Atomic oxygen in the Martian thermosphere
Abstract
Modern models of thermospheric composition and temperature and of excitation and radiative transfer processes are used to simulate the OI 130-nm emission from Mars measured by the Mariner 9 ultraviolet spectrometer. We use the Mars thermospheric general circulation model calculations (MTGCM) of Bougher et al. (1988a) and the Monte Carlo partial frequency redistribution multiple scattering code of Meier and Lee (1982). We find that the decline in atomic oxygen through the daylight hours predicted by the MTGCM cannot be reconciled with the excess afternoon brightness seen in the data. Oxygen concentrations inferred from the data show a positive gradient through the day, in agreement with the original analysis by Strickland et al. (1973), although the absolute amounts are somewhat less because we use a larger photoelectron impact excitation and a somewhat larger solar flux in the 130-nm triplet. In addition, the data suggest that the oxygen abundance increases toward high southerly latitudes, in contrast with the MTGCM prediction of high values in the northern (winter) hemisphere. It appears that solar forcing alone cannot account for the observed characteristics of the Martian thermosphere and what wave and tidal effects may profoundly affect the structure, winds, and composition.
- Publication:
-
Journal of Geophysical Research
- Pub Date:
- January 1992
- DOI:
- 10.1029/91JA02489
- Bibcode:
- 1992JGR....97...91S
- Keywords:
-
- Airglow;
- Atmospheric Composition;
- Mars Atmosphere;
- Oxygen Atoms;
- Thermosphere;
- Ultraviolet Radiation;
- Atmospheric General Circulation Models;
- Diurnal Variations;
- Mariner 9 Space Probe;
- Ultraviolet Spectrometers;
- Planetology: Solid Surface Planets: Atmospheres-composition and chemistry;
- Atmospheric Composition and Structure: Airglow and aurora;
- Atmospheric Composition and Structure: Thermosphere-composition and chemistry;
- Meteorology and Atmospheric Dynamics: Thermospheric dynamics