Momentum Flux Convergence From Internal Tides in the North Equatorial Countercurrent Upstream of a Submarine Ridge Near Merir Island, Palau

AbstractInternal-wave-driven dissipation rates ε and diapycnal diffusivities K are inferred globally using a finescale parameterization based on vertical strain applied to ~30 000 hydrographic casts. Global dissipations are 2.0 ± 0.6 TW, consistent with internal wave power sources of 2.1 ± 0.7 TW from tides and wind. Vertically integrated dissipation rates vary by three to four orders of magnitude with elevated values over abrupt topography in the western Indian and Pacific as well as midocean slow spreading ridges, consistent with internal tide sources. But dependence on bottom forcing is much weaker than linear wave generation theory, pointing to horizontal dispersion by internal waves and relatively little local dissipation when forcing is strong. Stratified turbulent bottom boundary layer thickness variability is not consistent with OGCM parameterizations of tidal mixing. Average diffusivities K = (0.3–0.4) × 10−4 m2 s−1 depend only weakly on depth, indicating that ε = KN2/γ scales as N2 such that the bulk of the dissipation is in the pycnocline and less than 0.08-TW dissipation below 2000-m depth. Average diffusivities K approach 10−4 m2 s−1 in the bottom 500 meters above bottom (mab) in height above bottom coordinates with a 2000-m e-folding scale. Average dissipation rates ε are 10−9 W kg−1 within 500 mab then diminish to background deep values of 0.15 × 10−9 W kg−1 by 1000 mab. No incontrovertible support is found for high dissipation rates in Antarctic Circumpolar Currents or parametric subharmonic instability being a significant pathway to elevated dissipation rates for semidiurnal or diurnal internal tides equatorward of 28° and 14° latitudes, respectively, although elevated K is found about 30° latitude in the North and South Pacific.

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Wind- versus Eddy-Forced Regional Sea Level Trends and Variability in the North Pacific Ocean

Journal of Climate ◽

10.1175/jcli-d-14-00479.1 ◽

2015 ◽

Vol 28 (4) ◽

pp. 1561-1577 ◽

Cited By ~ 25

Author(s):

Bo Qiu ◽

Shuiming Chen ◽

Lixin Wu ◽

Shinichiro Kida

Keyword(s):

Pacific Ocean ◽

Sea Level ◽

Momentum Flux ◽

North Pacific Ocean ◽

Kuroshio Extension ◽

The Past ◽

The North ◽

The Pacific ◽

Regional Sea Level ◽

Sea Level Trend

Abstract Regional sea level trend and variability in the Pacific Ocean have often been considered to be induced by low-frequency surface wind changes. This study demonstrates that significant sea level trend and variability can also be generated by eddy momentum flux forcing due to time-varying instability of the background oceanic circulation. Compared to the broad gyre-scale wind-forced variability, the eddy-forced sea level changes tend to have subgyre scales and, in the North Pacific Ocean, they are largely confined to the Kuroshio Extension region (30°–40°N, 140°–175°E) and the Subtropical Countercurrent (STCC) region (18°–28°N, 130°–175°E). Using a two-layer primitive equation model driven by the ECMWF wind stress data and the eddy momentum fluxes specified by the AVISO sea surface height anomaly data, the relative importance of the wind- and eddy-forced regional sea level trends in the past two decades is quantified. It is found that the increasing (decreasing) trend south (north) of the Kuroshio Extension is due to strengthening of the regional eddy forcing over the past two decades. On the other hand, the decreasing (increasing) sea level trend south (north) of the STCC is caused by the decadal weakening of the regional eddy momentum flux forcing. These decadal eddy momentum flux changes are caused by the background Kuroshio Extension and STCC changes in connection with the Pacific decadal oscillation (PDO) wind pattern shifting from a positive to a negative phase over the past two decades.

