Understanding the Plasma and Magnetic Field Evolution of a Filament Using Observations and Nonlinear Force-free Field Modeling

Abstract

Abstract We present observations and magnetic field models of an intermediate filament present on the Sun in 2012 August, associated with a polarity inversion line that extends from AR 11541 in the east into the quiet Sun at its western end. A combination of Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly, SDO/Helioseismic and Magnetic Imager (HMI), and Global Oscillation Network Group Hα data allow us to analyze the structure and evolution of the filament from 2012 August 4 23:00 UT to 2012 August 6 08:00 UT when the filament was in equilibrium. By applying the flux rope insertion method, nonlinear force-free field models of the filament are constructed using SDO/HMI line-of-sight magnetograms as the boundary condition at the two times given above. Guided by observed filament barbs, both modeled flux ropes are split into three sections each with a different value of axial flux to represent the nonuniform photospheric field distribution. The flux in the eastern section of the rope increases by 4 × 1020 Mx between the two models, which is in good agreement with the amount of flux canceled along the internal PIL of AR 11541, calculated to be 3.2 × 1020 Mx. This suggests that flux cancellation builds flux into the filament’s magnetic structure. Additionally, the number of field line dips increases between the two models in the locations where flux cancellation, the formation of new filament threads, and growth of the filament is observed. This suggests that flux cancellation associated with magnetic reconnection forms concave-up magnetic field that lifts plasma into the filament. During this time, the free magnetic energy in the models increases by 0.2 × 1031 ergs.