Abstract
Between 5 and 25% of the total momentum transferred between the
atmosphere and ocean is transmitted via the growth of long surface
gravity waves called ‘swell’. In this paper, we use large eddy
simulations to show that swell-transmitted momentum excites
near-inertial waves and drives turbulent mixing that deepens a rotating,
stratified, turbulent ocean surface boundary layer. We find that
swell-transmitted currents are less effective at producing turbulence
and mixing the boundary layer than currents driven by an effective
surface stress. Overall, however, the differences between swell-driven
and surface-stress-driven boundary layers are relatively minor. In
consequence, our results corroborate assumptions made in Earth system
models that neglect the vertical structure of swell-transmitted momentum
fluxes and instead parameterize all air-sea momentum transfer processes
with an effective surface stress.