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Magnetic field plays an important role in various solar eruptions likeflares, coronal mass ejections, etc. The formation and evolution ofcharacteristic magnetic field topology in solar eruptions are critical problemsthat will ultimately help us understand the origination of these eruptions inthe solar source regions. With the development of advanced techniques andinstruments, observations with higher resolutions in different wavelengths andfields of view have provided more quantitative information for finerstructures. So it is essential to improve our method to study the magneticfield topology in the solar source regions by taking advantage ofhigh-resolution observations. In this study, we employ a nonlinear force-freefield (NLFFF) extrapolation method based on a nonuniform grid setting for anM-class flare eruption event (SOL2015-06-22T17:39) with embedded magnetogramsfrom the Solar Dynamics Observatory (SDO) and the Goode Solar Telescope (GST).The extrapolation results employing the embedded magnetogram for the bottomboundary are obtained by maintaining the native resolutions of thecorresponding GST and SDO magnetograms. We compare the field line connectivitywith the simultaneous GST/H$\alpha$ and SDO/AIA observations for fine-scalestructures associated with precursor brightenings. Then we perform atopological analysis of the field line connectivity corresponding to fine-scalemagnetic field structures based on the extrapolation results. The resultsindicate that by combining the high-resolution GST magnetogram with a largerHMI magnetogram, the derived magnetic field topology is consistent with ascenario of magnetic reconnection among sheared field lines across the mainpolarity inversion line during solar flare precursors.

Coronal Magnetic Field Extrapolation and Topological Analysis of Fine-Scale Structures during Solar Flare Precursors