Numerical simulation of wave field in the South China Sea using WAVEWATCH III

Wave fi elds of the South China Sea(SCS) from 1976 to 2005 were simulated using WAVEWATCH III by inputting high-resolution reanalysis wind fi eld datasets assimilated from several meteorological data sources. Comparisons of wave heights between WAVEWATCH III and TOPEX/Poseidon altimeter and buoy data show a good agreement. Our results show seasonal variation of wave direction as follows: 1. During the summer monsoon(April–September), waves from south occur from April through September in the southern SCS region, which prevail taking about 40% of the time; 2. During the winter monsoon(December–March), waves from northeast prevail throughout the SCS for 56% of the period; 3. The dominant wave direction in SCS is NE. The seasonal variation of wave height H s in SCS shows that in spring, H s ≥1 m in the central SCS region and is less than 1 m in other areas. In summer, H s is higher than in spring. During September–November, infl uenced by tropical cyclones, H s is mostly higher than 1 m. East of Hainan Island, H s 2 m. In winter, H s reaches its maximum value infl uenced by the north-east monsoon, and heights over 2 m are found over a large part of SCS. Finally, we calculated the extreme wave parameters in SCS and found that the extreme wind speed and wave height for the 100-year return period for SCS peaked at 45 m/s and 19 m, respectively, SE of Hainan Island and decreased from north to south.     

海浪搅拌混合对北太平洋海表面温度模拟的影响

利用NCEP再分析风场驱动WAVEWATCH III海浪模式对北太平洋海域的海浪过程进行模拟,利用浮标观测资料对模拟出的海浪要素有效波高进行验证,发现他们之间具有很好的一致性。基于模式输出的有效波高等波浪要素,利用特征波参数化理论,在海洋环流模式中引入海浪搅拌混合作用,分析其对北太平洋海表面温度模拟的影响,初步数值模拟结果表明,sbPOM模式在考虑海浪搅拌混合作用以后,模拟精度进一步提升,这对提供一个准确的大气模式下边界条件具有重要作用。     

基于现场和卫星有效波高数据评估WAVEWATCH III的输入/耗散项

基于WAVEWATCH III,在输入相同的风场条件下,评估了三个输入耗散项WAM3,WAM4以及TC96在是否考虑大气稳定性时的模拟能力。通过5组实验,用南海的测波雷达数据以及研究区域内HY-2高度计的有效波高数据对不同源项的模拟结果进行了比较分析,研究区域为100-135°E,0-35°N。对TC96中的风速校正参数进行了敏感性分析。结果表明,这几种源项在涌浪占主导时的模拟效果都不太理想;考虑大气不稳定性的TC96源项模拟的效果最好;大气不稳定性的影响是以一种所谓的“高效风速”的策略来反映的,其中最重要的一个参数为风速转换参数,这个参数非常敏感,在对特定区域进行模拟之前,应先分析出这个参数的最优值。     

The temporal and spatial variations in the Pacific wind and wave fields for the period 2002–2011

本文利用第三代海浪模式（WAVEWATCH III）分析了2002-2011年太平洋风速和海浪场的时空变化特征。首先,使用浮标观测数据对模式模拟的有效波高结果进行验证。结果表明模式可以有效地后报太平洋的有效波高。模式偏差较大的区域为中低纬度地区。随后将太平洋分为多个子区域,分别讨论了其风速和有效波高的时空变化特征。多年平均太平洋风速和有效波高存在类似的纬向分布特征,各子区域之间风速和有效波高的季节变化存在差别。模式刻画的太平洋有效波高年际变化最大的区域为南半球中高纬区域。进一步,我们研究了波浪能量的输入与耗散。相应的源函数项的各区域平均值显示了量化的表面波的变化。最后,对日平均的风速与有效波高值进行功率谱分析寻找序列的显著周期。结果表明有效波高时间变化对应的频谱和风速谱具有一定的差异。     

