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International Journal of Geophysics
Volume 2012 (2012), Article ID 625831, 17 pages
http://dx.doi.org/10.1155/2012/625831
Research Article

Regional Climate Model Sensitivity to Domain Size for the Simulation of the West African Summer Monsoon Rainfall

1Department of Physics, University of Cape Coast, Cape Coast, Ghana
2Earth System Physics (ESP) Section, International Centre for Theoretical Physics (ICTP), 34151 Trieste, Italy

Received 2 May 2011; Revised 29 August 2011; Accepted 5 November 2011

Academic Editor: Alessandra Giannini

Copyright © 2012 Nana A. K. Browne and Mouhamadou B. Sylla. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

We use the International Centre for Theoretical Physics (ICTP) Regional Climate Model (RegCM3) to study the impact of different domain sizes on the simulation of the West African summer monsoon rainfall and circulation features. RegCM3 simulates drier conditions over the default domain (RegCM-D1) and its westward extension (RegCM-D2), much less dryness over the eastward extended domain (RegCM-D3) and excessive wetness in the domain extended northward into the extratropical regions (RegCM-D4). This overestimation is related to the existence of larger source of humidity due to the inclusion of a more significant portion of the Atlantic Ocean and to a weakening of the African Easterly Jet (AEJ), which both favor stronger westerlies advecting moisture towards the land. The best performance is, however, captured in the RegCM-D3 experiment, and this originates from a simulation of moderate westerly moisture fluxes along with a stronger AEJ and occurrences of more frequent African Easterly Waves (AEWs). Therefore, the choice of the domain for regional climate model simulation of the West African summer monsoon rainfall is of critical importance, and caution needs to be taken to account for the main regional forcings including mostly the necessary humidity sources of the tropical Atlantic Ocean and the AEWs genesis region upstream of Sudanese Highlands.