Ocean kinetic energy backscatter parametrizations on unstructured grids: Impact on mesoscale turbulence in a channel

Juricke, Stephan; Danilov, Sergey; Kutsenko, Anton A.; Oliver, Marcel

doi:10.1016/j.ocemod.2019.03.009

Cited by 32 publications

(115 citation statements)

References 39 publications

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“…Klöwer et al () developed their model for the dissipation fraction in the context of western boundary intensification in a double gyre North Atlantic box setup. Thus, it is adjusted to the pathways of dissipation in turbulent western boundary currents but does not accommodate for effects of coastal shelves; neither Klöwer et al () nor Juricke et al () included complex bottom topography or transient forcing by variable winds or buoyancy fluxes. Thus, the question how the fraction of physically dissipated energy should be modeled to properly include the effects of transient forcing, shelf turbulence, and underresolved viscous boundary layers requires further study.…”

Section: Results Of the Main Simulationsmentioning

confidence: 99%

“…The Rossby radius on shelves is also very small, which is why any inverse energy cascade is difficult to resolve, especially with the resolution of the current setup. This is why backscatter may need to be substantially reduced here, since it relies on an at least partly resolved inverse cascade (Juricke et al, ). While this is generally the case in the open ocean, additional pathways to energy dissipation will need to be accounted for close to the coastlines.…”

Section: Discussion and Outlookmentioning

confidence: 99%

“…Simulation REF is an extension of the control and uses the same parameter settings: a time step of 20 min and the modified harmonic Leith viscosity with biharmonic background viscosity (see Fox-Kemper & Menemenlis, 2008, and the appendix of Juricke et al, 2019, for more details). The only difference to the control is that the GM eddy parametrization (Gent & McWilliams, 1990) for non-eddy-resolving grids was switched off entirely in REF, while the control used the resolution-scaled GM parametrization following Wang et al (2014).…”

Section: Methodsmentioning

confidence: 99%

“…Further details on model setup as well as temporal and spatial discretizations can be found in Danilov et al (2017) and Scholz et al (2019). The implementation of backscatter follows Juricke et al (2019).…”

Section: Model Setupmentioning

confidence: 99%

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Ocean Kinetic Energy Backscatter Parametrization on Unstructured Grids: Impact on Global Eddy‐Permitting Simulations

Juricke

Danilov

Koldunov

et al. 2020

J Adv Model Earth Syst

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In this study we demonstrate the potential of a kinetic energy backscatter scheme for use in global ocean simulations. Ocean models commonly employ (bi)harmonic eddy viscosities causing excessive dissipation of kinetic energy in eddy-permitting simulations. Overdissipation not only affects the smallest resolved scales but also the generation of eddies through baroclinic instabilities, impacting the entire wave number spectrum. The backscatter scheme returns part of this overdissipated energy back into the resolved flow. We employ backscatter in the FESOM2 multiresolution ocean model with a quasi-uniform 1/4 • mesh. In multidecadal ocean simulations, backscatter increases eddy activity by a factor 2 or more, moving the simulation closer to observational estimates of sea surface height variability. Moreover, mean sea surface height, temperature, and salinity biases are reduced. This amounts to a globally averaged bias reduction of around 10% for each field, which is even larger in the Antarctic Circumpolar Current. However, in some regions such as the coastal Kuroshio, backscatter leads to a slight overenergizing of the flow and, in the Antarctic, to an unrealistic reduction of sea ice. Some of the bias increases can be reduced by a retuning of the model, and we suggest related adjustments to the backscatter scheme. The backscatter simulation is about 2.5 times as expensive as a simulation without backscatter. Most of the increased cost is due to a halving of the time step to accommodate higher simulated velocities. Plain Language SummaryThe weather of the oceans is determined by so-called mesoscale eddies, which carry a large portion of the kinetic energy of ocean currents. They are responsible for the transport of heat and dissolved substances; they can affect the large and fast mean currents of the ocean and interact strongly with the atmosphere above. However, these eddies are not well represented in current ocean and climate models. With this study, we apply a new method to better represent the effect of ocean weather in ocean models. We show that this leads to improvements of the simulation of ocean currents and their variability and reduces biases in ocean temperatures and salinity. While increasing the resolution of ocean models also helps to improve the representation of mesoscale eddies, such a resolution increase is computationally expensive. The new backscatter parametrization can help to save computational costs by allowing improved eddy simulations comparable to much higher resolution.

