The Effect of Currents on Large Surface Gravity Waves Under Cyclonic Conditions in the South/Southeastern Brazil

Abstract

Although ocean surface currents are not accounted for in most wave modeling studies, recent works have demonstrated that ocean circulation features may have a great impact on surface gravity waves. In this case study, we coupled in a one‐way mode the hydrodynamic model Regional Ocean Modeling System (ROMS) and the wave model Simulating WAves Nearshore (SWAN) to study the effect of currents on large wave events (LWEs) produced under the influence of cyclones in south/southeastern Brazil. For the five LWEs studied, chosen due to the distinct importance that current‐to‐wave effects had for the period, the results indicate that the addition of currents on the wave model improved the accuracy of the peaks of significant wave height, generally increasing them (by as much as 27%). The increase in wave height occurred mainly near the shelf edge and slope, where the southwestward‐flowing Brazil Current opposes the dominant direction of cyclone‐generated waves (usually from S/SE to S/SW). Modulation of wave height by currents in the subinertial band explained up to 95% of the total variance of the difference between results with and without ocean currents, and this band was largely related to the Brazil Current. Its near‐inertial counterpart explained up to 22% of the total variance and was primarily due to near‐inertial currents in the region. This study provides, for the first time, conclusive evidence that wave‐current interaction can impact LWEs in south/southeastern Brazil.