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Pressure Gradients Driving Ion Transport in the Topside Martian Atmosphere.

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Title: Pressure Gradients Driving Ion Transport in the Topside Martian Atmosphere.
Authors: Hamil, O.1,2 oliver.hamil@eas.gatech.edu, Cravens, T. E.1, Rahmati, A.3, Connerney, J. E. P.4, Andersson, L.5
Source: Journal of Geophysical Research. Space Physics. Jul2019, Vol. 124 Issue 7, p6117-6126. 10p.
Subject Terms: *Atmospheric evolution, Plasma flow, Magnetic fields, Electron density, Electron temperature, Zenith distance
Abstract: Magnetic and thermal pressure gradient forces drive plasma flow in the topside ionosphere of Mars. Some of this flow can contribute to ion loss from the planet and thus affect atmospheric evolution. MAVEN measurements of the magnetic field, electron density, and electron temperature, taken over a 3‐year time period, are used to obtain averaged magnetic and thermal pressures in the topside ionosphere versus altitude, solar zenith angle, and latitude. Magnetic pressures are several times greater than thermal pressures for altitudes greater than about 300 km; that is, the plasma beta is less than one. The total pressure increases with altitude in the ionosphere and decreases with increasing solar zenith angle. Using these pressure patterns in the dayside ionosphere to estimate the pressure gradient force in the fluid momentum equation, we estimate horizontal day‐to‐night plasma flow speeds of a few kilometers per second near 400 km. Key Points: Ions are driven from the subsolar point toward the dawn/dusk terminator modeled from large‐scale MHD calculations using MAVEN dataThis study demonstrates that above about 300 km, the plasma motion should dominantly be driven by magnetic field pressureWe demonstrate quantitative agreement of magnetic pressure versus solar zenith angle over most of the dayside between MGS and MAVEN [ABSTRACT FROM AUTHOR]
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Abstract:Magnetic and thermal pressure gradient forces drive plasma flow in the topside ionosphere of Mars. Some of this flow can contribute to ion loss from the planet and thus affect atmospheric evolution. MAVEN measurements of the magnetic field, electron density, and electron temperature, taken over a 3‐year time period, are used to obtain averaged magnetic and thermal pressures in the topside ionosphere versus altitude, solar zenith angle, and latitude. Magnetic pressures are several times greater than thermal pressures for altitudes greater than about 300 km; that is, the plasma beta is less than one. The total pressure increases with altitude in the ionosphere and decreases with increasing solar zenith angle. Using these pressure patterns in the dayside ionosphere to estimate the pressure gradient force in the fluid momentum equation, we estimate horizontal day‐to‐night plasma flow speeds of a few kilometers per second near 400 km. Key Points: Ions are driven from the subsolar point toward the dawn/dusk terminator modeled from large‐scale MHD calculations using MAVEN dataThis study demonstrates that above about 300 km, the plasma motion should dominantly be driven by magnetic field pressureWe demonstrate quantitative agreement of magnetic pressure versus solar zenith angle over most of the dayside between MGS and MAVEN [ABSTRACT FROM AUTHOR]
ISSN:21699380
DOI:10.1029/2019JA026670