Properties of white light flares

Abstract

All four large EUV bursts (peak 10–1030 A flux enhancements ⩾ 2 ergs cm−2 s−1 at 1 AU as deduced from sudden frequency deviations), for which there were available concurrent white light observations of at least fair quality, were detected as white light flares. The rise times and maxima of the white light emissions coincided with rise times and maxima of the EUV bursts. The frequency of strong EUV bursts suggests that white light flares may occur at the rate of five or six per year near sunspot maximum. All of the white light flare areas coincided with intense bright areas of the Hα flares. These small areas appeared to be sources of high velocity ejecta in Hα. The white light flares occurred as several knots or patches of 2 to 15 arc-sec diameter, with bright cores perhaps less than 2 arc-sec diameter (1500 km). They preferred the outer penumbral borders of strong sunspots within 10 arc-sec of a longitudinal neutral line in the magnetic field. The peak continuum flux enhancement over the 3500–6500 A wavelength range is about the same order of magnitude as the peak 10–1030 A flux enhancement.