The influence of explicit tidal forcing in a climate ocean circulation model

The eight main tidal constituents have been implemented in the global ocean general circulation model with approximate 1° horizontal resolution.Compared with the observation data,the patterns of the tidal amplitudes and phases had been simulated fairly well.The responses of mean circulation,temperature and salinity are further investigated in the global sense.When implementing the tidal forcing,wind-driven circulations are reduced,especially those in coastal regions.It is also found that the upper cell transport of the Atlantic meridional overturning circulation（AMOC） reduces significantly,while its deep cell transport is slightly enhanced from 9×106m3/s to 10×106 m3/s.The changes of circulations are all related to the increase of a bottom friction and a vertical viscosity due to the tidal forcing.The temperature and salinity of the model are also significantly affected by the tidal forcing through the enhanced bottom friction,mixing and the changes in mean circulation.The largest changes occur in the coastal regions,where the water is cooled and freshened.In the open ocean,the changes are divided into three layers：cooled and freshened on the surface and below 3 000 m,and warmed and salted in the middle in the open ocean.In the upper two layers,the changes are mainly caused by the enhanced mixing,as warm and salty water sinks and cold and fresh water rises;whereas in the deep layer,the enhancement of the deep overturning circulation accounts for the cold and fresh changes in the deep ocean.

The performance of a z-level ocean model in modeling the global tide

The performance of a z-level ocean model, the Modular Ocean Model Version 4（MOM4）, is evaluated in terms of simulating the global tide with different horizontal resolutions commonly used by climate models. The performance using various sets of model topography is evaluated. The results show that the optimum filter radius can improve the simulated co-tidal phase and that better topography quality can lead to smaller rootmean square（RMS） error in simulated tides. Sensitivity experiments are conducted to test the impact of spatial resolutions. It is shown that the model results are sensitive to horizontal resolutions. The calculated absolute mean errors of the co-tidal phase show that simulations with horizontal resolutions of 0.5° and 0.25° have about 35.5% higher performance compared that with 1° model resolution. An internal tide drag parameterization is adopted to reduce large system errors in the tidal amplitude. The RMS error of the best tuned 0.25° model compared with the satellite-altimetry-constrained model TPXO7.2 is 8.5 cm for M_2. The tidal energy fluxes of M_2 and K_1 are calculated and their patterns are in good agreement with those from the TPXO7.2. The correlation coefficients of the tidal energy fluxes can be used as an important index to evaluate a model skill.

Synthetic tidal parameters for gravity over China and its neighbor area

The synthetic tidal parameters with high spatial resolution for gravity over China and its neighbor area are constructed with Earth＇s tidal model and ocean tide loading calculated using TPXO7 global ocean tide model as well as tidal data over China seas. The comparison between synthetic parameters and ones observed by spring gravimeters at some seismic network stations and Hong Kong station and one observed by super-conducting gravimeter at Wuhan station shows that the average differences in amplitude factors and phases are smaller than 0.005 and 0.5° respectively; and that the discrepancies between observational and synthetic parameters are dependent on gravimetric technique in that the synthetic parameters are in well agreement with the superconducting gravimetric observations. This also indicates that the synthetic result is a good estimation for tidal gravity, and the numerical results in the present paper not only can provide ground and space gravimetry such as absolute gravimetry with correction model of tidal gravity, but also provide effective tidal parameters over areas where no observation is carried out.

Tidal energy budget in the Zhujiang(Pearl River) Estuary

Tidal energy budget in the Zhujiang（Pearl River） Estuary（ZE） is evaluated by employing high-resolution baroclinic regional ocean modeling system（ROMS）. The results obtained via applying the least square method on the model elevations are compared against the tidal harmonic constants at 18 tide stations along the ZE and its adjacent coast. The mean absolute errors between the simulation and the observation of M_2, S_2, K_1 and O_1 are 4.6, 2.8, 3.2 and 2.8 cm in amplitudes and 9.8°, 15.0°, 4.6° and 4.6° in phase-lags, respectively. The comparisons between the simulated and observed sea level heights at 11 tide gauge stations also suggest good model performance. The total tidal energy flux incoming the ZE is estimated to be 343.49 MW in the dry season and larger than 336.18 MW in the wet season, which should due to higher mean sea level height and heavier density in the dry season. M_2, K_1, S_2, O_1 and N_2, the top five barotropic tidal energy flux contributors for the ZE,import 242.23（236.79）, 52.97（52.08）, 24.49（23.96）, 16.22（15.91） and 7.10（6.97） MW energy flux into the ZE in dry（wet） season, successively and respectively. The enhanced turbulent mixing induced by eddies around isolated islands and sharp headlands dominated by bottom friction, interaction between tidal currents and sill topography or constricted narrow waterways together account for the five energy dissipation hotspots, which add up to about 38% of the total energy dissipation inside the ZE.

