南海北部内孤立波非线性陡斜的数值研究

基于三维海洋环流模式MITgcm,对非线性陡斜在南海北部内孤立波形成和传播过程中的作用进行了研究,探讨了内孤立波的三维演变过程。研究发现,吕宋海峡处正压潮流激发的斜压潮能射线在其西侧形成强斜压扰动,该扰动在西传过程中受到地形浅化的影响,发生非线性陡斜,波长变小,波形变陡,最终在南海北部陆架坡折处形成大振幅内孤立波,即南海北部的大振幅内孤立波主要是由吕宋海峡西侧的强斜压扰动发展而来,而非来自吕宋海峡巴坦岛附近经潮地相互作用所形成的强波动信号。同时,模式也揭示了a、b波的演变过程,在吕宋海峡西侧约120°E以东的海域,没有发现a、b波,经过西传过程中的非线性陡斜作用,a、b波才演变出来,表明传播过程在a、b波的形成中具有重要意义。     

南海文昌海域内孤立波特征观测研究

内孤立波对大陆架边缘海区的混合和生态有着显著影响，近年来已成为物理海洋学研究的热点。但是南海北部陆架的内波现场资料极为缺乏。2005年4—7月，中国科学院海洋研究所在文昌海区进行了文昌内波实验。通过此次现场观测数据发现，在4月下旬文昌海域有着强盛的内孤立波，其振幅在40m左右，产生的斜压流接近1m／s，且传播方向平行于等深线切线方向，向西南方向传播。分析还得出此类内孤立波并非发源于吕宋海峡，应该属于潮地相互作用局地生成的内孤立波。     

吕宋海峡内波传播演化的数值模拟

吕宋海峡生成的内波在往南海西部传播的过程中,具有明显的二维辐射特征,这是传统的一维KdV模式无法刻画的.基于弱二维的KP方程,并结合南中国海吕宋海峡附近内孤立波的观测资料,模拟了潮成内波的演化特征.数值结果较好地反应了内孤立波的二维特征.相比于一维的KdV方程,KP在内孤立波的仿真反演方面具有更大的优势.     

双曲余弦海脊上海啸俘获波的解析与数值研究

海啸能被大洋海脊引导以俘获波的形式沿其传播上万千米，且因其特殊的运动方式，携带巨大能量影响远场地区的港口，严重威胁海岸安全。本文首先基于线性浅水方程，推导了双曲余弦平方海脊上俘获波的波面解，其为μ阶ν次的连带勒让德函数的第一类解和第二类解的组合。进一步推导出其对应的频散关系，其中对于确定的频率ω，存在无穷多个波数k_y与之对应。采用MIKE21-BW模型，模拟了产生于海脊脊顶处的海啸在理想双曲余弦平方海脊上的传播变形过程。结果表明，小部分能量以自由先驱波进行传播，海啸波的波能大部分被海脊俘获。海脊俘获波沿着海脊方向为行进波，随着海啸波传播时间的增加，波浪在沿着海脊方向的延展范围也逐渐增大，波高逐渐减小、波的个数逐渐增加。俘获波能量主要由不同频率以相同速度传播的具有孤立波特性的波浪成分和能量主要集中在特定频率范围内的波浪成分组成。     

南海北部内孤立波绕东沙岛传播特性的数值研究

使用三维非静压环流模式MITgcm探究生成于吕宋海峡并向东沙岛传播的内孤立波。模式结果再现了东沙岛附近内孤立波的垂向振幅变化和到达时间。在不同纬向断面中,经向不对称的等密线起伏表现出内孤立波在南海的三维性特征。东沙岛附近的海表高度梯度变化表明,内孤立波在绕过东沙岛后,分离为2个短波峰线内波,此后两者相互作用。内孤立波在大陆坡浅化过程中相速逐渐减小,并与具有半日周期的理论线性相速度吻合一致。内孤立波与东沙岛碰撞后,在岛东北部会出现反射信号。本文利用斜压潮能通量,分析了反射能与入射之比在大潮期与小潮期的差异,发现小潮期的比值大于大潮期。选取东沙岛附近的3个站点,其垂向振幅表明A波与B波在大小潮转变时有不同的变化特征。在东沙岛西部和西北部的两个站位(WB和WN),A、B波均能被显著观测到;但在东沙岛南部站位(WS)只能观测到振幅具有正弦变化趋势的B波信号。     

