共查询到20条相似文献，搜索用时 15 毫秒
1.
Laboratory Studies Of Wind Stress Over Surface Waves 总被引：4，自引：0，他引：4
Simultaneous laboratory observations of wind speed, wind stress, and surfacewind-wave spectra are made under a variety of wind forcing patterns using cleanwater as well as water containing an artificial surfactant. Under typical experimentalconditions, more than half of the total stress is supported by the wave-induced stressrather than by the surface viscous stress. When the surfactant reduces the shortwind-wave spectra, the wind stress also decreases by as much as 20–30% at agiven wind speed. When the wind forcing is modulated in time, the wind stresstends to be higher under decreasing wind than under increasing wind at a givenwind speed, mainly because the response of short wind-wave spectra to varyingwind forcing is delayed in time. These examples clearly demonstrate that therelationship between the wind speed and the wind stress can be significantlymodified if the surface wave field is not in equilibrium with the wind forcing.Next, we examine whether the wind stress is estimated accurately if the wave-inducedstress by all surface wave components is explicitly evaluated by linear superpositionand is added to the surface viscous stress. It is assumed that the surface viscous stressis uniquely related to the wind speed, and that the wind input rate is determined by thelocal, reduced turbulent stress rather than the total stress. Our wind stress estimatesincluding the wave contributions agree well with observed wind stress values, evenif the surface wave field is away from its equilibrium with the wind in the presenceof surface films and/or under time-transient wind forcing. These observations stronglysuggest that the wind stress is accurately evaluated as a sum of the wave-induced stressand the surface viscous stress. At very high winds, our stress estimates tend to be lowerthan the observations. We suspect that this is because of the enhancement of wind stressover very steep (or breaking) short wind-waves. 相似文献
2.
S. A. Hsu 《Boundary-Layer Meteorology》1983,25(4):417-421
Estimates of the latent heat flux at the air-sea interface made by the profile method are compared to estimates by a wind-wave interaction (WWI) method that takes into account both wind and wave characteristics. A data set that consisted of profile measurements (six levels) of wind, temperature, and humidity over the Arabian Sea was used to compare the methods, and the agreement is good. It is shown that this WWI method can be used to compute the shear velocity, and then the results can be applied in the computation of latent heat flux. The parameters used in the WWI method are wind speed and direction, air temperature and humidity, sea-surface temperature, and significant wave height and period. All these data may be obtained from standard ship observations. 相似文献
3.
V. K. Makin 《Boundary-Layer Meteorology》2003,106(3):593-600
A new parameterization of the sea drag is based on a wind-over-wavescoupling theory. The parameterization accounts for the wind speed, wave ageand finite depth dependencies of the sea drag. The latter two are introducedthrough the integral parameters of the wind-wave field: the dominant waveheight and the wavenumber at the spectral peak, and the water depth. Theparameterization is checked against the wind-over-waves model results andtwo field datasets obtained in a wide range of the wind speed and wave age.The comparison is encouraging. The parameterization is aimed for use inoperational ocean-state and atmosphere models. 相似文献
4.
Sanshiro Kawai 《Boundary-Layer Meteorology》1981,21(1):93-104
An intermittently-smoking smoke-wire was devised to visualize the airflow structure over individual crests of actual wind waves. The device was used under a moderate wind 6 m s-1 (maximum speed in the vertical cross-section) at a fetch 3.8 m in a wind-wave tunnel. Airflow patterns with separation were clearly visualized over wind-wave crests which were not accompanied by wave breaking characterized by air entrainment. A classification of 41 samples of airflow structures showed that two distinct patterns (with and without separation) exist, with significant frequency of occurrence for each. 相似文献
5.
E. P. Anisimova G. E. Kononkova V. V. Kuznetsov A. S. Orlov G. I. Popov A. A. Speranskaya 《Boundary-Layer Meteorology》1974,6(1-2):5-11
Research results are presented, under natural and laboratory conditions, concerning the process of wind-wave generation. The complementary problem, the effect of waves on the structure of the wind field above them, is also studied. 相似文献
6.
An experimental scheme was designed to obtain laboratory-scale verification of Hasselmann's nonlinear wave—wave interaction and white-cap dissipation theories. Water wave height and fluctuating air pressure were measured simultaneously in a fixed reference frame as a function of fetch in the Stanford Wind, Water-Wave Research Facility under the conditions of a steady wind and a stationary wave spectrum. All the data were obtained 5 mm above the highest point of the wind waves for five stations (3 m apart on average) and at three wind speeds (7.1, 8.0 and 8.9 m/sec). The wave height and fluctuating pressure were measured by a capacitance wave-height gauge and a crystal pressure transducer, respectively.Based on the experimental results, Hasselmann's nonlinear wave—wave interaction theory appears to be valid. Barnett's approximate parametric equation for calculating the energy transfer of nonlinear wave—wave interaction and Hasselmann's white-capping dissipation model were also verified and appeared to be applicable in the relatively low and intermediate frequency region of a wave spectrum for a normalized fetch range of 100–500. Based on the results of an overall energy balance in a gravity wind-wave spectrum, the nonlinear wave—wave interaction mechanism is shown to play a dominant role in the energy transfer processes after the wave spectrum is generated. 相似文献
7.
