Investigation of a Confined C‐Class Flare in an Arch Filament System Close to a Regular Sunspot

Abstract

A moderate C1.1 class confined flare is investigated here, which occurred on 24 September 2013 at 22:56 UT, in an arch filament system close to a regular, unipolar sunspot. Spectropolarimetric observations from the Tenerife Infrared Polarimeter at the 70-cm German Vacuum Tower Telescope were combined with data from the Helioseismic Magnetic Imager and the Atmospheric Imaging Assembly to identify the processes that triggered the flare. The legs of this arch filament were anchored in the leading sunspot and the network flux region of opposite polarity. The flare was driven by small-scale, flux cancellation at the weak neutral line underlying the arch filament, which resulted in two small flaring events within an hour of the C1.1 flare. Flux cancellation was facilitated by the moat flow from the leading sunspot wherein small-scale magnetic fragments stream toward patches of preexisting flux. The cancellation of flux led to the destabilization of the arch filament, which was seen as an increase in the twist along the arch filament. The horizontal fields across the weak neutral line decay rapidly, which cannot prevent the filament from rising that results in a two-ribbon flare at the neutral line. The arch filament unwinds as it rises but is confined by the higher, overlying fields between the two polarities of the active region that decay much more slowly.Unlike PIL filaments, arch filament systems (AFSs) are a bunch of dark filament threads crossing the PIL and connecting the regions of opposite polarity, sometimes extending into sunspots (Bruzek, 1967;Weart & Zirin, 1969;Zwaan, 1985). The arches in the AFS exhibit an upward motion of about 10-15 km/s and downwflows of about 10-50 km/s along their legs. Flares occurring in AFS arise from reconnection with