Three-dimensional kinetic picture of bursty reconnection in the magnetotail

Abstract:

Bursty reconnection in the Earth’s magnetotail has important features that distinguish it from similar processes in other space plasma regions and the simplest theoretical models. First, its possibility has long been questioned because of the stabilizing effect of electrons magnetized by the north-south (Bz) magnetic field component. Second, reconnection in the tail competes with non-reconnection ballooning/interchange and flapping motions. Third, it is distinguished by the so-called dipolarization fronts, kinetic-scale shock-like plasma structures which dominate the energy conversion. Tearing stability theory shows that a necessary condition for the reconnection onset is a tailward gradient of the Bz field, which is indeed observed in the late substorm growth phase. 3D PIC simulations show that, when such an instability develops, it starts from the generation of an earthward plasma bulk flow with a dipolarization front at its leading edge and is followed by a magnetic topology change. These processes are accompanied by interchange and flapping motions that result in structuring of the tail activity in the local time but do not destroy the global reconnection-dominated picture. Simulations show that, in contrast to simple models, the energy conversion in the tail is largely provided by dipolarization fronts and the corresponding ion and electron temperature increases are consistent with THEMIS observations. We discuss virtual satellite observations, which reveal the potential of the MMS observations in resolving the primary plasma modes associated with the magnetotail reconnection. We also discuss the role of the dipole magnetic field in the tail structure and dynamics.