On the non-Gaussian nature of wind waves

The asymmetry and curtosis for different wave conditions have been computed using experimentally-derived measurement data on sea surface roughness. It is shown that the asymmetry and curtosis values are essentially different from zero and practically do not depend on the slope of waves and their age.Translated by Mikhail M. Trufanov.     

Prediction of ocean waves based on the single-parameter growth equation of wind waves

A method for the prediction of ocean waves was developed on the basis of the single-parameter growth equation of wind waves, proposed byToba (1978) on the basis of similarity in growing wind waves. The applicability of the method to actual problems was tested by hindcasting the wave characteristics with the method, for two cases with differing time and space scales, one in Kii Channel Approach, Japan, and the other in the North Atlantic Ocean. The results showed that the present method can predict waves within an error of 1.3 m in wave heights, which ranged from 3 to 12 m.     

Turbulent structure in water under laboratory wind waves

The structure of the turbulent boundary layer underneath laboratory wind waves was studied by using a combination of a high-sensitivity thermometer array with a two-component sonic flowmeter. The temperature fluctuations are used to detect movements of water parcels, with temperature as a passive quantity. The turbulence energy was dominant in the frequency range (0.01 0.1 Hz), which was much smaller than the wind-wave frequency (2 5 Hz), and in which the turbulence was anisotropic. There was a frequency range (0.2 2 Hz for velocity, 0.2 5 Hz for temperature fluctuation) where the turbulence was isotropic and had a –5/3 slope in the energy spectrum. These points are the same as those in previous works. However, by analyses of the time series by using a variable-interval time-averaging technique (VITA), it has been found that conspicuous events in this main turbulence energy band are the downward bursting from the vicinity of the water surface. Thus the structure of the water layer underneath the wind waves has characters which are similar to the familiar turbulent boundary layer over a rough solid wall, as already conceived. It has been found that, at the same time, the turbulence energy can be related to quantities of the wind waves (the root mean squared water level fluctuation and the wave peak frequency), for different wind and wave conditions. That is, the turbulence underneath the wind waves develops under a close coupling with the wind waves.     

南麂站定常波风浪波高与风速的经验关系

本文以南麂海洋站１９８３～１９９０年风、浪的实测资料为依据，建立了南麂海城春、夏、秋、冬季定常波风浪波高与风速的经验关系式。检验结果表明，曲线回归显著，计算值与实测值吻合良好。文中还对偏ＮＮＥ向和偏ＳＳＷ向计算波高随风速增大的快慢，同一方向在同一风速作用下计算波高的季节变化及其机理作了初浅的讨论。     

On the growth of ocean waves

The availability of 10 h of continuous, uninterrupted field measurements of wind waves recorded in the western Pacific and containing a complete wave growth episode, has provided a distinct opportunity for us to make a novel, unprecedented examination of detailed wave growth processes. We found that the significance of the size of data used in the measurement, which can only be addressed with continuous and uninterrupted measurements, reflected the ineptness of the conventional approach toward further detailed understanding of realistic wave growth processes, as the conventional 20 min data size essentially stamped out any dynamics with time scale below 20 min. While our conventional understanding and modeling were generally operative and useful, they left no real vestige on time localized mechanisms such as wave grouping or wave breaking processes all with time scales much less than 20 min.     

On the intensification of decimeter-range wind waves in film slicks

The physical influence of the intensification of decimeter waves on a water surface covered by a surfactant film is proposed. The damping of a long wave caused by the loss of its energy on the modulation of short (centimeter) wind waves is analyzed. The damping coefficient of waves of decimeter-meter lengths is calculated, and this coefficient is shown to decrease in the presence of a surfactant film. The strong suppression of the spectrum of centimeter wind waves in a film slick is the physical factor responsible for such a decrease. Due to a decrease in the damping coefficient of decimeter-meter waves, their intensity in the slick increases. Within the framework of a model of the spectrally local energy balance of wind waves, the results of calculations satisfactorily agree with the experiment.     

