Enhanced Stokes Drift via Internal Solitary Wave Interaction

We investigate the enhancement of Stokes drift at the ocean surface due to the interaction between surface gravity waves (SGWs) and internal solitary waves (ISWs). Using a high-order spectral method to solve the Zakharov equation, we model the nonlinear evolution of SGWs propagating through large-scale, depth-independent horizontal currents induced by ISWs. Simulations reveal that addition of the drifts resulting from ISWs and SGWs acting in isolation does not accurately estimate the drift resulting from superposed and interacting SGWs and ISWs. When ISWs and SGWs co-propagate, this additive approach underestimates the drift, resulting in relative errors of 10-25%. In the case of counter-propagating waves, it also underestimates the drift, and if the relative error surpasses 100%, it may even predict the wrong direction of drift. These findings highlight the importance of nonlinear wave interactions in accurately modeling surface transport in ocean environments.