The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform
Ichiro Fukumori - One of the best experts on this subject based on the ideXlab platform.
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interannual to decadal variations of tropical subtropical exchange in the pacific ocean boundary versus interior Pycnocline transports
Journal of Climate, 2003Co-Authors: Tong Lee, Ichiro FukumoriAbstract:Abstract Interannual-to-decadal variations of tropical–subtropical mass exchange in the Pacific Ocean are investigated using a near-global ocean general circulation model along with satellite observations of sea level and wind and a data assimilation product. The analysis focuses on the variability of Pycnocline transports through the western boundary and interior near 10°N and 10°S. In contrast to time-mean exchange, where boundary and interior Pycnocline transports are both equatorward, the variations of boundary and interior Pycnocline transports are found to be generally anticorrelated to each other. Moreover, the variation of the boundary Pycnocline transport is smaller than that of the interior, again different from time-mean exchange, where the boundary transport at 10°N is substantially larger than that through the interior. Interannual variations of the boundary and interior transports are consistent with near-surface geostrophic flow inferred from sea level data. Interior Pycnocline flow into th...
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Interannual-to-Decadal Variations of Tropical–Subtropical Exchange in the Pacific Ocean: Boundary versus Interior Pycnocline Transports
Journal of Climate, 2003Co-Authors: Tong Lee, Ichiro FukumoriAbstract:Abstract Interannual-to-decadal variations of tropical–subtropical mass exchange in the Pacific Ocean are investigated using a near-global ocean general circulation model along with satellite observations of sea level and wind and a data assimilation product. The analysis focuses on the variability of Pycnocline transports through the western boundary and interior near 10°N and 10°S. In contrast to time-mean exchange, where boundary and interior Pycnocline transports are both equatorward, the variations of boundary and interior Pycnocline transports are found to be generally anticorrelated to each other. Moreover, the variation of the boundary Pycnocline transport is smaller than that of the interior, again different from time-mean exchange, where the boundary transport at 10°N is substantially larger than that through the interior. Interannual variations of the boundary and interior transports are consistent with near-surface geostrophic flow inferred from sea level data. Interior Pycnocline flow into th...
Tong Lee - One of the best experts on this subject based on the ideXlab platform.
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interannual to decadal variations of tropical subtropical exchange in the pacific ocean boundary versus interior Pycnocline transports
Journal of Climate, 2003Co-Authors: Tong Lee, Ichiro FukumoriAbstract:Abstract Interannual-to-decadal variations of tropical–subtropical mass exchange in the Pacific Ocean are investigated using a near-global ocean general circulation model along with satellite observations of sea level and wind and a data assimilation product. The analysis focuses on the variability of Pycnocline transports through the western boundary and interior near 10°N and 10°S. In contrast to time-mean exchange, where boundary and interior Pycnocline transports are both equatorward, the variations of boundary and interior Pycnocline transports are found to be generally anticorrelated to each other. Moreover, the variation of the boundary Pycnocline transport is smaller than that of the interior, again different from time-mean exchange, where the boundary transport at 10°N is substantially larger than that through the interior. Interannual variations of the boundary and interior transports are consistent with near-surface geostrophic flow inferred from sea level data. Interior Pycnocline flow into th...
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Interannual-to-Decadal Variations of Tropical–Subtropical Exchange in the Pacific Ocean: Boundary versus Interior Pycnocline Transports
Journal of Climate, 2003Co-Authors: Tong Lee, Ichiro FukumoriAbstract:Abstract Interannual-to-decadal variations of tropical–subtropical mass exchange in the Pacific Ocean are investigated using a near-global ocean general circulation model along with satellite observations of sea level and wind and a data assimilation product. The analysis focuses on the variability of Pycnocline transports through the western boundary and interior near 10°N and 10°S. In contrast to time-mean exchange, where boundary and interior Pycnocline transports are both equatorward, the variations of boundary and interior Pycnocline transports are found to be generally anticorrelated to each other. Moreover, the variation of the boundary Pycnocline transport is smaller than that of the interior, again different from time-mean exchange, where the boundary transport at 10°N is substantially larger than that through the interior. Interannual variations of the boundary and interior transports are consistent with near-surface geostrophic flow inferred from sea level data. Interior Pycnocline flow into th...
Sutanu Sarkar - One of the best experts on this subject based on the ideXlab platform.
