Generation of shock/discontinuity compound structures through magnetic reconnection in the geomagnetic tail

Abstract

We use 1-D hybrid code to simulate the generation and evolution of MHD discontinuities associated with magnetic reconnection in a current sheet. It is found that the leakage of slow shock (SS) downstream particles to upstream region tends to increase the ion parallel temperature and temperature anisotropy with βi||/βi⊥≫1, where βi||(βi⊥) is the ion parallel (perpendicular) beta. As a result, the propagation speed of rotational discontinuity (RD) is highly reduced and RD becomes attached to SS, leading to formation of various compound structures in the reconnection outflow region. Four types of compound structure are found in our simulations: (a) RD-SS compound structure: the RD is attached to the leading part of SS, (b) SS-RD (DD) compound structure: RD is attached to the rear part of SS, (c) SS-RD-SS compound structure: RD is trapped inside SS, and (d) switch-off slow shock (SSS) with a rotational wave train. The type of compound structure generated depends on initial ion beta βi0 and magnetic shear angle ϕ. RD tends to move in front of SS to form an RD-SS compound structure for cases with low βi0. RD stays behind SS and form an SS-RD (DD) compound structure for large βi0. The SS-RD-SS compound structure is formed for intermediate values of βi0. When the shear angle is 180°, SSS with a wave train is formed.