Assimilation of Geosat Altimeter Data for the Agulhas Current using the Ensemble Kalman Filter with a Quasi-Geostrophic Model

The ring-shedding process in the Agulhas Current is studied using the ensemble Kalman lter to assimilate Geosat altimeter data into a two layer quasi-geostrophic ocean model. The properties of the ensemble Kalman lter are further explored with focus on the analysis scheme and the use of gridded data. The Geosat data consist of 10 elds of gridded sea-surface height anomalies separated 10 days apart which are added to a climatic mean eld. This corresponds to a huge number of data values and a data reduction scheme must be applied to increase the e ciency of the analysis procedure. Further, it is illustrated how one can resolve the rank problem occurring when a too large data set or a small ensemble is used.