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degradation of an internal wave beam by parametric subharmonic instability in an upper ocean Pycnocline
Journal of Geophysical Research, 2013Co-Authors: Bishakhdatta Gayen, Sutanu SarkarAbstract:[1] Numerical simulations are performed to investigate the interaction of a semidiurnal internal wave (IW) beam with the nonuniform stratification of an upper ocean Pycnocline. During the initial stage of the interaction, higher harmonics originate after reflection of the IW beam at the caustic and are trapped in the Pycnocline. In cases where the Pycnocline thickness is sufficiently large (approximately larger than twice the dominant wavelength in the beam), the incoming beam undergoes a parametric subharmonic instability (PSI) during refraction through the Pycnocline at later time. Consequently, there is significant energy transfer to subharmonic motions that exhibit exponential growth with a rate of 2/3 day−1. The instability is demonstrated to be a resonant triad interaction by diagnostics in both wave frequency and wave number spaces. Smaller vertical scales originate during the PSI, lead to wave steepening, and produce convective overturns. This work identifies a potential mechanism that drives IW beam degradation during its propagation through the upper ocean.
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Internal gravity waves generated by a turbulent bottom Ekman layer
Journal of Fluid Mechanics, 2007Co-Authors: John Taylor, Sutanu SarkarAbstract:Internal gravity waves excited by the turbulent motions in a bottom Ekman layer are examined using large-eddy simulation. The outer flow is steady and uniformly stratified while the density gradient is set to zero at the flat lower wall. After initializing with a linear density profile, a mixed layer forms near the wall separated from the ambient stratification by a Pycnocline. Two types of internal wave are observed. Waves with frequencies larger than the free-stream buoyancy frequency are seen in the Pycnocline, and vertically propagating internal waves are observed in the outer layer with characteristic frequency and wavenumber spectra. Since a signature of the Pycnocline waves is observed in the frequency spectrum of the mixed layer, these waves may affect the boundary-layer turbulence. The dominant outer-layer waves have a group velocity directed 35-60° from the vertical axis, which is consistent with previous laboratory studies. The energy flux associated with the radiated waves is small compared to the integrated dissipation in the boundary layer, but is of the same order as the integrated buoyancy flux. A linear model is proposed to estimate the decay in wave amplitude owing to viscous effects. Starting from the observed wave amplitudes at the bottom of the Pycnocline, the model prediction for the spectral distribution of the outer layer wave amplitude compares favourably with the simulation results.
Alan Brandt - One of the best experts on this subject based on the ideXlab platform.
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experimental study of nonlinear harmonic generation by internal waves incident on a Pycnocline
Experiments in Fluids, 2015Co-Authors: Scott Wunsch, Ian Delwiche, Gary Frederick, Alan BrandtAbstract:Internal waves propagating in variable stratification exhibit nonlinear generation of harmonics. Here, synthetic schlieren is used to study a laboratory internal wave beam propagating from a uniformly stratified layer into a region of increased stratification (Pycnocline) below a mixed layer. The results demonstrate the formation of harmonic (double-frequency) internal waves as the beam refracts into the Pycnocline layer. For beam incidence angles <30° to the horizontal, harmonic internal waves are radiated back to the uniformly stratified layer. The harmonic wavenumber is approximately double the incident wavenumber, while its amplitude increases with the Pycnocline buoyancy frequency gradient. Beams with larger incidence angles generate harmonics that are trapped within the Pycnocline layer. In this case, the specific wavenumber of the trapped harmonic is determined by the normal modes of the stratification profile.
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Experimental study of nonlinear harmonic generation by internal waves incident on a Pycnocline
Experiments in Fluids, 2015Co-Authors: Scott Wunsch, Ian Delwiche, Gary Frederick, Alan BrandtAbstract:Internal waves propagating in variable stratification exhibit nonlinear generation of harmonics. Here, synthetic schlieren is used to study a laboratory internal wave beam propagating from a uniformly stratified layer into a region of increased stratification (Pycnocline) below a mixed layer. The results demonstrate the formation of harmonic (double-frequency) internal waves as the beam refracts into the Pycnocline layer. For beam incidence angles
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Laboratory experiments on internal wave interactions with a Pycnocline
Experiments in Fluids, 2012Co-Authors: Scott Wunsch, Alan BrandtAbstract:Laboratory experiments have been performed to investigate the interaction of internal waves with a Pycnocline. An oscillating cylinder generated internal wave beams, which were observed using the synthetic schlieren technique. Internal waves incident on the Pycnocline layer excited higher-frequency modes. In the absence of shear, a discrete spectrum of harmonic modes was generated due to nonlinear effects. These harmonic modes might play a role in the formation of internal solitary waves which have been observed in ocean Pycnoclines. With shear, a continuous spectrum of excited modes was found.
