scholarly journals The Poisson Link between Internal Wave and Dissipation Scales in the Thermocline. Part II: Internal Waves, Overturns, and the Energy Cascade

2020 ◽  
Vol 50 (12) ◽  
pp. 3425-3438 ◽  
Author(s):  
Robert Pinkel
Keyword(s):  
Correlation Function ◽  
Internal Wave ◽  
Buoyancy Frequency ◽  
Additional Parameter ◽  
Turbulent Dissipation ◽  
The Pacific ◽  
Spectral Models ◽  
Thorpe Scale ◽  
Correlation Scale ◽  
Vertical Correlation

AbstractThe irregular nature of vertical profiles of density in the thermocline appears well described by a Poisson process over vertical scales 2–200 m. To what extent does this view of the thermocline conflict with established models of the internal wavefield? Can a one-parameter Poisson subrange be inserted between the larger-scale wavefield and the microscale field of intermittent turbulent dissipation, both of which require many parameters for their specification? It is seen that a small modification to the Poisson vertical correlation function converts it to the corresponding correlation function of the Garrett–Munk (GM) internal wave spectral model. The linear scaling relations and vertical wavenumber dependencies of the GM model are maintained provided the Poisson constant κ0 is equated with the ratio of twice the displacement variance to the vertical correlation scale of the wavefield. Awareness of this Poisson wavefield relation enables higher-order strain statistics to be determined directly from the strain spectrum. Using observations from across the Pacific Ocean, the average Thorpe scale of individual overturning events is found to be nearly equal to the inverse of κ0, the metric of background thermocline distortion. If the fractional occurrence of overturning ϕ is introduced as an additional parameter, a Poisson version of the Gregg–Henyey relationship can be derived. The Poisson constant, buoyancy frequency, and ϕ combine to create a complete parameterization of energy transfer from internal wave scales through the Poisson subrange to dissipation. An awareness of the underlying Poisson structure of the thermocline will hopefully facilitate further improvement in both internal wave spectral models and ocean mixing parameterizations.

A viscous internal wave in a stratified fluid whose buoyancy frequency varies with altitude

1975 ◽  
Vol 69 (3) ◽  
pp. 615-624 ◽  
Author(s):  
D. Gordon ◽  
U. R. Klement ◽  
T. N. Stevenson
Keyword(s):  
Internal Wave ◽  
Small Amplitude ◽  
Wave Amplitude ◽  
Stratified Fluid ◽  
Similarity Solutions ◽  
Buoyancy Frequency ◽  
Experimental Measurements ◽  
Two Dimensional ◽  
Dimensional Theory ◽  
Curved Paths

A viscous incompressible stably stratified fluid with a buoyancy frequency which varies slowly with altitude is considered. A simple harmonic localized disturbance generates an internal wave in which the energy propagates along curved paths. Small amplitude similarity solutions are obtained for two-dimensional and axisymmetric waves. It is found that under certain conditions the wave amplitude can increase with height. The two-dimensional theory compares quite well with experimental measurements.

scholarly journals Estimates of wind power and radiative near-inertial internal wave flux

2020 ◽  
Vol 70 (11) ◽  
pp. 1357-1376
Author(s):  
Georg S. Voelker ◽  
Dirk Olbers ◽  
Maren Walter ◽  
Christian Mertens ◽  
Paul G. Myers
Keyword(s):  
Energy Transfer ◽  
Internal Wave ◽  
Wind Power ◽  
Mixed Layer ◽  
North Atlantic ◽  
Mixed Layer Depth ◽  
Deep Ocean ◽  
Wave Radiation ◽  
Buoyancy Frequency ◽  
The North

