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  • 1
    Online Resource
    Online Resource
    Impacts of Convergence on Structure Functions from Surface Drifters in the Gulf of Mexico
    American Meteorological Society ; 2019
    In:  Journal of Physical Oceanography Vol. 49, No. 3 ( 2019-03), p. 675-690
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 49, No. 3 ( 2019-03), p. 675-690
    Abstract: There are limitations in approximating Eulerian statistics from surface drifters, due to biases from surface convergences. By contrasting second- and third-order Eulerian and surface drifter structure functions obtained from a model of the Gulf of Mexico, the consequences of the semi-Lagrangian nature of observations during the summer Grand Lagrangian Deployment (GLAD) and winter Lagrangian Submesoscale Experiment (LASER) are estimated. By varying launch pattern and location, the robustness and sensitivity of these statistics are evaluated. Over scales less than 10 km, second-order structure functions of surface drifters consistently have shallower slopes (~ r 2/3 ) than Eulerian statistics (~ r ), suggesting that surface drifter structure functions differ systematically and do not reproduce the scalings of the Eulerian fields. Medians of Eulerian and cluster release second-order statistics are also significantly different across all scales. Synthetic cluster release statistics depend on launch location and weakly on launch pattern. The observations suggest little seasonal difference in the second-order statistics, but the LASER third-order structure function shows a sign change around 1 km, while GLAD and the synthetic cluster releases show a third-order structure function sign change around 10 km. Further, synthetic surface drifter cluster releases (and therefore likely the GLAD observations) show robust biases in the negative third-order structure functions, which may lead to significant overestimation of the spectral energy flux and underestimation of the transition scale to a forward energy cascade. The Helmholtz decomposition, and curl and divergence statistics, of Eulerian and cluster releases differ, particularly on scales less than 10 km, in agreement with observations of drifters preferentially sampling convergences in coherent structures.
    Type of Medium: Online Resource
    ISSN: 0022-3670 , 1520-0485
    URL: Article
    DOI: 10.1175/JPO-D-18-0029.1
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2019
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 2
    Online Resource
    Online Resource
    Assessing the Effects of Langmuir Turbulence on the Entrainment Buoyancy Flux in the Ocean Surface Boundary Layer
    American Meteorological Society ; 2017
    In:  Journal of Physical Oceanography Vol. 47, No. 12 ( 2017-12), p. 2863-2886
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 47, No. 12 ( 2017-12), p. 2863-2886
    Abstract: Large-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.
    Type of Medium: Online Resource
    ISSN: 0022-3670 , 1520-0485
    URL: Article
    DOI: 10.1175/JPO-D-17-0085.1
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2017
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 3
    Online Resource
    Online Resource
    The Growth and Saturation of Submesoscale Instabilities in the Presence of a Barotropic Jet
    American Meteorological Society ; 2018
    In:  Journal of Physical Oceanography Vol. 48, No. 11 ( 2018-11), p. 2779-2797
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 48, No. 11 ( 2018-11), p. 2779-2797
    Abstract: Motivated by recent observations of submesoscales in the Southern Ocean, we use nonlinear numerical simulations and a linear stability analysis to examine the influence of a barotropic jet on submesoscale instabilities at an isolated front. Simulations of the nonhydrostatic Boussinesq equations with a strong barotropic jet (approximately matching the observed conditions) show that submesoscale disturbances and strong vertical velocities are confined to a small region near the initial frontal location. In contrast, without a barotropic jet, submesoscale eddies propagate to the edges of the computational domain and smear the mean frontal structure. Several intermediate jet strengths are also considered. A linear stability analysis reveals that the barotropic jet has a modest influence on the growth rate of linear disturbances to the initial conditions, with at most a ~20% reduction in the growth rate of the most unstable mode. On the other hand, a basic state formed by averaging the flow at the end of the simulation with a strong barotropic jet is linearly stable, suggesting that nonlinear processes modify the mean flow and stabilize the front.
