Sea Wind Waves Research Articles

Buoy observations of the influence of swell on wind waves in the open ocean

The influence of longer (swell) on shorter, wind sea waves is examined using an extensive database of directional buoy measurements obtained from a heave-pitch-roll buoy moored in deep water in the South Atlantic. This data set is unique for such an investigation due to the ubiquitous presence of a young swell component propagating closely in direction and frequency with the wind sea, as well as a longer, opposing swell. Our results show, within the statistical limits of the regressions obtained from our analysis when compared to measurements in swell free environments, that there is no obvious influence of swell on wind sea growth. For operational purposes in ocean engineering this means that power-laws from fetch limited situations describing the wind sea growth can be applied in more realistic situations in the open sea when swell is present.

Wind Stress Vector over Ocean Waves

Previous investigations of the wind stress in the marine surface layer have primarily focused on determining the stress magnitude (momentum flux) and other scalar variables (e.g., friction velocity, drag coefficient, roughness length). However, the stress vector is often aligned with a direction different from that of the mean wind flow. In this paper, the focus is on the study of the stress vector direction relative to the mean wind and surface-wave directions. Results based on measurements made during three field campaigns onboard the R/P Floating Instrument Platform (FLIP) in the Pacific are discussed. In general, the wind stress is a vector sum of the 1) pure shear stress (turbulent and viscous) aligned with the mean wind shear, 2) wind-wave-induced stress aligned with the direction of the pure wind-sea waves, and 3) swell-induced stress aligned with the swell direction. The direction of the wind-wave-induced stress and the swell-induced stress components may coincide with, or be opposite to, the direction of wave propagation (pure wind waves and swell, respectively). As a result, the stress vector may deviate widely from the mean wind flow, including cases in which stress is directed across or even opposite to the wind.

Assessment of the reliability of wave observations from voluntary observing ships: Insights from the validation of a global wind wave climatology based on voluntary observing ship data

This paper describes development and validation of a global climatology of basic wave parameters based on the voluntary observing ship (VOS) data from the Comprehensive Ocean‐Atmosphere Data Set collection. Climatology covers the period 1958–1997 and presents heights and periods for the wind sea, swell, and significant wave height (SWH) over the global ocean on 2° × 2° spatial resolution. Significant wave height has been derived from separate sea and swell estimates by taking square root of the sum of squares for the seas and swells propagating approximately in the same direction and assuming SWH to be equal to the higher of the two components in all other cases. Special algorithms of corrections were applied to minimize some biases, inherent in visual wave data. Particularly, we corrected overestimation of small seas, corrected underestimation of periods, and analyzed separation between sea and swell. Validation included estimation of random observational errors, observation of sampling errors, and comparison with the alternative wave data. Estimates of random observational errors show that for the majority of locations, observational uncertainties are within 20% of mean values, which allows us to discuss quantitatively the produced climatology. Biases associated with inadequate sampling were quantified using the data from high‐resolution WAM hindcast for the period 1979–1993. The highest sampling biases are observed in the South Ocean, where wave height may be underestimated by 1–1.5 m because of poor sampling, primarily associated with a fair weather bias of ship routing and observation. Comparison to the other VOS‐based products shows in general higher SWH in our climatology, especially in the midlatitudes. However, comparison with the altimeter data shows that even for well‐sampled regions, high waves are still underestimated in VOS, suggesting a ubiquitous fair weather bias. Further ways of improving VOS‐based wave climatologies and possible applications are discussed.

Automated Analysis of Ocean Surface Directional Wave Spectra

Abstract To facilitate investigations of surface wave processes in the open ocean, a wave spectral partitioning method with automated swell tracking and storm source identification capabilities has been developed. These tools collectively form the Wave Identification and Tracking System (WITS) and have been assembled entirely within the Matlab programming environment. A series of directional wave spectra, with supporting wind observations, is the only required input. Wave spectrum peaks representing specific wind sea and swell wave systems are extracted based on topographic minima, with wind sea peaks identified by wave age criteria. A swell tracking algorithm, combined with linear wave theory, provides a unique approach to storm source identification using the assimilated wave system statistics. The nature of the partitioned spectra allows the continuous, automated identification and tracking of multiple swell generation areas over space and time. Over a 6-day wave record in the Gulf of Alaska, 44 specif...

Comments on “Estimates of Kinetic Energy Dissipation under Breaking Waves”

It is noted that the results of recent experiments on the enhancement of turbulent kinetic energy (TKE) dissipation below surface waves can be stated as follows. TKE dissipation is enhanced by a factor 15Hws/z at depths 0.5Hws < z < 20Hws with respect to the wall-layer result ϵ = u3∗w/κz, where u∗w is the friction velocity in water and Hws is the significant windsea wave height. For open ocean conditions, this reduces in most cases to an enhancement factor 106u2∗w/gz ≈ u210/gz.

Effects of Tides and Storm Surges on North Sea Wind Waves

Abstract Effects of tides and storm surges on wind waves in shelf seas are assessed by hindcasting three North Sea storm cases. It is shown that tides and storm surges in shelf seas should be considered as an unsteady medium for wind wave Propagation if wave–current interactions are assessed. Tides mainly result in oscillations of mean wave Parameters whereas surges result in systematic variations. Due to accumulation of effects, small wind-induced currents might have a larger impact on wave parameters than larger but oscillating tidal currents. Although these results are obtained from typical North Sea conditions, it is expected that they are fairly representative for tides and surges in shelf seas in general. For the North Sea relatively small tide and surge-induced modulations of mean wave parameters such as the significant wave height or the mean wave period have been found (typically 5 % to 10%). Modulations of the spectral density of the wave energy can be of the order of 50% to 100%. Effects of cur...

Energy of sea wind waves and principles of its conversion

The given recommendations determining the energy potential of wind waves and classification of wave power plants according to the character of energy will be useful in subsequent works on development of the new energy source.