storm recovery phase)for the ring current to return to the original level of quiet times.In this paper,we present some recent studies concerning the relative contributions of different particle species,especially oxygen ions,to the ring current and the loss mechanism of the ring current during the magnetic storm recovery phase.Partial pressures of different species increase significantly at high auroral elec-trojet levels with hydrogen pressure being dominant inside the plasmasphere.The pressures of the heavy ions and electrons increase outside the plasmapause and develop a strong dawn-dusk asymmetry with ion pressures peaking at dusk and electron pressures peaking at dawn.In addition,ring current hydrogen with energies ranging from 50 keV up to several hundred keV is the dominant component of plasma pressure during both quiet and active times,while helium contribution is generally small.Oxygen with 10 keV<E<50 keV and electrons with 0.1 keV<E<40 keV become increasingly important during active times contributing more than 25%and 20%on the nightside,respectively.O^(+)ions'contribution to ring current is strongly connected geomagnetic activity.During large storms when sym-H<−60 nT,abundant O^(+)ions are always present without exception and the relative pressure contribution can be comparable to that of H+ions(ratio between O^(+)ions pressure and H+ions pressure>0.8)and occasionally even larger than 1 when L<3.Compared with the situation without much O^(+)ions contributing to the ring current,the O^(+)pressure and total pla

关 键 词：环电流 离子成分 氧离子 电荷交换 环电流衰减 

分 类 号：P354.1[天文地球—空间物理学]