Abstract
Non-thermal particles generated in the impulsive phase of solar flares are observed mainly in microwave, hard X-rays, and gamma-rays. Observations in Halpha can also give important informations about non-thermal particles precipitating into the chromosphere with a higher spatial resolution than in other wavelengths. We observed an X2.3 flare which occurred in the active region NOAA 9415 on 10 April 2001, in Halpha with Sartorius Telescope at Kwasan Observatory, Kyoto University. Thanks to the short exposure time given for the flare, the Halpha images show fine structures inside the flare ribbons. In addition to Halpha, we analyze microwave, hard X-ray, and EUV data obtained with Nobeyama Radioheliograph , Yohkoh/HXT, and TRACE, respectively. In Halpha, several bright kernels are observed in the flare ribbons. On the other hand, the hard X-ray images show only a single pair of bright sources which correspond to one of several pairs of Halpha kernels. Examining the difference in the magnetic field strength and in the time profiles of Halpha emission for these kernels, we discuss the reason why only one pair kernels are bright in the hard X-ray among the other bright Halpha kernels. Comparing the Halpha images with EUV images, we also examine the three-dimensional structure of solar flares. While broad and network-like ribbons are observed in Halpha, the width of EUV ribbons is relatively narrow, and EUV ribbons are located at the outer edges of the corresponding Halpha ribbon.