**Effects of Rotation and Convection on the Large Scale Structure of Planetary Atmospheric Circulation**

**M. de la Torre Juárez (JPL/NRC)**

The combined effect of rotation and convection due to differential heating of the planetary atmospheres by the Sun are very likely responsible for some of the large scale patterns observed in their atmospheres. The results of a linear stability analysis are presented for a three dimensional flow in a rotating spherical shell with a temperature gradient established by heating at the inner boundary with smooth temperature variation between equator and poles. Similar simple models were used before on the major planets (Busse 1983, Sun et al. 1993), where the inner surface was heated and the outer boundary cooled, both isothermaly. We add here a smooth meridional temperature gradient that can originate baroclinic instabilities. Fang and Tung (1996) used heating in the form of a delta function at ITCZ for the Earth. They analysed an axisimmetric Hadley convection solution, where preliminary results from our model show that rotation will break axisymetry as soon as baroclinic convection starts.

A spectral method is used. Spectral methods use functions representing, each, a flow regime over the whole planet. One spectral mode represents a temporal and spatial feature at global planetary scale. Usually GCM models discretize the planet into small numerical cells, solve the equations locally within one and connect with another solution in the next. This allows to include topography or local inhomogeneities but is possibly inadequate for trying to understand large scale global flows not due to topography or local phenomena.

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