Magnetosheath Reconnection Before Magnetopause Reconnection Driven by Interplanetary Tangential Discontinuity: A Three-Dimensional Global Hybrid Simulation With Oblique Interplanetary Magnetic Field

Abstract

Terrestrial dayside dynamics associated with a southward turning, oblique interplanetary magnetic field (IMF) carried by an interplanetary tangential discontinuity (TD) is investigated by performing a three-dimensional global-scale hybrid simulation systematically for cases in which the incoming solar wind TD possesses various magnetic field rotation angles Delta Phi = 90 degrees to 180 degrees and half widths w = 2d(i0) to w = 30d(i0) where d(i0), is the ion inertial length in the solar wind. Overall, the TD is compressed while being transmitted into the magnetosheath, with different compression processes downstream of the quasi-parallel (Q-parallel to) and quasi-perpendicular (Q-perpendicular to) shocks. It is found that magnetosheath reconnection may take place downstream of both the Q-parallel to and Q-perpendicular to shocks due to interaction of the directional TD with the bow shock and magnetopause, but the existence of magnetosheath reconnection depends on w and Delta Phi. Magnetosheath flux ropes are formed through three-dimensional patchy reconnection in the thinned current sheet, with a longer rope lengths under a larger Delta Phi. There exists a dawn-dusk asymmetry in the spatial extent of the flux ropes, which becomes more significant as Delta Phi decreases. When Delta Phi decreases to 90 degrees, no reconnection flux ropes are found. Magnetopause reconnection is initiated when the magnetic fluxes with a southward turning IMF (on the sunward side) reach the magnetopause, and the magnetopause flux ropes can be mixed with the magnetosheath ones. Our simulation demonstrates that the effects of a southward turning of the IMF may not be a simple field direction change that leads to reconnection only at the magnetopause.