Diurnal variations and modulation by easterly waves of the size distribution of convective cloud clusters over West Africa and the Atlantic Ocean

Journal Article · Fri Jan 01 00:00:00 EST 1993 · Monthly Weather Review; (United States)

DOI:https://doi.org/10.1175/1520-0493(1993)121<0037:DVAMBE>2.0.CO;2· OSTI ID:6729894

Machado, L A.T.; Duvel, J Ph; Desbois, M ^[1]

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1. Ecole Polytechnique, Palaiseau (France)

Short time-scale fluctuations of the size distribution of tropical convective cloud clusters for July to September 1989 were studied using Meteosat data. A cluster at a given brightness-temperature threshold was defined as the area covered by adjacent cloudy pixels with brightness temperature lower than the threshold. The clusters were classified according to the area covered and the position of their center of mass. Over land regions of West Africa the size distribution underwent a coherent diurnal behavior with development of small cells between noon and 1500 LST. Over the Atlantic Ocean, the highest cloudiness had a weak maximum extent in early morning, while cloudiness at lower levels was more extended in the afternoon. This diurnal behavior was primarily due to large cloud clusters, suggesting that the diurnal variation over the ocean resulted from internal variations of large convective systems and not from the initiation of convection at a given hour of the day. This was confirmed by the analysis of 15 large convective systems propagating over the ocean. The authors have ascertained that the high cloud cover was maximized within the trough of eastrly waves. The cluster size was dependent upon the wave amplitude with a larger mean cluster size when the amplitude was largr. The trough phase of the wave was found to promote the development of large clusters more than it favored the initial stage of convection. 30 refs., 11 figs.

• OSTI ID: 6729894
• Journal Information: Monthly Weather Review; (United States), Vol. 121:1; ISSN 0027-0644
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
CLOUDS
DISTRIBUTION
GENERAL CIRCULATION MODELS
EVALUATION
AFRICA
ATLANTIC OCEAN
ATMOSPHERIC CIRCULATION
CLOUD COVER
COMPILED DATA
CONVECTION
INFRARED RADIATION
SATELLITES
TIME DEPENDENCE
TROPICAL REGIONS
DATA
ELECTROMAGNETIC RADIATION
ENERGY TRANSFER
HEAT TRANSFER
INFORMATION
MASS TRANSFER
MATHEMATICAL MODELS
NUMERICAL DATA
RADIATIONS
SEAS
SURFACE WATERS
540110*