Tropical Cloudiness from All-Sky Cameras on Barbados and Adjacent Atlantic Ocean

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  • 1 Cumulus Group, National Hurricane and Experimental Meteorology Laboratory-NOAA, Coral Gables, Fla. 33124
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Abstract

Analysis of 1885 all-sky photographs was made to objectively determine low, middle, high and total cloud cover. Pictures were taken during each summer of 1963 and 1968 at one location on Barbados, and aboard a research ship east of Barbados. Methods and equipment are described. The relative weight which analysis grids ascribe to overhead and near-horizon clouds is discussed.

Average cloudiness was 52% on Barbados and 35% at sea. Since these years were drier than normal, extrapolation to a normal summer raised the figure by 5% on land and 11% at sea. The total cloudiness on land was due entirely to more low clouds over land than ocean. The 1968 camera site on Barbados was higher than in 1963, and this factor increased 1968 total and low cloudiness. Stratifying data into five disturbance modes based on daily percentage of rainy Barbados stations, low clouds did not change much, while upper cloud increased greatly with mode, and thus total cloud also.

A broad midday maximum of Barbados total and low clouds was found, with sunrise and sunset minima. At sea, low clouds were greatest on disturbed days in early morning. More middle plus high clouds occurred on land and sea during afternoon than morning. Oceanic and upper clouds were strongly dependent on mode.

Previous climatological figures for this area may have overestimated oceanic cloudiness by up to 5%, while island figures agreed with this study.

Abstract

Analysis of 1885 all-sky photographs was made to objectively determine low, middle, high and total cloud cover. Pictures were taken during each summer of 1963 and 1968 at one location on Barbados, and aboard a research ship east of Barbados. Methods and equipment are described. The relative weight which analysis grids ascribe to overhead and near-horizon clouds is discussed.

Average cloudiness was 52% on Barbados and 35% at sea. Since these years were drier than normal, extrapolation to a normal summer raised the figure by 5% on land and 11% at sea. The total cloudiness on land was due entirely to more low clouds over land than ocean. The 1968 camera site on Barbados was higher than in 1963, and this factor increased 1968 total and low cloudiness. Stratifying data into five disturbance modes based on daily percentage of rainy Barbados stations, low clouds did not change much, while upper cloud increased greatly with mode, and thus total cloud also.

A broad midday maximum of Barbados total and low clouds was found, with sunrise and sunset minima. At sea, low clouds were greatest on disturbed days in early morning. More middle plus high clouds occurred on land and sea during afternoon than morning. Oceanic and upper clouds were strongly dependent on mode.

Previous climatological figures for this area may have overestimated oceanic cloudiness by up to 5%, while island figures agreed with this study.

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