Better representation of dust can improve climate models with too weak an African monsoon

Abstract

The amount of short wave radiation absorbed by dust has remained uncertain. We have developed a more accurate representation of dust absorption that is based on the observed dust mineralogical composition and accounts for very large particles. We analyze the results from two fully coupled climate simulations of 100 years in terms of their simulated precipitation patterns against observations. A striking benefit of the new dust optical and physical properties is that tropical precipitation over the Sahel, tropical North Atlantic and West Indian Ocean are significantly improved compared to observations, without degrading precipitations elsewhere. This alleviates a common persistent bias in Earth system models that exhibit a summer African monsoon that does not reach far enough north. We show that the improvements documented here for the IPSL-CM61 climate model result from both a thermodynamical and dynamical response to dust absorption, which is unrelated to natural variability. Aerosol absorption induces more water vapor advection from the ocean to the Sahel region, thereby providing an added supply of moisture available for precipitation. This work, thus, provides a path towards improving precipitation patterns in these regions by accounting for both physical and optical properties of the aerosol more realistically.