Aspects of Deep Ocean Mixing

The turbulent motions responsible for ocean mixing occur on scales much smaller than those resolved in numerical simulations of oceanic flows. Great progress has been made in understanding the sources of energy for mixing, the mechanisms, and the rates. On the other hand, we still do not have adequate answers to first order questions such as the extent to which the thermohaline circulation of the ocean, and hence the earth's climate, is sensitive to the present mixing rates in the ocean interior. Internal waves, generated by either wind or flow over topography, appear to be the principle cause of mixing. Mean and eddy flows over topography generate internal lee waves, while tidal flows over topography generate internal tides. The relative importance of these different internal wave sources is unknown. There are also great uncertainties about the spatial and temporal variation of mixing. Calculations of internal tide generation are becoming increasingly robust, but we do not know enough about the subsequent behavior of internal tides and their eventual breakdown into turbulence. It does seem, however, that most internal tide energy flux is radiated away from generation sites as low modes that propagate over basin scales. The mechanisms of wave-wave interaction and topographic scattering both act to transfer wave energy from low modes to smaller dissipative scales. This revised version was published online in August 2006 with corrections to the Cover Date.     

赤道西太平洋 1°45''''S,156°E 海区的半日内潮波特性

通过对TOGA-COARE期间的一组锚系仪器阵列资料的分析得出:在赤道西太平洋1°45′S,156°E.海域存在显著的半日潮频内波,它的水平波数(波长)、垂向波数、水平传播速度和垂向传播速度分别约为:3.3×10-2 km-1 (210 km),-1.6×10-3 m-1,2.0 m/s,-3.8 cm/s.波形向斜下方传播,亦即波能向斜上方传输.它在观测点西南方生成后,向东北方向传播,到达观测海区.流速矢量旋转谱水平随深度的变化呈马鞍形,低谷及深处的峰所在深度分别与南赤道流及赤道潜流的南边界所在深度大体一致.旋转椭圆主轴方位角随深度变化,在浅层(40 m处)为北偏东30°,到深处(324 m)转为东偏南14°.总体上呈东北方向,表明波来自西南方向.     

赤道西太平洋1°45′S,156°E海区的半日内潮波特性(英文)

通过对TOGA-COARE期间的一组锚系仪器阵列资料的分析得出:在赤道西太平洋1°45′S,156°E。海域存在显著的半日潮频内波,它的水平波数(波长)、垂向波数、水平传播速度和垂向传播速度分别约为:3.3×10-2km-1(210km),-1.6×10-3m-1,2.0m/s,-3.8cm/s。波形向斜下方传播,亦即波能向斜上方传输。它在观测点西南方生成后,向东北方向传播,到达观测海区。流速矢量旋转谱水平随深度的变化呈马鞍形,低谷及深处的峰所在深度分别与南赤道流及赤道潜流的南边界所在深度大体一致。旋转椭圆主轴方位角随深度变化,在浅层(40m处)为北偏东30°,到深处(324m)转为东偏南14°。总体上呈东北方向,表明波来自西南方向。     

The slanting property of semi-diurnal internal tide propagation in the Pacific Ocean at 1°45′S, 156°E

1Introduction DuringtheTOGA COARE,extensivejointin ternationaloceanicobservationswerecarriedoutin thewesternequatorialPacificOceanandavasta mountofvaluabledatawereobtained.Themaindata usedhereincludethedatafromasinglemooringin strumentarrayat1°45′S,156°E,deployedbythe WoodsHoleOceanographicInstitution(WHOI)and theCTD(profilerofconductivity-temperature-depth)datacollectedbytheChineseRVXiangy anghongNo.5.Fangetal.(2000)described brieflytheseobservationdataandanalyzedthedis persion…     

The slanting property of semi-diurnal internal tide propagation in the Pacific Ocean at 1°45′S, 156°E

By analyzing a data set collected using a moored instrument array and CTD during TOGA-COARE, it is found that there exist remarkable internal tides in the western equatorial Pacific Ocean around 1°45′S,156°E, whose horizontal wavenumber (wavelength), vertical wavenumber, h 156° orizontal propagation speed and vertical propagation speed are 3.3×10-2km-1(210 km),-1.6×10-3m, 2.0 m/s and -3.8 cm/s, respectively, that is, the waveform propagates downwards slantingly. Moreover, the propagating direction rotates statistically clockwise as the depth increases and its cause is unclear.     

