AN EXACT SOLUTION OF INTERNAL TIDES GENERATED AT CONTINENTAL SLOPE

By using a coordinate transformation,an exact solution of internal tides is obtained when the bot- tom slope is linear and the V(?)is(?)la frequency is constant.Consequently the dispersion relations of free waves are presented.Compared with Baines solution,the solution derived here is more consistent with experiment     

PROGRESS OF STUDIES ON THE INTERNAL TIDE GENERATED BY THE PASSAGE OF BAROTROPIC TIDE OVER CONTINENTAL SHELF/SLOPE

Various aspects of studies on internal tides are reviewed .Both beam-like structure and modal structure of internal tides may exist in the ocean . Bottom intensifications are caused by many factors .e.g. upstream blocking , which is the result of nonlinear interaction among waves . The energy may decay very fast so that internal tides are mostly locally generated .Internal tides may have considerable residual currents.In a 3-D frame, numerical study revealed that internal waves may interfere with each other to cause strong motions fer from the generation sources.The mechanism that determines how the lee waves break to form various nonlinear waves such as solitary waves, hydraulic jumps and internal surges or bores remains unclear. Analytic study is difficult , so numerical method may be effective . A radiation condition on the open boundary must be employed. A complete 3-D model may gain interesting result.Study on internal tides in China is limited to field observations and data analysis .     

Propagation of internal waves up continental slope and shelf

In a two-dimensional and linear framework, a transformation was developed to derive eigensolutions of internal waves over a subcritical hyperbolic slope and to approximate the continental slope and shelf. The transformation converts a hyperbolic slope in physical space into a flat bottom in transform space while the governing equations of internal waves remain hyperbolic. The eigensolutions are further used to study the evolution of linear internal waves as it propagates to subcritical continental slope and shelf. The stream function, velocity, and vertical shear of velocity induced by internal wave at the hyperbolic slope are analytically expressed by superposition of the obtained eigensolutions. The velocity and velocity shear increase as the internal wave propagates to a hyperbolic slope. They become very large especially when the slope of internal wave rays approaches the topographic slope, which is consistent with the previous studies.     

A layered numerical model for simulating the generation and propagation of internal tides over continental slope III. Numerical experiments and simulation

The layered model in Part I was used to simulate the internal tide in a stratified, two layer, and rectangular sea area with step-like topography. The internal tide current velocities of the upper and lower layers and the interfacial elevations were computed and the effect of the upper layer water depth and density difference were studied. Numerical experiments verified that the model can correctly simulate internal tides. The model was also applied to the northwestern part of the South China Sea to simulate the internal tides there with real topography. The distributions of internal tide amplitude in interfaces were delineated. Contribution No. 3590 from the Institute of Oceanology, Chinese Academy of Sciences. Project 49676275 supported by NSFC and also supported by National Special Research Program 97-926-05-02.     

A layered numerical model for simulating the generation and propagation of internal tides over continental slope

A layered three-dimensional nonlinear numerical model was constructed to simulate the generation and propagation of internal tides over the continental slope. The simulation was split into external mode computation (EMC) and internal mode computation (IMC) to minimize the computational load. IMC was carried out once after EMC was implemented N times. As to EMC, a semi-implicit numerical scheme was applied in such a way that the pressure gradient terms and the velocity divergence terms were discretized semi-implicitly, but the other terms were discretized explicitly. Eulerian-Lagrangian explicit discretization was applied to the convective terms simultaneously. As a result, the stability of EMC did not depend on the wave celerity and time step was not limited by the CFL condition. More than that, use of the conjugate gradient accelerated Jacobi method further improved the computational efficiency of the model. Contribution No. 3588 from the Institute of Oceanology, Chinese Academy of Sciences. Project 49676275 supported by NSFC and National Special Research Program 97-925-05-02.     

Vertical structure of the tidal currents on the continental shelf of the East China Sea

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.     

Scattering process of internal waves propagating over a subcritical strait slope onto a shelf region

The scattering process, which means the redistribution of energy fluy in modenumber space, is analyzed for internal waves propagating from the abyssal ocean onto a subcritical strait slope and then a shelf region. In light of Wunsch＇s work, the waves are analytically expressed as superimposition of eigensolutions distribution of energy flux in the shelf region： one is the ratio of water depth in and the other is the ratio of the slope of the internal tide rays to the topographic energy flux distribution： the energy flux is focused around one modenumber or case, the range of modenumbers where energy flux is distributed is narrow. Two parameters have evident effects on the the shelf region to that in the abyssal ocean slope. Generally, there are two patterns of focused around two modenumbers. In any case, the range of modenumbers where energy flux is distributed is narrow.     

