共查询到20条相似文献，搜索用时 31 毫秒
1.
Klaus Hasselmann 《Boundary-Layer Meteorology》1974,6(1-2):107-127
Summary The effect of white capping on the spectral energy balance of surface waves is investigated by expressing the white-cap interactions in terms of an equivalent ensemble of random pressure pulses. It is shown first that the source function for any non-expansible interaction process which is weak-in-the-mean is quasi-linear. In the case of white capping, the damping coefficient is then shown to be proportional to the square of the frequency, provided the wave scales are large compared with the white-cap dimensions. The remaining free factor is determined indirectly from consideration of the spectral energy balance. The proposed white-capping dissipation function is consistent with the structure of the energy balance derived from JONSWAP, and the existence of a
–5 spectrum governed by a non-local energy balance between the atmospheric input, the nonlinear energy transfer and dissipation. However, closure of the energy balance involves hypotheses regarding the structure of the atmospheric input function which need to be tested by further measurements. The proposed set of source functions may nevertheless be useful for numerical wave-prediction. According to the model, nearly all the momentum transferred across the air-sea interface enters the wave field. For fetchlimited and fully developed spectra in a stationary, uniform wind field, the drag coefficient remains approximately constant. However, for more general wind conditions, this will not be the case and the wave spectrum should be included in an accurate parameterisation of the air-sea momentum transfer.Contribution from the Sonderforschungsbereich Meeresforschung Hamburg of the Deutsche Forschungsgemeinschaft. 相似文献
2.
高精度迎风偏斜格式的比较与分析 总被引：1，自引：0，他引：1
利用一种具有任意阶精度的一般显式有限差分公式构造出高精度迎风偏斜格式，并利用 Fourier分析法评估了这些迎风偏斜格式的耗散误差与频散误差。结果表明，偶阶精度格式的数值相速度快于实际相速度，而奇阶精度格式的数值相速度慢于实际相速度。并且，偶阶精度格式的耗散误差与频散误差低于相邻的奇阶精度格式。为了检验这些格式的计算性能，在一维问题上进行了应用。首先，考虑恒定风场条件下的一维平流试验。主要选择两种不同的初始条件来评价数值格式的精度，这两种试验问题分别是高斯函数、方波函数。试验结果表明，随着数值格式精度的提高，数值格式的误差逐渐减小。而对于高于六阶精度的格式来说，改进的程度并不是很大。其次，应用各阶格式到具有两种不同初始条件的无粘Burgers方程。数值结果表明，随着数值格式阶数的增加，数值结果也得到了明显改进。而对于高于六阶精度的格式来说，进一步的变化并不明显。总之，在兼顾效率与精度条件下六阶迎风偏斜格式是最好的。 相似文献
3.
Some Basic Properties of the Surrogate Subgrid-Scale Heat Flux in the Atmospheric Boundary Layer 总被引：3，自引：3，他引：0
Fernando Porté-Agel Charles Meneveau Marc B. Parlange 《Boundary-Layer Meteorology》1998,88(3):425-444
The development of improved subgrid-scale (SGS) models for large-eddy simulation of scalar transport in the atmospheric boundary layer requires an improved understanding of basic properties of the SGS fluxes. High frequency atmospheric wind speed and temperature data sampled at a height of 1.7 m are used to measure SGS heat fluxes and dissipation of temperature variance, by means of one-dimensional filtering and invoking Taylor's hypothesis. Conditional averaging is used to isolate interesting features of the SGS signals, and to relate them to the large-scale characteristics of the flow, such as the presence of coherent structures. Both mean and conditionally averaged SGS quantities are compared with those obtained using a standard eddy-diffusivity model. Within the limitations imposed by the one-dimensional data analysis, we observe that the model appears unable to reproduce important features of the real signals, such as the negative dissipation of temperature variance associated with strong negative resolved temperature gradients due to the ejection of warm air under unstable atmospheric stability conditions. 相似文献
4.
5.
