大尺度场向电流的控制因素

将ＩＳＥＥ－１和ＩＳＥＥ－２飞般测量的地球内磁层场向电流作为行星际磁场与极区地磁活动水平（由ＡＬ表征）的函数。发现大约７５％的场向电流发生在行星际磁场南向时，其余２５％发生在行星际磁场由南向转到北向的半小时内。而且，发生在ＡＬ〈－１５０ｎＴ的场向电流也大约是７５％。场向电流的强度和密度随行星际磁场南向分量及ＡＬ的负值增加而增大。由此而得出结论，内磁层场向电流的产生主要是由行星际磁场控制的，是太阳风

DEPENDENCE OF FIELD-ALIGNED CURRENTS ON THE ORIENTATION OF THEINTERPLANETARY MAGNETIC FIELD

Field-aligned currents (FACs) measured in the inner magnetosphere by theISEE-1 and -2 spacecraft are investigated as a function of the Interplanetary Mag-netic Field (IMF) orientation and the level of geomagnetic activity, as indicatedby the AL index. It is found that ~75% of the FACs observed are associated withsouthward IMF. The remaining 25% occur during the period of IMF turning fromsouthward to northward- Very few are associated with sustained intervals of north-ward IMF. Approximately 75% of the FACs occur when the AL index is < -150 nT.The current intensity and density are higher for both southward IMF and high gecrmagnetic activity. These results show that the occurrence of FACs within the innermagnetosphere is controlled mainly by the IMF, with the actual occurrence being aconsequence of enhanced electrodynamic coupling between. the solar wind and themagnetosphere- ionosphere system.