Multi-layer quasi-geostrophic ocean dynamics in Eddy-resolving regimes

Shevchenko, Igor; Berloff, Pavel

doi:10.1016/j.ocemod.2015.07.018

Cited by 41 publications

(44 citation statements)

References 16 publications

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“…In particular, these results suggested that the eddies have to maintain the eastward jet extension of the western boundary currents and its adjacent recirculation zones and to slow down the western parts of the subtropical and subpolar gyres. In turn, these results are consistent with the actual eddy effects in the nonlinear double-gyre solutions (e.g., [26,48]). Second, from the equivalent eddy PV fluxes and the underlying large-scale PV gradients, we calculated a spatially inhomogeneous and anisotropic eddy diffusivity tensor.…”

Section: Discussionsupporting

confidence: 81%

Dynamically Consistent Parameterization of Mesoscale Eddies—Part II: Eddy Fluxes and Diffusivity from Transient Impulses

Berloff

2016

Fluids

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This work continues development of the framework for dynamically consistent parameterization of mesoscale eddy effects in non-eddy-resolving ocean circulation models. Here, we refine and extend the previous results obtained for the double gyres and aim to account for the eddy backscatter mechanism that maintains eastward jet extension of the western boundary currents. We start by overcoming the local homogeneity assumption and by taking into account full large-scale circulation. We achieve this by considering linearized-dynamic responses to finite-time transient impulses. Feedback from these impulses on the large-scale circulation are referred to as footprints. We find that the local homogeneity assumption yields only quantitative errors in most of the gyres but breaks down in the eastward jet region, which is characterized by the most significant eddy effects. The approach taken provides new insights into the eddy/mean interactions and framework for parameterization of unresolved eddy effects. Footprints provide us with maps of potential vorticity anomalies expected to be induced by transient eddy forcing. This information is used to calculate the equivalent eddy potential vorticity fluxes and their divergences that partition the double-gyre circulation into distinct geographical regions with specific eddy effects. In particular, this allows approximation of the real eddy effects that maintain the eastward jet extension of the western boundary currents and its adjacent recirculation zones. Next, from footprints and their equivalent eddy fluxes and from underlying large-scale flow gradients, we calculate spatially inhomogeneous and anisotropic eddy diffusivity tensor. Its properties suggest that imposing parameterized source terms, that is, equivalent eddy flux divergences, is a better parameterization strategy than implementation of the eddy diffusion.

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Section: Discussionsupporting

confidence: 81%

Dynamically Consistent Parameterization of Mesoscale Eddies—Part II: Eddy Fluxes and Diffusivity from Transient Impulses

Berloff

2016

Fluids

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“…Our conclusions do not imply that all eddies move within eddy trains, and isolated and nonzonally propagating eddies are certainly possible (e.g., Chelton et al 2011). Findings of the paper have to be extended to and verified in much more turbulent and eddy-resolving flow regimes, like the ones achieved by Shevchenko and Berloff (2015).…”

Section: Discussionmentioning

confidence: 91%

Eddy Trains and Striations in Quasigeostrophic Simulations and the Ocean

Chen

Kamenkovich

Berloff

2016

Journal of Physical Oceanography

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This study explores the relationship between coherent eddies and zonally elongated striations. The investigation involves an analysis of two baroclinic quasigeostrophic models of a zonal and double-gyre flow and a set of altimetry sea level anomaly data in the North Pacific. Striations are defined by either spatiotemporal filtering or empirical orthogonal functions (EOFs), with both approaches leading to consistent results. Coherent eddies, identified here by the modified Okubo-Weiss parameter, tend to propagate along well-defined paths, thus forming ''eddy trains'' that coincide with striations. The striations and eddy trains tend to drift away from the intergyre boundary at the same speed in both the model and observations. The EOF analysis further confirms that these striations in model simulations and altimetry are not an artifact of temporal averaging of random, spatially uncorrelated vortices. This study suggests instead that eddies organize into eddy trains, which manifest themselves as striations in low-pass filtered data and EOF modes.

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“…The explored flow regime was studied earlier by Shevchenko & Berloff (2015), who focused on the flow dependencies on the Reynolds number and other physical parameters.…”

Section: Problem Formulationmentioning

confidence: 99%

On low-frequency variability of the midlatitude ocean gyres

et al. 2016

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This paper studies the large-scale low-frequency variability of the wind-driven midlatitude ocean gyres and their western boundary currents, such as the Gulf Stream or Kuroshio, simulated with the eddy-resolving quasi-geostrophic model. We applied Empirical Orthogonal Functions Analysis to turbulent flow solutions and statistically extracted robust and significant large-scale decadal variability modes concentrated around the eastward jet extension of the western boundary currents. In order to interpret these statistical modes dynamically, we linearized the governing quasi-geostrophic equations around the timemean circulation and solved for the corresponding full set of linear eigenmodes with their eigenfrequencies. We then projected the extracted decadal variability on the eigenmodes and found that this variability is a multi-modal coherent-pattern phenomenon rather than a single mode or a combination of several modes as in the flow regimes preceding developed turbulence.

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Multi-layer quasi-geostrophic ocean dynamics in Eddy-resolving regimes

Abstract: The multi-layer quasi-geostrophic model of the wind-driven ocean gyres is numerically investigated using a combi- convergence of the solutions, we found the empirical dependency between the eddy viscosity and the required grid

Cited by 41 publications

References 16 publications

Dynamically Consistent Parameterization of Mesoscale Eddies—Part II: Eddy Fluxes and Diffusivity from Transient Impulses

Dynamically Consistent Parameterization of Mesoscale Eddies—Part II: Eddy Fluxes and Diffusivity from Transient Impulses

Eddy Trains and Striations in Quasigeostrophic Simulations and the Ocean

On low-frequency variability of the midlatitude ocean gyres

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