地磁暴前地面宇宙线强度变化Morlet小波特征分析

THE WAVELET CHARACTER OF COSMIC RAY INTENSITY BEFORE GEOMAGNETIC STROMS

用Morlet小波变换对Oulu台站和Apatity台站(主要是Apatity台站)1998-2002年间宇宙线静日和地磁暴前的地面宇宙线强度变化特征进行分析,得到:在宇宙线静日期间普遍存在准24 h周期变化特征,并且在当地时间0200,1400左右分别出现最小值和最大值;对12个例子的分析可以看到地面宇宙线强度在地磁暴之前1-2天均出现了不同于宇宙线静日期间变化特征,或有小尺度周期出现,或周期变化完全消失,或有异常24h周期变化,这种变化特征在一定程度上可作为地磁预报的先兆特征之一.

In this paper, Morlet wavelet is applied to analyze the character of cosmic ray intensity of Apatity station (latitude: 67.56°N, longitude: 33.4°E, Russia) and Oulu station (latitude: 65.05°N, longitude: 25.47°E, Finland) respectively during quiet period of geomagnetic field and before geomagnetic storms from 1998 to 2002. Fourteen examples are selected including two examples of quiet period and 12 examples before geomagnetic storms. The level of major storms selected in this paper is that index Dst is less than -100 nT. By Morlet wavelet transform, cosmic ray intensity of different condition shows different variety. Results show that 24 h periodicity exists and is distinct during quiet time, and usually minimum value of cosmic ray intensity appears around about 0200 local time and maximum value appears around about 1400 local time; Twelve examples before geomagnetic storms period show that variety of 24 h periodicity all change. Some minish, some disappear, and some have anomalous 24 h periodicity, and these varieties differ from that of quiet time. These characters before geomagnetic storms may provide a sign that can be used to forecast the coming of geomagnetic storms of coming of geomagnetic storms.