The Role of Stratospheric Ozone in the Zonal and Seasonal Radiative Energy Balance of the Earth-Troposphere System

The role of ozone in the tropospheric-surface energy balance is discussed in the context of its latitudinally and seasonally varying modulation of solar and longwave energy fluxes. We analyze in detail the various radiative energy inputs to the stratosphere and the radiative fluxes from the stratosphere to the troposphere. To a very close approximation, on an annual and hemispherical mean, longwave emission from the stratosphere balances the absorbed radiant energy. The stratosphere absorbs about twice as much longwave radiation from the troposphere as it does solar radiation. About 20% of the longwave flux from the stratosphere to the troposphere is directly due to O2. A change in O3 concentrations perturbs the stratospheric and tropospheric-surface energy balances through a number of distinct mechanisms involving changes in solar and longwave fluxes and which are separated into direct effects due to the change of O3 and indirect effects due to the accompanying change of stratospheric temperature. The relative importance of average versus spatial varying changes in ozone is examined. We confirm the result of past analyses that, for a uniform change in ozone, the global average perturbation in radiative fluxes to the troposphere and surface is small since the perturbations in solar and infrared fluxes nearly cancel. However, this result probably severely underestimates the contribution of changes in the distribution of ozone to global climate. First, there generally are significant latitudinal and seasonal variations in the perturbation radiative fluxes to the troposphere. Second, vertical redistribution of Oe can produce larger perturbation fluxes to the troposphere than do uniform changes, and possibly of opposite sign. Third, most of the perturbation solar heating is deposited at or near the earth's surface, whereas much of the perturbation longwave fluxes are deposited in the upper troposphere with consequences for changes in the tropospheric lapse rates. Thus, it is difficult to evaluate the changes in tropospheric radiation needed to determine a change of climate due to a change of O3. Not even the net global average perturbation radiative fluxes to the troposphere can be calculated without knowing the change of the vertical ozone profile, and the vertical and latitudinal variations of the troposphere-surface perturbation heating rates are likely to be more important for climate change than the net global values.