Ion heat flux associated with the Kelvin-Helmholtz instability in a non-uniform plasma: Numerical hybrid-Vlasov results

Abstract

The presence of a velocity shear layer in a plasma can lead to the development of the Kelvin-Helmholtz instability (KHI). KHI is characterised by the growth of waves that roll up to form non-linear vortices. An example of such velocity shear layer is found at either flank of Earth's magnetopause, where KHI acts a driver of mass and energy transfer from the solar wind into the magnetosphere. Within the rolled-up vortices, kinetic length scales may be attained, allowing vortex-induced magnetic reconnection and kinetic-scale diffusion to operate. In the present study, we have considered the realistic case of a density/temperature jump across the magnetopause and modelled the development of the KHI using a local hybrid-Vlasov simulation with the Vlasiator code. For a case with a northward directed magnetic field, we find that an enhanced ion heat flux arises at vortex boundaries whose thickness approaches the ion gyroscale. Furthermore, the direction of the heat flux vector closely follows the direction of the vortex boundary tangent vector. As such, this signature could provide observational evidence of ion diffusion occurring within KHI, and also information on vortex boundary geometry with single spacecraft data. To validate our results, we compare our simulation run with data from the Magnetospheric Multiscale Mission.