<p>Material tracers at the ocean surface disperse under the influence of th... more <p>Material tracers at the ocean surface disperse under the influence of the quasi-random forces that act on the ocean surface. These forces may include ocean turbulence, wind, and surface waves. Currently, wind and ocean turbulence are assumed to be the important drivers of dispersion of the floating tracer particles. Despite some theoretical results and laboratory experiments, the experimental proof of the significant contribution of wave induced dispersion in overall transport of large-scale geophysical systems remains elusive. This is mainly due to a lack of practical observations.</p><p>In this study we aim to estimate the contribution of wave-induced dispersion in comparison with conventional mechanisms of dispersion due to ocean turbulence. We do so through the analysis of in-situ observations of surface drifters deployed across the seas and oceans.  The experimental dataset include data from the Global Drifter Program and newly obtained data through cluster deployment of Spotter wave buoys. The results suggest that waves during marine storm conditions may be a critical driver of surface tracer dispersion during the first ten days after the storm and at horizontal length scales up to the order of 10 km. Our results imply that accurate information of wave conditions is required for accurate prediction of tracer dispersion at short to intermediate time and length scales.</p>
Dispersion of a passive tracer by water waves is of significant importance for many scientific an... more Dispersion of a passive tracer by water waves is of significant importance for many scientific and technological problems including bio-diversity of marine life, ecological impact of anthropogenic incidents, planning of rescue operation and global oceanic transport. Formally, turbulent dispersion of a passive tracer by surface waves is a Brownian motion caused by a prescribed noise, viz., random fluctuations of the wave field. From this perspective, it is similar to the conventional dispersion by tracer particles by turbulent flows initially described in the seminal work of Richardson, Taylor and Obukhov. The additional challenges of this problem are imposed by the complexity of the underlining wave field—different dispersion relations and correlation structure, directionality and its spread, wave breaking—and this complexity necessitates further theoretical and experimental research. The aim of the present study is experimental validation of scaling relations for the mean drift and mean variance of tracer particles predicted by the wave turbulence theory. We report results of a set of targeted experiments in a large three-dimensional wave tank where the positions of the tracer particles—modelled as surface drifters—were tracked down with optical cameras. The experimental data are analysed and discussed in the light of the weak turbulence theory.
The wind/wave climatology for the Arctic Seas will be developed based on altimeter observations. ... more The wind/wave climatology for the Arctic Seas will be developed based on altimeter observations. It will have a major scientific and applied significance as presently there is no reference climatology for this region of the ocean available. The new versions of wave models for Beaufort and Chukchi Seas will include new physics that is already under development, and the novel physics presently unavailable. In particular, it is planned to use a wave boundary layer model to replace traditional wind-input parameterisations. The models will be suitable for operational forecast. Altimeter climatology and the wave models will be used to study the current and future wind/wave and ice trends.
The wind/wave climatology for the Arctic Seas will be developed based on altimeter observations. ... more The wind/wave climatology for the Arctic Seas will be developed based on altimeter observations. It will have a major scientific and applied significance as presently there is no reference climatology for this region of the ocean available. The new versions of wave models for the Beaufort and Chukchi Seas will include new physics that is already under development, and the novel physics presently unavailable. In particular, it is planned to use a wave boundary layer model to replace traditional wind-input parameterisations. The models will be suitable for operational forecast. Altimeter climatology and the wave models will be used to study the current and future wind/wave and ice trends.
This paper reviews the research activities that were carried out under the auspices of the Nation... more This paper reviews the research activities that were carried out under the auspices of the National Ocean Partnership Program (NOPP) to advance research in wind wave modeling and transfer maturing technologies into operational community models. Primary focus of research activities that were funded under this program was to improve the source terms associated with deep water wind waves with a secondary focus on shallow water processes. While the focus has been on developing capabilities for stochastic phase averaged models, some of the research work reported here also touches on phase resolved models as well as updates that are needed to the classical stochastic equations to be applicable in shallow water conditions. The primary focus is on the development of new source terms to account for wave generation, dissipation and nonlinear wave-wave interactions. A direct result of this program has been the development of new physics packages in operational wave models that have improved fo...
