The observed analysis on the wave spectra of Hurricane Juan (2003)

Hurricane Juan provides an excellent opportunity to probe into the detailed wave spectral patterns and spectral parameters of a hurricane system, with enough wave spectral observations around Juan＇s track in the deep ocean and shallow coastal water. In this study, Hurricane Juan and wave observation stations around Juan＇s track are introduced. Variations of wave composition are discussed and analyzed based on time series of one-dimensional frequency spectra, as well as wave steepness around Juan＇s track： before, during, and after Juan＇s passing. Wave spectral involvement is studied based on the observed one-dimensional spectra and two-dimensional spectra during the hurricane. The standardization method of the observed wave spectra during Hurricane Juan is discussed, and the standardized spectra show relatively conservative behavior, in spite of the huge variation in wave spectral energy, spectral peak, and peak frequency during this hurricane. Spectral widths＇ variation during Hurricane Juan are calculated and analyzed. A two-layer nesting WW3 model simulation is applied to simulate the one-dimensional and two-dimensional wave spectra, in order to examine WW3＇s ability in simulating detailed wave structure during Hurricane Juan.

Estimation Approaches of ηUV,PUV and UV Directional Wave Spectra and Their Comparison

The observation and estimation of directional spectra of sea waves is one of the essential subjects of study of oceanic dynamics. On the basis of the irregular linear wave theory, estimation methods for i/UV, PUV and VV directional wave spectra are derived. By using ij and PUV data measured in-situ, directional wave spectra are estimated, meanwhile the virtues and defects of various spectra are comparied. This method provide a basis for the observations of sea waves.

On the Bandwidth Parameter of Wind-Wave Spectra

In Light of the analysis of the physical implication and underlying assumption of the bandwidth parameter epsilon of wave spectrum, a time-averaging method is used to evaluate epsilon of the JONSWAP spectrum for different sea states. The resulting values of epsilon, which vary from 0.44 to 0.53 depending on the dimensionless fetch, are physically meaningful and reasonable. The same method is also used to compute epsilon from wind-wave records measured in a flume under different wind speeds at different fetches. The computed values of epsilon, which vary with wind fetches and speeds too, are compared with those evaluated for the JONSWAP spectrum.

A new modulation transfer function for ocean wave spectra retrieval from X-band marine radar imagery

When imaging ocean surface waves by X-band marine radar,the radar backscatter from the sea surface is modulated by the long surface gravity waves. The modulation transfer function(MTF) comprises tilt,hydrodynamic,and shadowing modulations. A conventional linear MTF was derived using HH-polarized radar observations under conditions of deep water. In this study,we propose a new quadratic polynomial MTF based on VV-polarized radar measurements taken from heterogeneous nearshore wave fields. This new MTF is obtained using a radar-observed image spectrum and in situ buoy-measured wave frequency spectrum. We validate the MTF by comparing peak and mean wave periods retrieved from X-band marine radar image sequences with those measured by the buoy. It is shown that the retrieval accuracies of peak and mean wave periods of the new MTF are better than the conventional MTF. The results also show that the bias and root mean square errors of the peak and mean wave periods of the new MTF are 0.05 and 0.88 s,and 0.32 and 0.53 s,respectively,while those of the conventional MTF are 0.61 and 0.98 s,and 1.39 and 1.48 s,respectively. Moreover,it is also shown that the retrieval results are insensitive to the coefficients in the proposed MTF.

PROPAGATION OF INTERNAL INERTIO-GRAVITY WAVE SPECTRA IN VERTICAL WIND SHEAR ENVIRONMENTS

The variation of the spectral structure of the internal inertio-gravity waves (ⅡGWs) propagating in the atmospheric wind shear environments is discussed in this paper. From the hydrodynamic equation set in Boussinesq approximation, a spectral propagation equation ⅡGWs satisfy is derived, then the spectral correspondence in the upper atmosphere is numerically calculated, after a forced spectrum is given as a Van- Zandt one at the lower boundary. The results show that if ⅡGWs do not encounter the critical-layer absorp- tion, then their spectral structure may be not changed significantly; otherwise it may be changed greatly, and a few of spectral components are filtered. Also the isotropy of the assumed VanZandt spectrum is distorted in upward-propagating process. That is the directional filtering effect of the atmospheric wind on the gravity wave spectrum.

