Aghullas ring trajectories and evolution from altimeter data

Oceanic vortices have been the subject of several experimental and theoretical studies. They play a key role in the energy budget of the global ocean. A better understanding of their physics, (e.g. interaction with the mean currents) would improved their knowledge of the ocean circulation. Satellite altimetry and numerical models are used to detect, track and analyze the strong anticyclonic eddies generated by the Aghullas retroflection. These rings have a long lifetime and can cross the South Atlantic basin. They could play a key role in the exchanges between the Indian and South Atlantic oceans. The LEGI QG model is a high resolution (1/6°) eddy resolving model. By means of a simple nudging data assimilation procedure along track altimeter data are introduced into the model to control the simulation. Using a Gaussian eddy model and the smooth variation of eddy propagation speed, a method has been developed, based on the analysis of along track altimeter data in terms of eddy characteristics (amplitude, size) to estimate the eddy trajectory. This trajectory is then used as a frame of reference to estimate the bidimensional eddy structure. Three Aghullas rings, detected during a WOCE campaign are studied. Their trajectories, determined from altimetry, is compared to the numerical model ones. Their structure and their evolution are analyzed and compared to model and in situ data. The influence of bottom topography, mean currents, eddy/eddy interaction is analyzed