Basic Physics of the Spontaneous Fast Reconnection Model

M. Ugai (Ehime University), K. Kondoh and T. Shimizu

Large dissipative events observed in space plasmas, such as geomagnetic
substorms and solar flares, result from explosive release of stored
magnetic energy into plasma energies. It is well known that the fast
reconnection mechanism involving standing slow shocks is most
responsible for the flare phenomena, so that an essential question has
been to seek the possible evolution of the fast reconnection mechanism
as an eventual solution. In this respect, we have proposed the
spontaneous fast reconnection model, which describes a nonlinear
instability by the positive feedback between microscopic (anomalous)
resistivities at the X reconnection point and macroscopic reconnection
flows. On the basis of the spontaneous fast reconnection model, it is
demonstrated by 2-D and 3-D MHD simulations for a variety of plasma
situations that once a current-driven anomalous resistivity is ignited,
the fast reconnection mechanism involving standing slow shocks can
drastically evolve and be established quasi-steadily as an eventual
solution of MHD equations.