scholarly journals On the Wave State Dependence of the Sea Surface Roughness at Moderate Wind Speeds under Mixed Wave Conditions

2020 ◽  
Vol 50 (11) ◽  
pp. 3295-3307
Author(s):  
Shuiqing Li ◽  
Zhongshui Zou ◽  
Dongliang Zhao ◽  
Yijun Hou
Keyword(s):  
Surface Roughness ◽  
Wind Wave ◽  
Wind Waves ◽  
Sea Surface ◽  
Wave Steepness ◽  
Threshold Behavior ◽  
Wind Speeds ◽  
Dominant Wave ◽  
Sea Surface Roughness ◽  
Mixed Wave

AbstractWind stress depends on the sea surface roughness, which can be significantly changed by surface wind waves. Based on observations from a fixed platform, we examined the dependences of the sea surface roughness length on dominant wave characteristic parameters (wave age, wave steepness) at moderate wind speeds and under mixed-wave conditions. No obvious trend was found in the wave steepness dependence of sea surface roughness, but a wave steepness threshold behavior was readily identified in the wave age dependence of sea surface roughness. The influence of dominant wind waves on the surface roughness was illustrated using a wind–wave coupling model. The wave steepness threshold behavior is assumed to be related to the onset of dominant wave breaking. The important role of the interaction between swell and wind wave was highlighted, as swell can absorb energy from locally generated wind wave, which subsequently reduces the wave steepness and the probability of dominant wave breaking.

scholarly journals A Novel Sea Surface Roughness Parameterization Based on Wave State and Sea Foam

2021 ◽  
Vol 9 (3) ◽  
pp. 246
Author(s):  
Difu Sun ◽  
Junqiang Song ◽  
Xiaoyong Li ◽  
Kaijun Ren ◽  
Hongze Leng
Keyword(s):  
Surface Roughness ◽  
Wind Speed ◽  
Drag Coefficient ◽  
Sea Surface ◽  
High Wind Speed ◽  
Wave State ◽  
Wind Speeds ◽  
Sea Surface Roughness ◽  
Extreme Wind ◽  
The Impact

A wave state related sea surface roughness parameterization scheme that takes into account the impact of sea foam is proposed in this study. Using eight observational datasets, the performances of two most widely used wave state related parameterizations are examined under various wave conditions. Based on the different performances of two wave state related parameterizations under different wave state, and by introducing the effect of sea foam, a new sea surface roughness parameterization suitable for low to extreme wind conditions is proposed. The behaviors of drag coefficient predicted by the proposed parameterization match the field and laboratory measurements well. It is shown that the drag coefficient increases with the increasing wind speed under low and moderate wind speed conditions, and then decreases with increasing wind speed, due to the effect of sea foam under high wind speed conditions. The maximum values of the drag coefficient are reached when the 10 m wind speeds are in the range of 30–35 m/s.

scholarly journals Drag of the Water Surface at Very Short Fetches: Observations and Modeling

2008 ◽  
Vol 38 (9) ◽  
pp. 2038-2055 ◽  
Author(s):  
Guillemette Caulliez ◽  
Vladimir Makin ◽  
Vladimir Kudryavtsev
Keyword(s):  
Wind Stress ◽  
Wave Breaking ◽  
Wind Wave ◽  
Wind Forcing ◽  
Wave Steepness ◽  
Surface Drag ◽  
Wave Fields ◽  
Wind Speeds ◽  
Dominant Wave ◽  
Wide Range

Abstract The specific properties of the turbulent wind stress and the related wind wave field are investigated in a dedicated laboratory experiment for a wide range of wind speeds and fetches, and the results are analyzed using the wind-over-waves coupling model. Compared to long-fetch ocean wave fields, wind wave fields observed at very short fetches are characterized by higher significant dominant wave steepness but a much smaller macroscale wave breaking rate. The surface drag dependence on fetch and wind then closely follows the dominant wave steepness dependence. It is found that the dimensionless roughness length z*0 varies not only with wind forcing (or inverse wave age) but also with fetch. At a fixed fetch, when gravity waves develop, z*0 decreases with wind forcing according to a −1/2 power law. Taking into account the peculiarities of laboratory wave fields, the WOWC model predicts the measured wind stress values rather well. The relative contributions to surface drag of the equilibrium-range wave-induced stress and the airflow separation stress due to wave breaking remain small, even at high wind speeds. At moderate to strong winds, the form drag resulting from dominant waves represents the major wind stress component.

