磁层氧离子向磁鞘泄漏的机制和效应

１９９７年 １月 １０日磁暴期间， Ｇｅｏｔａｉｌ卫星在向阳侧的磁鞘中观测到了磁层氧离子突增事件．这些氧离子的出现和磁鞘中存在很强的南向行星际磁场有关．事件期间向阳面发生了准静态的磁重联，氧离子流存在由北向南的速度分量．通量突增过程具有逆向和正向能量色散现象，磁层内部只有氧离子有可能被梯度漂移输送到重联区，所以只有氧离子在磁鞘中持续地被观测到．估计氧离子的逃逸速率为 ０．６１× １０２３／ｓ，大约为环电流氧离子输入率的 ３３％．大量的环电流氧离子由磁层跑到了磁鞘，导致环电流指数 ＡＳＹ－Ｈ呈现明显的非对称性．

ESCAPE OF MAGNETOSPERIC O~+ OXYGEN IONS INTO THE MAGNETOSHEATH: MECHANISM AND EFFECTS

During the magnetic storm of January 10, 1997, Geotail spacecraft observed a mgnetospheric O+ burst event just on the outside of the dayside magnetopause. Energetic oxygen ions were seen to flow downward in the magnetosheath. The appearance of this O+ burst event was in close connection with the strong southward interplanetary magnetic field. The Principle Axis Analysis (PAA) indicates that the dayside magnetopause during this time period was a rotational discontinuity, magnetic reconnection took place in the magnetopause current sheet. Observations showed that reconnection was of the quasi-steady state type and that the O+ flow has a southward component. Both normal and inverse energy (velocity) dispersion were seen in the O+ flux enhancement process which were caused by the Time Of Fly (TOF) effect of oxygen ions escaping along the reconnected magnetic field lines. Only O+ can be transported by the gradient drift from the magnetosphere into the reconnection region, therefore they can be continuously detected in the magnetosheath. The escape rate of O+ in this event is estimated to be 0.61 x 1023 s-1, which was approximately 33% of the total input rate of the ring current oxygen ions. It is the escape of a great number of oxygen ions from the duskside of the inner magnetosphere (ring current region) that leads to the pronounced asymmetry in the ring current ASY-H index.