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Internal wave energetics modulated by Indonesian Throughflow at Lombok Strait

10.5194/egusphere-egu2020-19083 ◽

2020 ◽

Author(s):

Zhenhua Xu

Keyword(s):

Solitary Waves ◽

Southern Oscillation ◽

Internal Tide ◽

Internal Tides ◽

Internal Solitary Waves ◽

Indonesian Throughflow ◽

Indonesian Seas ◽

The North ◽

Tide Propagation ◽

Seasonal And Interannual Variations

<p>The interaction between the energetic internal waves in the Indonesian Seas and the Indonesian Throughflow (ITF) is not well known. Here we conduct a series of high-resolution numerical simulations surrounding the Lombok Strait, Indonesia, which is an important exit channel for the ITF, to explore the influences of the ITF on the spatiotemporal variations of M2 internal tides and associated internal solitary waves from the Strait. The ITF enhances the north-south asymmetry of internal tide propagation from the Lombok Strait, thus resulting in the spatial variability of northward and southward internal solitary waves. Interannual variability of internal tide generation and dissipation are due to ITF and air-sea freshwaterflux induced stratification variations associated with El Ni&#241;o-Southern Oscillation. The local dissipation efficiency q exhibits substantial seasonal and interannual variations, which may provide effective feedback to the climate processes in the low-latitude equatorial oceans.</p>

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Internal Tide Convergence and Mixing in a Submarine Canyon

Journal of Physical Oceanography ◽

10.1175/jpo-d-16-0073.1 ◽

2017 ◽

Vol 47 (2) ◽

pp. 303-322 ◽

Cited By ~ 14

Author(s):

Amy F. Waterhouse ◽

Jennifer A. Mackinnon ◽

Ruth C. Musgrave ◽

Samuel M. Kelly ◽

Andy Pickering ◽

...

Keyword(s):

Continental Shelf ◽

Internal Wave ◽

Wave Energy ◽

Internal Tide ◽

Submarine Canyon ◽

Internal Tides ◽

North Coast ◽

Semidiurnal Tide ◽

The North ◽

Tidally Driven

AbstractObservations from Eel Canyon, located on the north coast of California, show that elevated turbulence in the full water column arises from the convergence of remotely generated internal wave energy. The incoming semidiurnal and bottom-trapped diurnal internal tides generate complex interference patterns. The semidiurnal internal tide sets up a partly standing wave within the canyon due to reflection at the canyon head, dissipating all of its energy within the canyon. Dissipation in the near bottom is associated with the diurnal trapped tide, while midwater isopycnal shear and strain is associated with the semidiurnal tide. Dissipation is elevated up to 600 m off the bottom, in contrast to observations over the flat continental shelf where dissipation occurs closer to the topography. Slope canyons are sinks for internal wave energy and may have important influences on the global distribution of tidally driven mixing.

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Thermally Driven and Eddy-Driven Jet Variability in Reanalysis

Journal of Climate ◽

10.1175/jcli-d-11-00145.1 ◽

2012 ◽

Vol 25 (5) ◽

pp. 1587-1596 ◽

Cited By ~ 46

Author(s):

Camille Li ◽

Justin J. Wettstein

Keyword(s):

Zonal Wind ◽

Momentum Flux ◽

Hadley Circulation ◽

Atlantic Sector ◽

Wind Variability ◽

The North ◽

The Pacific ◽

Thermally Driven ◽

Jet Variability ◽

The North Atlantic Oscillation

Two important dynamical processes influence the extratropical zonal wind field: angular momentum transport by the thermally direct Hadley circulation (thermal-driving T) and momentum flux convergence by atmospheric waves (eddies) that develop in regions of enhanced baroclinicity (eddy-driving E). The relationship between extratropical zonal wind variability and these driving processes is investigated using 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40) data. Indices representing the processes (iT and iE) are defined based on vertically integrated diabatic heating and meridional convergence of the meridional flux of zonal momentum by eddies, respectively. Zonal wind signatures associated with these indices are identified via composite analysis. In the Atlantic sector, zonal wind variability is mainly associated with momentum flux convergence by baroclinic eddies, supporting the established view that the Atlantic jet is primarily eddy driven. In the Pacific sector, zonal wind variability is associated with both driving processes, evidence that the Pacific jet is both thermally driven and eddy driven. The thermally driven Pacific signature reflects changes in jet strength (intensity and longitudinal extent) with some resemblance to the zonal wind anomalies of the Pacific–North America (PNA) pattern. The eddy-driven signature reflects a latitudinal shift of the jet exit region in both sectors that resembles the zonal wind anomalies of the North Atlantic Oscillation (NAO) or West Pacific (WP) patterns.