海啸俘获波在弯曲海脊上的传播规律

越洋海啸会受大洋海脊的引导以俘获波的形式沿其传播上万千米,其携带的巨大能量会严重影响远场地区、威胁海岸地区的安全。本文基于MIKE21-BW模型,分别模拟0°(直海脊)至90°(直角弯曲海脊)不同弯曲角度海脊上俘获波的传播变形过程,并定量比较其能量分配。结果表明,海脊俘获波传至海脊转弯处,少部分能量会泄露出海脊重新以自由波的形式扩散至整个海域;部分能量会被反射回来形成与初始海啸波相反方向的俘获波沿海脊传播,反射的能量会随着海脊弯曲角度的增加而增加;还有一部分能量继续沿着弯曲的海脊向前传播,其随着海脊弯曲的角度增加而减小。     

南海北部内孤立波生成对黑潮响应的初步研究

为了研究南海北部黑潮入侵对内孤立波生成造成的影响,本研究在对合成孔径雷达图像处理分析的基础上,运用二维非静力模式,对南海北部内孤立波生成以及其对黑潮入侵的响应做了初步的模拟和分析。对4 a(2007~2010年)的合成孔径雷达(SAR)图像统计分析发现,内波出现频率呈现明显的季节变化。月平均数据表明,内波出现频率在5月到8月期间较高并在6月达到峰值,占全年总数的29%;而在11月到次年的2月份期间出现频率较低并在12月和1月达到最低,各占全年的0.5%。通过二维、非静力近似数值模拟研究发现:黑潮入侵引起的平流对吕宋海峡区域内孤立波的激发产生具有明显的影响。具体表现为,黑潮入侵引起的的西向平均流拉伸了内孤立波波形并加强内孤立波的能量的频散,使得大振幅内孤立波演变成多个分散的波动,波长变长、振幅变小。敏感性实验通过替换夏季温盐场为冬季温盐场,对模拟结果并无实质上的影响,表明冬夏季温盐场的差异并非是SAR观测内波出现频率呈季节变化的重要因素。     

黑潮对吕宋海峡全日内潮生成与传播影响的数值模拟研究

基于一套环流-潮汐耦合模型的模拟结果,本文探究并比较了2015—2016年的三种黑潮形态下,吕宋海峡全日内潮以及全日非相干内潮生成与传播的空间分布特征。结果表明,当黑潮以流套形态流经吕宋海峡时,全日内潮非相干性最强,具体表现为全日非相干内潮能量生成最大,全日内潮的传播速度变化率最大。由于传播速度的变化会改变全日内潮的位相,进而会影响全日内潮的非相干性,导致在吕宋海峡内全日内潮的非相干性最强。本研究结果对理解黑潮背景动力过程下吕宋海峡内潮的时空变化有重要意义。     

抛物型对称海脊引导波完整解析理论

越洋海啸能够被大洋海脊引导并沿海脊传播至远场地区,虽然传播速度较慢,但携带较大的能量,会对远场地区造成灾害影响,相关研究对于提高海啸传播特性本质的认识具有重要意义。本文基于线性长波方程,推导出了抛物型对称海脊引导波完整解析理论。研究表明对称型海脊同时存在对称与反对称引导波,其自由水面波动可以表示为虚宗量Bessel函数形式。利用海脊中心对称条件给出了描述其频率与波数的频散关系。基于所提理论进一步分析讨论了引导波的运动特性,包括频散关系、波速度、能量传播速度与波面空间分布等。本研究为揭示地形坡度由脊顶至两侧逐渐增加的海脊引导波运动特征,预测实际越洋海啸中最具威胁性海啸波的到达时间提供了理论依据。     

