X-Ray Observations of Motions and Structure above a Solar Flare Arcade

Abstract

In this Letter, we describe a solar flare that was observed by Yohkoh in 1999 January 20. This long-duration event is notable because the Yohkoh images show not only the formation of the arcade associated with the coronal mass ejection but also a considerable amount of motion above the arcade in the region normally identified with a large-scale current sheet or the outflow from magnetic reconnection in the current sheet. A number of arcade events of this morphological type (i.e., a fan of spikelike rays above the posteruption loops) have been seen by Yohkoh, but in this case we have a much clearer view of mass motions in the region above the arcade. The motions indicate field-line retraction without the formation of long-lasting cusps during the rise phase of the flare, and a downward flow above the arcade during the decay phase. The late-phase downward motion is in the form of X-ray dark voids moving at 100-200 km s-1, i.e., at velocities much smaller than the free-fall speed or the assumed Alfven speed. We interpret the voids as cross sections of evacuated flux tubes resulting from intermittent reconnection following the associated coronal mass ejection. We believe these data represent the first direct evidence of high-speed flows in the region immediately above the flare loops.