IMPLICATIONS OF VARIATIONS IN THE 15-MU-M CO2 BAND COOLING IN THE MESOSPHERE AND LOWER THERMOSPHERE ASSOCIATED WITH CURRENT CLIMATOLOGIES OF THE ATOMIC OXYGEN MIXING-RATIO

Higher values for the deactivation rate constant, k(O), for collisions CO2(01(1)0)-O have gained acceptance recently. As a result, in the me sosphere and lower thermosphere, the latitude and height structure of the CO2 cooling is significantly modified, and the sensitivity of this cooling to variations in the atomic oxygen mixing ratio is increased. The magnitude of these effects depends on the value of k(O) chosen. R esults are presented which illustrate the tendencies in the structure of the CO2 cooling as the rate constant is varied, so that its impact on atmospheric modeling may be discerned and possible constraints inve stigated. The latitudinal variability of the sensitivity of the coolin g rate to variations in atomic oxygen is also examined. The latitudina l variation in heating rate for current climatological models of atomi c oxygen, associated with the new rate constants, has a small but non negligible effect on the large-scale circulation. Latitudinal variatio ns in the oxygen mixing ratio result in changes in the residual circul ation by about 20% relative to calculations with a single vertical pro file of the atomic oxygen mixing ratio. Use of the larger rate constan ts does not result in significant changes to the latitudinal gradients in the temperature field and hence to the zonal winds. The sensitivit y of the local heating rate to variations in the atomic oxygen mixing ratio shows a strong latitudinal variation. The sensitivity is greates t over the summer pole and least over the winter pole. The summer pole is the region most likely to exhibit the constituent-driven convectiv e processes mentioned by Ward and Fomichev (1993).