Coronal Magnetometry and Energy Release in Solar Flares

This dissertation focuses on studies that utilize microwave imaging spectroscopy observations made by the Expanded Owens Valley Solar Array (EOVSA) to diagnose the nonthermal electrons and coronal magnetic field in solar flares. In the first study, the microwave counterpart of a partially erupted twisted filament in Hα and EUV images is observed by EOVSA during an M1.4-class flare on September 6, 2017. The derived magnetic field strength along the filament spine ranges from 600-1400 Gauss from its apex to the legs, which agrees well with the non-linear force-free magnetic model extrapolated from the pre-flare photospheric magnetogram. The second study focuses on another eruptive solar flare event on August 20, 2017, which features three post-impulsive X-ray and microwave bursts immediately following its main impulsive phase. A tight positive correlation between the flux rope acceleration and electron energization is found during the post-impulsive phase bursts, conforming to the standard flare-coronal-mass-ejection scenario. The observations suggest a weakening guide field may contribute to the hardening of the nonthermal electron spectrum throughout the main- and post-impulsive phases of the event. Finally, I will briefly discuss an ongoing study of a supra-arcade downflow event observed jointly by EOVSA in microwaves and SolO/STIX in X-rays.