地球内磁层场向电流的统计特征

THE STATISTICAL CHARACTERISTICS OF FIELDALIGNED CURRENT IN THE EARTH'S INNER MAGNETOSPHERE

利用ISEE－1和ISEE-2飞船观测的磁场数据，分析了地球内磁层场向电流的统计特征，包括场向电流的空间（L值和地方时）分布；流进和流出电离层的场向电流随地方时的变化；场向电流发生率与地磁活动水平（以AL指数表征）、行星际磁场（IMF）Bz的关系，电流强度和密度随地磁活动水平的变化等．发现，场向电流大都发生在夜间，且集中在L为6—10区域内，场向电流发生率，强度和密度随地磁活动增强而增大，行星际磁场南向时的发生率远远高于北向时的发生率．这些结果表明，内磁层场向电流的产生是太阳风和磁层、电离层间电动耦合增加的结果．

The characteristics of field-aligned currents (FACs) in the inner magnetosphere are determined from ISEE-1 and 2 observations. These characteristics are included the spatial (L-value and local time) distribution of FACs, and the relationship between the occurrence rate and the levels of geomagnetic activity (measured by AL), the dependence of the current intensity and density on geomagnetic activity. It was found that most of the FACs observations were detected around the pre-midnight and the dawn / dusk meridian. The occurrence rate, current intensity and current density of FACs increase with increasing geomagnetic activity; The occurrence rate of FACs is higher when interplanetary magnetic field Bz is southward. Pre-midnight FACs are known to be associated with substorms.These result show that the occurrence of FACs within the inner magnetosphere is a consequence of both enhanced electrodynamics coupling betWeen the solar wind and the ionosphere.