吕宋海峡附近中尺度涡特征的统计分析

采用1993年1月到2008年12月16a融合海面高度距平数据,追踪吕宋海峡附近海域(18°～23°N,116°～126°E)中尺度涡的移动轨迹,结果表明:时间分辨率为7d的卫星高度计资料难以观测到中尺度涡从西北太平洋通过吕宋海峡传进南海的过程,但对1994年吕宋海峡中部观测到的一个气旋涡及其附近中尺度涡的运动轨迹进行分析可见,西北太平洋海面高度变化会与吕宋海峡内部海面高度耦合后向南海传播。海面高度距平数据的时间-经度图表明,西北太平洋海面高度变化信号在西传至吕宋海峡附近(121°～122°E)时出现信号不连续。对21°N,116°～140°E断面的海面高度距平数据按周期分别为1～3月、3～6月、330～390d(年信号)进行分段带通滤波,发现不同周期的西北太平洋信号穿过吕宋海峡传入南海受到的阻隔作用、向西传播的速度以及它们所受的强迫机制均不同。     

Mooring observations of internal solitary waves in the deep basin west of Luzon Strait

A total of 137 internal solitary waves （ISWs） are captured during a field experiment conducted in the deep basin west of the Luzon Strait （LS） from March to August, 2010. Mooring observations reveal that a fully developed ISW owns a maximum westward velocity of more than 1.8 m/s and an amplitude of about 200 m. The ISWs in the South China Sea （SCS） are most active in July, which may be due to the strong stratification in summer. Most of the ISW episodes are detected around and after the 1st or 15th lunar day, indicating that the ISW in the SCS is triggered by astronomic tides. Half part of the observed ISWs were detected around 19：00 local time, which can be explained by the fact that type-a ISWs emerged in the evening at roughly the same time each day. The propagation direction of the ISWs and the astronomic tides in the LS show that the area south of the Batan Island is probably the main source region of the type-a ISWs, while the area south of Itbayat Island and south of the Batan Island is likely the main source region of the type-b ISWs observed at the mooring. Moreover, for the resonance of semidiurnal internal tides emitting from the double ridges in the LS, the underwater ridge south of the Itbayat Island and south of the Batan Island is believed to favor the generation of the energetic ISWs.     

Assessing the west ridge of Luzon Strait as an internal wave mediator

The Luzon Strait is blocked by two meridional ridges at depths, with the east ridge somewhat higher than the west ridge in the middle reaches of the Strait. Previous numerical models identified the Luzon Strait as the primary generation site of internal M₂ tides entering the northern South China Sea (Niwa and Hibiya, 2004), but the role of the west-versus-east ridge was uncertain. We used a hydrostatic model for the northern South China Sea and a nonhydrostatic, process-oriented model to evaluate how the west ridge of Luzon Strait modifies westward propagation of internal tides, internal bores and internal solitary waves. The dynamic role of the west ridge depends strongly on the characteristics of internal waves and is spatially inhomogeneous. For M₂ tides, both models identify the west ridge in the middle reaches of Luzon Strait as a dampener of incoming internal waves from the east ridge. In the northern Luzon Strait, the west ridge is quite imposing in height and becomes a secondary generation site for M₂ internal tides. If the incoming wave is an internal tide, previous models suggested that wave attenuation depends crucially on how supercritical the west ridge slope is. If the incoming wave is an internal bore or internal solitary wave, our investigation suggests a loss of sensitivity to the supercritical slope for internal tides, leaving ridge height as the dominant factor regulating the wave attenuation. Mechanisms responsible for the ridge-induced attenuation are discussed.     

ON generation source sites of internal in the Luzon strait

This effort aims to determine the generation source sites in the Luzon Strait for energetic, long-crest, transbasin internal waves (IW) observed in the northern South China Sea (NSCS). The roles of islands distributed on eastern side of the strait, Kuroshio, submarine ridges, shoaling thermocline, and strait configuration played in the IW generation are examined using the cruise data analysis, satellite data interpretation, and dynamical analysis. The islands and channels on eastern side of the strait are excluded from a list of possible IW source sites owing to their unmatched horizontal dimensions to the scale of IW crest line length, and the relative low Reynolds number. The Kuroshio has a potential to be a radiator for the long-crest IW disturbances, meanwhile, the Kuroshio west (east) wing absorbs the eastward (westward) propagating IW disturbance. Namely, the Kuroshio blockades the outside west-east propagating IW disturbances. The 3-D configuration of the Luzon Strait is characterized by a sudden, more than one order widening of the cross-section areas at the outlets on both sides, providing a favorable condition for IW type initial disturbance formation. In the Luzon Strait, the thermocline is featured by a westward shoaling all the year around, providing the dynamical conditions for the amplitude growth (declination) to the westward (eastward) propagating IW type disturbance. Thus,the west slope of western submarine ridge at the western outlet of the Luzon Strait is a high possibility source sites for energetic,long-crest, transbasin Iws in the NSCS. The interpretation results of satellite SAR images during a 13 a period from 1995 to 2007 provide the convincing evidence for the conclusions.     

