On the late northward propagation of the West African monsoon in summer 2006 in the region of Niger/Mali - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Journal of Geophysical Research: Atmospheres Année : 2009

On the late northward propagation of the West African monsoon in summer 2006 in the region of Niger/Mali

Résumé

This paper investigates the fine-scale dynamical processes at the origin of the late northward migration of the monsoon flow in summer 2006 in the region of Niger and Mali (onset on 3 July 2006 compared to the climatological onset date, 24 June). Compared to a 28-year climatology, 2006 NCEP-2 reanalyses show evidence of an anomalous pattern during 10 days between 25 June and 3 July 2006, characterized by the African Easterly Jet (AEJ) blowing from the northeast along a narrow northeast/southwest band located over the Hoggar and Air mountains associated with an unusually strong northeasterly harmattan in the lee of the mountains. Using data collected during the African Monsoon Multidisciplinary Analysis (AMMA) experiment and mesoscale numerical simulations, this study shows evidence of interaction between the AEJ and the orography supported by the reduced gravity shallow water theory which explains the enhancement of the harmattan downstream of the Hoggar and Air mountains in summer 2006. The enhanced harmattan contributes to move southward the intertropical discontinuity (ITD) defined as the interface between the cool moist southwesterly monsoon flow and the warm dry harmattan. Finally, an interaction between the ITD and African Easterly waves contributes to propagate the ITD southward retreat about 1500 km to the west of the Hoggar and Air mountains.
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Dates et versions

hal-00372652 , version 1 (24-02-2016)

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Philippe Drobinski, Sophie Bastin, Serge Janicot, Olivier Bock, Alain Dabas, et al.. On the late northward propagation of the West African monsoon in summer 2006 in the region of Niger/Mali. Journal of Geophysical Research: Atmospheres, 2009, 114 (D9), pp.D09108. ⟨10.1029/2008JD011159⟩. ⟨hal-00372652⟩
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