The nature of precursors of solar flares and their relationship with subsequent flares are still not clear. This is due, in particular, to the lack of systematic statistical work, the relatively incomplete studies of individual events (out of the context of evolution of the entire active region), and the ambiguity of the term “precursor” itself. In this paper, we consider the dynamics of the NOAA 12230 active region (AR), in which a series of homologous flares (C5-C9) occurred on December 9, 2014 within 12 hours with a mean occurrence rate of about 2 hours. This AR is characterized by rapidly increasing flare activity followed by a rapid decay, which can serve as a good example for studying potential precursors of a series of flares. We investigated the evolution of AR NOAA 12230 over a relatively long time interval (several days) and its transition from the ‘no-flare’ state to the flare-active regime. For this purpose, we studied the magnetic field dynamics using SDO/HMI vector magnetograms, UV-EUV images based on SDO/AIA data, and GOES/XRS and RHESSI X-ray data. Thus, we identified several phases in the AR evolution in terms of the magnetic-field dynamics and flare activity. A method for building hourly integral maps of UV variations based on AIA 1600 data was proposed. It was concluded that significantly increased variations in the chromospheric radiation against small soft X-ray and UV emission fluxes from the corona observed on December 8, 2014, together with the emergence of a magnetic flux, can be considered as a precursor to a series of flares. We also analyzed the appearance of X-ray sources of weak bursts before the series of flares. X-ray bursts developed in the same plasma structures where future flares occurred. The results obtained show the importance and prospects of using new methods of synoptic observations of the Sun for collecting statistics (“history”) of the energy release in AR in different ranges of the electromagnetic spectrum. In other words, it is important to monitor not only the dynamics of the magnetic field structure but also how the AR releases the stored magnetic energy. An integrated approach will allow the development of new methods for predicting flares, perhaps, more advanced than simply taking into account the magnetic field structure.
G.G. Motorina (Wed,) studied this question.