Temporal Evolution of the Guide Field in Eruptive Flares
Abstract
Solar flares are explosive space weather events that rapidly convert stored magnetic energy into bulk motion, plasma heating, and particle acceleration via magnetic reconnection. For all flares, the free energy source is ultimately the highly sheared magnetic field of a filament channel above a polarity inversion line. During the flare, the shear field becomes the reconnection guide field, the strength of which is widely believed to control the efficiency of reconnection-driven particle acceleration. We present new high-resolution 3D MHD simulations that calculate the evolution of the magnetic shear/guide field throughout an eruptive flare. The magnetic shear evolves in three distinct phases: shear first builds up in a narrow region about the PIL, expands outward to drive the formation of a thin current sheet, and is finally transferred by the flare reconnection into sheared post-flare loops and erupting flux rope. We show that the guide field weakens more than an order of magnitude over the course of the flare, and instantaneously varies over a similar range along the three-dimensional current sheet. We demonstrate how the guide field may be inferred from observations of sheared post-flare loops. Interestingly, we find that the number of plasmoids in the flare reconnecting current sheet increases with weakening guide field, underscoring the important role of the guide field in particle acceleration. We discuss implications for observations by IRIS, SDO/AIA, and DKIST. This work was supported by NASA via the SOLFER DRIVE Center at UMD, the H-ISFM program, and the HGI program.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFMSH23B..07D