Electron Inertia Effects in an MHD Scale Kelvin-Helmholtz Vortex

Details Electron Inertia Effects in an MHD Scale Kelvin-Helmholtz Vortex Electron Inertia Effects in an MHD Scale Kelvin-Helmholtz Vortex

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsm11b0435n&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #SM11B-0435

Physics

0654 Plasmas, 7524 Magnetic Fields, 7843 Numerical Simulation Studies, 7859 Transport Processes, 7871 Waves And Instabilities

Scientific paper

We study the effects of the electron inertia in an MHD scale Kelvin-Helmholtz (KH) vortex by two-dimensional two-fluid simulations including electron inertia. An LLBL like situation, that is, an MHD/ion scale velocity shear with density gradient, is set up and the evolution of a MHD-scale KH-mode followed. The magnetic field is assumed to be perpendicular to the flow and the simulation plane. When the electron dynamics is not considered (MHD), the highly rolled up MHD-scale vortex is generated and remains rather stable. The vortex behaves just as in MHD studies even when the ion inertia is included (Hall MHD). However, when the electoron dynamics is taken into account, that is, when the effects of electron inertia is considered, we observe the decay of the MHD-scale vortex for the duskside-like situation. In the duskside case, small vortices appear inside the MHD-scale vortex. As the small vortices grow quickly in time and expand outward, the parent MHD-scale vortex is destroyed. The nature of the small vortices is as follows: First, an ion-electron hybrid-scale instability is driven by the electron inertia at the hyperbolic point. Then the fluctuations produced by this instability are convected by the electron flow along the outer region of the parent vortex. A velocity gradient exists at this part of the vortex and the fluctuations become the seed for the secondary KH instability within the parent KH vortex, which produces the small vortices. That is, the coupling between the hybrid-scale phenomenon and the MHD-scale phenomoenon within the parent vortex makes it to decay. This naturally explains the self-similarity observed in the decay process when the thickness of the initial velocity shear layer is varied. In the dawnside-like case, since the fluctuations produced by the hybrid-scale instability do not propagate to the velocity shear region, the small vortices don't grow within the parent vortex and its decay does not proceed. We will present results of detailed analyses that support the above story for the newly found vortex decay process. We will also discuss the implications of the decay process in the context of magnetospheric physics.

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