Wave‐Enhanced Tracer Dispersion

Thomas, Jim; Gupta, Aman

doi:10.1029/2020jc017005

Cited by 4 publications

(3 citation statements)

References 58 publications

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“…For example, studies investigating lateral dispersion of tracers in the ocean find that tracer stirring is more efficient than that expected based on QG turbulence scaling [216][217][218][219][220][221][222]. Although observational datasets, ocean model outputs and idealized studies have pointed out that waves can enhance lateral dispersion of tracers [223][224][225][226], the detailed role of different kinds of internal waves across broad parameter regimes in modifying lateral dispersion of tracers and turbulent tracer diffusivity remain unclear. An in-depth study in this direction would benefit the oceanographic community in developing diffusivity parametrizations at mesoscales and submesoscales for large-scale ocean models.…”

Section: (B) Futurementioning

confidence: 99%

Turbulent wave-balance exchanges in the ocean

Thomas

2023

Proc. R. Soc. A.

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Oceanic flows are turbulent and multi-scale in nature, and are composed of fast internal waves and slowly evolving balanced eddies. Contrary to conventional wisdom in physical oceanography, the past two decades of in situ , satellite altimeter and realistically forced global scale ocean model outputs have revealed that internal gravity waves can have comparable or higher energy levels than geostrophically balanced flows at 10–100 km scales in different parts of the world’s oceans. These relatively recent findings have fuelled a wide range of research activities aimed at understanding how fast internal gravity waves interact with slowly evolving balanced flows, particularly with the goal of deducing whether internal waves can form an energy sink for oceanic balanced flows. In this paper, we comprehensively review theoretical, numerical and observational investigations undertaken to study internal wave-balance flow exchanges. Theoretical calculations, inspired by different wave-balance regimes seen in observational and global ocean model outputs, are used to point out that internal waves can affect balanced flow dynamics. The theoretical results are followed up by a detailed discussion of numerical results on wave-balance interactions in a broad set of parameter regimes. The numerical results reveal how different kinds of waves exchange energy with balance flow, affect energy flux across scales of balanced flow and facilitate the generation of small-scale dissipative balanced flow structures. The numerical simulation results and global internal wave energy and balanced energy maps are used to conjecture that out of the 0.8 TW of power going to balanced flow kinetic energy in the ocean, at least 0.1 TW could be dissipated by internal gravity waves. We therefore hypothesize that internal waves can form a non-negligible energy sink for balanced flow in the world’s oceans.

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Section: (B) Futurementioning

confidence: 99%

Turbulent wave-balance exchanges in the ocean

Thomas

2023

Proc. R. Soc. A.

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“…Dispersive waves are ubiquitous in geophysical flows, such as flows in the atmosphere and world's oceans. These waves can spontaneously generate slowly evolving mean flows, enhance turbulent diffusivity of flows and are hypothesized to form an energy sink for balanced vortical flows (Bretherton 1969;Francois et al 2014;Suanda et al 2018;Xia et al 2019;Thomas & Daniel 2020, 2021Thomas & Gupta 2022). The balanced vortical mode in geophysical flows contain a major fraction of the total flow energy and mechanisms by which such mean flows can dissipate their energy is an unresolved question.…”

Section: Introductionmentioning

confidence: 99%

“…2018; Xia et al. 2019; Thomas & Daniel 2020, 2021; Thomas & Gupta 2022). The balanced vortical mode in geophysical flows contain a major fraction of the total flow energy and mechanisms by which such mean flows can dissipate their energy is an unresolved question.…”

Section: Introductionmentioning

confidence: 99%

Upscale transfer of waves in one-dimensional rotating shallow water

Thomas

Ding

2023

J. Fluid Mech.

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We study the inverse flux of waves in one of the simplest geophysical fluid dynamics models: one-dimensional rotating shallow water equations. Based on direct numerical integration of the governing equations, we find that waves injected at small scales get transferred upscale predominantly via resonant quartic interactions between wave modes. The waves’ upscale transfer is non-local and involves turbulent transfer between disparate scales of the flow. Our analysis reveals that the upscale transfer of waves is extremely intermittent and is a result of localized-in-time bursts in wave action flux. These intermittent events of flux bursts lead to shallower waves’ spectrum and relatively higher amplitude wave fields in physical space. On examining statistics of the flow fields, we find that low-energy high wavenumbers more or less comply with the assumptions used in wave turbulence theory, such as uniformly distributed wave phases and the Gaussian distribution of fields, while non-uniform distribution of wave phases and non-Gaussian statistics dominate at large scales or low wavenumbers that contain a major share of the flow energy. Our findings point out that the one-dimensional rotating shallow water equations, despite being a simple geophysical fluid dynamic model, harbour complex and intricate features associated with the upscale transfer of waves that have not been recognized in the past.

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S‐2DV: A New Reduced Model Generating Submesoscale‐Like Flows

Gowthaman,

Thomas

2024

J Adv Model Earth Syst

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Oceanic mesoscale flows are characterized by an inverse kinetic energy cascade and the subsequent formation of large coherent vortices, and these flow features are captured well by the quasi‐geostrophic (QG) model. Oceanic submesoscale flow dynamics are however significantly different from those of mesoscales. The increase in unbalanced energy levels and the Rossby number at submesoscales results in cyclone‐anticyclone asymmetry in vorticity structures, forward kinetic energy cascades, and enhanced small‐scale dissipation. In this paper, we develop a reduced single‐equation model that can generate submesoscale‐like flows in two dimensions. We start from the two‐dimensional barotropic QG equation and add an external random vorticity field, to mimic the effect of unbalanced flow components. Thereafter, we add a vorticity‐squared term, to generate asymmetry in the vorticity structures. By varying the strength of these two terms, we observe that the model can generate submesoscale‐like flows that compare qualitatively well with realistic flows generated by complex ocean models. The reduced model is seen to be capable of generating flows that are intermittent in nature, are characterized by a forward energy flux, and are composed of small‐scale flow structures along with enhanced energy dissipation. We further demonstrate the practical utility of the model by applying it to a passive tracer dispersion and a plankton patchiness problem, these being applications that require submesoscale‐like flows. Our investigation points out that the new model could serve as a convenient platform for various applications that require submesoscale‐like flows, such as testing and developing different kinds of parameterizations.

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Wave‐Enhanced Tracer Dispersion

Cited by 4 publications

References 58 publications

Turbulent wave-balance exchanges in the ocean

Turbulent wave-balance exchanges in the ocean

Upscale transfer of waves in one-dimensional rotating shallow water

S‐2DV: A New Reduced Model Generating Submesoscale‐Like Flows

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