Radiative heating in the lower stratosphere and the distribution of ozone in a two‐dimensional model

The sensitivity of a two‐dimensional model to the diabatic heating rates used in the lower stratosphere is discussed. Different radiation schemes are described; in particular a longwave scheme which allows for interaction between surface temperature, ozone amounts and the heating rates in the ozone 9·6 μm band. Near‐infrared heating is also included. A model run including the new radiation schemes is compared with a control run in which radiative equilibrium is assumed in the 150–30 mb region (as in previous versions of this model) and with a run in which fixed heating rates are adopted in the same region. The temperature and ozone distributions of each run are discussed. The ozone structure is very sensitive to the scheme used and the inclusion of the new schemes improves the model's ozone distribution. The importance of the diabatic heating in determining the mean meridional circulation and the transport of trace constituents is stressed. Perturbation experiments of Haigh and Pyle are repeated in the model including the new schemes. The effect on ozone of increasing CO2 is found to have a stronger latitudinal and seasonal variation. The effect of including chlorofluorocarbons is a larger ozone depletion at all latitudes. The problems associated with assessing the uncertainties in model predictions are discussed. A simple scheme for representing cloud cover in the longwave scheme is described. The effect of inclusion of clouds on heating in the ozone 9·6 μm band, and thus on the ozone distribution, is discussed. The results of changing the effective albedo in the solar heating scheme are considered briefly.