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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 three dissipative ice models with or without the utilization of Sother in the ice-infested seas. A clear downward trend in the peak frequency fp is found as Hs increases. As fp decreases, the dominant wave components of a wave spectrum will experience reduced damping by sea ice, and finally result in the flattening of dHs/dx for Hs > 3 m in this specific case. Nonetheless, Sother should not be disregarded within a more general modeling perspective, as our simulations suggest Sother could be comparable to Sice in the Beaufort Sea case where wave and ice conditions are remarkably different. more...

We present a method for predicting wave dissipation by sea ice that is based on the dimensional analysis of data with a scaling defined by ice thickness. Applying the method to an extensive dataset... more...

Observations of ocean surface waves at three sites along the northern coast of Alaska show a strong coupling with seasonal sea ice patterns. In the winter, ice cover is complete, and waves are abse... more...

Alaskan Arctic coastlines are protected seasonally from ocean waves by the presence of coastal and shorefast sea ice. \ud This study presents field observations collected during the autumn 2019 freeze up near Icy Cape, a coastal headland in the Chukchi Sea of the Western Arctic. The evolution of the coupled air-ice-ocean-wave system during a four-day wave event was monitored using drifting wave buoys, a cross-shore mooring array, and ship-based measurements. The incident wave field with peak period of 2.5 s was attenuated by coastal pancake and frazil sea ice, reducing significant wave height by 40\% over less than 5 km of cross-shelf distance spanning water depths from 13 to 30 m. Spectral attenuation coefficients are evaluated with respect to wave and ice conditions and the proximity to the ice edge. Attenuation rates are found to be three times higher within 500 m of the ice edge, relative to values farther in the ice cover. Attenuation coefficients are in the range of $\langle 2.3,2.7\rangle$ \si{\meter^{-1}}, and follow a power-law dependence on frequency. more...

Alaskan Arctic coastlines are protected seasonally from ocean waves by the presence of coastal and shorefast sea ice. This study presents field observations collected during the autumn 2019 freeze up near Icy Cape, a coastal headland in the Chukchi Sea of the Western Arctic. The evolution of the coupled air-ice-ocean-wave system during a four-day wave event was monitored using drifting wave buoys, a cross-shore mooring array, and ship-based measurements. The incident wave field with peak period of 2.5 s was attenuated by coastal pancake and frazil sea ice, reducing significant wave height by 40\% over less than 5 km of cross-shelf distance spanning water depths from 13 to 30 m. Spectral attenuation coefficients are evaluated with respect to wave and ice conditions and the proximity to the ice edge. Attenuation rates are found to be three times higher within 500 m of the ice edge, relative to values farther in the ice cover. Attenuation coefficients are in the range of $\langle 2.3,2.7\rangle$ \si{\meter^{-1}}, and follow a power-law dependence on frequency. more...

Interaction between surface gravity waves and sea-ice in the marginal ice zone is complex, and most of the prior research focus has been in deeper oceans. Here, the regional wave model Simulating W... more...

Langmuir circulation (LC) is believed to be one of the leading causes of turbulent mixing in the upper ocean. Large eddy simulation (LES) models that solve the Craik–Leibovich equations are used to study LC in the upper ocean, yielding new insights that could not be obtained from field observations or turbulent closure models alone. The present study expands our previous LES modeling investigations of LC to real ocean conditions with large-scale environmental motion due to strong horizontal density gradient, which is introduced to the LES model through scale separation analysis. The model is applied to field observations in the Gulf of Mexico when a measurement site was impacted by fresh water inflow. Model results suggest that LC can enhance turbulence in the water column and deepen the mixed layer (ML) with or without the large scale motions, being consistent with previous studies. The strong salinity gradient is shown to be able to reduce the mean flow in the ML, align Langmuir cells with the pressure gradient direction and inhibit turbulence in the ocean surface boundary layer. more...

The reduction of the sea ice coverage increases the importance of wind waves in the Arctic. Updates to the standard spectral wave models in recent years have included many aspects of wave-ice interaction. Here we use high-resolution wave parameters retrieved from TerraSAR-X images and in situ SWIFT buoy observations to evaluate the performance of WAVEWATCH III® in ice-free waters in the western Arctic over a 7-week period including the fall freeze-up. About two thirds of the analyzed data sets show a good agreement between observations and model results. In other cases, more accurate representation of the wind input fields and the ice coverage could improve the model predictions. Two data sets with larger discrepancy are discussed in more detail. In these two cases of low model skill, with off-ice wind conditions, we show that the model wind‐sea growth is too weak to match TerraSAR‐X observations, and this situation is improved only slightly by including the effects of atmospheric stability using existing methods. Application of an effective fetch parameterization, which allows for reduced wave generation within the marginal ice zone prior to the open ocean, provides the best estimation of wave growth during off-ice winds. more...

