A Parameterization with a Constrained Potential Energy Conversion Rate of Vertical Mixing Due to Langmuir Turbulence

AbstractIn this study we develop a new parameterization for turbulent mixing in the ocean surface boundary layer (OSBL), including the effect of Langmuir turbulence. This new parameterization builds on a recent study (Reichl and Hallberg 2018, hereafter RH18), which predicts the available energy for turbulent mixing against stable stratification driven by shear and convective turbulence. To investigate the role of Langmuir turbulence in the framework of RH18, we utilize data from a suite of previously published large-eddy simulation (LES) experiments (Li and Fox-Kemper 2017, hereafter LF17) with and without Langmuir turbulence under different idealized forcing conditions. We find that the parameterization of RH18 is able to reproduce the mixing simulated by the LES in the non-Langmuir cases, but not the Langmuir cases. We therefore investigate the enhancement of the integrated vertical buoyancy flux within the entrainment layer in the presence of Langmuir turbulence using the LES data. An additional factor is introduced in the RH18 framework to capture the enhanced mixing due to Langmuir turbulence. This additional factor depends on the surface-layer averaged Langmuir number with a reduction in the presence of destabilizing surface buoyancy fluxes. It is demonstrated that including this factor within the RH18 OSBL turbulent mixing parameterization framework captures the simulated effect of Langmuir turbulence in the LES, which can be used for simulating the effect of Langmuir turbulence in climate simulations. This new parameterization is compared to the KPP-based Langmuir entrainment parameterization introduced by LF17, and differences are explored in detail.

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Reply to “Comments on ‘Langmuir Turbulence and Surface Heating in the Ocean Surface Boundary Layer’”

Journal of Physical Oceanography ◽

10.1175/jpo-d-17-0176.1 ◽

2018 ◽

Vol 48 (2) ◽

pp. 459-462

Author(s):

Brodie C. Pearson ◽

Alan L. M. Grant ◽

Jeff A. Polton ◽

Stephen E. Belcher

Keyword(s):

Boundary Layer ◽

Ocean Surface ◽

Nocturnal Boundary Layer ◽

Surface Heating ◽

Surface Boundary ◽

Langmuir Turbulence ◽

Layer Depth ◽

Surface Boundary Layer ◽

Surface Buoyancy ◽

Surface Buoyancy Flux

AbstractThe differences between the conclusions of Noh and Choi and of Pearson et al., which are largely a result of defining different length scales based on different quantities, are discussed. This study shows that the layer over which Langmuir turbulence mixes (nominally hTKE) under a stabilizing surface buoyancy flux should be scaled by a combination of the Langmuir stability length LL and initial/nocturnal boundary layer depth h0 rather than by the Zilitinkevich length.

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A global perspective on Langmuir turbulence in the ocean surface boundary layer

Geophysical Research Letters ◽

10.1029/2012gl052932 ◽

2012 ◽

Vol 39 (18) ◽

Cited By ~ 167

Author(s):

Stephen E. Belcher ◽

Alan L. M. Grant ◽

Kirsty E. Hanley ◽

Baylor Fox-Kemper ◽

Luke Van Roekel ◽

...

Keyword(s):

Boundary Layer ◽

Ocean Surface ◽

Global Perspective ◽

Surface Boundary ◽

Langmuir Turbulence ◽

Surface Boundary Layer

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LESbrary: A library of large eddy simulation data for the calibration and uncertainty quantification of ocean surface boundary layer turbulence parameterizations

10.5194/egusphere-egu21-16199 ◽

2021 ◽

Author(s):

Gregory Wagner ◽

Andre Souza ◽

Adeline Hillier ◽

Ali Ramadhan ◽

Raffaele Ferrari

Keyword(s):

Boundary Layer ◽

Turbulent Mixing ◽

Large Scale ◽

Ocean Surface ◽

Limited Area ◽

Surface Boundary ◽

Model Errors ◽

Surface Boundary Layer ◽

Large Eddy ◽

Free Parameters

<p>Parameterizations of turbulent mixing in the ocean surface boundary layer (OSBL) are key Earth System Model (ESM) components that modulate the communication of heat and carbon between the atmosphere and ocean interior. OSBL turbulence parameterizations are formulated in terms of unknown free parameters estimated from observational or synthetic data. In this work we describe the development and use of a synthetic dataset called the &#8220;LESbrary&#8221; generated by a large number of idealized, high-fidelity, limited-area large eddy simulations (LES) of OSBL turbulent mixing. We describe how the LESbrary design leverages a detailed understanding of OSBL conditions derived from observations and large scale models to span the range of realistically diverse physical scenarios. The result is a diverse library of well-characterized &#8220;synthetic observations&#8221; that can be readily assimilated for the calibration of realistic OSBL parameterizations in isolation from other ESM model components. We apply LESbrary data to calibrate free parameters, develop prior estimates of parameter uncertainty, and evaluate model errors in two OSBL parameterizations for use in predictive ESMs.</p>