A deep understanding of turbulence structure is important for investigating the characteristics of the atmospheric boundary layer, especially over heterogeneous terrain. In the present study, turbulence intensity and turbulent kinetic energy (TKE) parameters are analyzed for different conditions with respect to stability, wind direction and wind speed over a valley region of the Loess Plateau of China during December 2003 and January 2004. The purpose of the study is to examine whether the observed turbulence intensity and TKE parameters satisfy Monin-Obukhov similarity theory (MOST), and analyze the wind shear effect on, and thermal buoyancy function of, the TKE, despite the terrain heterogeneity. The results demonstrate that the normalized intensity of turbulence follows MOST for all stability in the horizontal and vertical directions, as well as the normalized TKE in the horizontal direction. The shear effect of the wind speed in the Loess Plateau region is strong in winter and could enhance turbulence for all stability conditions. During daytime, the buoyancy and shear effect together constitute the generation of TKE under unstable conditions. At night, the contribution of buoyancy to TKE is relatively small, and mechanical shearing is the main production form of turbulence. 相似文献
8.
Patricia Jones Boyle Kenneth L. Davidson Donald E. Spiel 《Dynamics of Atmospheres and Oceans》1987,10(4)
Surface stress values obtained from the NOAA Ship OCEANOGRAPHER during STREX indicate that wind speed and stability dependent bulk derived stress values are two to three times too low in surface pre-frontal, pre-trough and pre-ridge regions of transiting synoptic systems. The measured stress values were based on calculations of turbulent kinetic energy dissipation rates using hot film measured velocity variances. Bulk stress values obtained with wind speed (neutral drag coefficient) and stability dependencies in the Large and Pond derivation agreed very well with the measured values in other regions of the synoptic systems. In situ wave information was not adequate to relate differences to coupled vector wind and wave fields. However, analyses and interpretation of wind and stability effects suggest that wind wave interaction was the reason for the observed sub-synoptic (mesoscale) stress enhancements. 相似文献
9.
Structure of air flow separation over wind wave crests 总被引：1，自引：0，他引：1
Sanshiro Kawai 《Boundary-Layer Meteorology》1982,23(4):503-521
Air flow over wind waves generated in a wind-wave tunnel was visualized by numerous tiny suspended particles (zinc stearate), and instantaneous air flow fields over about one wavelength of wind waves were obtained. Air flow separation was detected over the wave crest in about a half of the samples. In such cases, the separation started near the crest about half of the time, with a vortex trapped over the convergence point of the surface flow which appeared at the leeward face of the crest. This structure was much different from a previously imagined picture in which the separation started at the convergence point. The high frequency of its occurrence suggested the stability of this structure. However, even when this structure was clearly seen, the structure behind the vortex to the next wave crest had various patterns. This variety seems to be related to an instability of the high-shear layer accompanied by separation. Other varieties were also seen, such as the occurrence of separation without the above mentioned structure, as well as the existence of non-separated air flow structures. These varieties seem to be related to the variability of individual wind wave crests. An analysis of correlation between the wave form and the air flow structure over it shows that there is a critical value of local gradient of wave form, above which the air flow always separates. This fact suggests a strong coupling between the air and the water, i.e., the local stress exerted on the water surface changes the nature of a wave crest, especially its form, and as a result, the air flow structure over it changes drastically.Decreased 21 November, 1981. Final draft of the paper prepared by Professor Yoshiaki Toba, Geophysical Institute, Tohoku University. 相似文献
10.
Microwave measurements over the North Sea 总被引：2，自引：0，他引：2
We investigate the applicability of SLAR (Side-Looking Airborne Radar) to detect waves and other phenomena at sea, for future operational use. Especially, we investigate radar measurements of wave patterns, oil pollution, shipping traffic, and ice reconnaissance and relate these to sea-truth information. The SLAR program benefits from earlier clutter measurements at sea and in a wind-wave tank (carried out by the Physics Laboratory TNO and NIWARS), which have been further elaborated and extended. These are summarized. Results obtained since 1974 lead to the conclusion that the SLAR is applicable for the aforementioned purposes, albeit in a somewhat restricted way. The large resolution cell used, containing a vast number of independent samples, improves the dynamic resolution to about l dB and so turns the SLAR into a sensor eminently suited for the detection of very slight modulations of capillary waves. For the detection of shorter gravity waves, however, especially under severe wind conditions, a finer geometrical resolution might be needed. Results emphasize the need for further fundamental studies of sensor-object interaction. 相似文献
11.
