Waves and Strongly Sheared Currents: Extensions to Coastal Ocean Models

Some of the strongest interactions between ocean surface waves and estuarine or coastal current systems occur in regions with strong vertical current shear resulting primarily from freshwater discharges and the resulting development of plume structures. This reality contrasts strongly with the theory embedded in typical coastal circulation and wave models, where formulations are based (at least at leading order) on the assumption of a depth-uniform current structure affecting the wave motion. In this talk, we (necessarily briefly) discuss: (1) The development of a framework for describing the wave-current problem in regimes with arbitrarily strong vertical current shear, including description of the action balance for waves and the wave forcing effects in models for circulation. (2) Approximations for the vertical structure of waves leading to computable versions of wave forcing in circulation models. (3) Possible pathways to introducing more accurate representations of current effects in group velocity estimates in existing wave models such as SWAN, based on minimal sets of additional information passed from circulation to wave models. In particular, we emphasize (with regard to item (3) ), that the present tendency to utilize the depth-weighted current described by Kirby and Chen (1989) as the current advection velocity is not accurate in a range of settings, and that there are (1) marked improvements to be made by a simple adjustment of this single estimate of current speed, and (2) the possibility of greatly extending the range of accuracy by using only one or two additional scalar values passed from the circulation model to the wave model. Finally, we also introduce the development of a theory for the nonlinear dynamics of weakly nonlinear waves in the Schrodinger equation context, with application to the dynamics of unsteady wave evolution near blocking points created by surface plumes.