Numerical modeling study of Martian aerosols: Non-condensable gases, dust, and water in the Martian atmosphere
Atmospheric dust, water vapor and ice, and minor gas species (argon, nitrogen) are known as tracers of the martian atmosphere because of their ability to track atmospheric circulation. Their abundance by mass in the martian atmosphere is negligible, with nitrogen being the largest contributor at ~2.5% by mass. Studying tracers with a general circulation model helps in the understanding of the current dynamical processes occurring in the martian atmosphere and, conversely, provides a diagnostic test for how well the model dynamics reproduce actual processes on Mars. The use of such a model is important for providing solutions to observed phenomenon that cannot currently be measured in situ. The last few years have been spent studying how effectively the NASA-Ames General Circulation Model captures the martian dynamics by trying to match tracer transport in the model to observation. The Ames GCM produces a 3-fold non-condensable gas enhancement in the south polar region and an approximate 1.4-fold increase in non-condensables in the north polar region during each poles respective fall and winter season. These model results are temporally consistent with observed values, but the observed enhancement magnitudes exceed those modeled by a factor of two, indicating excessive eddy mixing off the pole in the GCM. The difference in strength and the season of formation between transient eddies in the southern and northern hemispheres play a large role in determining the different character of the north and south polar enhancements. At night, in the model, air in contact with the ground cools via conduction and radiation and flows down the slope of the topography. Upon reaching the condensation temperature, this moisture-laidened air produces a ground fog and precipitates onto the surface. A wave number two longitudinal pattern of deposition occurs in the model over Arabia and Tharsis. If conditions at the locations of maximum water ice deposition are thermodynamically conducive, they have the potential to hydrate the equatorial water equivalent hydrogen reservoirs at these locations through the retention of precipitate by hydrous minerals such as MgSO 4 . Dust and water vapor interaction during cloud formation has the greatest effect upon each aerosol during northern spring and summer. Cloud production is most active during this time because the atmosphere is coolest during the aphelion season and moisture laden.
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