The correlation among the rise velocity of a soft X-ray loop, the ejection velocity of a plasmoid, and the height above the loop top of the hard X-ray source in Masuda-type flares, and its interpretation based on the reconnection model of flares

One of the most important results on solar flares obtained by Yohkoh is finding impulsive compact-loop flares associated with a hard X-ray (HXR) loop-top source well above a soft X-ray (SXR) loop, which are called Masuda-type flares. This finding supports the reconnection model of flares in which magnetic reconnection occurs above the closed loop observed in the soft X-ray during a flare. Although this model qualitatively explains the observed feature of Masuda-type flares, quantitative investigations into physical processes in these flares are still insufficient, which is the main subject of this Letter. We used 15 Masuda-type flares (seven are newly found and eight are previously reported) to examine the correlation among the rise velocity of an SXR loop, the ejection velocity of a plasmoid, and the height of the HXR source above the SXR loop (i.e., the difference in the apparent heights of the HXR and SXR sources). The main conclusion is that there is a positive correlation among these three quantities, and we explain the physical origin of this correlation using a reconnection model of flares.