Numerical simulation and preliminary analysis of typhoon waves during three typhoons in the Yellow Sea and East China Sea

In this study, typhoon waves generated during three typhoons(Damrey(1210), Fung-wong(1416), and Chan-hom(1509)) in the Yellow Sea and East China Sea were simulated in a simulating waves nearshore(SWAN) model, and the wind forcing was constructed by combining reanalyzed wind data with a Holland typhoon wind model. Various parameters, such as the Holland fitting parameter(B) and the maximum wind radius(R), were investigated in sensitivity experiments in the Holland model that affect the wind field construction. Six different formulations were considered and the parameters determined by comparing the simulated wind results with in-situ wind measurements. The key factors affecting wave growth and dissipation processes from deep to shallow waters were studied, including wind input, whitecapping, and bottom friction. Comparison with in-situ wave measurements suggested that the KOMEN scheme(wind input exponential growth and whitecapping energy dissipation) and the JONSWAP scheme(dissipation of bottom friction) resulted in good reproduction of the significant wave height of typhoon waves. A preliminary analysis of the wave characteristics in terms of wind-sea and swell wave revealed that swell waves dominated with the distance of R to the eye of the typhoon, while wind-sea prevailed in the outer region up to six to eight times the R values despite a clear misalignment between wind and waves. The results support the hypothesis that nonlinear wave-wave interactions may play a key role in the formation of wave characteristics.     

WIND WAVES SIMULATION IN THE NORTH AREA OF THE SOUTH CHINA SEA

A third generation wave model was developed to simulate wind waves in the South China Sea near Hong Kong. The model solves the energy conservation equation of the two dimensional wave spectrum by directly computing the nonlinear energy interaction among waves of different frequencies, thus avoiding the imposition of restrictions on the shape of the predicted spectra. The use of an upwind difference scheme in the advective terms produces an artificial diffusion which partly compensates the dispersive effect due to the phase velocity differences among various wave components. The use of a semi-implicit scheme for the source terms together with a special treatment of the high frequency tail of the spectrum allows a large time integration step. Verification of the model was done for wave hindcasting studies under conditions of two typhoons and two cold fronts in the north part of the South China Sea near Hong Kong . The model results agree well with the field measurements except that the presence of a dista     

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Directional spectrum of wind waves: Part I—model and derivation

A new model on the directional spectrum of wind waves for deep water is proposed based on the statistics of wind waves. This model contains three parameters: the wave age, the inverse spectral bandwidth and the local spectral-peak angular frequency. The inverse spectral bandwidth is a robust parameter for describing the spectral steepness of wind waves. Using the inverse spectral bandwidth parameter, the proposed model can well describe various observations obtained from the open ocean and laboratory tank.     

Directional Spectrum of Wind Waves: Part Ⅰ- Model and Derivation

1　Introduction　Numerousinvestigationsondeepwaterwindwavespectrumhavebeen performed (Phillips ,195 8;Bretschneider,195 9;PiersonandMoscowitz ,196 4;Hasselmannetal.,1973;Donelanetal.,1985 ;Ban ner ,1990 ;Wenetal.,1999) .Ondimensionalground ,Phillips (195 8)suggestedthattheequilibriumfre quencyspectrumofwindwavesfordeepwatershouldbe proportionaltoω- 5,andthecorrespondingwavenumberspectrumshouldbe proportionaltok- 4,whereωistheangularfrequencyandkisthewavenumber.Forfully developedwindwaves…     

两种海浪模式对一次台风浪过程的模拟分析

以CCMP（Cross—Calibrated,Multi—Platfoml）风场为驱动场,分别驱动目前国际先进的第3代海浪模式ww3（WAVEWATCH—III）、SWAN（Simulating WAves Nearshore）,对2010年9月发生在东中国海的台风“圆规”所致的台风浪进行数值模拟,就台风浪的特征进行分析,并对比分析两个海浪模式的模拟效果。结果表明：1）以CCMP风场分别驱动WW3、SWAN海浪模式,可以较好地模拟发生在东中国海的台风浪,风向与波向保持了大体一致,波高与风速的分布特征保持了很好的一致性;2）综合相关系数、偏差、均方根误差、平均绝对误差来看,两个模式模拟的有效波高（SWH—Significant Wdve Height）都具有较高精度,SWAN模拟的SWH略低于观测值,WW3模拟的SWH与观测值更为接近;3）台风浪可给琉球群岛海域带来5m左右的大浪,台风浪进入东海后,波高、风速都有一定程度的增加,当台风沿西北路径穿越朝鲜半岛时,受到半岛地形的巨大影响,风速和波高都明显降低。     