scholarly journals Influence of Wave State and Sea Spray on the Roughness Length: Feedback on Medicanes

Atmosphere ◽  
2018 ◽  
Vol 9 (8) ◽  
pp. 301 ◽  
Author(s):  
Umberto Rizza ◽  
Elisa Canepa ◽  
Antonio Ricchi ◽  
Davide Bonaldo ◽  
Sandro Carniel ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Single Case ◽  
Wind Waves ◽  
Wave Model ◽  
Atmospheric Model ◽  
Sea Surface ◽  
Sea Spray ◽  
High Wind ◽  
Wave State ◽  
Sea Surface Roughness

Occasionally, storms that share many features with tropical cyclones, including the presence of a quasi-circular “eye” a warm core and strong winds, are observed in the Mediterranean. Generally, they are known as Medicanes, or tropical-like cyclones (TLC). Due to the intense wind forcings and the consequent development of high wind waves, a large number of sea spray droplets—both from bubble bursting and spume tearing processes—are likely to be produced at the sea surface. In order to take into account this process, we implemented an additional Sea Spray Source Function (SSSF) in WRF-Chem, model version 3.6.1, using the GOCART (Goddard Chemistry Aerosol Radiation and Transport) aerosol sectional module. Traditionally, air-sea momentum fluxes are computed through the classical Charnock relation that does not consider the wave-state and sea spray effects on the sea surface roughness explicitly. In order to take into account these forcing, we implemented a more recent parameterization of the sea surface aerodynamic roughness within the WRF surface layer model, which may be applicable to both moderate and high wind conditions. The implemented SSSF and sea surface roughness parameterization have been tested using an operative model sequence based on COAWST (Coupled Ocean Atmosphere Wave Sediment Transport) and WRF-Chem. The third-generation wave model SWAN (Simulating Waves Nearshore), two-way coupled with the WRF atmospheric model in the COAWST framework, provided wave field parameters. Numerical simulations have been integrated with the WRF-Chem chemistry package, with the aim of calculating the sea spray generated by the waves and to include its effect in the Charnock roughness parametrization together with the sea state effect. A single case study is performed, considering the Medicane that affected south-eastern Italy on 26 September 2006. Since this Medicane is one of the most deeply analysed in literature, its investigation can easily shed some light on the feedbacks between sea spray and drag coefficients.

scholarly journals On the Dependence of Sea Surface Roughness on Wind Waves

1998 ◽  
Vol 28 (9) ◽  
pp. 1702-1716 ◽  
Author(s):  
H. K. Johnson ◽  
J. Højstrup ◽  
H. J. Vested ◽  
S. E. Larsen
Keyword(s):  
Surface Roughness ◽  
Wind Waves ◽  
Sea Surface ◽  
Sea Surface Roughness

A stochastic model of sea-surface roughness. I. Wave crests

1987 ◽  
Vol 410 (1838) ◽  
pp. 19-34 ◽  
Keyword(s):  
Surface Roughness ◽  
Random Noise ◽  
Wave Spectrum ◽  
Short Wave ◽  
Sea Surface ◽  
Scale Model ◽  
Wave Steepness ◽  
Wave Interactions ◽  
Long Wave ◽  
Sea Surface Roughness

In this paper we develop a two-scale model of sea-surface roughness, in which for the first time the randomness of both long and short waves is taken fully into account. The model includes long–wave-short-wave interactions, dissipation of the short-wave energy by breaking, and regeneration by the wind. This leads to an integral equation for the short-wave steepness, which is solved by iteration. The effects of wind speed and of long-wave steepness upon the distribution of roughness at the long-wave crests are calculated and discussed. Also the effect of a band-width parameter for the long-wave spectrum. A random noise source can be included.

scholarly journals On the Impact of Sea State on GNSS-R Polarimetric Observations