The mechanism of flattening of surface wind waves in the centimetre wavelength range under the action of internal waves and in the presence of surfactants is considered. It is shown that internal waves give rise to perturbations of surfactant concentration proportional to the orbital velocities of wave particles. Accordingly, the damping coefficient of centimetre wavelength ripples is also modulated. Evolution of the wind wave spectrum is described by the energy balance equation. In the right-hand side of the equation the Phillips excitation mechanism, the Miles mechanism with a nonlinear spectrum limitation, and the dissipation caused by a surface-active film are taken into account. Assuming that the energy source and sink balance of the wind wave spectrum over the centimetre wavelength range is local, relative spectra (contrasts) for the case of gentle breeze are calculated. It is shown that the spectral components of ripples in the slicks can be order less than the uperturbed spectrum values. 相似文献
6.
Abstract The frequency and directional wave‐modelling capability of the Ocean Data Gathering Program (ODGP) deep water spectral wave model is assessed through comparison with WAVEC data gathered at Hibernia. Both qualitative and quantitative analyses indicate better agreement with observations during storms and with the wind‐driven component of the wave spectra. There is statistically poor modelling of the swell. A coherence analysis on derived wave vectors indicates that the ODGP model does not simulate geophysical variability with time‐scales less than about 30 h for overall spectral energy and less than 24 h for wave energy of frequency greater than 0.6 rad s?1 (0.095 Hz). The signals associated with swell waves are incoherent at nearly all time‐scales. 相似文献
7.
Abraham Zangvil 《Boundary-Layer Meteorology》1981,21(1):39-46
The meaningfulness of spectral presentations, and of spectral peaks in particular, is considered by the use of simple examples. First, we derive analytically the spectra of sinusoidal finite-length waves and subject the spectra to several area-conserving transformations. The peak of the logarithmic spectrum (power density per unit natural logarithm of frequency) is shown to be the most appropriate for defining the scales (or frequencies) of the waves. The advantage of the logarithmic spectrum becomes even more apparent when a wave consisting of the positive part of a sine wave is considered. In that case, the conventional frequency presentation is misleading because in addition to the erroneous location of the spectral peak, an increase of power density towards low frequencies occurs, giving the spectra the appearance of red noise. For the same wave, it is shown that the logarithmic spectrum has a single peak at the position corresponding with the actual wave frequency. 相似文献
8.
Numerical experiments on forcing dissipation and heating response of dipole (unipole) are carried out using global spectral models with quasi-geostrophic barotropic vorticity equations. For each experiment model integration is run for 90 days on the condition of three-wave quasi-resonance. The results are given as follows: Under the effects of dipole (unipole) forcing source and basic flow intensity, there exist strong interactions among the three planetary waves and quasi-biweekly and intraseasonal oscillation of the three planetary waves. In the meantime, the changes in the intensity of dipole or unipole forcing source and basic flow have different frequency modulation effects on LFO in the middle and higher latitudes. The results of the stream function field of three quasi-resonant waves evolving with time confirm that the low-frequency oscillation exists in extratropical latitude. 相似文献
9.
B. A. Kader 《Boundary-Layer Meteorology》1992,61(4):323-347
Methods are studied which permit one to evaluate turbulent fluxes from the results of spectral measurements in turbulent laboratory flows and an unstable atmospheric surface layer. The well known dissipation method of flux measurements, which uses spectral data related to the inertial range, is reanalyzed. New theoretical ideas and the latest experimental data are used to specify this method in cases of moderately and very strongly unstable thermal stratifications.Moreover, it is also explained how to estimate momentum and heat fluxes from data in the low frequency parts of the velocity and temperature spectra in the low frequency ranges beyond the lower limit of the inertial range. This permits one to estimate fluxes using rather simple and cheap instruments (e.g., Pilot-tubes and thermocouples in laboratory flows or cup anemometers and crude resistance thermometers in meteorological studies). The equations for flux determination are based in such cases on the recent models by Kader (1987, 1988) and Kader and Yaglom (1990, 1991) of spectral shapes at mesoscale wave numbers; these models agree quite satisfactorily with many (though not all) data of direct spectral measurements. It is shown that estimated momentum and heat fluxes in the laboratory and in an unstably stratified atmospheric surface layer obtained by the method suggested in this paper agree satisfactorily with direct flux measurements. 相似文献
10.
