Evolution of Solar Active Region 12673 by Ratan-600 and Sdo Data

Abstract

Context: We continue our previous researches of solar active regions (ARs) where strong flares occurred to reveal features indicate that a strong flare is about to take place. Aims: The aim of this paper is to study AR NOAA 12673 on pre-flare phase in the beginning of September 2017. We focus on the behavior of microwave emission and magnetic field structure before the first M-class flare on September 4. Methods: We studied microwave emission and magnetic-field characteristics of AR as based on RATAN-600 and SDO/HMI data. For comparison we considered a well-developed AR NOAA 12674, in which there were only a few weak flares of the C-class. Results: As in the previously investigated cases, we registered a sharp increase of the magnetic field gradient with its decrease directly before the flare and a significant increase of microwave emission before the first M-class flare in NOAA 12673. In NOAA 12674 it was not detected significant changes in the gradient of the magnetic field and microwave radiation. The distance between regions of opposite magnetic polarity decrease initially. Then it begins to increase. On the phase of its increasing the flares occurred. The increase of microwave emission may be interpreted as a result of development of neutral line associated source.