Stokes漂流近似公式对海洋表层流场估算的影响

本文采用波浪订正的Ekman模型,研究分析了三种Stokes漂流近似公式(单波公式、e指数公式、Phillips谱近似公式)对海洋表层流场估算的影响。海表总流场由海表面高度(SSH)数据计算的地转流和海浪模式WAVEWATCH Ⅲ输出结果计算的非地转流组成,并采用拉格朗日浮标观测数据对计算结果进行了验证。研究表明,随着Stokes漂流近似公式精度的提高,其计算的拉格朗日流速更接近于谱积分公式的计算结果,更贴近拉格朗日浮标观测数据。与谱积分公式计算的海表拉格朗日流速相比,单波公式的平均相对偏差为0.0834,e指数公式的平均相对偏差为0.0392,Phillips谱近似公式的平均相对偏差为0.0101,说明Phillips谱近似公式在不同风速下均能对谱积分公式有良好的近似效果。在低风速条件下,由Stokes漂流近似公式精度引起的海洋表层流场估算误差可以忽略不计,但随着风速增加,由近似公式精度引起的偏差逐渐变大,此时应该选择Phillips谱近似公式计算Stokes漂流,来减小误差。     

海浪数值预报误差的统计分析

针对海浪资料同化中预报误差的统计性质难以确定的问题,利用WAVEWATCHⅢ和Topex/Posei-don(T/P)有效波高观测资料,对东中国海区的有效波高预报误差进行了统计分析。结果表明,预报误差符合正态分布;不同网格点的预报误差协方差随距离增长呈指数关系递减,并且空间上表现出弱各向异性;在预报模式空间网格为0.5°×0.5°条件下相关距离为3.0°~5.9°。     

Examination of wind-wave interaction source term in WAVEWATCH III with tropical cyclone wind forcing

Results of drag coefficient(CD) from field observations and laboratory wave tank experiments indicate that the operational wave model can overestimate wind energy input under high wind conditions. The wind-wave interaction source term in WAVEWATCH Ⅲ has been modified to examine its behavior with tropical cyclone wind forcing. Using high resolution wind input,numerical experiments under idealized wind field and tropical cyclone Bonnie(1998) were designed to evaluate performance of the modified models. Both experiments indicate that the modified models with reduced CD significantly decrease wind energy input into the wave model and then simulate lower significant wave height(SWH) than the original model. However,the effects on spatial distribution of SWH,mean wavelength,mean wave direction,and directional wave spectra are insignificant. Due to the reduced wind energy input,the idealized experiment shows that the modified models simulate lower SWH than the original model in all four quadrants. The decrease in the front quadrants is significantly larger than that in the rear quadrants;it is larger under higher winds than lower winds. The realistic experiment on tropical cyclone Bonnie shows that the modified model with the various downward trends of CD in high winds creates a simulation that agrees best with scanning radar altimeter observations.     

Climatology of Wind-Seas and Swells in the China Seas from Wave Hindcast

The wind-sea and swell climates in the China Seas are investigated by using the 27-yr Integrated Ocean Waves for Geophysical and other Applications(IOWAGA)hindcast data.A comparison is made between the significant wave height from the IOWAGA hindcasts and that from a jointly calibrated altimetry dataset,showing the good performance of the IOWAGA hindcasts in the China Seas.A simple but practical method of diagnosing whether the sea state is wind-sea-dominant or swell-dominant is proposed based on spectral partitioning.Different from the characteristics of wind-seas and swells in the open ocean,the wave fields in the enclosed seas such as the China Seas are predominated by wind-sea events in respect of both frequencies of occurrences and energy weights,due to the island sheltering and limited fetches.The energy weights of wind-seas in a given location is usually more significant than the occurrence probability of wind-sea-dominated events,as the wave energy is higher in the wind-sea events than in the swell events on average and extreme wave heights are mostly related to wind-seas.The most energetic swells in the China Seas(and other enclosed seas)are‘local swells’,having just propagated out of their generation areas.However,the swells coming from the West Pacific also play an important role in the wave climate of the China Seas,which can only be revealed by partitioning different swell systems in the wave spectra as the energy of them is significantly less than the‘local swells’.     

海浪破碎对北太平洋海表面温度模拟的影响

基于海浪模式WAVEWATCH Ⅲ模拟北太平洋海浪要素,结合NDBC浮标资料进行验证,发现模拟出的有效波高与浮标测量值具有很好的一致性。基于改进型白冠覆盖率耗散模型,利用海浪模式模拟出的有效波高、有效波周期和摩擦速度等海浪要素计算出单位面积水柱内因海浪破碎产生的湍动能通量。通过改变环流模式sbPOM湍动能方程的上边界条件,引入海浪破碎产生的湍动能通量,并探究海浪破碎对北太平洋海表面温度模拟的影响。研究表明,由于海浪破碎的引入,环流模式sbPOM对北太平洋海表面温度模拟的准确程度得到提升,这为大气模式提供一个准确的北太平洋下边界条件具有重要意义。