Sea Level Anomaly Assimilation in an Eddy Resolving Model of the South Atlantic

Model performance and assimilation skills are evaluated in the process of constructing an operational forecast system for the southwestern South Atlantic, within the scope of the Oceanographic Modeling and Observation Network (REMO), a Brazilian initiative in operational oceanography. Assimilation of Sea Level Anomaly (SLA) data is conducted in an eddy resolving (1/12 degree resolution) nested Tropical and South Atlantic (from 7ºN to 36ºS, and from the Brazil coast to 20ºW) ocean model. Different experiments are performed with the Hybrid Coordinate Ocean Model - HYCOM under synoptic atmospheric forcing, and with the main tidal components imposed at the open boundaries. Vertical projection of surface along track AVISO data with the Cooper and Haines (C&H) dynamic method, and with the Ensemble Optimal Interpolation (EnOI) statistical method are analyzed , and compared to in situ XBT temperature data, and ADCP current data. The SLA assimilation affects the simulated mass structure down to few hundred meters, as well as the mean transport and mesoscale variability of the Brazil Current, and of the North Brazil Current in both experiments. The EnOI vertical projection, however, strongly depends on the variability of the ensemble, and in the present case produces more ephemeral mesoscale features. Overall, the C&H method show better skills in representing the mesoscale, with more robust eddies, that live longer and have a more coherent signal in subsurface layers, in accordance to observations.