Vortical and Internal Wave Shear and Strain

Pinkel, Robert

doi:10.1175/jpo-d-13-090.1

Cited by 23 publications

(22 citation statements)

References 44 publications

(40 reference statements)

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“…The flattening and steepening of the spectral decay slopes in this work have similar patterns to those of the pycnocline (or oxycline) depths observed in the eastern boundary current system, such that

k^{- 5 / 3}

(

λ > λ_{I}

k^{- 1}

(

λ_{D} \leq λ < λ_{I}

), and

k^{- 2}

(

λ \leq λ_{D}

), where

λ_{I} = 2

km and

λ_{D} = 0.5

km (e.g., Grados et al, ), Although the corresponding injection and dissipations scales are slightly different, the observational analyses in this paper may stimulate additional investigations of the submesoscale vertical structure associated with internal waves using subsurface observations (e.g., ADCP or CTD profiles) (e.g., Kim, ; Pinkel, ) and numerical model runs driven by individual driving forcings (e.g., Kim et al, ). Moreover, these resources allow us to examine the submesoscale energy spectra and KE fluxes as well as their potential associations with internal waves (e.g., Wortham et al, ; Wunsch, ; Zang & Wunsch, ).…”

Section: Discussionsupporting

confidence: 77%

Regional Variability and Turbulent Characteristics of the Satellite‐sensed Submesoscale Surface Chlorophyll Concentrations

Lee

Kim

2018

JGR Oceans

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The regional variability and turbulent characteristics of submesoscale surface chlorophyll concentrations are examined with hourly maps of geostationary ocean color imagery‐derived chlorophyll concentrations at a 0.5 km resolution for a period of 5 years (2011–2015) over the East/Japan Sea with concurrent mesoscale and submesoscale observations. Two seasonal blooms occur in the spring and fall within 250 km off the coast that are associated with constructive combinations of light exposure, nutrients, and vertical stratification. Another bloom occurs in the summer and is closely related to regional wind‐driven upwelling events. The spring and fall blooms are more significant near the coast (within 40 km from the coast) than offshore because of the more energetic submesoscale horizontal shear and vortical phenomena onshore as well as their propagation in the cross‐shore direction. In addition, the regional spring bloom starts offshore and migrate onshore with a time delay of 1 month, which may result from the onshore propagation of geostrophic currents, the deepening of the mixed layer, and favorable nutrient fluxes from the subsurface. The wavenumber‐domain energy spectra of chlorophyll concentrations exhibit anisotropy, which may be closely related to bathymetric effects and regional circulations. The spectral decay slopes change from k−5/3 to k−1 at the O(10) km scales and from k−1 to k≤−3 at the O(1) km scales and have weak seasonality. These results are consistent with the two‐dimensional quasi‐geostrophic turbulence theory and can be interpreted with the baroclinic instability energized from the moderate seasonal mixed layer under mesoscale regional circulations.

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k^{- 5 / 3}

(

λ > λ_{I}

k^{- 1}

(

λ_{D} \leq λ < λ_{I}

), and

k^{- 2}

(

λ \leq λ_{D}

), where

λ_{I} = 2

km and

λ_{D} = 0.5

Section: Discussionsupporting

confidence: 77%

Regional Variability and Turbulent Characteristics of the Satellite‐sensed Submesoscale Surface Chlorophyll Concentrations

Lee

Kim

2018

JGR Oceans

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“…The observation of waves is rendered difficult by the sweeping effect when waves and eddies share the same angular frequency ω and angle θ. As a result, the sweeping effect needs to be taken into account to separate eddies and waves [16] when they share the same location in the (θ, ω) parametric space, i.e., when they are mixed in frequency and direction.…”

Section: Introductionmentioning

confidence: 99%

Partitioning Waves and Eddies in Stably Stratified Turbulence

2020

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We consider the separation of motion related to internal gravity waves and eddy dynamics in stably stratified flows obtained by direct numerical simulations. The waves’ dispersion relation links their angle of propagation to the vertical θ , to their frequency ω , so that two methods are used for characterizing wave-related motion: (a) the concentration of kinetic energy density in the ( θ , ω ) map along the dispersion relation curve; and (b) a direct computation of two-point two-time velocity correlations via a four-dimensional Fourier transform, permitting to extract wave-related space-time coherence. The second method is more computationally demanding than the first. In canonical flows with linear kinematics produced by space-localized harmonic forcing, we observe the pattern of the waves in physical space and the corresponding concentration curve of energy in the ( θ , ω ) plane. We show from a simple laminar flow that the curve characterizing the presence of waves is distorted differently in the presence of a background convective mean velocity, either uniform or varying in space, and also when the forcing source is moving. By generalizing the observation from laminar flow to turbulent flow, this permits categorizing the energy concentration pattern of the waves in complex flows, thus enabling the identification of wave-related motion in a general turbulent flow with stable stratification. The advanced method (b) is finally used to compute the wave-eddy partition in the velocity–buoyancy fields of direct numerical simulations of stably stratified turbulence. In particular, we use this splitting in statistics as varied as horizontal and vertical kinetic energy, as well as two-point velocity and buoyancy spectra.

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“…Indeed, there is an approximate equipartition of the KE between vortex and wave components between 40 and 100 km. A gap could appear in the vertical wavenumber spectra of other quantities such as shear and strain variance (Pinkel 2014). The extent to which inertia-gravity waves and geostrophic flows interact to generate the observed spectra deserves further investigation.…”

mentioning

confidence: 98%

Mesoscale to Submesoscale Wavenumber Spectra in Drake Passage

Rocha

Chereskin

Gille

et al. 2016

Journal of Physical Oceanography

243

300

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This study discusses the upper-ocean (0-200 m) horizontal wavenumber spectra in the Drake Passage from 13 yr of shipboard ADCP measurements, altimeter data, and a high-resolution numerical simulation. At scales between 10 and 200 km, the ADCP kinetic energy spectra approximately follow a k 23 power law. The observed flows are more energetic at the surface, but the shape of the kinetic energy spectra is independent of depth. These characteristics resemble predictions of isotropic interior quasigeostrophic turbulence. The ratio of across-track to along-track kinetic energy spectra, however, significantly departs from the expectation of isotropic interior quasigeostrophic turbulence. The inconsistency is dramatic at scales smaller than 40 km. A Helmholtz decomposition of the ADCP spectra and analyses of synthetic and numerical model data show that horizontally divergent, ageostrophic flows account for the discrepancy between the observed spectra and predictions of isotropic interior quasigeostrophic turbulence. In Drake Passage, ageostrophic motions appear to be dominated by inertia-gravity waves and account for about half of the near-surface kinetic energy at scales between 10 and 40 km. Model results indicate that ageostrophic flows imprint on the sea surface, accounting for about half of the sea surface height variance between 10 and 40 km.

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Vortical and Internal Wave Shear and Strain

Cited by 23 publications

References 44 publications

Regional Variability and Turbulent Characteristics of the Satellite‐sensed Submesoscale Surface Chlorophyll Concentrations

Regional Variability and Turbulent Characteristics of the Satellite‐sensed Submesoscale Surface Chlorophyll Concentrations

Partitioning Waves and Eddies in Stably Stratified Turbulence

Mesoscale to Submesoscale Wavenumber Spectra in Drake Passage

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