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Fatima Karbou, Florence Rabier, Jean-Philippe Lafore, Jean-Luc Redelsperger, and Olivier Bock

observations. Indeed, the fit of other observations against FGs or analyses is not altered when surface-sensitive temperature or humidity observations are assimilated over land. The fit of the SSM/I and High Resolution Infrared Radiation Sounder (HIRS) observations compared to that the FG is even better than in CTL for EXP4–EXP6, especially over the tropics. These observations are very informative about the humidity in the atmosphere. Figure 5 shows the model fit in terms of bias and standard deviation

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Peter Knippertz and Andreas H. Fink

-level disturbances intruding from the extratropical North Atlantic into the tropics ( Seck 1962 ; Griffiths 1972 ; Borgne 1979 ; Gaye et al. 1994 ; Issar 1995 ; Buckle 1996 ; Leroux 2001 ). Recently, Knippertz and Fink 2008a , hereafter KF08 ) documented a case of an unusual northward penetration of the rain zone into the countries of Ghana, Togo, Benin, and Nigeria in January 2004. Despite their rare occurrence, dry-season wet events can have substantial impacts on the local hydrology and human

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Fatima Karbou, Elisabeth Gérard, and Florence Rabier

minus CTL). For AMA4, the correlations have been improved for all three experiments with respect to CTL. The correlation change varies with surface type and is maximal over snow areas (more than 20% of the improvement in the correlations). The best results are obtained with EXP2 and EXP3 with a mean improvement of 20%–5% from the high latitudes to the tropics. Regarding the AMB2 results, one may notice the large improvement in the correlations between the observations and the simulations in EXP2 and

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O. Bock and M. Nuret

framework of the African Monsoon Multidisciplinary Analyses (AMMA; information online at http://www.amma-international.org ), NWP models thus play a crucial role in many scientific research areas. One of the main objectives of AMMA is that of improving our knowledge of land, ocean, and atmosphere processes and the interactions of the West African monsoon (WAM) system ( Redelsperger et al. 2006 ). The skill of NWP models in predicting rainfall over West Africa, and the tropics in general, is especially

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Anna Agustí-Panareda, Anton Beljaars, Carla Cardinali, Iliana Genkova, and Chris Thorncroft

entrainment and adjustment, vertical diffusion reduction in the free atmosphere, new soil hydrology, and new operational radiosonde temperature and humidity bias correction. Bechtold et al. (2008) showed that the changes in the model physical parameterizations led to an improved precipitation forecast in the short range over the tropics and in particular over West Africa, where the ITCZ shifts northward by approximately 1° ( Agustí-Panareda and Beljaars 2008 ). The AMMA radiosonde humidity bias

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Adrian M. Tompkins and Laura Feudale

1. Introduction In the tropics the sea surface temperature (SST) and its spatial gradients have a significant influence on both local and remote precipitation, documented in both observational studies ( Graham and Barnett 1987 ; Zhang 1993 ) and idealized integrations using cloud-resolving models (e.g., Grabowski et al. 2000 ; Tompkins 2001 ). The thermal inertia and assumed predictability of the SSTs imply that reliable seasonal predictions in the tropics are a realizable aim. This paper

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Benjamin Sultan, Serge Janicot, and Cyrille Correia

variability of convection in other regions of the tropics. Most of these examples concern the prediction of the Madden–Julian oscillation (MJO), which is the dominant oscillatory mode in the tropics ( Madden and Julian 1972 ). Skillful predictions of the MJO have been obtained at a medium lead time (less than 10 days) using either dynamical forecasts or statistical methods. For instance, the National Centers for Environmental Prediction (NCEP) Medium-Range Forecast (MRF) model shows skillful forecasts of

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

, Meteosat, and ECMWF data. Bull. Amer. Meteor. Soc. , 80 , 1045 – 1074 . 10.1175/1520-0477(1999)080<1045:VOTSDP>2.0.CO;2 Krishnamurti, T. N. , Bhaskar J. , Bedi H. S. , and Mohanty U. C. , 2000 : Diabatic effects on potential vorticity over the global tropics. J. Meteor. Soc. Japan , 78 , 527 – 542 . 10.2151/jmsj1965.78.5_527 Montgomery, M. T. , Nichols M. E. , Cram T. A. , and Saunders A. B. , 2006 : A vortical hot tower route to tropical cyclogenesis. J. Atmos. Sci. , 63

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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

TRMM-3B42 and TRMM-3B42RT products provide very close results in the present case. 2 ARPEGE-Tropiques allows the assimilation of more data from the tropics than does the operational ARPEGE NWP system; it is also found to provide better analyses than ARPEGE over West Africa ( Nuret et al. 2007 ). Note that both analyses are much closer to each other than to the ECMWF analysis though. For more information on forecasts over West Africa, see also Lafore et al. (2006) . 3 That is, an initially cloud

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