Abstract Energy transfer mechanisms between the atmosphere and the deep ocean have been studied for many years. Their importance to the ocean’s energy balance and possible implications on mixing are widely accepted. The slab model by Pollard (Deep-Sea Res Oceanogr Abstr 17(4):795–812, 1970) is a well-established simulation of near-inertial motion and energy inferred through wind-ocean interaction. Such a model is set up with hourly wind forcing from the NCEP-CFSR reanalysis that allows computations up to high latitudes without loss of resonance. Augmenting the one-dimensional model with the horizontal divergence of the near-inertial current field leads to direct estimates of energy transfer spectra of internal wave radiation from the mixed layer base into the ocean interior. Calculations using this hybrid model are carried out for the North Atlantic during the years 1989 and 1996, which are associated with positive and negative North Atlantic Oscillation index, respectively. Results indicate a range of meridional regimes with distinct energy transfer ratios. These are interpreted in terms of the mixed layer depth, the buoyancy frequency at the mixed layer base, and the wind field structure. The average ratio of radiated energy fluxes from the mixed layer to near-inertial wind power for both years is approximately 12%. The dependence on the wind structure is supported by simulations of idealized wind stress fronts with variable width and translation speeds.

Impact of the Quasi-Biennial Oscillation on the boreal winter tropospheric circulation in CMIP5/6 models

2020 ◽  
Author(s):  
Jian Rao ◽  
Chaim Garfinkel ◽  
Ian White ◽  
Chen Schwartz
Keyword(s):  
Pacific Ocean ◽  
Southern Oscillation ◽  
Polar Vortex ◽  
Buoyancy Frequency ◽  
Maritime Continent ◽  
Quasi Biennial Oscillation ◽  
Stratospheric Polar Vortex ◽  
Enso Events ◽  
The Pacific ◽  
Biennial Oscillation

<p>Using 17 CMIP5/6 models with a spontaneously-generated quasi-biennial oscillation (QBO)-like phenomenon, this study explores and evaluates three dynamical pathways for impacts of the QBO on the troposphere: (i) the Holtan-Tan (HT) effect on the stratospheric polar vortex and the northern annular mode (NAM), (ii) the subtropical zonal wind downward arching over the Pacific, and (iii) changes in local convection over the Maritime Continent and Indo-Pacific Ocean. More than half of the models can reproduce at least one of the three pathways, but few models can reproduce all of the three routes. Firstly, most models are able to simulate a weakened polar vortex during easterly QBO (EQBO) winters, in agreement with the observed HT effect. However, the weakened polar vortex response during EQBO winters is underestimated or not present at all in other models, and hence the QBO → vortex → tropospheric NAM/AO chain is not simulated. For the second pathway associated with the downward arching of the QBO winds, seven models incorrectly or poorly simulate the extratropical easterly anomaly center over 20–40°N in the Pacific sector during EQBO, and hence the negative relative vorticity anomalies poleward of the easterly center is not resolved in those models, leading to an underestimated or incorrectly modelled height response over North Pacific. However the other ten do capture this effect. The third pathway is only observed in the Indo-Pacific Ocean, where the strong climatological deep convection and the warm pool are situated. Nine models can simulate the convection anomalies associated with the QBO over the Maritime Continent, which is likely caused by the near-tropopause low buoyancy frequency anomalies. No robust relationship between the QBO and El Niño–Southern Oscillation (ENSO) events can be established using the ERA-Interim reanalysis, and nine models consistently confirm little modulation of the ocean basin-wide Walker circulation and ENSO events by the QBO.</p>

On internal waves generated by travelling wind

1993 ◽  
Vol 254 ◽  
pp. 529-559 ◽  
Author(s):  
Pijush K. Kundu
Keyword(s):  
Surface Layer ◽  
Internal Waves ◽  
Large Fraction ◽  
Deep Ocean ◽  
Buoyancy Frequency ◽  
Vertical Acceleration ◽  
Mean Flow ◽  
Moving Line ◽  
Vertical Correlation ◽  
Low Order

