Global Hybrid Simulations of Interaction Between Interplanetary Rotational Discontinuity and Bow Shock/ Magnetosphere: Can Ion-Scale Magnetic Reconnection be Driven by Rotational Discontinuity Downstream of Quasi-Parallel Shock?

摘要

Ion-scale magnetic reconnection has been observed downstream of the terrestrial quasiparallel (Q-‖) shock. Whether it is driven by interplanetary discontinuities or turbulent Q-‖ shock,however, is unclear. Using three-dimensional global hybrid simulation, we investigate the generation of magnetic reconnection downstream of the Q-‖ shock, while an interplanetary rotational discontinuity (RD) is launched to the bow shock. Cases with various solar wind Alfvén Mach numbers, M_A = 3.0 to 8,and propagation directions of the RD are presented. The propagation direction n is assumed to be in the GSE xz plane and pointing earthward, with n = (-sin(θ_(12)/2),0,-cos(θ_(12)/2)), where θ_(12 )is the angle between the upstream (B_1) and downstream (B_2) magnetic fields across the transmitted RD. It is found that magnetic reconnection occurs inside the RD downstream of the Q-‖ shock, forming flux ropes extending along the dawn-dusk direction about tens of ion inertial lengths. Large-amplitude low-frequency waves originated from the Q-‖ shock lead to the bending and squeezing of the field lines around the RD,which play an important role in triggering reconnection inside the RD. As the RD impacts the dayside magnetopause, magnetopause reconnection takes place between the field lines behind the RD and geomagnetic field lines. Nevertheless, no reconnection is found downstream of the Q-‖ shock itself or outside the RD in the magnetosheath. The existent and structure of reconnection in the magnetosheath are found to strongly depend on the parameters M_A and n. Our simulation shows that ion-scale magnetic reconnection is driven by an external driver in the form of the compression of an RD around the bow shock and in the magnetosheath, rather than caused by the turbulent Q-‖ shock alone.