http://arxiv.org/abs/1402.2010
The paper presents for the first time a quantification of the photospheric electric current ribbon evolutions during an eruptive flare, accurately predicted by the standard 3D flare model. The standard flare model in 3D has been developed with the MHD code OHM, which models the evolution of an unstable flux rope. Through a series of paper, the model has been successful in explaining observational characteristics of eruptive flares, as well as the intrinsic 3D reconnection mechanism. Such a model also explains the increase of the photospheric currents as a consequence of the evolution of the coronal current layer where reconnection takes place. The photospheric footprints of the 3D current layer reveal a ribbon shape structure. In the present paper, the evolution of the current density is analyzed for the X-class flare that occurred on 15/02/2011 in AR 11158. We first describe the structural evolution of the high vertical current density regions derived with the UNNOFIT inversion code from magnetograms (HMI, every 12 mn). These currents develop in current ribbons at similar locations to the flare ribbons. Their evolutions remain continuous during the flare. These ribbons are J-shaped, and they show a widening and an elongation during the impulsive phase of the flare. Spatial integration of the electric current density over small parts of the ribbons shows an increase up to 2x the pre-flare values. The EUV data show similar evolutions for the flare ribbons as pointed out for the electric current ribbons. This evolution characterizes the sudden collapse of the coronal current layer that is predicted in the standard 3D model. Finally, this study further enhances the close correspondence obtained between the theoretical predictions of the 3D model and flare observations indicating that the main key physical elements are incorporated in the model.
M. Janvier, G. Aulanier, V. Bommier, et. al.
Tue, 11 Feb 14
45/55
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