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Journal Article: ID no. (ISBN etc.):  1477-870X BibTeX citation key:  Couvreux2009a
Couvreux, F., Guichard, F., Bock, O., Campistron, B., Lafore, J.-P. & Redelsperger, J.-L. (2009) Synoptic variability of the monsoon flux over West Africa prior to the onset. IN Quarterly Journal of the Royal Meteorological Society, 136. 159–173.
Added by: Fleur Couvreux 2009-09-17 08:29:52    Last Edited by: Fanny Lefebvre 2010-11-17 16:02:23
Categories: Atmospheric processes
Keywords: Atmospheric Boundary Layer
Creators: Bock, Campistron, Couvreux, Guichard, Lafore, Redelsperger
Collection: Quarterly Journal of the Royal Meteorological Society
Bibliographies: cnrm, Prior150410

Peer reviewed
Number of views:  1031
Popularity index:  52.63%
Maturity index:  accepted

This study investigates the synoptic variability of the monsoon flux during the establishment of the West African monsoon using observations and ECMWF analyses. It highlights variability at a 3–5-day time scale, characterized by successive northward excursions of the monsoon flux. Their characteristics and climatology prior to the monsoon onset are presented. These penetrations follow a maximum of intensity of the heat-low (extension and minimum of pressure) and are concomitant with an acceleration of the low-level meridional wind. Some penetrations are stationary whereas others propagate westward simultaneously with African easterly waves. Both types are investigated in more detail by casestudies.
This enables us to distinguish the boundary-layer mechanisms involved in such penetrations. A similar conceptual model holds for both. It is argued that the heat-low dynamics is a major driver of these synoptic penetrations, pointing to the predominantly continental nature of this phenomenon. In turn, the heat-low can be partitioned by the penetrations.
Horizontal advection is the main process that eventually accounts for these surges; nevertheless, turbulent mixing also plays a significant role by vertically redistributing moisture, and in more subtle ways by its contribution to the shaping of the low-level synoptic environment within which the surges take place.
Added by: Fleur Couvreux    Last Edited by: Fanny Lefebvre