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Wave dissipation characteristics in SWAN (Simulating Waves Nearshore) model are investigated through numerical experiments. It is found that neither the fully developed integral parameters of wind waves (significant wave height and peak frequency) nor the high frequency spectral tail can be well reproduced by the default wave dissipation source terms. A new spectral dissipation source term is proposed, which comprises saturation based dissipation above two times of peak frequency and improved whitecapping dissipation at lower frequency spectrum. The reciprocal wave age (u /c p ) is involved into the whitecapping model to adjust dissipation rate at different wind speed. The Phillips higher frequency saturation parameter in the saturation-based dissipation is no longer taken as a constant, but varies with wave age. Numerical validations demonstrate that both the wind wave generation process and higher frequency spectrum of wind waves can be well simulated by the new wave dissipation term. 相似文献
3.
G. S. Golitsyn 《Izvestiya Atmospheric and Oceanic Physics》2010,46(1):6-13
The problems of wind-induced waves on the sea surface are considered. To this end, the empirical fetch laws that determine
variations in the basic periods and heights of waves in relation to their fetch are used. The relation between the fetch and
the physical time is found, as are the dependences of the basic characteristics of waves on the time of wind forcing. It is
found that about 5% of wind energy dissipated in the near-water air layer contributes to the growth of wave heights, i.e.
wave energy, although this quantity depends on the age of waves and the exponent in the fetch laws. With consideration for
estimates of the probability distribution functions for the wind over the world ocean [11], it is found that the rate of wind-energy
dissipation in the near-water air layer is on the order of 1 W/m2. The calculations of wind waves [19] for the world ocean for 2007 have made it possible to assess the mean characteristics
of the cycle of wave development and their seasonal variations. An analysis of these calculations [19] shows that about 20%
of wind energy is transferred to the water surface. The remaining amount (80%) of wind energy is spent on the generation of
turbulence in the near-water air layer. About 2%, i.e., one tenth of the energy transferred to water, is spent on turbulence
generation due to the instability of the vertical velocity profile of the Stokes drift current and on energy dissipation in
the surf zones. Of the remaining 18%, 5% is spent directly on wave growth and 13% is spent on the generation of turbulence
during wave breaking and on a small-scale spectral region. These annually and globally mean estimates have a seasonal cycle
with an amplitude on the order of 20% in absolute values but with a smaller amplitude in relative values. According to [19]
and to the results of this study, the annually mean height of waves is estimated as 2.7 m and their age is estimated as 1.17. 相似文献
4.
Adjustment of Wind Waves to Sudden Changes of Wind Speed 总被引：1，自引：0，他引：1
An experiment was conducted in a small wind-wave facility at the Ocean Engineering Laboratory, California, to address the following question: when the wind speed changes rapidly, how quickly and in what manner do the short wind waves respond? To answer this question we have produced a very rapid change in wind speed between U low (4.6 m s?1) and U high (7.1 m s?1). Water surface elevation and air turbulence were monitored up to a fetch of 5.5 m. The cycle of increasing and decreasing wind speed was repeated 20 times to assure statistical accuracy in the measurement by taking an ensemble mean. In this way, we were able to study in detail the processes by which the young laboratory wind waves adjust to wind speed perturbations. We found that the wind-wave response occurs over two time scales determined by local equilibrium adjustment and fetch adjustment, Δt 1/T = O(10) and Δt 2/T = O(100), respectively, in the current tank. The steady state is characterized by a constant non-dimensional wave height (H/gT 2 or equivalently, the wave steepness for linear gravity waves) depending on wind speed. This equilibrium state was found in our non-steady experiments to apply at all fetches, even during the long transition to steady state, but only after a short initial relaxation Δt 1/T of O(10) following a sudden change in wind speed. The complete transition to the new steady state takes much longer, Δt 2/T of O(100) at the largest fetch, during which time energy propagates over the entire fetch along the rays (dx/dt = c g) and grows under the influence of wind pumping. At the same time, frequency downshifts. Although the current study is limited in scale variations, we believe that the suggestion that the two adjustment time scales are related to local equilibrium adjustment and fetch adjustment is also applicable to the ocean. 相似文献
5.
