| Presentation Title: | Modeling the Shear Evolution of Post-Reconnection Flare Loops |
| Author(s): | Drake Osaben, Jiong Qiu, Dana Longcope |
Abstract:
Observations of solar flares suggest a strong-to-weak shear evolution of post-reconnection flare loops (PRFLs). We quantify magnetic shear as the complement of the angle formed between the PRFLs (projected in the image plane) and the photospheric magnetic polarity inversion line (PIL) where the radial magnetic field switches sign. Previous work uses the evolution of the flare ribbons to infer magnetic shear. In this work, we construct the 3D magnetic field of a PRFL arcade by fitting linear force free field (LFFF) lines to observed PRFLs. The two-ribbon flare SOL20141218T21:40 observed by the Solar Dynamics Observatory is investigated, for which we have identified more than 2500 PRFLs observed by the Atmosphere Imaging Assembly in EUV passbands. An optimal fitting is achieved by tracing field lines for a range of LFFF parameters and heights, then minimizing the distance between observed and modeled field lines projected in the image plane. The modeled field lines are further constrained by the flare ribbons observed in the UV 1600 passband, where they must be anchored. We successfully fit over 95% of the observed loops and find that the optimal force free parameter decreases in magnitude from over 0.1 to less than 0.01 Mm^-1 during the flare. This indicates that later formed PRFLs are more potential-like. We also computed the shear angle of modeled loops projected in the image plane, finding the average shear decreasing from 50 degrees to under 20. This study confirms the strong-to-weak shear evolution in this flare and provides a method for modeling the 3D magnetic field after reconnection.