Experimental study on strong interaction between regular waves and wind waves—I

The interaction between mechanically generated regular waves and wind waves is experimentally investigated in a wind-wave tunnel. It is shown that the growth process of regular waves is divided into the four distinct stages as follows: (1) almost independent coexistence of wind waves and regular waves, (2) attenuation of wind waves with simultaneous growth of regular waves, (3) rapid growth of regular waves after disappearance of wind waves, and (4) transition of regular waves to wind waves after the wave breaking. At the second stage there is an apparent relation between the attenuation of wind waves and the growth of regular waves. This fact suggests that there is some strong nonlinear interactions which transfers energy effectively from wind waves to regular waves.     

高度计风速反演算法比较及波浪周期反演初探

利用浮标实测数据和TOPEX/Poseidon高度计资料的时空配准数据,对迄今为止已提出的有代表性的7种卫星高度计海面风速反演模式函数进行了分析比较,指出考虑波浪状态影响的解析算法在均方根误差和对称性方面的优越性,讨论了目前在波浪周期反演方面存在的问题以及可能的解决途径.     

On interaction between intermediate-depth long waves and deep-water short waves

The interaction between a unidirectional deep-water short-wave train and an intermediate water-depth long wave is studied. The steady solutions are derived up to third order in wave steepness, respectively, using two different approaches: a conventional perturbation method employing linear phase functions to describe both long- and short-wave phases and a phase modulation method using a modulational phase function to model the short-wave phase. The two results are shown to be identical for a parametric range χ₁ coth Kdχ₃ ≤ 0.5, where χ₃ is the short-to-long wavelength ratio, χ₁ and K are, respectively, the long-wave steepness and wavenumber, and d the water depth. When χ₁ coth Kd approaches χ₃, the conventional solution converges slowly and eventually diverges for χ₁ coth Kdχ₁. The slow convergence of the conventional solution results from the approximation of a modulated short-wave phase by a linear phase formulation. In addition to the increasing modulation of the short-wave phase, amplitude and wavenumber as the water depth decreases, it is found that the modulation of the short-wave intrinsic frequency and potential amplitude along the long-wave surface become significant. Previous results about virtually non-modulated short-wave intrinsic frequency and potential amplitude are only limited to the case of unidirectional wave modulation in very deep water.     

Intensification of nonlinear wind waves on clean water and in the presence of an oil film

The intensification of gentle plane waves at the initial stage of their generation by a steady wind flow in a laboratory setup is investigated. It is found that the wave form is changed by eddies that are formed in the viscous layer of a steady air flow on the leeward slope: the water surface rises under the action of eddies to form a complexly shaped slope. Calculated and measured data for gentle nonlinear waves on clean water are in good compliance with each other. It is shown that, in the presence of an oil film, the region of eddy separation encompasses the wave trough as well, because oil flows down and the film is thickened in passing from the slope to the trough. The water-surface rise by eddies in the trough restricts an increase in the amplitude and steepness of the wave.     

Statistical study on the local equilibrium between wind and wind waves by using data from ocean data buoy stations

The local equilibrium between the wind and wind waves, which is defined by a range of the coefficient of the 3/2-power law between the non-dimensional significant wave height and period, is statistically investigated by using wind and wave data obtained at four ocean data buoy stations in the seas near Japan. The friction velocity is calculated from the wind speed measured at one height together with the significant wave period by using formulas of the wave dependent drag coefficient proposed by Tobaet al. (1990). The data for small waves or for weak winds indicate that the waves do not satisfy the criterion for the local equilibrium, because they may be affected by changing winds or remotely generated swells. In the seas near Japan, the data which satisfy the local equilibrium are about 6% through a year. Otherwise swells are dominant in most situations. Changing winds also cause deviations from the local equilibrium. The degree of satisfaction of the local equilibrium can be classified by ranges of the significant wave height. As the significant wave height exceeds 4 m, the local equilibrium is more frequently satisfied.     

