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Author
Ali, A. ; Christensen, K.H. ; Breivik, Ø. ; Malila, M. ; Raj, R.P. ; Bertino, L. ; Chassignet, E.P. ; Bakhoday-Paskyabi, M.
Title
A comparison of Langmuir turbulence parameterizations and key wave effects in a numerical model of the North Atlantic and Arctic Oceans
Type
$loc['typeJournal Article']
Year
2019
Publication
Ocean Modelling
Abbreviated Journal
Ocean Modelling
Volume
137
Issue
Pages
76-97
Keywords
Langmuir mixing parameterization Mixed layer depth Sea surface temperature Ocean heat content Stokes penetration depth
Abstract
Five different parameterizations of Langmuir turbulence (LT) effect are investigated in a realistic model of the North Atlantic and Arctic using realistic wave forcing from a global wave hindcast. The parameterizations mainly apply an enhancement to the turbulence velocity scale, and/or to the entrainment buoyancy flux in the surface boundary layer. An additional run is also performed with other wave effects to assess the relative importance of Langmuir turbulence, namely the Coriolis-Stokes forcing, Stokes tracer advection and wave-modified momentum fluxes. The default model (without wave effects) underestimates the mixed layer depth in summer and overestimates it at high latitudes in the winter. The results show that adding LT mixing reduces shallow mixed layer depth (MLD) biases, particularly in the subtropics all year-around, and in the Nordic Seas in summer. There is overall a stronger relative impact on the MLD during winter than during summer. In particular, the parameterization with the most vigorous LT effect causes winter MLD increases by more than 50% relative to a control run without Langmuir mixing. On the contrary, the parameterization which assumes LT effects on the entrainment buoyancy flux and accounts for the Stokes penetration depth is able to enhance the mixing in summer more than in winter. This parametrization is also distinct from the others because it restrains the LT mixing in regions of deep MLD biases, so it is the preferred choice for our purpose. The different parameterizations do not change the amplitude or phase of the seasonal cycle of heat content but do influence its long-term trend, which means that the LT can influence the drift of ocean models. The combined impact on water mass properties from the Coriolis-Stokes force, the Stokes drift tracer advection, and the wave-dependent momentum fluxes is negligible compared to the effect from the parameterized Langmuir turbulence.
Address
Corporate Author
Thesis
Publisher
Place of Publication
Editor
Language
Summary Language
Original Title
Series Editor
Series Title
Abbreviated Series Title
Series Volume
Series Issue
Edition
ISSN
1463-5003
ISBN
Medium
Area
Expedition
Conference
Funding
Approved
$loc['no']
Call Number
COAPS @ user @
Serial
1001
Permanent link to this record
Author
Gouillon, F
Title
Internal Wave Propagation and Numerically Induced Diapycnal Mixing in Oceanic General Circulation Models
Type
$loc['typeManuscript']
Year
2010
Publication
Abbreviated Journal
Volume
Issue
Pages
Keywords
spurious mixing, numerical modeling, internal wave, tide
Abstract
Numerical ocean models have become powerful tools for providing a realistic view of the ocean state and for describing ocean processes that are difficult to observe. Recent improvements in model performance focus on simulating realistic ocean interior mixing rates, as ocean mixing is the main physical process that creates water masses and maintains their properties. Below the mixed layer, diapycnal mixing primarily arises from the breaking of internal waves, whose energy is largely supplied by winds and tides. This is particularly true in abyssal regions, where the barotropic tide interacts with rough topography and where high levels of diapycnal mixing have been recorded (e.g., the Hawaiian Archipelago). Many studies have discussed the representation of internal wave generation, propagation, and evolution in ocean numerical models. Expanding on these studies, this work seeks to better understand the representation of internal wave dynamics, energetics, and their associated mixing in several different classes of widely used ocean models (e.g., the HYbrid Coordinate Ocean Model, HYCOM; the Regional Ocean Modeling System, ROMS; and the MIT general circulation model, MITgcm). First, a multi-model study investigates the representation of internal waves for a wide spectrum of numerical choices, such as the horizontal and vertical resolution, the vertical coordinate, and the choice of the numerical advection scheme. Idealized configurations are compared to their corresponding analytical solutions. Some preliminary results of realistic baroclinic tidal simulations are shown for the Gulf of Mexico. Second, the spurious diapycnal mixing that exists in models with fixed vertical coordinates (i.e., geopotential and terrain following) is documented and quantified. This purely numerical error arises because, in fixed-coordinate models, the numerical framework cannot properly maintain the adiabatic properties of an advected water parcel. This unrealistic mixing of water masses can be a source of major error in both regional and global ocean models. We use the tracer flux method to compute the spurious diapycnal diffusivities for both a lockexchange scenario and a propagating internal wave field using all three models. Results for the lock exchange experiments are compared to the results of a recent study. Our results, obtained by using three different model classes, provide a comprehensive analysis of the impact of model resolution choice and numerical framework on the magnitude of the spurious diapycnal mixing and the representation of internal waves.