Starting from the anelastic equations describing deep convection in cylindrical coordinates, the WKBJ method is used to discuss the stability of asymmetric three-dimensional inhomogeneous vortex under the conditions of nonhydrostatic and non-equilibrium gradient wind. From the equation of wave action, the development of disturbance is qualitatively analyzed. 相似文献
12.
13.
The phase-averaged characteristics of the turbulent velocity fields beneath steep short wind waves are investigated. A scheme
was developed to compute the phase of individual wind waves using spatial surface displacement data. This information was
used to analyze the two-dimensional velocity data acquired using particle image velocimetry (PIV) in a wind-wave tank. The
experiments were conducted at a fetch of 5.5m and at wind speeds that ranged from 4 to 10ms−1. Under these conditions previous studies have shown that a significant percentage of the waves are microscale breaking waves.
An analysis of the phase-averaged results suggests under these conditions (short fetches and moderate wind speeds) a wind-driven
water surface can be divided into three regions based on the intensity of the turbulence. These are the crests of microscale
breaking waves, the crests of non-breaking waves and the troughs of all waves. The turbulence is most intense beneath the
crests of microscale breaking waves. In the crest region of microscale breaking waves coherent structures were observed that
were stronger and occurred more frequently than beneath the crests of non-breaking waves. Beneath the crests of non-breaking
waves the turbulence is a factor of two to three times weaker and beneath the wave troughs it is a factor of six weaker. These
findings provide additional support for the hypothesis that approximately two-thirds of the gas and heat fluxes occur across
the turbulent wakes produced by microscale breaking waves. 相似文献
14.
Development and Validation of an Evaporation Duct Model.Part Ⅰ:Model Establishment and Sensitivity Experiments 总被引：1，自引：0，他引：1 
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下载免费PDF全文 Based on the Coupled Ocean-Atmospheric Response Experiment（COARE）bulk algorithm and the Naval Postgraduate School（NPS）model,a universal evaporation duct（UED）model that can flexibly accommodate the latest improvements in component（such as stability function,velocity roughness,and scalar roughness）schemes for different stratification and wind conditions,is proposed in this paper.With the UED model,the sensitivity of the model-derived evaporation duct height（EDH）to stability function（Ψ）,ocean wave effect under moderate to high wind speeds,and scalar roughness length parameterization,is investigated,and relative contributions of these factors are compared.The results show that the stability function is a key factor influencing the simulated EDH values.Under unstable conditions,the EDH values from stability functions of Fairall et al.（1996）and Hu and Zhang（1992）are generally higher than those from others;while under stable conditions,unreasonably high EDHs can be avoided by use of the stability functions of Hu and Zhang（1992）and Grachev et al.（2007）.Under moderate to high wind speeds,the increase in velocity roughness length z0 due to consideration of the true ocean wave effect acts to reduce modeled EDH values;this trend is more pronounced under stable conditions.Although the scalar roughness length parameterization has a minor effect on the model-derived EDH,a positive correlation is found between the scalar roughness length z0qand the model-derived EDH. 相似文献
15.
Despite its importance for momentum and mass transfer across the air–sea interface, the dynamics of airflow over breaking
waves is largely unknown. To fill this gap, velocity and vorticity distributions above short-gravity breaking waves have been
measured in a wind-wave tank. A Digital Particle Image velocimetry technique (DPIV) was developed to accomplish these measurements
above single breaking waves, propagating in mechanically-generated wave groups and forced by the wind. By varying the wind
speed and initial characteristics of the groups, the airflow structure was captured over waves at different stages of the
breaking process, and breaking with various intensities. The instantaneous airflow that separates from a sharp breaking crest
is very similar to that occurring over a backward facing step. The separation bubble is however strongly unsteady: the steeper
the wave crest and the larger the Reynolds number based on the crest-height, the higher the separated layer and the farther
downwind the reattachment point. Instantaneous flow topology displays specific features of three-dimensional separation patterns.
The tangential stress above the wave profile does not exhibit spikes at reattachment but grows progressively downwind from
zero at reattachment to a value at the next crest approximately that found at the upwind breaking crest. Static pressure measurements
revealed that large pressure falls are generated by vortices in the separated layer, as found in separated flows over solids.
This study may provide useful data for theoretical and numerical modelling of the flow and associated phenomena. 相似文献
16.
