Intercomparison and analyses of the climatology of the West African Monsoon in the West African Monsoon Modeling and Evaluation project (WAMME) first model intercomparison experiment

Abstract

This paper briefly presents the West African Monsoon (WAM) Modeling and Evaluation Project (WAMME) and evaluates WAMME general circulation models' (GCM) performances in simulating variability of WAM precipitation, surface temperature, and major circulation features at seasonal and intraseasonal scales in the first WAMME experiment. The analyses indicate that models with specified sea surface temperature generally have reasonable simulations of the pattern of spatial distribution of WAM seasonal mean precipitation and surface temperature as well as the averaged zonal wind in latitudeheight cross-section and low level circulation. But there are large differences among models in simulating spatial correlation, intensity, and variance of precipitation compared with observations. Furthermore, the majority of models fail 123Clim Dyn (2010) 35:3-27 DOI 10.1007 to produce proper intensities of the African Easterly Jet (AEJ) and the tropical easterly jet. AMMA Land Surface Model Intercomparison Project (ALMIP) data are used to analyze the association between simulated surface processes and the WAM and to investigate the WAM mechanism. It has been identified that the spatial distributions of surface sensible heat flux, surface temperature, and moisture convergence are closely associated with the simulated spatial distribution of precipitation; while surface latent heat flux is closely associated with the AEJ and contributes to divergence in AEJ simulation. Common empirical orthogonal functions (CEOF) analysis is applied to characterize the WAM precipitation evolution and has identified a major WAM precipitation mode and two temperature modes (Sahara mode and Sahel mode). Results indicate that the WAMME models produce reasonable temporal evolutions of major CEOF modes but have deficiencies/ uncertainties in producing variances explained by major modes. Furthermore, the CEOF analysis shows that WAM precipitation evolution is closely related to the enhanced Sahara mode and the weakened Sahel mode, supporting the evidence revealed in the analysis using ALMIP data. An analysis of variability of CEOF modes suggests that the Sahara mode leads the WAM evolution, and divergence in simulating this mode contributes to discrepancies in the precipitation simulation.

Impact of soil moisture initialisation and lateral boundary conditions on regional climate model simulations of the West African Monsoon

“…These strong results support Druyan et al's (2009) comparison of WAMME participating RCMs, which showed HadRM3P achieved particularly high precipitation scores, although the simulated rainfall deficit over the Fouta Djallon and Cameroon highlands remains a common feature in many of these models. Thus, these results provide us with more confidence to use HadRM3P to perform the sensitivity experiments discussed in the following section.…”

“…The objective of the present study is to improve our understanding of the influence of initial SM and lateral boundary conditions (LBCs) on RCM simulations of the WAM climate in the framework of the West African Monsoon Modeling and Evaluation project (WAMME, Xue et al 2009). This is an international initiative in conjunction with the Coordinated Enhanced Observing Period (CEOP) and the African Monsoon Multidisciplinary Analyses project (AMMA; Redelsperger et al 2006), and investigates the role of various forcing feedbacks on the WAM dynamics using state-of-the-art GCM and RCM simulations.…”

Assessment of uncertainties in the response of the African monsoon precipitation to land use change simulated by a regional model

“…Thus land degradation affects the availability of moisture not only through the change in ET, but more importantly, through changes in circulation and moisture transport. A study using the AMMA Land Surface Model Intercomparison Project (ALMIP, Boone et al 2009) data indicated that the ratio of evaporation over precipitation in the West African monsoon area is about 52 % (Xue et al 2010). Another West African climate study with one GCM (Xue 1997) showed that evaporation change accounts for about 53 % of precipitation change after the LULC was changed.…”

“…The African monsoon circulation is forced by the Sahara heat low (Xue et al 2010) and the associated mid-tropospheric high. The former drives cyclonic, near surface moist southwesterly winds from the Gulf of Guinea and the high associated with this heat low in turn drives mid-tropospheric anticyclonic circulation (African Easterly Jet) that transports moisture westward out of the Sahel region into the Atlantic (Hagos and Cook 2008;Hagos and Zhang 2010).…”

A review on regional dynamical downscaling in intraseasonal to seasonal simulation/prediction and major factors that affect downscaling ability

“…Unfortunately, thus far, there have not been many such studies carried out with full scientific rigor. In a model intercomparison project, the West African Monsoon Modeling and Evaluation (WAMME, Xue et al, 2010a;Druyan et al, 2010), both GCMs and RCMs were employed for seasonal simulations. The GCM results in Fig.…”