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1.
《中国海洋湖沼学报》2016,(6)
Coherent and incoherent internal tides(CITs and ICITs) in the southern South China Sea were investigated from two sets of _18-month mooring current records. The CITs were mainly composed of diurnal Q _1, O _1, P _1 and K _1 and semidiurnal M_2. The observed diurnal internal tides(ITs) were more coherent than the semidiurnal constituents. Coherent diurnal variance accounted for approximately 58% of the diurnal motion, whereas semidiurnal tides contained a much smaller fraction(35%) of coherent motion. The ICITs mainly consisted of motion at non-tidal harmonic frequencies around the tidal frequency, and showed clear intermittency. The modal decomposition of CITs and ICITs showed that CITs were dominated by mode-1, whereas mode-1 and higher modes in ICITs signals showed comparable amplitudes. CITs and ICITs accounted for approximately 64% and 36% of the total kinetic energy of internal tides, respectively. 相似文献
2.
《中国海洋大学学报(英文版)》2020,(3)
The spatial-temporal characteristics of the barotropic tides and internal tides(ITs) northeast of Taiwan Island are examined, based on a 1-year mooring current observations from May 23, 2017 to May 19, 2018. The results of harmonic tidal analysis show that the barotropic tides are dominated by semidiurnal tides, which is mainly controlled by M_2 tidal components. Moreover, the vertical structures of diurnal and semidiurnal ITs show that the semidiurnal IT shows notable seasonal variation, whereas seasonal variations of the diurnal IT energy is not significant. The semidiurnal IT energy in winter half year is twice that in summer half year. The seasonal variation of semidiurnal IT is mainly modulated by the direction change of the current rather than by the topographic features and stratification. In summer(winter) half year cyclonic(anti-cyclonic) eddies meanly control at this point, so the flow direction is mainly in the southwest(northeast) direction, causing the background flow to flow along(perpendicular to) the isobath. When crossing the isobath, the ITs are generated by the interaction of the barotropic tide and the topography, resulting in the increase of the tidal energy in the winter half year. 相似文献
3.
《中国海洋湖沼学报》2017,(6)
Recent satellite altimeter observations have indicated that internal tides(ITs) from the Luzon Strait(LS) propagate more than 2 500 km into the Western Pacific(WP). This study used a high-resolution three-dimensional numerical model to reproduce and examine the ITs radiation process. The propagation of diurnal and semidiurnal ITs showed dif ferent patterns and variations. Diurnal ITs with lower frequency were af fected more by the earth's rotation and they were bent more toward the equator than semidiurnal ITs. ITs phase speeds are functions of latitude and diurnal ITs showed greater distinctions of phase speeds during propagation. For M_2 ITs, the wavelength remained nearly unchanged but the beam width increased significantly during propagation away from the LS. For diurnal ITs(K_1 and O_1), the wavelength decreased noticeably with latitude, while the beam width varied little during propagation because of blocking by land. Baroclinic energy was also examined as a complement to satellite results reported by Zhao(2014). The magnitude of the generated baroclinic energy flux reduced remarkably within 300 km from the generation site but it then decayed slowly when propagating into abyssal sea. Baroclinic energy of diurnal ITs was found to dissipate at a slower rate than semidiurnal ITs along the main propagation path in the WP. 相似文献
4.
Vertical structure of the tidal currents on the continental shelf of the East China Sea 总被引：1，自引：0，他引：1
The available data on tidal currents spanning periods greater than six months for the continental shelf of the East China Sea (26°30.052′N, 122°35.998′E) were analyzed using several methods. Tidal Current Harmonic Analysis results demonstrated that semi-diurnal tides dominated the current movement. The tidal currents of the principal diurnal and semidiurnal rotated clockwise with depth, with the deflection of the major semi-axes to the right in the upper layer and to the left in the lower layer. The vertical structures of two principal semi-diurnal constituents-M2 and S2-were similar, which indicates that the tidal currents are mainly barotropic in this area. The main features of the variation of the four principal tidal constituents with depth demonstrate that the currents in this region are influenced by the upper and lower boundary layers. Therefore, the tidal constituents of the shallow water are similar. Different vertical modes were calculated based on the Empirical Orthogonal Function (EOF) analysis of the Eastern and Northern components of the tidal currents, with a variance contribution for the zero-order model of at least 90%. The variance contribution of the baroclinic model is minimal, which further reveals a strong barotropic character for the tidal currents of this region. 相似文献
5.
