Published online by Cambridge University Press: 12 April 2016
The 21 May event was a large two-ribbon flare which occurred in active region 2456 at S13W15. The flare was extensively documented by coordinated Hα, X-ray, and magnetograph observations. In particular, spatially resolved images in hard X-rays were obtained by the Hard X-ray Imaging Spectrometer (HXIS) aboard SMM. Hence this flare comprises an ideal example for studying the spatial relationship between the X-ray and Hα-ribbon morphologies. Although evidence has been reported for magnetic flux emergence at the beginning of this flare (Harvey, 1983), it appears that a potential field (rising source-surface) model may adequately represent the major large-scale features of the magnetic configuration believed to result from fieldline reconnection in the corona during the decay phase (Kopp and Pneuman, 1976).