Despite the importance of diffraction of irregular ocean waves, there is a lack of reported measurements over scales larger than a few tens of wavelengths. In the coastal zone, Satellite Altimetry is hindered because the backscatter characteristics of waveforms deviate from Brown's theoretical model, specially up to 20 km from the coastline. Here, we combine a novel set of retracked — reprocessed — altimeter data with directional buoy spectra and simulations with a spectral numerical model where diffraction is computed with an approximation based on the Mild Slope Equation. The Channel Islands, off the coast of California, is an ideal spot for the analysis because of the sharp variations in bathymetry in the vicinity of the archipelago, increasing the relative importance of diffraction over refraction. Spatial variations of wave energy in the lee of the islands are investigated along and across the wave propagation direction. For the first time the lateral rate of energy spreading — across the wave propagation direction — was computed in oceanic conditions and are of the same magnitude as those found in previously published experiments in a wave tank. The importance of diffraction as a non-dissipative process during wave propagation in situations normally encountered in the ocean is also discussed. more...

This paper presents a wave-in-ice model calibration study. Data used were collected in the thin ice of the advancing autumn marginal ice zone of the western Arctic Ocean in 2015, where pancake ice was found to be prevalent. Multiple buoys were deployed in seven wave experiments; data from four of these experiments are used in the present study. Wave attenuation coefficients are calculated utilizing wave energy decay between two buoys measuring simultaneously within the ice covered region. Wavenumbers are measured in one of these experiments. Forcing parameters are obtained from simultaneous in-situ and remote sensing observations, as well as forecast/hindcast models. Cases from three wave experiments are used to calibrate a viscoelastic model for wave attenuation/dispersion in ice cover. The calibration is done by minimizing the difference between modeled and measured complex wavenumber, using a multi-objective genetic algorithm. The calibrated results are validated using two methods. One is to directly apply the calibrated viscoelastic parameters to one of the wave experiments not used in the calibration and then compare the attenuation from the model with measured data. The other is to use the calibrated viscoelastic model in WAVEWATCH III® over the entire western Beaufort Sea and then compare the wave spectra at two remote sites not used in the calibration. Both validations show reasonable agreement between the model and the measured data. The completed viscoelastic model is believed to be applicable to the fall marginal ice zone dominated by pancake ice. more...

Mudbanks (MBs) are a unique natural phenomenon, and form along the southwest coast of India during the southwest monsoon. They are characterized by a calm-water region, bordered by a rough sea. In order to quantify the wave energy dissipation, wave data were collected at two water depths (15 m and 7 m) before and during the period of formation of MBs off Alappuzha, Kerala. The observations indicate that MBs exist even in deeper water beyond 15 m water depth, contrary to earlier findings that they only form in depths of 0–5 m. The analysis showed 65–70% wave height attenuation. As spectral density evolves with shoaling, energy dissipation was examined using the concept of wave energy flux. The combination of high frequency dissipation and nonlinear energy transfer from higher-frequency to low-frequency waves resulted in a reduction of energy across a wide frequency range. The WAVEWATCH III ® (WW3) model with wave-mud interaction physics was used to capture the signature of wave energy dissipation due to MBs. The accuracy of prediction of significant wave heights (H s ) of the WW3 model was verified using H s of measured waves and ERA- Interim (ECMWF Reanalysis Interim data). The model accurately reproduced both the wave heights in the MB region and their general characteristics. The measurements and model results complement each other in explaining changes associated with an apparent shift of the MBs. 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 ofwaves 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. more...