Journal of Advances in Modeling Earth Systems, 2021
Global wave hindcasts are developed using the third generation spectral wave model WAVEWATCH III ... more Global wave hindcasts are developed using the third generation spectral wave model WAVEWATCH III with the observation-based source terms (ST6) and a hybrid rectilinear-curvilinear, irregular-regular-irregular grid system (approximately at 0.25 0.25 ). Three distinct global hindcasts are produced: (a) a long-term hindcast (1979-2019) forced by the ERA5 conventional winds 10 U and (b) two short-term hindcasts (2011-2019) driven by the NCEP climate forecast system (CFS)v2 10 U and the ERA5 neutral winds 10,neu U , respectively. The input field for ice is sourced from the Ocean and Sea Ice Satellite Application Facility (OSI SAF) sea-ice concentration climate data records. These wave simulations, together with the driving wind forcing, are validated against extensive in-situ observations and satellite altimeter records. The performance of the ST6 wave hindcasts shows promising results across multiple wave parameters, including the conventional wave characteristics (e.g., wave height s H and wave period) and high-order spectral moments (e.g., the surface Stokes drift and mean square slope). The ERA5-based simulations generally present lower random errors, but the CFS-based run represents extreme sea states (e.g., 10 s H m) considerably better. Novel wave parameters available in our hindcasts, namely the dominant wave breaking probability, wave-induced mixed layer depth, freak wave indexes and wavespreading factor, are further described and briefly discussed. Inter-comparisons of s H from the long-term (41 years) wave hindcast, buoy measurements and two different calibrated altimeter data sets highlight the inconsistency in these altimeter records arising from different calibration methodology. Significant errors in the low-frequency bins (period 15 T s) for both wave energy and directionality call for further model development. Plain Language Summary Ocean surface waves are fundamentally important for ocean engineering design, ship navigation, air-sea exchange of gas, heat, momentum and energy, upper ocean dynamics, and remote sensing of the ocean. Spectral wave modeling is an indispensable tool to estimate sea state information. In this study, we present new global wave hindcasts developed using the stateof-the-art model physics and numerics and the modern reanalysis winds and satellite sea ice records. It is demonstrated through validation against in-situ observations and altimeter records that the global wave hindcasts perform well across multiple parameters. Meanwhile, intercomparisons of wave height from the long-term hindcast, buoys, and altimeters reveal inconsistency and potential inhomogeneity in these different data sets. The wave hindcasts we developed, in combination with global wave databases published previously, will form a large ensemble of realizations of historical evolution of sea states simulated with distinct wave physics and wind forcing, which will help quantify sea states in real oceans more accurately. LIU ET AL.
Three dissipative (two viscoelastic and one viscous) ice models are implemented in the spectral w... more Three dissipative (two viscoelastic and one viscous) ice models are implemented in the spectral wave model WAVEWATCH III to estimate the ice-induced wave attenuation rate. These models are then explored and intercompared through hindcasts of two field cases: one in the autumn Beaufort Sea in 2015 and the other in the Antarctic marginal ice zone (MIZ) in 2012. The capability of these dissipative models, along with their limitations and applicability to operational forecasts, are analyzed and discussed. The sensitivity of the simulated wave height to different source terms—the ice-induced wave decay Sice and other physical processes Sother (e.g., wind input, nonlinear four-wave interactions)—is also investigated. For the Antarctic MIZ experiment, Sother is found to be remarkably less than Sice and thus contributes little to the simulated significant wave height Hs. The saturation of dHs/dx at large wave heights in this case, as reported by a previous study, is well reproduced by the t...
It is known that drag coefficient varies in broad limits depending on wind velocity and wave age ... more It is known that drag coefficient varies in broad limits depending on wind velocity and wave age as well as on wave spectrum and some other parameters. All those effects produce large scatter of the drag coefficient, so, the data is plotted as a function of wind velocity forming a cloud of points with no distinct regularities. Such uncertainty can be overcome by the implementation of the WBL model instead of the calculations of drag with different formulas. The paper is devoted to the formulation of the Wave Boundary Layer (WBL) model for the parameterization of the ocean-atmosphere interactions in coupled ocean-atmosphere models and wave prediction models. The equations explicitly take into account the vertical flux of momentum generated by the wave-produced fluctuations of pressure, velocity and stresses (WPMF). Their surface values are calculated with the use of the spectral beta-functions whose expression was obtained by means of the 2-D simulation of the WBL. Hence, the model d...
The generation and evolution of ocean waves by wind is one of the most complex phenomena in geoph... more The generation and evolution of ocean waves by wind is one of the most complex phenomena in geophysics, and is of great practical significance. Predictive capabilities of respective wave models, however, are impaired by lack of field in situ observations, particularly in extreme Metocean conditions. The paper outlines and highlights important gaps in understanding the Metocean processes and suggests a major observational program in the Southern Ocean. This large, but poorly investigated part of the World Ocean is home to extreme weather around the year. The observational network would include distributed system of buoys (drifting and stationary) and autonomous surface vehicles (ASV), intended for measurements of waves and air-sea fluxes in the Southern Ocean. It would help to resolve the issues of limiting fetches, extreme Extra-Tropical cyclones, swell propagation and attenuation, wave-current interactions, and address the topics of wave-induced dispersal of floating objects, wave-ice interactions in the Marginal Ice Zone, Metocean climatology and its connection with the global climate.
Numerical wave models are powerful tools for investigating global wave climate. Here a global wav... more Numerical wave models are powerful tools for investigating global wave climate. Here a global wave hindcast is employed to estimate the global pattern of crossing swells. However, the global patterns of crossing swells derived from the model are different from those derived from the synthetic aperture radar (SAR) wave mode products of quasi-linear inversion, indicating one of them is questionable. The comparison shows that the first two most energetic swells inversed by SAR are often not in accordance with the first two most energetic swells in the model, and this will have a large impact on the statistics of the data. Before this problem is solved, SAR wave products of quasi-linear inversion should be treated with care in wave climate studies.