Study on Wave Characteristics from the South Atlantic Ocean to the Gulf of Guinea Based on Short-Term Numerical Simulation in Winter Season

Waves play a major role in the ocean phenomena in the Gulf of Guinea(GoG). In order to reveal the spatial-temporal distribution characteristics and the propagation mechanism of waves from the South Atlantic Ocean to the GoG, 4typical points located in mid-latitude of South Atlantic(14°30′W, 30°0′S), south of the GoG(10°30′W, 15°0′S), offshore of the GoG(0°0′, 0°0′) and near shore of the GoG(6°4′58.8″W, 4°3′36″S) are selected, and waves from Atlantic Ocean to GoG are simulated by using a two-layer-nesting wave numerical model SWAN(Simulating Waves Nearshore). The results show that the hybrid waves(waves hereafter) and the swells have strong relationship with local wind in Roaring Forties and at mid-latitude of South Atlantic Ocean, while there is no obvious correlation between waves and local winds in the GoG. Swells are generated in the South Atlantic Ocean and propagate into the GoG. 2D wave spectra at the four selected typical points are simulated. The spectral pattern and wave component structure indicate that the wave system in GoG is dominated by the S-SW swells generated from Roaring Forties and mid-latitude of South Atlantic, whether it is at maximum(2.2-2.8 m), medium(1.8-2.2 m) or minimum(1.2 m) significant wave height in the GoG during simulation period.

A speckle noise suppression method based on surface waves investigation and monitoring data

The internal energy distribution of waves can be described using ocean-wave spectra.In many ways,obtaining wave spectra on a global scale is critical.Surface waves investigation and monitoring onboard the Chinese-French oceanography satellite is the first space-borne instrument for detecting wave spectra specially,which was launched on October 29,2018.It can avoid the shortage of synthetic aperture radar detection results while still having some problems,especially with the effects of speckle noise.In this study,a method to suppress the speckle noise is proposed.First,the empirical formula for background speckle noise is established.Second,many spatio-temporal representative fluctuation spectra are classified and averaged.Third,rational transfer function filtering is used to obtain speckle noise close to the along-track direction.Finally,a signal-to-noise ratio threshold is used to suppress the abnormal speckle noise.This method solves the problems existing in previous denoising methods,such as excessive denoising in the along-track direction and the inability of some abnormal noises to be denoised in the two-dimensional directional wave spectra.

Study on the growth of wind wave frequency spectra generated by cold waves in the northern East China Sea

The growth of frequency spectra and spectral parameters of wind waves generated by cold waves, a kind of severe weather system, in the northern East China Sea is studied in this paper. Based on a third-generation wave action model(the Simulating WAves Nearshore model), simulations were developed to analyze the spatiotemporal characteristics of wind waves and to output spectral data. It is shown that the cold wave-induced spectra can be well described by the modified Joint North Sea Wave Project spectral form. The growth of wave spectra is comprehensively reflected by the evolution of the three characteristic parameters: peak frequency, spectral peak and wave energy. Besides, the approximations of dependences between spectral parameters and the three types of universal induced factors are obtained with the least squares method and compared systematically. Fetch and peak frequency turn out to be suitable parameters to describe the spectral parameters, while the dependences on the inverse wave age vary in different sea areas. In general, the derived relationships improve on results from previous studies for better practical application of the wind wave frequency spectrum in the northern East China Sea.

NUMERICAL SIMULATION OF SEA SURFACE DIRECTIONAL WAVE SPECTRA UNDER TYPHOON WIND FORCING

Numercial simulation of sea surface directional wave spectra under typhoon wind forcing in the South China Sea （SCS） was carreid out using the WAVEWATCH-Ⅲ wave model. The simulation was run for 210 h until the Typhoon Damrey （2005） approached Vietnam. The simulated data were compared with buoy observations, which were obtained in the northwest sea area of Hainan Island. The results show that the significant wave height, wave direction, wave length and frequency spetra agree well with buoy observations. The spatial characteristics of the signifciant wave height, mean wave period, mean wave length, wave age and directional spectra depend on the relative position from the typhoon center. Also, the misalignment between local wind and wave directions were investigated.

Study on wave packet dynamics of E^1Σ_g^+ state of Li_2 with femtosecond-resolved photoelectron spectra

Wave packet dynamics of the Li2 molecule are investigated by using the time-dependent quantum wave packet method, and the time-resolved photoelectron spectra of the Li2 molecule are calculated. The time-resolved wave packet theory is used to reasonably interpret the phenomena of the photoelectron spectra for different parameters. Our calculation shows that the loss of the wave packets in the shelf state area of E1∑g＋ plays a prominent role in the process of photoionization with the increase of the delay time. Moreover, the oscillation of the wave packet on the E1∑g＋ curve symbolizes a decreasing process of energy.

