Thermodynamic and magnetic evolution of an eruptive C-class solar flare observed with SST/TRIPPEL-SP
Abstract
We investigate the physical processes driving a C5.1-class solar flare and filament eruption in active region NOAA 12561 on July 7, 2016. High-resolution spectropolarimetric observations of the chromospheric Ca II 8542 Å line and nearby photospheric lines obtained with the TRIPPEL-SP instrument at the Swedish 1-m Solar Telescope (SST) were analyzed using non-local thermodynamic equilibrium (NLTE) inversions and non-force-free field (NFFF) magnetic extrapolations. During the precursor phase, the region exhibited a complex, sheared magnetic topology with high free energy (~2 × 10³⁰ erg). Persistent, localized heating (approximately 2000 K) and strong downflows (10–20 km/s) were detected deep in the atmosphere, co-spatial with a bald-patch region, suggesting that low-altitude magnetic reconnection triggered the filament’s destabilization. The filament erupted with a total speed exceeding ~70 km/s, and post-flare loops formed as free energy decreased by ~30%. Flare ribbons showed significant heating to ~8500 K and downflows of ~10 km/s, consistent with energy deposition along reconnected loops.
Figure 10: Magnetic topology above the pore before (07:36 UT, top) and after (09:00 UT, middle and bottom) the flare. Field lines are colored by BxB_{x} to highlight the shear. The bottom panel shows the post-flare arcade (green) overlaid on the AIA 304 Å image and the FOV of the previous two panels with a dashed-white square.