The long-term goals of the present project are two: wind/wave climatology for the Arctic Seas and... more The long-term goals of the present project are two: wind/wave climatology for the Arctic Seas and their current and potential future trends; and WAVEWATCH-III® and SWAN wave models with new physics, adapted and validated for the Beaufort and Chukchi Seas. DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited.
Using the well-observed hurricane case Ivan (2004) as an example, we investigate and intercompare... more Using the well-observed hurricane case Ivan (2004) as an example, we investigate and intercompare the performance of two wave models under hurricane conditions. One is the WAVEWATCH III model (WW3) and the other is the University of Miami Wave Model (UMWM). Within WW3, four different source term packages (ST2/3/4/6) of wind input, wave breaking dissipation and swell decay are chosen for comparison purposes. Based on the comparisons between model results and measurements from various platforms, we concluded that UMWM shows less accuracy than WW3 in specification of bulk wave parameters. This is possibly because (i) UMWM-estimated drag coefficient does not clearly show a saturation trend when wind speeds are beyond ∼ 35 m s −1 and (ii) the four-wave interaction term of UMWM disagrees evidently with the full solution of the Boltzmann integral in detail. Among the four WW3 source term packages, the older parameterization ST2 is basically the least accurate because of its systematic underestimation of high waves. The remaining three packages (ST3/4/6) are performed well under Ivan. However, we also find that they tend to overestimate energy of waves traveling in the oblique and opposing winds. It is shown that enhancing the strength of negative wind input properly can effectively improve model skills in such situations. Limited by the uncertainty in the wind forcing, we could not determine the most accurate package among ST3/4/6 unambiguously.
The paper outlines principles of phase-resolving and phase-average wave models, with emphasis on ... more The paper outlines principles of phase-resolving and phase-average wave models, with emphasis on the state of the art of wave-current interaction physics. We argue that these interactions are the least well-developed part of such models. Linear and nonlinear dynamics of waves on currents are discussed; depth-integrated and depth-varying approaches are described. Finally, examples of numerical model performance for waves on currents in realistic oceanic scenarios are presented.
Recent developments in the physical parameterizations available in spectral wave models have alre... more Recent developments in the physical parameterizations available in spectral wave models have already been validated, but there is little information on their relative performance especially with focus on the higher order spectral moments and wave partitions. This study concentrates on documenting their strengths and limitations using satellite measurements, buoy spectra, and a comparison between the different models. It is confirmed that all models perform well in terms of significant wave heights; however higher-order moments have larger errors. The partition wave quantities perform well in terms of direction and frequency but the magnitude and directional spread typically have larger discrepancies. The high-frequency tail is examined through the mean square slope using satellites and buoys. From this analysis it is clear that some models behave better than the others, suggesting their parameterizations match the physical processes reasonably well. However none of the models are entirely satisfactory, pointing to poorly constrained parameterizations or missing physical processes. The major space-time differences between the models are related to the swell field stressing the importance of describing its evolution. An example swell field confirms the wave heights can be notably different between model configurations while the directional distributions remain similar. It is clear that all models have difficulty in describing the directional spread. Therefore, knowledge of the source term directional distributions is paramount in improving the wave model physics in the future. Highlights ► The best 4 spectral wave parameterizations have been compared to satellites and buoys. ► Higher order spectral moments and wave partitions are rigorously validated. ► All models describe the loworder wave moments; some perform better for higher ones. ► The models are sensitive to the far-field swell and have similar spatial distribution. ► The directional spread within the wave spectra performs poorly and needs improvement. Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site.
Volume 2A: Structures, Safety and Reliability, 2013
Design criteria in ocean engineering, whether this is one in 50 years or one in 5000 years event,... more Design criteria in ocean engineering, whether this is one in 50 years or one in 5000 years event, are hardly ever based on measurements, and rather on statistical distributions of relevant metocean properties. Of utmost interest is the tail of these distributions, that is rare events such as the highest waves with low probability. Engineers have long since realised that the superposition of linear waves with narrow-banded spectrum as depicted by the Rayleigh distribution underestimates the probability of extreme wave crests, and is not adequate for wave heights either, which is a critical shortcoming as far as the engineering design is concerned. Ongoing theoretical and experimental efforts have been under way for decades to address this issue. Here, we will concentrate on short-term statistics, i.e. probability of crests/heights of individual waves. Typical approach is to treat all possible waves in the ocean or at a particular location as a single ensemble for which some comprehen...
Following the 13th International Workshop on Wave Hindcasting and Forecasting and 4th Coastal Haz... more Following the 13th International Workshop on Wave Hindcasting and Forecasting and 4th Coastal Hazards Symposium in October 2013 in Banff, Canada, a topical collection has appeared in recent issues of Ocean Dynamics. Here we give a brief overview of the history of the conference since its inception in 1986 and of the progress made in the fields of wind-generated ocean waves and the modelling of coastal hazards before we summarize the main results of the papers that have appeared in the topical collection.
