Understanding the mechanisms behind the northward extension of the West African Monsoon during the Mid-Holocene

Abstract : Understanding the West African monsoon (WAM) dynamics in the mid-Holocene (MH) is a crucial issue in climate modelling, because numerical models typically fail to reproduce the extensive precipitation suggested by proxy evidence. This discrepancy may be largely due to the assumption of both unrealistic land surface cover and atmospheric aerosol concentration. In this study, the MH environment is simulated in numerical experiments by imposing extensive vegetation over the Sahara and the consequent reduction in airborne dust concentration. A dramatic increase in precipitation is simulated across the whole of West Africa, up to the Mediterranean coast. This precipitation response is in better agreement with proxy data, in comparison with the case in which only changes in orbital forcing are considered. Results show a substantial modification of the monsoonal circulation, characterized by an intensification of large-scale deep convection through the entire Sahara, and a weakening and northward shift (~6.5°) of the African easterly jet. The greening of the Sahara also leads to a substantial reduction in African easterly wave activity and the associated precipitation. The reorganization of the regional atmospheric circulation is driven by the vegetation effect on radiative forcing and associated heat fluxes, with the reduction in dust concentration to enhance this response. The results for the WAM in the MH present important implications for understanding future climate scenarios in the region and in teleconnected areas, in the context of projected wetter conditions in West Africa.
Type de document :
Article dans une revue
Journal of Climate, American Meteorological Society, 2017, 30 (19), pp.7621-7642. 〈10.1175/JCLI-D-16-0299.1〉
Liste complète des métadonnées

Littérature citée [40 références]  Voir  Masquer  Télécharger

https://hal-insu.archives-ouvertes.fr/insu-01545606
Contributeur : Catherine Cardon <>
Soumis le : mardi 27 juin 2017 - 12:16:46
Dernière modification le : mardi 29 mai 2018 - 12:51:08
Document(s) archivé(s) le : mercredi 17 janvier 2018 - 21:21:10

Fichier

jcli-d-16-0299.1.pdf
Fichiers produits par l'(les) auteur(s)

Identifiants

Collections

Citation

Marco Gaetani, Gabriele Messori, Qiong Zhang, Cyrille Flamant, Francesco S. R. Pausata. Understanding the mechanisms behind the northward extension of the West African Monsoon during the Mid-Holocene. Journal of Climate, American Meteorological Society, 2017, 30 (19), pp.7621-7642. 〈10.1175/JCLI-D-16-0299.1〉. 〈insu-01545606〉

Partager

Métriques

Consultations de la notice

193

Téléchargements de fichiers

114