Modelling the upwelling off the east Hainan Island coast in summer 2010

A synoptic-scale upwelling event that developed off the east coast of the Hainan Island（EHIU） in the summer of 2010 is defi ned well via processing the Moderate Resolution Imaging Spectroradiometer（MODIS） sea surface temperature（SST） data. The Regional Ocean Modeling System（ROMS） with high spatial resolution has been used to investigate this upwelling event. By comparing the ROMS results against tide station data, Argo fl oat profi les and MODIS SST, it is confi rmed that the ROMS reproduces the EHIU well. The cooler-water core（CWC） distinguished by waters（27） 27.5℃ in the EHIU, which occurred in the east Qiongzhou Strait mouth area and was bounded by a high temperature gradient, was the focus of this paper. Vertical structure of the CWC suggests that interaction between the westward fl ow and the bathymetry slope played a signifi cant role in the formation of CWC. Numerical experiments indicated that the westward fl ow in the Qiongzhou Strait was the result of tidal rectifi cation over variable topography（Shi et al., 2002）, thus tides played a critical role on the development of the CWC. The negative wind stress curl that dominated the east Qiongzhou Strait mouth area suppressed the intensity of the CWC by 0.2–0.4℃. Further, nonlinear interaction between tidal currents and wind stress enhanced vertical mixing greatly, which would benefi t the development of the CWC.

Adaptability of the ocean and earth tidal models based on global observations of the superconducting gravimeters

The adaptability of recent ocean tidal models and Earth tidal models is investigated comprehensively by means of 22 high precision tidal gravity observation series at 20 stations of the Global Geodynamics Project. Careful preprocessing of the original observations was carried out using international standard algorithms and the tidal gravity parameters were computed. The gravity load vectors of 8 main constituents are obtained based on loading computation theory and various global ocean models. The loading corrections of 14 secondary constituents are obtained based on a two-dimensional interpolation technique. Considering different characteristics of the wave amplitude, a method of “non-identical weighted mean” is developed for computing the av-eraged observed residual and remaining residual vectors at each station. The efficiency of the loading correction and the discrepancy between corrected amplitude factors and theoretical ones are analyzed. Meanwhile the calibration problem of the instruments is also discussed. After loading correction, the averaged tidal gravity parameters for all stations are obtained. The results show that the discrepancies between the global mean amplitude factors and theoretical values are less than 0.3%, the largest calibration error of the instruments is less than 0.5%. On the other hand, there are indications that the slight phase advance of K1 with respect to O1 in Mathews’ theory could be verified by ground based tidal gravity observations.

北部湾三维潮汐潮流数值模拟

潮汐潮流变化对海洋建设、民生、国防等方面都有重大意义,深入了解北部湾潮汐潮流变化可为北部湾沿海港口航道建设等提供重要的参考依据。本文基于有限体积海岸海洋模型(Finite-volume coastal ocean model,FVCOM)建立了一个三维潮汐潮流数值模型,对北部湾的潮汐潮流进行数值模拟分析,同时收集了历史潮位站、2个实测潮位站以及4个海流实测站点数据对模型结果进行对比验证。结果表明,北部湾湾内以规则全日潮为主,湾内同时存在规则全日潮流、不规则全日潮流以及不规则半日潮流,潮流运动形式主要以往复式潮流为主。在涨落急流场中,最大流速点位于琼州海峡口处,流速达到157 cm/s,计算得到的最大可能流速也位于琼州海峡内。北部湾内余流平均流速为2 cm/s,余流通过琼州海峡从外海进入北部湾,并沿着广西近岸流动,在湾内形成一个气旋式环流。通过与实测资料对比,本研究所进行的数值模拟结果与实测资料基本吻合,能够反应出近年来北部湾水动力状况,为北部湾海洋工程建设以及环境保护提供了重要的科学依据。

Geomorphology visualization modeling and tidal current virtual reality for coastal ocean

The new technology of geomorphology visualization modeling and virtual reality for tidal current numerical simulation are the important methods utilized in coastal ocean research. In the project of studying the evolutionary trend of radial sand ridges in South Yellow Sea of China, this method becomes the key to reveal the correlation betweenthe seabed topography and the hydrodynamic factor——tidal current. It is proved that using the geomorphology visualization and tidal virtual reality techniques, oceanog-raphers might be able to intuitively discover the interaction pattern of sand ridges and tidal current, predicting the development of sand ridge stability in the future. Furthermore,a prototypic software system——VROcean was designed andimplemented to examine the performance of the new visualization technology on the contrast to traditional methods.

