太阳风在地球激波前兆区减速的统计研究

Statistical study of the solar wind deceleration in the Earth's foreshock region

本文首次利用完全相同两颗卫星(CLUSTER C1和C3)的数据对地球激波前兆区太阳风的减速和偏转特性进行了统计研究.结果表明,在激波前兆坐标系中,太阳风减小的速度随观测点到激波的距离D_(BS)增大而减小,随行星际磁场与激波法向夹角θ_(BN)增大也减小,在ULF波动区深度D_(WS)小于6R_e(R_e为地球半径)的范围内最为显著;伴随着太阳风减速的另外一个现象——太阳风的偏转,也存在相似的规律.其最大减速和最大偏转角度分别为10 km/s和3°.太阳风减速和偏转,以及随之变化的太阳风动压,可能会引起地球磁层顶位置和形状发生改变,同时也为激波前兆区弥散(diffuse)离子的起源及加热提供了一种可能的机制.

The data from two same satellites （CLUSTER C1 and C3） were used to make a statistical study of the solar wind deceleration and deflection in the Earth＇s foreshock region for the first time. In the foreshock coordinates, the magnitude of deceleration is inversely proportional to DBS measuring the distance between the satellite and the bow shock along the interplanet magnetic field （IMF）, and also inversely proportional to θBN （the angle between the IMF and the bow shock normal）. The decelerations mainly occur when Dws （the distance from satellite to the ULF wave boundary along X direction） is less than 6Re. On the other hand, the solar wind deflection, displays a similar feature. The largest values of deceleration and deflection are, respectively, estimated as 10 km/s and 3°. These decelerations and deflections not only lead to a variation of the magnetopause＇s position and shape, but also supplies a possible generation mechanism of the diffuse ions in the foreshock region.