新岛台地电场的潮汐响应与地震

本文通过采用频谱分析和BAYTAP-G方法对位于日本伊豆群岛的新岛台跨度达三年（1998～2000年）的地电场的观测资料进行了分析研究,对该台地电场的潮汐响应进行了定量提取与分析,得到了地电场潮汐响应的一些主要特征,例如除了存在全日分潮、半日分潮等不同周期的潮汐成分外,还呈现出明显的半月、半年等不同周期的活动规律.进一步的定量分析显示与新岛台若乡（Wakago）关联的测线的潮汐响应在2000年夏季的群发地震前呈现出不同程度的异常变化,而在所分析的另一条测线中并未检测到类似的异常,这也许可以成为地震电磁信号的“选择性”现象的一种新的证据.     

台湾海峡地震引发的津浪特征

根据福建沿海验潮站的汐自动记录图，介绍发近年来台湾海峡发生的几次Ｍｓ≥４．５级地震引发的津浪及其沿海地区带来的不可忽视影响。通过整理海洋潮汐的长期变化资料，指出潮汐变化与地震发生二者之间存在某种相关性，地震大多发生在潮差变化最大的月份和潮汐变化的高峰年，有时也发生在低潮时刻。     

武汉基准台重力合成潮信号确定

合成潮是一种半理论和半实测的潮汐信号,综合采用武汉国际重力潮汐基准值,非弹性地球潮汐理论模型,地球近周日摆地周日重力潮汐观测的共振影响以及全球和局部海洋潮汐的负荷效应,精密确定了武汉基准台的重务合成潮信号,与同一段时间内超导重力仪的实测潮汐信号的均方差为０．２２５＊１０＾－８ｍ／ｓ＾２。     

南海北部深海潮汐的季节性变化特征

深海潮汐是深海混合过程的主要能量来源,对深海环流变异和沉积物搬运具有重要的调控作用.文章利用深水锚系观测系统在南海北部2100m水深处开展了近两年的高分辨率海流剖面观测,用于研究深海潮汐的季节性变化特征.通过谱分析显示,南海北部深海潮汐以全日潮为主,且在观测区域的深海中,全日潮和半日潮以垂向第一模态结构为主.斜压全日潮具有显著的季节性变化特征,夏季最强,深度平均的最大动能达86.7cm2s-2,分别是冬季的1.5倍、春秋季的2倍;而斜压半日潮没有明显的季节性变化.通过对比发现斜压全日潮的季节性变化受控于吕宋海峡附近的正压潮.另外,观测期间有三个强中尺度涡经过锚系站位,其中一个气旋式中尺度涡对深海海流影响较小,而另外两个反气旋式中尺度涡经过研究海域时可影响全水深海流,激发强亚惯性流,对深海潮汐产生边缘强化效应,并使深海斜压全日潮冬季的异相成分增强,占全日潮的85%.同时,中尺度涡对深海海水混合的增强弱化了海水层结,导致冬季的斜压全日潮流速减弱,低于夏季.南海北部深海潮汐季节性变化为研究深海盆沉积物在不同时间尺度上的分布及搬运过程提供了重要的动力机制.     

我国沿海若干验潮站的19年潮汐分析

对我国沿海葫芦岛、秦皇岛、坎门3个验潮站进行了19年潮汐总体分析,计算了分辨率△σ≥0.0022°/h的472个分潮的振幅和位相;依据得到的交点潮、近点潮和极潮对平均海面的超长周期性变化进行了预测;还对以上3站及塘沽、龙口等站进行了19年的逐年潮汐分析,从天文因素、非线性效应及海底地形变迁等方面的影响探讨逐年潮汐分析的稳定性.     

南北地震带潮汐触发地震的统计学证据

自19世纪90年代以来,潮汐是否会触发地震这个问题一直备受关注.本研究选用1970年1月1日至2017年5月31日期间南北地震带(20°N—40°N,97°E—105°E)M_L≥2.0地震目录资料,通过测量南北地震带地区地震事件与潮汐的相关性来研究潮汐是否能触发地震.选用完备性检测、G-C法、R/S分析方法对原始地震目录进行预处理,分别构成未去除余震和去除余震每日地震数量时间序列,利用经验模态分解和快速傅里叶方法,对比分析了潮汐与每日地震数量构成的时间序列频谱特征.结果表明,在本文研究区域,两种每日地震数量时间序列均与潮汐的月潮周期、半月潮周期存在相关性,并且去除余震后的每日地震时间序列的优势频率更加集中,表现的相关性更好.此外,Schuster’s测试结果也进一步证明,研究区域地震活动性与固体潮汐存在显著统计相关性.     

