Onset mechanism and a physics-based prediction of large solar flares

What determines the onset of large solar flares is still an open question. Because of the ambiguity of the onset mechanism, their prediction mostly relies on empirical methods, and the accurate prediction of large flares is still difficult. Here, we report a new physics-based method, -scheme, that can predict imminent large solar flares (Kusano et al. 2020, Science). The -scheme is based on the theoretical model of the tether-cutting scenario, in which a small magnetic reconnection between two sheared magnetic loops triggers the new ideal MHD instability, named the double-arc instability (Ishiguro & Kusano 2017, ApJ), that drives a solar flare. We applied the -scheme to 198 active regions with the largest sunspots recorded from 2006 to 2019 and demonstrated that the -scheme can predict the onset and the precise location of imminent large solar flares with a small number of exceptions. Based on the results, we conclude that magnetic twist flux density close to a magnetic polarity inversion line is an important physical parameter to determine the onset of large solar flares. Finally, we discuss also the extension of the -scheme to predict the eruptivity of solar flares (Lin et al. 2020 & 2021, ApJ).