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Communication Dans Un Congrès Année : 2010

Assessment of water budgets from NWP model analyses and reanalyses over West Africa

Résumé

Water budgets from ECMWF reanalysis ERA-Interim and NCEP reanalysis I and II are inter-compared and compared to GPS precipitable water and to a 6-yr so-called "hybrid" budget dataset composed of ALMIP (AMMA Land surface Model Intercomparison Project) offline simulations forced with TRMM precipitation data. Deficiencies are evidenced in the reanalyses which are the most pronounced over the Sahel. Results from operational models (ECMWF-IFS, NCEP-GFS, and ARPEGE-Tropiques) and the special ECMWF AMMA reanalysis confirm and help understand these findings. A bias (~1-2 mm day-1) in precipitation and evapotranspiration leads to an unrealistic view of West Africa as a moisture source. North of the rainband (13-16°N), moisture flux convergence shows a minimum in the NCEP models and divergence in the ECMWF models not consistent with the hybrid dataset. This feature, added to presence of a deep dry air layer to the north which was advected at mid-levels (800-400 hPa), is thought to block the development of deep convection in the models and the northward propagation of the monsoonal rainband. The northerly flow is part of a shallow meridional circulation that is driven by the Saharan Heat-Low. This circulation appears too strong in some of the models, a possible consequence of the too approximate representation of physical processes and land surface properties over the Sahel. In most of the models, evapotranspiration shows poor connection with precipitation. This is linked with large analysis increments in precipitable water, soil moisture, and moisture flux convergence. Despite the large biases affecting the water budget components in the models, temporal variations (seasonal and inter-annual) might nevertheless be recovered with reasonable accuracy.
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Dates et versions

hal-04115196 , version 1 (02-06-2023)

Identifiants

Citer

O. Bock, Remi Meynadier, F. Guichard, J. Redelsperger, A. Boone, et al.. Assessment of water budgets from NWP model analyses and reanalyses over West Africa. American Geophysical Union Fall Meeting 2010, Dec 2010, San Francisco, United States. pp.abstract id. A53E-0307. ⟨hal-04115196⟩
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