Computation of infrared cooling rates in the water vapor bands

A fast and accurate method is developed for calculating the infrared radiative terms due to water vapor - specifically, the atmospheric cooling rates. The accuracy is achieved by avoiding the constraints of band models and working directly with the absorption coefficient, which is a function of temperature and pressure as well as wavenumber. The method is based on calculation of an equivalent water vapor amount between atmospheric pressure levels and a table look-up procedure. Compared to line-by-line calculations, the present method has errors up to 4% of the maximum cooling rate. The use of a scaling factor, based on the far-wing approximation, limits the applicability of the method to the troposphere and lower stratosphere, where the line wings are responsible for most of the radiative cooling associated with water vapor.