Statistical research into low-power solar flares. Main phase duration

Abstract

This paper is a sequel to earlier papers on time parameters of solar flares in the Hα line. Using data from the International Flare Patrol, an electronic database of solar flares for the period 1972–2010 has been created. The statistical analysis of the duration of the main phase has shown that it increases with increas-ing flare class and brightness. It has been found that the duration of the main phase depends on the type and features of development of solar flares. Flares with one brilliant point have the shortest main phase; flares with several intensity maxima and two-ribbon flares, the longest one. We have identified more than 3000 cases with an ultra-long duration of the main phase (more than 60 minutes). For 90 % of such flares the duration of the main phase is 2–3 hrs, but sometimes it reaches 12 hrs.