The timemean circulation in the Agulhas region determined with the ensemble smoother
نویسنده
چکیده
The time-mean circulation in the Agulhas Retroflection area is determined by combining TOPEX/POSEIDON data and a two-layer quasi-geostrophic model using the ensemble smoother. By taking the time-mean circulation as the unknown in the data assimilation procedure, the time-varying altimeter signal is used to constrain the time-mean field. The quasi-geostrophic model is applied as a strong constraint, with only the time-mean circulation containing errors. Inspection of the posterior penalty function showed that the inversion was successful. The errors in the time-mean sea surface topography reduced from about 10 to about 3 cm. A cyclonic recirculation cell over the Agulhas Plateau was found, related to the northward meander of the Agulhas Return Current. Another cyclonic recirculation cell was found west of Africa, probably related to the passage of anticyclonic Agulhas Rings south of it. The new field is compared with advanced very high resolution radiometer infrared satellite data, confirming the northward meander of the Agulhas Return Current.
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