Oceanic internal waves forced by a latitude-independent wind field travelling eastward at speed U is investigated, extending the hydrostatic f-plane model of Kundu & Thomson (1985). The ocean has a well-mixed surface layer overlying a stratified interior with a depth-dependent buoyancy frequency N(z), and f can vary with latitude. Solutions are found by decomposition into vertical normal modes. Problems discussed are (i) the response to a slowly moving line front, and (ii) the response in a variable f ocean.For the slowly moving line front assuming a depth-independent N, the trailing waves are found to have large frequencies, and the vertical acceleration ∂w/∂t is important (that is the dynamics are non-hydrostatic) if the frequency ω is larger than a few times (Nf)½. The wake contains waves associated with all vertical modes, in contrast to hydrostatic dynamics in which slowly moving line fronts do not generate trailing waves of low-order modes. It is argued that slowly moving wind fields can provide an explanation for the frequently observed broad peak in the spectrum of vertical motion at a frequency somewhat smaller than N, and of the vertical coherence of the associated waves in the upper ocean.To study lower-frequency internal waves, the hydrostatic constant-f model of Kundu & Thomson is extended to variable f. Various sections through such a flow clearly illustrate the development of a meridional wavelength λy = 2π/βt as predicted by D'Asaro (1989), in addition to the zonal wavelength λx due to translation of the wind. The two effects combine to cause a greater horizontal inhomogeneity, so that energy from the surface layer descends quickly, travelling equatorward and downward. Since waves at any point arrive from different latitudes, spectra no longer consist of discrete peaks but are more continuous and broader than those in the constant-f model. The waves are more intermittent because of the larger spectral width, and vertically less correlated in the thermocline because of a larger bandwidth of vertical modes. The vertical correlation in the deep ocean, however, is still high because the response is dominated by one or two low-order modes after 30 days of integration. As U decreases, the larger bandwidth of frequency increases the intermittency, and the larger bandwidth of vertical wavenumber decreases the vertical correlation. A superposition of travelling wind events intensifies the high-frequency end of the spectrum; a month-long travelling series of realistic strength can generate waves with amplitudes of order 4 cm/s in the deep ocean.It is suggested that propagating winds and linear dynamics are responsible for the generation of a large fraction of internal waves in the ocean at all depths. The main effect of nonlinearity and mean flow may be to shape the internal wave spectra to a ω-2 form.

scholarly journals Spatial and temporal covariability in early ocean survival of Chinook salmon (Oncorhynchus tshawytscha) along the west coast of North America

2014 ◽  
Vol 71 (7) ◽  
pp. 1671-1682 ◽  
Author(s):  
D. Patrick Kilduff ◽  
Louis W. Botsford ◽  
Steven L. H. Teo
Keyword(s):  
Chinook Salmon ◽  
Oncorhynchus Tshawytscha ◽  
Survival Rates ◽  
Central Valley ◽  
Vancouver Island ◽  
Regional Patterns ◽  
Migration Patterns ◽  
The Pacific ◽  
Spatial Coverage ◽  
Correlation Scale

Abstract Knowledge of the spatial and temporal extent of covariation in survival during the critical ocean entry stage will improve our understanding of how changing ocean conditions influence salmon productivity and management. We used data from the Pacific coastwide coded-wire tagging program to investigate local and regional patterns of ocean survival of Chinook salmon (Oncorhynchus tshawytscha) from the Central Valley of California to southeastern Alaska from 1980–2006. Ocean survival of fish migrating as subyearlings covaried strongly from Vancouver Island to California. Short-term correlations between adjacent regions indicated this covariability increased, beginning in the early 1990s. Chinook salmon survivals exhibited a larger spatial scale of variability (50% correlation scale: 706 km) than those reported for other northeast Pacific Ocean salmon. This scale is similar to that of environmental variables related to ecosystem productivity, such as summer upwelling (50% correlation scale: 746 km) and sea surface temperature (50% correlation scale: 500–600 km). Chinook salmon ocean survival rates from southeastern Alaska and south of Vancouver Island were not inversely correlated, in contrast to earlier observations based on catch data, but note that our data differ in temporal and spatial coverage from those studies. The increased covariability in Chinook salmon ocean survival suggests that the marine phase contributes little to the reduction in risk across populations attributable to the portfolio effect. In addition, survival of fish migrating as yearlings from the Columbia River covaried with Chinook salmon survival from the northernmost regions, consistent with our understanding of their migration patterns.

