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Tracking mesoscale exchange within a regional model of the Southern Africa Basin
Andrea M. Doglioli, Sabrina Speich, Bruno Blanke, Guillaume Lapeyre
Laboratoire de Physique des Océans, UMR CNRS/IFREMER/UBO, Université de Bretagne Occidentale, Brest
Andrea.Doglioli@univ-brest.fr(Abstract received 03/10/2005 for session B)
ABSTRACT
Eulerian and Lagrangian observations, satellite data and numerical model have already shown the complexity of the regime of turbulent interocean exchange between the Indian and the Atlantic, upstream and within the Cape Basin. Rings and eddies pinch off from the Agulhas retroflection, before they penetrate into the Atlantic. They interact with the Agulhas Current and its retroflection, as well as with neighboring mesoscale structures. They are thought to impact the dynamics and variability of the South Benguela upwelling region, which represents one of the richest ecosystems and a major fishing area in the world. Satellite measurements allow rough transport estimates achieved by the eddy field, but gaps in knowledge of the full 3D identity of these structures are handicaps that prevent more accurate diagnostics. On the other hand, the Lagrangian analysis of eddies simulated by regional ocean models offers promising bases for the development of more robust estimates of the propagation and conservation of eddy properties. Our numerical simulations were run with the ROMS model (for the regional RIBA configuration developed by P. Penven and S. Speich with a 1/10° horizontal resolution). They represent fairly well the crucial properties of the Southern Africa Basin eddy field. We use a technique based on wavelet decomposition to identify coherent eddy structures and to follow water mass properties along their tracks. Then we disseminate Lagrangian numerical particles (ARIANE tool, B. Blanke) in selected cyclones and anticyclones to diagnose their water mass origin and to evaluate the associated mass transfer. The results are here discussed mostly in terms of temperature and salinity temporal evolution, and are compared, where possible, with observations.
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2005 LAPCOD Meeting, Lerici, Italy, June 13-17, 2005