分层海洋中运动物体生成的内波

该文提供分层海洋中运动物体生成内波的理论、数值和实验研究的背景资料的综述 ,并给出理论研究的 Green函数、正交模态模式和极点回避等方法的评述。数值研究给出数值求解Wronsky行列式的源求解方法及介绍直接差分计算含源内波方程和积分方程的方法。有关源致内波的实验研究 ,作者介绍物体在分层流水槽运动时生成内波的两个典型实验及其主要实验结果。最后评述船舶在海洋表面处生成表面波的研究方法 ,以此指导水下 Rankine卵形体生成内波的实验研究。     

浅海内波及声场起伏数值研究

为探讨声学方法监测(反演)海洋内波的可行性,分析ASIAEX2001亚洲海海洋声学实验定点温度链实验数据,结果表明：实验期间存在M2内潮波、周期10～30min非线性内波现象,并观测到双温跃层同相传播“双非线性内波”。分别对垂直和平行于内波传播方向传播声场进行了数值计算分析。垂直于内波传播方向的声传播计算结果表明：简正波波数时间演化函数的频谱与内波引起的声速剖面变化频谱基本一致;简正波系数(模值)时间演化函数的频谱与内波引起的声源位置处的声速演化函数的频谱基本一致;高阶简正波波数差随时间的变化要比低阶简正波波数差小约1个量级。平行于内波传播方向的声传播计算结果表明：内潮波主要导致相邻简正波间耦合;非线性内波包能够导致跨号甚至垮多号简正波间耦合。讨论了2种海洋内波声学监测方法。     

关于南沙海域内波与细结构研究

作者综述了南沙海域内波及细结构研究现状。首先介绍研究中所用的国际或国内首次使用的一些研究方法,它们包括最基础的ＣＴＤ资料质量控制的方法,浮力频率计算方法、频散关系和波函数计算方法,细结构概率分布假设检验方法,内波检测方法,内潮计算的谱差分方法等。而后总结所得的研究成果（其中一部分是首次发表的）,它们包括南沙海区浮力频率的分类及其随地域和季节的变化规律;内波频散关系和波函数;细结构特性及其与内波的关系;细结构的非高斯概率分布特性;垂向波数谱特性及其随季节、地域及水层的变化;频率特性;Ｃｏｘ 数及其概率分布;内潮特性等。最后对今后研究方向作了展望。     

Influence of Coupled Rossby Waves on Primary Productivity and Tuna Abundance in the Indian Ocean

Interannual coupled Rossby waves in the extratropical Indian Ocean propagate westward in covarying pycnocline depth, sea surface temperature, and meridional surface wind anomalies from the west coast of Australia between 15°S and 35°S, taking 3–4 years to transit the interior ocean to Madagascar. In the interior subtropical gyre, where the tuna longline catch (TLC) mainly concerns two species (albacore and bigeye), these waves have been observed to affect year-to-year changes in catch, with wave crests (troughs) in the main pycnocline associated with high (low) TLC anomalies. This suggested that tuna longline catch is associated with the entrainment of nutrient-rich pycnocline water into the photic zone and a subsequent increase in primary productivity there. Here, this hypothesis is examined within the context of SeaWiFS chlorophyll concentration (CC). We find the situation the opposite of that expected, with wave crests (troughs) in the main pycnocline associated with low (high) CC anomalies averaged over the photic zone. These results are shown to be consistent with a model relating the anomalous CC tendency to upper-layer divergence in the wave, not unlike that relating surface slicks to upper-layer divergence in internal gravity waves. Thus, the connection between interannual coupled Rossby waves and TLC in the interior subtropical gyre does not appear to derive from wave-induced modulation of the pelagic food web. This revised version was published online in July 2006 with corrections to the Cover Date.     

南海西北陆坡区内潮与近惯性内波观测研究

通过对2006年南海西北部海域近3个月的全水深流速观测资料的分析,研究了该海区正压潮、内潮及近惯性内波的时空分布特征。结果表明,全日内潮明显强于半日内潮,且最大潮流均出现在海洋上层;内潮的主轴方向基本沿东南-西北方向,近似与局地等深线垂直;内潮能量显示出明显的时间长度约为半月的大小潮调制周期;全日内潮的coherent部分占全日内潮能量的70%,而半日内潮的coherent部分占半日内潮能量的53%;进一步研究发现半日内潮主要由第一模态主导,而全日内潮第三模态能量占总能量的比例仅次于第一模态且量值上与之相当;强风过程可激发出强的近惯性运动,暖涡使得近惯性内波能量更有效地向海洋深层传播,冷涡则不利于近惯性内波能量向下传播。     

