Effects of Wave Streaming and Wave Variations on Nearshore Wave-driven Circulation

Using numerical simulations, we studied the effects of wave streaming and wave variations on the wave-driven circulation at nearshore regions, i.e. surf zone and inner shelf. Wave streaming is a near-bottom Eulerian current in the direction of surface waves propagation, due to the bottom friction on waves. Rooting in stochastic waves, wave variations are random deviations from the mean wave characteristics, such as mean wave amplitude, period, and incident angle. Wave streaming causes a Lagrangian overturning circulation at inner shelf, which does not exist if wave streaming is missing. This overturning circulation creates a front at stratified inner shelf, which then develops baroclinic instability and produces submesoscale shelf eddies. Variations of stochastic waves lead to alongshore-dependent wave breaking, which generates surf eddies and transient rip currents; however, oblique wave incidence suppresses the eddy generation associated with alongshore variations of wave breaking. By tracer experiments, we demonstrated that both wave streaming and wave variations promote cross-shelf material exchange. Further, we discussed how current bottom drag, current effects on waves (CEW), and rotation affect the wave-driven circulation in the presence of wave streaming and wave variations.