Occurrence of a White-Light Flare Over a Sunspot and the Associated Change of Magnetic Flux

A white-light flare (WLF) on 10 March 2001 was well observed in the Hα line and the Ca ii λ8542 line using the imaging spectrograph installed on the Solar Tower Telescope of Nanjing University. Three small sunspots appeared in the infrared continuum image. In one sunspot, the infrared continuum is enhanced by 4–6% compared to the preflare value, making the sunspot almost disappear in the continuum image for about 3 min. A hard X-ray (HXR) source appeared near the sunspot, the flux of which showed a good time correlation with the profile of the continuum emission. In the sunspot region, both positive and negative magnetic flux suffered a substantial change. We propose that electron precipitation followed by radiative back-warming may play the chief role in heating the sunspot. The temperature rise in the lower atmosphere and the corresponding energy requirement are estimated. The results show that the energy released in a typical WLF is sufficient to power the sunspot heating.