Forty years (1979-2019) of global wave hindcasts are developed with the third generation spectral wave model WAVEWATCH III® using the state-of-the-art observation-based source term parameterizations (i.e., ST6) and the advanced irregular-regular-irregular (IRI) 1/4 grid system. The wave model has been forced with two distinct wind databases sourced from the latest NCEP Climate Forecast System (CFS) and the fifth generation of the ECMWF climate reanalyses (ERA5), together with the ice concentration available from the EUMETSAT OSI SAF (version 2). The hindcasts not only include traditional integral wave parameters (e.g., wave height, period) but also provide various novel parameters such as the dominant wave breaking probability, wave-induced mixed layer depth and whitecap coverage that are derived from wave spectrum based on previous theoretical and empirical studies. Wave parameters are extensively validated against observations from in-situ buoys and satellite altimeters on a global scale. Possible applications of these hindcasts in the fields of freak waves, sea spray and air-sea gas transfer will also be discussed. more...

International audience; Ocean surface waves propagating through sea ice are scattered and dissipated. The net attenuation occurs preferentially at the higher frequencies, and thus the spectral bandwidth of a given wave field is reduced, relative to open water. The reduction in bandwidth is associated with an increase in the groupiness of the wave field. Using Surface Wave Instrument Float with Tracking buoy data from the 2015 Arctic Sea State experiment, bandwidth is compared between pancake ice and open water conditions, and the linkage to group envelopes is explored. The enhancement of wave groups in ice is consistent with the simple linear mechanism of superposition of waves with narrowing spectral bandwidth. This is confirmed using synthetic data. Nonlinear mechanisms, which have been shown as significant in other ice types, are not found to be important in this data set. more...

Objective Research comparing English and Spanish administrations of Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT) have consistently found differences in performance on various cognitive composites. Few studies have examined the effect of bilingualism on baseline and post-concussion assessments. This study examined whether monolingual English-speakers (MO) and bilingual Spanish/English speakers (BI) differed in cognitive performance at baseline (BL) and post-concussion (PC). Methods Participants were selected from a larger database of high school athletes administered ImPACT in English at BL and PC. Participants included 86 BI athletes (Mage = 14.53; 65.10% male) and 86 MO athletes matched on age, gender, sport type, and probable concussion as defined by number of PC follow-up assessments (PCF; 0 vs. ≥1). To examine group differences and changes over time in cognitive composites, a general linear modeling approach was used with language and PCF as between-subjects factors and time as a within-subjects factor. Results There was a significant Language x Time x PCF interaction for Visual Memory (VM), Visual Motor Speed (VMS), and Reaction Time (RT). On VM and RT, MO with multiple PCF performed the worst at PC, while MO with 0 PCF performed the best at PC. On VMS, BI with 0 PCF performed the worst at BL. Conclusion Visual memory and reaction time were less affected in bilingual compared to monolingual athletes with probable concussion. However, at baseline, bilingual athletes had slower visual motor speed compared to monolingual athletes. Future research should focus on how bilingualism may serve as both a protective and risk factor for cognitive functioning after probable concussion. more...

This investigation considers theoretical models and empirical studies related to the dispersion of ocean surface gravity waves propagating in ice covered seas. In theory, wave dispersion is related to the mechanical nature of the ice. The change of normalized wavenumber is shown for four different dispersion models: the mass-loading model, an elastic plate model, an elastic plate model extended to include dissipation, and a viscous-layer model. For each dispersion model, model parameters are varied showing the dependence of deviation from open water dispersion on ice thickness, elasticity, and viscosity. In all cases, the deviation of wavenumber from the open water relation is more pronounced for higher frequencies. The effect of mass loading, a component of all dispersion models, tends to shorten the wavelength. The Voigt model of dissipation in an elastic plate model does not change the wavelength. Elasticity in the elastic plate model and viscosity in the viscous-layer model tend to increase the wavelength. The net effect, lengthening or shortening, is a function of the particular combination of ice parameters and wave frequency. Empirical results were compiled and interpreted in the context of these theoretical models of dispersion. A synopsis of previous measurements is as follows: observations in a loose pancake ice in the marginal ice zone, often, though not always, showed shortened wavelengths. Both lengthening and shortening have been observed in compact pancakes and pancakes in brash ice. Quantitative matches to the flexural-gravity model have been found in Arctic interior pack ice and sheets of fast ice. more...

In this study, Donelan, M.A., Babanin, A.V., Young, I.R., Banner, M.L., 2006. J. Phys. Oceanogr. 36, 1672–1688 source function is used to calculate drag coefficients from both the scanning radar altimeter (SRA) measured two dimensional wave spectra obtained during hurricane Ivan in 2004 and the WAVEWATCH III simulated wave spectra. The drag coefficients disagree between the SRA and model spectra mainly in the right/left rear quadrant of the hurricane where the observed spectra appear to be bimodal while the model spectra are single peaked with more energy in the swell frequencies and less energy in the wind sea frequencies. These results suggest that WAVEWATCH III is currently not capable of providing sensible stress calculations in the rear quadrants of the hurricane. more...