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The southern stratospheric gravity-wave hot spot: individual waves and their momentum fluxes measured by COSMIC GPS-RO

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-3173-2015 ◽

2015 ◽

Vol 15 (3) ◽

pp. 3173-3217 ◽

Cited By ~ 1

Author(s):

N. P. Hindley ◽

C. J. Wright ◽

N. D. Smith ◽

N. J. Mitchell

Keyword(s):

Southern Ocean ◽

Gravity Wave ◽

Momentum Flux ◽

Hot Spot ◽

The North ◽

Large Numbers ◽

Analysis Technique ◽

Modelling Studies ◽

Quantitative Identification ◽

Wave Momentum

Abstract. During austral winter the mountains of the southern Andes and Antarctic Peninsula are a known hot spot of intense gravity wave momentum flux. There also exists a long leeward region of increased gravity wave energy that sweeps eastwards from the mountains out over the Southern Ocean, the source of which has historically proved difficult to determine. In this study we use Global Positioning System (GPS) Radio Occultation (RO) data from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) satellite constellation to investigate the distribution, variability and sources of waves in the hot spot region and over the Southern Ocean. We present evidence that suggests a southward focusing of waves into the stratospheric jet from sources to the north. We also describe a wavelet analysis technique for the quantitative identification of individual waves from COSMIC temperature profiles. This analysis reveals different geographical regimes of wave amplitude and short-timescale variability in the wave field over the Southern Ocean. Finally, we take advantage of the large numbers of closely spaced pairs of profiles from the deployment phase of the COSMIC constellation in 2006 to make estimates of gravity wave horizontal wavelengths. We show that, given sufficient numbers of these pairs, GPS-RO can then produce physically reasonable estimates of stratospheric gravity wave momentum flux in the hot spot region that are consistent with other studies. The results are discussed in the context of previous satellite and modelling studies to build up a better picture of the nature and origins of waves in the southern winter stratosphere.

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On the Momentum Flux of Internal Tides

Journal of Physical Oceanography ◽

10.1175/jpo-d-18-0165.1 ◽

2019 ◽

Vol 49 (4) ◽

pp. 993-1013 ◽

Cited By ~ 6

Author(s):

Callum J. Shakespeare ◽

Andrew McC. Hogg

Keyword(s):

Momentum Flux ◽

Internal Tide ◽

Flow Speed ◽

Internal Tides ◽

Fourth Power ◽

Upper Ocean ◽

Seafloor Topography ◽

Tidal Waves ◽

Net Flux ◽

Wave Momentum

AbstractThe action of the barotropic tide over seafloor topography is the major source of internal waves at the bottom of the ocean. This internal tide has long been recognized to play an important role in ocean mixing. Here it is shown that the internal tide is also associated with a net (domain integrated) momentum flux. The net flux occurs as a result of the Doppler shifting of the internal tide at the point of generation by near-bottom mean flows. Linear theory is presented that predicts the amplitude of the wave momentum flux. The net flux scales with the bottom flow speed and the topographic wavenumber to the fourth power and is directed opposite to the bottom flow. For realistic topography, the predicted peak momentum flux occurs at scales of order 10 km and smaller, with magnitudes of order 10−3–10−2 N m−2. The theory is verified by comparison with a suite of idealized internal wave-resolving simulations. The simulations show that, for the topography considered, the wave momentum flux radiates away from the bottom and enhances mean and eddying flow when the tidal waves dissipate in the upper ocean. Our results suggest that internal tides may play an important role in forcing the upper ocean.

