Vol. 11, issue 08, article # 9

Abstract:

Influence of the effects caused by random cloud geometry on the mean shortwave absorption in a cloud layer and in the entire atmosphere is studied. It is shown that the spectral absorption in broken clouds depends strongly both on the cloud type (cumulus or stratus) and on the cloud layer position in space. In the optically dense cumulus clouds the integrated absorption is a nonmonotonic function of a solar zenith angle, whereas in the stratus clouds it decreases with increasing ξ. The difference between the absorption by cumulus and stratus clouds is maximum at ξ≥ 60° and reaches about 4% for optically dense clouds. The integrated absorption in the atmosphere A_atm is sensitive to the cloud top height and depends only slightly on cloud layer geometrical thickness. Typically, variations of the absorption A_atm by different cloud types do not exceed 1%; however, they increase up to 2-3% for intermediate cloud fractions in optically dense low-level clouds (≈60°) and optically thin middle-level clouds (≥ 75°).