MMM SEMINAR NCAR
A Revised View of the West
African Monsoon and Its Implications for Interannual
and Interdecadal Variability
Department of
Meteorology
The classic view of the West African
monsoon was created by colonial meteorologists active in forecasting in the
1950s. The basic elements were that rainfall was linked to the Inter-tropical
Convergence Zone but convection was substantially equatorward
of the ITCZ because a certain depth of the moist monsoon layer was required to
sustain deep convective clouds. A new analysis based on NCEP Reanalysis Data
suggests a substantially different picture in which the ITCZ plays little role
in the precipitation process and the major players are the African Easterly Jet,
the Tropical Easterly Jet and a low-level off-equatorial westerly jet. In
most years the ITCZ is completely decoupled from these features. In this study, factors affecting both the
intensity and location of the rains over West Africa are considered. Critical
factors are the pressure gradient over the equatorial
These factors explain both interannual
and interdecadal variability.
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