An approximate solution of wave-modified Ekman current for gradually varying eddy viscosity 总被引：1，自引：0，他引：1
Jin-Bao Song Yan-Song Huang 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(6):668-676
An approximate steady solution of the wave-modified Ekman current is presented for gradually varying eddy viscosity by using the WKB method with the variation of parameters technique. The parameters involved in the solution can be determined by the two-dimensional wavenumber spectrum of ocean waves, wind speed, the Coriolis parameter and the densities of air and water. The solution reduces to the exact solution when the eddy viscosity is taken as a constant. As illustrative examples, for a fully developed wind-generated sea with different wind speeds and a few proposed gradually varying eddy viscosities, the current profiles calculated from the approximate solutions are compared with those of the exact solutions or numerical ones by using the Donelan and Pierson wavenumber spectrum, the WAM wave model formulation for wind input energy to waves, and wave energy dissipation converted to currents. It is shown that the approximate solution presented has an elegant form and yet would be valid for any given gradually varying eddy viscosity. The applicability of the solution method to the real ocean is discussed following the comparisons with published observational data and with the results from a large eddy simulation of the Ekman layer. 相似文献
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7.
Based on the refraction-diffraction theory of irregular waves in the waters of slowly-varying cur-rents and depths,and the generation dissipation theory of wind wave,a model for nonlinear irregular wavesin coastal area is developed.In light of the specific conditions of coastal wave character and engineering ap-plication,a practical mathematical model for the nonlinear irregular waves is presented.with directional spec-trum in coastal area.Coast effect,refraction,whitecapping.bottom friction.current,wind and nonlinearaction are considered in this model.The numerical methods and schemes for wave refraction ray,energy con-servation of propagation,energy balance of the generation and dissipation of wind waves have been studied.Finally,the model is used for the directional wave spectrum computation in the Daya Bay.Compared withthe measured data with 956 wave bouys in the Daya Bay,the model results are in good agreement with themeasured results. 相似文献
8.
M. V. Kosnik V. A. Dulov V. N. Kudryavtsev 《Izvestiya Atmospheric and Oceanic Physics》2010,46(3):369-378
We investigate the role of different physical mechanisms in the generation of the capillary-gravity wind wave spectrum. This
spectrum is calculated by integrating a nonstationary kinetic equation until the solution becomes stready. The mechanisms
of spectrum generation under consideration include three-wave interactions, viscous dissipation, energy influx from wind,
nonlinear dissipation, and the generation of a parasitic capillary ripple. The three-wave interactions are taken into account
as an integral of collisions without additional simplifications. It is shown that the three-wave interactions lead to solution
instability if the kinetic equation takes into account only linear sources. To stabilize the solution, the kinetic equation
should incorporate a nonlinear dissipation term, which in the range of short gravity waves corresponds to energy losses during
wave breaking and microscale wave breaking. In the range of capillary waves, the account of nonlinear dissipation is also
needed to ensure a realistic level of the spectrum for large wind velocities. For the steady-state spectrum, the role of three-wave
interactions remains essential merely in the range of the minimum of phase velocity, where a trough on the curvature spectrum
is formed. At the remaining intervals of the spectrum, the main contribution into the spectral energy balance is provided
by the mechanisms of wave injection, nonlinear dissipation, and the generation of parasitic capillaries. 相似文献
9.
