关于行星际磁场螺旋扇形过渡区稳定性的分析

本文利用四层模式,讨论了ME型行星际磁场螺旋扇形过渡区的稳定性。结果表明:(1)ME型过渡区中可以激发三种大尺度波动,且三种波动都存在低频截止;(2)随着波数k增大,不稳定性的增长率都有上升的趋势,但其中A型波动的增长率存在一个极大值和一个极小值;(3)当k与扇形区中太阳风速度V_q呈平行或反平行时,波动最易被激发;随着k与V_q之间夹角变大,截止波长逐渐向短波段移动;当k与V_q相垂直时,波动则不能被激发;(4)当k与V_q夹角呈75°时,可以激发波长为5×104km、相速为340 km/s的波动,这与Voyager 1飞船在磁层顶处的观测结果相一致。由此推断,螺旋扇形过渡区中激发的波动可能是导致磁层顶K-H不稳定性的一种扰动源。 

Analysis of Stabilities of the Spiral Sector Transition Region in the Interplanetary Magnetic Fields

By using a four-layer model, the stabilities of ME type spiral sector transition region in the interplanetary magnetic field are discussed. The results show that (1) three kinds of large-scale waves may be excited in MB type transition region, and for all of them, there exists a low-frequency cut-off; (2) the growth rates of these three kinds of instabilities all increases as k increases, but among them only the growth rate of model A has a maximum and a minimum; (3) whenk is parallel or antiparallel to the velocity V_q of solar wind in the sector regions, the excitation of waves is easier; when the angle between k and V_q become larger, the cut-off wave length moves to the shot end; when k is perpendicular to V_q, the waves can not be excited; (4) when the angle between k and V_q is 75°, the wave with a wave length of 5×104 km and phase velocity 340 km/s may be excited, this is in agreement with teh observations at the earth's magnetopause obtained from Voyager 1. Hence, we deduce that the waves in the spiral sector transition region may be a perturbation source causing the K-H instability in the magnetopause.