Double‐polytropic closure in the magnetosheath
Open Access
- 22 October 1993
- journal article
- Published by American Geophysical Union (AGU) in Geophysical Research Letters
- Vol. 20 (20) , 2255-2258
- https://doi.org/10.1029/93gl02491
Abstract
The magnetosheath plasma is usually neither isotropic nor adiabatic. This paper contains an attempt to decribe its thermodynamic properties in terms of two polytropic laws, p⟂/ρBγ⟂−1 = C⟂ and p∥Bγ∥−1 / ργ∥ = C∥, such that for γ⟂ = 2, γ∥ = 3 the usual Chew‐Goldberger‐Low double‐adiabatic expressions are recovered and for γ⟂ = 1, γ∥ = 1 double‐isothermal conditions are obtained. Using data from the AMPTE/IRM spacecraft, we show that the subsolar magnetosheath plasma may be better described by the double‐polytropic laws than by the mirror instability threshold, in particular in the low beta region near the magnetopause. The inferred polytropic exponents vary from event to event but are typically in the ranges of γ⟂ = 0.94 ± 0.10 and γ∥ =1.14 ± 0.13 for the 29 cases we have examined.Keywords
This publication has 6 references indexed in Scilit:
- Low‐frequency magnetic fluctuation spectra in the magnetosheath and plasma depletion layerJournal of Geophysical Research, 1994
- On slow‐mode waves in an anisotropic plasmaGeophysical Research Letters, 1993
- Ion anisotropies in the magnetosheathGeophysical Research Letters, 1993
- Structure of the dayside magnetopause for low magnetic shearJournal of Geophysical Research, 1993
- Magnetic pulsations from 0.1 to 4.0 Hz and associated plasma properties in the Earth's subsolar magnetosheath and plasma depletion layerJournal of Geophysical Research, 1993
- The Boltzmann equation an d the one-fluid hydromagnetic equations in the absence of particle collisionsProceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, 1956