    Type of Medium: Online Resource
    ISSN: 0022-3670 , 1520-0485
    URL: Article
    DOI: 10.1175/JPO-D-18-0022.1
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2018
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 4
    Online Resource
    Online Resource
    Symmetric and Geostrophic Instabilities in the Wave-Forced Ocean Mixed Layer
    American Meteorological Society ; 2015
    In:  Journal of Physical Oceanography Vol. 45, No. 12 ( 2015-12), p. 3033-3056
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 45, No. 12 ( 2015-12), p. 3033-3056
    Abstract: Here, the effects of surface waves on submesoscale instabilities are studied through analytical and linear analyses as well as nonlinear large-eddy simulations of the wave-averaged Boussinesq equations. The wave averaging yields a surface-intensified current (Stokes drift) that advects momentum, adds to the total Coriolis force, and induces a Stokes shear force. The Stokes–Coriolis force alters the geostrophically balanced flow by reducing the burden on the Eulerian–Coriolis force to prop up the front, thereby potentially inciting an anti-Stokes Eulerian shear, while maintaining the Lagrangian (Eulerian plus Stokes) shear. Since the Lagrangian shear is maintained, the Charney–Stern–Pedlosky criteria for quasigeostrophic (QG) baroclinic instability are unchanged with the appropriate Lagrangian interpretation of the shear and QG potential vorticity. While the Stokes drift does not directly affect vorticity, the anti-Stokes Eulerian shear contributes to the Ertel potential vorticity (PV). When the Stokes shear and geostrophic shear are aligned (antialigned), the PV is more (less) cyclonic. If the Stokes-modified PV is anticyclonic, the flow is unstable to symmetric instabilities (SI). Stokes drift also weakly impacts SI through the Stokes shear force. When the Stokes and Eulerian shears are the same (opposite) sign, the Stokes shear force does positive (negative) work on the flow associated with SI. Stokes drift also allows SI to extract more potential energy from the front, providing an indirect mechanism for Stokes-induced restratification.
    Type of Medium: Online Resource
    ISSN: 0022-3670 , 1520-0485
    URL: Article
    DOI: 10.1175/JPO-D-15-0044.1
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2015
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 5
    Online Resource
    Online Resource
    Numerical modelling in a multiscale ocean
    Journal of Marine Research/Yale ; 2017
    In:  Journal of Marine Research Vol. 75, No. 6 ( 2017-11-01), p. 683-725
    Details
    In: Journal of Marine Research, Journal of Marine Research/Yale, Vol. 75, No. 6 ( 2017-11-01), p. 683-725
    Type of Medium: Online Resource
    ISSN: 0022-2402
    URL: Article
    DOI: 10.1357/002224017823523964
    Language: English
    Publisher: Journal of Marine Research/Yale
    Publication Date: 2017
    detail.hit.zdb_id: 410655-6
    detail.hit.zdb_id: 2066603-2
    SSG: 12
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  • 6
    Online Resource
    Online Resource
    Can we use sea surface temperature and productivity proxy records to reconstruct Ekman upwelling?
    Copernicus GmbH ; 2019
    In:  Climate of the Past Vol. 15, No. 6 ( 2019-11-28), p. 1985-1998
    Details
    In: Climate of the Past, Copernicus GmbH, Vol. 15, No. 6 ( 2019-11-28), p. 1985-1998
    Abstract: Abstract. Marine sediments have greatly improved our understanding of the climate system, but their interpretation often assumes that certain climate mechanisms operate consistently over all timescales of interest and that variability at one or a few sample sites is representative of an oceanographic province. In this study, we test these assumptions using modern observations in an idealized manner mimicking paleo-reconstruction to investigate whether sea surface temperature and productivity proxy records in the Southern California Current System can be used to reconstruct Ekman upwelling. The method uses extended empirical orthogonal function (EEOF) analysis of the covariation of alongshore wind stress, chlorophyll, and sea surface temperature as measured by satellites from 2002 to 2009. We find that EEOF1 does not reflect an Ekman upwelling pattern but instead much broader California Current processes. EEOF2 and 3 reflect upwelling patterns, but these patterns are timescale dependent and regional. Thus, the skill of using one site to reconstruct the large-scale dominant patterns is spatially dependent. Lastly, we show that using multiple sites and/or multiple variables generally improves field reconstruction. These results together suggest that caution is needed when attempting to extrapolate mechanisms that may be important on seasonal timescales (e.g., Ekman upwelling) to deeper time but also the advantage of having multiple proxy records.
