Observations of turbulence, internal waves and background flows : an inquiry into the relationships between scales of motion

Polzin, Kurt L.

doi:10.1575/1912/5484

Cited by 11 publications

(3 citation statements)

References 102 publications

(255 reference statements)

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“…Estimates of oceanic velocity, temperature, salinity, and turbulent kinetic energy (e) and thermal (X) dissipation rates are generally available. Detailed descriptions of the HRP and data processing are given by Schmitt et al [1988] and Polzin [1992, Appendix 1]. EPSONDE [Oakey, 1988] is a loosely tethered profiler used to obtain estimates of temperature, e, and X.…”

Section: Fine-scale Sampling and Backgroundmentioning

confidence: 99%

Fine structure and microstructure characteristics across the northwest Atlantic Subtropical Front

Polzin¹,

Oakey²,

Toole³

et al. 1996

J. Geophys. Res.

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Vertical profiles of temperhture, salinity, horizontal velocity, rate Of dissipation Of turbulent kinetic energy, and thermal variance are used to examine the parameterizat. ion of turbulent mixing associated with internal Waves in an upper ocean front. Previous attempts to quantify the rate of turbulent dissipation [e.g., Gregg, 1989; Polzin et al., 1995] are based upon dynamical models of wave-wave interactions using the Garkett and ?flunk [1979] (GM) spectrum. Non-GM conditions (vertical and horizontal anisotropy,. deviations in vertical wavenumber and frequency spectral shape s, and the presence of a background flow) may affect the character of wave interactions, altering the upwavenumber energy flux, which is equated with the rate of turbulent dissipation. Non-GM condifiohs in the data are documented, and revisions to the wave-wave interaction models are discussed. Additionally, the strength of wave-wave interactions is directly compared with the strength of wave'mean flow interactions. These data indicate that the dissipation rate is relatively insensitive to the presence of a background flow and anisotropic wave conditions, in agreement with theoretical expectations based upon wavewave inferaction models and a model. of wave-mean flow interaction at high background RichardsOn number. These data support the findings of Polzin et al. [1995], who argue that the dissipation rate is most sensitive to variations in wave frequency. 1. Introduction Oceanic fronts, generally characterized by abrupt spatial changes of sea surface temperature and water mass characteristics aligned with a jet-like horizontal velocity field, are believed to be sites of enhanced mixing and dissipati6n. Conceptually, one might envision a downscale cascade of energy: the presence of mesoscale features enhances "large"-scale internal wave variability, which in turn influences the fine-scale parameters, which play a role in the producti6n of turbulence. However, the relationships between •he frontal fields with vertical scales of 100 m and horizontal scales of 10 km and the turbulence responsible for the mixing at the microscale, around 1 cm, are not well understood. Observations of internal waves in a background flow tend to reveal heightened spectral levels in regions of negative relative vorticity [Kunze and Sanford, t984; Kunze, 1986; Weller, 1985; Mied et al., 1986]. Kunze [1985] examines the problem of a single near-inertial wave propagating wRhin a front. The study concludes that the lower bound for a freely, propagating nearinertial internal wave is altered from f to f + •/2 owing the presence of the background flow (• being the relative vorticity of the background flow). Waves within a frontal zone having frequencies less than f encounter horizontal turning points and Paper number 96JC01020. 0148-0227/96/96JC-01020509.00 vertical critical layers and are trapped in regions of negative relative •vorticity. • Internal waves can also interact with a background flow through Doppler shifting. Near-inertial interhal waves propagating with...

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Section: Fine-scale Sampling and Backgroundmentioning

confidence: 99%

Fine structure and microstructure characteristics across the northwest Atlantic Subtropical Front

Polzin¹,

Oakey²,

Toole³

et al. 1996

J. Geophys. Res.

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show abstract

“…This simple idea, however, has not stood in the light of recent micro-3 structure data. Polzin (1992) demonstrates that equally important in the scaling of K from internal wave dissipation, are the energy levels and frequency content of the internal wave field. Through out most of the ocean's volume these are well described by the Garrett and Munk model (Garrett and Munk, 1975), and the resulting diffusivities are small (-0. lcm 2 s' 1 ), in agreement with the values found away from the bottom in the present model.…”

mentioning

confidence: 96%

Exchanges between hemispheres and gyres : a direct approach to the mean circulation of the equatorial Pacific

Wijffels¹

1993

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“…The empirical

C D F true(R i^{- 1} true)

are shown in Figure , where they are in excellent agreement with the following CDF of simple exponential distribution:

C D F true(x, μ true) = 1 - e^{- x / μ}, x \geq 0,

where

x = R i^{- 1}

μ

is the mean, and

μ^{2}

is the variance. The parameter μ is

μ_{(40 - 75)} = 0.67 \pm 0.03

for

R i^{- 1}

in the depth range Dz = 40–75 and

μ_{(75 - 150)} = 1.16 \pm 0.035

for

R i^{- 1}

in the range Dz = 75–150 m. The exponential distribution of

R i^{- 1}

has been already utilized by Anderson [] and Polzin [] (unpublished manuscripts referred to by Pinkel and Anderson []). The behavior of (3) is similar to a probability distribution for

R i^{- 1}

suggested by Pinkel and Anderson [].…”

Section: Internal Wavesmentioning

confidence: 99%

A snapshot of internal waves and hydrodynamic instabilities in the southern Bay of Bengal

et al. 2016

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Measurements conducted in the southern Bay of Bengal (BoB) as a part of the ASIRI‐EBoB Program portray the characteristics of high‐frequency internal waves in the upper pycnocline as well as the velocity structure with episodic events of shear instability. A 20 h time series of CTD, ADCP, and acoustic backscatter profiles down to 150 m as well as temporal CTD measurements in the pycnocline at z = 54 m were taken to the east of Sri Lanka. Internal waves of periods ∼10–40 min were recorded at all depths below a shallow (∼20–30 m) surface mixed layer in the background of an 8 m amplitude internal tide. The absolute values of vertical displacements associated with high‐frequency waves followed the Nakagami distribution with a median value of 2.1 m and a 95% quintile 6.5 m. The internal wave amplitudes are normally distributed. The tails of the distribution deviate from normality due to episodic high‐amplitude displacements. The sporadic appearance of internal waves with amplitudes exceeding ∼5 m usually coincided with patches of low Richardson numbers, pointing to local shear instability as a possible mechanism of internal‐wave‐induced turbulence. The probability of shear instability in the summer BoB pycnocline based on an exponential distribution of the inverse Richardson number, however, appears to be relatively low, not exceeding 4% for Ri < 0.25 and about 10% for Ri < 0.36 (K‐H billows). The probability of the generation of asymmetric breaking internal waves and Holmboe instabilities is above ∼25%.

show abstract

Observations of turbulence, internal waves and background flows : an inquiry into the relationships between scales of motion

Cited by 11 publications

References 102 publications

Fine structure and microstructure characteristics across the northwest Atlantic Subtropical Front

Fine structure and microstructure characteristics across the northwest Atlantic Subtropical Front

Exchanges between hemispheres and gyres : a direct approach to the mean circulation of the equatorial Pacific

A snapshot of internal waves and hydrodynamic instabilities in the southern Bay of Bengal

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