A ten-year data set for fetch- and depth-limited wave growth 总被引：1，自引：0，他引：1
This paper presents the key results from a ten-year data set for Lake IJssel and Lake Sloten in The Netherlands, containing information on wind, storm surges and waves, supplemented with SWAN 40.51 wave model results. The wind speeds U10, effective fetches x and water depths d for the data set ranged from 0–24 m s− 1, 0.8–25 km and 1.2–6 m respectively. For locations with non-sloping bottoms, the range in non-dimensional fetch x? ( = gxU10− 2) was about 25–80,000, while the range in dimensionless depth d? ( = g d U10− 2) was about 0.03–1.7. Land–water wind speed differences were much smaller than the roughness differences would suggest. Part of this seems due to thermal stability effects, which even play a role during near-gale force winds. For storm surges, a spectral response analysis showed that Lake IJssel has several resonant peaks at time scales of order 1 h. As for the waves, wave steepnesses and dimensionless wave heights H? ( = gHm0U10− 2) agreed reasonably well with parametric growth curves, although there is no single curve to which the present data fit best for all cases. For strongly depth-limited waves, the extreme values of d? (0.03) and Hm0 / d (0.44) at the 1.7 m deep Lake Sloten were very close to the extremes found in Lake George, Australia. For the 5 m deep Lake IJssel, values of Hm0 / d were higher than the depth-limited asymptotes of parametric wave growth curves. The wave model test cases of this study demonstrated that SWAN underestimates Hm0 for depth-limited waves and that spectral details (enhanced peak, secondary humps) were not well reproduced from Hm0 / d = 0.2–0.3 on. SWAN also underestimated the quick wave response (within 0.3–1 h) to sudden wind increases. For the remaining cases, the new [Van der Westhuysen, A.J., Zijlema, M., and Battjes, J.A., 2007. Nonlinear saturation-based whitecapping dissipation in SWAN for deep and shallow water, Coast. Eng., 54, 151–170] SWAN physics yielded better results than the standard physics of Komen, G.J., Hasselmann, S., Hasselmann, K., 1984. On the existence of a fully developed wind-sea spectrum. J. Phys. Oceanogr. 14, 1271–1285, except for persistent overestimations that were found for short fetches. The present data set contains many interesting cases for detailed model validation and for further studies into the evolution of wind waves in shallow lakes. 相似文献
10.
为研究海洋环境信号在OBS(Ocean Bottom Seismograph)原始数据中的规律及应用,根据OBS原始数据的波形及频谱特征,将研究区划分为5个时间段,依次为旧涌浪阶段、风浪渐强阶段、风浪全盛阶段、风浪消退阶段和新涌浪阶段。结合海洋天气预报,认为上述现象是由偏南风风浪对海流的影响造成的。参考野外地震数据采集记录班报,得到各阶段的时长和距离,计算风浪渐强、全盛和消退阶段OBS附近海流的平均速度。结果表明:OBS原始资料中浅海海洋环境噪音增强的主要因素是风浪,且风浪引起的噪音信号的波形变化特征是渐进式的;OBS可用于接收某种特殊阶段(如台风、海啸等)的噪音信号,并根据噪音信号的波形特征、频谱变化规律和持续时间估算该阶段的海流速度变化。 相似文献
11.