2020 ◽  
Author(s):  
Mostafa Hoseini ◽  
Maximilian Semmling ◽  
Erik Rennspiess ◽  
Markus Ramatschi ◽  
Rüdiger Haas ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Tide Gauge ◽  
Empirical Relation ◽  
Sea Surface ◽  
Sea State ◽  
Sea Levels ◽  
Wind Speeds ◽  
Sea Surface Roughness ◽  
Different Response ◽  
The Impact

<p>We investigate a long-term ground-based GNSS-R dataset to evaluate the effect of sea state on the polarization of the reflected signals. The dataset consists of one-year polarimetric observations recorded at Onsala space observatory in Sweden in 2016 using right- and left-handed circular polarization (RHCP and LHCP) antennas. One up-looking antenna to receive direct signal and two side-looking antennas to collect reflections are installed at about 3 meters above sea level. The data is collocated with the measurements from a nearby tide-gauge and meteorological station.</p><p>We focus on precise power estimation using a polarimetric processor based on Lomb–Scargle periodogram at precisely observed sea levels. The processor converts 0.1 Hz coherent in-phase and quadrature correlation sums provided by a reflectometry receiver to power estimates of the direct and reflected signals. The power estimates are reduced to three power ratios, i.e. cross-, co-, and cross to co-polarization. A model, describing the elevation dependent power loss due to sea surface roughness, is then utilized to invert the calculated power ratios to the standard deviation of sea surface height.</p><p>Analysis of about 14000 events found in the dataset (~40 continuous tracks per day) shows a fair agreement with the wind speeds as an indicator of the sea state. Although an increasing sensitivity to sea state is observed for all the power ratios at elevation angles above 10 degrees, the measurements from the co-polar link seem to be less affected by the surface roughness. The results reveal that the existing model cannot predict the effect of sea surface roughness in a comprehensive way. The different response of RHCP and LHCP observations to roughness is evident, however, the polarization dependence is not covered by the model. The deviations from the model are particularly clear at lowest elevations (<5 deg) where the roughness effect is expected to vanish. The results indicate that roughness also affect observations at lowest elevation angles. In this elevation range the expected dominance of the RHCP component above the LHCP component is not observed.  A different approach is required to model the influence of sea state in GNSS-R. The increasing amount of reflectometry data may allow to retrieve an empirical relation between coherent reflection power and sea state in future investigation.</p>

Effect of Wave Age on Wind Gust Spectra Over Wind Waves

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Dag Myrhaug ◽  
Muk Chen Ong
Keyword(s):  
Surface Roughness ◽  
Wind Stress ◽  
Wind Waves ◽  
Local Equilibrium ◽  
Offshore Structures ◽  
Department Of Energy ◽  
Sea Surface ◽  
Wind Gust ◽  
Wave Age ◽  
Sea Surface Roughness

This paper considers the effect of wave age on wind gust spectra over wind waves. Here, two wind gust spectra based on maritime data are used to serve the purpose of demonstrating the effect of wave age; the spectra according to Wills et al. (1986 “Offshore Mean Wind Profile,” Department of Energy, Offshore Technical Report No. OTH86226) and Ochi and Shin (1988, “Wind Turbulent Spectra for Design Considerations of Offshore Structures,” Proceedings of the 20th Offshore Technology Conference, Houston, TX, Paper No. 5736, pp. 461–467). The effect of wave age is taken into account by using the Volkov (2001, “The Dependence on Wave Age,” in Wind Stress Over the Ocean, Cambridge University Press, Cambridge, UK, pp. 206–217) sea surface roughness formula. The wave age independent Charnock (1955, “Wind Stress on a Water Surface,” Q. J. R. Meteorol. Soc., 81, pp. 639–640) sea surface roughness is used as a reference. The results are valid for wind waves in local equilibrium with steady wind in laterally homogeneous flow. An example of results demonstrates a clear effect of wave age on the wind gust spectra; also, distinct differences between the two spectra for a given wave age are demonstrated. Finally, an example of application is provided, demonstrating clear effects of the two spectra and the sea surface roughness on slowly varying surge motion of a marine structure due to wind gust.

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