Directional Spectrum of Wind Waves: Part Ⅱ- Comparison and Confirmation

1　Introduction1.1　Proposed ModelonDirectionalFrequencySpec trum　ThisisthePartⅡofthetwo papersetondirection alspectraofwindwaves.Anewmodelonthedirec tionalspectrumofwindwavesfordeepwaterispro posedbasedonthestatisticsofwindwavesinthePartⅠ .Substituting (4 5 )ofPartⅠinto (4 0 )andaddingapeak enhancementitemγΓ,weobtainS(ω ,) =0 .0 0 93αaαwD( ,k) ωpω2 ξ- 4g2ω5×exp - 2 ξ+14[bωp +(1-b)ωp]4ω4 γΓ. (1)Here ,αaisthewaveagefactorofspectralcoefficientdefinedbyαa = ω0 .55…     

Numerical simulation and preliminary analysis on ocean waves during Typhoon Nesat in South China Sea and adjacent areas

Using the wave model WAVEWATCH III(WW3), we simulated the generation and propagation of typhoon waves in the South China Sea and adjacent areas during the passage of typhoon Nesat(2011). In the domain 100°–145°E and 0°–35°N, the model was forced by the cross-calibrated multi-platform(CCMP) wind fi elds of September 15 to October 5, 2011. We then validated the simulation results against wave radar data observed from an oil platform and altimeter data from the Jason-2 satellite. The simulated waves were characterized by fi ve points along track using the Spectrum Integration Method(SIM) and the Spectrum Partitioning Method(SPM), by which wind sea and swell components of the 1D and 2D wave spectra are separated. There was reasonable agreement between the model results and observations, although the WW3 wave model may underestimate swell wave height. Signifi cant wave heights are large along the typhoon track and are noticeably greater on the right of the track than on the left. Swells from the east are largely unable to enter the South China Sea because of the obstruction due to the Philippine Islands. During the initial stage and later period of the typhoon, swells at the fi ve points were generated by the propagation of waves that were created by typhoons Haitang and Nalgae. Of the two methods, the 2D SPM method is more accurate than the 1D SIM which overestimates the separation frequency under low winds, but the SIM method is more convenient because it does not require wind speed and wave direction. When the typhoon left the area, the wind sea fractions decreased rapidly. Under similar wind conditions, the points located in the South China Sea are affected less than those points situated in the open sea because of the infl uence of the complex internal topography of the South China Sea. The results reveal the characteristic wind sea and swell features of the South China Sea and adjacent areas in response to typhoon Nesat, and provide a reference for swell forecasting and offshore structural designs.     

A THREE-DIMENSIONAL THERMOCLINE MODEL FOR THE YELLOW SEA AND NORTHERN EAST CHINA SEA

A time-dependent, three-dimensional finite difference model is presented for simulating the stratifiedYellow Sea and northem East China Sea. The mode is forced by time-dependent observed wind, surfaceflux of heat, and tidal turbulence. With this model, momentum and temperature distribution can be computed,and an approximation for the sub-grid scale effects is introduced by the use of mass and momentumexchange coefficients. The vertical exchanges are quite dependent on these assumed coefficents, whichare complicated functions of the turbulence energy of tide and wind, of the stratified strength and otherfactors. This model was applied to describe the mechanics of the variations in strength and thickness ofthe thermocline covering almost the whole Yellow Sea and northern East Chna Sea in summer. Comparisonsof the computed output with obtained survey data led to some important conclusions.     

Comparison of TOPEX/POSEIDON altimeter derived wave period with ocean buoy data in the East China Sea and South China Sea

Altimeter wave period data obtained from continental shelf seas are analyzed in this paper. Empirical models are introduced for zero up-crossing and peak wave period calculation with TOPEX/POSEIDON data. Their performances are assessed using independent validation dataset in four sites in the open ocean of China. To provide more accurate wave period estimation, new coefficients are applied to reliable in situ data. Comparison of our estimated the wave periods with new linear calibrations based on independent data of Seapac 2100 deployed in the East China Sea and South China Sea showed that the accuracy was improved over estimates determined from earlier empirical models. Regional analysis indicated that the wave period model works better under wind sea condition.     