GRAPES_GFS中三维参考大气的研究：参考态构造和实际预报试验 总被引：1，自引：0，他引：1
GRAPES_GFS（Global Regional Assimilation and PrEdiction System, Global Forecast System）采用基于等温大气构造的一维参考大气,前期的研究工作已在GRAPES_GFS的动力框架中引入了三维参考大气,并通过一系列理想试验检验了新方法的正确性以及计算精度。本部分研究工作,主要针对实际资料的预报试验,对比分析了不同三维参考态给定方法的优劣,并采用气候平均法,进行夏季两个月的四维变分循环预报试验。检验结果显示,使用三维参考大气后,模式的综合预报性能得到了提升,对流层高度场、温度场的预报偏差有所减小,长期积分过程中模式质量损失较为严重的问题也得到了明显的缓解。另外,通过动能谱的对比也可以看到使用三维参考大气后,模式在高层的能量耗散明显较小,能谱变化与观测更加吻合。 相似文献
11.
Orographic effects on monthly-and seasonal-scale low frequency oscillation are investiged in terms of a five-level global spectral model with a triangle truncation at wavenumber 10 that contains relatively full physical parameterization, followed by analysis and comparison of the lowpass filtered data separately obtained from models with and without orography. Results show that remarkable seasonal characteristics are displayed in the orographic forcing-generated low frequency wavetrain on monthly and seasonal scales. It is found that the Northern Hemisphere summer orography-produced tropical heating acts as source of the low-frequency wavetrain for both hemispheres. Besides, the simulations indicate that the orographic wavetrain perturbation can give rise to the anomaly in the equatorial zonal flow, whose transient forcing will cause a new wavetrain in the Southern Hemisphere, thus completing the cross-equatorial propagation of the northern wave in interhemispheric action. 相似文献
12.
A systematic evaluation is conducted of the smoothed spectrum, which is a spectral estimate obtained by averaging over a window of contiguous frequencies. The technique is extended to the ogive, as well as to the cross-spectrum. It is shown that, combined with existing variance estimates for the periodogram, the variance—and therefore the random error—associated with these estimates can be calculated in a straightforward way. The smoothed spectra and ogives are biased estimates; with simple power-law analytical models, correction procedures are devised, as well as a global constraint that enforces Parseval’s identity. Several new results are thus obtained: (1) The analytical variance estimates compare well with the sample variance calculated for the Bartlett spectrum and the variance of the inertial subrange of the cospectrum is shown to be relatively much larger than that of the spectrum. (2) Ogives and spectra estimates with reduced bias are calculated. (3) The bias of the smoothed spectrum and ogive is shown to be negligible at the higher frequencies. (4) The ogives and spectra thus calculated have better frequency resolution than the Bartlett spectrum, with (5) gradually increasing variance and relative error towards the low frequencies. (6) Power-law identification and extraction of the rate of dissipation of turbulence kinetic energy are possible directly from the ogive. (7) The smoothed cross-spectrum is a valid inner product and therefore an acceptable candidate for coherence and spectral correlation coefficient estimation by means of the Cauchy–Schwarz inequality. The quadrature, phase function, coherence function and spectral correlation function obtained from the smoothed spectral estimates compare well with the classical ones derived from the Bartlett spectrum. 相似文献
13.
