On the decadal scale correlation between African Dust and Sahel rainfall: the role of Saharan heat Low-forced winds
Résumé
A large body of work has shown that year-to-year variations in North African dust emission are inversely proportional to previous year monsoon rainfall in the Sahel, implying that African dust emission is highly sensitive to vegetation changes in this narrow transitional zone. However, such a theory is not supported by field observations or modeling studies, as both suggest that interannual variability in dust is due to changes in wind speeds over the major emitting regions, which lie to the north of the Sahelian vegetated zone. Here we reconcile this contradiction showing that interannual variability in Sahelian rainfall, and surface wind speeds over the Sahara, are the result of changes in lower tropospheric air temperatures over the Saharan Heat Low (SHL). As the SHL warms an anomalous tropospheric circulation develops that reduces windspeeds over the Sahara and displaces the monsoonal rainfall northward, thus simultaneously increasing Sahelian rainfall and reducing dust emission from the major dust “hot-spots” in the Sahara. Our results shed light on why climate models are, to-date, unable to reproduce observed historical variability in dust emission and transport from this region.
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