Upper Ocean Mixing, Coastal Mixing, LIWI, and CM AASERT

See also ADM002252. Sponsored in part by ONR grants N00014-97-1-0136 and N00014-97-1-0647.

My long-term goals are to identify and quantify the major mixing processes in the upper ocean and to relate them to the larger scale processes producing the mixing as quantitatively as possible. When successful, this will take the form of parameterizations that can be used in numerical models. My scientific objectives are to measure mixing directly with microstructure sensors and to relate these measurements to the larger scales producing the mixing in such a way that the results can be compared with either the large-scale changes resulting from the mixing or with theoretical predictions of mixing rates. My technological objectives are to develop instruments and sensors to measure the major mixing parameters. Because a first-order understanding of mixing in the open ocean is rapidly being developed, our approach has shifted to obtaining a similar understanding of mixing near coasts and in estuaries. Because dissipation rates are higher in these waters, we have also shifted our technological developments to improve the spatial resolution of microstructure sensors and to adapt open-ocean measurements of fine-scale velocity to shallow water. We demonstrated that sometimes flow in the Bosphorus is strongly quasi-steady. We were also able to estimate the surface slope along the strait from the observed mean density and velocity fields. The surface slopes most steeply where the zero-flow surface dips. The LIWI observations give the best evidence we know of to date for mixing in a tidal beam. Microstructure measurements were taken continuously along a fan ridge for five semidiurnal tidal periods. We observed a beam of enhanced turbulence mixing emanating from the shelf-break, extending for about four km. The vertical scale of the beam is about 50 m. The beam of enhanced turbulence follows the slope of characteristics of semidiurnal internal tides. Strong turbulence mixing also exists within 100 m off the bottom on the continental slope.