Numerical simulations of the wind-wave spectrum are conducted on the basis of the new wind input ... more Numerical simulations of the wind-wave spectrum are conducted on the basis of the new wind input and wave dissipation functions obtained in the Lake George field experiment. This experiment allowed simultaneous measurements of the source functions in a broad range of conditions, including extreme wind-wave circumstances. Results of the experiment revealed new physical mechanisms in the processes of spectral input/dissipation of wave energy, which are presently not accounted for in wave forecast models. These results were parameterised as source terms in a form suitable for spectral wave models. The simulations were conducted by means of the two-dimensional research WAVETIME model with an exact solution for the nonlinear term. Physical constraints were imposed on the source functions in terms of the known experimental dependences for the total wind-wave momentum flux. Enforcing the constraints in the course of wave spectrum evolution allowed fine tuning of experimental parameters of the new input and dissipation functions. The resulting time-limited evolution of integral, spectral and directional wave properties, based on implementation of the new physically-justified source/sink terms and constraints, is then analysed. Good agreement of the simulated evolution with known experimental dependences is demonstrated.
This paper is the product of the wave modelling community and it tries to make a picture of the p... more This paper is the product of the wave modelling community and it tries to make a picture of the present situation in this branch of science, exploring the previous and the most recent results and looking ahead towards the solution of the problems we presently face. Both theory and applications are considered. The many faces of the subject imply separate discussions. This is reflected into the single sections, seven of them, each dealing with a specific topic, the whole providing a broad and solid overview of the present state of the art. After an introduction framing the problem and the approach we followed, we deal in sequence with the following subjects: (Section) 2, generation by wind; 3, non-linear interactions in deep water; 4, white-capping dissipation; 5, non-linear interactions in shallow water; 6, dissipation at the sea bottom; 7, wave propagation; 8, numerics. The two final sections, 9 and 10, summarize the present situation from a general point of view and try to look at the future developments. Keywords Wind waves Wind wave generation Wave-wave interaction Wave propagation Wave dissipation Wave-current interaction Numerics List of contents 1. Introduction 2. Brief Review of Wind-wave Generation 2.1. Linear theory 2.2. Nonlinear effects 2.3. Gustiness 2.4. Open issues Damping of low-frequency swells Momentum transfer for high wind speeds Quality of modelled wind fields 3. Modelling Nonlinear Four-wave Interactions in Discrete Spectral Wave Models 3.1. Theory 3.2. Solution methods 3.3. Properties 3.4. Development in computational methods 3.5. Inter-comparison of computational methods 3.6. Questions and actions 4. Spectral Dissipation in Deep Water 4.1. Theoretical and experimental research of physics of the spectral dissipation Spectral dissipation due to wave breaking Wave-turbulence interactions Wave-wave modulations 4.2. Modelling the spectral dissipation function 5. Nonlinear Interactions in Shallow Water Waves 5.1. Nonlinearity in shallow water 5.2. Deterministic models: time-domain and spectral-domain 5.3. Stochastic models 5.4. Dissipation and wave breaking in shallow water 5.5. Open problems 6. Bottom Dissipation 6.1. Wave energy dissipation due to bottom friction Common formulations for spectral wave models: waves only Common formulations for spectral wave models: waves and currents Bottom roughness models for movable beds 6.2. Energy dissipation due to wave-bottom interaction 6.3. Wave scattering and reflection 6.4. Discussion and outstanding problems 7. Wave Propagation 7.1. Dispersion, geometrical optics and the wave action equation 7.2. Limitations of geometrical optics: diffraction, reflection and random scattering 7.3. Waves over varying currents, non-linear wave effects and the advection velocity 7.4. Waves blocking 7.5. Unsteady water depths and currents 7.6. Waves in the real ocean 8. Numerics and Resolution in Large-scale Wave Modelling 8.1. A description of the problem Error due to the numerical scheme for geographic propagation on a grid Diffusion Numerical dispersion Combined effect of diffusion and dispersion Error due to the numerical scheme for spectral propagation Error due to coarse geographic resolution Error due to coarse spectral resolution Errors in source term integration 8.2. Existing solutions Improved numerical schemes for propagation on a grid Alternatives to the finite difference schemes on a grid Addressing error due to coarse geographic resolution Garden Sprinkler Effect correction methods Errors in source terms integration 8.3. Relative importance of problem Error due to the numerical scheme for geographic propagation Argument Counter-argument Error due to the numerical scheme for spectral propagation Geographic resolution Spectral resolution Source term integration 8.4. Future solutions The numerical scheme for geographic propagation Geographic resolution Spectral resolution Errors in source term integration 8.5. Numerics and resolution: Problems particular to finite depth and high resolution applications 9. Where We Are 10.Where to Go Acknowledgements References List of authors, affiliations and addresses
