Observed and model-simulated intraseasonal wam variability for the 2005 rainy season

Instantaneous (i.e, 15-minutes) rainfall intensities, as derived from a multi-sensor precipitation estimation approach, involving geostationary (MSG) and polar (SSMI) satellite data, are used to investigate the dynamical mechanisms driving the African warm season precipitation episodes, and to evaluate the capability of a Regional Atmospheric Modelling System (RAMS) to reproduce this variability for the Sahelian area. Coherent precipitation patterns are presented for the 2005 rainy season, from June to August, with emphasis on a qualitative and quantitative inspection of intraseasonal variability of the West Africa Monsoon (WAM), investigating the longitudinal distribution of rainfall and the zonal component of motion. We also analyzed the periodicity and phase of precipitation within and beyond the diurnal cycle. Consistent with previous studies, the pattern of the diurnal cycle of summer precipitation is characterized by afternoon maxima, initiated mainly over the African highlands (Jos Plateau, Darfur, Ethiopian highlands). Furthermore, a Regional Reanalysis strategy has been developed based on RAMS model forced by NCEP/NCAR Reanalysis. The RAMS better physical description, with respect to the NCEP/NCAR dataset, along with its higher spatial resolution (50km), provide a coherent and reliable atmospheric dataset especially for what concerns surface-atmosphere interaction governing monsoon dynamics. Diurnal precipitation patterns, produced by RAMS model, are investigated and compared with those obtained by MSG-based algorithm. Some guidelines, used on model setup, are presented as well. Statistical skill scores (POD, FAR, etc.), based on 3-hourly NOAA CMORPH rainfall data, have been evaluated to assess the reliability of this method for