5:15 PM - 6:45 PM
[AOS16-P13] Mass transport and consequent counter-transport induced by waves (2) - response in a rotating system
Keywords:wave-current interaction, surface waves, coastal circulation, material transport
Ocean surface waves induce net mass transport known as the Stokes transport, commonly directed toward the coast, with a typical magnitude of order O(0.1)Sv per 1000km coastline. Mass conservation tells us that the same amount of water is returned shoreward in some way, resulting in the coast-shore water exchange that has a potential impact on the coastal environment. To assess its influence and improve the predictability of the coastal ocean, we first need to better understand the dynamical process of landward Stokes transport and accompanying shoreward counter-transport. The simulations were conducted in the wave-averaged framework, where the Stokes drift-associated effects are parameterized through the vortex force and the Coriolis-Stokes force in the momentum equation, and the Stokes mass flux in the continuity equation. In this work, we investigated the subinertial counter transport response to a horizontally inhomogeneous landward Stokes transport field that develops over a timescale longer than the inertial period.
The simulation results revealed that two different processes are involved in the counter transport. First, the inertial adjustment to the Coriolis-Stokes force results in an anti-Stokes current that locally cancels the Stokes drift velocity in the absence of viscosity. This effect is widely known in mixed-layer dynamics studies, where usually the problem is considered in a horizontally infinite domain. Our result shows that this effect is still valid when the Stokes drift has convergence and divergence due to the presence of horizontal boundary. Second, when the Stokes transport field has horizontal shear, a geostrophic current is induced, resulting in horizontal circulation that survives as long as the Stokes transport persists. It is induced by the convergence/divergence of lateral water displacement associated with the inertial adjustment to the Coriolis-Stokes force. This response is scale-dependent: the Stokes transport curl field smaller than the Rossby radius contributes to the net circulation.
The simulation results revealed that two different processes are involved in the counter transport. First, the inertial adjustment to the Coriolis-Stokes force results in an anti-Stokes current that locally cancels the Stokes drift velocity in the absence of viscosity. This effect is widely known in mixed-layer dynamics studies, where usually the problem is considered in a horizontally infinite domain. Our result shows that this effect is still valid when the Stokes drift has convergence and divergence due to the presence of horizontal boundary. Second, when the Stokes transport field has horizontal shear, a geostrophic current is induced, resulting in horizontal circulation that survives as long as the Stokes transport persists. It is induced by the convergence/divergence of lateral water displacement associated with the inertial adjustment to the Coriolis-Stokes force. This response is scale-dependent: the Stokes transport curl field smaller than the Rossby radius contributes to the net circulation.