Filling factors of flare loops in the decay phases

Abstract

We investigate the energetics during the decay phases of 59 impulsive solar flares observed by soft X-ray instruments on board Yohkoh. All the 59 flares show that the total energy loss (via conduction and radiation) estimated in a flare loop exceeds the time derivative of thermal energy contents in the same loop. Though the footpoint pressure is “apparently” less than the loop top pressure, no flow along the loop is detected in the soft X-ray line profile. We introduce a cross sectional filling factor which equates the footpoint pressure with the loop top pressure. This filling factor can result in near equality between the total energy loss and the time derivative of thermal energy contents.