Dynamics of magnetic fields of active regions in pre-flare states and during solar flares

Abstract

Solar flares observed in the active regions NOAA 10656, NOAA 11429, and NOAA 10930 are analyzed. The magnetic fluxes were constant to within 2% during these flares, as well as the distribution of the magnetic fields in the active regions. The analysis supports earlier conclusions that large (class X) solar flares arise when the magnetic fluxes of the active regions exceed 1022 Mx. The observation of a high magnetic flux in an active region is not sufficient for the appearance of a large flare: complex sγδ field structures must also be observed before flares. Such active regions can generate singular lines of the magnetic field in the corona, in whose vicinities current sheets form. Magnetic-field lines above simple dipolar active regions have arched forms; singular lines are absent and no current sheets are created. Dipolar-type active regions do not generate flares. Imbalances in the magnetic flux of an active region and the growth rate of the magnetic flux are not any indications of the imminent appearance of a flare.