Jin-Bao Song 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(5):659-671
The response of near-surface current profiles to wind and random surface waves are studied based on the approach of Jenkins [1989. The use of a wave prediction model for driving a near surface current model. Dtsch. Hydrogr. Z. 42, 134–149] and Tang et al. [2007. Observation and modeling of surface currents on the Grand Banks: a study of the wave effects on surface currents. J. Geophys. Res. 112, C10025, doi:10.1029/2006JC004028]. Analytic steady solutions are presented for wave-modified Ekman equations resulting from Stokes drift, wind input and wave dissipation for a depth-independent constant eddy viscosity coefficient and one that varies linearly with depth. The parameters involved in the solutions can be determined by the two-dimensional wavenumber spectrum of ocean waves, wind speed, the Coriolis parameter and the densities of air and water, and the solutions reduce to those of Lewis and Belcher [2004. Time-dependent, coupled, Ekman boundary layer solutions incorporating Stokes drift. Dyn. Atmos. Oceans. 37, 313–351] when only the effects of Stokes drift are included. As illustrative examples, for a fully developed wind-generated sea with different wind speeds, wave-modified current profiles are calculated and compared with the classical Ekman theory and Lewis and Belcher's [2004. Time-dependent, coupled, Ekman boundary layer solutions incorporating Stokes drift. Dyn. Atmos. Oceans 37, 313–351] modification by using the Donelan and Pierson [1987. Radar scattering and equilibrium ranges in wind-generated waves with application to scatterometry. J. Geophys. Res. 92, 4971–5029] wavenumber spectrum, the WAM wave model formulation for wind input energy to waves, and wave energy dissipation converted to currents. Illustrative examples for a fully developed sea and the comparisons between observations and the theoretical predictions demonstrate that the effects of the random surface waves on the classical Ekman current are important, as they change qualitatively the nature of the Ekman layer. But the effects of the wind input and wave dissipation on surface current are small, relative to the impact of the Stokes drift. 相似文献
12.
内波破碎引起的能量耗散和混合是海洋内部的重要物理过程。通过在二维内波水槽进行实验室实验,分析内波与地形的作用,探究内孤立波与平顶海山地形作用时波要素、能量以及湍耗散率的时空变化。本实验利用重力塌陷法在两层流体中制造第一模态内孤立波,通过粒子图像测速技术(particle image velocimetry, PIV)获得内孤立波与地形作用时的流场结构,定量分析整个作用过程。结果表明,地形会改变波形甚至引起破碎,内波与地形作用时,振幅和能量密度会在内孤立波爬坡时迅速增大,在地形前缘产生强烈能量耗散。入射波的能量与塌陷高度呈二次函数关系,透射波能量随地形升高减小,反射波能量随地形升高增大。地形前缘局地湍耗散率极值时间序列在部分实验中呈双峰结构,对应内孤立波界面处剪切加强引起湍流耗散和波后缘翻转破碎。破碎引起的地形前缘区域平均湍耗散率量级在10~(-5)m~2/s~3,局地湍耗散率极值与入射波振幅呈指数关系,所有实验中局地湍耗散率的最大值接近10~(-3) m~2/s~3量级。 相似文献
13.
S. A. Kitaigorodskii 《Izvestiya Atmospheric and Oceanic Physics》2009,45(3):372-379
New experimental data that make it possible to explain and predict the observed variability of turbulent-energy dissipation in the upper ocean are discussed. For this purpose, the dependence of the energy dissipation rate of breaking wind waves on their propagation velocity (see [1]) is used. The turbulent-energy dissipation values obtained earlier in [2, 3] by a direct method are compared to the results of radar measurements of individual breaking events presented in [1]. On the basis of this comparison, a strong dependence of the turbulent-energy dissipation value on the stage of wind-wave development, which is characterized by the ratio U a /c p (U a is the wind speed and c p is the phase speed of the peak of the wind-wave spectrum) is confirmed. This dependence was found earlier purely empirically. Moreover, it is shown that the theoretically obtained dependence (c p /U a )4, does not contradict the available empirical data. The results of this study opens possibilities for scientifically substantiated calculations of greenhouse-gas exchange (specifically, CO2 exchange between the ocean and the atmosphere). 相似文献
14.
