Failed eruptions of two intertwining small-scale filaments

Abstract

Abstract Using multi-wavelength observations of the New Vacuum Solar Telescope (NVST), the Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO), we study the topology and evolutions of two filaments observed in NOAA active region (AR) 12031 on 2014 April 7. Before their eruptions, the two filaments (F1 and F2) were sinistral filaments, and the left part of F1 (LP) was located above F2, the right part of F1 (RP) under F2. They show an overall intertwining structure. LP erupted first and rotated clockwise. The total rotation angle was about 470° (≈2.61π). With its rotation, most of the plasma fell back, and thus it was a failed eruption. Meanwhile, when LP erupted to a higher altitude, the overlying magnetic loops were partially pushed from the northeast to the southwest with projected speeds from 36 to 105 km s−1. Next, F2 began to erupt and, when reaching a certain height, the plasma of F2 started to fall down to their footpoints. Using the potential-field source-surface (PFSS) model, the decay indexes at five positions along the polarity inversion line of AR 12031 were calculated to be from 1.03 to 1.25 with an average value of 1.20 that was lower than the critical value for torus instability. These results imply that the kink instability was the main triggering mechanism for the eruption of F1, and the eruption of F2 was due to the decreasing of overlying magnetic loops caused by the eruption of F1. The eruptions of two filaments were confined by the large-scale overlying magnetic loops.