A model-data inversion is applied to an extensive observational dataset collected in the Southern Ocean north of the Ross Sea during late autumn to early winter, producing estimates of the frequency-dependent rate of dissipation by sea ice. The modeling platform is WAVEWATCH III® which accounts for non-stationarity, advection, wave generation, and other relevant processes. The resulting 9477 dissipation profiles are co-located with other variables such as ice thickness to quantify correlations which might be exploited in later studies to improve predictions. An average of dissipation profiles from cases of thinner ice near the ice edge is fitted to a simple binomial. The binomial shows remarkable qualitative similarity to prior observation-based estimates of dissipation, and the power dependence is consistent with at least three theoretical models, one of which assumes that dissipation is dominated by turbulence generated by shear at the ice-water interface. Estimated dissipation is lower closer to the ice edge, where ice is thinner, and waveheight is larger. The quantified correlation with ice thickness may be exploited to develop new parametric predictions of dissipation. more...

The existence and evolution of bedforms on the seafloor have significant effects in the areas of oceanography, marine geophysics, and underwater acoustics including the transport of sediment, wave energy attenuation, and seabed sonar scattering and penetration. Here, we present a wave-seafloor modeling system that couples a spectral seafloor boundary layer model (NSEA) with an operational wave model (SWAN) that includes the dynamic feedback between the predicted wave spectra and the wave generated bedforms on the seafloor through a bottom roughness parameter. NSEA is a seafloor spectral model that uses hydrodynamic input forcing forecasted by the wave model SWAN to predict the evolving seafloor spectra given a sediment grain diameter and an estimation of the biologic activity. The system can be used to determine the spatially and temporally varying bottom roughness under given wave forcing important for coastal morphology and acoustic applications.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/u66k6lZbEbw more...

A laboratory experimental study conducted in a freshwater wave flume installed in a refrigerated room characterized the modifications of wave propagation along on-site manufactured ice covers. Monochromatic surface waves of various amplitudes and frequencies were generated and propagated through three types of ice covers: sheet ice, broken ice floes, and grease ice. This study characterized the spatial evolutions of wave height attenuation and phase speed changes. Wave phase speed increased significantly in sheet ice relative to open water values while no significant changes in phase speed were present with other ice covers. The modifications by sheet ice are consistent with thin plate model predictions based on the elasticity of ice, using measured mechanical properties of sheet ice. Attenuation was strongest for shorter waves in sheet ice followed by grease ice and ice floes. Attenuation under grease ice is shown to be related to the surface wave orbital velocity, similar to dissipation by bottom friction and swell dissipation. The attenuation coefficient of grease ice normalized by wavenumber is proportional to wave steepness with a coefficient varying with ice properties. This laboratory experimental study examined and characterized wave dispersion and attenuation under these different ice properties and wave characteristics, which could be useful in understanding and modeling wave-ice interaction processes in open waters. 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. more...

The article of record as published may be found at https://doi.org/10.1002/2018JC013766 A large collaborative program has studied the coupled air‐ice‐ocean‐wave processes occurring in the Arctic during the autumn ice advance. The program included a field campaign in the western Arctic during the autumn of 2015, with in situ data collection and both aerial and satellite remote sensing. Many of the analyses have focused on using and improving forecast models. Summarizing and synthesizing the results from a series of separate papers, the overall view is of an Arctic shifting to a more seasonal system. The dramatic increase in open water extent and duration in the autumn means that large surface waves and significant surface heat fluxes are now common. When refreezing finally does occur, it is a highly variable process in space and time. Wind and wave events drive episodic advances and retreats of the ice edge, with associated variations in sea ice formation types (e.g., pancakes, nilas). This variability becomes imprinted on the winter ice cover, which in turn affects the melt season the following year. This program was supported by the Office of Naval Research, Code 32, under Program Managers Scott Harper and Martin Jeffries. The crew of R/V Sikuliaq provide outstanding support in collecting the field data, and the US National Ice Center, German Aerospace Center (DLR), and European Space Agency facilitated the remote sensing collections and daily analysis products. RADARSAT‐2 Data and Products are from MacDonald, Dettwiler, and Associates Ltd., courtesy of the U.S. National Ice Center. Data, supporting information, and a cruise report can be found at http://www.apl.uw.edu/arcticseastate more...

