An Efficient Method for Computing the Absorption of Solar Radiation by Water Vapor

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  • 1 Laboratory for Atmospheric Sciences, Goddard Space Flight Center, Greenbelt, MD 20771
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Abstract

An efficient method has been developed to compute the absorption of solar radiation by water vapor. The method is based on the molecular line parameters compiled by McClatchey et al. (1973) and makes use of the far-wing scaling approximation and k-distribution approach previously applied by Chou and Arking (1980) to the computation of the infrared cooling rates. The entire near-IR spectrum between 0.83 and 4 μm is treated as one region with the effect of the variation of the incoming solar flux with wavenumber incorporated into precomputed functions. For clear atmospheres, the solar fluxes are computed from a table in which the scaled water vapor amount is the independent variable. For cloudy atmospheres, the k-distribution method is used. Using the line-by-line method as a standard, the maximum error introduced by this method is ∼4% of the peak heating rate. The present method has the additional advantage over previous methods in that it can be applied to any portion of the spectral region containing the water vapor bands.

Abstract

An efficient method has been developed to compute the absorption of solar radiation by water vapor. The method is based on the molecular line parameters compiled by McClatchey et al. (1973) and makes use of the far-wing scaling approximation and k-distribution approach previously applied by Chou and Arking (1980) to the computation of the infrared cooling rates. The entire near-IR spectrum between 0.83 and 4 μm is treated as one region with the effect of the variation of the incoming solar flux with wavenumber incorporated into precomputed functions. For clear atmospheres, the solar fluxes are computed from a table in which the scaled water vapor amount is the independent variable. For cloudy atmospheres, the k-distribution method is used. Using the line-by-line method as a standard, the maximum error introduced by this method is ∼4% of the peak heating rate. The present method has the additional advantage over previous methods in that it can be applied to any portion of the spectral region containing the water vapor bands.

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