On energy transport and group velocity of water waves

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A quasi-similarity between wind waves and solid surfaces in their roughness characteristics

A formulation for the aerodynamic roughness length of air flow over wind waves $$z_0 = \gamma {\text{ }}u_* /\sigma p$$ which was proposed by Toba (1979) and Toba and Koga (1986) from dimensional considerations with some data analysis, is shown to correspond with a formulation for irregular solid surfaces $$(z_0 /h) = a(h/l)^{1 + \beta } $$ which resulted from work by Woodinget al. (1973) and Kustas and Brutsaert (1986);u _* is the friction velocity,σ _p the spectral peak frequency of wind waves,h the mean height of the solid obstacles,l the mean distance between their crests, andα,Β, andγ are constants. This correspondence is reached by the existence of a statistical 3/2-power law and an effective dispersion relationship for wind waves. Because both approaches of parameterizingz ₀ were arrived at independently, they provide each other mutual reinforcement.     

On spectral and statistical characteristics of shallow water waves

Spectral, zero up-crossing and Tucker's methods of analysis are examined for shallow water wave records. Among the wave height parameters H_s and are most reliable and consistent irrespective of the analysis technique. Tucker analysis, though simple, seems versatile for estimating these wave height parameters. The standard period parameters are less consistent. For practical purposes every period that might reasonably occur has to be considered along with their corresponding height estimate. Joint distribution of heights and periods is in agreement with the function proposed by CNEXO.     

An experimental study of the relations between bispectra and nonlinear apparent features of wind waves

To investigate the nonlinear properties of wind waves, experiments are carried out in a wind-wave flume with slope bottom at different wind speeds and fetches. Both the internal structure and apparent features of the nonlin-earity of wind waves are studied by using bispectral and statistical analysis of surface elevations. The relations between bispectra and nonlinear apparent characteristics of wind waves are established and confirmed.     

Prediction of ocean waves based on the single-parameter growth equation of wind waves (II) introduction of grid method

The present study is a modification of the wave prediction model presented in the first paper of this title (Kawai et al., 1979) based on the Toba's (1978) single parameter equation of the wind wave growth. The introduction of a grid method reduces the two defects pointed out inKawai et al., i.e., the absence of the prediction of certain instants at fixed points, and the concentration of wave energy at certain points in the wind direction, arising from the lack of treatment of the lateral spreading of wave energy around the wind direction. The new model is applied to the same set of data. The results shows overall improvements, such as the elimination of certain overestimate in the first study and the coincidence of the predicted maximum with the measured one. The swells are separately hindcasted and a very good agreement with measurement is obtained.     

北部湾沿海最大风速分布特征及工程设计风速推算

利用北部湾沿海7个气象站建站至2008年的年最大风速资料,采用指数律风速廓线公式和＂时次换算＂方法对年最大风速进行订正,得到长年代10m高度10min平均年最大风速序列;采用离差系数Cv分析最大风速的年际变化,应用极值Ⅰ型分布推算北部湾沿海距地10m高50a一遇和100a一遇风速的极大值.结果表明,北部湾沿海年最大风速多出现在7～9月,年最大风速离差系数Cv为0.22～0.35,与沿海城市上海、福州、广州相近;北部湾沿海50a一遇、100a一遇风速的极大值分别为22.9～42.6和24.8～46.5m/s,其空间分布特征是：越靠近海的地方多年一遇风速的极大值就越大.     

Manifestations of water dynamics in the coastal zone in the field of breaking of wind waves

In the coastal zone, as a result of mixing of waters, it is difficult to identify turbulent phenomena with a spatial scale of 0.1–1 km accompanied by strong vertical flows according to the data of measuring temperature. On the basis of the data of direct measurements, it is shown that turbulent structures are well pronounced in the field of breaking of wind waves. We deduce empirical estimates of the response of the intensity of wave breaking to the magnitude of divergence of the current and develop a theoretical model of the influence of inhomogeneities of currents on wave breaking capable of describing the experimental data. Translated by Peter V. Malyshev and Dmitry V. Malyshev