Numerical simulation of wave fi eld 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.

WAVEWATCHⅢ同化模块的建立和检验

将基于最优插值（OI）的同化并行模块植入全谱空间的第三代海浪模式 WAVEWATCH III ver-sion3.14,建立数据同化的海浪模式预报系统,并通过实际的预报个例对同化系统进行检验。个例实验是以5°S以北的印度洋海域为目标计算区域,海面风场强迫采用业务单位的中尺度天气预报模式WRF （weather research and forecast）提供的逐时海面风场预报产品。模式积分过程中连续同化2010年12月15日、16日和17日过境北印度洋的Jason-2卫星高度计沿轨有效波高（SWH）数据（需要指出的是,每次同化得到新的SWH分析场后需重构相应的二维海浪谱用于谱模式）。SWH同化分析值和无同化的对照组分别与高度计沿轨观测数据比较发现,就日平均统计来看,同化较无同化使SWH分析值的均方根误差减小约25%-50%。以 SWH同化分析场作为初始场的预报表明,同化对预报影响的时效性可延长至48-60 h。本研究目的是通过将高度计测量的SWH数据同化到海浪模式进一步提升海浪数值预报的准确度。

An evaluation of input/dissipation terms in WAVEWATCH Ⅲ using in situ and satellite significant wave height data in the South China Sea

A WAVEWATCH III version 3.14(WW3) wave model is used to evaluate input/dissipation source term packages WAM3, WAM4 and TC96 considering the effect of atmospheric instability. The comparisons of a significant wave height acquired from the model with different packages have been performed based on wave observation radar and HY-2 altimetry significant wave height data through five experiments in the South China Sea domain spanning latitudes of 0°–35°N and longitudes of 100°–135°E. The sensitivity of the wind speed correction parameter in the TC96 package also has been analyzed. From the results, the model is unable to dissipate the wave energy efficiently during a swell propagation with either source packages. It is found that TC96 formulation with the "effective wind speed" strategy performs better than WAM3 and WAM4 formulations. The wind speed correction parameter in the TC96 source package is very sensitive and needs to be calibrated and selected before the WW3 model can be applied to a specific region.

Evaluation of the simulation capability of the Wavewatch Ⅲ model for Pacific Ocean wave

Wave climate analysis and other applications for the Pacific Ocean require a reliable wave hindcast. Five source and sink term packages in the Wavewatch III model(v3.14 and v4.18) are compared and assessed in this study through comprehensive observations, including altimeter significant wave height, advanced synthetic aperture radar swell, and buoy wave parameters and spectrum. In addition to the evaluation of typically used integral parameters, the spectra partitioning method contributes to the detailed wave system and wave maturity validation. The modified performance evaluation method(PS) effectively reduces attribute numbers and facilitates the overall assessment. To avoid possible misleading results in the root mean square error-based validations, another indicator called HH(indicating the two authors) is also calculated to guarantee the consistency of the results. The widely used Tolman and Chalikov(TC) package is still generally efficient in determining the integral properties of wave spectra but is physically deficient in explaining the dissipation processes. The ST4 package performs well in overall wave parameters and significantly improves the accuracy of wave systems in the open ocean. Meanwhile, the newly published ST6 package is slightly better in determining swell energy variations. The two packages(ACC350 and BJA) obtained from Wavewatch III v3.14 exhibit large scatters at different sea states. The three most ideal packages are further examined in terms of reproducing waveinduced momentum flux from the perspective of transport. Stokes transport analysis indicates that ST4 is the closest to the NDBC-buoy-spectrum-based transport values, and TC and ST6 tend to overestimate and underestimate the transport magnitude, respectively, in swell mixed areas. This difference must be considered,particularly in air–wave–current coupling research and upper ocean analysis. The assessment results provide guidance for the selection of ST4 for use in a background Pacific Ocean hindcast for high wave climate research and China Sea swell type analysis.