Sea ice floe size distribution and lead properties in the Beaufort and Chukchi Seas are studied in the summer-fall transition 2014 to examine the impact on the sea ice cover from storms and surface waves. Floe size distributions are analyzed from MEDEA, Landsat8, and RADARSAT-2 imagery, with a resolution span of 1–100 m. Landsat8 imagery is also used to identify the orientation and spacing of leads. The study period centers around three large wave events during August–September 2014 identified by SWIFT buoys and WAVEWATCH III® model data. The range of floe sizes from different resolutions provides the overall distribution across a wide range of ice properties and estimated thickness. All cumulative floe size distribution curves show a gradual bending toward shallower slopes for smaller floe sizes. The overall slopes in the cumulative floe size distribution curves from Landsat8 images are lower than, while those from RADARSAT-2 are similar to, previously reported results in the same region and seasonal period. The MEDEA floe size distributions appeared to be sensitive to the passage of storms. Lead orientations, regardless of length, correlate slightly better with the peak wave direction than with the mean wave direction. Their correlation with the geostrophic wind is stronger than with the surface wind. The spacing between shorter leads correlates well with the local incoming surface wavelengths, obtained from the model peak wave frequency. The information derived shows promise for a coordinated multisensor study of storm effects in the Arctic marginal ice zone. more...

The possibility of teleconnections between Southern Ocean swells and sea surface temperature (SST) anomalies on interannual time scales in the eastern Pacific Niño-3 region and southeastern Indian Ocean is investigated using numerical wave models. Two alternative parameterizations for swell dissipation are used. It is found that swell dissipation in the models is not directly correlated with large interannual variations such as El Niño–Southern Oscillation (ENSO) or the Indian Ocean dipole (IOD). However, using one of the two swell dissipation parameterizations, a correlation is found between observed SST anomalies and the modification of turbulent kinetic energy flux (TKEF) by Southern Ocean swells due to the damping of short wind waves: modeled reduction of TKEF is opposite in phase to the SST anomalies in the Niño-3 region, indicating a potential positive feedback. The modeled bimonthly averaged TKEF reduction in the southeastern Indian Ocean is also well correlated with the IOD mode. more...

A variational data assimilation algorithm is developed for the ocean wave prediction model [Wave Model (WAM)]. The algorithm employs the adjoint-free technique and was tested in a series of data assimilation experiments with synthetic observations in the Chukchi Sea region from various platforms. The types of considered observations are directional spectra estimated from point measurements by stationary buoys, significant wave height (SWH) observations by coastal high-frequency radars (HFRs) within a geographic sector, and SWH from satellite altimeter along a geographic track. Numerical experiments demonstrate computational feasibility and robustness of the adjoint-free variational algorithm with the regional configuration of WAM. The largest improvement of the model forecast skill is provided by assimilating HFR data (the most numerous among the considered types). Assimilating observations of the wave spectrum from a moored platform provides only moderate improvement of the skill, which disappears after 3 h of running WAM in the forecast mode, whereas skill improvement provided by HFRs is shown to persist up to 9 h. Space-borne observations, being the least numerous, do not have a significant impact on the forecast skill but appear to have a noticeable effect when assimilated in combination with other types of data. In particular, when spectral data from a single mooring are used, the satellite data are found to be the most beneficial as a supplemental data type, suggesting the importance of spatial coverage of the domain by observations. more...

Airborne scanning lidar was used to measure the evolution of the surface wave field in the marginal ice zone (MIZ) during two separate wave events in the Beaufort Sea in October 2015. The lidar data consisted of a 2‐D field of surface elevation with horizontal resolutions between 17 and 33 cm, over a swath approximately 150‐220 m wide, centred on the ground track of the aircraft. Those data were used to compute directional wavenumber spectra of the surface wave field. Comparison with nearly collocated buoy data found the lidar and buoy measurements to be generally consistent. During the first event, waves travelling from open water into the ice were attenuated by the ice. The low spectral spreading and k7/4 spectral dependence of the attenuation was consistent with dissipative models that treat sea ice as a highly viscous fluid floating on a less viscous ocean. Upper‐ocean eddy viscosities calculated using that model were found to be significantly lower than those from previous work. The second event was in off‐ice winds and cold temperatures, allowing measurement of the wave fetch relation in ice‐forming conditions. The wave growth rate was found to be slightly higher than previous measurements under unstable atmospheric conditions without ice formation. Comparison with WAVEWATCH III model output highlighted the importance of accurate ice information and fine geographic computational resolution when making predictions near the ice edge. Finally, the very short scales over which the wave field was observed to evolve in the MIZ are discussed. more...

