Ray-based description of normal modes in a deep ocean acoustic waveguide

2009 ◽  
Vol 125 (3) ◽  
pp. 1362-1373 ◽  
Author(s):  
A. L. Virovlyansky ◽  
A. Yu. Kazarova ◽  
L. Ya. Lyubavin
Keyword(s):  
Normal Modes ◽  
Deep Ocean ◽  
Acoustic Waveguide

Near-inertial waves modulated by background flow in realistic global ocean simulations

2021 ◽  
Author(s):  
Keshav Raja ◽  
Maarten Buijsman ◽  
Oladeji Siyanbola ◽  
Miguel Solano ◽  
Jay Shriver ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Normal Modes ◽  
Deep Ocean ◽  
Ocean Model ◽  
Global Ocean ◽  
Inertial Waves ◽  
Flux Divergence ◽  
Large Wave ◽  
Wind Input ◽  
Anticyclonic Eddies

<p>Wind generated near-inertial waves (NIWs) are a major source of energy for deep-ocean mixing by transmitting wind energy from the ocean surface into the interior. Recently, it has been established that the NIW energy transmission to ocean depths is significantly modulated by background mesoscale vorticity. Thus, understanding NIW energetics in the presence of mesoscale eddies on a global scale is crucial.</p><p>We study the generation, propagation and dissipation of NIWs in global 1/25<sup>o</sup> Hybrid Coordinate Ocean Model (HYCOM) simulations with realistic tidal forcing. The model has 41 layers with uniform vertical coordinates in the mixed layer and isopycnal coordinates in the ocean interior. The model is forced by 1/3hr wind from the NAVGEM atmospheric model. We analyze one month of model data for May-June 2019. The 3D HYCOM fields are projected on vertical normal modes to compute the wind input, wave kinetic energy (KE), flux divergence and dissipation per mode.</p><p>We find that the globally integrated wind input in surface near-inertial motions is 0.21 TW for the 30-day period and is consistent with previous studies. The sum of the wind input to the first 5 modes accounts to only 31% of the total wind input while the sum of the NIW kinetic energy in the first 5 modes adds up to 60% of the total NIW KE. The difference in the fraction of the total between the wind input and NIW KE (31% and 60%) suggests that a significant portion of wind-induced near-inertial motions is dissipated close to the surface without being projected onto modes. We also find that NIW horizontal fluxes diverge from areas with cyclonic vorticity and converge in areas with anticyclonic vorticity, i.e., anticyclonic eddies are a sink for NIW energy in the global ocean.</p><p>The residual NIW KE that does not project onto modes is found to be largely trapped in anticyclonic eddies. In a next step, we will study the fate of this energy, which most likely propagate downward as beam-like features with large wave numbers. We will compute the near-inertial wave energy balance for fixed subsurface layers and consider the energy exchange between these layers to understand the vertical structure of NIW energy dissipation. We find that the downward NIW radiation to the ocean interior at 500 m depth is 19% of the surface near-inertial wind input for the 30-day period.</p>

scholarly journals On the Resonance Hypothesis of Tsunami and Storm Surge Runup

2016 ◽  
Author(s):  
Nazmi Postacioglu ◽  
M. Sinan Özeren ◽  
Umut Canlı
Keyword(s):  
Normal Modes ◽  
Deep Ocean ◽  
Storm Surges ◽  
Underlying Mechanism ◽  
Radiation Damping ◽  
Resonant Frequencies ◽  
Constant Slope ◽  
Incident Waves ◽  
Determining Factor ◽  
Significant Resonance

Abstract. Resonance has recently been proposed as the fundamental underlying mechanism that shapes the amplification in coastal runup for both Tsunamis and storm surges. It is without doubt that the resonance plays a rôle in runup phenomena of various kinds, however we think that the extent at which it plays its role has not been completely understood. For incident waves, the best approach to investigate the rôle played by the resonance would be to calculate the normal modes by taking radiation damping into account and then test how those modes are excited by the incident waves. There are a small number of previous works that attempt to calculate the resonant frequencies but they do not relate the amplitudes of the normal modes to those of the incident wave. This is because, by not including radiation damping, they automatically induce a resonance that leads to infinite amplitudes, thus preventing them from predicting the exact contribution of the resonance to coastal runup. In this study we consider two different coastal geometries: an infinitely wide beach with a constant slope connecting to a flat-bottomed deep ocean and a bay with sloping bottom, again, connected to a deep ocean. For the fully 1-D problem we find significant resonance if the bathymetric discontinuity is large. For the 2-D ocean case the analysis shows that the wave confinement is very effective when the bay is narrow. The bay aspect-ratio is the determining factor for the radiation damping.

