München 1997 – scientific programme
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EP: Extraterrestrische Physik
EP 2: Magnetosph
äre 1
EP 2.3: Talk
Monday, March 17, 1997, 09:00–09:15, 302
Proton temperature anisotropy and adiabatic index values in the magnetosheath — •M.I. Pudovkin 1), C.-V. Meister 2), B.P. Besser 3), and S.A. Zaitseva 1) — 1) Inst. of Physics, Univ. St. Petersburg, 2) Univ. Potsdam, WIP Space Plasma Phys., 3) Inst. for Space Res. Graz
The effective (γeff) as well as perpendicular (γ⊥) and parallel (γ∥) with respect to the magnetic field adiabatic indices in a convective collisionless magnetized plasma with unisotropic temperature are obtained. The values of γ⊥, γ∥ and γeff are shown to depend on the characteristics of the plasma flow and on the temperature anisotropy and may be less than unity as well as larger than unity. The influence of the energy transfer between the perpendicular (T⊥) and parallel (T∥) proton temperatures on the temperature and adiabatic index profiles across the magnetosheath is discussed, and a method of estimating the characteristic time of the temperature anisotropy relaxation τ is proposed. The value of τ obtained from the T∥ profiles is shown to be systematically larger than the value found from the T⊥ profiles, which suggests the existence of some sinks of the perpendicular proton thermal energy. In spite of the rather complicated behaviour of γ⊥ and γ∥ across the magnetosheath, the effective index γeff calculated for the entire magnetosheath equals 1.6-1.7. At the same time, for short duration processes, when the energy transfer between T⊥ and T∥ may be neglected, one has γeff≈2−3 near the bow shock and γeff<1 in the magnetopause vicinity.