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Section: Results Of the Main Simulationsmentioning

confidence: 99%

Section: Discussion and Outlookmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Model Setupmentioning

confidence: 99%

See 2 more Smart Citations

Ocean Kinetic Energy Backscatter Parametrization on Unstructured Grids: Impact on Global Eddy‐Permitting Simulations

Juricke

Danilov

Koldunov

et al. 2020

J Adv Model Earth Syst

Self Cite

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“…The magnitude of the backscatter is regulated via an explicit subgrid KE budget, which closes the energy budget and stabilizes the parameterization despite the presence of a negative viscosity. The energy budget‐based backscatter parameterization has so far been tested in a number of idealized configurations, including baroclinic channel flows (Jansen & Held, ; Jansen et al, ; Juricke et al, ) and a barotropic gyre model (Klöwer et al, ), where it substantially improves the solutions at resolutions where the largest eddies are at least marginally resolved. Unfortunately, even so‐called eddy‐permitting global ocean and climate models today reach this resolution only over part of the world's ocean while remaining non‐eddying in other regions (e.g., Hallberg, ).…”

Section: Introductionmentioning

confidence: 99%

Toward an Energetically Consistent, Resolution Aware Parameterization of Ocean Mesoscale Eddies

Jansen

Adcroft

Khani

et al. 2019

J Adv Model Earth Syst

138

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A subgrid‐scale eddy parameterization is developed, which makes use of an explicit eddy kinetic energy budget and can be applied at both “non‐eddying” and “eddy‐permitting” resolutions. The subgrid‐scale eddies exchange energy with the resolved flow in both directions via a parameterization of baroclinic instability (based on the established formulation of Gent and McWilliams) and biharmonic and negative Laplacian viscosity terms. This formulation represents the turbulent cascades of energy and enstrophy consistent with our current understanding of the turbulent eddy energy cycle. At the same time, the approach is simple and general enough to be readily implemented in ocean climate models, without adding significant computational cost. The closure has been implemented in the Modular Ocean Model Version 6 and tested in the “Neverworld” configuration, which employs an idealized analytically defined topography designed as a testbed for mesoscale eddy parameterizations. The parameterization performs well over a range of resolutions, seamlessly connecting non‐eddying and eddy‐resolving regimes.

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Spatial Covariance Modeling for Stochastic Subgrid-Scale Parameterizations Using Dynamic Mode Decomposition

Gugole¹,

Franzke²

2019

Preprint

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Stochastic parameterizations are increasingly being used in climate modeling to represent subgrid-scale processes. While different parameterizations are being developed considering different aspects of the physical phenomena, less attention is given to technical and numerical aspects. In particular, empirical orthogonal functions (EOFs) are employed when a spatial structure is required. Here, we provide evidence they might not be the most suitable choice. By applying an energy-consistent parameterization to the two-layer quasi-geostrophic (QG) model, we investigate the model sensitivity to a priori assumptions made on the parameterization. In particular, we consider here two methods to prescribe the spatial covariance of the noise: first, by using climatological variability patterns provided by EOFs, and second, by using time-varying dynamics-adapted Koopman modes, approximated by dynamic mode decomposition (DMD). The performance of the two methods are analyzed through numerical simulations of the stochastic system on a coarse spatial resolution and the outcomes compared to a high-resolution simulation of the original deterministic system. The comparison reveals that the DMD-based noise covariance scheme outperforms the EOF-based one. The use of EOFs leads to a significant increase of the ensemble spread and to a meridional misplacement of the bimodal eddy kinetic energy (EKE) distribution. Conversely, using DMDs, the ensemble spread is confined, the meridional propagation of the zonal jet stream is accurately captured, and the total variance of the system is improved. Our results highlight the importance of the systematic design of stochastic parameterizations with dynamically adapted spatial correlations, rather than relying on statistical spatial patterns.Plain Language Summary Exact and accurate representations of the climate system would require enormous amounts of computational resources and data storage. Hence, to circumvent this problem, climate models resolve explicitly only the large slow scales, while the fast small modes are represented inside climate models via parameterizations. Due to the different evolution times of the resolved and unresolved scales, the latter can be represented by means of a stochastic process. While different parameterizations are being developed considering different aspects of the physical phenomena, less attention is given to the technical and numerical aspects. In particular, the use of a constant in time noise covariance for the noise is very common. In the framework of a simplified model for the large-scale dynamics, we propose an alternative method to define the noise covariance, which allows it to be regularly updated during the simulation. This might be of crucial importance in the context of climate change. The results show that a dynamically adapted spatial correlation leads to a reduced growth of the uncertainties and better captures the system behavior.

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Ocean kinetic energy backscatter parametrizations on unstructured grids: Impact on mesoscale turbulence in a channel

Cited by 32 publications

References 39 publications

Ocean Kinetic Energy Backscatter Parametrization on Unstructured Grids: Impact on Global Eddy‐Permitting Simulations

Ocean Kinetic Energy Backscatter Parametrization on Unstructured Grids: Impact on Global Eddy‐Permitting Simulations

Toward an Energetically Consistent, Resolution Aware Parameterization of Ocean Mesoscale Eddies

Spatial Covariance Modeling for Stochastic Subgrid-Scale Parameterizations Using Dynamic Mode Decomposition

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