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Françoise Guichard, Nicole Asencio, Christophe Peugeot, Olivier Bock, Jean-Luc Redelsperger, Xuefeng Cui, Matthew Garvert, Benjamin Lamptey, Emiliano Orlandi, Julia Sander, Federico Fierli, Miguel Angel Gaertner, Sarah C. Jones, Jean-Philippe Lafore, Andrew Morse, Mathieu Nuret, Aaron Boone, Gianpaolo Balsamo, Patricia de Rosnay, Bertrand Decharme, Philip P. Harris, and J.-C. Bergès

(PROMES) model; the Met Office Unified Model (MOUM); and the Weather Research and Forecasting (WRF) model. We also include below the results from the global ECMWF Integrated Forecast System (IFS) run in operational mode. This model is of interest in the present study (i) because it has a high spatial resolution of approximately 0.25° × 0.25° in the horizontal and (ii) because it was used to generate initial and boundary conditions for the mesoscale model intercomparison presented in section 5 . Note

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Xuefeng Cui, Douglas J. Parker, and Andrew P. Morse

surface evaporation, and other processes (see, e.g., Eltahir 1998 ). Wallace and Holwill (1997) have indicated that in the vicinity of Niamey most of the evaporation occurs during the first day directly after rain. Currently, it is not realistic to ask the operational NWP models to represent this type of feedback in terms of precipitation forecasting in West Africa as the diurnal variation of the atmospheric boundary layer in this area is complex ( Parker et al. 2005 ). However, it is important to

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Ryan D. Torn

inflation standard deviation of 0.1; after approximately 5 days, the inflation factor for each state variable reaches an equilibrium value. Ensemble initial and boundary conditions for this North Africa domain are taken from a comparable parent ensemble data assimilation system cycled over a larger domain. This parent ensemble has 108-km horizontal resolution and extends from the western United States to India and from northern Europe to South Africa; all other model settings are the same as in the

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Sen Chiao and Gregory S. Jenkins

portion of the Atlantic (6°–18°N, 23°–6°W). All simulations used the same initial and lateral boundary conditions, which are generated from the National Center for Atmospheric Research (NCEP) Global Forecasting System (GFS) 180-h forecasts with boundary conditions, updated every 3 h at 1° × 1° resolution. The forecast for domain 1 was initialized at 0000 UTC 19 August 2006, and domain 2 was initialized at 0600 UTC, which included enough model spinup time to adapt to the strong diurnal cycle. Both

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Adrian M. Tompkins and Laura Feudale

the seasonal rainfall anomaly for the Sahel region from 10° to 20°N and 10°W to 10°E ( Fig. 4a ) reveals apparent limited ability to predict JAS rainfall from the 1 May start date, with positive anomalies predicted in many of the drought years, including 1983 and 1984. It is notable that in the latter years the model is able to reproduce an upward trend in rainfall that was also observed, while the general change from wet to drought conditions from the 1960s to the 1980s was not reproduced. If the

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C. Faccani, F. Rabier, N. Fourrié, A. Agusti-Panareda, F. Karbou, P. Moll, J.-P. Lafore, M. Nuret, F. Hdidou, and O. Bock

1. Introduction The African Monsoon Multidisciplinary Analysis (AMMA) is an international project focused on the study of the African monsoon ( Redelsperger et al. 2006 ). Rainfall changes during this particular period of the year are important to the people living in the monsoon areas. As a matter of fact, over the last few decades, West Africa experienced abundant rainfall during the 1950s and 1960s, and very dry conditions between the 1970s and 1990s. The environmental and socioeconomical

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Robert S. Ross, T. N. Krishnamurti, S. Pattnaik, and A. Simon

factors constitute the necessary and sufficient conditions for development, assuming that the large-scale environment within which the wave is embedded is not hostile. Another conclusion was that baroclinic energy conversion was not a clear and definitive factor that could explain either the development or nondevelopment of the waves studied. A quick accounting of all seven NAMMA waves using 700-hPa wind flow gave a favorable confirmation of the conclusions concerning the role and nature of barotropic

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Peter Knippertz and Andreas H. Fink

into the continent. This is clearly indicated by the northward shift of the 14°C contour of TD2M (thick lines in Fig. 2a ) that is often used as an indicator for the position of the intertropical discontinuity (ITD), the boundary between dry Saharan and moist tropical air over West Africa ( Buckle 1996 ). A maximum MSLP anomaly of −8 hPa with respect to the long-term February mean is analyzed over northern Niger near 20°N, 10°E (not shown). Nine hours later, CLAUS BTs show a TP along the

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O. Bock and M. Nuret

biases, depending on the type and age of the sondes, and on the environmental conditions of use ( Wang et al. 2002 ). Since radiosonde data are assimilated into NWP models, their biases can be transferred to the NWP model analyses and can impact subsequent forecasts ( Andersson et al. 2005 , 2007 ; Bock et al. 2007 ). Both dry and wet biases have been evidenced in the AMMA radiosonde network operated during summer 2006 using the GPS PWV estimates ( Bock et al. 2008a ). In the present work we extend

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