Turbulence Scaling Comparisons in the Ocean Surface Boundary Layer

Abstract

Direct observations of the dissipation rate of turbulent kinetic energy, ϵ, under open ocean conditions are limited. Consequently, our understanding of what chiefly controls dissipation in the open ocean, and its functional form with depth, is poorly constrained. In this study, we report direct open ocean measurements of ϵ from the Air‐Sea Interaction Profiler (ASIP) collected during five different cruises in the Atlantic Ocean. We then combine these data with ocean‐atmosphere flux measurements and wave information in order to evaluate existing turbulence scaling theories under a diverse set of open ocean conditions. Our results do not support the presence of a “breaking” or a “transition layer,” which has been previously suggested. Instead, ϵ decays as |z|−1.29 over the depth interval, which was previously defined as “transition layer,” and as |z|−1.15 over the mixing layer. This depth dependency does not significantly vary between nonbreaking or breaking wave conditions. A scaling relationship based on the friction velocity, the wave age, and the significant wave height describes the observations best for daytime conditions. For conditions during which convection is important, it is necessary to take buoyancy forcing into account.

The Variability of Winds and Fluxes Observed Near Submesoscale Fronts

“…For example, the convergence at a SF can result in the water mass subducting at rates of 10–100 m/day, compared to typical rates of 1–10 m/day (an order of magnitude less) over an ambient ocean surface (Ferrari, ). The rapid vertical velocities may also lead to the enhancement of sub‐surface turbulence, which may contribute to the enhancement of air‐sea heat flux (D'Asaro, ; Esters et al, ). The enhancement may also affect the exchange rate of heat and other gases between the atmosphere and the ocean (Esters et al, ).…”

Wave effects on coastal upwelling and water level

“…The impact of the TKE flux is confined to the wave-breaking zone, and decays rapidly with depth (e.g. Terray et al, 1996;Janssen, 2012;Thomson et al, 2016;Esters et al, 2018). The importance of wave-generated turbulence near the sea surface was also demonstrated by Davies et al (2000), for the bottom layer by Jones and Davies (1998) and for wave-induced turbulence by Babanin (2006), Huang and Qiao (2010), Babanin et al (2010) and Babanin and Chalikov (2012).…”

Feeding of Plankton in a Turbulent Environment: A Comparison of Analytical and Observational Results Covering Also Strong Turbulence

“…Firstly, the turbulent energy dissipation rate generated from surface wind mixing is not vertically homogeneous through the upper part of the mixing layer as suggested by [23] but decreases by some empirical function [13] as for example in (14). Recent empirical studies based on the measurements from state-of-the-art turbulence profiler show that the turbulent energy dissipation rate changes with depth as Z −1.15 over the mixing layer [72]. Secondly, there are indications of a certain variation in encounter rate with light intensity [22].…”

“…This implies that the cod larvae by a change in vertical position may be able to adjust their turbulence-induced encounter rates to the optimum [13] and thereby avoid turbulence levels exceeding those for optimum encounter-capture rates. Over the vertical range observed for cod larvae (i.e., surface layer to 50 m depth) the wind-generated turbulent energy dissipation rate changes by two orders of magnitude [72]. The previous field experiments [21,22] covered wind-induced turbulence for wind speeds up to 11 m s −1 .…”