Solar radiation absorption due to water vapor: Advanced broadband parameterizations

Abstract

Accurate parameterizations for calculating solar radiation absorption in the atmospheric column due to water vapor lines and continuum are proposed for use in broadband shortwave radiative transfer codes. The error in the absorption values is less than 1.5 W m-2 as compared with the values obtained by the line-by-line method for the three standard atmospheres and solar zenith angles of 30° and 75°. The error in the heating rates is less than 0.1 K day-1 at most of the atmospheric levels. The additional absorption of polar radiation due to the water vapor continuum was also estimated. Its magnitude in the total near-infrared region of the solar spectrum is noticeable and reaches 13.0 W m-2 (6.4% from the water vapor absorption in lines) for the tropical atmosphere and solar zenith angle of 30°. Therefore, using of the proposed parameterizations can help to obtain better agreements between the solar radiative fluxes calculated and measured at the earth's surface.