Establishment and tests of EnOI assimilation module for WAVEWATCH Ⅲ

A bstrac t In this paper,we propose a parallel data assimilation module based on ensemble optimal interpolation(En OI). We embedded the method into the full-spectral third-generation wind-wave model,WAVEWATCH III Version 3.14,producing a wave data assimilation system. We present our preliminary experiments assimilating altimeter significant wave heights(SWH) using the En OI-based wave assimilation system. Waters north of 15°S in the Indian Ocean and South China Sea were chosen as the target computational domain,which was two-way nested into the global implementation of the WAVEWATCH III. The wave model was forced by six-hourly ocean surface wind velocities from the cross-calibrated multi-platform wind vector dataset. The assimilation used along-track SWH data from the Jason-2 altimeter. We evaluated the effect of the assimilation on the analyses and hindcasts,and found that our technique was effective. Although there was a considerable mean bias in the control SWHs,a month-long consecutive assimilation reduced the bias by approximately 84% and the root mean-square error(RMSE) by approximately 65%. Improvements in the SWH RMSE for both the analysis and hindcast periods were more significant in July than January,because of the monsoon climate. The improvement in model skill persisted for up to 48 h in July. Furthermore,the SWH data assimilation had the greatest impact in areas and seasons where and when the sea-states were dominated by swells.

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.

1307号台风“苏力”台风浪数值模拟

以T639预报风场驱动目前国际先进的第三代海浪模式WW3(WAVEWATCH-III),对发生在2013年7月中旬的1307号台风"苏力"所致的海浪场进行数值模拟,并利用来自台湾岛、朝鲜半岛、日本的浮标观测资料,验证模拟台风浪场的有效性,进而对台风浪的结构特征进行分析,以期为台风浪场的数值预报、防灾减灾等提供科学依据.结果表明:1)以T639预报风场驱动WW3海浪模式,模拟的台风浪场较好地刻画了台风"苏力"的结构特征;2)与浮标观测资料对比发现,模拟有效波高整体上具有较高精度,与观测值在曲线走势上保持了较好的一致性,在数值上稍大于观测值;3)澎湖浮标站处的模拟有效波高与观测值出现较大差异,这应该与台湾海峡的复杂地形、T639预报风场在台湾海峡的准确度有关;4)台风海浪场与海表风场表现出较好的一致性,台风位于大洋时,高值中心的有效波高可达13m以上,台风逼近福建沿海时,带来了11m左右的巨浪.

利用WW3模式实现中国海击水概率数值预报

海浪对掠海飞行有着重要影响,以T639预报风场驱动WW3(WAVEWATCH-III)海浪模式,对2013年3月发生在中国海的一次冷空气海浪场进行数值模拟.结合飞行高度探测的标准差、海浪浪高的标准差,进一步实现了击水概率的数值预报,为低空飞行器的航迹规划提供科学依据.主要计算了5m高度、10m高度、15m高度的击水概率,并对比不同飞行高度击水概率的差异.结果表明,以T639预报风场驱动WW3海浪模式,可以较好地预报中国海海浪场、击水概率场.在冷空气影响下,中国海的击水概率出现明显增幅.飞行高度低于10 m时,海浪会对掠海飞行器的安全造成很大威胁.

近10年南海波候特征分析及波浪能研究

基于第三代海浪数值模式WAVEWATCH-Ⅲ,以QuikSCAT/NCEP混合风场为驱动场,得到南海1999年8月～2009年7月的海浪场,分析了近10年南海的波候及波浪能特征,为波浪发电的选址提供参考。研究发现:南海的海浪场、海表风场受季风影响显著,海浪场与海表风场具有较好的对应关系,尤其体现在南海南部海域;南海的海表风场、海浪场与nino3指数存在显著的负相关;南海极值风速、极值波高的大值区分布于南海北部海域;南海蕴藏着较丰富的波浪能资源,年均值能流密度在4～20kW/m,大部分海域2kW/m以上能流密度出现频率在70%以上,且大部分海域能流密度的变异系数在0.4以内,稳定性较好,利于波浪能的开发与利用。

