Studies of Solar Heating by CO2 in the Upper Atmosphere Using a Non-LTE Model and Satellite Data

Abstract

Solar heating and thermal cooling rates by the CO2 near-infrared bands in the mesosphere and lower thermosphere are derived from measurements of the CO2 4.3 ?m atmospheric emission by the Stratospheric and Mesospheric Sounder on Nimbus 7. A detailed analysis of the relaxation of the solar energy initially absorbed by the different bands, before it escapes to space or is thermalized, is included. The isotopic and hot bands of CO2 near 4.3 ?m play an important role since they produce a significant heating in the mesosphere and are important emitters of the solar energy absorbed at 4.3 ?m and 2.7 ?m around the mesopause. The pathways followed by the fraction of the electronic energy of O(1D) that is transferred into the CO2(00°1)-N2(1) system have been studied, resulting that an important fraction of this energy is emitted by the CO2 4.3 ?m fundamental band in the lower thermosphere. Sensitivity studies of the net heating rates to the atomic oxygen and carbon dioxide concentrations and to the rate of vibrational energy transfer are also presented. Global distributions of solar heating rates by CO2 for solstice and equinox situations are shown. They present a double peak structure with maxima situated around 95 and 75 km; the latter being particularly important because other components of the radiative balance have at a minimum at the same region.