Dynamic Precursors of Flares in Active Region NOAA 10486

Abstract

Four different methods are applied here to study the precursors of flare activity in the Active Region NOAA 10486. Two approaches track the temporal behaviour of suitably chosen features (one, the weighted horizontal gradient W G M , is generalised form the horizontal gradient of the magnetic field, G M ; another is the sum of the horizontal gradient of the magnetic field, G S , for all sunspot pairs). W G M is a photospheric indicator that is a proxy measure of magnetic non-potentiality of a specific area of the active region, i.e. it captures the temporal variation of the weighted horizontal gradient of magnetic flux summed up for the region where opposite magnetic polarities are highly mixed. The third one, referred to as the separateness parameter, S l−f , considers the overall morphology.

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

“…Magnetographic studies of AR 12242 showed that, during the development of the group, opposite polarity fields converged in the AR and strong gradients were formed near the neutral line, i.e., two days before the flare, a so-called it SHIL (strong-field, high-gradient polarity inversion line) formed in the AR that is now recognized by many researchers as the clearest AR precursor for a large flare The study of the evolution of the total gradient (flare index) of AR 12242 showed that, before the X-flare, the index first increased and then, after the maximum was passed (20 h before the flare), decreased before the X flare. Note that a similar conclusion was made by Korsos et al (2014Korsos et al ( , 2015, who analyzed the parameters of sunspot groups in a number of flare regions and found that there is usually a sharp increase in the magnetic field gradient before large flares that reaches a high maximum, followed by its decrease just before the flare.…”

Solar Magnetic Flux Ropes

“…In conclusion, the inherent plasma and magnetic field changes and the similar changes in the ambient corona may lead the dynamics and instability of the solar magnetic flux ropes. In spite of that, some canonical processes may also subject in making the magnetic flux ropes unstable (Török & Kleim 2005;Srivastava et al 2010;Cheng et al 2014b;Korsós, Baranyi, & Ludmány 2014;Korsós et al 2015, and references cited there). Better understanding the physics of solar magnetic flux ropes: their formation, identification, stability, and instability conditions are of great importance in solar and heliospheric physics as they are the precursor of huge coronal mass ejections and geomagnetic storms.…”

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

“…[9]. Аналогичный характер изменения расстояния между областями максимальных магнитных полей противоположных полярностей обнаружен и другими авторами [5] и может быть объяснен моделью магнитного жгута, зажатого между двумя сближающимися магнитными центрами (пятнами), согласно которой сначала сближение пятен обеспечивает накопление свободной магнитной энергии в жгуте, а затем, при расхождении пятен, в нем начинается вспышечное энерговыделение [6,7]. Выявленные свойства микроволнового излучения (резкое возрастание интенсивности, увеличение наклона спектра, уменьшение степени поляризации на 3 см) позволяют предположить, что 4 сентября в АО развился NLSисточник [1], который может рассматриваться как предвестник больших вспышек.…”