Abstract
A 37-year simulation of global climate by a 9-level GCM on an 8°×10° grid showed realistic interannual variation of the computed precipitation over the African Sahel. The model includes an interactive ocean so that interannual variations of sea-surface temperature (SST) also occur. Comparison of an ensemble of five summers that were rainy over the Sahel with five summers of simulated drought showed that insufficient ambient moisture was the immediate cause of the lack of moist convection. The drier conditions are shown to result from weaker moisture advection over the southeast Atlantic Ocean. Weaker southerly winds there and lower sea-level pressure gradients seemed to result from anomalously warm SST. Such SST anomalies have been linked to Sahelian drought in previous observational studies. These regional circulations that were conducive to lower rainfall rates during the north African summer monsoon were not manifestations of the more generalized zonal mean circulation.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Chervin R, Druyan L (1984) The influence of ocean surface temperature gradient and continentality on the Walker circulation. Part I: Prescribed tropical changes. Mon Wea Rev 112:1510–1523
Dennett M, Elston J, Rogers J (1985) A reappraisal of rainfall trends in the Sahel. J Climatol 5:353–361
Druyan L (1982a) Studies of the Indian summer monsoon with a coarse-mesh general circulation model, Part I. J Climatol 2:127–139
Druyan (1982b) Studues of the Indian summer monsoon with a coarse-mesh general circulation model, Part II. J Climatol 2:347–355
Folland C, Palmer T, Parker D (1986) Sahel rainfall and worldwide sea temperatures, 1901–85. Nature 320: 602–607
Hansen J, Russell G, Rind D, Stone P, Lacis A, Lebedeff S, Ruedy R, Travis L (1983) Efficient three-dimensional global models for climate studies: models I and II. Mon Wea Rev 111:609–662
Hansen J, Lacis A, Rind D, Russell G, Stone P, Fung I, Ruedy R, Lerner J (1984) Climate sensitivity: an analysis of feedback mechanisms. Climate Processes and Climate Sensitivity, Geophysical Monograph 29, Maurice Ewing Vol. 5, Amer Geophys Union, 130–162
Kidson J (1977) African rainfall and its relation to the upper air circulation. Quart J R Met Soc 103:441–456
Lamb P (1978) Large-scale tropical Atlantic surface circulation patterns associated with Subsaharan weather anomalies. Tellus 30:240–251
Lough J (1986) Tropical Atlantic sea surface temperatures and rainfall variations in Subsaharan Africa. Mon Wea Rev 114:561–570
Miller J, Russell G, Tsang L (1983) Annual ocean heat transports computed from an atmospheric model. Dyn Atmos Oceans 7:95–109
Newell R, Kidson J (1984) African mean wind changes between Sahelian wet and dry periods. J Climatol 4:27–33
Nicholson S (1980) The nature of rainfall fluctuations in subtropical West Africa. Mon Wea Rev 108:473–487
Nicholson (1981) Rainfall and atmospheric circulation during drought periods and wetter years in West Africa. Mon Wea Rev 109:2191–2208
Stone P, Chervin R (1984) The influence of ocean surface temperature gradient and continentality on the Walker circulation. Part II: Prescribed global changes. Mon Wea Rev 112:1524–1534
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Druyan, L.M. GCM studies of the African summer monsoon. Climate Dynamics 2, 117–126 (1987). https://doi.org/10.1007/BF01054494
Issue Date:
DOI: https://doi.org/10.1007/BF01054494