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

radiosonde network in August 2000 provided the most important source of information for an accurate representation of the African easterly jet (AEJ) in the European Centre for Medium-Range Weather Forecasts (ECMWF) analysis. The aim of this paper is to assess the impacts of the enhanced AMMA radiosonde network on the ECMWF analysis and forecast during August 2006 (i.e., within the peak of the monsoon season). To do this, observational system experiments (OSEs) were performed by comparing two scenarios

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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

bias present in the data is removed, the analysis will be improved. b. Impact on the wind field It is also interesting to study the changes in the wind field, particularly at the level of the African easterly jet (AEJ). It is found that the AEJ changes if the configuration of the radiosonde network is changed. Figure 7 presents the lower boundary of the AEJ (i.e., the zonal wind at 700 hPa). Differences between AMMA and PREAMMA ( Fig. 7 , top right) show an increase in the AEJ on the southeastern

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Adrian M. Tompkins and Laura Feudale

. 1997 ; Eltahir 1998 ), extratropical intrusions ( Roca et al. 2005 ), cloud and aerosol radiative forcing ( Tompkins et al. 2005a ), the African and tropical easterly jets ( Cook 1999 ; Thorncroft et al. 2003 ), and mesoscale organized phenomena such as squall lines and African easterly waves ( Albignat and Reed 1980 ; Diongue et al. 2002 ; Grist 2002 ; Fink and Reiner 2003 ; Mekonnen et al. 2006 ). Representing these interactions poses a particularly demanding challenge for dynamical

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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

also larger (especially to the east in the present case). Overall, these differences in the synoptic structure result in an eastward shift on longitude–time diagrams ( Figs. 20a and 20b ). Convection developed more eastwardly in MNHAT compared to MNHEC; it was also stronger. Generally, comparisons of ECMWF and ARPEGE-Tropiques (or ARPEGE) indicated a reasonable correspondence of the synoptic dynamical structures, from the height of the tropical easterly jet (TEJ) around 200 mb to the height of the

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Benjamin Sultan, Serge Janicot, and Cyrille Correia

significant at the 90% level, are low even for the 1-day time lag. The discrepancy between the model analyses and forecasts has already been shown by Thorncroft et al. (2003) within the context of the JET2000 experiment. The authors found that although the ECMWF analyses were able to accurately represent the characteristics of the African easterly jet in 2000, despite the absence of upper-air observations at this latitude, it was very difficult to see any African easterly jet at all in the ECMWF 5-day

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Sen Chiao and Gregory S. Jenkins

cyclogenesis in close proximity to the African continent ( Zipser and Gautier 1978 ). In this study we will address the following: 1) the structure and evolution of the mesoscale convective system and its connection to TD-4, 2) the impacts of the mesoscale environment (e.g., African easterly Jet, monsoonal flow, dry-air intrusions, and vertical shear associated with the SAL) on the evolution of the MCS–vortex, and 3) the role of the Guinea Highlands in the initiation and/or maintenance of the MCS

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

cyclones that it engulfs but that those tropical cyclones that emerge from its influence can rapidly develop into strong hurricanes. The negative influences on development include increased stability from the low-level temperature inversion, increased vertical wind shear induced by the midlevel African easterly jet (AEJ), and dry air intrusion into the tropical cyclone circulation. Synoptic-scale wave structure and dynamics and their relationship to tropical cyclogenesis have been studied by many

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Ryan D. Torn

Pasch 1992 ). Much of the work to date has focused on understanding the structure, dynamics, and growth mechanisms of these features. In general, AEWs are characterized by a periodicity of between 2 and 5 days ( Burpee 1972 ) and have amplitudes that are peaked at around 650 hPa ( Reed et al. 1977 ). Composite AEW studies and idealized models indicate that AEWs grow via baroclinic and barotropic conversion processes in the region of the African easterly jet (e.g., Reed et al. 1977 ; Thorncroft and

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

: Satellite detection of soil moisture impacts on convection at the mesoscale. Geophys. Res. Lett. , 33 , L03404 . doi:10.1029/2005GL025252 . Taylor, C. M. , Ellis R. J. , Parker D. J. , Burton R. R. , and Thorncroft C. D. , 2003 : Linking boundary-layer variability with convection: A case study from JET2000. Quart. J. Roy. Meteor. Soc. , 129 , 2233 – 2254 . 10.1256/qj.02.134 Taylor, C. M. , Parker D. J. , and Harris P. P. , 2007 : An observational case study of mesoscale

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

Rabier F. , 2010 : Global 4DVAR assimilation and forecast experiments using AMSU observations over land. Part I: Impacts of various land surface emissivity parameterizations. Wea. Forecasting , 25 , 5 – 19 . 10.1175/2009WAF2222243.1 Leroux, S. , and Hall N. M. J. , 2009 : On the relationship between African easterly waves and the African easterly jet. J. Atmos. Sci. , 66 , 2303 – 2316 . 10.1175/2009JAS2988.1 Liebmann, B. , and Smith C. A. , 1996 : Description of a complete

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