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Laboratory experiments on intrusive flows and internal waves in a Pycnocline
Journal of Fluid Mechanics, 2001Co-Authors: Vladimir Maderich, Van Gjf Gert-jan Heijst, Alan BrandtAbstract:A laboratory study has been performed to simulate intrusive flows generated by internal wave-breaking activity in the oceanic Pycnocline. Two different cases were considered. In the first set of experiments a short-duration source of motion was modelled by creating a finite region of well-mixed fluid. The collapse of this region resulted in intrusive flows and internal waves in the Pycnocline. Attention was focused on the formation and subsequent evolution of solitary ‘bulges’ in the intrusion. Detailed flow measurements have revealed that the weak motion inside these bulges (which contain well-mixed fluid from the source) is organized in a four-vortex structure. Numerical flow simulations provided important information about the dynamics of this four-cell structure: the outer cells are associated with baroclinic generation of vorticity, while the inner cells are characterized by a balance between the advective and the viscous terms in the vorticity equation. In the second set of experiments continuous mixing was induced by a vertically oscillating, horizontal grid centred in the Pycnocline. The mixed region collapses, thus forming an intrusive flow into the Pycnocline and internal waves that propagate along the Pycnocline at higher speed than the intrusion. It was found that the velocity of the intrusive flow is approximately constant and that its dynamics is controlled by an inertial–buoyancy balance. The parameters of the internal waves in both cases were compared with theory.
Scott Wunsch - One of the best experts on this subject based on the ideXlab platform.
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experimental study of nonlinear harmonic generation by internal waves incident on a Pycnocline
Experiments in Fluids, 2015Co-Authors: Scott Wunsch, Ian Delwiche, Gary Frederick, Alan BrandtAbstract:Internal waves propagating in variable stratification exhibit nonlinear generation of harmonics. Here, synthetic schlieren is used to study a laboratory internal wave beam propagating from a uniformly stratified layer into a region of increased stratification (Pycnocline) below a mixed layer. The results demonstrate the formation of harmonic (double-frequency) internal waves as the beam refracts into the Pycnocline layer. For beam incidence angles <30° to the horizontal, harmonic internal waves are radiated back to the uniformly stratified layer. The harmonic wavenumber is approximately double the incident wavenumber, while its amplitude increases with the Pycnocline buoyancy frequency gradient. Beams with larger incidence angles generate harmonics that are trapped within the Pycnocline layer. In this case, the specific wavenumber of the trapped harmonic is determined by the normal modes of the stratification profile.
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Experimental study of nonlinear harmonic generation by internal waves incident on a Pycnocline
Experiments in Fluids, 2015Co-Authors: Scott Wunsch, Ian Delwiche, Gary Frederick, Alan BrandtAbstract:Internal waves propagating in variable stratification exhibit nonlinear generation of harmonics. Here, synthetic schlieren is used to study a laboratory internal wave beam propagating from a uniformly stratified layer into a region of increased stratification (Pycnocline) below a mixed layer. The results demonstrate the formation of harmonic (double-frequency) internal waves as the beam refracts into the Pycnocline layer. For beam incidence angles
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Unstable modes of a sheared Pycnocline above a stratified layer
Dynamics of Atmospheres and Oceans, 2013Co-Authors: Scott Wunsch, Kurt KellerAbstract:Abstract Internal waves incident on a sheared ocean Pycnocline are studied using analytic and numerical methods. Linear analysis of the unstable modes of a sheared ocean Pycnocline is used to demonstrate interactions between internal waves and shear instabilities. A new analytic solution for an asymmetric shear layer over a stratified layer is presented, illustrating modes which couple to internal waves, in addition to the well-known Holmboe modes. The robustness of these solutions is demonstrated using numerical methods for realistic shear profiles. Fully nonlinear numerical simulations illustrate the growth of these modes and demonstrate the excitation of shear instabilities by incident internal waves. The results may have implications for internal wave interactions with the ocean Pycnocline and the local generation of internal solitary waves.
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Laboratory experiments on internal wave interactions with a Pycnocline
Experiments in Fluids, 2012Co-Authors: Scott Wunsch, Alan BrandtAbstract:Laboratory experiments have been performed to investigate the interaction of internal waves with a Pycnocline. An oscillating cylinder generated internal wave beams, which were observed using the synthetic schlieren technique. Internal waves incident on the Pycnocline layer excited higher-frequency modes. In the absence of shear, a discrete spectrum of harmonic modes was generated due to nonlinear effects. These harmonic modes might play a role in the formation of internal solitary waves which have been observed in ocean Pycnoclines. With shear, a continuous spectrum of excited modes was found.
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Unstable modes of a sheared Pycnocline above a stratified layer
Bulletin of the American Physical Society, 2012Co-Authors: Scott Wunsch, Kurt KellerAbstract:Internal waves incident on a sheared ocean Pycnocline are studied using analytic and numerical methods. Linear analysis of the unstable modes of a sheared ocean Pycnocline is used to demonstrate interactions between internal waves and shear instabilities. A new analytic solution for an asymmetric shear layer over a stratified layer is presented, illustrating modes which couple to internal waves, in addition to the well-known Holmboe modes. The robustness of these solutions is demonstrated using numerical methods for realistic shear profiles. Fully nonlinear numerical simulations illustrate the growth of these modes and demonstrate the excitation of shear instabilities by incident internal waves. The results may have implications for internal wave interactions with the ocean Pycnocline and the local generation of internal solitary waves. © 2012 Elsevier B.V. All rights reserved.
