Implications of variations in the 15‐μm CO2 band cooling in the mesosphere and lower thermosphere associated with current climatologies of the atomic oxygen mixing ratio

Abstract

Higher values for the deactivation rate constant, kO, for collisions CO2(0110)‐O have gained acceptance recently. As a result, in the mesosphere 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 kO chosen. Results 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 investigated. The latitudinal variability of the sensitivity of the cooling rate to variations in atomic oxygen is also examined. The latitudinal variation in heating rate for current climatological models of atomic oxygen, associated with the new rate constants, has a small but non negligible effect on the large‐scale circulation. Latitudinal variations in the oxygen mixing ratio result in changes in the residual circulation by about 20% relative to calculations with a single vertical profile of the atomic oxygen mixing ratio. Use of the larger rate constants does not result in significant changes to the latitudinal gradients in the temperature field and hence to the zonal winds. The sensitivity of the local heating rate to variations in the atomic oxygen mixing ratio shows a strong latitudinal variation. The sensitivity is greatest over the summer pole and least over the winter pole. The summer pole is the region most likely to exhibit the constituent‐driven convective processes mentioned by Ward and Fomichev (1993).