Address
Department of Oceanography
Corporate Author
Thesis
$loc['Ph.D. thesis']
Publisher
Florida State University
Place of Publication
Tallahassee, FL
Editor
Language
Summary Language
Original Title
Series Editor
Series Title
Abbreviated Series Title
Series Volume
Series Issue
Edition
ISSN
ISBN
Medium
Area
Expedition
Conference
Funding
Approved
$loc['no']
Call Number
COAPS @ mfield @
Serial
571
Permanent link to this record
Author
Hiester, H.R. ; Piggott, M.D. ; Farrell, P.E. ; Allison, P.A.
Title
Assessment of spurious mixing in adaptive mesh simulations of the two-dimensional lock-exchange
Type
$loc['typeJournal Article']
Year
2014
Publication
Ocean Modelling
Abbreviated Journal
Ocean Modelling
Volume
73
Issue
Pages
30-44
Keywords
Lock-exchange ; Diapycnal mixing ; Adaptive mesh ; Finite-element methods
Abstract
Address
Corporate Author
Thesis
Publisher
Place of Publication
Editor
Language
Summary Language
Original Title
Series Editor
Series Title
Abbreviated Series Title
Series Volume
Series Issue
Edition
ISSN
1463-5003
ISBN
Medium
Area
Expedition
Conference
Funding
Approved
$loc['no']
Call Number
COAPS @ mfield @
Serial
129
Permanent link to this record
Author
Luecke, C.A. ; Arbic, B.K. ; Bassette, S.L. ; Richman, J.G. ; Shriver, J.F. ; Alford, M.H. ; Smedstad, O.M. ; Timko, P.G. ; Trossman, D.S. ; Wallcraft, A.J.
Title
The Global Mesoscale Eddy Available Potential Energy Field in Models and Observations
Type
$loc['typeJournal Article']
Year
2017
Publication
Journal of Geophysical Research: Oceans
Abbreviated Journal
J. Geophys. Res. Oceans
Volume
122
Issue
11
Pages
9126-9143
Keywords
eddy available potential energy ; mesoscale eddies ; mixing ; model-data comparison ; ocean energy reservoirs ; Argo
Abstract
Address
Corporate Author
Thesis
Publisher
Place of Publication
Editor
Language
Summary Language
Original Title
Series Editor
Series Title
Abbreviated Series Title
Series Volume
Series Issue
Edition
ISSN
2169-9275
ISBN
Medium
Area
Expedition
Conference
Funding
Approved
$loc['no']
Call Number
COAPS @ mfield @
Serial
464
Permanent link to this record
Author
Luecke, C.A. ; Arbic, B.K. ; Bassette, S.L. ; Richman, J.G. ; Shriver, J.F. ; Alford, M.H. ; Smedstad, O.M. ; Timko, P.G. ; Trossman, D.S. ; Wallcraft, A.J.
