Collaborative Research: Turbulent fluxes and boundary layer structure due to near-shore internal tides

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Internal tides are a generic feature of near shore flows, playing a fundamental role in the ecology, biogeochemistry, and sedimentary environment of the near shore. For example, on coral reefs, turbulent mixing, as modified by stratification, can determine the strength of coupling between the water column and the reef. In a like fashion, internal waves can also be important to such environments as kelp forests where they may be a critical means of cross-shore transport of larval organisms. Thus, understanding the behavior of internal waves and the mixing they produce in shallow water is a fundamental problem in coastal oceanography. More generally, the high spatial and temporal resolution of physical measurements will result in a unique data set capable of linking large and small-scale physical processes on the continental slope and shelf. This data will be useful in developing more accurate parameterizations of boundary layer turbulence and mixing. In particular, it will be able to determine simple empirical relations like those found in lab experiments and computations but valid at field scales, that can be used in a wide range of circulation models.This project will measure Reynolds stresses, turbulent buoyancy fluxes, and turbulence dissipation rates in the near shore bottom boundary layer in the presence of shoaling internal tides and surface waves. Taking advantage of the capabilities of the Kilo Nalu Observatory operated by the University of Hawaii, these measurements will be made in 20 meters of water on the south shore of Oahu. Like many inner shelf regions, the proposed field site provides an environment in which both internal tides and surface waves are common. All the turbulence instruments will be cabled to shore, allowing acquisition of the data at high rates not limited by power or memory. Leveraging ongoing observations of surface waves and internal tides, the turbulence measurements will be supplemented by mean flow measurements made with ADCPs, thermistor and salinity sensor chains, and wave/tide gauges. The field measurements will yield a high quality turbulence data set, made in a setting for which we will have a fairly complete overall description of the mean flow. The field program will involve graduate and undergraduate students from University of Hawaii and Stanford University. These will be involved in all phases of the work, in particular, the scientific diving operations needed to install and recover the instrument suite. This group will include several women Ph. D. students and postdocs at both institutions.