scholarly journals Energy Transfer from High-Shear, Low-Frequency Internal Waves to High-Frequency Waves near Kaena Ridge, Hawaii

2012 ◽  
Vol 42 (9) ◽  
pp. 1524-1547 ◽  
Author(s):  
Oliver M. Sun ◽  
Robert Pinkel
Keyword(s):  
Internal Waves ◽  
High Frequency ◽  
Low Frequency ◽  
Buoyancy Frequency ◽  
Reynolds Stresses ◽  
Turbulent Dissipation ◽  
Transfer Rates ◽  
Energy Transfers ◽  
High Frequency Waves ◽  
Parametric Subharmonic Instability

Abstract Evidence is presented for the transfer of energy from low-frequency inertial–diurnal internal waves to high-frequency waves in the band between 6 cpd and the buoyancy frequency. This transfer links the most energetic waves in the spectrum, those receiving energy directly from the winds, barotropic tides, and parametric subharmonic instability, with those most directly involved in the breaking process. Transfer estimates are based on month-long records of ocean velocity and temperature obtained continuously over 80–800 m from the research platform (R/P) Floating Instrument Platform (FLIP) in the Hawaii Ocean Mixing Experiment (HOME) Nearfield (2002) and Farfield (2001) experiments, in Hawaiian waters. Triple correlations between low-frequency vertical shears and high-frequency Reynolds stresses, 〈uiw∂Ui/∂z〉, are used to estimate energy transfers. These are supported by bispectral analysis, which show significant energy transfers to pairs of waves with nearly identical frequency. Wavenumber bispectra indicate that the vertical scales of the high-frequency waves are unequal, with one wave of comparable scale to that of the low-frequency parent and the other of much longer scale. The scales of the high-frequency waves contrast with the classical pictures of induced diffusion and elastic scattering interactions and violates the scale-separation assumption of eikonal models of interaction. The possibility that the observed waves are Doppler shifted from intrinsic frequencies near f or N is explored. Peak transfer rates in the Nearfield, an energetic tidal conversion site, are on the order of 2 × 10−7 W kg−1 and are of similar magnitude to estimates of turbulent dissipation that were made near the ridge during HOME. Transfer rates in the Farfield are found to be about half the Nearfield values.

scholarly journals Seismic imaging of a thermohaline staircase in the western tropical North Atlantic

2010 ◽  
Vol 7 (1) ◽  
pp. 361-389
Author(s):  
I. Fer ◽  
P. Nandi ◽  
W. S. Holbrook ◽  
R. W. Schmitt ◽  
P. Páramo
Keyword(s):  
Internal Wave ◽  
North Atlantic ◽  
Vertical Mixing ◽  
Global Ocean ◽  
Turbulent Dissipation ◽  
Tropical North Atlantic ◽  
Seismic Reflection Method ◽  
Order Of Magnitude ◽  
Salt Fingering ◽  
Wave Induced

