Fast Radiation Parameterization Schemes for Mesoscale and Short-Range Forecast Models

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Abstract
Three fast and simple longwave broadband radiation parameterization schemes were tested against a reference narrow-band model in clear sky conditions. The three schemes gave rather similar results. The emissivity dependence on water vapor path length was tuned to give best fit to the reference. The smaller other gas, aerosol and continuum circus were added in a simple fashion both to the radiative cooling and to the longwave downward flux at the surface. Clouds are handled as blackbodies. In the shortwave scheme the attenuation of solar radiation due to variable water vapor and gray clouds, but average ozone and other gas absorption, aerosols and Rayleigh scattering are taken into account and tuned by surface observations of solar flux. The water vapor absorptivity for solar heating was fitted by line-by-line model results. Abstract Three fast and simple longwave broadband radiation parameterization schemes were tested against a reference narrow-band model in clear sky conditions. The three schemes gave rather similar results. The emissivity dependence on water vapor path length was tuned to give best fit to the reference. The smaller other gas, aerosol and continuum circus were added in a simple fashion both to the radiative cooling and to the longwave downward flux at the surface. Clouds are handled as blackbodies. In the shortwave scheme the attenuation of solar radiation due to variable water vapor and gray clouds, but average ozone and other gas absorption, aerosols and Rayleigh scattering are taken into account and tuned by surface observations of solar flux. The water vapor absorptivity for solar heating was fitted by line-by-line model results.

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