Statistics of gravity wave spectra in the troposphere and lower stratosphere over Beijing

We utilize the temperature profiles with a height resolution of 50-m obtained over the Beijing Observatory in the period between January of 2002 and December of 2002 to study vertical wavenumber spectra of normalized temperature fluctuations in the 1.67-8.02 km and 13.57-19.92 km altitude ranges and compare them with linear saturation model.Results indicate that individual vertical wavenumber spectra reveal a considerable variability in both slope and amplitude.The observed variability is not consistent with the predictions of linear saturation model.However,mean vertical wavenumber spectra in the troposphere measured at different seasons and different local times show great similarities with fairly uniform negative slopes of ～3.0 and amplitudes proportional to N 4,suggesting that the seasonal mean spectra observed in the troposphere completely obey the linear saturation model and are unique at present.In contrast,while the spectral slopes of the mean vertical wavenumber spectra in the lower stratosphere tend to support the explanation of the observed temperature fluctuations by linear saturation model,the spectral amplitudes diverge significantly from linear saturation model,suggesting that the seasonal mean spectra in the lower stratosphere do not obey the linear saturation model and are unique at present.The dominant vertical wavelengths derived from the observed mean vertical wavenumber spectra are estimated to be ～3.2-～2.1 km in the troposphere and lower stratosphere,which is generally consistent with those reported in the literature.

THEORETICAL ANALYSIS AND EXPERIMENTAL VERIFICATION ON TERNARY-WAVES METHOD TO COMPILE ACCELERATED SPECTRA

The equivalent damage calculation formulae of fatigue crack formation andgrowth are established. In order to compile the fatigue crack formation and growth accelerated loadspectra, the main wave shapes and load sequence of the actual load spectrum are kept constant, andthe carrier waves are cut off. And secondary waves are put together into new secondary waves toshorten the test time according to the equivalent damage calculation formulae respectively. Then bythe fatigue cumulative damage calculation of the fatigue crack formation and growth accelerated loadspectra, the one corresponding to the bigger damage is determined as the fatigue accelerated testload spectrum. Therefore in the test process, the fatigue accelerated test spectrum may be appliedtill fatigue failure, the engineering fatigue crack length of full-scale structure need not beinspected, and the fatigue crack formation accelerated load spectrum need not be transferred intothe fatigue crack growth accelerated load spectrum. Finally, it is verified by tests of two kinds ofspecimens that the damages of the specimens caused by the accelerated load spectra are near tothose by the actual load spectra; namely, the tested life of actual load spectra is similar to thatof accelerated load spectra. But the test time of accelerated load spectra is shortened by aboutthree-quarters that of actual load spectra. From these tests, it is also found that the fatigueaccelerated test spectrum has an advantage over FALSTAFF spectra.

REPRESENTATION OF STATISTICAL PROPERTIES OF WAVE GROUPS FOR SEA PROCESSES WITH DOUBLE-PEAKED SPECTRA

A method using group-induced second-order long waves(GSLW) to represent statistical properties of wave groups with double-peaked spectra is put forward in this paper on the basis of the GSLW theory. The GSLW is regarded as a weighted linear superimposition of the second-order long Wave induced by the low peak frequency section and that induced by the high peak frequency section. There is a parabolic relationship between the GSLW and the wave envelope. Then the probability density function and the distribution function of the GSLW amplitude are derived. Thus the formulas for the average time duration and the mean length of runs can be derived. Good agreement between theoretical results and measured values was achieved. as verified with the measured double-peaked spectra in different regions.

Power and Cross-Spectra for the Turbulent Atmospheric Motion and Transports in the Domain of Wave Number Frequency Space: Theoretical Aspects

The study of large-scale atmospheric turbulence and transport processes is of vital importance in the general circulation of the atmosphere. The governing equations of the power and cross-spectra for the atmospheric motion and transports in the domain of wave number frequency space have been derived. The contributions of the nonlinear interactions of the atmospheric waves in velocity and temperature fields to the conversion of kinetic and potential energies and to the meridional transports of angular momentum and sensible heat in the atmosphere have been discussed.

Simulation of Typhoon-Driven Waves in the Yangtze Estuary with Multiple-Nested Wave Models

Typhoon-generated waves are simulated with two numerical wave models, the SWAN model for the coastal and Yangtze Estuary domain, nested within the WAVEWATCHIII （WW3） for the basin-scale East China Sea domain. Typhoon No. 8114 is chosen because it was very strong, and generated high waves in the Estuary. WW3 was implemented for the East China Sea coarse-resolution computational domain, to simulate the waves over a large spatial scale and provide boundary conditions for SWAN model simulations, implemented on a fine-resolution nested domain for the Yangtze Estuary area. The Takahashi wind model is applied to the simulation of the East China Sea scale （3-hourly） and Yangtze Estuary scale （1-hourly） winds. Simulations of significant wave heights in the East China Sea show that the highest waves are on the right side of the storm track, and maxima tend to occur at the eastern deep-water open boundary of the Yangtze Estuary. In the Yangtze Estuary, incoming swell is dominant over locally generated waves before the typhoon approaches the Estuary. As the typhoon approaches the Estuary, wind waves and swell coexist, and the wave direction is mainly influenced by the swell direction and the complex topography.