A layered numerical model for simulating the generation and propagation of internal tides over continental slope II stability analysis

INTRODUCTIONAsoneofthemethodsenablingnumericalsolutionofdifferentialequations,thefinite differ encemethodiswidelyacceptedinthestudyofphysicaloceanography.Afinite differenceschememusthavepropertiesofconvergence ,consistencyandstabilitytoyieldusefulapproximatesolutionoftherelevantdifferentialequations.However,thepropertiesneednotbeverifiedonebyonebecausethewell knownLaxLawassuresthattheconvergenceisequivalenttothestabilityforafinitediffer enceschemewithconsistence .Twomainmethodsforstudyin…     

pCO2 distribution and CO2 flux on the inner continental shelf of the East China Sea during summer 2011

Measurements of pH,total alkalinity(TA),partial pressure of CO2(pCO2) and air-sea CO2 flux(FCO2) were conducted for the inner continental shelf of the East China Sea(ECS) during August 2011.Variations in pCO2 distribution and FCO2 magnitude during the construction of the Three Gorges Dam(TGD)(2003-2009),and the potential effects of the TGD on the air-sea CO2 exchange were examined.Results showed that the ECS acts as an overall CO2 sink during summer,with pCO2 ranging from 107 to 585 μatm and an average FCO2 of-6.39 mmol/(m2·d).Low pCO2(<350 μatm) levels were observed at the central shelf(28°-32°N,123°-125.5°E) where most CO2-absorption occurred.High pCO2(>420 μatm) levels were found in the Changjiang estuary and Hangzhou Bay which acted as the main CO2 source.A negative relationship between pCO2 and salinity(R2=0.722 0) in the estuary zone indicated the predominant effect of the Changjiang Diluted Water(CDW) on the seawater CO2 system,whereas a positive relationship(R2=0.744 8) in the offshore zone revealed the influence of the Taiwan Current Warm Water(TCWW).Together with the historical data,our results indicated that the CO2 sink has shown a shift southwest while FCO2 exhibited dramatic fluctuation during the construction of the TGD,which is located in the middle reaches of the Changjiang.These variations probably reflect fluctuation in the Changjiang runoff,nutrient import,phytoplankton productivity,and sediment input,which are likely to have been caused by the operations of the TGD.Nevertheless,the potential influence of the TGD on the CO2 flux in the ECS is worthy of further study.     

Gravity-driven sedimentation on the northwestern continental slope in the South China Sea: Results from high-resolution seismic data and piston cores

mODUCnONGravityflowsedimentationonthenorthwsterncontinentalsl0PeoftheSOuthChinaSea(SCS)are0fgreatinterestfromthescientificandengineeringP0intofview-Th0roughknOWedgofcontinentalsloPepmeessesanddepositionfeatUresispreregUisiteforhydID-carbenexploraion0fdeepwaerandforprotectionofoffhoredrineeopneeringstrUcbes(PlaifonnsandpiPelines)againstnaedhed.ManykindsofmassmovmentPIDCess-eswerefoUndtobeactiveonthen0rthernSCS(Damuth,l979;l98O).High-freqUency(3.5ffo)echo-chaIaCterInaPPingisawell…     

Distribution and generic composition of culturable marine actinomycetes from the sediments of Indian continental slope of Bay of Bengal

Actinomycetes population from continental slope sediment of the Bay of Bengal was studied. Samples were collected during two voyages of FORV Sagar Sampada in 2004 （May-June） and 2005 （July） respectively from 11 transects （each transect had ca. 200 m, 500 m, and 1 000 m depth stations）. The physicochemical parameters of overlying water, and sediment samples were also recorded. The actinomycete population ranged from 5.17 to 51.94 CFU/g dry sediment weight and 9.38 to 45.22 CFU/g dry sediment weight during the two cruises respectively. No actinomycete colony was isolated from stations in 1 000 m depth. Two-way analysis of variance showed significant variation among stations （ANOVA two-way, P〈0.05）, but no significance was found between the two cruises （ANOVA two-way, P〈0.05）. Populations in stations in 500 m depth in both cruises were higher than that of 200 m depth stations with statistically insignificant difference （ANOVA two-way, P〉0.05）. Three actinomycetes genera were identified. Streptomyces was found to be the dominating one in both the cruises, followed by Micromonospora, and Actinomyces. The spore of Streptomyces isolates showed the abundance in spiral spore chain. Spore surface was smooth. Multiple regression analysis revealed that the influencing physico-chemical factors were sediment pH, sediment temperature, TOC, porosity, salinity, and pressure. The media used in the present study was prepared with seawater. Thus, they may represent an autochthonous marine flora and deny the theory of land runoff carriage into the sea for adaptation to the salinity of the seawater and sediments.     

