The role of Hall-MHD in magnetic reconnection on the sun

Magnetic reconnection is widely believed to be the most important process by which magnetic fields transfer energy to plasmas and, consequently, has been invoked as the explanation for a multitude of phenomena observed in space, astrophysical, and laboratory plasmas. Solar flares and CMEs dissipate the magnetic energy rapidly via magnetic reconnection on the Sun. In order to release magnetic energy via solar flare or CME, one needs to generate small length-scales in sheets or filaments, as the time scale for magnetic dissipation is 1014 s for the parameters global solar coronal length-scale (L=107 m) and coronal temperature (T=106 °K), while the flares happen on typical time scale of few minutes. At such small scales, the standard MHD is not valid and one may have to include other terms of the generalized Ohm's law. The Hall term comes into play in generalised Ohm's law when the thickness ∆ of the Sweet -Parker current sheet becomes smaller than the ion skin depth, i.e., when d_e < ∆ < d_i. Hall term may lead to increment in the reconnection rate from Sweet-Parker like (slow reconnection) to Petschek like (fast reconnection). We plan to do simulations to capture the change in reconnection rate by including Hall term and its effect on the large scale reconnections which are responsible for flares and CMEs. (author)