Electron inertial effects in highly rolled-up MHD-scale Kelvin-Helmholtz vortices

In order to understand the universality of substantial non-MHD effects within MHD-scale (large scale) Kelvin-Helmholtz (K-H) vortices, we have performed two-dimensional simulations by a two-fluid system including finite electron inertial effects. An MHD-scale velocity shear with density gradient between the two regions is set up and evolution of MHD-scale K-H mode is followed. Here we concentrate on the cases with in-the-plane magnetic field component. We particularly focus on the case where magnetic field lines on both sides of the shear layer are parallel to each other. In this case, magnetic reconnection within the MHD-scale vortex occurs by the electron inertial effects when the vortex highly rolls-up. In the highly rolled-up vortex, the field lines are stretched into an anti-parallel geometry overcoming the tension of in-the-plane magnetic field. The number of the magnetic islands formed by reconnection and the degree of the electron acceleration in the islands depend on the size of the vortex measured by the ion inertial length and the electron inertial length, respectively. On the basis of these results, we advocate the general importance of the electron effects in an MHD-scale K-H vortex and discuss its relevance to dynamics of the LLBL. The electron inertia effectively affects the structures of highly rolled-up MHD-scale vortices over a wide parameter range including the representative LLBL parameter, by which fascinating effects that are not expected in pure-MHD are likely to be produced.