海洋空间信息基准技术进展与发展方向

简要分析了海洋空间信息基准的基本发展历程和当前的技术状态,梳理和评述了近年来关于验潮站垂直基准确定方法的改进与完善、验潮站控制下的垂直基准的实现形式、长期验潮站在维持垂直基准方面的作用、海洋潮汐模型构建、特征潮面模型构建与转换等有关海洋垂直基准及与其相关的海洋潮汐研究的主要进展,预测了海洋空间信息基准在海上高精度位置服务、垂直基准面及转换模型精化、空间基准应用等重点发展方向。

中国台湾地区海洋负荷潮汐对重力、位移、倾斜和应变固体潮观测的影响

利用最新的由卫星测高数据解算获得的 Csr4 .0全球海潮模型、中国近海海潮资料和标准地球模型负荷格林函数 ,采用积分格林函数方法研究了台湾地区 10个台站的重力、位移、倾斜和应变固体潮观测中的海潮负荷效应。给出了 4个主要潮波 (O1、K1、M2、S2 )的负荷振幅和相位 ,研究了负荷应变花分布特征 ,构制了台北站的负荷时变特征。数值结果说明 ,台湾地区各台站受海潮影响十分明显 ,因此在实施重力、位移。

GPS精密定位中的海潮位移改正

根据海洋负荷潮理论 ,利用NAO99b全球海潮模型 ,计算了中国部分IGS站的海潮位移改正 ,并将海潮位移改正应用到GPS数据处理当中。在GAMIT软件的解算过程中 ,分别按加入和不加入海潮位移改正 ,对GPS基线分量和测站坐标分别进行了计算和比较分析。结果表明 ,海潮位移改正无论是对GPS基线分量还是对测站坐标 。

海潮模型和格林函数对海潮位移改正的影响

根据海洋负荷潮理论 ,海潮位移改正的计算取决于海潮模型和格林函数的选取。因此 ,针对不同的海潮模型和不同的格林函数分别计算了海潮位移改正 ,并且比较和分析了它们对海潮位移改正所带来的影响。结果表明 ,不同海潮模型和不同格林函数对海潮改正的计算值有一定的影响 ,而且相对来说 ,不同海潮模型所引起的差别较大 ,但是这种差别对GPS数据处理的最终结果影响不大。

植被对潮沟发育影响的遥感研究——以崇明东滩为例

根据现场测量,通过高分辨率航空图像提取崇明东滩潮沟的空间形态、植被类型及植被盖度指数。结合多时相卫星图像及海洋数值模式,利用水边线法及宽深比法反演潮沟沟底高程并构建了研究区潮沟三维地形,分析了植被对潮沟发育的影响。结果表明:1潮沟反演的均方根误差为0.545 m,且高潮滩反演精度高于低潮滩地区;2从低潮滩到高潮滩的潮沟深度先增大再减小,主要原因是高潮滩水动力条件较弱,加之植被根系的固滩作用,下蚀作用较弱,潮沟深度较浅,低潮滩由于水域开阔,水动力条件较弱,无植被覆盖侧蚀作用增强,潮沟变宽变浅;3潮沟深度空间分布表现出南深北浅的特征,崇明东滩潮沟密度与植被盖度呈现明显的负相关(r=0.560 4,p<0.02),在高盖度植被覆盖的潮滩地区潮沟大多不发育,潮沟密度较低。潮沟长度与植被类型表现出较强的相关关系,在互花米草-芦苇群落为优势的区域潮沟长度普遍比以海三棱藨草群落为优势的区域长。

泰国湾及邻近海域潮汐潮流的数值模拟

本文基于FVCOM(Finite-Volume Coastal Ocean Model)模式,模拟了泰国湾及其周边海域K1、O1、M2和S2四个主要分潮。采用47个验潮站实测调和常数与模拟结果进行比较,所得4个分潮的均方差分别为4.06cm、3.76cm、8.22cm和4.71cm,符合良好。根据计算结果分析了泰国湾及其周边海域的潮汐、潮流的分布特征和潮波的传播特征。数值试验表明,现有的数字水深资料(ETOPO1,ETOPO5,DBDB-V)的准确度不足以合理地模拟泰国湾潮波。

中国大陆精密重力潮汐改正模型

利用理论和实验重力固体潮模型,充分考虑全球海潮和中国近海潮汐的负荷效应,建立了中国大陆的精密重力潮汐改正模型.结果表明,采用不同的固体潮模型会对重力潮汐结果产生相对变化幅度小于0.06%的差异;在沿海地区海潮负荷的影响约为整个潮汐的4%,而中部地区约为1%,其中中国近海潮汐模型的影响约占整个海潮负荷的1 0%,内插或外推潮波的负荷约占海潮负荷的3%.通过比较实测的重力数据表明,本文给出的重力潮汐改正模型的精度远远优于0.5×10^(-8)m·s^(-2),说明了本文构建的模型的实用性,可为中国大陆高精度重力测量提供有效参考和精密的改正模型.

