Collaborative Research: LES & Modeling of Turbulence on Shallow Shelves under Combined Langmuir, Tidal & Convective Forcing with Comparison to VADCP Observations

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Intellectual Merit: Langmuir supercells (LSC), Langmuir circulations that engulf the entire water column during strong wind/wave forcing of shallow seas, were first identified in 2003 from vertical-beam acoustic Doppler current profiler measurements at the LEO15 cabled observatory off New Jersey. Similar measurements have been made more recently at the Navy's R2 tower on mid-shelf off the coast of Georgia, under different wind, wave and tidal forcing conditions. These unique data sets provide an opportunity, when combined with large-eddy simulations (LES) to investigate the interaction of several turbulence generating mechanisms in shallow seas. It is proposed to study the interaction between LSC, the tidally-forced bottom boundary layer, wave breaking and stratification (stable and unstable) from analysis of the LEO15 and R2 data sets and large-eddy simulation of LSC carefully guided by the observations. Once validated by comparison with the observations over the range of forcing ratios that characterize these data sets, the multi-process LES will allow exploration of non-dimensional forcing parameters outside this range, allowing assessment of the effect of LC on shelves other than those for which measurements exist. Simulations will be performed spanning parameter space. In traversing the parameter space, different turbulent regimes will be encountered such as Langmuir-dominated turbulence, convection-dominated turbulence and shear-dominated turbulence. Regime diagrams will help establish bulk forcing conditions for which LSC is dominant. Understanding of the interactions will lead to increased understanding of the dynamics of these various kinds of turbulence and to improved turbulence parameterizations for inclusion in large-scale coastal circulation models accounting for Langmuir turbulence. The modified parameterizations are expected to lead to improved predictions of vertical mixing on shallow shelves, ultimately leading to improved prediction of cross-shelf flows.Broader impacts: This project will result in improved shallow-water turbulence parameterizations accounting for wave-current interaction implemented within a number of widely used circulation models available to the general oceanography community. The proposed developments are focused in the coastal ocean where the effect of the bottom is important. Many continental shelves are biologically highly productive, for example the Bering Sea Shelf, one of the major United States fisheries. This research will increase understanding of the mechanisms controlling vertical mixing and cross shelf transport of biologically active materials and sediment. The parameterizations developed and the inclusion of important physics should improve the accuracy of models of coastal ocean flows at different resolution levels, ultimately proving important for coupled physical-chemical-biological models. This project will provide funding for a post-doctoral fellow who will train in multidisciplinary fields spanning fluid dynamics, physical oceanography, numerical methods and experimental methods. Dr. Tejada-Martínez, one of the co-PIs, is a scientist in an under-represented minority group. For outreach, Dr. Savidge participates yearly in training sessions for high school teachers through Skidaway?s local connections, and through research colloquia for pre-service teachers at Armstrong Atlantic State University in Savannah. Visual displays will be provided for the general public, adding to a computer-based interactive presentation BOTTOMS-UP in the Marine Education Center and Aquarium on Skidaway Island and on Jekyll Island, in conjunction with Savidge's planned HF-radar installation there. Important results from this modeling project will be incorporated in these developing displays. While details of modeling may be difficult to express to non-scientists, it will be possible to illustrate improvements in model performance during major wind-forcing events, and to emphasize the importance of such models in predicting larval and sediment transport in the nearshore coastal ocean that is of most interest to the general public.