Representation of the west african water cycle by the LMDZ GCM during the AMMA campaign

Abstract

The AMMA program deployed an important number of observations in west Africa region during a several year with a focus on the wet season of 2006. The LMDZ General Circulation Model is used in the nudging version with Re-analysis. Some statistical tools, FAR, POD, correlation and the modele-to-satellite approach are used to evaluate the day to day variability of water cycle. Sensitivity experiments have been performed in order to highlight the behaviour of the nudged model under a wide range of conditions: spatial and vertical resolution, surface scheme formulation as well as for the forcing and driving parameters: relaxation time, type of analysis (ECMWF, NCEP/GFS), Sea Surface Temperature (climatology vs. 2006) and the nudging variables (wind, temperature, and combination). The evaluation shows that the LMDZ GCM captures fairly well the mean West african monsoon features with a good localization of the ITCZ and overestimates the free troposphere humidity. The sensitivity of the physical parametrization shows an important difference between the region of Dakar influenced by the large scale oceanic circulation and the region of Niamey where the parametrization of convection determines the monsoon variability.A case study of dry intrusion during AMMA SOP3 (Special Observing Period) highlights the inhibiting role of this dry air mass in the Dakar region.