《Deep Sea Research Part I: Oceanographic Research Papers》2003,50(3):371-395
Dissipation rate statistics in the near-surface layer of the ocean were obtained during the month-long COARE Enhanced Monitoring cruise with a microstructure sensor system mounted on the bow of the research vessel. The vibration contamination was cancelled with the Wiener filter. The experimental technique provides an effective separation between surface waves and turbulence, using the difference in spatial scales of the energy-containing surface waves and small-scale turbulence. The data are interpreted in the coordinate system fixed to the ocean surface. Under moderate and high wind-speed conditions, we observed the average dissipation rate of the turbulent kinetic energy in the upper few meters of the ocean to be 3–20 times larger than the logarithmic layer prediction. The Craig and Banner (J. Phys. Oceanogr. 24 (1994) 2546) model of wave-enhanced turbulence with the surface roughness length from the water side z0 parameterized according to the Terray et al. (J. Phys. Oceanogr. 26 (1996) 792) formula z0=cHs provides a reasonable fit to the experimental dissipation profile, where z is the depth (defined here as the distance to the ocean surface), c≈0.6, and Hs is the significant wave height. In the wave-stirred layer, however, the average dissipation profile deviates from the model (supposedly because of extensive removing of the bubble-disturbed areas close to the ocean surface). Though the scatter of individual experimental dissipation rates (10-min averages) is significant, their statistics are consistent with the Kolmogorov's concept of intermittent turbulence and with previous studies of turbulence in the upper ocean mixed layer. 相似文献
15.
《Ocean Modelling》2009,26(3-4):154-171
Ocean surface mixing and drift are influenced by the mixed layer depth, buoyancy fluxes and currents below the mixed layer. Drift and mixing are also functions of the surface Stokes drift Uss, volume Stokes transport TS, a wave breaking height scale Hswg, and the flux of energy from waves to ocean turbulence Φoc. Here we describe a global database of these parameters, estimated from a well-validated numerical wave model, that uses traditional forms of the wave generation and dissipation parameterizations, and covers the years 2003–2007. Compared to previous studies, the present work has the advantage of being consistent with the known physical processes that regulate the wave field and the air–sea fluxes, and also consistent with a very large number of in situ and satellite observations of wave parameters. Consequently, some of our estimates differ significantly from previous estimates. In particular, we find that the mean global integral of Φoc is 68 TW, and the yearly mean value of TS is typically 10–30% of the Ekman transport, except in well-defined regions where it can reach 60%. We also have refined our previous estimates of Uss by using a better treatment of the high frequency part of the wave spectrum. In the open ocean, Uss ≃ 0.013U10, where U10 is the wind speed at 10 m height. 相似文献
16.
A. K. Laing 《新西兰海洋与淡水研究杂志》2013,47(4):541-553
A model is described for hindcasting or forecasting waves in finite‐depth waters. The model is particularly applicable to coastal sites where the water is depth‐limited. The wave energy density spectrum is modelled in the frequency‐directional domain. For each spectral component a ray is defined along which wave energy propagates to reach the site. For sites exposed to the open ocean a background spectral wave model is required to provide input to the ray endpoints. Further growth and dissipation is then effected along the rays according to the local wind and water depth. The model was used to hindcast wave spectra over a period of 9 months for a site in the Canterbury Bight, New Zealand. The results were compared with measurements from a Waveridcr buoy at the site. The model succeeds in explaining about 40% of the variance in measured significant wave heights. However, the present application is handicapped by errors inherent in the background spectral model and in specifying the local wind. 相似文献
17.
The formation of a stationary (equilibrium) range in a wind-wave spectrum is investigated by numerical simulation. The equation of evolution of the wind-wave spectrum is solved using the exact calculation of the Hasselmann kinetic integral and involving various modifications of known parameterizations of the mechanisms of wave pumping by wind (In) and of wave dissipation (Dis). It is shown that it is these two mechanisms that are responsible for the shape of the stationary range of the wind-wave spectrum, whereas the nonlinear mechanism plays a stabilizing but subsidiary role. With an appropriate choice of mathematical representations for In and Dis, any known empirical shape of the stationary range of the spectrum can be obtained. During the calculations it is found that, for real wind waves, the known representations of In and Dis do not ensure the existence of the inertial interval required for Kolmogorov-type spectra formation due to the nonlinear interactions between waves. 相似文献
18.
