The Periodic about Variation An 155-day of the Solar Flare Activity for the 21st Cycle

Recently,from the observed data in different wave bands and different time intervals many people have obtained an 152-day-158-day periodicity of solar flare activity.In this paper the time series made by the daily weighted solar Ha flare numbers for the.21st solar cycle(1976-1985) are annually analysed by the maximum entropy spectrum analysis method.The results show that about 155-day period of solar flare activity is only relatively remarkable during three years after the maximum epoch of sunspot activity.The results will have a certain practical value for the understanding the basic mechanism of the solar flare activity,the variation of solar-terrestrial physical parameters relative to the solar flare,and the forecasting of medium and long term solar activity.