<p>Material tracers at the ocean surface disperse under the influence of th... more <p>Material tracers at the ocean surface disperse under the influence of the quasi-random forces that act on the ocean surface. These forces may include ocean turbulence, wind, and surface waves. Currently, wind and ocean turbulence are assumed to be the important drivers of dispersion of the floating tracer particles. Despite some theoretical results and laboratory experiments, the experimental proof of the significant contribution of wave induced dispersion in overall transport of large-scale geophysical systems remains elusive. This is mainly due to a lack of practical observations.</p><p>In this study we aim to estimate the contribution of wave-induced dispersion in comparison with conventional mechanisms of dispersion due to ocean turbulence. We do so through the analysis of in-situ observations of surface drifters deployed across the seas and oceans.  The experimental dataset include data from the Global Drifter Program and newly obtained data through cluster deployment of Spotter wave buoys. The results suggest that waves during marine storm conditions may be a critical driver of surface tracer dispersion during the first ten days after the storm and at horizontal length scales up to the order of 10 km. Our results imply that accurate information of wave conditions is required for accurate prediction of tracer dispersion at short to intermediate time and length scales.</p>
Dispersion of a passive tracer by water waves is of significant importance for many scientific an... more Dispersion of a passive tracer by water waves is of significant importance for many scientific and technological problems including bio-diversity of marine life, ecological impact of anthropogenic incidents, planning of rescue operation and global oceanic transport. Formally, turbulent dispersion of a passive tracer by surface waves is a Brownian motion caused by a prescribed noise, viz., random fluctuations of the wave field. From this perspective, it is similar to the conventional dispersion by tracer particles by turbulent flows initially described in the seminal work of Richardson, Taylor and Obukhov. The additional challenges of this problem are imposed by the complexity of the underlining wave field—different dispersion relations and correlation structure, directionality and its spread, wave breaking—and this complexity necessitates further theoretical and experimental research. The aim of the present study is experimental validation of scaling relations for the mean drift and mean variance of tracer particles predicted by the wave turbulence theory. We report results of a set of targeted experiments in a large three-dimensional wave tank where the positions of the tracer particles—modelled as surface drifters—were tracked down with optical cameras. The experimental data are analysed and discussed in the light of the weak turbulence theory.
The wind/wave climatology for the Arctic Seas will be developed based on altimeter observations. ... more The wind/wave climatology for the Arctic Seas will be developed based on altimeter observations. It will have a major scientific and applied significance as presently there is no reference climatology for this region of the ocean available. The new versions of wave models for Beaufort and Chukchi Seas will include new physics that is already under development, and the novel physics presently unavailable. In particular, it is planned to use a wave boundary layer model to replace traditional wind-input parameterisations. The models will be suitable for operational forecast. Altimeter climatology and the wave models will be used to study the current and future wind/wave and ice trends.
The wind/wave climatology for the Arctic Seas will be developed based on altimeter observations. ... more The wind/wave climatology for the Arctic Seas will be developed based on altimeter observations. It will have a major scientific and applied significance as presently there is no reference climatology for this region of the ocean available. The new versions of wave models for the Beaufort and Chukchi Seas will include new physics that is already under development, and the novel physics presently unavailable. In particular, it is planned to use a wave boundary layer model to replace traditional wind-input parameterisations. The models will be suitable for operational forecast. Altimeter climatology and the wave models will be used to study the current and future wind/wave and ice trends.
This paper reviews the research activities that were carried out under the auspices of the Nation... more This paper reviews the research activities that were carried out under the auspices of the National Ocean Partnership Program (NOPP) to advance research in wind wave modeling and transfer maturing technologies into operational community models. Primary focus of research activities that were funded under this program was to improve the source terms associated with deep water wind waves with a secondary focus on shallow water processes. While the focus has been on developing capabilities for stochastic phase averaged models, some of the research work reported here also touches on phase resolved models as well as updates that are needed to the classical stochastic equations to be applicable in shallow water conditions. The primary focus is on the development of new source terms to account for wave generation, dissipation and nonlinear wave-wave interactions. A direct result of this program has been the development of new physics packages in operational wave models that have improved fo...
