南向行星际磁场事件与磁暴关系的研究

利用172-182年IMP-8飞船的太阳风观测资料和相应地磁活动性指数Dst和AE,研究了43个南向行星际磁场事件期间太阳风和磁层的耦合问题. 与这43个事件对应的地磁暴是中等的和强的磁暴(Dst＜-50nT). 结果表明:(1) 在43个事件中有11个(约占25.6髎)紧随激波之后,18个处于激波下游流场中(占42髎),其余14个(占33髎)和激波没有关连. 绝大多数事件都伴有太阳风动压和总磁场强度的增加;(2) 当行星际晨昏向电场强度EI＞-4mV/m时,只引起磁亚暴,对Dst指数没有明显影响. 仅当EI＜-5mV/m时,磁亚暴和磁暴才会同时出现;(3) 太阳风动压的增加会增强能量向环电流的输入,但不是密度和速度单独起作用,而是以PK=ρV2的组合形式影响能量的输入;(4) 虽然行星际磁场(IMF)南向分量BZ对太阳风和磁层的耦合起着关键作用,但IMF的BX和BY分量相对于BZ的大小对太阳风向磁层的能量传输也有一定影响. 当BX、BY相对BZ较大时能量耦合加强.

STUDY ON RELATIONSHIP BETWEEN SOUTHWARD IMF EVENTS AND GEOMAGNETIC STORMS

The solar wind magnetosphere coupling is investigated in terms of forty three moderate and intense storms （ D st <-50nT） and the associated southward IMF events occurring during 1972 to 1982. The solar wind data come from spacecraft IMF 8 and the geomagnetic storms are described by D st and AE. The results show that （1） Twenty nine events （67%） of all 43 events are related to shocks, among which 11 events （25.6%） closely follow a shock, and 18 events （42%） occur in the downstream of a shock. The remainder 14 events bear no relation to the interplanetary shocks. Most of these events are accompained with increases of the magnetic field and the dynamic pressure of the solar wind; （2） When the interplanetary electric field （IEF） is less than 4 mV/m, only substorms occur. On the other hand, when the IEF is greater than 5 mV/m; both of magnetic storms and substorms occur; （3） The ring current energization is related to the dynamic pressure （ ρV 2 ）, rather than the density or the velocity alone; （4） Although the southward IMF component B z is crucial, the relative strength of B x , B y to the B z also play a certain role in the energy transfer from solar wind to the magnetosphere. The energy coupling between the solar wind and the magnetosphere is enhanced if B x , B y are larger relative to the B z .