Theory and simulations of a multi-scale magnetotail current sheet model

One of the key problems in modeling of the solar wind-magnetosphere interaction is the description of the magnetotail reconnection onset. It is widely accepted, that the explosive release of energy accumulated in the magnetotail, which occurs during substorms and bursty bulk flows, must involve some form of unsteady magnetic reconnection. However, the specific features of the magnetotail reconnection and its proper description at the kinetic level, not to speak about its reduced form suitable for global MHD modeling, remain poorly understood. Moreover, until recently the onset of spontaneous reconnection was thought to be fully prohibited, because the sufficient stability criterion of the corresponding plasma wave, the ion tearing mode, was fulfilled within the WKB approximation for all types of the considered magnetotail equilibria. Recently it was found (Sitnov and Schindler, 2010), that the ion tearing stability criterion might be relaxed in the tail current sheet models, which have more than two characteristic spatial scales. In particular, the substantial tearing destabilization takes place for equilibria with accumulation of the magnetic flux at the tailward end of an extended thin current sheet. We consider generalizations of the Sitnov-Schindler model including seed X-lines, and analyze their linear and nonlinear stability properties, as well as implications of the new stability criterion for global MHD models. The nonlinear stability issues are investigated with the help of an open-boundary modification of the full-particle code P3D (Zeiler et al., 2002).