Parameterization of the Optical Properties for Water Clouds in the Infrared

T. H. Lindner Canadian Centre for Climate Modelling and Analysis, Atmospheric Environment Service, University of Victoria, Victoria, British Columbia, Canada

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J. Li Canadian Centre for Climate Modelling and Analysis, Atmospheric Environment Service, University of Victoria, Victoria, British Columbia, Canada

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Abstract

A parameterization is presented for the optical properties of water clouds in the infrared spectrum. The cloud optical properties are parameterized in terms of the cloud’s liquid water content and the effective radius defined from the droplet size distribution. Rational functions are used for the parameterization. The coefficients for the rational functions are derived by doing least square fitting to points calculated by exact Mie theory. The optical properties are presented for 36 individual wavelengths. Also, parameterizations in 12 spectral bands between 4 and 1000 μm are shown. The parameterization is valid for effective radius between 2 and 40 μm. The accuracy of the parameterization is mostly within 5% compared to the exact Mie calculations.

Corresponding author address: Dr. Jiangnan Li, Canadian Centre for Climate Modelling and Analysis, Atmospheric Environment Service, P.O. Box 1700, University of Victoria, Victoria, BC V8P 2Y2, Canada.

Email: Jiangnan.Li@ec.gc.ca

Abstract

A parameterization is presented for the optical properties of water clouds in the infrared spectrum. The cloud optical properties are parameterized in terms of the cloud’s liquid water content and the effective radius defined from the droplet size distribution. Rational functions are used for the parameterization. The coefficients for the rational functions are derived by doing least square fitting to points calculated by exact Mie theory. The optical properties are presented for 36 individual wavelengths. Also, parameterizations in 12 spectral bands between 4 and 1000 μm are shown. The parameterization is valid for effective radius between 2 and 40 μm. The accuracy of the parameterization is mostly within 5% compared to the exact Mie calculations.

Corresponding author address: Dr. Jiangnan Li, Canadian Centre for Climate Modelling and Analysis, Atmospheric Environment Service, P.O. Box 1700, University of Victoria, Victoria, BC V8P 2Y2, Canada.

Email: Jiangnan.Li@ec.gc.ca

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