MAGNETIC-FIELD RECONNECTION PATTERNS AT THE DAYSIDE MAGNETOPAUSE - AN MHD SIMULATION STUDY

Magnetic field configurations associated with dayside reconnection are studied by a global two-dimensional incompressible MHD simulation. Possible dayside reconnection patterns revealed in the simulation include magnetic field configurations associated with steady state single X line reconnection, impulsive multiple X line reconnection, and bursty single X line reconnection. Three physical parameters, the global magnetic Reynolds number R(m), the critical current density J(c) for the resistivity enhancement, and the solar wind Alfven Mach number M(Asw), are found to be the most important parameters in determining the reconnection pattern. First, it is found that single X line reconnection tends to occur for small R(m) (< 100) and multiple X line reconnection takes place for large R(m) (> 200). Second, in the presence of a current-dependent resistivity and large R(m), various patterns of multiple X line reconnection are observed. Third, for a large M(Asw), dayside reconnection tends to occur in the high-latitude region. It is found in particular that multiple X line reconnection can indeed generate the primary flux transfer event signature, i.e., the bipolar pulse of normal magnetic field component. In addition, at the trailing edge of the bipolar pulses, enhanced plasma speed is observed in the simulation.