Collaborative Research: Generation and Transport of Vorticity and Effects on Mean Surface Currents: Wave Averages and Wave Resolving Formulations.

摘要

Our long term goal is to understand the mechanisms controlling the intensity and spatial distribution of vortical structures, such as eddies and rip currents, evolving in the surfzone, and to understand how these flow features influence time-averaged currents, sediment transport and wave statistics. Recent computations (Kirby et al, 2003a, b) have shown that computations of shear waves using either wave-averaged circulation models on the one hand, or wave-resolving Boussinesq models on the other hand, can predict very different nearshore circulation patterns when configured similarly and applied to the same field cases. This discrepancy is troubling, in that a clear basis has not been established for determining which results are typically closer to observed field conditions. In order to resolve this issue, we plan to perform comparisons of model runs for a number of time periods from the SandyDuck field experiment, and compare results to both array measurements of long-shore and crossshore velocities as well as Doppler Sonar measurements of the study area, which provide more information on the spatial structure of flow features. Specific objectives in support of this effort include: (1) Re-examine the energetics and spatial structure of low-frequency vortical motions as predicted by the Boussinesq model FUNWAVE and the wave-averaged circulation model SHORECIRC. The comparison will be performed using a newly-revised Boussinesq formulation which preserves an approximation for potential vorticity which is consistent with Boussinesq ordering in powers of; (2) Test model predictions against available array data and Doppler sonar data; (3) Examine the instantaneous structure of forcing for vorticity derived from Boussinesq simulations, based on the curl of momentum-preserving dissipative terms; (4) Examine the time-averaging of this forcing in the context of forcing of wave- averaged vorticity.