中国大陆沿岸波浪能分布初步研究

波浪能作为可持续利用的清洁能源,日益被人们所关注,本文基于WAVEWATCHⅢ全球波浪模式,建立了较高精度的中国沿岸海域波浪数学模型,重点对中国大陆沿岸-30m等深线上的波浪能分布进行了研究,在已有研究成果的基础上进一步细化了中国沿岸海域波浪能的时空分布规律,为合理开发、利用波浪能提供了一定的数据支持。研究认为,中国沿岸波浪能储量相对较小,南北分布以长江口为界,以南海域波能整体较大,波能季节性差异明显,在开发利用时,需要对工程区域的波浪能特征充分论证,科学合理地选用波浪能转化设备,防止造成巨大经济损失。

1957～2002年南海—北印度洋海浪场波候特征分析

利用ERA-40海表10 m风场驱动第三代海浪数值模式WAVEWATCH-Ⅲ,得到南海—北印度洋1957年9月至2002年8月的海浪场,并分析其波候(风候)特征.研究发现如下主要特征:(1)该海域的波高波向、风速风向受季风影响显著;(2)北印度洋大部分海域的海表风速呈显著性逐年线性递增趋势,大约0.01～0.02 m/(s·a),南海线性递增的区域则较少,有效波高呈显著性逐年线性递增的区域主要集中在低纬度中东印度洋(约0.003～0.006 m/a)、索马里附近海域(大约0.002～0.005 m/a)、南海大部分海域(约0.002～0.004 m/a),线性递减的区域主要集中在孟加拉湾海域(约-0.002 m/a);(3)Nino3指数与南海—北印度洋的海表风场、浪场存在密切的关系;(4)南海—北印度洋的海表风速与有效波高存在5.2a左右的共同周期,南海的海表风速、有效波高还存在2.0a左右的共同周期,北印度洋的海表风速、有效波高还存在26.0a的长周期震荡.

热带气旋风场对海浪分布特征的影响

设计了一系列理想的数值实验,利用高分辨率的WAVEWATCHIII海浪模式定量分析热带气旋移动速度、强度、最大风速半径和热带气旋移动时的转向等风场细节因素对热带气旋下表面海浪分布特征的影响。实验结果表明,热带气旋移动速度、最大风速半径和热带气旋移动时的转向会影响海浪的空间非对称分布。最大风速半径增大会使最大有效波高的位置向后移动,而移动速度增大会使最大有效波高位置向前移动。移动速度增大会使右侧象限内的有效波高增大,左侧象限内有效波高减小。最大风速半径增大和强度增强使各象限内有效波高均增高。热带气旋的转向使各象限内有效波高增高,除了右后象限。这些风场特征对各个象限内海浪的平均波长、平均周期、平均波向、和波峰方向都有很重要的影响,尤其以左后象限最为显著。

近45年北印度洋海表风、浪特征研究

基于第三代海浪数值模式（WAVEWAZTCH-III），以ERA．40海表风场为驱动场，得到北印度洋1957年9月-2002年8月的海浪场，并分析其特征。研究发现，北印度洋1958～2001年年平均海表风速和有效波高均呈缓慢递增趋势；北印度洋的海表风速、有效波高存在2．36～5．2a左右的共同周期及26a的长周期震荡；北印度洋海域年平均海表风速、有效波高的突变形势与冬季相似，突变期在20世纪80年代初。本研究可以为在北印度洋这一重要战略通道上作业的船只提供重要参考。

WWATCH Ⅲ模式模拟南海冷空气过程海浪场的有效性检验

利用Jason-1卫星高度计观测资料,验证了WWATCH Ⅲ海浪模式在模拟南海冷空气过程海浪场的有效性和准确性。结果发现,以NCEP再分析风场驱动的WWATCH Ⅲ模式能够较好地模拟冷空气影响南海时的海浪变化,模拟结果与Jason-1卫星高度计的观测资料有比较好的一致性。在近海岸地区以及冷空气活动末期,模拟值与观测值的相关系数有所降低,但平均相对误差和均方根误差均在可以接受的范围内。说明WWATCH Ⅲ模式可以作为我国南海地区海浪模拟预测研究的有效工具之一。