Title
The Global Mesoscale Eddy Available Potential Energy Field in Models and Observations: GLOBAL LOW-FREQUENCY EDDY APE
Type
$loc['typeJournal Article']
Year
2017
Publication
Journal of Geophysical Research: Oceans
Abbreviated Journal
J. Geophys. Res. Oceans
Volume
122
Issue
11
Pages
9126-9143
Keywords
eddy available potential energy ; mesoscale eddies ; mixing ; model‐ ; data comparison ; ocean energy reservoirs ; Argo
Abstract
Global maps of the mesoscale eddy available potential energy (EAPE) field at a depth of 500 m are created using potential density anomalies in a high‐resolution 1/12.5° global ocean model. Maps made from both a free‐running simulation and a data‐assimilative reanalysis of the HYbrid Coordinate Ocean Model (HYCOM) are compared with maps made by other researchers from density anomalies in Argo profiles. The HYCOM and Argo maps display similar features, especially in the dominance of western boundary currents. The reanalysis maps match the Argo maps more closely, demonstrating the added value of data assimilation. Global averages of the simulation, reanalysis, and Argo EAPE all agree to within about 10%. The model and Argo EAPE fields are compared to EAPE computed from temperature anomalies in a data set of “moored historical observations” (MHO) in conjunction with buoyancy frequencies computed from a global climatology. The MHO data set allows for an estimate of the EAPE in high‐frequency motions that is aliased into the Argo EAPE values. At MHO locations, 15–32% of the EAPE in the Argo estimates is due to aliased motions having periods of 10 days or less. Spatial averages of EAPE in HYCOM, Argo, and MHO data agree to within 50% at MHO locations, with both model estimates lying within error bars observations. Analysis of the EAPE field in an idealized model, in conjunction with published theory, suggests that much of the scatter seen in comparisons of different EAPE estimates is to be expected given the chaotic, unpredictable nature of mesoscale eddies.
Address
Corporate Author
Thesis
Publisher
Place of Publication
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Summary Language
Original Title
Series Editor
Series Title
Abbreviated Series Title
Series Volume
Series Issue
Edition
ISSN
2169-9275
ISBN
Medium
Area
Expedition
Conference
Funding
Approved
$loc['no']
Call Number
COAPS @ rl18 @
Serial
992
Permanent link to this record
Author
Magaldi, M.G. ; Özgökmen, T.M. ; Griffa, A. ; Chassignet, E.P. ; Iskandarani, M. ; Peters, H.
Title
Turbulent flow regimes behind a coastal cape in a stratified and rotating environment
Type
$loc['typeJournal Article']
Year
2008
Publication
Ocean Modelling
Abbreviated Journal
Ocean Modelling
Volume
25
Issue
1-2
Pages
65-82
Keywords
Cape ; Headland ; Eddy generation ; Modeling ; Form drag ; Mixing
Abstract
Address
Corporate Author
Thesis
Publisher
Place of Publication
Editor
Language
Summary Language
Original Title
Series Editor
Series Title
Abbreviated Series Title
Series Volume
Series Issue
Edition
ISSN
1463-5003
ISBN
Medium
Area
Expedition
Conference
Funding
Approved
$loc['no']
Call Number
COAPS @ mfield @
Serial
417
Permanent link to this record
Author
Timko, P.G. ; Arbic, B.K. ; Hyder, P. ; Richman, J.G. ; Zamudio, L. ; O'Dea, E. ; Wallcraft, A.J. ; Shriver, J.F.