Journal of Advances in Modeling Earth Systems, 2021
Global wave hindcasts are developed using the third generation spectral wave model WAVEWATCH III ... more Global wave hindcasts are developed using the third generation spectral wave model WAVEWATCH III with the observation-based source terms (ST6) and a hybrid rectilinear-curvilinear, irregular-regular-irregular grid system (approximately at 0.25 0.25 ). Three distinct global hindcasts are produced: (a) a long-term hindcast (1979-2019) forced by the ERA5 conventional winds 10 U and (b) two short-term hindcasts (2011-2019) driven by the NCEP climate forecast system (CFS)v2 10 U and the ERA5 neutral winds 10,neu U , respectively. The input field for ice is sourced from the Ocean and Sea Ice Satellite Application Facility (OSI SAF) sea-ice concentration climate data records. These wave simulations, together with the driving wind forcing, are validated against extensive in-situ observations and satellite altimeter records. The performance of the ST6 wave hindcasts shows promising results across multiple wave parameters, including the conventional wave characteristics (e.g., wave height s H and wave period) and high-order spectral moments (e.g., the surface Stokes drift and mean square slope). The ERA5-based simulations generally present lower random errors, but the CFS-based run represents extreme sea states (e.g., 10 s H m) considerably better. Novel wave parameters available in our hindcasts, namely the dominant wave breaking probability, wave-induced mixed layer depth, freak wave indexes and wavespreading factor, are further described and briefly discussed. Inter-comparisons of s H from the long-term (41 years) wave hindcast, buoy measurements and two different calibrated altimeter data sets highlight the inconsistency in these altimeter records arising from different calibration methodology. Significant errors in the low-frequency bins (period 15 T s) for both wave energy and directionality call for further model development. Plain Language Summary Ocean surface waves are fundamentally important for ocean engineering design, ship navigation, air-sea exchange of gas, heat, momentum and energy, upper ocean dynamics, and remote sensing of the ocean. Spectral wave modeling is an indispensable tool to estimate sea state information. In this study, we present new global wave hindcasts developed using the stateof-the-art model physics and numerics and the modern reanalysis winds and satellite sea ice records. It is demonstrated through validation against in-situ observations and altimeter records that the global wave hindcasts perform well across multiple parameters. Meanwhile, intercomparisons of wave height from the long-term hindcast, buoys, and altimeters reveal inconsistency and potential inhomogeneity in these different data sets. The wave hindcasts we developed, in combination with global wave databases published previously, will form a large ensemble of realizations of historical evolution of sea states simulated with distinct wave physics and wind forcing, which will help quantify sea states in real oceans more accurately. LIU ET AL.
Three dissipative (two viscoelastic and one viscous) ice models are implemented in the spectral w... more Three dissipative (two viscoelastic and one viscous) ice models are implemented in the spectral wave model WAVEWATCH III to estimate the ice-induced wave attenuation rate. These models are then explored and intercompared through hindcasts of two field cases: one in the autumn Beaufort Sea in 2015 and the other in the Antarctic marginal ice zone (MIZ) in 2012. The capability of these dissipative models, along with their limitations and applicability to operational forecasts, are analyzed and discussed. The sensitivity of the simulated wave height to different source terms—the ice-induced wave decay Sice and other physical processes Sother (e.g., wind input, nonlinear four-wave interactions)—is also investigated. For the Antarctic MIZ experiment, Sother is found to be remarkably less than Sice and thus contributes little to the simulated significant wave height Hs. The saturation of dHs/dx at large wave heights in this case, as reported by a previous study, is well reproduced by the t...
It is known that drag coefficient varies in broad limits depending on wind velocity and wave age ... more It is known that drag coefficient varies in broad limits depending on wind velocity and wave age as well as on wave spectrum and some other parameters. All those effects produce large scatter of the drag coefficient, so, the data is plotted as a function of wind velocity forming a cloud of points with no distinct regularities. Such uncertainty can be overcome by the implementation of the WBL model instead of the calculations of drag with different formulas. The paper is devoted to the formulation of the Wave Boundary Layer (WBL) model for the parameterization of the ocean-atmosphere interactions in coupled ocean-atmosphere models and wave prediction models. The equations explicitly take into account the vertical flux of momentum generated by the wave-produced fluctuations of pressure, velocity and stresses (WPMF). Their surface values are calculated with the use of the spectral beta-functions whose expression was obtained by means of the 2-D simulation of the WBL. Hence, the model d...
The generation and evolution of ocean waves by wind is one of the most complex phenomena in geoph... more The generation and evolution of ocean waves by wind is one of the most complex phenomena in geophysics, and is of great practical significance. Predictive capabilities of respective wave models, however, are impaired by lack of field in situ observations, particularly in extreme Metocean conditions. The paper outlines and highlights important gaps in understanding the Metocean processes and suggests a major observational program in the Southern Ocean. This large, but poorly investigated part of the World Ocean is home to extreme weather around the year. The observational network would include distributed system of buoys (drifting and stationary) and autonomous surface vehicles (ASV), intended for measurements of waves and air-sea fluxes in the Southern Ocean. It would help to resolve the issues of limiting fetches, extreme Extra-Tropical cyclones, swell propagation and attenuation, wave-current interactions, and address the topics of wave-induced dispersal of floating objects, wave-ice interactions in the Marginal Ice Zone, Metocean climatology and its connection with the global climate.
Numerical wave models are powerful tools for investigating global wave climate. Here a global wav... more Numerical wave models are powerful tools for investigating global wave climate. Here a global wave hindcast is employed to estimate the global pattern of crossing swells. However, the global patterns of crossing swells derived from the model are different from those derived from the synthetic aperture radar (SAR) wave mode products of quasi-linear inversion, indicating one of them is questionable. The comparison shows that the first two most energetic swells inversed by SAR are often not in accordance with the first two most energetic swells in the model, and this will have a large impact on the statistics of the data. Before this problem is solved, SAR wave products of quasi-linear inversion should be treated with care in wave climate studies.