《中国海洋大学学报(英文版)》2021,20(5)
In this study, power spectral density and inverse analyses were performed to obtain the frequency characteristics and spatial distribution of temperature in the Qiongzhou Strait using reciprocal sound transmission data obtained in a coastal acoustic tomography experiment conducted in 2013. The results reveal three dominant types of internal tides(diurnal, semidiurnal, and terdiurnal).Spectral analysis of the range-average temperature deviation along the northern and southern transmission paths shows that along the northern path, the energy of the diurnal internal tides was significantly larger than that of the semidiurnal tides. The semidiurnal internal tides, in contrast, were more pronounced along the southern path. A terdiurnal spectrum with an energy level equivalent to that of the semidiurnal internal tide was discernable for both the northern and southern paths. These three types of internal tides can also be recognized in the time variation of the zonal-average temperature deviation. The diurnal internal tides were strengthened along the northern coast, implying their westward propagation and the existence of coastally trapped effects. The other two types of internal tides, which have smaller wavelengths than the diurnal internal tides, were less resolved over the entire tomographic domain due to the insufficient resolution of the inversion. The data quality was verified to be satisfactory by error estimation. 相似文献
6.
Temporal variations in multimodal structures of diurnal (D 1) and semidiurnal (D 2) internal tides were investigated on the continental slope of the Dongsha Plateau, based on 2-month moored acoustic Doppler current profiler observations. Harmonic analysis indicated that the D 1 components (K 1 and O 1) dominated the internal tide field. The vertical structure of the K 1 constituent presented a first-mode structure while the M 2 constituent seemed to exhibit a high-mode structure. Amplitude spectra analysis of the current data revealed differences in baroclinic current amplitudes between different water depths. Temporal variations in modal structures ware analyzed, based on the D 1 and D 2 baroclinic tides extracted from the baroclinic velocity field with band-pass filters. Analysis showed that the magnitude of the D 1 internal tide current was much larger than the D 2 current, and temporal variations in the modal structure of the D 1 internal tide occurred on an approximately fortnightly cycle. The EOF analyses revealed temporal transformation of multimodal structures for D 1 and D 2 internal tides. The enhancement of the D 1 internal tide was mainly due to the superposition of K 1 and O 1, according to the temporal variation of coherent kinetic energy. 相似文献
7.
A two-dimensional spectral-difference mode (with vorticity and density equations) of internal tides isdeveloped for studying the genration and propagration of internal tides generated at the continentalshelf/slope. In general, internal tides propagate seaward in deep sea regions and shoreward on the shelf,and are dissipated rapidly. When the Vaisala frequency decreases vertically, waves may be mostly limited to thecontinental slope region. in deep sea region, motions may have either boam-like structure or modal structure,depending on the stratification strerigth and structure, whereas a modal structure may always exist onthe shelf. Waves show strong bottom intensification on the slope when strong stratification exists on thebottom. The barotropic tidal advection may affed the temporal character of internal tides at thecontinental slope, shelf break and shelf regions. but may have little influence on the energy density and energy flux of internal tides. ln the case of strong stratification, waverforms of 相似文献
8.
The motions of diurnal, semidiurnal, and shallow-water tides and tidal current in the Bohai Sea are computed using a finite-difference
method based on two-dimensional tidal wave equations. Good agreement of the computed results with the observed data is achieved
for diurnal and semidiurnal tides. The general pattern of the computed quarterdiurnal tide conforms to the observed pattern,
but the computed amplitudes are on the high side. This is attributed to the ineligibility of the friction terms in the two-dimensional
governing equations to dissipate the energy of high frequency tidal waves. It is found that the existing semidiurnal cotidal
charts have considerable differences in Laizhou Bay. The difference is likely caused by the movement of the coastline of the
Yellow River Delta. The present result coincides with the recent empirical cotidal chart. The computation shows a new current-amphidromic
point for both semidiurnal and durnal tidal currents. The diurnal current has two current-amphidromic points in the Bohai
Sea with co-phase lines progressing clockwise round these points. The semi-diurnal current has also two current-amphidromic
points with co-phase lines progressing counterclockwise. The distributions of tide-induced residual elevation and currents
are illustrated, and the tidal energy fluxes are computed.
Institute of Marine Scientific and Technological Information, State Oceanic Administration
Contribution No. 1125, Institute of Oceanology, Academia Sinica, Qingdao, China. 相似文献
9.
