第23太阳活动周强磁暴行星际源的统计分析

Analysis on the interplanetary causes of intense geomagnetic storms during solar cycle 23

统计了第23太阳活动周(1996-2006)发生的90次强地磁暴(Dst≤-100nT)的行星际源.在第23太阳活动周内,当行星际磁场(Interplanetary Magnetic Field,IMF)Bz分量南向翻转并持续较长时间时,通常会引起强磁暴的发生,进而引起电离层暴.文中分析了强磁暴的年分布状况以及引起强磁暴的不同行星际结构在同样活动周的分布特征,并且分析了中国地区电离层暴事件的行星际源.统计结果显示,1)行星际日冕物质抛射(Interplanetary Coronal Mass Ejection,ICME)是引起强磁暴的主要行星际源.在ICME中,相对于非磁云结构,磁云结构是引起强磁暴的主要行星际源.2)强磁暴主要在太阳活动极大年和下降年份,在太阳活动低年出现次数较少.强磁暴在太阳活动周的分布呈三峰结构,并认为可能跟1999年强磁暴发生次数异常少,使1998年凸显出来的现象有关.3)ICME引起的电离层暴事件是共轭作用区(Corotating Interaction Region,CIR)引起电离层暴的7倍多,这说明ICME也是电离层暴事件的行星际源.

The interplanetary causes of 90 intense geomagnetic storms （Dst^--lOOnT） and their solar dependence occurring during solar cycle 23 （1996--2006） are identified. During this solar cycle, magnetic reconnection between the southward IMF and magnetopause fields are happened when the interplanetary magnetic field was southwardly directed for long durations of time, which induces the cause of the geomag- netic storms and ionospheric storms. In addition, the relationships between ionospheric storms and the so- lar activity are investigated. It is found that.. 1） Interplanetary coronal mass ejection （ICME） is the main cause of intense geomagnetic storms. Moreover, in the associated ICMEs, magnetic cloud ICME is more important than non magnetic cloud ICME, which is the main cause of intense geomagnetic storms. 2） We have found more storms in the maximum and declining phase than in the rising phase. There is a three peak distribution of intense geomagnetic storms, 1998, 2001--2002 and 2004--2005. The peaks at 2001-- 2002 and 2004--2005 correspond to the solar maximum and declining phase peaks. One possibility is that 1999could be an unusual year, with a low rate of intense geomagnetic storms. 3） ionospheric storms cau-sed by ICME are seven times more than that caused by CIR, which shows that CME is also the main cause of ionospheric storms.