J. Phys. IV France
Volume 139, December 2006
Page(s) 81 - 99
From Regional Climate Modelling to the Exploration of Venus
C. Boutron
J. Phys. IV France 139 (2006) 81-99

DOI: 10.1051/jp4:2006139007

Dynamics of the West African monsoon

N.M.J. Hall1 and P. Peyrillé2

1  CNRS/LTHE, BP. 53, 38041 Grenoble Cedex 9, France
2  CNRM, Météo France, 42 avenue Gaspard Coriolis, 31057 Toulouse Cedex 01, France

(Published online: 9 January 2007)

A review is given of the dynamical mechanisms responsible for the monsoon circulation over West Africa. Features of the circulation are first described, including the seasonal displacement of the rain bands, the structure of the heat low over the Sahara, the meridional circulation to the south and the associated zonal jets. Simple theories for the zonal-mean meridional circulation are then presented, using the principles of angular momentum conservation, thermal wind balance and moist convective equilibrium. The application of these theories to the West African monsoon reveals a sensitivity to the low-level meridional gradient of equivalent potential temperature, which helps explain observed variability in the monsoon onset. Processes leading to east-west asymmetries in the circulation are also described, and mechanisms linking West African rainfall anomalies with remote events in the tropics are discussed. These dynamical considerations are then placed in the broader context of the ongoing AMMA research program.

© EDP Sciences 2006