长周期潮汐与全球地震能量释放

采用1850-2012年期间USGS全球M≥5.0地震目录资料,构成全球地震能量-时间序列,进行小波变换和准周期分析. 结果表明,全球地震能量释放的时间序列存在9年、19年和45年的3个准周期,其中,45年准周期最为突出. 结合起潮力周期的物理背景,对长周期潮汐起潮力与地震能量释放准周期的关系进行了探讨,没有发现全球地震活动的能量释放与潮汐短周期相关的准周期.     

潮汐相位滞后变化与地震的关系

根据楚雄台倾斜固体潮潮汐分析遥结果,发现地震前潮汐相位滞后出现３￣４个月的短期减小。从构造物理学上探讨了潮汐相位滞后、介质粘滞性与潮汐形变的关系,并且用楚雄应变潮调和分析结果好应变潮汐振幅因子迅速增大所证实。研究表明,潮汐相位滞后用于地城预报是一种很有前途的短临预报方法。     

武汉和阿德莱德大气太阴N2潮及M2潮的对比分析

利用阿德莱德（35°S,138°E）和武汉（30.6°N,114.5°E）的流星雷达观测数据首次给出了80~100 km高度上周期为12.66太阳时的大气太阴半日潮汐（N₂潮）的季节、高度、年度变化及其与周期为12.42太阳时的大气太阴半日潮汐（M₂潮）的对比分析.分析结果表明：武汉和阿德莱德的N₂潮和M₂潮均有明显的季节、高度和年度变化.N₂潮与M₂潮的幅度比值大于其引力势之比0.191,在某些年份的不同季节和高度上,N₂潮的幅度甚至大于M₂潮的幅度.大多幅度之比接近或超过N₂潮和M₂潮引力势之比的2倍.中低热层的大气太阴N₂潮汐值得关注.     

重力潮汐观测资料的改正和异常背景值的显示问题

本文系统地研究了重力潮汐观测的改正和作为地震预报研究的异常背景值的显示问题.文章讨论了仪器弹性系统流变模型改正和惯性改正以及海洋潮汐等的资料精确化问题和气压、地下水等对重力潮汐观测的影响,并给出了相应的结果.文章还讨论了台站重力测量中非潮汐信息的提取问题,从理论上论证并对比了几种滤波器的实质.      

Waves and tides responsible for the intermittent closure of the entrance of a small, sheltered tidal wetland at San Francisco, CA

Crissy Field Marsh (CFM; http://www.nps.gov/prsf/planyourvisit/crissy-field-marsh-and-beach.htm) is a small, restored tidal wetland located in the entrance to San Francisco Bay just east of the Golden Gate. The marsh is small but otherwise fairly typical of many such restored wetlands worldwide. The marsh is hydraulically connected to the bay and the adjacent Pacific Ocean by a narrow sandy channel. The channel often migrates and sometimes closes completely, which effectively blocks the tidal connection to the ocean and disrupts the hydraulics and ecology of the marsh. Field measurements of waves and tides have been examined in order to evaluate the conditions responsible for the intermittent closure of the marsh entrance. The most important factor found to bring about the entrance channel closure is the occurrence of large ocean waves. However, there were also a few closure events during times with relatively small offshore waves. Examination of the deep-water directional wave spectra during these times indicates the presence of a small secondary peak corresponding to long period swell from the southern hemisphere, indicating that CFM and San Francisco Bay in general may be more susceptible to long period ocean swell emanating from the south or southwest than the more common ocean waves coming from the northwest. The tidal records during closure events show no strong relationship between closures and tides, other than that closures tend to occur during multi-day periods with successively increasing high tides. It can be inferred from these findings that the most important process to the intermittent closure of the entrance to CFM is littoral sediment transport driven by the influence of ocean swell waves breaking along the CFM shoreline at oblique angles. During periods of large, oblique waves the littoral transport of sand likely overwhelms the scour potential of the tidal flow in the entrance channel.     