舟山群岛海域波浪能资源评估

舟山群岛海域岛屿众多,东临东海,波能利用具有一定应用前景,本文采用WAVEWATCH III和SWAN耦合波浪数值模式,嵌套计算了舟山群岛海域2008年的波浪逐时过程,着重统计了-30 m等深线上波浪能储量及其分布特征,研究成果对波能开发具有一定参考价值。

台风马鞍对东中国海波浪的影响研究

利用第三代海浪模式WAVEWATCH III驱动合成风场,模拟西北太平洋台风马鞍作用期间东中国海的波浪,从而研究台风马鞍对东中国海波浪的影响。研究结果表明,台风马鞍作用期间东中国海的中部和南部海域的混合浪以涌浪为主,涌浪波向主要为东向。台风对东中国海的东南部海域影响最强,在该海域形成5~8 m大涌浪,最远影响到黄海中部海域,同时在我国东南沿海海域形成小波高长周期涌浪。

再分析风场驱动下的南海波浪模拟误差

本文采用国际上广泛应用的3种再分析风场驱动WAVEWATCH III模型得到了南海波浪后报数据,并基于全球卫星高度计波高数据和我国沿海浮标实测数据对不同的风场计算结果进行了对比分析,分析表明3种风场的误差特征相差明显,其中ERA-40风场偏小,CFSR风场非常适合模拟常见天气的波浪过程,NCDC风场适合模拟大浪过程。论文重点以NCDC风场后报波浪数据分析了波浪模型模拟误差特点,发现在台风频发的的南海北部海域,再分析风场易低估大值波高,而在季风影响明显的南海南部海域,再分析风场易高估波高。浮标周边2°范围海域内的卫星高度计波高模拟误差趋势与浮标波高模拟误差趋势相似,浮标波高数据的统计特征值与“2度法”提取的卫星高度计数据统计特征值具有较高一致性。

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’.

理论风浪谱修正方法及数值验证

为了研究特定海域范围内海浪的内部能量相对于频率的分布规律,本文以目标岛屿处"波浪骑士"式浮标提供的实际观测资料为依据,提出了一种基于实测资料的风浪数据筛选和理论风浪谱修正方法。通过讨论实测频谱与理论频谱的谱峰位置关系筛选出研究针对的风浪数据点,将实测风浪频谱与理论频谱进行对比分析,进而提出理论风浪谱的修正方法,并以增加参数的JONSWAP谱为靶谱对实测风浪数据进行拟合,得到了可以表达目标岛屿处风浪内部能量的理论谱形式,并进行了对比验证。研究结果表明:所提出的理论风浪谱修正方法,能够有效地筛选出实测数据集中的风浪数据,并完成对特定海域处风浪频谱的描述表达。

数据同化的南海台风浪后报模式

将基于最优插值(OI)的同化并行模块植入第三代海浪模式WAVEWATCH III version3.14,建立数据同化的台风海浪模式预报系统。该系统的强迫风场采用模型台风风场与台风来前海区背景风场混成的风场。以模式后报2010年7月严重影响南海北部的"康森"和"灿都"台风引起的海浪场为例,首先对所构造的混合风场的台风海面风场结构进行定性检验,并用高度计沿轨风速对混合风场精度进行定量验证。在此基础上,海浪模式在混合风场强迫下边积分边同化。同化数据采用上述台风过境南海期间Jason-2卫星高度计沿轨有效波高(SWH)。值得指出的是,同化时只取SWH沿轨数据的一部分用于同化计算,而另一部分沿轨数据则用于对同化分析结果进行检验。先后同化了4条轨道上的SWH数据。将SWH的同化分析与无同化的对照组结果分别与高度计测量SWH比较,发现同化较无同化可使均方根误差获得50%以上的明显改进。以同化分析场作为初始场,同化影响预报(这里是后报)的时效性约在48 h以内。本研究目的是通过同化高度计SWH数据进一步提升台风海浪模式预报的准确度。