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Along-wind dispersion by horizontal turbulent jets in the upper ocean

Journal of Physical Oceanography ◽

10.1175/jpo-d-20-0285.1 ◽

2021 ◽

Author(s):

Tobias Kukulka ◽

Todd Thoman

Keyword(s):

Turbulent Jets ◽

Surface Boundary ◽

Surface Boundary Layer ◽

Near Surface ◽

Idealized Model ◽

Eddy Simulation ◽

Wind Dispersion ◽

Shear Dispersion ◽

Coherent Jet ◽

Local Shear

AbstractDispersion processes in the ocean surface boundary layer (OSBL) determine marine material distributions such as those of plankton and pollutants. Sheared velocities drive shear dispersion, which is traditionally assumed to be due to mean horizontal currents that decrease from the surface. However, OSBL turbulence supports along-wind jets; located in near-surface convergence and downwelling regions, such turbulent jets contain strong local shear. Through wind-driven idealized and large eddy simulation (LES) models of the OSBL, this study examines the role of turbulent along-wind jets in dispersing material. In the idealized model, turbulent jets are generated by prescribed cellular flow with surface convergence and associated downwelling regions. Numeric and analytic model solutions reveal that horizontal jets substantially contribute to along-wind dispersion for sufficiently strong cellular flows and exceed contributions due to vertical mean shear for buoyant surface-trapped material. However, surface convergence regions also accumulate surface-trapped material, reducing shear dispersion by jets. Turbulence resolving LES results of a coastal depth-limited ocean agree qualitatively with the idealized model and reveal long-lived coherent jet structures that are necessary for effective jet dispersion. These coastal results indicate substantial jet contributions to along-wind dispersion. However, jet dispersion is likely less effective in the open ocean because jets are shorter lived, less organized, and distorted due to spiraling Ekman currents.

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A review of studies on turbulent mixing in ocean surface boundary layer

Oceanography in Japan ◽

10.5928/kaiyou.26.5_239 ◽

2017 ◽

Vol 26 (5) ◽

pp. 239-250 ◽

Cited By ~ 1

Author(s):

Yutaka Yoshikawa ◽

Takahiro Endoh

Keyword(s):

Boundary Layer ◽

Turbulent Mixing ◽

Ocean Surface ◽

Surface Boundary ◽

Surface Boundary Layer

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Effects of Wind on Convection in Strongly and Weakly Baroclinic Flows with Application to the Labrador Sea*

Journal of Physical Oceanography ◽

10.1175/1520-0485-32.9.2603 ◽

2002 ◽

Vol 32 (9) ◽

pp. 2603-2618 ◽

Cited By ~ 10

Author(s):

Fiammetta Straneo ◽

Mitsuhiro Kawase ◽

Robert S. Pickart

Keyword(s):

Deep Convection ◽

Labrador Sea ◽

Surface Boundary ◽

Surface Boundary Layer ◽

Convective Mixing ◽

Slantwise Convection ◽

Horizontal Density Gradient ◽

Surface Buoyancy ◽

Convective Layer ◽

Buoyancy Loss

Abstract Large buoyancy loss driving deep convection is often associated with a large wind stress that is typically omitted in simulations of convection. Here it is shown that this omission is not justified when overturning occurs in a horizontally inhomogeneous ocean. In strongly baroclinic flows, convective mixing is influenced both by the background horizontal density gradient and by the across-front advection of buoyancy due to wind. The former process—known as slantwise convection—results in deeper convection, while the effect of wind depends on the relative orientation of wind with respect to the baroclinic front. For the case of the Labrador Sea, wintertime winds act to destabilize the baroclinic Labrador Current causing a buoyancy removal roughly one-third as large as the air–sea buoyancy loss. Simulations using a nonhydrostatic numerical model, initialized and forced with observed fields from the Labrador Sea, show how the combination of wind and lateral gradients can result in significant convection within the current, in contrast with previous ideas. Though the advection of buoyancy due to wind in weakly baroclinic flows is negligible compared to the surface buoyancy removal typical of convective conditions, convective plumes are substantially deformed by wind. This deformation, and the associated across-front secondary circulation, are explained in terms of the vertical advection of wind-generated vorticity from the surface boundary layer to deeper depths. This mechanism generates vertical structure within the convective layer, contradicting the historical notion that properties become vertically homogenized during convection. For the interior Labrador Sea, this mechanism may be partly responsible for the vertical variability observed during convection, which modeling studies have until now failed to reproduce.

