磁暴数统计特性研究

Analysis on the Distribution of Geomagnetic Storm Number

Dst是一个表征磁暴强度的空间天气指数.通过统计1957—2008年发生的中等磁暴(-100<Dst≤-50 nT)和强磁暴(Dst≤-100 nT)在太阳活动周上升年、极大年、下降年和极小年的时间分布情况,分析其随季节变化的统计特性,进而讨论了引起磁暴的原因.结果表明,对于同一太阳活动周,极大年地磁暴发生次数远大于极小年地磁暴的发生次数,这与太阳黑子数的变化趋势是一致的;通常太阳活动周强磁暴出现双峰结构,而第23周中等磁暴出现双峰结构,强磁暴则出现三峰结构,这可能与1999年强磁暴发生次数异常少,使1998年凸显出来的现象有关;磁暴主要发生在分季,随着Dst指数的增加,磁暴发生次数明显增加.

A geomagnetic storm is a global disturbance in Earth's magnetic field,which is caused by various solar phenomenon.Dst index is the most widely used index which denotes the intensity of magnetic storm activity.The distributions of moderate geomagnetic storms(-100 < Dst ≤- 50 nT)and intense geomagnetic storms(Dst ≤-100 nT) and their causes in 1957-2008 are identified.Moreover,annual average number of geomagnetic storm in ascending phase,maximum phase,declining phase,and minimum phase of solar activity was analyzed according to different kinds of geomagnetic storms.It is found that the total number of geomagnetic storm in maximum phase year is greater than that in minimum phase year of the same solar activity,and there is close relation between the average number of Sun spots per year and the total number of geomagnetic storm.A dominant dual-peak distribution usually exists in the solar cycle variability of intense geomagnetic storm,but a dual-peak distribution of moderate geomagnetic storm exists and a trinal-peak distribution appears in intense geomagnetic storm.The presence of the extra peak might be attributing to a typical year compared to other rising phase years.On the other hand,another possibility is that 1999 could be an unusual year,with a low rate of intense magnetic storm.The magnetic storms mainly happen in equinox,and the number of magnetic storm is obviously changed with the increased Dst index.