On the disappearance of H-alpha filaments and soft X-ray enhancements as seen from Yohkoh SXT

Abstract

We have studied H-alpha images of the sun taken at Kodaikanal and Mitaka observatories and soft X-ray images obtained by SXT onboard Yohkoh for the years 1993 and 94. From events of disappearing quiescent H-alpha filaments and associated soft X-ray brightenings we find that in some cases H-alpha filament appears broken and diffused about a day earlier than beginning of the soft X-ray transient brightening which lasted for 7 - 10 hours. Further, enhancements began along filament channels and then moved along arches which were inclined to the filament direction. From these observations we postulate that heating of plasma in the filament begins when it appears broken and less dark and continues till it triggers some physical process, responsible to begin soft X-ray enhancement. It is not possible to say that if the H-alpha filament disappears earlier than the beginning of soft X-ray enhancement or vice versa as there is time difference between H-alpha and soft X-ray observations.