Lack of thermal equilibrium between <formula>H+ and <formula>O+ temperatures in the Venus nightside ionosphere

Details Lack of thermal equilibrium between <formula>H+ and <formula>O+ temperatures in the Venus nightside ionosphere Lack of thermal equilibrium between <formula>H+ and <formula>O+ temperatures in the Venus nightside ionosphere

Feb 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997jgr...102.2185k&link_type=abstract

Journal of Geophysical Research, Volume 102, Issue A2, p. 2185-2192

Physics

Planetology: Solid Surface Planets: Ionospheres, Ionosphere: Planetary Ionospheres, Ionosphere: Modeling And Forecasting, Ionosphere: Plasma Temperature And Density

Scientific paper

Analysis of orbiter retarding potential analyzer (ORPA) ion data recorded in the nightside Venus hydrogen bulge region has revealed that the temperature of the H+ ions is substantially cooler by approximately 2000°K than that of the O+ ions above 200 km altitude. Below 200 km altitude the H+ and O+ temperatures cross, with the H+ temperature becoming the hotter temperature. Frequently, the velocity distribution of the H+ ions appears to be non-Maxwellian with too large a fraction of the ions having small velocities. We suggest that this may be the result of H+ ions, created from charge exchange collisions, not having completely thermalized with the ambient H+ gas. Charge exchange collisions between cold neutral hydrogen atoms at a temperature of 100°K and the hot O+ and H+ ion gases create H+ ions at a temperature of 100°K. The temporal and spatial extent of the cooled H+ gas has not been investigated in this study. We have attempted to understand the processes responsible for the observed temperature behavior by solving numerically the coupled electron, H+, and O+ energy equations in one-dimensional form. Neglecting convective transport terms but including for the first time cooling processes resulting from charge exchange between H+ and O+ ions with cold neutral hydrogen atoms and using separate H+, O+, and electron thermal conductivities corrected for collisions, we have obtained temperature profiles for the H+ and O+ gases which are consistent with the observed profiles. The process primarily responsible for the observed behavior of the H+ and O+ temperatures appears to be the difference in the thermal conductivity of the two ion gases with the thermal conductivity of H+ being several times larger than that of O+ given the same temperature and density. This result must be tempered with the fact that several processes or conditions, which may be important, have been neglected.

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