Abstract This study investigates the impact of winds, tides, and river discharges on the coastal current and salinity variability of Southern Brazil’s inner shelf. Data on wind speed, current, surface salinity, and temperature were collected for analysis from a metocean buoy of the Brazilian Coastal Monitoring System (SiMCosta). The observed current time series can be interpreted as a sum of highly variable flows correlated with local wind stress, and a residual mean current flowing southward along the coast at a few centimeters per second. Tidal currents were predominantly diurnal, albeit negligible, representing approximately 1.7% of the current variance in the region. We observed a prevalence of northwest winds and southeastward currents on the inner shelf, as well as an intermittent flow in both the alongshore and cross-shore directions due to meteorological frontal system passages. The power spectrum of both current components presented similar frequency patterns, indicating the prevalence of high-energy events in periods of 3 to 10 days over the entire time series. The alongshore current is highly correlated (r=0.73, p<0.05) with alongshore wind and a delay of 3 hours. In the low- (period >40 h) and high-frequency (period <40 h), the temporal lags were of 5 and 3 hours, respectively, with correlations of 0.79 (p<0.05) and 0.60 (p<0.05). The wavelet analysis has shown that high-energy events in alongshore wind stress are more common between August and October and less often between February and March, with similar surface currents and salinity patterns. A decrease in surface salinity during the winter season was observed due to the high level of Patos Lagoon’s outflow. Mean daily salinity correlated negatively with Patos Lagoon’s outflow, however part of this variability is associated with the intrusion of Patos Lagoon’s plume and the passage of frontal systems.

Abstract A performance evaluation of ocean color chlorophyll-a algorithms was conducted based on the in situ fluorescence chlorophyll concentration (Fchl) measured by a sensor on the buoy SiMCosta-SC01 in coastal waters of South Brazil. The operational algorithms are used in MODIS and VIIRS sensors to derive satellite chlorophyll concentration (Csat). Fchl values were successfully corrected for nonphotochemical quenching (NPQ) by an interpolation of sunrise and sunset daily measurements. A laboratory-derived calibration coefficient was applied to convert the unquenching Fchl values into chlorophyll concentration (Cflu). Overall, linear regression analysis between Cflu and Csat for both sensors showed good results, with the coefficient of determination (R2) varying between 0.88 and 0.96, slopes between 0.92 and 1.02 and intercepts between -0.17 and 0.13. The MODIS algorithm (R2 = 0.96, slope = 1.02, RMSE = 0.16 mg m-3, BIAS = 0.16 mg m-3, for N = 222 and time interval ±1 h) presented slightly better performance than VIIRS (R2 = 0.92, slope = 0.96, RMSE = 0.25 mg m-3, BIAS = -0.25 mg m-3, for N = 284 and time interval ±1 h). These results represent the most comprehensive satellite data analysis for this region, suggesting that the approach may be applicable to other SiMCosta buoys.

Abstract Important global oceanic processes, such as the meridional overturning circulation, are governed by the temperature and salinity of the ocean. As such, it is essential that these properties be correctly represented in high-quality global climate models. This study aims to evaluate thermohaline properties both historically and under two simulations of the Brazilian Earth System Model BESM-OA2.5 in the South Atlantic Ocean (Representation Concentration Pathway (RCP) 4.5 and 8.5). Since error assessment in the global climate model (GCM) is fundamental to infer climate change projections, comparisons were made for thermohaline properties among four GCMs (HadGEM2-ES, MIROC-ESM-CHEM, MIROC5, and BESM-OA2.5) against data from ocean monitoring programs and from ORAS5-ECMWF. The results show common surface spatial pattern errors in all models, commonly related to mesoscale processes. Specific to BESM-OA2.5 over the Southern Ocean, we observed an increase in the temperature bias during autumn and summer, probably due to subsurface temperature overestimation linked to North Antarctic Deep Water (NADW) formation. With respect to salinity, the underestimations in the Subtropical/Subantarctic Zones and in the north of the South Atlantic subtropical gyre were linked to simulation errors in the Malvinas current. All models presented overestimated annual historical temperature rates, with BESM-OA2.5 being the closest to ORAS5. In the subsurface, the BESM-OA2.5 did not easily simulate the South Atlantic Central Water (SACW) formation, though in deep water, the model was able to better simulate the Antarctic Intermediate Water and NADW patterns. Statistically, the multi-model means performed better, while the BESM-OA2.5 performed worst among the models in both methodologies applied. In terms of projected scenarios, the models demonstrated sensitivity to variations in greenhouse gas emissions between the RCPs, with higher magnitude warming predicted in the equatorial zone, except for BESM-OA2.5.

A sensibilidade de um modelo de irradiância espectral, incidente sobre a superfície do mar, variando três parâmetros atmosféricos (ozônio, visibilidade e vapor de água precipitável), é analisada, com especial ênfase para as bandas do sensor Sea-viewing Wide Field-of-view Sensor (SeaWiFS). São também analisadas as razões entre bandas de reflectância geralmente utilizadas nos algoritmos bio-óticos, para mapeamento da biomassa fitoplanctônica do espaço. Os resultados mostram que a visibilidade é o parâmetro que mais causa alteração nos valores de irradiância, embora o seu efeito nas razões entre bandas seja menor do que o efeito do ozônio. O vapor de água precipitável não causou alteração significativa nem nas irradiâncias e nem nas razões entre bandas. Os valores extremos destes parâmetros não causaram diferenças significativas para ângulos solares entre 0 e 60º. Para se obter a razão entre reflectâncias das bandas 490/510, 490/555 e 510/555 em ângulos solares menores que 60º, valores médios destes parâmetros atmosféricos testados neste trabalho são suficientes para se modelar a razão entre irradiâncias.

A sensitivity analysis of an irradiance spectral attenuation model is performed by varying three atmospheric parameters: total ozone, visibility and total precipitable water. The incident solar spectral irradiance over the sea surface is calculated at the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) bands for remote sensing applications. The effects of these atmospheric parameters over some remote sensing reflectance ratios usually used for mapping chlorophyll a concentration from the space are also assessed. The results have shown that visibility is the most important parameter which exerts influence on modeled spectral irradiance but its effect on the remote sensing ratios is smaller than that from total ozone. The total precipitable water did not alter both modeled spectral irradiances and remote sensing ratios for solar zenith angles smaller than 60º. No significant differences were found when solar zenith angles varied from 0 and 60º, even when we used extremely high values of atmospheric parameters. For remote sensing reflectance band ratios 490/510, 490/555 and 510/555 under solar zenith angles smaller than 60º, average values of these atmospheric parameters tested here are enough to model irradiance band ratios.