A test of the Hall‐MHD Model: Application to low‐frequency upstream waves at Venus

Abstract

Early studies suggested that in the range of parameter space where the wave angular frequency is less than the proton gyrofrequency and the plasma beta, the ratio of the thermal to magnetic pressure, is less than 1 magnetohydrodynamics provides an adequate description of the propagating modes in a plasma. However, recently, Lacombe et al. [1992] have reported significant differences between basic wave characteristics of the specific propagation modes derived from linear Vlasov and Hall‐MHD theories even when the waves are only weakly damped. In this paper we compare the magnetic polarization and normalization magnetic compression ratio of ULF upstream waves at Venus with magnetic polarization and normalized magnetic compression ratio derived from both theories. We find that while the “kinetic” approach gives magnetic polarization and normalized magnetic compression ratio consistent with the data in the analyzed range of beta (0.5 < beta < 5) for the fast magnetosonic mode, the same wave characteristics derived from the Hall‐MHD model strongly depend on beta arid are consistent with the data only at low beta for the fast mode and at high beta for the intermediate mode.