Enhanced Turbulence and Energy Dissipation at Ocean Fronts

Abstract

The ocean surface boundary layer mediates air-sea exchange. In the classical paradigm and in current climate models, its turbulence is driven by atmospheric forcing. Observations at a 1-kilometer-wide front within the Kuroshio Current indicate that the rate of energy dissipation within the boundary layer is enhanced by one to two orders of magnitude, suggesting that the front, rather than the atmospheric forcing, supplied the energy for the turbulence. The data quantitatively support the hypothesis that winds aligned with the frontal velocity catalyzed a release of energy from the front to the turbulence. The resulting boundary layer is stratified in contrast to the classically well-mixed layer. These effects will be strongest at the intense fronts found in the Kuroshio Current, the Gulf Stream, and the Antarctic Circumpolar Current, all of which are key players in the climate system.

Open-Ocean Submesoscale Motions: A Full Seasonal Cycle of Mixed Layer Instabilities from Gliders

“…From this characterization, it becomes clear that submesoscale processes are intensified in regions of strong lateral buoyancy gradients, strong vorticity, and weak vertical stratification. These conditions are often met in or near western boundary currents of the Pacific (D'Asaro et al 2011) and Atlantic (Thomas et al 2013;Shcherbina et al 2013), in coastal oceans, and in the Southern Ocean.…”

“…There are a number of reasons to investigate whether these features and their associated surface flow fields are sufficient to generate submesoscale variability. First, submesoscale instabilities are an efficient mechanism for generating a forward energy cascade that transfers energy from large-scale geostrophically balanced motions to smaller turbulent scales associated with dissipation (Capet et al 2008;D'Asaro et al 2011;Thomas et al 2013). SI is an example of this process.…”

“…Observations of submesoscale processes are challenging because of the constraint of capturing intermittent events that evolve rapidly on the order of 1 to 10 days. Observational programs have largely focused on regions that are preconditioned toward an active submesoscale field, for example, western boundary currents, including strong surface forcing and strong frontal gradients (D'Asaro et al 2011;Thomas et al 2013). The prevalence of these motions in more quiescent regions of the ocean remains unresolved.…”

Global air-sea surface carbon-dioxide transfer velocity and flux estimated using ERS-2 data and a new parametric formula

“…The currents enhance the air-sea interface mixing causing the transfer velocities to increase (Smith, 1999). Also, because of the enhanced turbulence and energy dissipation at ocean fronts (D'Asaro et al, 2011), there are the high transfer velocities near the polar front. Based on the same reason, there are the high transfer velocities near the Azores Current and the Azores front.…”

The Application of the Generalized Differential Formulation of the First Law of Thermodynamics for Evidence of the Tidal Mechanism of Maintenance of the Energy and Viscous-Thermal Dissipative Turbulent Structure of the Mesoscale Oceanic Eddies

“…Substituting relations (40) and (41) (40) into the following refined [45] semi-empirical relation (refined [45] by introducing the empirical coefficient…”