    Type of Medium: Online Resource
    ISSN: 1814-9332
    URL: Article
    DOI: 10.5194/cp-15-1985-2019
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2019
    detail.hit.zdb_id: 2217985-9
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  • 7
    Online Resource
    Online Resource
    Ocean Climate Observing Requirements in Support of Climate Research and Climate Information
    Frontiers Media SA ; 2019
    In:  Frontiers in Marine Science Vol. 6 ( 2019-7-31)
    Details
    In: Frontiers in Marine Science, Frontiers Media SA, Vol. 6 ( 2019-7-31)
    Type of Medium: Online Resource
    ISSN: 2296-7745
    URL: Article
    DOI: 10.3389/fmars.2019.00444
    Language: Unknown
    Publisher: Frontiers Media SA
    Publication Date: 2019
    detail.hit.zdb_id: 2757748-X
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  • 8
    Online Resource
    Online Resource
    Scale Transition From Geostrophic Motions to Internal Waves in the Northern South China Sea
    American Geophysical Union (AGU) ; 2019
    In:  Journal of Geophysical Research: Oceans Vol. 124, No. 12 ( 2019-12), p. 9364-9383
    Details
    In: Journal of Geophysical Research: Oceans, American Geophysical Union (AGU), Vol. 124, No. 12 ( 2019-12), p. 9364-9383
    Abstract: The transition of KE from geostrophic flows to unbalanced motions is found to be larger than 200 km in the upper ocean of the NSCS The frequency‐wavenumber analysis reveals the dominated processes for the transition The semidiurnal internal tides are found to have a significant contribution to the variance of sea surface height in the NSCS
    Type of Medium: Online Resource
    ISSN: 2169-9275 , 2169-9291
    URL: Article
    DOI: 10.1029/2019JC015575
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2019
    detail.hit.zdb_id: 2016804-4
    detail.hit.zdb_id: 161667-5
    detail.hit.zdb_id: 3094219-6
    SSG: 16,13
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  • 9
    Online Resource
    Online Resource
    Log-Normal Turbulence Dissipation in Global Ocean Models
    American Physical Society (APS) ; 2018
    In:  Physical Review Letters Vol. 120, No. 9 ( 2018-2-26)
    Details
    In: Physical Review Letters, American Physical Society (APS), Vol. 120, No. 9 ( 2018-2-26)
    Type of Medium: Online Resource
    ISSN: 0031-9007 , 1079-7114
    URL: Article
    DOI: 10.1103/PhysRevLett.120.094501
    RVK:
    UA 1000
    RVK:
    UA 6520
    Language: English
    Publisher: American Physical Society (APS)
    Publication Date: 2018
    detail.hit.zdb_id: 1472655-5
    detail.hit.zdb_id: 208853-8
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  • 10
    Online Resource
    Online Resource
    The role of mixed-layer instabilities in submesoscale turbulence
    Cambridge University Press (CUP) ; 2016
    In:  Journal of Fluid Mechanics Vol. 788 ( 2016-02-10), p. 5-41
    Details
    In: Journal of Fluid Mechanics, Cambridge University Press (CUP), Vol. 788 ( 2016-02-10), p. 5-41
    Abstract: Upper-ocean turbulence at scales smaller than the mesoscale is believed to exchange surface and thermocline waters, which plays an important role in both physical and biogeochemical budgets. But what energizes this submesoscale turbulence remains a topic of debate. Two mechanisms have been proposed: mesoscale-driven surface frontogenesis and baroclinic mixed-layer instabilities. The goal here is to understand the differences between the dynamics of these two mechanisms, using a simple quasi-geostrophic model. The essence of mesoscale-driven surface frontogenesis is captured by the well-known surface quasi-geostrophic model, which describes the sharpening of surface buoyancy gradients and the subsequent breakup in secondary roll-up instabilities. We formulate a similarly archetypical Eady-like model of submesoscale turbulence induced by mixed-layer instabilities. The model captures the scale and structure of this baroclinic instability in the mixed layer. A wide range of scales are energized through a turbulent inverse cascade of kinetic energy that is fuelled by the submesoscale mixed-layer instability. Major differences to mesoscale-driven surface frontogenesis are that mixed-layer instabilities energize the entire depth of the mixed layer and produce larger vertical velocities. The distribution of energy across scales and in the vertical produced by our simple model of mixed-layer instabilities compares favourably to observations of energetic wintertime submesoscale flows, suggesting that it captures the leading-order balanced dynamics of these flows. The dynamics described here in an oceanographic context have potential applications to other geophysical fluids with layers of different stratifications.
    Type of Medium: Online Resource
    ISSN: 0022-1120 , 1469-7645
    URL: Article
    DOI: 10.1017/jfm.2015.700
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2016
    detail.hit.zdb_id: 1472346-3
    detail.hit.zdb_id: 218334-1
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