R/V Lance serendipitously encountered an energetic wave event around 77°N, 26°E on 2 May 2010. Onboard GPS records, interpreted as the surface wave signal, show the largest waves recorded in the Arctic region with ice cover. Comparing the measurements with a spectral wave model indicated three phases of interaction: (1) wave blocking by ice, (2) strong attenuation of wave energy and fracturing of ice by wave forcing, and (3) uninhibited propagation of the peak waves and an extension of allowed waves to higher frequencies (above the peak). Wave properties during fracturing of ice cover indicated increased groupiness. Wave-ice interaction presented binary behavior: there was zero transmission in unbroken ice and total transmission in fractured ice. The fractured ice front traveled at some fraction of the wave group speed. Findings do not motivate new dissipation schemes for wave models, though they do indicate the need for two-way, wave-ice coupling. more...

Ocean surface waves (sea and swell) are generated by winds blowing over a distance (fetch) for a duration of time. In the Arctic Ocean, fetch varies seasonally from essentially zero in winter to hundreds of kilometers in recent summers. Using in situ observations of waves in the central Beaufort Sea, combined with a numerical wave model and satellite sea ice observations, we show that wave energy scales with fetch throughout the seasonal ice cycle. Furthermore, we show that the increased open water of 2012 allowed waves to develop beyond pure wind seas and evolve into swells. The swells remain tied to the available fetch, however, because fetch is a proxy for the basin size in which the wave evolution occurs. Thus, both sea and swell depend on the open water fetch in the Arctic, because the swell is regionally driven. This suggests that further reductions in seasonal ice cover in the future will result in larger waves, which in turn provide a mechanism to break up sea ice and accelerate ice retreat. more...

In this paper, the accuracy of predictions of the narrowness in frequency space of elevation spectra for wind-generated surface gravity waves is evaluated with the specific objective of determining the impact of the method for computing quadruplet interactions, S nl 4 . Alternate metrics are presented for concise quantification of this narrowness and applied to a case study: a 10-day duration hindcast for Lake Michigan during 2002 conducted using the Discrete Interaction Approximation (DIA) for S nl 4 . Under-prediction of frequency narrowness relative to observational data is clearly identifiable using non-concise methods. Two of four concise methods for quantifying spectral narrowness are found to adequately register this bias. By comparing with a hindcast that uses an expensive, exact solution for four-wave nonlinear interactions, it is determined that much of the bias can be attributed to the approximation used for the solution of these interactions in the first hindcast, which corresponds to the DIA, which is the solution method used today in nearly all routine, phase-averaged wave modeling. more...

The article of record as published may be found at http://dx.doi.org/10.1016/j.ocemod.2016.02.009 The sea state of the Beaufort and Chukchi seas is controlled by the wind forcing and the amount of ice-free water available to generate surface waves. Clear trends in the annual duration of the open water season and in the extent of the seasonal sea ice minimum suggest that the sea state should be increasing independent of changes in the wind forcing. Wave model hindcasts from four selected years spanning recent conditions are consistent with this expectation. In particular, larger waves are more common in years with less summer sea ice and/or a longer open water season, and peak wave periods are generally longer. The increase in wave energy may affect both the coastal zones and the remaining summer ice pack, as well as delay the autumn ice-edge advance. However, trends in the amount of wave energy impinging on the ice-edge are inconclusive, and the associated processes, especially in the autumn period of new ice formation, have yet to be well-described by in situ observations. There is an implicit trend and evidence for increasing wave energy along the coast of northern Alaska, and this coastal signal is corroborated by satellite altimeter estimates of wave energy. more...

The spatial variability of open ocean wave fields on scales of O (10km) is assessed from four different data sources: TerraSAR-X SAR imagery, four drifting SWIFT buoys, a moored waverider buoy, and WAVEWATCH III Ⓡ model runs. Two examples from the open north-east Pacific, comprising of a pure wind sea and a mixed sea with swell, are given. Wave parameters attained from observations have a natural variability, which decreases with increasing record length or acquisition area. The retrieval of dominant wave scales from point observations and model output are inherently different to dominant scales retrieved from spatial observations. This can lead to significant differences in the dominant steepness associated with a given wave field. These uncertainties have to be taken into account when models are assessed against observations or when new wave retrieval algorithms from spatial or temporal data are tested. However, there is evidence of abrupt changes in wave field characteristics that are larger than the expected methodological uncertainties. more...

