Measurements of Turbulence and Flow Structure in the Coastal Ocean using PIV

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This project continues our effort to measure the flow structure and turbulence in the bottom 10 m of the water column of the coastal ocean, and study their dependence on elevation, circulation, wave field, bottom topography and stratification. The turbulence measurements were performed using a submersible Particle Image Velocimetry (PIV) system mounted on a telescopic profiling platform with a 10 m profiling range that can align the sample area in any desired direction. The data consist of time series of instantaneous, 2-D velocity distributions in two independent sample areas. The sample areas are spaced to obtain the Reynolds stresses with minimal wave contamination using structure functions. With varying magnifications, the PIV data resolve length scales ranging between 1.2 mm to 1 m, enabling direct calculation of dissipation rate. Preliminary results from the deployments that motivate the present analysis proposal include evidence of: a) Variations of Reynolds stresses and mean current with wave phase. b) Turbulence production lower than the dissipation rate, and variations of stresses with depth in the outer portions of the bottom boundary layer. The stresses seem to scale with the mean current. c) Turbulent energy spectra that increase in similarity to the universal spectrum with increasing Reynolds number, but still indicate anisotropy at all scales, including the dissipation range. e) At moderate, but typical tidal flows, the production is intermittent, occurring during periods of gusts, while the dissipation changes little.Proper modeling of oceanic circulation is essential for improvements in predictions of climate, weather and human impact on the coastal ocean. Transport of pollutants, nutrients and sediment in coastal waters affect many aspects of human life along the coast including the economy, health, tourism, fisheries and food production. It is essential to obtain the knowledge and understanding that leads to development of improved prediction of oceanic transport, circulation and mixing.