In this study, a long-term comparative assessment of the potential of wave power in the Black Sea was conducted using the calibrated and validated SWAN (Simulating WAves Nearshore) model forced by two well-known wind fields. The European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim and National Centers for Environmental Prediction/Climate Forecast System Reanalysis (NCEP/CFSR) wind fields were used, covering data from 1979 to 2018. In general, the wave power potential based on the results of the CFSR wind field was found to be slightly higher than that obtained with the ERA-Interim wind field. The greatest discrepancy between the results of the ERA-Interim and CFSR wind fields was observed in the northeastern Black Sea. The spatial distributions of the wave power were also evaluated on a seasonal scale using wave parameters obtained from the calibrated SWAN model. The wave climate obtained from both long-term and seasonal assessments indicates that the western Black Sea, especially the southwestern Black Sea, is characterized by higher wave power potential and lower variability, while the eastern Black Sea has lower wave power potential and higher variability. Stable and powerful long-term wave conditions in the southwestern Black Sea can indicate that this region is a suitable location for wave farms. In contrast, the effect of the long-term variability on wave power is greatest in the eastern Black Sea owing to the highly variable wave conditions in this region. 相似文献
17.
Lei Xiaoen 《大气科学进展》1985,2(2):225-233
Using the turbulent statistical form of the vertical vortex diffusion coefficient K, in the planetary boundary layer (PBL) and Ekman spiral wind profile, the three-dimensional diffusion equation is solved by the numeri-cal method. The influences of vertical shear of both wind direction and wind speed on pollution trajectory and horizontal diffusion parameters σy are numerically analysed. The expressions of both pollution trajectory and σy, including the factor of wind shear, are obtained. The results show that the vertical shear of wind is important among all factors affecting the mesoscale dispersion. Specifically, from neutral to stable atmospheric conditions, vertical shear of wind makes greater contribution to σy than turbulence, thus it is the most important factor. In this paper, we have compared horizontal dispersion pattern with both Pasquill's dispersion pattern considering wind direction shear, and experimental data collected at 9 different sites rang-ing from 10 to 100 km, and the results show that our dispersion pattern is closer to the experimental values than Pasquill's results, and his correction to shear of wind direction is too large under the stable conditions. 相似文献
18.
New evidence for a relation between wind stress and wave age from measurements during ASGAMAGE 总被引：7，自引：0，他引：7
Data from the 1996 ASGAMAGE experiment, performed in the southern North Sea at research platform Meetpost Noordwijk (MPN), are analysed for the parameters affecting the momentum flux. The stress turns out to be quadratically related to the 10-m wind speed and linearly to the wind speed at a wavelength related level. The Charnock parameter (dimensionless roughness length) shows a pronounced correlation with wave age. This implies, due to a coupling between wave age and the steepness of the waves, a connection between the stress and the steepness. We find that our North Sea results are consistent withopen ocean observations. For a given wind speed the mean stress at MPN turns out to be higher because the wave age there is in general lower. We define and give an expression for a drag coefficient at a wavelength related level that can be calculated straightforwardly from the wave age and then reduced to a standard level. 相似文献
19.
Xiaoli Guo Lars n Vladimir K. Makin Ann-Sofi Smedman 《Journal of Atmospheric & Ocean Science》2003,9(3):97-120
Measurements from the Baltic Sea and a wind-over-wave coupled model are used to study the wave impact on the sea drag. The study has been carried out for different wave conditions, namely a pure wind-sea, following-swell/ mixed sea and cross-swell/ mixed sea. Measurements reveal the fact that the sea drag is dependent on the sea-state. In stationary conditions and in the absence of severe cross-swell, swell reduces drag compared to wind-sea at the same wind speed. The cross-swell enhances the drag as compared to the following-swell case and the magnitude of the drag coefficient is increased with increasing the angle of swell propagation to the wind. It is shown that the agreement between the model results and measurements is good for pure wind-sea and stationary mixed-sea cases. Discrepancies occur at light winds, where most of the data represent pure swell conditions. During these pure swell conditions the data are characterized by a large variation of the drag coefficient. The variation is caused by mesoscale variability in the stress co-spectra, wind-cross-swell effects and nonstationarity in the wave and wind fields not represented in the model. 相似文献
20.
Experiments were conducted in a wind-wave tank to study the long-standing discrepancy between wind stresses over a water surface determined with the profile and eddy-correlation methods. Inasmuch as the eddy-correlation method measures the turbulence flux directly, such a discrepancy is considered as an error in the way the profile data are analyzed. Uncertainties in selections of the zero reference plane for the logarithmic velocity profile and of the value for the von Karman constant are suggested to be major sources of the error. To match the results obtained with two methods, the displacement height needs to vary with wave conditions, and the value of the von Karman constant is also discussed. 相似文献