Observations of winds, waves, and turbulence at the ocean surface are compared with several analytic formulations and a numerical model for the input of turbulent kinetic energy by wave breaking and the subsequent dissipation. The observations are generally consistent with all of the formulations, although some differences are notable at winds greater than 15 m s−1. The depth dependence of the turbulent dissipation rate beneath the waves is fit to a decay scale, which is sensitive to the choice of vertical reference frame. In the surface-following reference frame, the strongest turbulence is isolated within a shallow region of depths much less than one significant wave height. In a fixed reference frame, the strong turbulence penetrates to depths that are at least half of the significant wave height. This occurs because the turbulence of individual breakers persists longer than the dominant period of the waves and thus the strong surface turbulence is carried from crest to trough with the wave orbital motion. more...

A new wind-input and wind-breaking dissipation for phase-averaged spectral models of wind-generated surface waves is presented. Both are based on recent field observations in Lake George, New South Wales, Australia, at moderate-to-strong wind-wave conditions. The respective parameterizations are built on quantitative measurements and incorporate new observed physical features, which until very recently were missing in source terms employed in operational models. Two novel features of the wind-input source function are those that account for the effects of full airflow separation (and therefore relative reduction of the input at strong wind forcing) and for nonlinear behavior of this term. The breaking term also incorporates two new features evident from observational studies; the dissipation consists of two parts—a strictly local dissipation term and a cumulative term—and there is a threshold for wave breaking, below which no breaking occurs. Four variants of the dissipation term are selected for evaluation, with minimal calibration to each. These four models are evaluated using simple calculations herein. Results are generally favorable. Evaluation for more complex situations will be addressed in a forthcoming paper. more...

The literature on ocean wave forecasting falls into two categories, physics-based models and statistical methods. Since these two approaches have evolved independently, it is of interest to determine which approach can predict more accurately, and over what time horizons. This paper runs a comparative analysis of a well-known physics-based model for simulating waves near shore, SWAN, and two statistical techniques, time-varying parameter regression and a frequency domain algorithm. Forecasts are run for the significant wave height, over horizons ranging from the current period (i.e., the analysis time) to 15 h. Seven data sets, four from the Pacific Ocean and three from the Gulf of Mexico, are used to evaluate the forecasts. The statistical models do extremely well at short horizons, producing more accurate forecasts in the 1–5 hour range. The SWAN model is superior at longer horizons. The crossover point, at which the forecast error from the two methods converges, is in the area of 6 h. Based on these results, the choice of statistical versus physics-based models will depend on the uses to which the forecasts will be put. Utilities operating wave farms, which need to forecast at very short horizons, may prefer statistical techniques. Navies or shipping companies interested in oceanic conditions over longer horizons will prefer physics-based models. more...

New parameterizations for the spectra dissipation of wind-generated waves are proposed. The rates of dissipation have no predetermined spectral shapes and are functions of the wave spectrum and wind speed and direction, in a way consistent with observation of wave breaking and swell dissipation properties. Namely, the swell dissipation is nonlinear and proportional to the swell steepness, and dissipation due to wave breaking is non-zero only when a non-dimensional spectrum exceeds the threshold at which waves are observed to start breaking. An additional source of short wave dissipation due to long wave breaking is introduced to represent the dissipation of short waves due to longer breaking waves. Several degrees of freedom are introduced in the wave breaking and the wind-wave generation term of Janssen (J. Phys. Oceanogr. 1991). These parameterizations are combined and calibrated with the Discrete Interaction Approximation of Hasselmann et al. (J. Phys. Oceangr. 1985) for the nonlinear interactions. Parameters are adjusted to reproduce observed shapes of directional wave spectra, and the variability of spectral moments with wind speed and wave height. The wave energy balance is verified in a wide range of conditions and scales, from gentle swells to major hurricanes, from the global ocean to coastal settings. Wave height, peak and mean periods, and spectral data are validated using in situ and remote sensing data. Some systematic defects are still present, but the parameterizations yield the best overall results to date. Perspectives for further improvement are also given., Comment: revised version for Journal of Physical Oceanography more...