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Accurate global cloud information is required for many climate studies, particularly for validation of climate model simulations. This paper reviews the cloud climatologies currently available, identifying and attempting to explain the differences between various global cloud assessments. The two types of cloud observations used to construct a cloud climatology, conventional surface observations and satellite-derived observations, are contrasted. Meridional profiles of zonally-averaged total cloud amount and the geographic distribution of total cloud amount from 17 cloud data sets are compared. There is at present no unique and/or agreed global cloud climatology. This review emphasizes the uncertainty and inaccuracies associated with the present knowledge of the global cloud distribution. Cloud climatologies constructed from either surface or satellite cloud observations will not be identical. The range of cloud amount available from current cloud climatologies must be noted by all users of global cloud data sets.
N. A. Hughes (Tue,) studied this question.