Small solar flares and local polarity inversion lines of the longitudinal magnetic field of the active region

Abstract

Using photospheric data and data on the longitudinal magnetic field from the SDO satellite, as well as observations in the Hα line from GONG ground stations, we have studied the flare activity of the NOAA 12673 sunspot group, which in September 2017 produced the largest X9.3 class flare in the last decade. The active region was distinguished by rapid development, complex topology, and magnetic field dynamics. We have established that in the active region almost throughout the development period due to movements of diverse polar magnetic fluxes and their convergence, numerous local polarity inversion lines (LPIL) of the magnetic field were formed. Small solar flares have been found to be closely related to LPIL and to occur in those areas of LPIL where the gradient of the longitudinal magnetic field over time reaches maximum values.