An Earth Outgoing Longwave Radiation Climate Model. Part I: Clear Sky Radiation

Abstract

An Earth outgoing longwave radiation (OLWR) climate model has been constructed for a monthly average radiation budget study. The model consists of the upward radiative transfer parameterization of Thompson and Warren and a monthly average climatology defined by the data from Crutcher and Meserve and Taljaard et al. Additional required information is provided by the empirical 100-mb water vapor mixing ratio equation of Harries and the mixing ratio interpolation scheme of Briegleb and Ramanathan. Clear sky cases are calculated and discussed for the global average, zonal averages and global distributions. The results agree well with some satellite observations. The clear-sky case shows that the OLWR field is highly modulated by water vapor, especially in the tropics, where the strongest longitudinal variations in OLWR occur. These variations can be primarily explained by the strong water vapor gradient. Although in the zonal-average case the tropics have a minimum of OLWR, the minimum is essentially contributed to by a few very low flux regions, such as the Amazon, Indonesia and the Congo. There are regions in the tropics such that their OLWR is as large as that of the subtropics. In the high latitudes where cold air contains less water vapor, OLWR is basically modulated by the surface temperature.