Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006dps....38.6008s&link_type=abstract
American Astronomical Society, DPS meeting #38, #60.08; Bulletin of the American Astronomical Society, Vol. 38, p.599
Astronomy and Astrophysics
Astronomy
Scientific paper
We use a simplified GCM to examine affects of radiation on Martian atmospheric dynamics. The model has a
simplified surface friction and a diabatic heating, calculated by a gray-gas model of IR radiation. There are no
surface latent heat fluxes and there are no convection or boundary layer parameterizations in the model. The
radiative model has a parameter (α) which determines the ratio of scale heights of the main atmospheric
component to the main IR absorber. This parameter controls the depth of the radiative forcing.
We find that the eddy dynamics display two distinct regimes in the radiative parameter α: 1) low α
- with features seen on Mars, and 2) high α - qualitatively resembling the Earth. In particular, we find
deep, highly regular eddies with large zonal scale in the low α case. This behavior is typical of present
Mars but we find it even when Earth-like parameters (such as the planet's radius, gravity and gas constant)
are used as long as we are in the low α regime. As α is increased we find a shift in the typical zonal
scale of eddies toward shorter waves. The waves also become shallower and more irregular, as is typical of eddies
on Earth. The transition between these regimes can be predicted from the radiation model. We claim that the
critical value of α is that for which the radiative equilibrium temperature becomes gravitationally unstable.
The cause of the two regimes in the model is the depth of the radiative forcing. It is possible that this
mechanism can explain the transition to larger scale waves during dust storms on Mars. Dust loading could cause
radiative heating rates to be spread through a deeper portion of the atmosphere, initiating a transition from
smaller to larger scale eddy phenomena.
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