Title
Assessment of shelf sea tides and tidal mixing fronts in a global ocean model
Type
$loc['typeJournal Article']
Year
2019
Publication
Ocean Modelling
Abbreviated Journal
Ocean Modelling
Volume
136
Issue
Pages
66-84
Keywords
HYCOM ; tides ; seasonal tidal mixing
Abstract
Tidal mixing fronts, which represent boundaries between stratified and tidally mixed waters, are locations of enhanced biological activity. They occur in summer shelf seas when, in the presence of strong tidal currents, mixing due to bottom friction balances buoyancy production due to seasonal heat flux. In this paper we examine the occurrence and fidelity of tidal mixing fronts in shelf seas generated within a global 3-dimensional simulation of the HYbrid Coordinate Ocean Model (HYCOM) that is simultaneously forced by atmospheric fields and the astronomical tidal potential. We perform a first order assessment of shelf sea tides in global HYCOM through comparison of sea surface temperature, sea surface tidal elevations, and tidal currents with observations. HYCOM was tuned to minimize errors in M2 sea surface heights in deep water. Over the global coastal and shelf seas (depths <200 m) the area-weighted root mean square error of the M2 sea surface amplitude in HYCOM represents 35% of the 50 cm root mean squared M2 sea surface amplitude when compared to satellite constrained models TPXO8 and FES2014. HYCOM and the altimeter constrained tidal models TPXO8 and FES2014 exhibit similar skill in reproducing barotropic tidal currents estimated from in-situ current meter observations. Through comparison of a global HYCOM simulation with tidal forcing to a global HYCOM simulation with no tides, and also to previous regional studies of tidal mixing fronts in shelf seas, we demonstrate that HYCOM with embedded tides exhibits quite high skill in reproducing known tidal mixing fronts in shelf seas. Our results indicate that the amount of variability in the location of the tidal mixing fronts in HYCOM, estimated using the Simpson-Hunter parameter, is consistent with previous studies when the differences in the net downward heat flux, on a global scale, are taken into account. We also provide evidence of tidal mixing fronts on the North West Australian Shelf for which we have been unable to find references in the existing scientific literature.
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Publisher
Place of Publication
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Summary Language
Original Title
Series Editor
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Abbreviated Series Title
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Series Issue
Edition
ISSN
1463-5003
ISBN
Medium
Area
Expedition
Conference
Funding
Approved
$loc['no']
Call Number
COAPS @ user @
Serial
1032
Permanent link to this record
Author
Xu, X. ; Rhines, P.B. ; Chassignet, E.P.
Title
On Mapping the Diapycnal Water Mass Transformation of the Upper North Atlantic Ocean
Type
$loc['typeJournal Article']
Year
2018
Publication
Journal of Physical Oceanography
Abbreviated Journal
J. Phys. Oceanogr.
Volume
48
Issue
10
Pages
2233-2258
Keywords
Atmosphere-ocean interaction ; Boundary currents ; Diapycnal mixing ; Fronts ; Thermocline circulation
Abstract
Diapycnal water mass transformation is the essence behind the Atlantic meridional overturning circulation (AMOC) and the associated heat/freshwater transports. Existing studies have mostly focused on the transformation that is forced by surface buoyancy fluxes, and the role of interior mixing is much less known. This study maps the three-dimensional structure of the diapycnal transformation, both surface forced and mixing induced, using results of a high-resolution numerical model that have been shown to represent the large-scale structure of the AMOC and the North Atlantic subpolar/subtropical gyres well. The analyses show that 1) annual mean transformation takes place seamlessly from the subtropical to the subpolar North Atlantic following the surface buoyancy loss along the northward-flowing upper AMOC limb; 2) mixing, including wintertime convection and warm-season restratification by mesoscale eddies in the mixed layer and submixed layer diapycnal mixing, drives transformations of (i) Subtropical Mode Water in the southern part of the subtropical gyre and (ii) Labrador Sea Water in the Labrador Sea and on its southward path in the western Newfoundland Basin; and 3) patterns of diapycnal transformations toward lighter and denser water do not align zonally�the net three-dimensional transformation is significantly stronger than the zonally integrated, two-dimensional AMOC streamfunction (50% in the southern subtropical North Atlantic and 60% in the western subpolar North Atlantic).
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Thesis
Publisher
Place of Publication
Editor
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Summary Language
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Series Editor
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Series Issue
Edition
ISSN
0022-3670
ISBN
Medium
Area
Expedition
Conference
Funding
Approved
$loc['no']
Call Number
COAPS @ user @
Serial
951
Permanent link to this record