On the heterogeneity of stratified-shear turbulence: Observations from a near-field river plume

Abstract

[1] The heterogeneity of turbulent structure in a near-field river plume is evaluated through the application of three distinct measurement techniques: turbulent overturn analysis, direct turbulence measurement using microstructure sensors mounted on an autonomous underwater vehicle (AUV), and a larger scale control volume approach. These techniques exploit the preturbulent potential energy available for conversion to turbulent energy, the kinetic energy associated with active turbulence, and the artifacts of turbulence demonstrated through a modified density structure, respectively. Comparisons between these methods indicate that all three techniques can provide robust estimates of mean turbulent kinetic energy dissipation rates. Results suggest a highly heterogeneous turbulent field, with significant overturns occupying a volume fraction of less than 10%, and active turbulence occupying a volume fraction only 2–3 times larger. The combined data sets are also used to estimate expected means and confidence limits for overturn-derived dissipation rates associated with varying sample sizes.