Ion passage over the solar wind termination shock under conservation of particle invariants in view of Voyager-2 observations H.-J. Fahr and M. Siewert Argelander Inst. für Astronomie der Univ. Bonn, Abt. f. Astrophysik und Extraterrestrische Forschung, Auf dem Hügel 71, 53121 Bonn, Germany
Received: 11 Aug 2010 – Revised: 12 Oct 2010 – Accepted: 12 Oct 2010 – Published: 15 Nov 2010
Abstract. We study the plasma passage over astrophysical MHD shocks with frozen-in magnetic fields in arbitrary inclinations
with respect to the bulk plasma motion. As a function of the compression ratio at the shock, we aim at the
prediction of ion plasma properties downstream of the shock, especially the resulting downstream temperatures,
pressures and pressure anisotropies as function of the upstream magnetic tilt angle.
Using dynamical invariants governing the ion motions, we derive the independent reactions of the ion velocity
components parallel and perpendicular to the local magnetic field at the shock passage. This allows us to
determine not only the associated downstream ion velocities, but the ion distribution function and its velocity
moments like pressures and temperatures. We find pronounced increases of the downstream ion temperatures with
respect to corresponding upstream values. The down-to-up temperature ratios thereby strongly depend on the
upstream magnetic tilt angle attaining maximum values in case of a quasi-perpendicular shock. We also obtain
fire-hose-unstable temperature anisotropies with values T⊥/T∥≪1 at small tilt
angles (quasi-parallel shock) and mirror-unstable values of anisotropies T⊥/T∥≫1
at tilt angles near π/2 (quasi-perpendicular shock).
Citation: Fahr, H.-J. and Siewert, M.: Ion passage over the solar wind termination shock under conservation of particle invariants in view of Voyager-2 observations, Astrophys. Space Sci. Trans., 6, 31-39, doi:10.5194/astra-6-31-2010, 2010.