Parameterization of IR cooling in a middle atmosphere dynamics model: 1. Effects on the zonally averaged circulation

A computationally efficient two‐stream parameterization of IR cooling is developed for a middle atmosphere dynamics model. The parameterization combines the monochromatic feature of an emissivity formulation with the computational simplicity of a single spatial integral to evaluate the monochromatic transfer equation. Our calculations show strong radiative control of the mesopause region (radiative relaxation rate > [5 days]−1) and the need for substantial deceleration of the mean zonal winds (∼40 m s−1 day−1) Calculated temperatures show good agreement in the summer hemisphere where planetary wave activity is negligible, but in the polar night of the winter hemisphere they are ∼30°K too cold which suggests planetary wave heating must make up the deficit. With observed ozone densities our globally averaged radiative equilibrium temperatures in the 65–75 km region are too cold and an additional heat source ∼1°K day−1 is required.