Collaborative Research: The role of wind and waves in mixing the upper ocean

This project will study the turbulence in a stratified layer at the air-water interface, as caused by waves and wind. The study will carry out simulations with laboratory experiments and with computer models. Simulations will test the hypothesis that to represent the deepening of a surface layer reliably, it is necessary to couple currents and waves. Simulations will also test a parametrization of turbulence related to waves (Craik-Leibovich parametrization), and the results of combining a couple of parametrizations. For broader impacts, the project could improve the reliability in representing the ocean surface boundary layer of Earth-system models. Moreover, the PIs would produce educational materials to be used at their home institutions. In addition to supporting 4 PIs, this effort would fund one postdoctoral scholar and one graduate student. The proposed study seeks to advance understanding of wind-driven and wave-driven near-surface turbulence in a stratified surface boundary layer. This goal would be pursued with a combination of a) controlled laboratory experiments of stratified turbulent mixing under the influence of surface waves in the surface boundary layer, and b) state-of-the-art (Large-Eddy Simulations) numerical experiments. Laboratory and numerical simulations will test the hypothesis that the coupling between waves and wind-driven currents is necessary to reliably represent the surface mixed-layer deepening. The comparison between lab measurements and numerical simulations would seek to i) assess the reliability of LES (Craik-Leibovich) simulations in representing lab observations of turbulent mixing beneath horizontally heterogenous surface waves, and (ii) determine the effects of combining coarser grids in LES simulations with a turbulence closure. As broader impacts, the project could potentially improve the accuracy of Earth-system numerical simulations of the ocean surface boundary layer. Moreover, the PIs would produce educational materials to be used at their home institutions. In addition to supporting 4 PIs, this effort would fund one postdoctoral scholar and one graduate student. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.