两层正压准平衡海洋模型的中纬度自由涡旋波动解 总被引：2，自引：2，他引：0
建立了具有瑞利摩擦且仅考虑大洋西海岸或同时考虑大洋东、西海岸的两层正压准平衡海洋模型,并做了解析求解,用以研究中纬度的自由涡旋波。得到的主要结论有:模型中该波动的解为波包。在仅考虑大洋西海岸时该波包的载频频率是连续谱;而同时考虑大洋东、西海岸时其为离散谱;且均有载频频率越高(周期越短)水平尺度越大的特点,对过分低频的波动,则会使准平衡的假定不再适用。模型中该波动波包载频的周期约在26天至24年。因考虑了摩擦,该波包的振幅随时间呈指数衰减,但摩擦系数的大小仅影响其衰减程度而不改变其空间结构,最终该波包振幅趋于0,故该两层正压海洋模型的解就趋于大气风场的强迫特解。模型中该波包的载频都是西传的;频率较高则西传较快,波包的特性和变形都很明显;频率低,则西传慢,其波形接近平面简谐波。在该两层正压模型中,该波动上层流场与正压模型中的流动类似,而下层海洋流动则其流速与上层海洋相同,而流向相反。该模型中该波动的性质是准平衡(准无辐散)的涡旋波,当摩擦不太大且其水平尺度在10km以上时,其性质则为准地转的Rossby波。 相似文献
14.
Models of the wave boundary layer 总被引：2，自引：1，他引：1
A general approach to model the structure of the wave boundary layer, based on the nonlinear Reynolds equations in a curvilinear system of coordinates, is described. Both spectral and numerical grid models are used. The energetic interactions between wind and wave in terms of Miles' parameter are studied. For waves outrunning or running against the wind, the range of the inverse flux of energy is found. For waves running slower than the wind, quadratic growth of is established. Vertical profiles of the wave momentum flux for different fetches are given. Following P. Janssen, a one-dimensional analytical model of the wave boundary layer is suggested. The effect of waves on the drag coefficient is analyzed. 相似文献
15.
资料同化中二维特征长度随模式分辨率变化的分析研究 总被引：3，自引：0，他引：3
特征长度是资料同化中的重要参量,决定了观测信息在空间的传递特征,而特征长度随模式水平分辨率增减而变化的特点与背景误差湍流功率谱分布特点密切相关。通过对不同来源实际资料计算获得的特征长度数据分析和对理想数据数值试验分析,结果表明随着模式分辨率的提高,特征长度会按照二次根的规律递减。特征长度的这种变化由背景误差湍流功率谱,特别是与次天气尺度（20～60波）到中尺度波（大于60波）的湍流功率谱斜率特征决定。当湍流功率谱斜率从-5/3变化到-4时,特征长度随模式分辨率变化的敏感性降低。作者估计出的温度场的实际背景误差湍流功率谱斜率在次天气尺度到中尺度大约在-2.8左右。对特征长度的估计除传统方法外,可以根据背景误差的湍流功率谱斜率特征来更方便地给出,该方法可作为传统方法的补充来匹配应用。 相似文献
16.
Fetch Limited Drag Coefficients 总被引：5，自引：1，他引：5
Measurements made at a tower located 2 km off the coast of Denmark inshallow water during the Risø Air Sea Experiment (RASEX) are analyzedto investigate the behaviour of the drag coefficient in the coastal zone.For a given wind speed, the drag coefficient is larger during conditions ofshort fetch (2-5 km) off-shore flow with younger growing waves than it isfor longer fetch (15-25 km) on-shore flow. For the strongest on-shorewinds, wave breaking enhances the drag coefficient. Variation of the neutral drag coefficient in RASEX is dominated byvariation of wave age, frequency bandwidth of the wave spectra and windspeed. The frequency bandwidth is proportional to the broadness of the waveheight spectra and is largest during conditions of light wind speeds. Usingthe RASEX data, simple models of the drag coefficient and roughness length are developed in terms of wind speed, wave age and bandwidth. An off-shoreflow model of the drag coefficient in terms of nondimensional fetch isdeveloped for situations when the wave state is not known. 相似文献
17.
