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Yoshiaki Toba - One of the best experts on this subject based on the ideXlab platform.
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sea surface drag fluctuation in relation to the saturation ratio of Wind Wave spectrum
Journal of Japan Society of Civil Engineers, 2010Co-Authors: Yasushi Suzuki, Yoshiaki Toba, Naoya Suzuki, Satoru KomoriAbstract:A new linear relation between sea surface drag coefficient and the saturation ratio of Wind Wave spectrum was obtained. The theory is based on the 3/2 power law of Wave heights and periods, which was proposed by Toba (1972). The saturation ratio of Wind Wave spectrum is calculated by using spectrum analysis in principle, however a new parameter derived by the 3/2 power law gives us a saturation ratio from significant Wave height and period instead of spectrum analysis. It is found that the negative correlation between sea surface drag and saturation ratio of Wind Wave spectrum exists. The relation can be explained that the saturated Wind Wave conditions reduce the momentum exchange from Wind to Wave, so the sea surface drag reduce in proportion to the momentum exchange.
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physical processes of microWave backscattering from laboratory Wind Wave surfaces
International Geoscience and Remote Sensing Symposium, 1993Co-Authors: Naoto Ebuchi, Hiroshi Kawamura, Yoshiaki TobaAbstract:MicroWave backscattering from Wind-Wave surfaces in a Wind-Wave tank is investigated by using an X-band (9.6 GHz) scatterometer. The radar beam is focused on the water surface by using an ellipsoidal antenna to clarify phase relationships between the backscattered signature and the Wind-Wave surfaces. At a slant incidence angle (45/spl deg/ upWind), the backscattered intensity and the Doppler velocity are in phase with the surface displacement. High Doppler velocity observed at the crests of the individual Waves coincides with the propagating speed of the crests. It is concluded that the fine structures of Wind-Wave surfaces, which are trapped near the crests and are propagating with the crests, are main contributor to the microWave backscattering. >
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physical processes of microWave backscattering from laboratory Wind Wave surfaces
Journal of Geophysical Research, 1993Co-Authors: Naoto Ebuchi, Hiroshi Kawamura, Yoshiaki TobaAbstract:Physical processes of microWave backscattering from Wind Wave surfaces are investigated in a Wind Wave tunnel by using a X-band (9.6 GHz) microWave scatterometer. Detailed analysis of time series of the backscattered intensity and Doppler spectrum shows that the physical processes of microWave backscattering are closely associated with the processes of the Wind Wave field. At slant incidence (45°) the backscattered intensity is in phase with the Wave profile, and the Doppler velocity also follows the phase of the individual Waves with high Doppler velocity observed at the crests of the individual Waves. This velocity is equal to the propagating speed of the crests. It is concluded that the fine structures of Wind Wave surfaces, which are trapped near the crests and propagating with the crests, are the main contributor to microWave backscattering. It is also pointed out that the effect of Wave breaking with bubble entrainment on the microWave backscattering is not significant under the condition of the present experiment. At normal incidence the backscattered intensity has a different phase relationship with the Wave profile. The intensity has two peaks, one at the crest and the other at the trough of the individual Waves. The peak at the trough is stronger than that at the crest. This result is consistent with specular point scattering and also with the asymmetrical features of young laboratory Wind Waves. At intermediate incident angles, backscattering processes are rather complicated because both specular point scattering and Bragg resonance scattering contribute to the radar backscattering.
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Statistical properties of microWave backscattering from laboratory Wind-Wave surfaces
Journal of Oceanography, 1992Co-Authors: Naoto Ebuchi, Hiroshi Kawamura, Yoshiaki TobaAbstract:The microWave backscattering from Wind-Wave surfaces is observed in a WindWave tunnel under various conditions of the Wind and Wind Waves, and its statistical features are investigated. The dependence of the backscattered power on the Wind speed and the incident angle shows similar features to those predicted by models proposed previously. However, the dependence of the backscattered power on the incident angles also corresponds to the asymmetrical feature of the Wind-Wave surfaces with respect to the Wind direction. The spectral analyses of time series of the backscattered intensity show that the propagating speed of fine structures of the Wind-Wave surface contributing to the backscattering at large incident angles does not coincide with the phase speed of the freely propagating BraggWaves. AtupWind incidence, the surface structures of Wind Waves contributing to the backscattering propagates with the dominant Waves at their phase speed. This result is inconsistent with the two-scale model in which the Bragg Waves are simply superimposed on longer Waves, but is consistent with the results of optical observation by Ebuchi et al. (1987). At downWind incidence, the propagating speed is slower than the phase speed of the dominant Waves.
