An Accurate Radiative Heating and Cooling Algorithm for Use in a Dynamical Model of the Middle Atmosphere

An IR radiative heating and cooling algorithm designed to be used with dynamic models of the middle atmosphere is described. A Curtis matrix is used to compute cooling by the 15- and 10- mu m bands of carbon dioxide. Escape of radiation to space and exchange with the lower boundary are used for the 9.6- mu m band of ozone. Voigt line shape, vibrational relaxation, line overlap, and the temperature dependence of line strength distributions and transmission functions are incorporated into the CO sub(2) Curtis matrices. Radiative damping rates derived from this algorithm give a damping rate of similar to 0.5 day super(-) super(1) for temperature disturbances in the mesosphere of vertical extent 25 km. When this algorithm is used in the dynamic model of Holton and Wehrbein (1980) to calculate the zonal mean circulation of the middle atmosphere, the zonal and meridional circulations generated are nearly twice as strong as those generated in the model of Holton and Wehrbein (1980), which used a Newtonian cooling algorithm based upon the radiation-to-space approximation of Dickinson (1973). Since the zonal circulation calculated with the new radiative algorithm is also stronger than that observed, this result supports the assertion that there is an efficient, but obscure, mechanical damping mechanism in the mesosphere.