B. W. Golding 《Meteorology and Atmospheric Physics》1992,50(1-3):89-103
Summary A semi-implicit non-hydrostatic mesoscale forescasting model, which is used operationally in the United Kingdom Meteorological Office, has been reformulated using two time levels and semi-Lagrangian advection so as to permit longer timesteps. The boundaries are found to be an important influence on the model's stability and two methods of suppressing wave reflection are described with the aid of a one-dimensional experiment. The model's responses to two dimensional flow over a ridge and to three-dimensional flow over an isolated mountain are then demonstrated. The reformulated model is more efficient than the original provided a timestep at least twice as long can be used. It is also superior both in having minimal damping (except at the boundaries), and in the accuracy of the advection scheme. 相似文献
18.
Second-Order Modelling of Turbulence in Katabatic Flows 总被引：1，自引：1，他引：0
Bruce Denby 《Boundary-Layer Meteorology》1999,92(1):65-98
A complete one-dimensional second-order closure model is used to simulate katabatic flows observed on glaciers and ice caps. The model is tested with two different closure assumptions for the viscous dissipation, one based on a prognostic equation for and the other on a diagnostic buoyant length scale. Both formulations give quite similar results. Model simulations are compared to observations made over sloping ice surfaces during periods dominated by katabatic flow. In general, good agreement is found for both mean wind and temperature profiles as well as eddy correlation measurements. It is also found that the turbulent transport terms play an important role in katabatic flows as opposed to the classical stable boundary layer where these terms are usually ignored. Even the turbulent transport of temperature variance, which leads to the well-known countergradient term in unstable boundary layers, is relatively important for modelling the observed temperature profiles. The effect of these terms on the flux-profile relationships, using observed and simulated profiles, is also discussed. 相似文献
19.
Gervásio Annes Degrazia Umberto Rizza Franciano Scremin Puhales Antônio Gledson Goulart Jonas Carvalho Guilherme Sausen Welter Edson Pereira Marques Filho 《Boundary-Layer Meteorology》2009,131(2):277-292
A variable vertical mesh spacing for large-eddy simulation (LES) models in a convective boundary layer (CBL) is proposed.
The argument is based on the fact that in the vertical direction the turbulence near the surface in a CBL is inhomogeneous
and therefore the subfilter-scale effects depend on the relative location between the spectral peak of the vertical velocity
and the filter cut-off wavelength. From the physical point of view, this lack of homogeneity makes the vertical mesh spacing
the principal length scale and, as a consequence, the LES filter cut-off wavenumber is expressed in terms of this characteristic
length scale. Assuming that the inertial subrange initial frequency is equal to the LES filter cut-off frequency and employing
fitting expressions that describe the observed convective turbulent energy one-dimensional spectra, it is feasible to derive
a relation to calculate the variable vertical mesh spacing. The incorporation of this variable vertical grid within a LES
model shows that both the mean quantities (and their gradients) and the turbulent statistics quantities are well described
near to the ground level, where the LES predictions are known to be a challenging task. 相似文献
20.
Hendrik Tolman 《Journal of Atmospheric & Ocean Science》2002,8(1):67-83
Third-generation ocean wave models include a so-called limiter in the integration of the source terms to guarantee numerical stability at economical numerical time steps. The original limiter has previously been associated with the sensitivity of model results to the numerical time step. More recent limiters appear to remove this sensitivity by eliminating the numerical convergence from the resulting integration scheme. This is contrary to rudimentary numerical principles as well as the underlying philosophy of third-generation wave models. The present study investigates the effects of limiters and large model time steps using time-limited wave growth test. It is shown that the conventional limiter results in stable model results even if the numerical time step violates the time scales of wave growth. Contrary to common belief, its impact is not necessarily limited to the equilibrium range of the spectrum, and the limiter systematically enhances growth rates in the intermediate stages of wave growth. Particularly initial growth errors increase significantly with increasing maximum discrete spectral frequency f max . Relaxation of the limiter is shown to reduce initial growth errors, but does so at the expense of notable errors in the spectral shape. In the present paper the limiter was relaxed by introducing a new asymmetric limiter that retains full convergence. Initial results obtained with this limiter are similar to those of the advocated nonconvergent limiters. Although this limiter still needs rigorous testing and further development, its initial results suggest that there is no justification for using nonconvergent limiters. 相似文献