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EP: Fachverband Extraterrestrische Physik

EP 15: Heliophysics III

EP 15.6: Talk

Thursday, April 2, 2009, 17:15–17:30, Zahnklinik

An analytic study of wave generation due to plasma anisotropies at perpendicular MHD shocks — •Mark Siewert and Hans-Jörg Fahr — Argelander-Inststut für Astronomie, Uni Bonn

We develop a kinetic model to describe the termination shock transition of anisotropic plasmas allowing to estimate the amount of energy pumped into the MHD wave field by a mirror-unstable ion distribution function downstream of the perpendicular MHD shock. Based on that kinetic model, we derive a full, completely analytical solution of the MHD jump conditions adequately describing the scenario. This allows us to derive a wave generation criterion for shock-induced mirror-unstable conditions, depending exclusively on two upstream parameters, the Alfven Mach number and the plasma beta. Using this formulation, it is easily possible to estimate whether or not a specific MHD shock system triggers wave generation. As it turns out, most perpendicular shocks, including the solar wind termination shock encountered by Voyager-1/2, are mirror-unstable, while only the weakest shocks lead to a stable, wave-quiet state on the downstream side without onset of wave-generating processes.