Wave Characteristics at the South Part of the Radial Sand Ridges of the Southern Yellow Sea

Based on one-year wave field data measured at the south part of the radial sand ridges of the Southern Yellow Sea, the wave statistical characteristics, wave spectrum and wave group properties are analyzed. The results show that the significant wave height （H1/3） varies from 0.15 to 2.22 m with the average of 0.59 m and the mean wave period （Tmean） varies from 2.06 to 6.82 s with the average of 3.71 s. The percentage of single peak in the wave spectra is 88.6 during the measurement period, in which 36.3% of the waves are pure wind waves and the rest are young swells. The percentage with the significant wave height larger than 1 m is 12.4. The dominant wave directions in the study area are WNW, W, ESE, E and NW. The relationships among the characteristic wave heights, the characteristic wave periods, and the wave spectral parameters are identified. It is found that the tentative spectral model is suitable for the quantitative description of the wave spectrum in the study area, while the run lengths of the wave group estimated from the measured data are generally larger than those in other sea areas.

Nearshore Wave Field Analysis Using SAR Images

Satellite remote sensing technique offers a wide range of information, and is one of the tools for ocean wave observation. This paper discusses the limitations of Synthetic Aperture Radar (SAR) images in wave field analysis. It is found that the wave field analysis is affected by the gray value distribution of image and the relationship between satellite travel and wave propagation directions. Since human activities and coastal engineering are performed in nearshore areas, some issues are discussed for nearshore SAR image analysis. Several case studies show that the wave parameters estimated from nearshore SAR images are quite different from in situ measurements, suggesting that the wave information derived from nearshore SAR images cannot appropriately represent the wave characteristics. One of the reasons is that the wave field is non homogeneous in the nearshore area.

基于云雷达资料的那曲对流云粒子相态识别研究

本文利用第三次青藏高原大气科学试验的Ka波段云雷达资料,结合微波辐射计和探空资料,提出了以模糊逻辑算法为框架的相态识别方法,并利用那曲两个典型对流云个例对方法效果进行了分析。通过与前人方法的对比和对不同相态粒子回波强度谱的统计,进一步验证了本文方法的可靠性。结果表明:利用雷达功率谱资料反演下落末速度并代替径向速度作为相态识别的参量之一,可提升对流云内粒子相态分类结果的合理性。零度层亮带和抬升凝结高度参量的使用,能够进一步优化相态识别的初步结果。固态云粒子的下落末速度远低于相同反射率因子的降水粒子,多模态/多谱峰的谱形态特征能够帮助识别混合相态粒子。

Spectra地震频谱能量吸收分析技术在乌审召地区天然气勘探中的应用

为了确定岩体内部的孔隙及流体性质，运用地震衰减分析来区分地震信号谱与振幅特征的变化，分析在包含孔隙和裂隙的复杂环境下岩石属性特征和波的传播特征，乌审召地区主要目标层为上古生界二叠系石盒子组盒8段储层．该目标砂岩发育，但储层横向变化快，通过对乌审召实际地震资料处理结果表明，在频率域吸收衰减异常与岩石中含气有关，通过方法实践，采用该地震分析方法计算的衰减模式与高产区的关系比较确定，能够帮助确定新的潜在区域和勘探目标。

Nonlinear interactions among internal tidal waves in the northeastern South China Sea

We used a set of 75-day long ADCP data from the northeastern South China Sea(SCS) to investigate nonlinear interactions among freely propagating internal tidal waves.The kinetic energy spectra displayed significant peaks at some higher tidal frequencies,such as O1M2(O1+M2),and M4(M2 +M2),where O1 is the lunar diurnal internal tide,M2 is the lunar semidiurnal internal tide,and M4 is the first higher harmonic frequency of M2.These higher tidal harmonic frequency peaks,as well as the fundamental tidal harmonic peaks,show a σ-2.3 spectral falloff rate with frequency.In addition,we explored the possible generation mechanism of higher tidal harmonics.Analysis on the rotary and bicoherence spectra suggests that strong forced non-resonant interaction induced by nonlinear advections was the dominant physical mechanism that induced these higher tidal harmonics.Moreover,the energetic,freely propagating semidiurnal(M2) internal tidal wave played the most crucial role in these interactions.These results indicate that strong nonlinear forced non-resonant interactions among internal tides can be one of the processes responsible for the redistribution of energy in the internal wave spectrum.