磁场偶极化过程中磁尾的电离层离子加速:Ⅰ离子分布函数的演化

A THEORETICAL STUDY ON THE ACCELERATION OF OUT-FLOWING IONS IN THE MAGNETOTAIL: I VARIATION OF ION DISTRIBUTION FUNCTION

采用动力学方程，对亚暴期间磁尾磁场向偶极形弛豫过程中离子分布函数的演化进行了模拟研究，主要结果为：（１）初始时刻分布函数为相对于速度呈指数下降的离子束，在随时间变化过程中，逐渐变为相对于速度（包括平行和垂直速度）的单峰结构，且单峰在速度空间的位置随时间的变化而向高速方向移动；（２）在速度空间中平行于磁场方向上单峰向高速方向移动得较慢，在垂直方向上移动得较快；（３）轻离子分布函数峰值的位置较重离子随时间的变化向高速方向移动较快。（４）初始能量较高时，离子分布函数的单峰位置向高速方向移动较快。（５）离子团在磁场偶极化过程中表现为一束地向流．本文还对上行离子受感应电场的加速进行了讨论．

Based on the dynamic equation, the variation of up-flowing ionsdistribution function during the dipolarizition of the substorm in the magnetotail issimulated. The results show that (1) the ion distribution function, initially decreasingexponentionly with increasing speed becomes single peak distribution, the peak movesin the direction of speed increasing, (2) the peak moves more quickly along V thanthat along V , (3) the peak moves more quickly for lighter ions than that for heavierions, (4) The more the initial energy is, the more quickly the peak move, (5) the ionmoves as an Earth-ward flow during the dipolarizition. The acceleration of theup-flowing ions in the induced electrical field is discussed, too.