Abstract :
The Japanese mission Yohkoh (sun-beam) observed three solar gamma-ray flares of October, November and December 1991, on the declining phase of solar cycle 22. Each flare has different spectral characteristics, strong narrow line flare, broad line flare and continuum gamma-ray flare.
The solar gamma-ray flares of October, November and December 1991 are produced from the three solar active regions NOAA/USAF 6891, 6919 and 6952 respectively. The aim of the present work is to study the general characteristics of these three active regions, and perform an evolution for the sunspots and their magnetic fields which lead to releasing highly energetic impulsive flares associated with gamma-ray emissions.
The method of cumulative summation curves for X-ray bursts and Hα flares produced from the active regions and also, cumulative summation curves for sunspots area and count number for the same active regions are applied to show any steep increase in the trend in the curves for few days prior to the γ-ray flare occurrences.
