West African Monsoon observed with ground-based GPS receivers during African Monsoon Multidisciplinary Analysis (AMMA)

Olivier Bock (1, 2) , Marie-Noëlle Bouin (2) , E. Doerflinger (3) , P. Collard (3) , F. Masson (4) , Rémi Meynadier (1) , Samuel Nahmani (2) , M. Koité , K. Gaptia Lawan Balawan , Francis Didé , D. Ouedraogo , S. Pokperlaar , Jean-Blaise Ngamini , Jean-Philippe Lafore (5) , Serge Janicot (6) , Françoise Guichard (5) , Mathieu Nuret (5)

1 SA - Service d'aéronomie
2 LAREG - LAboratoire de Recherche en Géodésie
3 Géosciences Montpellier
4 IPGS - Institut de physique du globe de Strasbourg
5 CNRM - Centre national de recherches météorologiques
6 LOCEAN - Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques

The impact of stratospheric ozone on the tropospheric general circulation of theSouthern Hemisphere (SH) is examined with a set of chemistry‐climate models participatingin the Stratospheric Processes and their Role in Climate (SPARC)/Chemistry‐ClimateModel Validation project phase 2 (CCMVal‐2). Model integrations of both the past andfuture climates reveal the crucial role of stratospheric ozone in driving SH circulationchange: stronger ozone depletion in late spring generally leads to greater polewarddisplacement and intensification of the tropospheric midlatitude jet, and greater expansion ofthe SH Hadley cell in the summer. These circulation changes are systematic as polewarddisplacement of the jet is typically accompanied by intensification of the jet and expansion ofthe Hadley cell. Overall results are compared with coupled models participating in theIntergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4), andpossible mechanisms are discussed. While the tropospheric circulation response appearsquasi‐linearly related to stratospheric ozone changes, the quantitative response to a givenforcing varies considerably from one model to another. This scatter partly results fromdifferences in model climatology. It is shown that poleward intensification of the westerly jetis generally stronger in models whose climatological jet is biased toward lower latitudes.This result is discussed in the context of quasi‐geostrophic zonal mean dynamics.

Mots clés: AMMA; GPS; West African Monsoon

Domaines: Climatologie; Milieux et Changements globaux

Olivier Bock, Marie-Noëlle Bouin, E. Doerflinger, P. Collard, F. Masson, et al.. West African Monsoon observed with ground-based GPS receivers during African Monsoon Multidisciplinary Analysis (AMMA). Journal of Geophysical Research: Atmospheres, 2008, 113 (D21), pp.D21105. ⟨10.1029/2008JD010327⟩. ⟨hal-00337060⟩