Observations of three-dimensional magnetic reconnection in an eruption of a quiescent filament

We analyze three-dimensional magnetic reconnection in SDO/AIA and Hinode/XRT observations of the 2012 August 31 quiescent filament eruption. The 3D nature of this event is manifested clearly by the existence of hooked ribbons. Flare loops are seen to slip along one of the hooks in both directions at velocities <85 km/s. The ribbon kernels at their footpoints were observed to move at equivalent velocities in the 1600 A channel of AIA. We also observed kernels with velocities up to 450 km/s, with no corresponding slipping loops. These kernels are usually moving along regions of weak magnetic field. In order to interpret the apparent anti-correlations between kernel velocities and the magnetic field strength, we examined distribution of the norm N, a quantity is closely related to the slippage velocity, in MHD model of a solar eruption adapted to the magnetic environment. We found that the modeled N and the observed velocities of kernels both reach their highest values in weak-field regions, one located in the ribbon hook and the other close to a parasitic polarity. Oppositely, slower kernels were observed at the tip of the hook, where the modeled N is low.

3D reconnection was in this event also manifested in the form of reconnection of field lines composing the erupting flux rope. After the onset of the eruption, the propagating hook started to sweep the footpoints of the erupting filament, which resulted in disappearance of bright filament strands rooted therein. Later on, we witnessed a formation of arcade of flare loops with footpoints corresponding to the footpoints of the filament strands. This phenomenon cannot be addressed by the standard CSHKP model of solar flares, as it does not include J-shaped endings of flare ribbons in which erupting flux ropes are rooted.