The long-term goals of the present project are two: wind/wave climatology for the Arctic Seas and... more The long-term goals of the present project are two: wind/wave climatology for the Arctic Seas and their current and potential future trends; and WAVEWATCH-III® and SWAN wave models with new physics, adapted and validated for the Beaufort and Chukchi Seas. DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited.
Using the well-observed hurricane case Ivan (2004) as an example, we investigate and intercompare... more Using the well-observed hurricane case Ivan (2004) as an example, we investigate and intercompare the performance of two wave models under hurricane conditions. One is the WAVEWATCH III model (WW3) and the other is the University of Miami Wave Model (UMWM). Within WW3, four different source term packages (ST2/3/4/6) of wind input, wave breaking dissipation and swell decay are chosen for comparison purposes. Based on the comparisons between model results and measurements from various platforms, we concluded that UMWM shows less accuracy than WW3 in specification of bulk wave parameters. This is possibly because (i) UMWM-estimated drag coefficient does not clearly show a saturation trend when wind speeds are beyond ∼ 35 m s −1 and (ii) the four-wave interaction term of UMWM disagrees evidently with the full solution of the Boltzmann integral in detail. Among the four WW3 source term packages, the older parameterization ST2 is basically the least accurate because of its systematic underestimation of high waves. The remaining three packages (ST3/4/6) are performed well under Ivan. However, we also find that they tend to overestimate energy of waves traveling in the oblique and opposing winds. It is shown that enhancing the strength of negative wind input properly can effectively improve model skills in such situations. Limited by the uncertainty in the wind forcing, we could not determine the most accurate package among ST3/4/6 unambiguously.
The paper outlines principles of phase-resolving and phase-average wave models, with emphasis on ... more The paper outlines principles of phase-resolving and phase-average wave models, with emphasis on the state of the art of wave-current interaction physics. We argue that these interactions are the least well-developed part of such models. Linear and nonlinear dynamics of waves on currents are discussed; depth-integrated and depth-varying approaches are described. Finally, examples of numerical model performance for waves on currents in realistic oceanic scenarios are presented.
Recent developments in the physical parameterizations available in spectral wave models have alre... more Recent developments in the physical parameterizations available in spectral wave models have already been validated, but there is little information on their relative performance especially with focus on the higher order spectral moments and wave partitions. This study concentrates on documenting their strengths and limitations using satellite measurements, buoy spectra, and a comparison between the different models. It is confirmed that all models perform well in terms of significant wave heights; however higher-order moments have larger errors. The partition wave quantities perform well in terms of direction and frequency but the magnitude and directional spread typically have larger discrepancies. The high-frequency tail is examined through the mean square slope using satellites and buoys. From this analysis it is clear that some models behave better than the others, suggesting their parameterizations match the physical processes reasonably well. However none of the models are entirely satisfactory, pointing to poorly constrained parameterizations or missing physical processes. The major space-time differences between the models are related to the swell field stressing the importance of describing its evolution. An example swell field confirms the wave heights can be notably different between model configurations while the directional distributions remain similar. It is clear that all models have difficulty in describing the directional spread. Therefore, knowledge of the source term directional distributions is paramount in improving the wave model physics in the future. Highlights ► The best 4 spectral wave parameterizations have been compared to satellites and buoys. ► Higher order spectral moments and wave partitions are rigorously validated. ► All models describe the loworder wave moments; some perform better for higher ones. ► The models are sensitive to the far-field swell and have similar spatial distribution. ► The directional spread within the wave spectra performs poorly and needs improvement. Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site.
Volume 2A: Structures, Safety and Reliability, 2013
Design criteria in ocean engineering, whether this is one in 50 years or one in 5000 years event,... more Design criteria in ocean engineering, whether this is one in 50 years or one in 5000 years event, are hardly ever based on measurements, and rather on statistical distributions of relevant metocean properties. Of utmost interest is the tail of these distributions, that is rare events such as the highest waves with low probability. Engineers have long since realised that the superposition of linear waves with narrow-banded spectrum as depicted by the Rayleigh distribution underestimates the probability of extreme wave crests, and is not adequate for wave heights either, which is a critical shortcoming as far as the engineering design is concerned. Ongoing theoretical and experimental efforts have been under way for decades to address this issue. Here, we will concentrate on short-term statistics, i.e. probability of crests/heights of individual waves. Typical approach is to treat all possible waves in the ocean or at a particular location as a single ensemble for which some comprehen...
Following the 13th International Workshop on Wave Hindcasting and Forecasting and 4th Coastal Haz... more Following the 13th International Workshop on Wave Hindcasting and Forecasting and 4th Coastal Hazards Symposium in October 2013 in Banff, Canada, a topical collection has appeared in recent issues of Ocean Dynamics. Here we give a brief overview of the history of the conference since its inception in 1986 and of the progress made in the fields of wind-generated ocean waves and the modelling of coastal hazards before we summarize the main results of the papers that have appeared in the topical collection.
