| Abstract: | The temporal variations of the occurrence of the (M–X) LDE flares (with the SXR duration exceeding 2 hours) throughout the 20th and the 21st cycles are considered. The characteristics of the 20th cycle: the maximum value of the observed yearly number of LDE flares was in the 1970 (with the total 225 LDE flares observed). The increased LDE flare activities were observed in the years 1972 and 1974 (see Tab. 1). The characteristics of the 21st cycle: the large occurrence of the (M–X) LDE flares was observed form 1979 to 1982. The yearly numbers of the (M–X) LDE flares in 1980–168, 1981–151 and 1982–135 are comparable. The fast decrease of the whole flare activity begun at 1983. The percentual representation of the (M–X) LDE flares in the occurrence rate of all Hα flares fluctuated between 1–3%. |