Is the small-scale turbulence an exclusive breaking product of oceanic internal waves

On the basis of the theoretical research results by the author and the literature published up to date, the analysis and the justification presented in this paper show that the breaking products of oceanic internal waves are not only turbulence, but also the fine-scale near-inertial internal waves (the oceanic reversible finestructure) for inertial waves and the internal solitary waves for internal tides respectively. It was found that the oceanic reversible finestructure may be induced by the effect of the horizontal component f (f = 2Ωcosφ) of the rotation vector on inertial waves. And a new instability of the theoretical shear and strain spectra due to the effect of f occurs at critical vertical wavenumber β c ≈ 0.1 cpm. It happens when the levels of shear and strain of the reversible finestructure are higher than those of inertial waves, which is induced by the effect of f along an "iso-potential-pycnal" of internal wave. If all breaking products of internal waves are taken into account, the average kinetic energy dissipation rate is an order of magnitude larger than the values of turbulence observed by microstructure measurements. The author’s theoretical research results are basically in agreement with those observed in IWEX, DRIFTER and PATCHEX experiments. An important impersonal fact is that on the mean temporal scale of thermohaline circulation these breaking products of internal waves exist simultaneously with turbulence. Because inertial waves are generated by winds at the surface, and internal tides are generated by strong tide-topography interactions, the analysis and justification in this paper support in principle the abyssal recipes Ⅱ:energetics of tidal and wind mixing by Munk & Wunsch in 1998, in despite of the results of microstructure measurements for the turbulent kinetic energy dissipation rate and the diapycnal turbulent eddy diffusivity.     

Multimodal structure of the internal tides on the continental shelf of the northwestern South China Sea

Based on the moored current and temperature observations during the summer of 2005, the vertical structure of the internal tides on the continental shelf of the northwestern South China Sea (SCS) is studied. The vertical structure of the internal tides was found to differ greatly between semidiurnal and diurnal constituents. Generally, the diurnal constituents are dominated by the first-mode motions, which are consistent with the overwhelming first-mode signals in the northeastern SCS. In contrast, the semidiurnal internal tides, unlike the predomination of the first-mode variations in the northeastern area, exhibit a higher modal structure with dominate second-mode signals in the observational region. Moreover, although the diurnal internal tides are much stronger than the semidiurnal component, the shear caused by the latter over various scales was found to be significant compared to that induced by the diurnal tides, probably due to the superposition of the first-mode and higher-mode (smaller scale) semidiurnal variations. Further analysis demonstrates that the shear induced by the diurnal internal tides is larger than that induced by the semidiurnal variations around 45 m depth, where the first-mode current reversal in the vertical happens, while below 45 m depth higher-mode semidiurnal internal tides generally produce larger shear than that by the diurnal component. The northwest-propagating semidiurnal internal tides of higher-mode with small vertical scale, probably do not originate from a distant source like Luzon Strait, but were likely generated near the experiment site.     

A Historical Note on the Study of Ocean Surface Waves

The modern study of ocean surface waves started with a pioneer study by Sverdrup and Munk (1947). More than half a century has passed since then and the study of ocean surface waves has greatly advanced. The current numerical wave models, supported by many fundamental studies, enable us to compute ocean surface waves on a global scale with sufficient accuracy for practical purposes. However, physical process controlling the energy balance of ocean surface waves is still not completely understood. The present note is a rough sketch of the historical development of the study of ocean surface waves in the latter half of the twentieth century when the Oceanographic Society of Japan was founded and grew. This revised version was published online in August 2006 with corrections to the Cover Date.     

南海北部孤立波对近岸波动的响应

On the basis of the time series observations from a temperature chain and an acoustic Doppler current profiler on the continental shelf of the northern South China Sea, a sequence of internal solitary waves （ISWs） and background waves （BWs, including internal tides and near-inertial waves） on the continental shelf were captured simultaneously after the transit of Typhoon Neast in October 2011. These measurementsprovided a unique opportunity to explore the influence of BWs on the ISWs. The BWs appeared a conversion on the current strength and vertical mode structure during the observational period. The BWs were dominated by weak and mode-one waves before October 2 and then turned to strong and high-mode waves after that time. Meanwhile, the ISWs displayed different wave structures before and after October 2, which was closely related to BWs＇ changes. According to the current profiles of BWs, the high-mode wave structure with strong current could significantly strengthen the vertical shear of ISWs in the near-surface layer and promote the breaking of ISWs, and thus it may play an important role in affecting the background current condition.     

