Ozone Photochemistry and Radiative Heating of the Middle Atmosphere

Abstract

The distributions of minor atmospheric constituents, principally O3 and O(3P), and their contributions to the heat sources and sinks in the earth?s middle atmosphere (30?100 km) are investigated. The latitudinal and seasonal distributions of radiative heating rates for the region 30?100 km are computed considering the absorption of solar UV by O2 and O3 and the chemical heat release by O(3P) recombination. Absorption of solar radiation by O3 is responsible for most of the radiative heating in the region 30?75 km. Between 75 and 90 km the heating rate is relatively small and is contributed to about equally by absorption by O2 and O3. Above 90 km the heating rate due to absorption by O O2 is of major importance, although non-equilibrium production of O(3P) in the summer results in reduced heating rates at these levels. At 100 km the ?effective? heating rate is ?40K day?1 at high latitudes during the summer. Recombination of O(3P) in the winter polar mesosphere and lower thermosphere results in a significant heat source for that region. Meridional gradients of computed heating rates in the upper atmosphere are found to be generally larger than previous results. The implications of this distribution with regard to the dynamics of this region is discussed.