Estimation of Diffusive Transport of Turbulent Kinetic Energy from Acoustic Doppler Current Profiler Data

Abstract

The analysis of turbulent mixing has historically relied upon either indirect estimates of turbulent mixing, such as the gradient Richardson number, or measurements of small-scale shear to define turbulent dissipation rates. Recent advances in instrumentation and analysis, however, have permitted the analysis of turbulence using characteristics of large-scale motions, specifically Reynolds stresses, shear production, and turbulent kinetic energy itself. In this paper, an analysis technique for use with acoustic Doppler current profiler data is presented that uses the third moments of the velocity measurements to estimate the nonlocal diffusive transport of the turbulent kinetic energy. Following the development of this analysis, a formal error analysis is presented to quantify the uncertainty associated with these estimates. Finally, the analysis is demonstrated using a dataset collected in San Francisco Bay. The results are consistent with both the expected structure of the transport terms and other measurements of the diffusive flux collected simultaneously. It is concluded that the analysis technique provides a reasonable estimate of the turbulent transport term in the turbulent kinetic energy equation, but requires care in the application due to the large uncertainty associated with the estimate.