Calculation of longwave radiation fluxes in atmospheres

Abstract

A technique for the computation of longwave radiative quantities using the line‐by‐line approach has been developed in the Soviet Union. The method has been applied to obtain fluxes and cooling rates for standard atmospheric profiles used in the Intercomparison of Radiation Codes Used in Climate Models (ICRCCM) sponsored by the World Meteorological Organization. The sensitivity of the result to changes in the vertical quadrature scheme, the angular integration, and the spectral line shape is evaluated. Fluxes and cooling rates in the troposphere are in general agreement with those obtained with different line‐by‐line models. Results from parameterized models, including a wideband statistical model and one employing the integral transmission function, have been compared to the line‐by‐line results. Flux errors in the simplified schemes are of the order of 10 W/m 2 . The sensitivity of these models to changes in atmospheric profiles, or to an increase in CO 2 amount, is similar to that of the line‐by‐line calculations.