Development of an M6.4 Circular Solar Flare According to the Observations in the Н α Line

The development of the 3N/M6.4 flare on July 19, 2000, in the active region NOAA 9087 was studied based on the analysis of its images in the Нα line. Нα filtergrams obtained at the Meudon Observatory were used. The flare-active region NOAA 9087 had a complex multipolar magnetic field structure. The flare of 3N/M6.4 class began with the appearance of two bright kernels near a large spot. A few minutes later, flare kernels appeared in the central part of the active region, where a coronal source of hard X-ray radiation was identified. The flare lasted 2.5 h. Its energy was released sequentially in different places of the active region. The flare kernels were located along the polarity inversion line at the boundaries of the chromospheric cells. The flare ribbons had a circular shape. An assumption is made about the magnetic topology of the fan-spine type containing a null point. In this case, flare ribbons are the intersections of the fan quasi-separatrix layer with the lower atmosphere. The successive appearance of flare kernels may indicate a slipping magnetic reconnection in the flare. The Нα images in the main phase of the flare show reconnecting loops in the eastern part of the active region that are clearly visible in the ultraviolet wavelength range.