scholarly journals Global Calculation of Tidal Energy Conversion into Vertical Normal Modes

2014 ◽  
Vol 44 (12) ◽  
pp. 3225-3244 ◽  
Author(s):  
Saeed Falahat ◽  
Jonas Nycander ◽  
Fabien Roquet ◽  
Moundheur Zarroug
Keyword(s):  
Normal Modes ◽  
Internal Tide ◽  
Deep Ocean ◽  
Direct Calculation ◽  
Tidal Energy ◽  
Horizontal Distribution ◽  
Internal Tides ◽  
Global Ocean ◽  
Vertical Scale ◽  
Vertical Distributions

Abstract A direct calculation of the tidal generation of internal waves over the global ocean is presented. The calculation is based on a semianalytical model, assuming that the internal tide characteristic slope exceeds the bathymetric slope (subcritical slope) and the bathymetric height is small relative to the vertical scale of the wave, as well as that the horizontal tidal excursion is smaller than the horizontal topographic scale. The calculation is performed for the M2 tidal constituent. In contrast to previous similar computations, the internal tide is projected onto vertical eigenmodes, which gives two advantages. First, the vertical density profile and the finite ocean depth are taken into account in a fully consistent way, in contrast to earlier work based on the WKB approximation. Nevertheless, the WKB-based total global conversion follows closely that obtained using the eigenmode decomposition in each of the latitudinal and vertical distributions. Second, the information about the distribution of the conversion energy over different vertical modes is valuable, since the lowest modes can propagate over long distances, while high modes are more likely to dissipate locally, near the generation site. It is found that the difference between the vertical distributions of the tidal conversion into the vertical modes is smaller for the case of very deep ocean than the shallow-ocean depth. The results of the present work pave the way for future work on the vertical and horizontal distribution of the mixing caused by internal tides.

Modeling the vertical directionality of wind-generated noise in deep ocean using Pekeris-branch-cut-based normal modes

2017 ◽  
Author(s):  
Guangyu Jiang ◽  
Chao Sun ◽  
Xionghou Liu ◽  
Lei Xie ◽  
Xuan Shao ◽  
...  
Keyword(s):  
Normal Modes ◽  
Deep Ocean ◽  
Branch Cut

scholarly journals Dimension-reduced generalized likelihood ratio detection based on sampling of normal modes in deep ocean

2019 ◽  
Vol 68 (17) ◽  
pp. 174301
Author(s):  
De-Zhi Kong ◽  
Chao Sun ◽  
Ming-Yang Li ◽  
Jie Zhuo ◽  
Xiong-Hou Liu
Keyword(s):  
Likelihood Ratio ◽  
Normal Modes ◽  
Deep Ocean ◽  
Generalized Likelihood Ratio ◽  
Ratio Detection

scholarly journals On the resonance hypothesis of storm surge and surf beat run-up

2017 ◽  
Vol 17 (6) ◽  
pp. 905-924 ◽  
Author(s):  
Nazmi Postacioglu ◽  
M. Sinan Özeren ◽  
Umut Canlı
Keyword(s):  
Fluid Velocity ◽  
Normal Modes ◽  
Deep Ocean ◽  
Storm Surges ◽  
Underlying Mechanism ◽  
Radiation Damping ◽  
Tokyo Bay ◽  
Wave Groups ◽  
Run Up ◽  
Incident Waves