Theoretical study of the effect of topographic height and width on generation of internal tides

Internal tides generated upon two-dimensional Gaussian topographies of different sizes and steepness are investigated theoretically in a numerical methodology. Compared with previous theoretical works, this model is not restricted by weak topography, but provides an opportunity to examine the influence of topography. Ten typical cases are studied using different values of height and/or width of topography. By analyzing the baroclinic velocity fields, as well as their first eight baroclinic modes, it is found that the magnitude of baroclinic velocity increases and the vertical structure becomes increasingly complex as height increases or width decreases. However, when both height and width vary, while parameter s （the ratio of the topographic slope to the characteristic slope of the internal wave ray） remains invariant, the final pattern is influenced primarily by width. The conversion rate is studied and the results indicate that width determines where the conversion rate reaches a peak, and where it is positive or negative, whereas height affects only the magnitude. High and narrow topography is considerably more beneficial to converting energy from barotropic to baroclinic fields than low and wide topography. Furthermore, parameter s, which is an important non-dimensional parameter for internal tide generation, is not the sole parameter by which the baroclinic velocity fields and conversion rate are determined.     

Simulating the Upper Ocean Circulation on the Belize Shelf： An Application of a Triply Nested-Grid Ocean Circulation Model

We present a three-level nested-grid ocean circulation modeling system for the Belize shelf of the western Caribbean Sea. The nested-grid system has three subcomponents： a coarse-resolution outer model of the western Caribbean Sea; an intermediate-resolution middle model of the southern Mest〉American Barrier Reef System; and a fine-resolution inner model of the Belize shelf. The two-way nesting technique based on the semi-prognostic method is used to exchange information between the three subcomponents. We discuss two applications of the nested-grid system in this study. In the first application we simulate the seasonal mean circulation in the region, with the nested system forced by monthly mean surface fluxes and boundary forcing. The model results reproduce the general circulation features on the western Caribbean Sea and mest〉scale circulation features on the Belize shelf. In the second application, we simulate the storm-induced circulation during Hurricane Mitch in 1998, with the nested-grid system forced by the combination of monthly mean forcing and idealized wind stress associated with the storm. The model results demonstrate that the storm-induced currents transport a large amount of estuarine waters from coastal regions of Honduras and Guatemala to offshore reef atolls.     

基于夜晚灯光数据和Google Earth的城市建成区提取分析

夜晚灯光数据已被广泛应用于提取城市建成区的研究,由于灯光具有溢出特性,因此确定最佳灯光阈值成为研究热点。本研究中总结4种常用最佳阈值确定方法的特点,并使用Google Earth影像空间比较法,确定夜晚灯光数据提取城市建成区的最佳阈值。由于地形、交通等因素影响城市形态,城市形态影响夜晚灯光数据提取城市建成区的最佳阈值大小,因此,根据城市形态将阈值结果分为2类,并得到块状城市和带状城市建成区的最佳灯光阈值分别为43和 47。Google Earth影像空间比较法与其他方法相比具有不受统计数据限制,以及简易操作等优势,且从形态上对城市建成区提取结果进行空间比较;其次,根据城市形态对最佳阈值结果分类,使不同类型的城市建成区提取结果更准确。该方法适用于在地形复杂、形态多样的大尺度空间中提取城市建成区。     

整合DMSP/OLS和NPP/VIIRS夜间灯光遥感数据的长江三角洲城市格局时空演化研究

本文基于1992-2012年DMSP/OLS和2012-2018年NPP/VIIRS夜间灯光遥感数据,对长江三角洲城市群时空演化格局进行监测.考虑到不同卫星夜间灯光遥感数据之间的不一致性以及城市核心区亮度过饱和问题,对DMSP/OLS和NPP/VIIRS数据进行连续性校正、去饱和处理和一致性校正,构建长江三角洲区域19...     

关于在平行断面法资源/储量估算中限制使用梯形体公式的建议

通过理论推导,指出在平行断面法资源／储量估算中,在块段相邻剖面不具有相等对应边的情况下,梯形体公式只是一个近似估算公式,存在着一定的误差。而截面圆锥体公式则是一个精确的通用公式,其使用不受相对面积差大小的限制。因此,在这种情况下,建议放弃使用梯形体公式,而统一使用截面圆锥体公式。     

A comparative study of the sensitivity of F v/F m to phosphorus limitation on four marine algae

We studied the effects of nitrogen (N) and phosphorus (P) supply on Fv/Fm (maximal quantum yield of photosystem II) in the algae Chaetoceros debilis, Dicrateria inornata, Platymonas subcordiformis and Heterosigma akashiwo to determine the sensitivity of Fv/Fm to P-limitation of the four species. Obvious decrease of Fv/Fm value was monitored in periods of P-depletion, the decrease showing different magnitudes among algal species. A more clear decrease of Fv/Fm in Platymonas subcordiformis and Het-erosigma akashiwo was observed, compared with that in Chaetoceros debilis and Dicrateria inornata. After the resupply of P, the index Fv/Fm of the four species all recovered quickly in 24 h. Cell division was maintained and chlorophyll content continued to increase until the end of the experiment in Platymonas subcordiformis and Heterosigma akashiwo, while in Chaetoceros debilis and Dicrateria inornata, the division stopped in the later period when the growth of organisms came into the stationary phase. The most obvious respond of chlorophyll content to P-additions was observed in Het-erosigma akashiwo culture in 24 h. The sensitivity of Fv/Fm to nutrient limitations is different among algal species, and much should be done to improve the application of this index.