Abstract. Multichannel seismic data acquired in the Lesser Antilles in the western tropical North Atlantic indicate that the seismic reflection method has imaged an oceanic thermohaline staircase. Synthetic modeling of observed density and sound speed profiles corroborates inferences from the seismic imagery. Laterally coherent, uniform layers are present at depths ranging from 550–700 m and have a separation of ~20 m, with thicknesses increasing with depth. Reflection coefficient, a measure of the acoustic impedance contrasts, associated with the interfaces is one order of magnitude greater than the background levels. Hydrography sampled in previous surveys puts a constraint on the longevity of these layers in this area to within a maximum of three years. Spectral analysis of layer horizons in the thermohaline staircase indicates that internal wave activity is anomalously low, suggesting weak internal wave-induced turbulence and mixing. Results from two independent measurements, the application of a finescale parameterization to observed high-resolution velocity profiles and direct measurements of turbulent dissipation rate, confirm the low levels of turbulence and mixing. The lack of internal wave-induced mixing allows for the maintenance of the staircase. Our observations show the potential that seismic oceanography can contribute to an improved understanding of temporal occurrence rates, and the geographical distribution of thermohaline staircases and can improve current estimates of vertical mixing rates ascribable to salt fingering in the global ocean.

scholarly journals Turbulence closure: turbulence, waves and the wave-turbulence transition – Part 1: Vanishing mean shear

2008 ◽  
Vol 5 (4) ◽  
pp. 545-580
Author(s):  
H. Z. Baumert ◽  
H. Peters
Keyword(s):  
Internal Wave ◽  
Internal Waves ◽  
Tidal Flow ◽  
Wave Turbulence ◽  
Mean Flow ◽  
Turbulent Length Scale ◽  
Turbulent Dissipation ◽  
New Model ◽  
Turbulence Transition ◽  
Ozmidov Scale

Abstract. A new two-equation, closure-like turbulence model for stably stratified flows is introduced which uses the turbulent kinetic energy (K) and the turbulent enstrophy (Ω) as primary variables. It accounts for mean shear – and internal wave-driven mixing in the two limits of mean shear and no waves and waves but no mean shear, respectively. The traditional TKE balance is augmented by an explicit energy transfer from internal waves to turbulence. A modification of the Ω-equation accounts for the effect of the waves on the turbulence time and space scales. The latter is based on the assumption of a non-zero constant flux Richardson number in the limit of vanishing mean-flow shear when turbulence is produced exclusively by internal waves. The new model reproduces the wave-turbulence transition analyzed by D'Asaro and Lien (2000). At small energy density E of the internal wave field, the turbulent dissipation rate (ε) scales like ε~E2. This is what is observed in the deep sea. With increasing E, after the wave-turbulence transition has been passed, the scaling changes to ε~E1. This is observed, for example, in the swift tidal flow near a sill in Knight Inlet. The new model further exhibits a turbulent length scale proportional to the Ozmidov scale, as observed in the ocean, and predicts the ratio between the turbulent Thorpe and Ozmidov length scales well within the range observed in the ocean.

Mixing Rates and Bottom Drag in Bering Strait

2020 ◽  
Vol 50 (3) ◽  
pp. 809-825
Author(s):  
Nicole Couto ◽  
Matthew H. Alford ◽  
Jennifer MacKinnon ◽  
John B. Mickett
Keyword(s):  
Friction Velocity ◽  
The Arctic ◽  
Bering Strait ◽  
Turbulent Dissipation ◽  
Dissipation Rates ◽  
The Pacific ◽  
Mixing Rates ◽  
The Pacific Ocean ◽  
High Turbulence ◽  
Property Changes

AbstractThree shipboard survey lines were occupied in Bering Strait during autumn of 2015, where high-resolution measurements of temperature, salinity, velocity, and turbulent dissipation rates were collected. These first-reported turbulence measurements in Bering Strait show that dissipation rates here are high even during calm winds. High turbulence in the strait has important implications for the modification of water properties during transit from the Pacific Ocean to the Arctic Ocean. Measured diffusivities averaging 2 × 10−2 m2 s−1 are capable of causing watermass property changes of 0.1°C and 0.1 psu during the ~1–2-day transit through the narrowest part of the strait. We estimate friction velocity using both the dissipation and profile methods and find a bottom drag coefficient of 2.3 (±0.4) × 10−3. This result is smaller than values typically used to estimate bottom stress in the region and may improve predictions of transport variability through Bering Strait.

Sign in / Sign up

Export Citation Format

Share Document