On generation source sites of internal waves in the Luzon Strait

This effort aims to determine the generation source sites in the Luzon Strait for energetic, long-crest, transbasin internal waves （IW） observed in the northern South China Sea （NSCS）. The roles of islands distributed on eastern side of the strait, Kuroshio, submarine ridges, shoaling thennocline, and strait configuration played in the IW generation are examined using the cruise data analysis, satellite data interpretation, and dynamical analysis. The islands and channels on eastern side of the strait are excluded from a list of possible IW source sites owing to their unmatched horizontal dimensions to the scale of IW crest line length, and the relative low Reynolds number. The Kuroshio has a potential to be a radiator for the long-crest IW disturbances, meanwhile, the Kurosbio west （east） wing absorbs the eastward （westward） propagating IW disturbance. Namely, the Kuroshio blockades the outside west-east propagating IW disturbances. The 3-D configuration of the Luzon Strait is characterized by a sudden, more than one order widening of the cross-section areas at the outlets on both sides, providing a favorable condition for IW type initial disturbance formation. In the Luzon Strait, the thermocline is featured by a westward shoaling all the year around, providing the dynamical conditions for the amplitude growth （declination） to the westward （eastward） propagating IW type disturbance. Thus, the west slope of western submarine ridge at the western outlet of the Luzon Strait is a high possibility source sites for energetic, long-crest, transbasin IWs in the NSCS. The interpretation results of satellite SAR images during a 13 a period from 1995 to 2007 provide the convincing evidence for the conclusions.     

基于调制不稳定性的吕宋海峡内孤立波生成机理探讨

The South China Sea (SCS) is a hot spot for oceanic internal solitary waves due to many factors, such as the complexity of the terrain environment. The internal solitary waves in the northern SCS mainl...     

汕尾市引发灾害性海浪的热带气旋特征研究

近年来,海浪灾害是威胁近海民众生命安全最为突出的海洋灾害,对我国造成的经济损失有整体上升的趋势。基于31 a(1986-2016年)汕尾市观测站的热带气旋影响期间白天的海浪数据,本文定义并提取了31次灾害性海浪(1/10大波波高≥4 m)事件。在灾害性海浪发生时,热带气旋主要位于观测站点的西侧(115.57°E以西)。31次灾害性海浪事件集中发生于6-9月;其中,虽然6月份影响研究海域的热带气旋数量相对较少,但引发灾害性海浪的概率约是7-9月份的两倍。有26个热带气旋生成于121°E以东的西太平洋海域,且移动路径相对较集中:途经吕宋海峡(16°-22°N)的热带气旋总数为25个,其中22个热带气旋途经16°-20°N之间,是最为重要的通道。途经此处的热带气旋在汕尾海域引发灾害性海浪的估算概率约为25%-50%。本研究可为汕尾市灾害性海浪的预警报和防灾减灾提供重要的参考。     

A numerical study of the generation and propagation of internal solitary waves in the Luzon Strait

A new composite model, which consists of a generation model of the internal tides and a regularized long wave propagation model, is presented to study the generation and evolution of internal solitary waves in the sill strait. Internal bores in the sill strait are first simulated by the generation model, and then the internal tidal field outside of the sill region is given as input for the propagation model. Numerical experiments are carried out to study the imposing tide, depth profile, channel width and shoaling effect, etc., on the generation and evolution of internal solitary waves. It is shown that only when the amplitude of internal tide at the forcing boundary of the propagation model is large enough that a train of internal solitary waves would be induced. The amplitude of the imposing tide in the generation model, shoaling effect, asymmetry of the depth profile and channel width have some effects on the amplitude of the induced internal solitary wave. The imposing tidal flow superimposed on a constant mean background flow has a great damping effect on the induced internal waves, especially on those propagate against the background flow direction. The generation and propagation of internal solitary waves in three possible straits among the Luzon Strait are simulated, and the reasons for the asymmetry of their propagation are also explained.     