An isopycnic-coordinate internal tide model and its application to the South China Sea 总被引：1，自引：0，他引：1
A three-dimensional isopycnic-coordinate ocean model for the study of internal tides is presented. In this model, the ocean interior is viewed as a stack of isopycnic layers, each characterized by a constant density. The isopycnic coordinate performs well at tracking the depth variance of the thermocline, and is suitable for simulation of internal tides. This model consists of external and internal modes, and barotropic and baroclinic motions are calculated in the two modes, respectively. The capability of simulating internal tides was verified by comparing model results with an analytical solution. The model was then applied to the simulation of internal tides in the South China Sea (SCS) with the forcing of M2 and K1 tidal constituents. The results show that internal tides in the SCS are mainly generated in the Luzon Strait. The generated M2 internal tides propagate away in three different directions (branches). The branch with the widest tidal beam propagates eastward into the Pacific Ocean, the most energetic branch propagates westward toward Dongsha Island, and the least energetic branch propagates southwestward into the basin of the SCS. The generated K1 internal tides propagate in two different directions (branches). One branch propagates eastward into the Pacific Ocean, and the other branch propagates southwestward into the SCS basin. The steepening process of internal tides due to shoaling effects is described briefly. Meridionally integrated westward energy fluxes into the SCS are comparable to the meridionally integrated eastward energy fluxes into the Pacific Ocean. 相似文献
10.
An investigation of the properties of low-frequency internal waves in the northeastern China Seas 总被引：1，自引：0，他引：1
A simple and practical method for separating low-frequency internal waves from low-frequency barotropic waves was employed
to analyze the observation data. Analysis of some data gathered in the northestern China Seas revealed strong semidiurnal
internal tides and near-inertial internal waves at the stations in the East China Sea and near-inertial waves but no semidiurnal
internal tides at the station in the centre of the Yellow Sea. The geographic properties of low-frequency internal waves in
the region are discussed primarily on the basis of the mechanism of internal tide generation on the continental shelfbreak,
and the mechanisms of local generation and global generation.
Project supported by the National Natural Science Foundation of China. 相似文献
11.
Three seabed-mounted TD/CTD chains and two upward-looking acoustic Doppler current profilers(ADCPs) in the southwest of Zhangzi Island are used and a simultaneous cruise observation in the northern North Yellow Sea(NYS) is conducted to study temperature variation in the bottom thermal front zone of the NYS Cold Water Mass(NYSCWM) during the summer of 2009. In the flood-ebb tidal cycles, the bottom temperature decreases(increases) during flood(ebb) tides, which are dominated by the tidal-current induced horizontal advection. The ebb tide-induced temperature increase is larger than the flood tide-induced temperature decrease due to seasonal warming. In the spring-neap tidal cycles, the temperature and the vertical temperature structure show notable fortnightly variation from 16 July to 25 August. The bottom temperature increases from neap to spring tides and decreases from spring to neap. The Richardson number demonstrates strengthened vertical mixing during spring tides but enhanced stratification during neap tides. The spring-neap variation in vertical shear caused by tidal current is the dominant factor that induces the fortnightly variation in vertical mixing and thus bottom temperature. 相似文献
12.
采用最大熵谱（MEM）分析法,计算河北省内昌黎、兴济、新乐、阳原、肥乡、大柏舍6个大地电场台站的数据,结合地磁场数据分析河北省内各台电场数据的谱成分特征。结果表明,河北省各台大地电场周期主要是以12 h半日波成分为主,24 h、8 h周期成分明显;磁暴时其谱值高于静日变化谱值;电场日变化主要周期成分来自外空间电流体系的变化。结果基本揭示了河北省内电场观测的背景谱成分特征,为电场数据在地震预报中的应用提供参考依据。 相似文献
13.
