Kelvin-Helmholtz vortices in the magneotail-flank

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The Kelvin-Helmholtz (KH) vortices are a candidate agent for large-scale plasma transport across the magnetotail flank boundary. To understand the nature of MHD-scale KH vortices in non-llinear regimes, we have performed two-dimensional numerical simulations including finite electron inertia. Non-zero in-plan magnetic field is assumed to be present.When the stabilizing magnetic tension is weak, nicely rolled-up vortices are formed and field lines are so stretched to form an anti-parallel geometry within the vortices. Then reconnection is triggered. Such a process has been studied in resistive MHD approaches, however, this study is the first to prove the process from the cross-scale coupling point of view.On the other hand, when the tension is strong, the results are drastically dofferent depending on whether the sign of the magnetic field component changes across the shear layer or not.(1) When the magnetic component does not change sign across the shear layer, the effects of the instability is only to broaden the shear layer.(2) When the magnetic component changes sign across the shear layer, already in the early phase of the instability growth, a part of the current sheet is pinched by the flow and reconnection takes place. Then the flow produced by reconnection assists the vortex to grow and the size of the vortex obtained in this situation I smuch larger than the one without reconnection. What is more, the large vortex is filled with mixed plasma, that is, large scale plasma mixing across the boundary is attained in this situationWhat is even more interesting, we have found that the combination of strong magnetic tension and anti-parallel geometry is the best for creating large scale plasma mixing across the velocity shear layer.