The double-adiabatic or Chew-Goldberger-Low (CGL) laws have been found to be severely violated in the magnetosheath. In this paper we show that the nonideal MHD effects including both the heat fluxes and the nonperfect conducting effects, for example, the resistive, the ion and electron inertial terms in the generalized Ohm's law, may render the CGL laws invalid; the entropy of the gyrotropic plasmas, however, may only be altered by the heat fluxes. It is shown from a magnetosheath crossing that the observed pressure anisotropy can be largely accomplished by the nonperfect conducting effects and that the constant entropy law, which can also be reduced from the double-adiabatic laws, is much more viable than the individual CGL relation; the slight decrease of the entropy toward the magnetopause implies a net heat loss in the system. Double polytropic closure in the magnetosheath Hau et al., 1993 implies that these nonideal MHD effects may be approximately lumped into two empirical polytropic exponents, gamma(parallel to) and gamma(perpendicular to), describing the thermodynamic behavior of the plasma; the case gamma(parallel to) = 3 and gamma(perpendicular to) = 2 corresponds to the double-adiabatic closure.
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