Numerical simulations of the wind-wave spectrum are conducted on the basis of the new wind input ... more Numerical simulations of the wind-wave spectrum are conducted on the basis of the new wind input and wave dissipation functions obtained in the Lake George field experiment. This experiment allowed simultaneous measurements of the source functions in a broad range of conditions, including extreme wind-wave circumstances. Results of the experiment revealed new physical mechanisms in the processes of spectral input/dissipation of wave energy, which are presently not accounted for in wave forecast models. These results were parameterised as source terms in a form suitable for spectral wave models. The simulations were conducted by means of the two-dimensional research WAVETIME model with an exact solution for the nonlinear term. Physical constraints were imposed on the source functions in terms of the known experimental dependences for the total wind-wave momentum flux. Enforcing the constraints in the course of wave spectrum evolution allowed fine tuning of experimental parameters of the new input and dissipation functions. The resulting time-limited evolution of integral, spectral and directional wave properties, based on implementation of the new physically-justified source/sink terms and constraints, is then analysed. Good agreement of the simulated evolution with known experimental dependences is demonstrated.
This paper is the product of the wave modelling community and it tries to make a picture of the p... more This paper is the product of the wave modelling community and it tries to make a picture of the present situation in this branch of science, exploring the previous and the most recent results and looking ahead towards the solution of the problems we presently face. Both theory and applications are considered. The many faces of the subject imply separate discussions. This is reflected into the single sections, seven of them, each dealing with a specific topic, the whole providing a broad and solid overview of the present state of the art. After an introduction framing the problem and the approach we followed, we deal in sequence with the following subjects: (Section) 2, generation by wind; 3, non-linear interactions in deep water; 4, white-capping dissipation; 5, non-linear interactions in shallow water; 6, dissipation at the sea bottom; 7, wave propagation; 8, numerics. The two final sections, 9 and 10, summarize the present situation from a general point of view and try to look at the future developments. Keywords Wind waves Wind wave generation Wave-wave interaction Wave propagation Wave dissipation Wave-current interaction Numerics List of contents 1. Introduction 2. Brief Review of Wind-wave Generation 2.1. Linear theory 2.2. Nonlinear effects 2.3. Gustiness 2.4. Open issues Damping of low-frequency swells Momentum transfer for high wind speeds Quality of modelled wind fields 3. Modelling Nonlinear Four-wave Interactions in Discrete Spectral Wave Models 3.1. Theory 3.2. Solution methods 3.3. Properties 3.4. Development in computational methods 3.5. Inter-comparison of computational methods 3.6. Questions and actions 4. Spectral Dissipation in Deep Water 4.1. Theoretical and experimental research of physics of the spectral dissipation Spectral dissipation due to wave breaking Wave-turbulence interactions Wave-wave modulations 4.2. Modelling the spectral dissipation function 5. Nonlinear Interactions in Shallow Water Waves 5.1. Nonlinearity in shallow water 5.2. Deterministic models: time-domain and spectral-domain 5.3. Stochastic models 5.4. Dissipation and wave breaking in shallow water 5.5. Open problems 6. Bottom Dissipation 6.1. Wave energy dissipation due to bottom friction Common formulations for spectral wave models: waves only Common formulations for spectral wave models: waves and currents Bottom roughness models for movable beds 6.2. Energy dissipation due to wave-bottom interaction 6.3. Wave scattering and reflection 6.4. Discussion and outstanding problems 7. Wave Propagation 7.1. Dispersion, geometrical optics and the wave action equation 7.2. Limitations of geometrical optics: diffraction, reflection and random scattering 7.3. Waves over varying currents, non-linear wave effects and the advection velocity 7.4. Waves blocking 7.5. Unsteady water depths and currents 7.6. Waves in the real ocean 8. Numerics and Resolution in Large-scale Wave Modelling 8.1. A description of the problem Error due to the numerical scheme for geographic propagation on a grid Diffusion Numerical dispersion Combined effect of diffusion and dispersion Error due to the numerical scheme for spectral propagation Error due to coarse geographic resolution Error due to coarse spectral resolution Errors in source term integration 8.2. Existing solutions Improved numerical schemes for propagation on a grid Alternatives to the finite difference schemes on a grid Addressing error due to coarse geographic resolution Garden Sprinkler Effect correction methods Errors in source terms integration 8.3. Relative importance of problem Error due to the numerical scheme for geographic propagation Argument Counter-argument Error due to the numerical scheme for spectral propagation Geographic resolution Spectral resolution Source term integration 8.4. Future solutions The numerical scheme for geographic propagation Geographic resolution Spectral resolution Errors in source term integration 8.5. Numerics and resolution: Problems particular to finite depth and high resolution applications 9. Where We Are 10.Where to Go Acknowledgements References List of authors, affiliations and addresses
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Papers by Alexander Babanin