磁暴主相多阶发展行星际起因的初步分析

本文利用1998~2006年与磁云有关的80起中强磁暴(Dst*≤-50 nT),对其主相期间不同发展阶数磁暴的行星际起因进行了统计分析.重点研究了鞘区磁场单独作用、磁云本体单独作用、鞘区与磁云共同作用以及其他复杂行星际结构在磁暴主相多阶发展中的相对重要性,并对导致磁暴主相增加一阶的行星际起因做了初步分析.统计结果表明:(1)有一半以上的中强磁暴主相具有多个发展阶段,其中一阶磁暴和多阶磁暴(包括二阶和二阶以上磁暴)在中等磁暴(-100 nTDst*≤-50 nT)中所占比例分别为53.8%和46.2%,在强磁暴(Dst*≤-100 nT)中所占比例分别为42.6%和57.4%;(2)随着磁暴主相发展阶数的增加,磁暴主相的平均持续时间也随之延长;(3)鞘区磁场单独作用、磁云本体单独作用、鞘区与磁云共同作用、磁云与其他行星际结构共同作用都可能引起磁暴主相的多阶发展;(4)有46.5%的多阶磁暴是由鞘区磁场与磁云本体共同作用引起,有34.9%的多阶磁暴是由鞘区磁场单独作用和磁云本体单独作用引起,其余的多阶磁暴是由其他复杂行星际结构引起;(5)在鞘区磁场单独作用的事件中,鞘区磁场结构是影响磁暴主相多阶发展的重要因素之一;(6)磁暴主相的多阶发展与晨昏电场Ey、行星际磁场Bz南向分量的发展密切相关,随着Ey和Bz阶段性的发展,磁暴主相也呈现多阶发展的趋势,且每阶Dst*极小值与该阶Eymax和Bzmin有很好的线性相关性,线性耦合方程分别为Dstmin* =-34.62-11.89×Eymax 和Dstmin* =-5.90+8.50×Bzmin.

Primary analysis on the interplanetary cause of multistep magnetic storms

Using eighty moderate intense geomagnetic storms (Dst^*≤-50 nT) induced by MCs from 1998 to 2006, we statistically examined the relations between the geomagnetic storms development in different steps during the main phases and their interplanetary sources. This paper has analyzed the relative importance of sheath region magnetic field ahead of MC、MC itself、the combination of sheath and MC, and other complicated interplanetary structures in the associated multistep storms, and the interplanetary drivers leading to Dst^* index further decrease were also investigagetd. It is found that: (1) above 1/2 moderate intense storms have a two-step or more than two steps development during their main phases (called multiple-step storms), and the percentages of one-step storms and multistep storms in the moderate storms (-100 nT*≤-50 nT) are 53.8% and 46.2%, and in intense storms(Dst^*≤-100 nT) the percentages are 42.6% and 57.4% respectively; (2) with the step number increases, the average duration of main phase is also prolonged; (3) sheath field itself, MC itself, the combination of sheath and MC, and other complicated interplanetary structures all can lead to multistep storms; (4) 46.5% of multistep storms were induced by the combinations of sheath and MC fields, 34.9% of multistep storms were induced by sheath field itself or MC itself, and the others were induced by the complicated interplanetary structures. (5) in the magnetic storms induced by the sheath region, the magnetic structures of sheath field were closely related to the development of the main phases; (6) the multistep storms have close relation to the intermittent development of the interplanetary southward component of magnetic field (B_z) and y component of electric field (E_y), and the prediction relationships for every step Dst_min* and the E_ymax/B_zmin during the step are: Dst_min* =-34.62-11.89×E_ymax and Dst_min* =-5.90+8.50×B_zmin.