On the stability of the ionopause of Venus

Abstract

We examine the stability of the of gravitation has not been considered before. In Venus ionopause in light of the importance of addition we intend to take into acco,•nt the gravitation and curvature. Using a one fluid effect of the curvature of the VenusJan ionoapproximation for the equation of motion of the pause. The centrifugal acceleration of the ionoplasma, and ignoring the effects of neutrals, we spheric plasma, g = V2/R (where V 2 is the sum of obtain a dispersion relation that includes the the squares of plasma thermal speed and bulk flow effects of magnetic field, sheared plasma flow, speed, and R is the radius of curvature of the buoyancy, centrifugal force and magnetic tension interface) and the curvature of the external due to boundary curvature. We find that buoyancy magnetic field destabilize the Venusian ionoacts to neutralize the flute instability. As pause, whereas gravity has a stabilizing effect. Gravity is importamt in the Venus ionopause • is the frequency. The wavelengths • of the stability problem. The effects of gravity have disturbances are assumed to be small in comparibeen studied only by Chandrasekhar [1961] (his son with the radius R of the curvature of the results were used by Wolf• et al. [lqBO] for the interface, so that kR = 2•R/• >> 1. For such case of Venus) and only fo• some special cases. disturbances the interface may be considered as The general case of arbitrary orientation and plane; we take this p_lane as z --0, with the z magnitude of the magnetic field, plasma bulk axis antiparallel to g. For disturbances propavelocity, and the wave vector • in the presence gating along the (approximately) plane interface, k z --O. The undisturbed (equilibrium) values, Copyright 1984 by the American Geophysical Union. denoted by subscript zero,_are not assumed to be uniform, but the terms (B ß V)B,o , (V ß V)•o, Paper number 3A1700. V%o, etc. are eliminated øby using t%e corre-0148-0227/84/003A-1700502.00 sponding equilibrium equations. As a result, 997 998 Elphic and Ershkovich: Brief Report

Ion Energization and Escape on Mars and Venus

“…The interface between the magnetosheath and ionospheric plasmas is also a site for possible fluid-like MHD instabilities (Wolff et al 1980;Dubinin et al 1980;Elphic and Ershkovich 1984;Thomas and Winske 1991;Arshukova et al 2004). The observations of the surface waves near the Venusian ionopause and detached clouds of ionospheric plasma in the magnetosheath ) confirm this suggestion.…”

The Mars Atmosphere and Volatile Evolution (MAVEN) Mission

“…Although few measurements are available at Mars, similar processes have been observed at Venus. There, thermal ion measurements made from Pioneer Venus revealed a complex morphology of the ionosphere upper boundary near the Venus terminator and in the wake, consisting of waves, streamers, and detached ionospheric "clouds" (Brace et al 1982), which might have been generated by Kelvin-Helmholtz (K-H) instability (Elphic and Ershkovich 1984) or by magnetic tension ("slingshot") related to the draped solarwind magnetic fields. At Mars, the presence of crustal magnetic fields interacting with shocked solar wind plasma makes possible additional bulk escape mechanisms, including magnetic reconnection (Eastwood et al 2008) and plasmoid-type structures (Brain et al 2010).…”

A comparison of magnetohydrodynamic instabilities at the Martian ionopause

“…This large separation in a direction perpendicular to the magnetosheath flow suggests that the ionospheric plasma in the clouds must have originated in the ionosphere upstream on the dayside, indicating that magnetohydrodynamic (MHD) instabilities may occur at the Venusian ionopause, which was first suggested by Wolff et al (1980). Elphic and Ershkovich (1984) analyzed the stability of the Venusian ionopause by using one-fluid MHD equations for a perfectly conducting, incompressible, inviscid fluid, and concluded that the Kelvin-Helmholtz instability is the dominant instability over most of the dayside ionopause. After that, the Venusian solar wind-ionosphere interaction was analyzed using analytical (e.g., Cloutier et al, 1983;Elphic and Ershkovich, 1984) and numerical models (e.g., Thomas and Winske, 1991).…”

“…Elphic and Ershkovich (1984) analyzed the stability of the Venusian ionopause by using one-fluid MHD equations for a perfectly conducting, incompressible, inviscid fluid, and concluded that the Kelvin-Helmholtz instability is the dominant instability over most of the dayside ionopause. After that, the Venusian solar wind-ionosphere interaction was analyzed using analytical (e.g., Cloutier et al, 1983;Elphic and Ershkovich, 1984) and numerical models (e.g., Thomas and Winske, 1991). Recently, Terada et al (2002) used a global hybrid simulation to describe the Kelvin-Helmholtz instability at Venus.…”