Andrea Rinaldo - One of the best experts on this subject based on the ideXlab platform.
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statistical mechanics of Wind Wave induced erosion in shallow tidal basins inferences from the venice lagoon
Geophysical Research Letters, 2013Co-Authors: Andrea Dalpaos, Luca Carniello, Andrea RinaldoAbstract:Wind Wave-induced erosional effects are among the chief landscape-forming processes in tidal biomorphodynamics. Wave-driven bottom erosion, in fact, controls the equilibrium elevation and dynamics of subtidal and tidal flat surfaces, and the impact of Waves against salt marsh margins influences their stability. The relevance of predictive studies projecting Wind Wave patterns in space and time is thus notable especially in view of the limited insight gained so far. Here we have employed a complete, coupled finite element model accounting for the role of Wind Waves and tidal currents on the hydrodynamic circulation in shallow basins to analyze the characteristics of combined current- and Wave-induced exceedances in bottom shear stress over a given threshold for erosion. The results of our analyses from the Venice Lagoon suggest that Wind Wave-induced resuspension events can be modeled as a marked Poisson process, thus allowing one to set up a theoretical framework which can be used to model Wind Wave effects through the use of Monte Carlo realizations. This bears important consequences for quantitative analyses of the long-term biomorphodynamic evolution of tidal landscapes.
Peter A. E. M. Janssen - One of the best experts on this subject based on the ideXlab platform.
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On the Transversal Instability of a Coupled Wind-Wave System at the Initial Stage of Wave Growth
Journal of Physical Oceanography, 1993Co-Authors: Lev S. Tsimring, Peter A. E. M. JanssenAbstract:Abstract The evolution of the growing surface Waves having a nonuniform transversal structure is discussed using the semiempirical equation for Wind velocity profile in two dimensions and the expression suggested by Plant and Wright for the initial growth rate of Waves. Positive feedback has been found in the coupled Wind-Wave system, leading to an algebraic growth of a weak transversal modulation of the Wave field.
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Data assimilation with a coupled Wind‐Wave model
Journal of Geophysical Research, 1992Co-Authors: Miriam M. De Las Heras, Peter A. E. M. JanssenAbstract:A first attempt to assimilate observations into a coupled Wind-Wave model system is presented. A special feature of the Wind model is that the drag coefficient depends on the Wave age, reflecting the dependence of the air flow on the Wave state. Usually, both Wind and Wave data are assimilated. The assimilation is carried out by means of the adjoint technique. This coupled Wind-Wave data assimilation not only corrects successfully both model fields, but their dynamical connection is retained. Furthermore, the assimilation of only Wave data results in enough information on the atmospheric state at the sea surface that it can correct both Wave and Wind fields as well. Moreover, there is still some impact of the assimilation during the forecast period. This persistence is found to be dependent on the typical relaxation time scale of the Wind model, and also to be related to the swell decay time scale due to Wave breaking. The computations reveal the importance of both the coupling and the coupled Wind-Wave data assimilation scheme that has been developed.
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quasi linear theory of Wind Wave generation applied to Wave forecasting
Journal of Physical Oceanography, 1991Co-Authors: Peter A. E. M. JanssenAbstract:Abstract The effect of Wind-generated gravity Waves on the airflow is discussed using quasi-linear theory of Wind-Wave generation. In this theory, both the effects of the Waves and the effect of air turbulence on the mean Wave profile are taken into account. The main result of this theory is that for young Wind sea most of the stress in the boundary layer is determined by momentum transfer from Wind to Waves, therefore, resulting in a strong interaction between Wind and Waves. For old Wind sea there is, however, hardly any coupling. As a consequence, a sensitive dependence of the aerodynamic drag on Wave age is found, explaining the scatter in plots of the experimentally observed drag as a function of the Wind speed at 10-m height. Also, the growth rate of Waves by Wind is found to depend on Wave age. All this suggests that a proper description of the physics of the momentum transfer at the air–sea interface can only be given by coupling an atmospheric (boundary-layer) model with an ocean-Wave prediction ...
Takuji Waseda - One of the best experts on this subject based on the ideXlab platform.
