Parameterization of the Radiative Properties of Clouds

Kuo-Nan Liou Department of Meteorology, University of Utah, Salt Lake City 84112

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Gerard D. Wittman Department of Meteorology, University of Utah, Salt Lake City 84112

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Abstract

Reflection, transmission and absorption of solar radiation by four cloud types (low cloud, middle cloud, high cloud and stratus) are computed as functions of the solar zenith angle and cloud liquid water/ice content. The reflection, transmission and emission of infrared radiation by cirrus clouds are calculated as functions of the cloud ice content. The plane-parallel radiative transfer program employed is based on the discrete-ordinate method with applications to inhomogeneous atmospheres covering the entire solar and infrared spectra and taking into account the gaseous absorption in scattering atmospheres. The resulting values of the solar radiative properties of clouds are fitted with known mathematical functions involving the solar zenith angle and cloud liquid water/ice content as variables. Effects of the atmospheric profile are discussed and the effects of surface reflectivity on the solar radiative properties of clouds are parameterized in terms of the water vapor absorbtivity below the cloud, ground reflection and average cloud reflection. Parameterized equations for the infrared flux reflectivity, transmissivity and emissivity of cirrus clouds are also presented as functions of the cloud ice content.

Abstract

Reflection, transmission and absorption of solar radiation by four cloud types (low cloud, middle cloud, high cloud and stratus) are computed as functions of the solar zenith angle and cloud liquid water/ice content. The reflection, transmission and emission of infrared radiation by cirrus clouds are calculated as functions of the cloud ice content. The plane-parallel radiative transfer program employed is based on the discrete-ordinate method with applications to inhomogeneous atmospheres covering the entire solar and infrared spectra and taking into account the gaseous absorption in scattering atmospheres. The resulting values of the solar radiative properties of clouds are fitted with known mathematical functions involving the solar zenith angle and cloud liquid water/ice content as variables. Effects of the atmospheric profile are discussed and the effects of surface reflectivity on the solar radiative properties of clouds are parameterized in terms of the water vapor absorbtivity below the cloud, ground reflection and average cloud reflection. Parameterized equations for the infrared flux reflectivity, transmissivity and emissivity of cirrus clouds are also presented as functions of the cloud ice content.

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