中国地壳运动网络的海潮位移改正

采用CSR4.0全球海潮模型 ,顾及中国近海海潮图 ,计算了海潮中 8个主要潮波(M2 ,N2 ,S2 ,K2 ,O1 ,P1 ,Q1 ,K1 波 )引起的中国地壳运动观测网中测站的海潮位移改正 .文中也讨论了海潮模型和格林函数对海潮位移改正的影响 .作为实例 ,把海潮影响加入GAMIT软件 ,用实测GPS数据检核出海潮对GPS基线向量的影响 .结果显示了海洋负荷潮引起测站位移和GPS基线向量改变的最大值大约分别为 2厘米和

南极中山站重力潮汐观测的海潮负荷效应

综合分析了LaCoste Romberg (LCR)ET2 1高精度弹簧重力仪 1 998年 1 2月 2 6日至 2 0 0 0年 1月 9日在南极中山站的重力潮汐观测资料 ,采用目前普遍使用的Schwiderski、Csr 3.0和Fes96.2全球海潮模型研究中山站重力潮汐观测的海潮负荷改正问题。结果表明在南极地区 ,目前的海潮模型存在较大的不确定性 ,还不足以精密确定该区域的海潮负荷改正。经海潮改正后 ,重力潮汐观测结果与潮汐理论值之间还存在比较大的差异 ,观测的周日 (O1 )和半日(M2 )潮波重力振幅因子与相应的理论值之间的平均偏差分别为 3.8%和 7.8%。南极地区附近海域海冰的变化将导致该地区海潮负荷响应非常明显的季节性系统变化。

周日、半日地球自转变化研究进展

主要介绍了周日、半日地球自转变化研究进展。首先介绍了周日、半日地球自转变化的研究发展历程以及主要激发因素,近几十年来,由于GPS、VLBI、SLR等观测技术和分析精度的提高,已能用几小时甚至1～2 h的观测数据求解地球自转参数(极移和自转速率变化),并从中检测到明显的周日、半日自转变化。与海潮模型所预测的结果进行比较,在主要的周日、半日潮波频率上,两者的振幅和相位符合得较好,特别是对UT1,符合度为90%左右,极移为60%左右。目前,仍有30%的极移周日、半日激发因素没有确定。然后对20世纪80年代以来关于极移和UT 1的周日、半日变化研究应用,以及不同的全球海潮改正模型作了较为全面的综述,现有的海潮改正模型存在10%～20%的误差,需要进一步的精化。最后对周日、半日地球自转变化的未来研究工作作了简单的展望。

波流耦合模式及其在理想潮汐通道中的应用

波浪和水流是近岸地区最重要的2种动力要素,为探究两者之间相互作用关系,本文利用MCT耦合器,将第3代海浪模型SWAN和区域海洋模型ROMS进行耦合,建立了SWAN-ROMS波流双向实时耦合模型。针对理想潮汐通道的典型算例进行波流耦合计算分析,分别对采用SWAN模型单独计算和采用SWAN与ROMS耦合计算的方案进行了数值试验,通过对照两者的结果,分析波流相互作用条件下对波浪和潮流的影响。研究发现建立的波流耦合模式能够较好模拟潮汐通道中的波、流相互作用关系,潮流的存在对波浪影响较为明显,周期性的潮流运动使得稳定的波浪场也产生了周期性变化,潮流与波浪向同一方向传播时,会导致波高减小,而相对运动则会导致波高增加。

佘山台倾斜固体潮观测的海潮负荷改正

采用FARRELL的负荷理论以及最新的TPXO6海潮模型和中国近海潮汐资料计算了海潮负荷对佘山台倾斜固体潮的影响,采用BAYTAP-G调和分析软件对佘山台倾斜固体潮观测进行了处理,获得不同潮波的潮汐参数。在此基础上进行海潮负荷改正。负荷改正后,东西分量的振幅因子和相位滞后与理论值较为接近,而南北分量的半日波振幅因子与理论值仍有较大的偏离。结果说明,佘山台倾斜东西分量主要受海潮负荷的影响,超过60%,甚至达到96%(O1);而南北分量受到的非潮汐的影响要比东西分量受到的影响大,如N2波甚至高达70%,但是这也可能是和海潮模型在近海的不精确有关。