2003年11月20日磁暴主相期间磁鞘的观测研究  

Cluster observations of the dusk-side magnetosheath during the storm main phase on 20 November 2003

作　　者：汤朝灵[1] 李中元[1] 路立[2] 

机构地区：[1]中国科学技术大学地球和空间科学学院,合肥230026 [2]中国科学院空间科学与应用研究中心,北京100080

出　　处：《地球物理学进展》2009年第3期842-847,共6页Progress in Geophysics

基　　金：国家自然科学基金项目(40674083和40390150)资助.

摘　　要：2003年11月20日磁暴主相期间,Cluster卫星正好处在黄昏侧的磁鞘附近.在主相期间磁鞘磁场B_z 分量大约为-60 nT,这和ACE卫星观测值基本一致.同时,磁鞘中的离子速度分布对磁鞘中的磁场方向有很强的依赖性.行星际电场E_y 在磁鞘中大约是50 mV/m.磁鞘中这些极端的磁场,电场和离子的流动驱动了迄今23个太阳活动周期中最大的磁暴,其Dst指数是-472 nT. Cluster卫星观测发现磁鞘中离子的数密度比较低,这可能是由磁云经过地球时太阳风的低密度造成的.磁鞘中能量范围为1-10 keV的H^+,He^+和He^(2+)的数密度主要是由磁鞘中太阳风的数密度决定的.同时,对磁鞘中存在大量的1-10 keV氧离子进行了讨论.在极端的南向行星际磁场条件下,磁层顶受到很强的压缩.氧离子可以利用较大的回旋半径,在强压缩的磁层顶和磁鞘对流的共同影响下进入磁鞘.这也表明了磁层对极端行星际条件的一种响应.Cluster卫星在11月20日磁暴事件中的观测研究,对进一步全面认识大磁暴事件有很重要的作用.We present cluster observations of the dusk side magnetosheath（MSH） during the storm main phase on 20 November 2003, which was associated with the passage of a large magnetic cloud past the Earth. During the interval, the Bz of the magnetic field in the magnetosheath was observed to be about - 60 nT, which is basically consistent with that observed by ACE. And, ion flow velocity in the magnetosheath has a strong dependence on the magnetosheath magnetic field orientation. The IMF electric field Ey in the magnetosheath is - 50 mV/m. These extreme fields and flows in the magnetosheath drove the largest geomagnetic storm to date in the solar cycle 23 with a Dst minimum of -472 nT. The ion number density in the magnetosheath is lower than the magnetospheric in our study, which is caused by the lower ion number density in solar wind when a large magnetic cloud past the Earth. The number densities of H^＋, He^＋ and He^2＋ with an energy of 1-10 keV in the magnetosheath are dependent on the density of solar wind in the magnetosheath. The magnetopause is strongly compressed for the extremely large southward magnetic field. The abundant energetic oxygen ions with an energy of 1-10 keV cross the magnetopause into the magnetosheath, because of their finite gyroradius （〉1000 km）, provided the MSH convection and magnetic field orientation are taken accordingly into consideration. This is the indication of the magnetospheric response to the extreme IMF condition. These may be important for us to better understand the large geomagnetic storm.

关 键 词：磁鞘 太阳风 高能离子 地磁暴 

分 类 号：P315[天文地球—地震学]