Energy origination and triggering mechanism of a series of homologous confined flares

TL;DR

This study investigates the energy buildup and triggering mechanisms of three homologous confined solar flares in active region NOAA 11861, highlighting the roles of magnetic flux emergence, shearing motions, and magnetic reconnection.

Contribution

It provides detailed observational evidence linking magnetic flux emergence and shearing motions to energy injection and flare triggering in homologous confined flares.

Findings

Magnetic flux emergence and shearing motions occur before each flare.

Energy injected from the photosphere is sufficient to power the flares.

Magnetic reconnection is observed during each flare event.

Abstract

Using the H$\alpha$ data from the New Vacuum Solar Telescope (NVST) at the Fuxian Solar Observatory together with multi-wavelength images and magnetograms obtained by Solar Dynamics Observatory (SDO), we study the detailed process of three homologous confined flares in active-region (AR) NOAA 11861 on 2013 October 12. All of the three flares occurred at same location, with similar morphologies and comparable class. Through analyzing the evolution of magnetic field and flow field, we found an emergence of magnetic flux and a strong shearing motion between two opposite polarities near the following sunspot. The magnetic flux and the average transverse field strength exhibited a decrease before each eruption and reached the lowest point at the onset of each eruption. By calculating the shearing and the emergence energy in the photosphere, we found that the integral of energy injected from the photosphere, for a few hours, could provide enough energy for the flares. The reconnection between different loops was observed in H$\alpha$ images during the occurrence of each flare. These results suggest that the emerging magnetic flux and the shearing motion in the photosphere can inject the energy to the sheared magnetic loops and the energy finally was released via magnetic reconnection to power the solar flares.