Revising the paradigm of tidal analysis – the uses of non-stationary data

Surface elevation and current records contain non-tidal variance, often dismissed as noise. The processes responsible for the non-tidal component may also modulate the tidal signal, altering its strength and frequency structure. Because of their manner of generation and propagation, internal tides are inherently irregular. The non-stationary character of these and other tidal processes provides an integral and useful property of tidal records, because it provides an opportunity to obtain insights into tidal dynamics and the interaction of tidal and non-tidal processes. It is, moreover, productive to use multiple approaches in analyzing coastal and estuarine tidal processes so that both the time-varying and average frequency content are determined. Only by confronting the causes of non-stationary behaviour in this way can some of the remaining challenges in tidal analysis and prediction be overcome, e.g. shelf and estuarine currents, river tides, internal tides, tide-surge interactions and tidally influenced ecological processes. Several examples illustrate the utility of non-stationary tidal analysis methods.Responsible Editor: Jens Kappenberg     

Flood–ebb and spring–neap variations of mixing,stratification and circulation in Chesapeake Bay

A three-dimensional hydrodynamic model is used to investigate intra-tidal and spring–neap variations of turbulent mixing, stratification and residual circulation in the Chesapeake Bay estuary. Vertical profiles of salinity, velocity and eddy diffusivity show a marked asymmetry between the flood and ebb tides. Tidal mixing in the bottom boundary layer is stronger and penetrates higher on flood than on ebb. This flood–ebb asymmetry results in a north–south asymmetry in turbulent mixing because tidal currents vary out of phase between the lower and upper regions of Chesapeake Bay. The asymmetric tidal mixing causes significant variation of salinity distribution over the flood–ebb tidal cycle but insignificant changes in the residual circulation. Due to the modulation of tidal currents over the spring–neap cycle, turbulent mixing and vertical stratification show large fortnightly and monthly fluctuations. The stratification is not a linear function of the tidal-current amplitude. Strong stratification is only established during those neap tides when low turbulence intensity persists for several days. Residual circulation also shows large variations over the spring–neap cycle. The tidally averaged residual currents are about 50% stronger during the neap tides than during the spring tides.     

地球引潮力极大值和强潮汐周期性指数的建立与定性分析

日、月对地球表层海水的引潮力导致潮汐的周期性变化是一种成熟理论.地球除具有日、月、年潮汐规律外,还具有明显的准1800年、200年、50~70年、18.6年、9.3年和2.5~7年不同尺度的周期.本文通过将地球赤道半径和月球轨道半径投影到黄道面上,标定二者矢量半径之和的模的极值状态,创建了引潮力极大值和强潮汐的周期性指数KSEM.这对探讨和预测潮汐的时间分布和推断地球自转角速度变化规律提供了一种新途径.行星系统中木星和金星对地球的摄动影响最突出,但目前还没有一个行之有效的模型将日、地、月、木星、金星作为一个统一整体,对地球潮汐极值状态进行刻画.通过辨析这五大天体运动预设的位置关系的结构特征,进而考察KSEM指数与月球升交点和月球近地点会合周期的对应关系,以及对月球轨道运动不同的特征周期的叠加和定性分析,这对探讨强潮汐周期、厄尔尼诺现象和地震的时间分布规律提供了重要参考.     

A two-dimensional analytical solution of groundwater responses to tidal loading in an estuary and ocean

Previous studies on tidal dynamics of coastal aquifers have focussed on the inland propagation of oceanic tides in the cross-shore direction, a configuration that is essentially one-dimensional. Aquifers at natural coasts can also be influenced by tidal waves in nearby estuaries, resulting in a more complex behaviour of head fluctuations in the aquifers. We present an analytical solution to the two-dimensional depth-averaged groundwater flow equation for a semi-infinite aquifer subject to oscillating head conditions at the boundaries. The solution describes the tidal dynamics of a coastal aquifer that is adjacent to a cross-shore estuary. Both the effects of oceanic and estuarine tides on the aquifer are included in the solution. The analytical prediction of the head fluctuations is verified by comparison with numerical solutions computed using a standard finite-difference method. An essential feature of the present analytical solution is the interaction between the cross- and along-shore tidal waves in the aquifer area near the estuary’s entry. As the distance from the estuary or coastline increases, the wave interaction is weakened and the aquifer response is reduced, respectively, to the one-dimensional solution for oceanic tides or the solution of Sun (Sun H. A two-dimensional analytical solution of groundwater response to tidal loading in an estuary, Water Resour Res 1997;33:1429–35) for two-dimensional non-interacting tidal waves.     

