| Abstract : | Solar coronal plasma, having a large magnetic Reynolds number (~10^12), exhibits explosive behavior in form of flares, coronal mass ejections and jets. The fundamental process causing such phenomena is magnetic reconnection, which in turn occurs due to the generation of small length scales in consequence of large scale (~10^6 m) magnetic field dynamics. A back-of-the-envelope calculation based on observed impulsive rise time of hard X-ray emission (~ few minutes) during the solar flares, suggests that reconnection length scale is of the order of few tens of meters. A straightforward order analysis of the induction equation at reconnection scale length indicates the significance of Hall effects during diffusive processes or magnetic reconnection on the Sun. Hall MHD supports the faster reconnection while also capturing the effects of small scale processes over large length scales. A detailed comparative study is carried out using the extended EULAG MHD model, in the presence and absence of Hall forcing term. This study aims to understand the possible magnetic reconnections causing flare brightening in solar active region NOAA 12734. Magnetic structure involved in the flare is identified to be a flux rope, with its overlying field lines constituting the quasi-separatrix layers (QSLs). The rope evolves through a series of consecutive slipping reconnections at the anchored footpoints---a distinct meachanism. Contrary to the MHD, the Hall MHD simulation shows a higher and faster ascend of the rope together with the overlying field lines, which further reconnect at the QSL located higher up in the corona. Additional feature captured, only in the Hall MHD, is the rotating field lines in a circular pattern at a cospatial chromospheric region where the plasma is seen to be rotating in AIA/SDO observations. |
