The West African Monsoon (WAM) is characterized by
strong decadal and multi-decadal variability and the impacts can be
catastrophic for the local populations. One of the factors put forward to
explain this variability involves the role of atmospheric dynamics, linked in
particular to the Saharan Heat Low (SHL). This article addresses this question
by comparing the sets of preindustrial control and historical simulation data
from climate models carried out in the framework of the CMIP5 project and
observations data over the 20th century. Through multivariate
statistical analyses, it was established that decadal modes of ocean
variability and decadal variability of Saharan atmospheric dynamics
significantly influence decadal variability of monsoon precipitation. These results also suggest the existence of external anthropogenic forcing, which is superimposed on the decadal natural variability
inducing an intensification of the signal in the historical simulations
compared to preindustrial control simulations. We have also shown that decadal
rainfall variability in the Sahel, once the influence of oceanic modes has been
eliminated, appears to be driven mainly by the activity of the Arabian Heat Low
(AHL) in the central Sahel, and by the structure of the meridional temperature
gradient over the inter-tropical Atlantic in the western Sahel.
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