Currents and mixing in the northern South China Sea 总被引：1，自引：0，他引：1
We investigated the vertical distribution of current velocity data of the entire water column at a site on the continental
shelf of the northern South China Sea (SCS) from August 4 to September 6, 2007, and found that the characteristics of barotropic
and baroclinic tides are mainly diurnal. During the observation period, we also estimated the mixing before and after the
passage of Typhoon Pabuk. We found that the internal-wave-scale dissipation rate, the turbulent dissipation rate, and the
mixing rate in every water layer increased by about an order of magnitude after the typhoon passage. We analyzed a case of
abrupt strong current and calculated the mixing rate before, during, and after the typhoon event. The results show that the
internal-wave-scale dissipation rate and the mixing rate in every water layer increased by about two orders of magnitude during
the event, while the turbulent dissipation rate increased by about an order of magnitude. Passage of the abrupt strong current
could also have increased the mixing rate of affected seawater by more than an order of magnitude. However, the passage of
the typhoon differed in that there was an increase in mixing only in the lower layer where the abrupt strong current was particularly
strong. The variation of the mixing rate may help us to understand the effects of typhoons and abrupt strong currents on the
mixing of seawater. 相似文献
14.
A fully nonlinear,three-dimensional nonhydrostatic model driven by four principal tidal constituents(M2,S2,K1,and O1) is used to investigate the spatial-temporal characteristics and energetics of internal tides in Luzon Strait(LS).The model results show that,during spring(neap) tides,about 64(47) GW(1 GW=109 W) of barotropic tidal energy is consumed in LS,of which 59.0%(50.5%) is converted to baroclinic tides.About 22(11) GW of the derived baroclinic energy flux subsequently passes from LS,among which 50.9%(54.3%) flows westward into the South China Sea(SCS) and 45.0%(39.7%) eastward into the Pacific Ocean,and the remaining 16(13) GW is lost locally owing to dissipation and convection.It is revealed that generation areas of internal tides vary with the spring and neap tide,indicating different source areas for internal solitary waves in the northern SCS.The region around the Batan Islands is the most important generation region of internal tides during both spring and neap tides.In addition,the baroclinic tidal energy has pronounced seasonal variability.Both the total energy transferred from barotropic tides to baroclinic tides and the baroclinic energy flux flowing out of LS are the highest in summer and lowest in winter. 相似文献
15.
We used a set of 75-day long ADCP data from the northeastern South China Sea (SCS) to investigate nonlinear interactions among
freely propagating internal tidal waves. The kinetic energy spectra displayed significant peaks at some higher tidal frequencies,
such as O1M2 (O1+M2), and M4 (M2+M2), where O1 is the lunar diurnal internal tide, M2 is the lunar semidiurnal internal tide, and M4 is the first higher harmonic frequency of M2. These higher tidal harmonic frequency peaks, as well as the fundamental tidal harmonic peaks, show a σ
−2.3 spectral falloff rate with frequency. In addition, we explored the possible generation mechanism of higher tidal harmonics.
Analysis on the rotary and bicoherence spectra suggests that strong forced non-resonant interaction induced by nonlinear advections
was the dominant physical mechanism that induced these higher tidal harmonics. Moreover, the energetic, freely propagating
semidiurnal (M2) internal tidal wave played the most crucial role in these interactions. These results indicate that strong nonlinear forced
non-resonant interactions among internal tides can be one of the processes responsible for the redistribution of energy in
the internal wave spectrum. 相似文献
16.
As one of the biggest marginal seas in the western Pacific margin, the South China Sea (SCS) experienced continental rifting and seafloor spreading during the Cenozoic. The northern continental margin of the SCS is classified as a passive continental margin. However, its depositional and structural evolution remains controversial, especially in the deep slope area. The lack of data hindered the correlation between continental shelf and oceanic basin, and prevented the establishment of sequence stratigraphic frame of the whole margin. The slope basins in the mid-northern margin of SCS developed in the Cenozoic; the sediments and basin infill recorded the geological history of the continental margin and the SCS spreading. Using multi-channel seismic dataset acquired in three survey cruises during 1987 to 2004, combined with the data of ODP Leg 184 core and industrial wells, we carried out the sequence stratigraphic division and correlation of the Cenozoic in the middle-northern margin of SCS with seismic profiles and sedimentary facies. We interpreted the seismic reflection properties including continuity, amplitude, frequency, reflection terminals, and 15 sequence boundaries of the Cenozoic in the study area, and correlated the well data in geological age. The depositional environment changed from river and lake, shallow bay to open-deep sea, in correspondence to tectonic events of syn-rifting, early drifting, and late drifting stages of basin evolution. 相似文献
17.
