The model used in this study is the Regional Ocean Modeling System (ROMS), which is a three dimensional, free surface, hydrostatic, eddy-resolving primitive equation ocean model. ROMS uses orthogonal curvilinear coordinates in the horizontal and sigma, terrain following coordinates in the vertical (Shchepetkin and McWilliams, 2005). We use the version ROMS_AGRIF (http://www.romsagrif.org), which offers the capability of a 2-way nesting procedure with high resolution “child” grids embedded into a coarser resolution “parent” grid. The parent grid extends 360˚ in the longitudinal direction and from Antarctica to 15.2˚ N. It has a spatial resolution of ¼˚, and 40 sigma levels in the vertical, with enhanced resolution at the surface. The first child grid extends from 82°W to 41°W and from 64°S to 20°S, covering the southern portion of South America with spatial resolution of 1/12˚.
The nested configuration is forced by the 3-day averaged ERA_Interim data set from 1979 to 2012 at the surface and by the climatology Simple Ocean Data Assimilation model (SODA) at the open boundary of the parent model (15.2°N). A detailed description of the technical configuration of the parent and first child model, as well as their performance, can be found in Combes and Matano (2014).
The 10-day averaged model solution of this nested configuration is used offline as the lateral boundary conditions for a second child grid from 2000 to 2012. The second child grid extends from 66°W to 44°W and from 44°S to 25°S, thus covering the southwestern Atlantic region with a horizontal resolution of 1/24° (Fig. 1), which is ~3.8 km at the latitude of Buenos Aires. The model is forced at the surface with QuickSCAT (period 2000-2007) and ASCAT (period 2008-2012) daily winds. The surface heat and freshwater fluxes are derived from the COADS data set (climatology). The model is also forced with a daily discharge of the Rio de la Plata, a constant discharge from the Dos Patos Lagoon (set to 2000 m3s-1) and 5 tidal components (M2, S2, N2, K1 and O1 harmonics).