A Study on Red Asymmetry of Hα Flare Ribbons Using a Narrowband Filtergram in the 2001 April 10 Solar Flare

Abstract

Abstract We report on a detailed examination of the “red asymmetry” of the H$\alpha$ emission line seen during the 2001 April 10 solar flare by using a narrowband filtergram. We investigated the temporal evolution and the spatial distribution of the red asymmetry by using H$\alpha$ data taken with the 60-cm Domeless Solar Telescope at Hida Observatory, Kyoto University. We confirmed that the red asymmetry clearly appeared all over the flare ribbons, and the strong red asymmetry is located on the outer narrow edges of the flare ribbons, with a width of about 1$.\!\!\!”$5–3$.\!\!\!”$0 (1000–2000 km), where strong energy releases occur. Moreover, we found that the red asymmetry, which also gives a measure of the Doppler shift of the H$\alpha$ emission line, concentrates on a certain value, not depending on the intensity of the H$\alpha$ kernels. This implies not only that the temporal evolutions of the red asymmetry and those of the intensity are not synchronous in each flare kernel, but also that the peak asymmetry (or velocity of the chromospheric condensation) of individual kernel is not a strong function of their peak intensity.