Nonlinear Processes in Oceanic and Atmospheric Flows

Presentation

Formation of a secondary upwelling front along the shelf break in simplified numerical models and in-situ data.

Author: Vincent Rossi, LEGOS / CNRS.

Names and affiliation of other authors:
Yves Morel (EPSHOM/CMO, Brest/Toulouse, FRANCE).
Véronique Garçon (LEGOS / CNRS Toulouse, FRANCE).

Oral or poster: Poster

Downloadable poster file:

Formation of a secondary upwelling front along the shelf break in simplified numerical models and in-situ data.

(shelfbreakupwelling_laspalmas2008_rossi_bis.pdf, 3543719 bytes)

Abstract:
The basic processes of upwelling formation are well-known, considering a coast meridionally oriented in the northern hemisphere: an southward along-shore dominant wind results in an offshore Ekman transport to the west in the surface mixed layer, compensated by a vertical transport of deep, cold and rich nutrient water at the coast. A coastal jet flowing equatorward and a poleward counter-current above the slope are often associated to this process. This cross shelf structure may be modulated by the local conditions including topographic features. In this work we address the question of the physical mechanism leading to the formation of secondary upwelling fronts. Indeed, during the cruise MOUTON 2007 which took place in the Iberian Peninsula Upwelling System, an east/west section located at 41°N reveals a nice snapshot of two upwelling fronts clearly characterized by cold water tongues. We first analyse the in situ data focussing on the formation of these two upwelling fronts, the classical one located at the shore and the other one above the shelf break. A simplified numerical model is then built in order to reproduce and understand the physical mechanisms behind this observation. We use a simple 2 dimensional model, derived from MICOM (or Miami Isopycnic Coordinate Ocean Model), with several distinct layers. The model is able to reproduce these two fronts under some -pretty general- circumstances. The mechanism is then analysed in terms of potential vorticity dynamics.

*Satellite images from NASA and ESA

Nonlinear Processes in Oceanic and Atmospheric Flows. July 2-4, 2008. Castro Urdiales, Cantabria, Spain.