Abstract. Resonance has recently been proposed as the fundamental underlying mechanism that shapes the amplification in coastal run-up for storm surges and surf beats, which are long-wavelength disturbances created by fluid velocity differences between the wave groups and the regions outside the wave groups. It is without doubt that the resonance plays a role in run-up phenomena of various kinds; however, we think that the extent to which it plays its role has not been completely understood. For incident waves, which we assume to be linear, the best approach to investigate the role played by the resonance would be to calculate the normal modes by taking radiation damping into account and then testing how those modes are excited by the incident waves. Such modes diverge offshore, but they can still be used to calculate the run-up. There are a small number of previous works that attempt to calculate the resonant frequencies, but they do not relate the amplitudes of the normal modes to those of the incident wave. This is because, by not including radiation damping, they automatically induce a resonance that leads to infinite amplitudes, thus preventing them from predicting the exact contribution of the resonance to coastal run-up. In this study we consider two different coastal geometries: an infinitely wide beach with a constant slope connecting to a flat-bottomed deep ocean and a bay with sloping bottom, again, connected to a deep ocean. For the fully 1-D problem we find significant resonance if the bathymetric discontinuity is large.The linearisation of the seaward boundary condition leads to slightly smaller run-ups. For the 2-D ocean case the analysis shows that the wave confinement is very effective when the bay is narrow. The bay aspect ratio is the determining factor for the radiation damping. One reason why we include a bathymetric discontinuity is to mimic some natural settings where bays and gulfs may lead to abrupt depth gradients such as the Tokyo Bay. The other reason is, as mentioned above, to test the role played by the depth discontinuity for resonance.

scholarly journals Propagation of Wind Energy into the Deep Ocean through a Fully Turbulent Mesoscale Eddy Field

2008 ◽  
Vol 38 (10) ◽  
pp. 2224-2241 ◽  
Author(s):  
Eric Danioux ◽  
Patrice Klein ◽  
Pascal Rivière
Keyword(s):  
Wind Energy ◽  
Mesoscale Eddy ◽  
Normal Modes ◽  
Deep Ocean ◽  
Relative Vorticity ◽  
Gradient Field ◽  
Small Scale ◽  
Motion Field ◽  
Deep Interior ◽  
Eddy Field

Abstract The authors analyze the 3D propagation of wind-forced near-inertial motions in a fully turbulent mesoscale eddy field with a primitive equation numerical model. Although the wind stress is uniform, the near-inertial motion field quickly becomes spatially heterogeneous, involving horizontal scales much smaller than the eddy scales. Analysis confirms that refraction by the eddy relative vorticity is the main mechanism responsible for the horizontal distortion of the near-inertial motions, which subsequently triggers their vertical propagation. An important result is the appearance of two maxima of near-inertial vertical velocity (both with rms values reaching 40 m day−1): one at a depth of 100 m and another unexpected one much below the main thermocline around 1700 m. The shallow maximum, captured by the highest vertical normal modes, involves near-inertial motions with a spatial heterogeneity close to the eddy vorticity gradient field. These characteristics match analytical results obtained with Young and Ben Jelloul’s approach. The deep maximum, captured by the lowest vertical normal modes, involves superinertial motions with a frequency of twice the inertial frequency and much smaller horizontal scales. Because of these characteristics, not anticipated by previous analytical studies, these superinertial motions may represent an energy source for small-scale mixing through a mechanism not taken into account in the present study: the parametric subharmonic instability (PSI). This reveals a pathway by which wind energy may have a significant impact on small-scale mixing in the deep interior. Further studies that explicitly take into account PSI are needed to estimate this potential impact.

Computational Speeds of Three Parabolic Approximations

2020 ◽  
Vol 28 (03) ◽  
pp. 1950018
Author(s):  
John L. Spiesberger ◽  
Dmitry Yu. Mikhin
Keyword(s):  
Exact Solution ◽  
Fourier Transform ◽  
Parabolic Equation ◽  
Sound Speed ◽  
Inverse Fourier Transform ◽  
Normal Modes ◽  
Deep Ocean ◽  
Element Model ◽  
Transmission Losses ◽  
Difference Model

Computational speeds are compared for modern implementations of three parabolic equation approximations. The split-step c0-insensitive model is 3.7 and 5.5 times faster than the finite-difference model OWWE and finite-element model RAM, respectively. Calculations are made between a source and receiver separated horizontally by 1000[Formula: see text]km at 600[Formula: see text]m depth near the minimum of sound speed in the deep ocean. Sound speed varies with depth but not range. The impulse response is computed by applying an inverse Fourier transform to equispaced discrete frequencies between 50[Formula: see text]Hz and 100[Formula: see text]Hz. At convergence, all implementations yield multipath travel times and transmission losses within 7[Formula: see text]ms and 2.4[Formula: see text]dB of an exact solution computed with normal modes via KRAKEN.

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