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

Yves Balkanski,Olivier Boucher,Rémy Bonnet,Ramiro Checa-Garcia,Jérôme Servonnat

doi:10.5194/acp-21-11423-2021

Abstract

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.

Highlights

Mineral dust influences precipitation through aerosol– radiation interactions (Miller et al, 2014), changing the vertical temperature profile, and is an efficient ice nucleus in the presence of feldspar (Atkinson et al, 2013), producing an indirect, cloud-mediated radiative perturbation
We show here how a better representation of dust aerosols leads to an unequivocal improvement in the simulation of precipitation over key climatic tropical regions in the IPSL-CM6 model, namely in the Sahel, tropical North Atlantic and West Indian Ocean, without degrading precipitation elsewhere around the globe, and we subsequently discuss the thermodynamically and dynamically driven mechanisms at play that affect the water cycle
To complete the analysis of the possible mechanisms that may have explained this improvement in the Sahel precipitation, we examined whether a different phasing of the Atlantic multidecadal variability (AMV; Enfield et al, 2001), a basinwide, low-frequency variation in the sea surface temperature over the North Atlantic, could be responsible for reproduc

Summary

Introduction

Mineral dust influences precipitation through aerosol– radiation interactions (Miller et al, 2014), changing the vertical temperature profile, and is an efficient ice nucleus in the presence of feldspar (Atkinson et al, 2013), producing an indirect, cloud-mediated radiative perturbation. It influences the water cycle through microphysical interactions with clouds (Nenes et al, 2014). We show here how a better representation of dust aerosols leads to an unequivocal improvement in the simulation of precipitation over key climatic tropical regions in the IPSL-CM6 model, namely in the Sahel, tropical North Atlantic and West Indian Ocean, without degrading precipitation elsewhere around the globe, and we subsequently discuss the thermodynamically and dynamically driven mechanisms at play that affect the water cycle

Methods

Results

Discussion

Conclusion