Vol. 11, issue 08, article # 10

Zhuravleva T.B. Influence of clouds on the absorption of short-wave radiation in the atmosphere. Part 2. Ratio of radiative forcings at the top of the atmosphere to those at the underlying surface. // Atmospheric and oceanic optics. 1998. V. 11. No. 08. P. 737-743.
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Abstract:

Two approaches are proposed to determine the ratio r of radiative forcings at the top of the atmosphere (TOA) to that at the underlying surface (short-wave radiation). According to the regression approach to r determination, random cloud geometry has little effect on the ratio of radiative forcings. The other approach assumes that r depends not only on the absorption change due to occurrence of clouds in the clear atmosphere, but also on the associated albedo variations at TOA. For this reason, the r difference between cumulus and stratus clouds, while being small at low surface albedo As ≤ 0.2, may increase by tens of per cent as As increases for optically thin clouds and (or) small cloud fractions at the solar zenith angle ≤ 30°. After the ratio of radiative forcings is averaged over the entire set of cloud optical and geometrical characteristics, the dependence of r on cloud type becomes much weaker. Also studied in this paper is the question on how accurately does the ratio of radiative forcings represent actual cloud absorption.

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