Dynamics of Microwave Sources Associated with the Neutral Line and the Magnetic-Field Parameters of Sunspots as a Factor in Predicting Large Flares

We studied the evolution of five active regions (ARs) where strong X-class flares occurred in 2011 – 2012 (NOAA ARs 11158, 11166, 11263, 11283 and 11520). Our study focuses on the pre-flare phase of these ARs (during a few days before the flare) to reveal features in the microwave radiation and magnetic-field characteristics of the ARs that indicate that a powerful flare is about to take place. One well-developed AR (NOAA AR 11654) that did not produce large flares was also studied. We used daily multiwavelength spectral-polarization solar observations in the range of 1.65 – 6.0 cm made with the RATAN-600 radio telescope and data obtained by the Solar Dynamics Observatory/Helioseismic and Magnetic Imager (SDO/HMI). Whenever X-class flares occurred, we found that a new compact microwave source developed that was associated with the neutral line of the photospheric magnetic field (neutral line associated source – NLS) above the place with highest gradient of magnetic field. In some cases this became predominant in radio emission of the AR one to two days before a large flare. No such source was detected in AR without a powerful flare. An analysis of magnetic-field characteristics of sunspots (based on SDO/HMI data) showed that the large X-flares we investigated occurred in ARs with high magnetic flux (∼ 10 22 Mx) and with an increasing magnetic-field gradient. We first identified the positions of the developing microwave source (NLS) with the location of the large flare that was registered in the AR one to two days later. Radio characteristics and dynamics of NLS detected before large flares possibly reflect the place in the corona where the energy for flaring is stored. Thus, an early detection of a rapidly developing microwave source NLS and an increasing magnetic-field gradient can be used as a factor in predicting large flares.