Researches on the Periodic Variation Characteristics of High-energy Electrons in Near-earth Space by Using the Wavelet Analysis

The variation of high-energy electron flux of GOES (Geostationary Operational Environmental Satellites) series satellites (GOES 10/11) from March 1999 to December 2010 and Fengyun-2 series satellites (FY 2C/2D) from October 2004 to May 2012 was studied by applying wavelet transformation. We found that the high-energy electrons observed by GOES are periodic and the periods are 13.9-day, 27.7-day, 187.0-day and 342.9-day. There are obvious 13.9-day, 27.7-day, 222.3-day and 374.0-day cycles for the high-energy electrons observed by FY. In some years, GOES and FY satellites both have a period of 9-day, which is highly similar to the geomagnetic Dst (equatorial ring current index) and AE (laser charged jet index) index cycles. We carry out the overlapping wavelet analysis of the high-energy electron flux and Dst and AE indexes. The data are finally decomposed at different frequencies by using the localization analysis methods of time domain and frequency domain based on the multi-resolution characteristics of the algorithm. So that the relationship between high-energy electron flux and geomagnetic index can be clearly seen from the reconstructed image of low-frequency coefficient and the crossed wavelet spectrum. Based on the good correlation of the high-energy electrons between the FY and GOES satellites, we made a further study of the same short period and different medium-to-long periods on multiple satellites. The anisotropy of high-energy electron flux in different geomagnetic disturbances is found. Small magnetic storms can also have the same effect on electron flux as strong ones, and sometimes exist in the same 24-hour cycle corresponding to local time. It is very important for us to study high-energy electrons in geomagnetic quiet period. At the same time, it is of great significance for understanding solar activity, predicting high-energy electron spectrum, warning deep charging events and verifying the magnetic storms and substorms.