On the Dependence of Sea Surface Roughness on Wind Waves

Johnson, Hakeem K.; Højstrup, Jørgen; Vested, Hans Jacob; Larsen, Søren Ejling

doi:10.1175/1520-0485(1998)028<1702:otdoss>2.0.co;2

Cited by 188 publications

(134 citation statements)

References 16 publications

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“…by including wave age [3] or wave steepness [4] as additional parameters. These additional parameters require wave measurements, which are often not available for wind power applications.…”

Section: Iivkruh Zlqg Uhvrxufh /Dqjh Hw Domentioning

confidence: 99%

Importance of thermal effects and sea surface roughness for offshore wind resource assessment

Lange

Larsen

Højstrup

et al. 2004

Journal of Wind Engineering and Industrial Aerodynamics

107

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The economic feasibility of offshore wind power utilisation depends on the favourable wind conditions offshore as compared to sites on land. The higher wind speeds have to compensate the additional cost of offshore developments. However, not only the mean wind speed is different, but the whole flow regime, as can e.g. be seen in the vertical wind speed profile. The commonly used models to describe this profile have been developed mainly for land sites. Their applicability for wind power prediction at offshore sites is investigated using data from the measurement program Rødsand, located in the Danish Baltic Sea.Monin-Obukhov theory is often used for the description of the wind speed profile.From a given wind speed at one height, the profile is predicted using two parameters, Obukhov length and sea surface roughness. Different methods to estimate these parameters are discussed and compared. Significant deviations to Monin-Obukhov theory are found for near-neutral and stable conditions when warmer air is advected from land with a fetch of more than 30 km. The measured wind shear is larger than predicted.As a test application, the wind speed measured at 10 m height is extrapolated to 50 m height and the power production of a wind turbine at this height is predicted with the different models. The predicted wind speed is compared to the measured one and the predicted power output to the one using the measured wind speed. To be able to quantify the importance of the deviations from Monin-Obukhov theory, a simple correction method to account for this effect has been developed and is tested in the same way. 2IIVKRUH ZLQG UHVRXUFH /DQJH HW DO page 3 of 64The models for the estimation of the sea surface roughness were found to lead only to small differences. For the purpose of wind resource assessment even the assumption of a constant roughness was found to be sufficient. The different methods used to derive the Obukhov length L were found to differ significantly for near-neutral and stable atmospheric stratification. Here again the simplest method using only bulk measurements was found to be sufficient.For situations with near-neutral and stable atmospheric stratification and long (>30 km) fetch, the wind speed increase with height is larger than what is predicted from Monin-Obukhov theory for all methods to estimate L and z 0 . It is also found that this deviation occurs at wind speeds important for wind power utilisation, mainly at 5-9 ms -1 .The power output estimation has also been compared with the method of the resource estimation program WAsP. For the Rødsand data set the prediction error of WAsP is about 4%. For the extrapolation with Monin-Obukhov theory with different L and z 0 estimations it is 5-9%. The simple wind profile correction method, which has been developed, leads to a clear improvement of the wind speed and power output predictions. When the correction is applied, the error reduces to 2-5%.

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“…by including wave age [3] or wave steepness [4] as additional parameters. These additional parameters require wave measurements, which are often not available for wind power applications.…”

Section: Iivkruh Zlqg Uhvrxufh /Dqjh Hw Domentioning

confidence: 99%

Importance of thermal effects and sea surface roughness for offshore wind resource assessment

Lange

Larsen

Højstrup

et al. 2004

Journal of Wind Engineering and Industrial Aerodynamics

107

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“…The coefficients proposed by Taylor and Yelland [68] yielded implausibly high z 0 when applied to steep young waves originated by a storm over the central Mediterranean Sea and by strong Mistral blowing off-shore of southern France, corresponding to 2.85% of our observations. These extreme z 0 led to absurdly high u * and k w , and thus we imposed a maximum roughness length of 0.01 m. This value roughly matches the maximum expected from the application of alternative formulations for the estimation of z 0 from the wave field [70][71][72][73][74].…”

