# A Magnetic Bald-Patch Flare in Solar Active Region 11117

## TL;DR

This study combines observations and MHD modeling to analyze a magnetic bald-patch flare in solar active region 11117, revealing detailed magnetic structures and flare triggering mechanisms.

## Contribution

It provides the first detailed analysis of a BP flare using combined SDO observations and data-constrained MHD modeling, linking magnetic topology to flare ribbons.

## Key findings

- Magnetic BPs are confirmed at the PILs matching flare ribbons.
- The BP separatrix surface aligns with flare ribbons and hot loop systems.
- Small flux emergence triggers the BP flare, with magnetic field changes well reproduced by models.

## Abstract

With SDO observations and a data-constrained MHD model, we identify a confined multi-ribbon flare occurred on 2010 October 25 in solar active region 11117 as a magnetic bald patch (BP) flare with strong evidences. From the photospheric magnetic field observed by SDO/HMI, we find there is indeed magnetic BPs on the PILs which match parts of the flare ribbons. From the 3D coronal magnetic field derived from a MHD relaxation model constrained by the vector magnetograms, we find strikingly good agreement of the BP separatrix surface (BPSS) footpoints with the flare ribbons, and the BPSS itself with the hot flaring loop system. Moreover, the triggering of the BP flare can be attributed to a small flux emergence under the lobe of the BPSS, and the relevant change of the coronal magnetic field through the flare is well reproduced by the pre-flare and post-flare MHD solutions, which match the corresponding pre and post-flare AIA observations, respectively. Our work contributes to the study of non-typical flares that constitute the majority of solar flares but cannot be explained by the standard flare model.