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formation of a secondary upwelling along the continental margin
Yves Morel, Vincent Rossi, Veronique Garcon
SHOM
(Abstract received 03/28/2009 for session X)
ABSTRACT
This work has been done by Vincent Rossi, PhD supervised by Veronique garcon and Yves Morel. We have studied the influence of the wind on the dynamics of the continental shelf and margin, in particular the formation of a secondary upwelling (or downwelling) front along the shelf-break. Observations during the MOUTON2007 campaign at sea along the Portuguese coast in summer 2007 reveal the presence of two upwelling fronts, one being located near the shelf break. Both upwellings are characterized by deep cold waters close to or reaching the surface and with high chlorophyll concentrations. Simplified numerical models are built in order to study a possible physical mechanism behind this observation. First, a simple shallow water model with three distinct layers is used to study the formation of secondary fronts by onshore transport of high potential vorticity anomalies on the shelf for upwelling favorable conditions. Sensitivity studies to bottom friction, shelf width, continental slope steepness, shelf \"length\" are analysed in terms of potential vorticity dynamics. A more realistic configuration, with bottom topography, wind forcing and stratification set up from observations, is then developed and the results confronted to the observations. It overestimates the velocity amplitude but exhibits good agreement in terms of density ranges brought over the shelf and general isopycnal patterns. The application and extension of the results to downwelling favorable conditions and to other more general oceanic regions is discussed too.
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2009 LOM Workshop, Miami, Florida Jume 1 - 3, 2009