Submesoscale current effects on surface waves

Abstract We present a numerical study of current effects on waves (CEW) at submesoscales (100’s of m - 10’s of km) with a realistic model configuration in Southern California. CEW is analyzed by comparing solutions forced by winds with and without current forcing through relative differences. The modulation of wave field due to currents is relatively larger for the wave-breaking variables (i.e., whitecap coverage, air-entrainment, and energy dissipation) followed by the resolved mean square slope, surface Stokes drift, and the significant wave height. Background currents on average increase the directional spreading by 0.9°and modulate the mean wave direction within ± 5°. CEW decreases with increasing wind speed because the rms current gradients also decrease while the wind forcing and breaking restore the wave field towards equilibrium faster at higher winds. Empirical scalings based on the mean wave period, rms current gradients, and friction velocity are found to explain 80% or more of the variability for the model differences due to CEW except for the significant wave height, explaining 66% of the variability. The statistics of model differences due to CEW are approximately Gaussian for the significant wave height, symmetric with finite excess kurtosis for the higher spectral moments, and positively skewed with excess kurtosis for the wave-breaking variables.