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Sen Chiao and Gregory S. Jenkins

western African coastline. 5. Discussion and conclusions The forecasting of developing tropical cyclones over the extreme eastern Atlantic remains challenging because of limited observations, the Guinea Highlands, and the interaction between mesoscale convective systems and larger-scale AEWs (2500–3000-km wavelength). Here, we have demonstrated the simulation of the disturbance associated with TD 4 (i.e., TS Debby) using 25- and 5-km grid spacings in the WRF model. This simulation, although not

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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

as the maximum centered on the Nigerian coast. The observed low rainfall amounts over Côte d’Ivoire toward 10°–5°W are captured qualitatively by all simulations. 3. Models, simulations, and outputs The forecasts presented above were obtained with operational global models. Simulations discussed below are performed with mesoscale models. Differences that will be found among them are to be linked to the models that are used, including their parameterizations as well as their initial and boundary

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Ryan D. Torn

via diabatic heating; the strong member grows faster due to a larger vertical gradient in diabatic heating (e.g., Hoskins et al. 1985 ). This result agrees with Hawblitzel et al. (2007) , who showed high correlation between convection and subsequent vorticity in ensemble forecasts of mesoscale convective vortexes (MCVs) over the central United States. Moreover, the surface-based convective available potential energy (CAPE) is similar in both member’s initial conditions (not shown), which

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Adrian M. Tompkins and Laura Feudale

. Climate , 20 , 4014 – 4032 . 10.1175/JCLI4218.1 Taylor, C. M. , Said F. , and Lebel T. , 1997 : Interactions between the land surface and mesoscale rainfall variability during HAPEX-Sahel. Mon. Wea. Rev. , 125 , 2211 – 2227 . 10.1175/1520-0493(1997)125<2211:IBTLSA>2.0.CO;2 Thomson, M. C. , Doblas-Reyes F. J. , Mason S. J. , Hagedorn R. , Connor S. J. , Phindela T. , Morse A. P. , and Palmer T. N. , 2006 : Malaria early warnings based on seasonal climate forecasts from

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

know the processes that govern the interactions on the shorter time scales of a few days and beyond. Satellite images reveal that the development of convective clouds in the Sahel is sensitive to wet surface soil moisture patches ( Taylor and Ellis 2006 ). The mechanisms behind their formation are mesoscale gradients in land surface properties; for example, soil moisture from recent rainfall can induce circulations in the atmosphere, which could lead to subsequent rainfall ( Taylor et al. 2003

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Benjamin Sultan, Serge Janicot, and Cyrille Correia

( Ingram et al. 2002 ), as the occurrence of dry spells can strongly impact yields of rain-fed crops ( Sultan et al. 2005 ). Although there is more and more evidence of specific intraseasonal variability in convective activity during the West African monsoon ( Janicot and Sultan 2001 ; Sultan and Janicot 2003 ; Matthews 2004 ; Mounier and Janicot 2004 ; Mounier et al. 2008 ), no study has investigated its predictability. Nevertheless, there are many examples of skillful forecasts of intraseasonal

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Peter Knippertz and Andreas H. Fink

forecasts? This question is addressed by splitting the composites discussed in section 6a into hits, misses, and false alarms ( section 6b ). 3) Are cases of misforecasts related to problems with predicting the synoptic-scale setting and/or problems with the mesoscale precipitation generation? This question is addressed with composites of differences between ERA-40 60-h forecasts and corresponding ERA-40 reanalysis fields ( section 6c ). Some results in this section are illustrated with short

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O. Bock and M. Nuret

are also extensively used for scientific research, either as large-scale forcings for mesoscale atmospheric simulations in case study experiments or as a full three-dimensional description of the atmospheric and surface parameters for climate research. In this latter case, reanalyses are of special interest since they are produced with a fixed version of an NWP model and the only changes in analysis and forecast performance result from changes in the observations that are assimilated. Within the

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

Multidisciplinary Analysis (AMMA) program, thus yielding the acronym NAMMA for NASA-AMMA. To formulate the genesis problem, we may ask to what extent each of the following areas determines the development or nondevelopment of AEWs: 1) the large-scale environment surrounding the wave, 2) the synoptic-scale wave structure and dynamics, 3) the convective and mesoscale processes and their interactions, and 4) the cloud microphysics, including the impacts of cloud condensation nuclei (CCN) in the form of Saharan

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