Reflection occurs when internal tides impact on a steep continental slope. Separating reflected internal tide signals from incident ones is crucial to develop the parameterization of internal tide-driven turbulent mixing on the continental slopes. In this study, the performances of three different methods for estimating internal tide reflections are examined by using two different cases. The Hilbert transform-based method is found to be more suitable than two other methods for both cases considered in this study. The two other methods are effective for westward-propagating mode-1 internal tides impacting a slope, but inappropriate in the case where internal tides radiate from a Gaussian ridge impact the slope because of their inaccurate estimation of incident internal tides in the latter case. Such inaccurate estimation further influences the extraction of reflected signals and calculation of the reflected and cross term of energy fluxes. In addition, it should be noted that, due to the use of filtering, the method based on Hilbert transform may result in slight bias when assessing the incident and reflected signals near topographic features. 相似文献
18.
The Taiwan Strait has recently been proposed as a promising site for dynamic tidal power systems because of its shallow depth and strong tides. Dynamic tidal power is a new concept for extracting tidal potential energy in which a coast-perpendicular dike is used to create water head and generate electricity via turbines inserted in the dike. Before starting such a project, the potential power output and hydrodynamic impacts of the dike must be assessed. In this study, a two-dimensional numerical model based on the Delft3D-FLOW module is established to simulate tides in China. A dike module is developed to account for turbine processes and estimate power output by integrating a special algorithm into the model. The domain decomposition technique is used to divide the computational zone into two subdomains with grid refinement near the dike. The hydrodynamic processes predicted by the model, both with and without the proposed construction, are examined in detail, including tidal currents and tidal energy flux. The predicted time-averaged power yields with various opening ratios are presented. The results show that time-averaged power yield peaks at an 8% opening ratio. For semidiurnal tides, the flow velocity increases in front of the head of the dike and decreases on either side. For diurnal tides, these changes are complicated by the oblique incidence of tidal currents with respect to the dike as well as by bathymetric features. The dike itself blocks the propagation of tidal energy flux. 相似文献
19.
Mooring observations were conducted from July 16, 2011 to March 30, 2012 east of Mindanao, Philippines(127°2.8′E, 8°0.3′N) to observe the abyssal current at about 5600 m deep and 500 m above the ocean bottom. Several features were revealed: 1) the observed abyssal current was highly variable with standard deviations of 57.3 mm/s and 34.0 mm/s, larger than the mean values of-31.9 and 16.6 mm/s for the zonal and meridional components, respectively; 2) low-frequency current longer than 6 days exhibited strong seasonal variation, flowing southeastward(mean flow direction of 119.0° clockwise from north) before about October 1, 2011 and northwestward(mean flow direction of 60.5° counter-clockwise from north) thereafter; 3) the high-frequency flow bands were dominated by tidal currents O 1, K 1, M 2, and S 2, and near-inertial currents, whose frequencies were higher than the local inertial frequency. The two diurnal tidal constituents were much stronger than the two semidiurnal ones. This study provides for the first time an observational insight into the abyssal western boundary current east of Mindanao based on long-term observations at one site. It is meaningful for further research into the deep and abyssal circulation over the whole Philippine Sea and the 3D structure of the western boundary current system in this region. More observational and high-resolution model studies are needed to examine the spatial structure and temporal variation of the abyssal current over a much larger space and longer period, their relation to the upper-layer circulation, and the underlying dynamics. 相似文献
20.
为了合理有效地分析和挖掘海洋涡旋移动数据中的规律和模式,本文以基于空间交互性流聚类的区域化方法为基础,提出了一种海洋涡旋移动特征的网格区域化方法。该方法以网格为统计单元,对涡旋移动数据进行组织,通过图论模型构建海洋涡旋的移动网络图,然后采用基于平均邻接的层次聚类和基于模块度的划分2个步骤,实现涡旋移动特征的区域划分。基于该算法,对1992-2011年中国南海海洋涡旋移动数据进行算法实验,结果表明,南海海洋涡旋按照其移动频繁性特征可分为越南东南部（R1）、越南东部-巴拉望岛（R2）、南海北部（R3）3个区域。其中,R1区域包含了南海西南部深海盆地区的涡旋活跃条带;R2区域体现了南海中部涡旋向西移动的活动规律;R3区域则包含了南海北部东北-西南走向条带。3个区域内冷涡和暖涡具有明显的季节性变化特征：R1和R3区域冷暖涡变化相似,暖涡在夏秋季移动最多,冬季最少,而冷涡则相反,夏秋季移动最少,随后逐渐增加,并在春季达到峰值;R2区域暖涡在春季移动最多,而冷涡在夏冬移动最多,春秋移动相对较弱。 相似文献