Motion of Flare Footpoint Emission and Inferred Electric Field in Reconnecting Current Sheets

A systematic motion of Ha kernels during solar Ñares can be regarded as the chromospheric signature of progressive magnetic reconnection in the corona, in that the magnetic Ðeld lines swept through by the kernel motion are those connected to the di†usion region at the reconnection point. In this paper, we present high-cadence and high-resolution Ha[1.3 A � observations of an impulsive Ñare that exhibits a systematic kernel motion and relate them to the reconnecting current sheet (RCS) in the corona. Through analyses of X-ray and microwave observations, we further examine the role of the macroscopic electric Ðeld inside the RCS in accelerating electrons. We measure the velocity of the kernel motion to be 20[100 km s~1. This is used together with the longitudinal magnetic Ðeld to infer an electric Ðeld as high as 90 V cm~1 at the Ñare maximum. This event shows a special magnetic Ðeld conÐguration and motion pattern of Ha kernels, in that a light bridge divides a Ñare kernel into two parts that move in di†erent manners: one moving into the stronger magnetic Ðeld and the other moving along the isogauss contour of the longitudinal magnetic Ðeld. The temporal variation of the electric Ðeld inferred from the former type of kernel motion is found to be correlated with 20È85 keV hard X-ray light curves during the rise of the major impulsive phase. This would support the scenario of magnetic energy release via