Earth Planets Space, Vol. 61 (No. 5), pp. 565-568, 2009LETTER
Brigitte Schmieder1, Guillaume Aulanier1, Pascal Démoulin1, and Etienne Pariat2
1Observatoire de Paris, LESIA, 92195 Meudon, France
2NRL, Washington DC, USA
(Received September 12, 2007; Accepted August 16, 2008; Online published May 29, 2009)
Solar two ribbon flares are commonly explained by magnetic field reconnections in the low corona. During the reconnection energetic particles (electrons and protons) are accelerated from the reconnection site. These particles are following the magnetic field lines down to the chromosphere. As the plasma density is higher in these lower layers, there are collisions and emission of radiation. Thus bright ribbons are observed at both ends of flare loops. These ribbons are typically observed in Hα and in EUV with SoHO and TRACE. As the time is going, these ribbons are expanding away of each other. In most studied models, the reconnection site is a separator line, where two magnetic separatrices intersect. They define four distinct connectivity domains, across which the magnetic connectivity changes discontinuously. In this paper, we present a generalization of this model to 3D complex magnetic topologies where there are no null points, but quasi-separatrices layers instead. In that case, while the ribbons spread away during reconnection, we show that magnetic field lines can quickly slip along them. We propose that this new phenomenon could explain fast extension of Hα and TRACE 1600 Å ribbons, fast moving HXR footpoints along the ribbons as observed by RHESSI, and that it is observed in soft X rays with Hinode/XRT.
Key words: Sun: flares, magnetosphere: aurora.