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Assessing the Effects of Langmuir Turbulence on the Entrainment Buoyancy Flux in the Ocean Surface Boundary Layer

Journal of Physical Oceanography ◽

10.1175/jpo-d-17-0085.1 ◽

2017 ◽

Vol 47 (12) ◽

pp. 2863-2886 ◽

Cited By ~ 30

Author(s):

Qing Li ◽

Baylor Fox-Kemper

Keyword(s):

Boundary Layer ◽

Climate Model ◽

Ocean Surface ◽

Buoyancy Flux ◽

Entrainment Rate ◽

Surface Boundary ◽

Langmuir Turbulence ◽

Convective Turbulence ◽

Surface Boundary Layer ◽

The Impact

AbstractLarge-eddy simulations (LESs) with various constant wind, wave, and surface destabilizing surface buoyancy flux forcing are conducted, with a focus on assessing the impact of Langmuir turbulence on the entrainment buoyancy flux at the base of the ocean surface boundary layer. An estimate of the entrainment buoyancy flux scaling is made to best fit the LES results. The presence of Stokes drift forcing and the resulting Langmuir turbulence enhances the entrainment rate significantly under weak surface destabilizing buoyancy flux conditions, that is, weakly convective turbulence. In contrast, Langmuir turbulence effects are moderate when convective turbulence is dominant and appear to be additive rather than multiplicative to the convection-induced mixing. The parameterized unresolved velocity scale in the K-profile parameterization (KPP) is modified to adhere to the new scaling law of the entrainment buoyancy flux and account for the effects of Langmuir turbulence. This modification is targeted on common situations in a climate model where either Langmuir turbulence or convection is important and may overestimate the entrainment when both are weak. Nevertheless, the modified KPP is tested in a global climate model and generally outperforms those tested in previous studies. Improvements in the simulated mixed layer depth are found, especially in the Southern Ocean in austral summer.

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Modelling vertical mixing in the surface boundary layer using artificial age tracers

Journal of Marine Systems ◽

10.1016/j.jmarsys.2005.11.009 ◽

2006 ◽

Vol 60 (1-2) ◽

pp. 115-128 ◽

Cited By ~ 9

Author(s):

Jørgen Bendtsen ◽

Karin E. Gustafsson ◽

Jens Kjerulf Petersen

Keyword(s):

Boundary Layer ◽

Vertical Mixing ◽

Surface Boundary ◽

Surface Boundary Layer

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Symmetric Instability, Inertial Oscillations, and Turbulence at the Gulf Stream Front

Journal of Physical Oceanography ◽

10.1175/jpo-d-15-0008.1 ◽

2016 ◽

Vol 46 (1) ◽

pp. 197-217 ◽

Cited By ~ 43

Author(s):

Leif N. Thomas ◽

John R. Taylor ◽

Eric A. D’Asaro ◽

Craig M. Lee ◽

Jody M. Klymak ◽

...

Keyword(s):

Boundary Layer ◽

Stability Analysis ◽

Gulf Stream ◽

Surface Boundary ◽

Unstable Flow ◽

Inertial Oscillations ◽

Surface Boundary Layer ◽

Eddy Simulation ◽

Symmetric Instability ◽

Shear Production

AbstractThe passage of a winter storm over the Gulf Stream observed with a Lagrangian float and hydrographic and velocity surveys provided a unique opportunity to study how the interaction of inertial oscillations, the front, and symmetric instability (SI) shapes the stratification, shear, and turbulence in the upper ocean under unsteady forcing. During the storm, the rapid rise and rotation of the winds excited inertial motions. Acting on the front, these sheared motions modulate the stratification in the surface boundary layer. At the same time, cooling and downfront winds generated a symmetrically unstable flow. The observed turbulent kinetic energy dissipation exceeded what could be attributed to atmospheric forcing, implying SI drew energy from the front. The peak excess dissipation, which occurred just prior to a minimum in stratification, surpassed that predicted for steady SI turbulence, suggesting the importance of unsteady dynamics. The measurements are interpreted using a large-eddy simulation (LES) and a stability analysis configured with parameters taken from the observations. The stability analysis illustrates how SI more efficiently extracts energy from a front via shear production during periods when inertial motions reduce stratification. Diagnostics of the energetics of SI from the LES highlight the temporal variability in shear production but also demonstrate that the time-averaged energy balance is consistent with a theoretical scaling that has previously been tested only for steady forcing. As the storm passed and the winds and cooling subsided, the boundary layer restratified and the thermal wind balance was reestablished in a manner reminiscent of geostrophic adjustment.

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