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Variations in Nimbus-7 Cloud Estimates. Part II: Regional Changes

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  • 1 Atmospheric Science Unit, Department of Land, Air. and Water Resources, University of California, Davis, California
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Abstract

Regional estimates of low, middle, high, and total cloud amounts derived from bispectral measurements from Nimbus-7 have been analyzed for the six-year period April 1979 through March 1985. Fractional cloud cover for the three height categories was used to calculate a proxy mean cloud-top height. Intra- and interannual standard deviations of total cloud amount and mean cloud height show realistic patterns throughout most of the globe except at very high latitudes. Over much of the cash, intra-annual and interannual variations in total cloud amount are strongly positively correlated with variations in cloud height. Furthermore, both total cloud amount and cloud height variations are moderately correlated with sea surface temperature variations. The strongest correlations are positive in the tropics for both intra-annual and interannual variations. In middle latitudes, moderate negative correlations are positive with intra-annual variations, whereas moderate positive correlations occur on interannual time frames. In the tropics 1°C changes in temperature are statistically related to a change of total cloudiness of at least 2% and a change in cloud height of more than 0.5 km.

Abstract

Regional estimates of low, middle, high, and total cloud amounts derived from bispectral measurements from Nimbus-7 have been analyzed for the six-year period April 1979 through March 1985. Fractional cloud cover for the three height categories was used to calculate a proxy mean cloud-top height. Intra- and interannual standard deviations of total cloud amount and mean cloud height show realistic patterns throughout most of the globe except at very high latitudes. Over much of the cash, intra-annual and interannual variations in total cloud amount are strongly positively correlated with variations in cloud height. Furthermore, both total cloud amount and cloud height variations are moderately correlated with sea surface temperature variations. The strongest correlations are positive in the tropics for both intra-annual and interannual variations. In middle latitudes, moderate negative correlations are positive with intra-annual variations, whereas moderate positive correlations occur on interannual time frames. In the tropics 1°C changes in temperature are statistically related to a change of total cloudiness of at least 2% and a change in cloud height of more than 0.5 km.

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