Understanding the West African Monsoon from the analysis of diabatic heating distributions as simulated by climate models

Gill Martin (1) , P. Peyrillé (2) , R. Roehrig (2) , Catherine Rio (3) , M. Caian (4) , Gilles Bellon (5) , Francis Codron (6) , Jean-Philippe Lafore (2) , D. E. Poan (2) , Abderrahmane Idelkadi (3)

1 MOHC - Met Office Hadley Centre
2 CNRM - Centre national de recherches météorologiques
3 LMD - Laboratoire de Météorologie Dynamique (UMR 8539)
4 SMHI - Swedish Meteorological and Hydrological Institute
5 University of Auckland [Auckland]
6 PARVATI - Processus de la variabilité climatique tropicale et impacts

Vertical and horizontal distributions of diabatic heating in the West African monsoon (WAM) region as simulated by four model families are analyzed in order to assess the physical processes that affect the WAM circulation. For each model family, atmosphere-only runs of their CMIP5 configurations are compared with more recent configurations which are on the development path toward CMIP6. The various configurations of these models exhibit significant differences in their heating/moistening profiles, related to the different representation of physical processes such as boundary layer mixing, convection, large-scale condensation and radiative heating/cooling. There are also significant differences in the models' simulation of WAM rainfall patterns and circulations. The weaker the radiative cooling in the Saharan region, the larger the ascent in the rainband and the more intense the monsoon flow, while the latitude of the rainband is related to heating in the Gulf of Guinea region and on the northern side of the Saharan heat low. Overall, this work illustrates the difficulty experienced by current climate models in representing the characteristics of monsoon systems, but also that we can still use them to understand the interactions between local subgrid physical processes and the WAM circulation. Moreover, our conclusions regarding the relationship between errors in the large-scale circulation of the WAM and the structure of the heating by small-scale processes will motivate future studies and model development.

Domaines: Océan, Atmosphère

Gill Martin, P. Peyrillé, R. Roehrig, Catherine Rio, M. Caian, et al.. Understanding the West African Monsoon from the analysis of diabatic heating distributions as simulated by climate models. Journal of Advances in Modeling Earth Systems, 2017, 70, pp.1297 - 1297. ⟨10.1002/2016MS000697⟩. ⟨hal-01507050⟩