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Wind Wave Growth at Short Fetch
Journal of Physical Oceanography, 2008Co-Authors: T. Lamont-smith, Takuji WasedaAbstract:Abstract Wave wire data from the large Wind Wave tank of the Ocean Engineering Laboratory at the University of California, Santa Barbara, are analyzed, and comparisons are made with published data collected in four other Wave tanks. The behavior of Wind Waves at various fetches (7–80 m) is very similar to the behavior observed in the other tanks. When the nondimensional frequency F* or nondimensional significant Wave height H* is plotted against nondimensional fetch x*, a large scatter in the data points is found. Multivariate regression to the dimensional parameters shows that significant Wave height Hsig is a function of U2x and frequency F is a function of U1.25x, where U is the Wind speed and x is the horizontal distance, with the result that in general for Wind Waves at a particular fetch in a Wave tank, approximately speaking, the Wave frequency is inversely proportional to the square root of the Wind speed and the Wavelength is proportional to the Wind speed. Similarly, the Wave height is proportio...
Hendrik L. Tolman - One of the best experts on this subject based on the ideXlab platform.
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directional Wind Wave coupling in fully coupled atmosphere Wave ocean models results from cblast hurricane
Journal of the Atmospheric Sciences, 2013Co-Authors: Shuyi S Chen, Wei Zhao, Mark A Donelan, Hendrik L. TolmanAbstract:AbstractThe extreme high Winds, intense rainfall, large ocean Waves, and copious sea spray in hurricanes push the surface-exchange parameters for temperature, water vapor, and momentum into untested regimes. The Coupled Boundary Layer Air–Sea Transfer (CBLAST)-Hurricane program is aimed at developing improved coupling parameterizations (using the observations collected during the CBLAST-Hurricane field program) for the next-generation hurricane research prediction models. Hurricane-induced surface Waves that determine the surface stress are highly asymmetric, which can affect storm structure and intensity significantly. Much of the stress is supported by Waves in the Wavelength range of 0.1–10 m, which is the unresolved “spectral tail” in present Wave models. A directional Wind–Wave coupling method is developed to include effects of directionality of the Wind and Waves in hurricanes. The surface stress vector is calculated using the two-dimensional Wave spectra from a Wave model with an added short-Wave s...
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A mosaic approach to Wind Wave modeling
Ocean Modelling, 2008Co-Authors: Hendrik L. TolmanAbstract:Abstract A mosaic or multi-grid approach to Wind Wave modeling is presented. In this approach, a series of grids with different resolutions are treated as individual Wave models, while simultaneously and continuously considering interactions between these grids. This converts a mosaic of grids into a single Wave model. For overlapping grids with distinctly different resolutions, two-way nesting is introduced. For overlapping grids with similar resolution, a reconciliation method is introduced. These techniques are implemented in the WaveWATCH III Wind Wave model and are tested for several idealized situations, and for a realistic Wave hindcast for coastal Alaskan waters. The mosaic approach is shown to give consistent results across grid scales and provides an effective and economical way to locally increase the spatial resolution of Wave models.
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neural network approximations for nonlinear interactions in Wind Wave spectra direct mapping for Wind seas in deep water
Ocean Modelling, 2005Co-Authors: Hendrik L. Tolman, Vladimir M Krasnopolsky, Dmitry ChalikovAbstract:Abstract The potential of Neural Networks (NN) to provide accurate estimates of nonlinear interactions for Wind Wave spectra by means of direct mapping is considered. Expanding on a previously reported feasibility study, an Empirical Orthogonal Functions (EOF) based NN for single peaked spectra is shown to be much more accurate than the well known Discrete Interaction Approximation (DIA), at the expense of a moderate increase of computational costs. This Neural Network Interaction Approximation (NNIA) gives reasonable results for modeled Wave spectra, but is not yet capable of providing acceptable model integrations. Methods to expand the NNIA to be suitable for model integration are discussed.
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source terms in a third generation Wind Wave model
Journal of Physical Oceanography, 1996Co-Authors: Hendrik L. Tolman, Dmitry ChalikovAbstract:Abstract A new third-generation ocean Wind Wave model is presented. This model is based on previously developed input and nonlinear interaction source terms and a new dissipation source term. It is argued that the dissipation source term has to be modeled using two explicit constituents. A low-frequency dissipation term analogous to Wave energy loss due to oceanic turbulence is therefore augmented with a diagnostic high-frequency dissipation term. The dissipation is tuned for the model to represent idealized fetch-limited growth behavior. The new model results in excellent growth behavior from extremely short fetches up to full development. For intermediate to long fetches results are similar to those of WAM, but for extremely short fetches the present model presents a significant improvement (although the poor behavior of WAM appears to be related to correctable numerical constraints). The new model furthermore gives smoother results and appears less sensitive to numerical errors. Finally, limitations of...
