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On the northward shift of the West African monsoon

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Abstract

The regional climate model (MAR) is used to perform a simulation of the year 1992 over West Africa. It is shown that MAR is able to simulate the main features of the rainy regime over West Africa and especially the discontinuous seasonal progression of the West African Monsoon along the year. One particular feature that is reasonably well reproduced is the abrupt shift of the rain band from 5° to 10°N at the end of June (also called “monsoon jump”). This study suggests that such a phenomenon is associated with the shift of the Saharan heat low between two favourite positions: one being over the Sahelian area (10–15°N) and the other over the Saharan area (20–25°N). These two favourite locations of the heat low are linked to the spatial distribution of surface albedo over West Africa that drives the spatio-temporal location of the surface temperature maxima. A detailed analysis of this “monsoon jump” is performed and the causes of the strong decrease in precipitation that precedes the northward shift of the rain band are also investigated.

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Acknowledgments

All major computations were realised with IDRIS computing resources. The authors thank the NCEP, ECMWF, UDEL institutions for their datasets. The GPCP merged analysis of pentad precipitation is created at the CPC of NOAA. Thanks to Bernard Fontaine and Frederic Hourdin for useful discussions and comments. We also thank the two anonymous reviewers for their help in improving this paper. This research was in part supported by the AMMA international program.

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Authors and Affiliations

  1. Laboratoire des Transferts en Hydrologie et Environnement—Observatoire des Sciences de l’Univers de Grenoble, CNRS-UJF-INPG-IRD, BP 53, 38041 , Grenoble Cedex 9, France

    Romain Ramel & Christophe Messager

  2. Laboratoire de Glaciologie et de Géophysique de l’Environnement—Observatoire des Sciences de l’Univers de Grenoble, CNRS, Grenoble, France

    Hubert Gallée

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  1. Romain Ramel
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  2. Hubert Gallée
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  3. Christophe Messager
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Correspondence to Christophe Messager.

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Ramel, R., Gallée, H. & Messager, C. On the northward shift of the West African monsoon. Clim Dyn 26, 429–440 (2006). https://doi.org/10.1007/s00382-005-0093-5

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  • DOI: https://doi.org/10.1007/s00382-005-0093-5

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