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On the Effect of Topographically Enhanced Mixing on the Global Ocean Circulation

Journal of Physical Oceanography ◽

10.1175/jpo2722.1 ◽

2005 ◽

Vol 35 (5) ◽

pp. 826-834 ◽

Cited By ~ 85

Author(s):

O. A. Saenko ◽

W. J. Merryfield

Keyword(s):

North Pacific ◽

Bottom Water ◽

North Pacific Ocean ◽

Bottom Topography ◽

Water Circulation ◽

Internal Tides ◽

Shear Instability ◽

Global Ocean ◽

Diapycnal Mixing ◽

The North

Abstract The strong influence of enhanced diapycnal mixing over rough topography on bottom-water circulation is illustrated using results from two global ocean model experiments. In the first, diapycnal diffusivity is set to the observed background level of 10−5 m2 s−1 in regions not subject to shear instability, convection, or surface-driven mixing. In the second experiment, mixing is enhanced above rough bottom topography to represent the dissipation of internal tides. Three important results are obtained. First, without the enhanced mixing in the abyssal ocean, the deep North Pacific Ocean becomes essentially a stagnant basin, with little bottom-water circulation and very weak deep stratification. Allowing for the enhanced diapycnal mixing above rough bottom topography leads to increased bottom-water circulation and deep stratification and a potential vorticity distribution in the North Pacific that is much more realistic. Second, the enhanced diapycnal mixing above rough topography results in a significant intensification and deepening of the Antarctic Circumpolar Current, as well as in stronger bottom-water formation around Antarctica. Last, our experiments suggest that dissipation of internal tides and the associated enhanced diapycnal mixing in the abyssal ocean play no part in the circulation of deep water forming in the North Atlantic Ocean and in the associated transport of heat in the ocean.

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Observations of Tidal Internal Wave Beams at Kauai Channel, Hawaii

Journal of Physical Oceanography ◽

10.1175/2008jpo3937.1 ◽

2009 ◽

Vol 39 (2) ◽

pp. 421-436 ◽

Cited By ~ 39

Author(s):

S. T. Cole ◽

D. L. Rudnick ◽

B. A. Hodges ◽

J. P. Martin

Keyword(s):

Internal Wave ◽

Energy Flux ◽

Momentum Flux ◽

Internal Tides ◽

Turbulent Dissipation ◽

Ridge Structure ◽

Almost Everywhere ◽

Hawaiian Ridge ◽

Internal Wave Generation ◽

Almost All

Abstract To observe the across-ridge structure of internal tides, density and velocity were measured using SeaSoar and a Doppler sonar over the upper 400–600 m of the ocean extending 152 km on each side of the Hawaiian Ridge at Kauai Channel. Eighteen sections were completed in about 18 days with sampling intentionally detuned from the lunar semidiurnal (M2) tide so that averaging over all sections was equivalent to phase averaging the M2 tide. Velocity and displacement variance and several covariances involving velocity and displacement showed one M2 internal wave beam on each side of the ridge and reflection of the beams off of the surface. Theoretical ray slopes aligned with the observed beams and originated from the sides of the ridge. Energy flux was in agreement with internal wave generation at the ridge. Inferred turbulent dissipation was elevated relative to open ocean values near tidal beams. Energy flux was larger than total dissipation almost everywhere across the ridge. Internal wave energy flux and dissipation at Kauai Channel were 1.5–2.5 times greater than at the average location along the Hawaiian Ridge. The upper 400–600 m was about 1/3 to 1/2 as energetic as the full-depth ocean. Tidal beams interact with each other over the entire length of the beams causing gradients along beams in almost all covariances, momentum flux divergences, and mean flows. At Kauai Channel, momentum flux divergences corresponded to mean flows of 1–4 cm s−1.

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