Features of Microwave Radiation and Magnetographic Characteristics of Solar Active Region NOAA 12242 Before the X1.8 Flare on December 20, 2014

TL;DR

This study analyzes microwave and magnetographic data of solar active region NOAA 12242 to identify precursors of the December 2014 X1.8 flare, highlighting a new microwave component that appears before large flares and can aid in prediction.

Contribution

It presents a detailed analysis of microwave radiation and magnetic field evolution as precursors to large solar flares, extending previous work with new observational evidence and classification of a pre-flare radio source.

Findings

A new microwave component appeared two days before the flare.

The dominant microwave source was linked to the site of magnetic field convergence.

The total magnetic field gradient peaked 20 hours before the flare.

Abstract

This paper continues the cycle of authors' works on the detection of precursors of large flares (M5 and higher classes) in active regions (ARs) of the Sun by their microwave radiation and magnetographic characteristics. Generalization of the detected precursors of strong flares can be used to develop methods for their prediction. This paper presents an analysis of the development of NOAA AR 12242, in which an X1.8 flare occurred on December 20, 2014. The analysis is based on regular multiazimuth and multiwavelength observations with the RATAN-600 radio telescope in the range 1.65-10 cm with intensity and circular polarization analysis and data from the Solar Dynamics Observatory (SDO). It was found that a new component appeared in the AR microwave radiation two days before the X-flare. It became dominant in the AR the day before the flare and significantly decreased after the flare. The use of multiazimuth observations from RATAN-600 and observations at 1.76 cm from the Nobeyama Radioheliograph made it possible to identify the radio source that appeared before the X-flare with the site of the closest convergence of opposite polarity fields near the neutral line in the AR. It was established that the X-flare occurred 20 h after the total gradient of the magnetic field of the entire region calculated from SDO/HMI data reached its maximum value. Analysis of the evolution of the microwave source that appeared before the X-flare in AR 12242 and comparison of its parameters with the parameters of other components of the AR microwave radiation showed that the new source can be classified as neutral line associated source (NLS), which were repeatedly detected by the RATAN-600 and other radio telescopes 1-3 days before the large flares.