Impacts of a large extra-tropical cyclonic system in Southern Brazilian Continental Shelf using the COAWST model

Abstract

Abstract. The Southern Brazilian Continental Shelf (SBCS) is an area with great ecological and economic importance to Brazil. In this region can be observed the recurrent passage of frontal systems and extra-tropical cyclones, which are more frequent during the winter months of the southern hemisphere. These systems act on the ocean surface layers as direct driving forces, which may change the thermohaline structure of the water column and induce sea level perturbations. This study used the coupled ocean-atmosphere regional model (COAWST) to evaluate the effect of the passage of a frontal system associated with an extra-tropical cyclone. The ROMS oceanic model was configured with two nested grids, in order to solve the hydrodynamic processes at different scales. The parent (20–40°\u2009S/40–60°\u2009W) and child (25–29.3°\u2009S/46.3–50°\u2009W) grid comprise the coastal region, with a horizontal resolution of 1/9° and 1/27°, respectively, with 32 vertical levels. The initial conditions are the Global Analysis Forecast from CMEMS and forcing files used the Climate Forecast System v.2 (CFSv2) data, from NCEP. This event took place on the continental shelf of the State of Santa Catarina, in September of 2016. The model results were compared to remote sensing data and to the tide gauges from the City of Imbituba (State of Santa Catarina, Brazil). The comparison showed a correlation higher than 78\u2009% between sea level rise data and the model results. The filtering of sea level data made it possible to identify the meteorological component in the model results. The comparison between the tidal-gauge and the model output presented values under 25\u2009cm. The model was capable of representing the sea level anomalies propagation associated with the passage of the atmospheric frontal system. The model output showed the presence of a sea level anomaly propagating northward along the continental shelf at 480\u2009km\u2009day−1, probably associated with the presence of a coastal-trapped wave.