Section: Transfer Velocitymentioning

confidence: 53%

The FuGas 2.3 Framework for Atmosphere–Ocean Coupling: Comparing Algorithms for the Estimation of Solubilities and Gas Fluxes

et al. 2018

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Accurate estimates of the atmosphere-ocean fluxes of greenhouse gases and dimethyl sulphide (DMS) have great importance in climate change models. A significant part of these fluxes occur at the coastal ocean which, although much smaller than the open ocean, have more heterogeneous conditions. Hence, Earth System Modelling (ESM) requires representing the oceans at finer resolutions which, in turn, requires better descriptions of the chemical, physical and biological processes. The standard formulations for the solubilities and gas transfer velocities across air-water surfaces are 36 and 24 years old, and new alternatives have emerged. We have developed a framework combining the related geophysical processes and choosing from alternative formulations with different degrees of complexity. The framework was tested with fine resolution data from the European coastal ocean. Although the benchmark and alternative solubility formulations generally agreed well, their minor divergences yielded differences of up to 5.8% for CH 4 dissolved at the ocean surface. The transfer velocities differ strongly (often more than 100%), a consequence of the benchmark empirical wind-based formulation disregarding significant factors that were included in the alternatives. We conclude that ESM requires more comprehensive simulations of atmosphere-ocean interactions, and that further calibration and validation is needed for the formulations to be able to reproduce it. We propose this framework as a basis to update with formulations for processes specific to the air-water boundary, such as the presence of surfactants, rain, the hydration reaction or biological activity.

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“…Recent results issued from in situ measurements, lab experiments, or theoretical works (Alamaro et al 2002;Powell et al 2003;Donelan et al 2004;Moon et al 2004a, b;Makin 2005) show that the sea surface drag coefficient is weaker under strong wind (∼30 m/s) conditions and could even be a decreasing function of the wind speed. It means that sea surface drag coefficient could be sizeably dependent to the wave state (Toba et al 1990;Smith et al 1992;Johnson et al 1998;Drennan et al 2003). Indeed, the aerodynamic roughness length associated with the surface wavefield (z 0 ) impacts atmospheric circulation and storm surges (Mastenbroek et al 1993;Saetra et al 2007;Nicolle et al 2009).…”

Section: Sea Surface Drag Formulations and Comparisonmentioning

confidence: 99%

Atmospheric storm surge modeling methodology along the French (Atlantic and English Channel) coast

et al. 2014

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Storm surge modeling and forecast are the key issues for coastal risk early warning systems. As a general objective, this study aims at improving high-frequency storm surge variations modeling within the PREVIMER system (www.previmer.org), along the French Atlantic and English Channel coasts. The paper focuses on (1) sea surface drag parameterization and (2) uncertainties induced by the meteorological data quality. The modeling is based on the shallowwater version of the model for applications at regional scale (MARS), with a 2-km spatial resolution. The model computes together tide and surge, allowing properly taking into account tide-surge interactions. To select the most appropriate parameterization for the study area, a sensitivity analysis on sea surface drag parameterizations is done, based on comparisons of modeled storm surges (extracted with a tidal component analysis) with four tidal gauges, during four storm events, and over about 7.5 years, where the observed water level is processed in the same way as the modeling results. The tested drag parameterizations are a constant one, as reported by Moon et al. (J Atmos Sci 61: 2321-2333, 2007, Makin (BoundLayer Meteorol 115: 169-176, 2005), and Charnock (J Roy Meteor Soc 81: 639-640, 1955). Charnock's parameterization, either constant with high value (0.022) or relying on a full statistical description of the sea state, enables to improve storm surges forecast with peak errors 10 cm smaller than those computed with the other drag coefficient formulations. The impact of the meteorological forcing quality is evaluated over January 2012 from the comparison between surges modeled with different meteorological data (ARPEGE, ARPEGE High Resolution and AROME) and observations. For event time scale, storm surge computation is highly improved with ARPEGE High Resolution data. For month time scale, statistics of model accuracy are less sensitive to the choice of meteorological forcing. As a conclusion, the Charnock's parameterization is advised to model storm surges on the French Atlantic and English Channel coasts, whereas the quality requirements regarding meteorological inputs depend on the time scale of interest. Within the PREVIMER system, aiming at forecasting events, ARPEGE High Resolution data are used.

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On the Dependence of Sea Surface Roughness on Wind Waves

Cited by 188 publications

References 16 publications

Importance of thermal effects and sea surface roughness for offshore wind resource assessment

Importance of thermal effects and sea surface roughness for offshore wind resource assessment

The FuGas 2.3 Framework for Atmosphere–Ocean Coupling: Comparing Algorithms for the Estimation of Solubilities and Gas Fluxes

Atmospheric storm surge modeling methodology along the French (Atlantic and English Channel) coast

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