Observed surface wave variations in the background current field of the Kuroshio Extension

Ocean wave-current interactions are important physical processes at the sea surface, which can potentially cause extreme sea states under certain conditions. Usually, such interactions are more notable in regions with strong waves and background currents. In this study, focusing on the Kuroshio Extension, we used buoy-measured and altimeter-derived wave data to determine variations in wave properties with the background currents. Statistically, the wave height can be underestimated (overestimated) by approximately 4% (3%) when the current and waves are in the opposite (same) direction. In regions with warm (cold) eddies, the wave height and wavelength inside the eddy are larger (smaller) than those outside by approximately 5% and 8% (4% and 4%), respectively, and the wave direction is deflected by 11° anticlockwise (clockwise). The wavenumber spectra of wave height and surface current speed are highly correlated with a power law of k− 2–k− 3 at scales of 20–200 km for swell-dominated cases. Additionally, the convergence and divergence of wave energy resulting from the current-induced refraction of swell are captured. From another perspective, the wave-induced Stokes drift calculated using the directional spectrum accounts for 54% of the reanalysis surface currents, and the accuracy of the estimated surface current can be improved by up to 14% by considering Stokes drift. This study provided quantitative analysis of observed surface wave variations in the Kuroshio Extension region from multiple perspectives.