内波研究的国内外发展现状

海洋内波与海洋水声学、海洋生物学、物理海洋学和军事海洋学等学科有着密切的联系,因而受到各国政府和海洋学家的普遍关注.本文基于近二十年来国外与国内在海洋内波方面的研究成果,首先从各个角度介绍了内潮波与内孤立波方面的国内外发展状况;其次介绍了有关赤道大洋内波方面的研究成果;最后对今后内波研究的发展方向做了展望.     

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.     

分层热带海洋模式中的Rossby波和Kelvin波——初始混合层深度异常与大气热力强迫激发波动

利用一个两层半的热带海洋模式,采用数值实验的方法研究了热带海洋对于初始海洋混合层深度异常和大气季节内时间尺度热力强迫激发产生的Ｒｏｓｓｂｙ波和Ｋｅｌｖｉｎ波。研究表明,初始海洋混合层深度异常和大气热力强迫,可以在两层半热带海洋模式中激发产生东向传播具有Ｋｅｌｖｉｎ波性质的波动和具有Ｒｏｓｓｂｙ波性质的波动。热力强迫激发产生海洋Ｒｏｓｓｂｙ波和Ｋｅｌｖｉｎ波所需时间长于初始海洋混合层深度异常和大气季节内动力强迫激发产生两波所需时间,与大气季节内动力强迫激发的Ｒｏｓｓｂｙ波相比,初始深度异常与大气热力强迫激发产生Ｒｏｓｓｂｙ波具有不同的热力性质。     

北印度洋半日潮波的数值模拟研究

基于FVCOM(Finite Volume Coast and Ocean Model)模型,建立北印度洋海域(31^°~102^°E,16^°S~31^°N)的M₂和S₂分潮潮波数值模式,研究北印度洋半日潮潮汐、潮流分布特征。对底摩擦系数进行数值试验,利用代价函数梯度下降法,得到分潮调和常数向量均方根偏差(RMSE)的变化曲线,逼近并确定最优的底摩擦系数。将采用该系数的模拟结果与TOPEX/Poseidon卫星高度计交叉点的调和常数数据、国际海道测量组织(IHO)及部分文献中的验潮站数据进行比较与验证,一致性较好。其中对比卫星数据的振幅偏差为2~4 cm、迟角偏差为7^°~8^°,与验潮站数据的振幅偏差为3~6 cm、迟角偏差为8^°~9^°。根据模拟结果,分析了北印度洋海域M₂和S₂分潮潮波传播特征和潮流椭圆的空间分布特征等。M₂分潮潮波在阿拉伯海南部有1个无潮点,在波斯湾内有2个无潮点,最大振幅超过80 cm;潮流在西北印度洋和孟加拉湾中部大多为顺时针旋转,其余海域大多为逆时针旋转;流速在阿拉伯海东北部、安达曼海、波斯湾和孟加拉湾北部较大,最大流速为160 cm/s,其他海域较小。S₂分潮的潮波传播特征、无潮点的位置和潮流椭圆的空间分布特征等都与M₂分潮类似,但潮波振幅和潮流流速等都相对M₂分潮较小。研究完善了北印度洋海域2个主要半日分潮M₂和S₂的整体特征。     

大洋科学钻探特点与发展趋势——基于国际大洋发现计划科学框架的对比分析

大洋科学钻探计划是地球科学领域迄今为止历时最长、成效最大的国际科学合作计划。自1968年以来,先后经历了深海钻探计划、国际大洋钻探计划、综合大洋钻探计划和国际大洋发现计划4个阶段。进入国际大洋发现计划,IODP工作组两次发布科学框架,文章对两个科学框架进行了对比分析。大洋科学钻探的特点和发展趋势是坚持解决重大科学问题,由地球拓展到太阳系,重视技术和大数据,以及扩大社会影响和宣传。这给我国发起国际大科学计划提供了启示,一要注重科技创新,运用大数据等先进技术;二要加强科学管理,促进开放和共享;三要重视提升影响力,扩大宣传和影响。     

2005黄海声学实验-声传播起伏

2005年夏末、秋初在黄海南部进行一次多家联合海洋声学实验研究,主要目的是研究浅海内波(线形、非线性)及其海洋温度峰面对远距离声传播的起伏效应及其声学方法监测海洋新方法研究。文章综述这几年实验数据处理的一些结果。