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Communication incl. Poster: BibTeX citation key:  Peyrillea
Peyrillé, P., Boone, A. & Lafore, J.-P. 2009. Analysis of the land surface-atmosphere coupling in West Africa using a two-dimensional model. Work presented at Third International AMMA Conference, July 20—24, at Ouagadougou, Burkina Faso.
Last Edited by: Deleted user 2009-09-04 14:06:38
Categories: Atmospheric processes, Land surface-atmosphere feedback, Monsoon system and its variability
Keywords: Atmospheric Boundary Layer
Creators: Boone, Lafore, Peyrillé
Publisher: African Monsoon Multidisciplinary Analyses (Ouagadougou, Burkina Faso)
Collection: Third International AMMA Conference

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The West African Monsoon (WAM) is a coupled ocean-continent-atmosphere system that experiences a strong spatio-temporal variability. The total rainfall or the date on the rainfall onset are difficult to forecast, even at short timescales. This is certainly due to the numerous interactions occurring at the heart on the WAM. One of the key factors modulating the WAM is the evolution the Atlantic sea Surface temperature, but other factors might influence the monsoon activity such as large-scale advection from the ocean, waves or the different couplings with the continental land surface. In particular, numerical studies have recently shown that the inclusion of vegetation-atmosphere interactions leads to a better representation of the inter-decadal WAM variability. However, there are not many studies dealing with the the role of vegetation at shorter timescales: it is not clear whether rainfall dictates the evolution of vegetation, or vegetation dynamics also interact with the atmosphere.
To address this question, an important issue is the determination of a suitable framework. Global or regional scale climate models are a logical choice, but the complexity of the interactions they represent are sometimes difficult to interpret, not to mention the associated computing expense for performing many sensitivity tests. Data analysis is another option, however it suffers from a low density over this region. An alternative approach is to consider simpler models containing less degrees of freedom. In that sense, we use an idealized meridional-vertical (2D) model which is sufficient to describe the major features of the WAM. Of particular interest is the effect of the vegetation dynamics and coupling on the monsoon jump and propagation, and rainfall intensity. The other aspect is to determine the key processes occurring at the annual timescale.
The main conclusion is that the coupling favors the monsoon inland penetration. Vegetation extends further north during the monsoon and further south during pre-onset (compared to the default climatology). These changes enhance low level equivalent potential temperature gradients during pre-WAM onset and favor larger humidity advection. However the role of vegetation interactions is modulated depending on the strength of large-scale conditions (advective forcing in this study). The coupling seems to give more precipitation after July in each case but the AMJ period is sensitive to the forcing. That may imply a different mechanism for the monsoon onset or at least a different equilibrium of the contributing processes. Perspectives for ongoing work are also presented.
Last Edited by: Deleted user