Turbulent mixing in the upper ocean(30-200 m) of the northwestern Weddell Sea is investigated based on profiles of temperature,salinity and microstructure data obtained during February 2014.Vertical thermohaline structures are distinct due to geographic features and sea ice distribution,resulting in that turbulent dissipation rates(ε) and turbulent diffusivity(K) are vertically and spatially non-uniform.On the shelf north of Antarctic Peninsula and Philip Ridge,with a relatively homogeneous vertical structure of temperature and salinity through the entire water column in the upper 200 m,both ε and K show significantly enhanced values in the order of O(10~(-7))-O(10~(-6)) W/kg and O(10~(-3))-O(10~(-2)) m~2/s respectively,about two or three orders of magnitude higher than those in the open ocean.Mixing intensities tend to be mild due to strong stratification in the Powell Basin and South Orkney Plateau,where s decreases with depth from O(10~(-8)) to O(10~(-9)) W/kg,while K changes vertically in an inverse direction relative to s from O(10~(-6)) to O(10~(-5)) m~2/s.In the marginal ice zone,K is vertically stable with the order of10~(-4) m~2/s although both intense dissipation and strong stratification occur at depth of 50-100 m below a cold freshened mixed layer.Though previous studies indentify wind work and tides as the primary energy sources for turbulent mixing in coastal regions,our results indicate weak relationship between K and wind stress or tidal kinetic energy.Instead,intensified mixing occurs with large bottom roughness,demonstrating that only when internal waves generated by wind and tide impinge on steep topography can the energy dissipate to support mixing.In addition,geostrophic current flowing out of the Weddell Sea through the gap west of Philip Passage is another energy source contributing to the local intense mixing. 相似文献
19.
《Journal of Sea Research》2002,47(3-4):209-222
Velocity and temperature measurements obtained with acoustic Doppler current profilers and thermistor strings are used to evaluate the production of internal wave band kinetic energy mainly in the frequency band σ>15 cpd. Results from a flat 19 m deep, vigorous tidal environment in a shelf sea are compared with energy production in a bottom boundary layer above a continental slope. In the tidal environment, maximum production occurs in the near-bottom and near-surface layers. A distinct mid-depth maximum in KE production occurs during a period when wind speeds exceed 10 m s−1 and significant wave height ∼2 m. At the same time, no significant changes in the along-shore current speed take place but the cross-shore current, generated by strong stratification, is weakened. This suggests a direct energy input from the wind via surface waves into the water column turbulence. Maximum kinetic energy production in the frequency band σ>1.9 cpd, thus including the semidiurnal tide, occurs at mid-depth when strong stratification is present. The overall magnitude of internal wave band kinetic energy production agrees well with independent dissipation estimates obtained from microstructure profilers. Above the sloping bottom, KE production is somewhat larger than observed in the shallow tidal environment, despite rms currents being ∼50% smaller and wind effects being small. Above the sloping bottom KE shear production was comparable to buoyancy production. The latter was negligible at the shelf sea site. 相似文献
20.
Recent numerical studies (Hibiya et al., 1996, 1998, 2002) showed that the energy cascade across the internal wave spectrum down to small dissipation scales was
under strong control of parametric subharmonic instabilities (PSI) which transfer energy from low vertical mode double-inertial
frequency internal waves to high vertical mode near-inertial internal waves. To see whether or not the numerically-predicted
energy cascade process is actually dominant in the real deep ocean, we examine the temporal variability of vertical profiles
of horizontal velocity observed by deploying a number of expendable current profilers (XCPs) at one location near the Izu-Ogasawara
Ridge. By calculating EOFs, we find the observed velocity profiles are dominated by low mode semidiurnal (∼double-inertial
frequency) internal tides and high mode near-inertial internal waves. Furthermore, we find that the WKB-stretched vertical
scales of the near-inertial current shear are about 250 sm and 100 sm. The observed features are reasonably explained if the
energy cascade down to small dissipation scales is dominated by PSI. 相似文献