Generation of internal waves by barotropic tidal flow over a steep ridge

A three-dimensional nonhydrostatic numerical model is used to study the generation of internal waves by the barotropic tidal flow over a steep two-dimensional ridge in an ocean with strong upper-ocean stratification. The process is examined by varying topographic width, amplitude of the barotropic tide, and stratification at three ridge heights. The results show that a large amount of energy is converted from the barotropic tide to the baroclinic wave when the slope parameter, defined as the ratio of the maximum ridge slope to the maximum wave slope, is greater than 1. The energy flux of internal waves can be normalized by the vertical integral of the buoyancy frequency over the ridge depths and the kinetic energy of the barotropic tides in the water column. A relationship between the normalized energy flux and the slope parameter is derived. The normalized energy flux reaches a constant value independent of the slope parameter when the slope parameter is greater than 1.5. It is inferred that internal wave generation is most efficient at the presence of strong upper-ocean stratification over a steep, tall ridge. In the Luzon Strait, the strength of the shallow thermocline and the location of the Kuroshio front could affect generation of internal solitary waves in the northern South China Sea.     

喀拉海峡潮-地相互作用激发非线性内波的数值模拟

Nonlinear internal waves(NIWs) are ubiquitous around the Kara Sea, a part of the Arctic Ocean that is north of Siberia. Three hot spot sources for internal waves, one of which is the Kara Strait, have been identified based on Envisat ASAR. The generation and evolution of the NIWs through the interactions of the tide and topography across the strait is studied based on a nonhydrostatic numerical model. The model captures most wave characteristics shown by satellite data. A typical inter-packets distance on the Barents Sea side is about 25 km in summer, with a phase speed about 0.65 m/s. A northward background current may intensify the accumulation of energy during generation, but it has little influence on the other properties of the generated waves. The single internal solitary wave(ISW) structure is a special phenomenon that follows major wave trains, with a distance about 5–8 km. This wave is generated with the leading wave packets during the same tidal period. When a steady current toward the Kara Sea is included, the basic generation process is similar, but the waves toward the Kara Sea weaken and display an internal bore-like structure with smaller amplitude than in the control experiment. In winter, due to the growth of sea ice, stratification across the Kara Strait is mainly determined by the salinity, with an almost uniform temperature close to freezing. A pycnocline deepens near the middle of the water depth(Barents Sea side), and the NIWs process is not as important as the NIWs process in summer. There is no fission process during the simulation.     

基于哨兵一号和高分三号卫星SAR数据的马六甲海峡内孤立波特性研究

漫长狭窄的马六甲海峡是重要的航道，研究该海峡内孤立波特征对潜艇、船只航行和海洋工程都是急需解决的问题。利用高空间分辨率的哨兵1号（Sentinel-1）和高分三号（GF-3）SAR遥感数据，对马六甲海峡的内孤立波特征开展了详细研究。利用哨兵一号2015年6月到2016年12月20景有内孤立波的SAR图像和高分三号2018年4月到2019年3月24景有内孤立波的SAR图像，统计分析了马六甲海峡海域的内孤立波空间分布特征。发现内孤立波多以内孤立波包以及单根内孤立波形式出现，内孤立波头波的波峰线最长可达39km。采用高阶非线性薛定谔方程反演模型可以计算出内孤立波的振幅与群速度，计算得到的内孤立波振幅和波包的传播群速度分别为4.7m ~ 23.9m和0.12m/s ~ 0.40m/s。由KdV方程得到的单根内孤立波的相速度为0.26m/s ~ 0.60m/s。可以得到，马六甲海峡内孤立波的振幅与传播速度与地形密切相关。