NONLOCAL THERMODYNAMIC-EQUILIBRIUM IN GENERAL-CIRCULATION MODELS OF THE MARTIAN ATMOSPHERE 1 - EFFECTS OF THE LOCAL THERMODYNAMIC-EQUILIBRIUM APPROXIMATION ON THERMAL COOLING AND SOLAR HEATING

Calculations of CO2 thermal cooling and near-IR solar heating rates un der non-local thermodynamic equilibrium (non-LTE) situations have been performed to understand and evaluate the effects of non-LTE on the en ergy balance of the upper atmosphere of Mars. We find that the 15-mu m cooling rates can be in error if LTE is assumed above 80 km. In gener al, the correct non-LTE values are significantly smaller than the LTE values above about 85 km, but the magnitude and sign of the error depe nd on the temperature structure and the top altitude of the model and, to a lesser extent, on the collisions with atomic oxygen. A detailed analysis of the relevance of the upper boundary layer and a suggested buffer region are presented for both LTE and non-LTE. Based on general considerations of the thermal profile in the mesosphere and lower the rmosphere, recommendations for general circulation models (GCM) are pr esented as a first guide for minimizing the LTE cooling rates inaccura cies. The error of assuming LTE on the CO2 near-IR solar heating rates is found to be about 20% at 85 km and increases strongly above this a ltitude. The dependences of this LTE-non-LTE difference on rate coeffi cients, thermal structure, surface pressure, and solar zenith angle (S ZA) are studied. In contrast to the large effect of the SZA on the sol ar heating rate, we find it is not important for the LTE-non-LTE relat ive difference, which permits a simple tabulation of the non-LTE effec t as a function of pressure only. A table of LTE correction factors fo r the solar heating rate is included for its potential use as a fast y et accurate operative scheme within GCMs.