近岸带波浪传播过程中波性质的统计对比分析

通过对粤东后江湾近岸带垂岸方向上4个测站,同步观测到的波浪数据进行频域统计分析,初步探讨分析了波浪近岸传播过程中波浪统计性质的变化规律。结果表明:碎波带内波的频谱多峰特征显著,峰频两侧均存在着显著能量峰值,峰频能量发生转移;波浪经过破碎后,约束长波能量被释放出来;波浪向岸过程中谱宽度(ε)变大,同时谱尖度(Qp)减小,显著波陡(Ss)增大,峰值周期(Tp)增大,平均周期(Tm02)减小。     

Comparison and analysis of Envisat ASAR ocean wave spectra with buoy data in the northern Pacific Ocean

The validation and assessment of Envisat advanced synthetic aperture radar (ASAR) ocean wave spectra products are important to their application in ocean wave numerical predictions. Six-year ASAR wave spectra data are compared with one-dimensional (1D) wave spectra of 55 co-located moored buoy observations in the northern Pacific Ocean. The ASAR wave spectra data are firstly quality control filtered and spatio-temporal matched with buoy data. The comparisons are then performed in terms of 1D wave spectra, significant wave height (SWH) and mean wave period (MWP) in different spatio-temporal offsets respectively. SWH comparison results show the evident dependence of SWH biases on wind speed and the ASAR SWH saturation effect. The ASAR wave spectra tend to underestimate SWH at high wind speeds and overestimate SWH at low wind speeds. MWP comparison results show that MWP has a systematic bias and therefore it should be bias-modified before used. The comparisons of 1D wave spectra show that both wave spectra agree better at low frequencies than at high frequencies, which indicates the ASAR data cannot resolve the high frequency waves.     

Wind energy input in coastal seas east of China

This study investigates the wind energy input, an important source of mechanical energy, in the coastal seas east of China. Using the wind field from the high-resolution sea surface meteorology dataset in the Bohai Sea, Yellow Sea, and East China Sea, we studied the wind energy input through surface ageostrophic currents and surface waves. Using a simple analytical formula for the Ekman Spiral with timedependent wind, the wind energy input through ageostrophic currents was estimated at ～22 GW averaged from 1960 to 2007, and through use of an empirical formula, the wind energy input through surface waves was estimated at ～169 GW. We also examined the seasonal variation and long-term tendency of mechanical energy from wind stress, and found that the wind energy input to the East China Sea decreased before the 1980s, and then subsequently increased, which is contrary to what has been found for the Bohai Sea and Yellow Sea. More complicated physical processes and varying diffusivity need to be taken into account in future studies.     

Interpretation of sea surface wind interannual vector EOFs over the China seas

Using interpolation and averaging methods, we analyzed the sea surface wind data obtained from December 1992 to November 2008 by the scatterometers ERS-1, ERS-2, and QuikSCAT in the area of 2°N–39 °N, 105°E–130°E, and we reported the monthly mean distributions of the sea surface wind field. A vector empirical orthogonal function (VEOF) method was employed to study the data and three temporal and spatial patterns were obtained. The first interannual VEOF accounts for 26% of the interannual variance and displays the interannual variability of the East Asian monsoon. The second interannual VEOF accounts for 21% of the variance and reflects the response of China sea winds to El Niño events. The temporal mode of VEOF-2 is in good agreement with the curve of the Niño 3.4 index with a four-month lag. The spatial mode of VEOF-2 indicates that four months after an El Niño event, the southwesterly anomalous winds over the northern South China Sea, the East China Sea, the Yellow Sea, and the Bohai Sea can weaken the prevailing winds in winter, and can strengthen the prevailing winds in summer. The third interannual VEOF accounts for 10% of the variance and also reflects the influence of the ENSO events to China Sea winds. The temporal mode of VEOF-3 is similar to the curve of the Southern Oscillation Index. The spatial mode of VEOF-3 shows that the northeasterly anomalous winds over the South China Sea and the southern part of the East China Sea can weaken the prevailing winds, and southwesterly anomalous winds over the northern part of the East China Sea, the Yellow Sea, and the Bohai Sea can strengthen the prevailing winds when El Niño occurs in winter. If El Niño happens in summer, the reverse is true.     

Trends in significant wave height and surface wind speed in the China Seas between 1988 and 2011

Wind and waves are key components of the climate system as they drive air-sea interactions and influence weather systems and atmospheric circulation. In marine environments, understanding surface wind and wave fields and their evolution over time is important for conducting safe and efficient human activities, such as navigation and engineering. This study considers long-term trends in the sea surface wind speed(WS) and significant wave height(SWH) in the China Seas over the period 1988–2011 using the Cross-Calibrated Multi-Platform(CCMP) ocean surface wind product and a 24-year hindcast wave dataset obtained from the WAVEWATCH-III(WW3) wave model forced with CCMP winds. The long-term trends in WS and SWH in the China Seas are analyzed over the past 24 years to provide a reference point from which to assess future climate change and offshore wind and wave energy resource development in the region. Results demonstrate that over the period 1988–2011 in the China Seas: 1) WS and SWH showed a significant increasing trend of 3.38 cm s~(-1)yr~(-1) and 1.52 cm yr~(-1), respectively; 2) there were notable regional differences in the long-term trends of WS and SWH; 3) areas with strong increasing trends were located mainly in the middle of the Tsushima Strait, the northern and southern areas of the Taiwan Strait, and in nearshore regions of the northern South China Sea; and 4) the long-term trend in WS was closely associated with El Ni?o and a significant increase in the occurrence of gale force winds in the region.     

