径向行星际磁场下的场向电流统计学研究

摘要

The characteristics of field-aligned currents ( FACs) and the related physical quantities under radial interplan-etary magnetic field ( RIMF) from 2001 to 2009 were investigated .Statistical analysis and comparison with FACs under normal conditions were performed using CHAllenging Minisatellite Payload ( CHAMP) data.The results showed that the intensity of noon FACs has clear dependence on the dipole tilt angle under normal conditions and that the ratio between summer and winter is about 3; however , the dependence disappears under RIMFs and the ratio decreases to 2.The magnitude of the interplanetary magnetic field (IMF), the merging electric field, solar wind dynamic pressure , and the auroral electrojet ( AE ) index decrease , while the disturbance storm time ( Dst ) index remains almost stable under RIMFs .The merging electric field is a controlling factor of FACs under normal conditions, but the control effect disappears during RIMFs .In the Northern Hemisphere , the intensity of FACs under IMF Bx <0 conditions is larger than that under IMF Bx >0 conditions ( the situation is the converse in the Southern Hemisphere ) .Although the intensity of FACs under normal conditions is greater than that under RIMFs , the probability that the density of FACs under RIMFs is greater than the yearly average is about 0.2, and some geomagnetic disturbances , such as substorms , still occur under RIMFs .%基于CHAMP卫星高精度磁场观测数据，对2001—2009年径向行星际磁场（ RIMF， radial interplanetary magnetic fields）条件下的场向电流的分布特征进行了统计学分析，并与2001—2009年期间场向电流的平均强度进行了对比研究，结果表明：正午时刻场向电流的平均强度对地偶极子倾角有明显线性依赖，冬夏季电流强度比值约为3左右， RIMF条件下冬夏季比值降为2；相对年平均值来说， RIMF条件下行星际磁场总幅度、重联电场、太阳风动压均有所减小， AE指数减弱， Dst指数略有降低；在通常情形下重联电场是场向电流很好的控制参数，但是在RIMF下，重联电场不再与电流强度相关；北半球电流强度在向地IMF条件下大于向日IMF，而南半球则相反，虽然RIMF条件下场向电流的均值小于年平均值，但是正午时段场向电流强度大于年平均值的概率大约为0．2， RIMF条件下仍然有地磁扰动事件（比如亚暴事件）发生。