Abstract
The generation of turbulence in pure shear-stratified environments is known to be driven by interfacial instabilities within the stratified shear layer, typically resulting in coherent overturning structures such as Kelvin-Helmholz billows (particularly for near-critical values of the gradient Richardson number) that subsequently decay to turbulence. Efforts to parameterize these processes using bulk flow variables have resulted in a variety of approaches, where non-dimensional forms of turbulent intensity, including the entrainment ratio, E, and a non-dimensional turbulent buoyancy flux, ξ, are typically assumed to be functions of a local bulk Richardson number, RiB. However, recent comparisons of laboratory data with data collected from the coastal ocean, including several supercritical river plume environments, indicates that geophysical turbulence (expressed either as E or ξ) falls several orders of magnitude below similarly generated laboratory turbulence at consistent values of RiB, suggesting that scale may play a critical role in the generation of turbulence. The goals of the current study are to bring together field and laboratory turbulence observations, along with DNS turbulence simulations, to bridge the gap across a wide range of scales, as represented by the Reynolds number, Re, and a broad range of RiB. Collectively, this data will be used to test a variety of predictive parameterizations. A power law approach, utilizing both Re and RiB shows some initial promise, and a weak to moderate inverse dependence of turbulent intensity on Re. The utility of other approaches, including available energy analyses utilizing the difference between shear and buoyancy time scales, are also explored. An enhanced understanding of the role of scale in the generation of shear-stratified turbulence will facilitate the use of laboratory data or direct numerical simulation (DNS) output to inform dynamics at geophysical scales, and may improve turbulence closure schemes for ocean models.