大磁暴中环电流离子成分的变化及其与磁暴演化的关系

ION COMPOSITION VARIATIONS IN THE RING CURRENT DURING INTENSE MAGNETIC STORMS AND THEIR RELATIONSHIP WITH EVOLUTION OF STORMS

利用CRRES/MICS的观测数据 ,研究了磁暴期间内磁层离子成分的变化 .对1 991年两个典型磁暴和 1 2个大磁暴的分析表明 ,组成暴时环电流的离子可以分成两组 ,一组由O+、低能H+和He+组成 ,起源于电离层 (IOP) ;另一组为高能H+和He++,主要来自太阳风 (SOP) .宁静时环电流主要成分为SOP ,大磁暴主相极大时环电流的主要成分是IOP .大磁暴期间离子可被注入到很低的高度 (L =3— 4) .IOP对环电流的贡献随磁暴强度增大而增加 ,在大磁暴主相极大时可达 80 % (数密度 ) .IOP中O+的快速增减是导致Dst指数在磁暴主相期间快速下降和恢复相中快速增长的主要原因 .小磁暴中 (Dst>- 50nT)

Ion composition variations in the inner magnetosphere during storm time are investigated using data set obtained from CRRES/MICS. Case study of the twin storms in July,1991 and statistical study of 12 intense storms in the same year both indicate that the storm time ring current particles can be divided into two groups:one consists of O +,low energy H + and He +,which are originated from the ionosphere (IOP),the other is composed of high energy H + and He ++ which are originated from the solar wind (SOP). It is shown that in quiet time the major particles of the ring current are SOP,whereas during the main phase of large storms the main component of the ring current particles is the IOP. Ring current particles of intense storms can be injected to low L altitudes ( L ～3-4). It is confirmed that the contribution of IOP to the ring current increases with increasing D st value. In large storms IOP are the major constituents of the ring current,even up to 80% of the total number density at the D st Maximum. There is clear evidence showing that it is the rapid enhancement and reduction of the O + flux of the ring current that leads the D st index to rapidly decrease during the main phase and to quickly recover in the early recovery phase. Further analyses indicate that during weak storms ( D st >-50nT) the contribution of O + ions to the ring current is negligible. [