Statistical Research On Moderate Storms

736moderate storms have been picked up from1957-2008and detail researches have been made in terms of solar cycle distribution, seasonal variation and the relationship between the intensity of moderate storms and solar wind parameters. The results are as follows:(1) Most moderate storms appeared after the solar maximum, and the yearly number of moderate storms have multi-peaks in each cycle with the highest peak appeared in the descending phase of the cycle. This means that the highest peak of moderate storms have a time lag with respect to the yearly number of sunspot numbers. The time lag is about2-3years. Phase difference between smoothed monthly mean moderate storm numbers and smoothed monthly mean sunspot numbers is also investigated in this paper and the result is different from that of the yearly number, the time lags in solar cycle20,21,22,23are33months,34months,13months and3months respectively.(2) There are not apparent seasonal variation characters in each year, but the total numbers of moderate storms in each solar cycle have obvious seasonal variation, March and October seem to be the months that the most moderate storms occur.(3) The solar wind parameters that have been studied in this paper are Ey, Bz and ε and the results show that these3parameters have very good correlation with the intensity of moderate storms.