Vertical structure and variability of currents on the southern Brazilian inner shelf at 32°S
DOI:
https://doi.org/10.1590/Keywords:
Costal circulation, direct current measurements, tidal currents, south Brazilian inner shelfAbstract
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.
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