Structure of an MHD-scale Kelvin-Helmholtz vortex: Two-dimensional two-fluid simulations including finite electron inertial effects

摘要

Our two-dimensional two-fluid simulations including finite electron inertial effects of an MHD-scale Kelvin-Helmholtz (KH) vortex show that the plasma mixing and transport across the Earth's tail-magnetopause during northward interplanetary magnetic field (IMF) conditions can be caused by the coupling between the KH vortex and magnetic reconnection. First, it is found by systematical two-dimensional simulations under various fundamental conditions that two types of magnetic reconnection are driven in a KH vortex that are crucial factors for determining the structure of the KH vortex itself. One, named “type I reconnection,” occurs in the case where the magnetic field components along the k vector of Kelvin-Helmholtz instability (KHI) are antiparallel across the velocity shear layer (antiparallel case). Another, named “type II reconnection,” is driven in the case where the velocity shear is strong enough to produce highly rolled-up KH vortices and highly stretched field lines therein (strong KHI case). It is also found that type I reconnection leads directly to plasma mixing across the shear layer and that type II reconnection forms magnetic islands and plasma contained in these magnetic islands can be transferred from one side to the other across the shear layer. Next, linear analyses of the Earth's magnetopause-like cases under northward IMF show that the antiparallel case is obtained rather commonly and also that there is a significant possibility that the strong KHI case may be important. Furthermore, two-fluid simulations of the magnetopause-like cases actually show the occurrence of type I and type II reconnection in two dimensions. These results indicate that type I and type II reconnection may play a substantial role in the plasma mixing and transport across the magnetopause.