Swells of the East China Sea

Over the past few decades, an increasing number of marine activities have been conducted in the East China Sea, including the construction of various marine structures and the passage of large ships. Marine safety issues are paramount and are becoming more important with respect to the likely increase in size of ocean waves in relation to global climate change and associated typhoons. In addition, swells also can be very dangerous because they induce the resonance of floating structures, including ships. This study focuses on an investigation of swells in the East China Sea and uses hindcast data for waves over the past 5 years in a numerical model, WAVEWATCH III (WW3), together with historical climate data. The numerical calculation domain covers the entire North West Pacific. Next, swells are separated and analyzed using simulated wave fields, and both the characteristics and generation mechanisms of swells are investigated.     

On the winter circulation of the northern South China Sea and its relation to the large scale oceanic current

The nonwind-driven mechanism of the winter circulation in the northern South China Sea is discussed. Linked by the Bashi Strait to the Pacific Ocean, the northern South Cnina Sea is treated as a part of the Pacific western boundary where the circulation variation (except the very thin surface layer) is closely related to that of the ocean interior and the effect of local wind might be neglected (at least for some seasons). Based on the assumption that the thick and strong westward current which flows in through the Bashi Strait can effectively prevent water exchange between the northern and southern South China Seas, the model sea only includes the northern part. Barotropic numerical experiments show that part of this westward current is deflected by the continental slope and forms the slope area NE current—the South China Sea Warm Current. Besides, the topographical flow fed by the extension of the western boundary current and the anticyclonic eddy born near the eastern boundary are also fundamental components of the South China Sea Warm Current. The reflection of the incident Rossby waves by the continental slope is found to be of significance in the intensification of the South China Sea Warm Current. Contribution No. 1362 from Institute of Oceanology, Academia     

Wind wave characteristics and engineering environment of the South China Sea

Wave simulation was conducted for the period 1976 to 2005 in the South China Sea (SCS) using the wave model, WAVEWATCH-III. Wave characteristics and engineering environment were studied in the region. The wind input data are from the objective reanalysis wind datasets, which assimilate meteorological data from several sources. Comparisons of significant wave heights between simulation and TOPEX/Poseidon altimeter and buoy data show a good agreement in general. By statistical analysis, the wave characteristics, such as significant wave heights, dominant wave directions, and their seasonal variations, were discussed. The largest significant wave heights are found in winter and the smallest in spring. The annual mean dominant wave direction is northeast (NE) along the southwest (SW)-NE axis, east northeast in the northwest (NW) part of SCS, and north northeast in the southeast (SE) part of SCS. The joint distributions of wave heights and wave periods (directions) were studied. The results show a single peak pattern for joint significant wave heights and periods, and a double peak pattern for joint significant wave heights and mean directions. Furthermore, the main wave extreme parameters and directional extreme values, particularly for the 100-year return period, were also investigated. The main extreme values of significant wave heights are larger in the northern part of SCS than in the southern part, with the maximum value occurring to the southeast of Hainan Island. The direction of large directional extreme H _s values is focus in E in the northern and middle sea areas of SCS, while the direction of those is focus in N in the southeast sea areas of SCS.     

The research on typhoon wave spectrum in northwestern South China Sea

Based upon the one-year wind wave measurement data, collected from the South China Sea (SCS) at coordinates 20° 36.298′N, 110°45.433′E. by Acoustic Wave And Current (AWAC), we analyzed the wave characteristics and concluded that the most common wave direction was E and the second most common direction was ENE, the mean and the maximum values of significant height was 1.2 m and 4.36 m, respectively. The mean period was 4.0 s. We also evaluated the wave spectrums under conditions existing in three typhoons: Rumbi, Jeti and Utor. We found that unimodal spectrums occurred more often than others, and the maximum spectrum peak was 30.7911 m² s. The minimum peak frequency was 0.0625 Hz, and the mean peak frequency was 0.126 Hz. The wave period is important for the design of marine structures, especially the position of peak frequency had a great influence on the stress calculation. Spectral analysis showed that the values of peak frequency distributed between 0.063 Hz and 0.217 Hz, with the mean value 0.114 Hz. We fit the normalized spectrum with 6 theoretical spectral models, out of which, the Wen spectrum, JONSWAP spectrum and Wallops spectrum were proved to give the best fit. What distinguished the Wen Spectrum from the rest was that it does not rely on the measured spectrum for parameter estimation. Hence, we recommend that the Wen spectrum should be widely used in marine construction.