Temporal Behaviors of Magnetic Helicity Injections by Self and Mutual Sunspot Rotations

Abstract

Magnetic helicity is a physical parameter used to quantify the complexity of magnetic fields, providing an indication of the energy state in the coronal magnetic structure. We investigate the temporal evolution of magnetic helicity and its relationship to the occurrence of a variety of flares in the solar active region NOAA 12297, which was well observed using the Solar Dynamics Observatory/Helioseismic and Magnetic Imager in 2015 March. The active region produced many M-class flares and an X-class flare in two distinctive areas, both of which had a similar magnetic evolution, i.e., the opposite polarity of an emerging flux developed beside a preexisting sunspot, but exhibited flares with different magnitudes and frequencies. We derived the spatiotemporal evolution of the magnetic helicity injections and evaluated how spinning and braiding helicity injections evolved with time in the two areas. In one area, we observed a remarkable evolution, in which a negative spinning helicity injection in the preexisting sunspot increased in a positive helicity system, followed by the occurrence of the X-class flare. The negative helicity injection was clearly caused by the flux emergence that developed along the outer edge of the preexisting sunspot. The other area showed positive braiding helicity injections, with spinning helicity injections fluctuating concurrently with flux emergence, changing their signs several times, i.e., variable energy, and helicity input. The observed temporal behaviors of the helicity injections may explain different types of flare occurrences in the regions.

Keywords

• Solar magnetic fields
• Solar flares