磁层亚暴膨胀相的近地触发模型

A NEAR-EARTH TRIGGERING MODEL FOR THE MAGNETOSPHERIC SUBSTORM EXPANSION PHASE

本文指出现有亚暴的中性线模型其源区在赤道面上离地球太远；以ＧＥＯＳ－２的观测资料为依据，提出了亚暴膨胀相的一个近地触发模型──气球模不稳定性模型．该模型认为，在增长相期间到达Ｒ≈（６－１０）ＲＥ的近地等离子体片内边缘区，出现指向地球方向的离子压强梯度，越尾电流强度增大，磁力线向磁尾拉伸．当等离子体片变薄，电子沉降增强，极光带电离层电导率骤增时，气球模不稳定性在近地等离子体片内边缘区被激发，场向电流急剧增大，导致越尾电流崩塌和亚暴电流体系的形成，从而触发膨胀相．与ＧＥＯＳ－２观测资料的进一步比较表明。

Based on GEOS-2 observations, a new substorm expansion phase model-the Near Earth Ballooning Instability Model (NEBIM) is proposed. It is shown in this model that during the growth phase, strong earthward energetic ion gradient is build up at the inner edge of the near Earth plasmasheet (IENEP) which arrives at (6-10) RE on the nightside; the tail current is greatly enhanced; and the magnetic field lines there are stretched out to the tail. Ballooning instability can be generated at the IENEP when the plasmasheet becomes very thin, and the electron precipitation and hence the conductivity in the auroral ionosphere are greatly increased, leading to the disruption and diversion of the tail current to the ionosphere, and the formation of the substorm current wedge. The substorm expansion phase is thus triggered. Further comparison with GEOS-2 data indicates that all features of the expansion phase predicted by the NEBIM are in good agreement with those observed by the spacecraft.