Generation of vortex‐induced tearing mode instability at the magnetopause

Abstract

A two‐dimensional magnetohydrodynamic simulation is performed to study the generation of the vortex‐induced tearing mode instability at the magnetopause. When a sheared magnetic field exists along with the velocity shear, the tearing mode will couple with the Kelvin‐Helmholtz (K‐H) instability. The shear Alfvén Mach number MA plays an essential role in determining the linear properties and nonlinear evolution of the coupled instability. When the magnetic field is fixed, if MA < 0.4, the spontaneous tearing mode is dominated; when 0.4 ≤ MA ≤ 1, the tearing mode is apparently modified by the K‐H instability; as 1 < MA, the coupled instability, called the vortex‐induced tearing mode (VITM) instability, appears to be intrinsically different from the conventional tearing mode instability. The long time asymptotic quasi‐static state for the VITM instability is characterized by a large‐scale fluid vortex together with a concentric magnetic island. The linear properties and nonlinear evolution of the VITM instability are not significantly changed with different Reynolds and magnetic Reynolds number used in the simulation.