The stokes drift and wave induced-mass flux in the North Pacific

Stokes drift and wave induced-mass flux in realistic wavefields and ocean currents in the North Pacific Ocean are studied using a third generation wave model with ambient geostrophic currents estimated from satellite altimetry data to directly estimate the Stokes drift for random directional waves. Comparison with in situ buoy data shows that the model performed well in representing the Stokes drift field and total wave momentum. In the North Pacific, the annual mean surface Stokes drift ranges from 2 to 10 cm/s and the mean Stokes e-folding depth is 1 to 2 m. The Stokes drift fields estimated using bulk wave parameters compare poorly against buoy data, and are shown to overestimate (underestimate) the Stokes e-folding depth (the surface Stokes drift) computed directly from wave spectra by as much as 5-20 times larger (2-10 times smaller). The spatial distributions of mean wave height and mass transport approximately follow the synoptic scale associated with atmospheric forcing, and the divergence of wave induced-mass flux is significantly modified by local fetch, the coast and ocean currents. Due to strong wave refraction along the Kuroshio extension, surface vertical velocity induced by Stokes divergence is comparable to the Ekman velocity, and may alter the meso-scale dynamics of the front.