Research Using VLF Method Topredict Solar Energetic Particles Sedimentation

Solar energetic particles sedimentation is great harm to the earth and it is significance to take an effective measure to predict the solar energetic particles sedimentation event. Aiming at the defects of the forecasting method of solar energetic particles sedimentation in the word, presents using the method of very low frequency, which cost is lower and phase is less affected by weather, to predict the solar energetic particles sedimentation event.A large amount of X-rays will be released during the flare burst. It will destroy the degree of ionization of ionosphere’s D layer, resulting in the reduction of equivalent heights of low ionosphere and leading to sudden phase anomaly(SPA) phenomenon of very low frequency(VLF) signal. This paper use the anomaly amplitude of VLF signal phase to in turn derived the variation of equivalent heights for low ionosphere, and then to judge the peak flows of X-rays when solar flare occur. Finally, according to the correlation between solar flare and high energy particles sedimentation event, the occurrence of solar energetic particles event will be predicted.The happened times and amplitudes of SPA phenomenon of VLF signals on 1991, which observed on the paths of G and E station of Omega navigation system to Zhongshan Station of Antarctic, have been given in this article. By comparing and analyzing them with the occurrence of solar flares which observed by GOES satellite and published by National Geophysical Data Center in US, find that when a part of the VLF signal observation path is in the daytime, the phase is very sensitive to the occurrence of solar flare. It also observes that the phase anomaly time of VLF signal is almost synchronous with the happened time of solar flare, and the phase anomaly amplitude is positively related with the level of solar flare. Through the phase anomaly amplitudes of VLF signals, it can calculate the equivalent heights’ decreased amount of low ionosphere, and then using least squares method in MATLAB to fit the correlation between the equivalent heights’ decreased amounts and the peak flows of X-rays. The result shows that there is an exponential relationship between them.Though comparing and analyzing the occurrence of solar flares and high energy particles sedimentation which observed by the two method of VLF, shows that the speed of solar wind is about 600~800km/h and the time of solar energetic particles sedimentation arriving the earth’s vicinity is generally late 50 to 70 hours than the occur of solar flare. This indicates it is very convenient to make a relatively timely and accurate judgment for the occurrence of solar flare only based on the phase anomaly amplitude of VLF signal, and then to make at least 2~3 days in advance forecast for the occurrence time of solar energetic particles sedimentation. It is also proved that there is a very good feasibility to use the method of VLF to predict solar energetic particles sedimentation.