The role of carbonaceous aerosols on short-term variations of precipitation over North Africa

Abstract

Subtropical North Africa has been subject to extensive droughts in the late 20th century, linked to changes in the sea surface temperature (SST). However, climate models forced by observed SSTs cannot reproduce the magnitude of the observed rainfall reduction. Here, we propose aerosol indirect effects (AIE) as an important positive feedback mechanism. Model results are presented using two sets of sensitivity experiments designed to distinguish the role of aerosol direct/semi-direct and indirect effects on regional precipitation. Changes in cloud properties due to the presence of carbonaceous aerosols are proposed as a key mechanism to explain the reduced rainfall over subtropical North Africa.