1998年5月磁暴磁层电流体系的地磁效应分析

VARIATIONS OF INNER MAGNETOSPHERIC CURRENTS DURING THE MAGNETIC STORM OF MAY 1998

低纬度地区地磁场的短时变化主要由以下电流体系产生 :电离层发电机电流(IDC)、对称环电流 (SRC)以及由部分环电流和Ⅱ区场向电流及其电离层回路组成的内磁层三维电流体系 (PRFI) .此外 ,由Ⅰ区场向电流及其电离层回路组成的电流体系 (FACI)所产生的低纬地磁场也是不可忽略的 .本文针对 1 998年 5月 1— 6日的大磁暴 ,首先利用多个同子午线台站对的数据分离并消去由IDC电流产生的Sq场 .然后 ,通过线性建模分离其他电流体系产生的磁场成分 .结果表明 :(1 )发生在 5月 1— 6日的磁暴可以分为两个过程 ,PRFI和FACI电流体系在 1— 3日不明显 ,在 4— 5日伴随着亚暴强烈发生 .(2 )SRC的变化情况在第一阶段同Dst指数相似 ,在第二阶段明显滞后于Dst指数 .(3 )在 5月 4— 5日 ,PRFI在SRC之前增强 ,随着PRFI和FACI的恢复 ,SRC开始增强 .

Transient variations of the geomagnetic field at low latitudes are mainly caused by the current system such as ionospheric dynamo current (IDC), symmetric ring current (SRC), partial ring current region Ⅱ field aligned current ionospheric current system (PRFI). On the other hand, the region Ⅰ field aligned current ionospheric current system (FACI) cannot be ignored. In this paper, we analyze the variations of the current systems during the large storm on May 1—6, 1998. Firstly, the S q -field caused by IDC is calculated by using several station pairs, and removed. Then, the fields of other sources are separated by fitting data to their field models. Results show that (1) The storm has two steps, during May1—3, PRFI and FACI were not developed significantly, they became strong during the substorms of May 4—5. (2) The variation of SRC is similar to D st variation during the first step and delays to D st in the second step. (3) In the second step, PRFI is developed before SRC, and SRC depresses associated with the PRFI and FACI recovery. It gives a clue to understand the formation of the ring current and field aligned currents and their relationship. [