Decay of Boundary-Layer Turbulence in Near Wake of a Slender Body

The evolution of upper ocean currents involves a set of complex, poorly understood interactions between submesoscale turbulence (e.g. density fronts and filaments and coherent vortices) and smaller-scale boundary-layer turbulence. Here we simulate the lifecycle of a cold (dense) filament undergoing frontogenesis in the presence of turbulence generated by surface stress and/or buoyancy loss. This phenomenon is examined in large-eddy simulations with resolved turbulent motions in large horizontal domains using${\sim}10^{10}$grid points. Steady winds are oriented in directions perpendicular or parallel to the filament axis. Due to turbulent vertical momentum mixing, cold filaments generate a potent two-celled secondary circulation in the cross-filament plane that is frontogenetic, sharpens the cross-filament buoyancy and horizontal velocity gradients and blocks Ekman buoyancy flux across the cold filament core towards the warm filament edge. Within less than a day, the frontogenesis is arrested at a small width,${\approx}100~\text{m}$, primarily by an enhancement of the turbulence through a small submesoscale, horizontal shear instability of the sharpened filament, followed by a subsequent slow decay of the filament by further turbulent mixing. The boundary-layer turbulence is inhomogeneous and non-stationary in relation to the evolving submesoscale currents and density stratification. The occurrence of frontogenesis and arrest are qualitatively similar with varying stress direction or with convective cooling, but the detailed evolution and flow structure differ among the cases. Thus submesoscale filament frontogenesis caused by boundary-layer turbulence, frontal arrest by frontal instability and frontal decay by forward energy cascade, and turbulent mixing are generic processes in the upper ocean.

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Measurements of the boundary layer and near wake of a supercritical airfoil at cruise conditions

10.2514/6.1981-1242 ◽

1981 ◽

Cited By ~ 1

Author(s):

D. JOHNSON ◽

F. SPAID

Keyword(s):

Boundary Layer ◽

Near Wake ◽

Supercritical Airfoil

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Boundary-layer turbulence spectra in stable conditions

Boundary-Layer Meteorology ◽

10.1007/bf00221819 ◽

1977 ◽

Vol 11 (1) ◽

pp. 3-14 ◽

Cited By ~ 59

Author(s):

S. J. Caughey

Keyword(s):

Boundary Layer ◽

Turbulence Spectra ◽

Boundary Layer Turbulence ◽

Stable Conditions

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Boundary layer turbulence and flow structure over a fringing coral reef

Limnology and Oceanography ◽

10.4319/lo.2006.51.5.1956 ◽

2006 ◽

Vol 51 (5) ◽

pp. 1956-1968 ◽

Cited By ~ 108

Author(s):

Matthew A. Reidenbach ◽

Stephen G. Monismith ◽

Jeffrey R. Koseff ◽

Gitai Yahel ◽

Amatzia Genin

Keyword(s):

Boundary Layer ◽

Coral Reef ◽

Flow Structure ◽

Boundary Layer Turbulence

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Parameterization of Eddy Fluxes near Oceanic Boundaries

Journal of Climate ◽

10.1175/2007jcli1510.1 ◽

2008 ◽

Vol 21 (12) ◽

pp. 2770-2789 ◽

Cited By ~ 84

Author(s):

Raffaele Ferrari ◽

James C. McWilliams ◽

Vittorio M. Canuto ◽

Mikhail Dubovikov

Keyword(s):

Boundary Layer ◽

Transition Layer ◽

General Circulation ◽

Mesoscale Eddies ◽

Turbulent Boundary Layers ◽

Mesoscale Variability ◽

Transition Layers ◽

Boundary Layer Turbulence ◽

Dynamical Coupling ◽

Eddy Fluxes

Abstract In the stably stratified interior of the ocean, mesoscale eddies transport materials by quasi-adiabatic isopycnal stirring. Resolving or parameterizing these effects is important for modeling the oceanic general circulation and climate. Near the bottom and near the surface, however, microscale boundary layer turbulence overcomes the adiabatic, isopycnal constraints for the mesoscale transport. In this paper a formalism is presented for representing this transition from adiabatic, isopycnally oriented mesoscale fluxes in the interior to the diabatic, along-boundary mesoscale fluxes near the boundaries. A simple parameterization form is proposed that illustrates its consequences in an idealized flow. The transition is not confined to the turbulent boundary layers, but extends into the partially diabatic transition layers on their interiorward edge. A transition layer occurs because of the mesoscale variability in the boundary layer and the associated mesoscale–microscale dynamical coupling.

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