Hydrodynamics of salt marsh creek systems: Implications for marsh morphological development and material exchange

Integrated ebb-aligned drainage systems are a feature of tide-dominated marshes, and are generally regarded as major conduits for material exchange. In north Norfolk, highly unsteady creek flows exhibit well-developed velocity and stress transients which result from the discontinuous nature of the tidal prism and the interaction of shallow water tidal inputs with hydraulically rough vegetated surfaces. Marsh morphological development is governed by a form-process feedback, in the sense that the marsh surface acts as a topographic threshold separating the depositional regime of below-marsh tides from the erosional (ebb-dominated) regime of over-marsh tides. Vertical marsh growth results in increasing intermittency of creek sediment transport. Furthermore, velocity transients are associated with large discharges which must be allowed for in material flux computations. Creek flux measurements are not in themselves sufficient to estimate total material budgets, since a large proportion of tidal exchange may take place via the marsh edge. Such studies should focus instead on direct measurement of marsh surface processes. These findings have relevance beyond this back-barrier setting to marshes of different geometry, occupying a broad range of the tidal energy spectrum.     

A coupled oscillator model of shelf and ocean tides

The resonances of tides in the coupled open ocean and shelf are modeled by a mechanical analogue consisting of a damped driven larger mass and spring (the open-ocean) connected to a damped smaller mass and spring (the shelf). When both masses are near resonance, the addition of even a very small mass can significantly affect the oscillations of the larger mass. The influence of the shelf is largest if the shelf is resonant with weak friction. In particular, an increase of friction on a near-resonant shelf can, perhaps surprisingly, lead to an increase in ocean tides. On the other hand, a shelf with large friction has little effect on ocean tides. Comparison of the model predictions with results from numerical models of tides during the ice ages, when lower sea levels led to a much reduced areal extent of shelves, suggests that the predicted larger tidal dissipation then is related to the ocean basins being close to resonance. New numerical simulations with a forward global tide model are used to test expectations from the mechanical analogue. Setting friction to unrealistically large values in Hudson Strait yields larger North Atlantic _M2$M_2$ amplitudes, very similar to those seen in a simulation with the Hudson Strait blocked off. Thus, as anticipated, a shelf with very large friction is nearly equivalent in its effect on the open ocean to the removal of the shelf altogether. Setting friction in shallow waters throughout the globe to unrealistically large values yields even larger open ocean tidal amplitudes, similar to those found in simulations of ice-age tides. It thus appears that larger modeled tides during the ice ages can be a consequence of enhanced friction in shallower water on the shelf in glacial times as well as a reduced shelf area then. Single oscillator and coupled oscillator models for global tides show that the maximum extractable power for human use is a fraction of the present dissipation rate, which is itself a fraction of global human power consumption.     

Modelling tidally induced sediment-transport paths over the northwest European shelf: the influence of sea-level reduction

A three-dimensional model covering the northwest European Shelf and part of the adjacent Atlantic Ocean is used to examine the influence of water depth change upon the distribution of maximum tidal bed stress. The direction of bed stress is an indicator of sediment movement as bed load and various regions of convergence and divergence in good agreement with observations are identified. Calculations are performed with water depths reduced by 35 m, corresponding to 10 000 years before present (B.P.). Initially, the model is forced by only the M₂ tide, although subsequently five constituents, namely M₂, S₂, N₂, K₁ and O_1, are used for tidal forcing. Although the distribution of extreme bed stresses computed with only M₂ tidal forcing is comparable to that computed with five tides, the additional tidal constituents modify the magnitude of the bed stress. In particular the diurnal tides show regions of local enhanced current amplitude in the shelf-edge region with corresponding changes in bed stress. When water depths are reduced such that the North Sea and English Channel are separated, then there is a significant change in the tidal distribution in the shallow Southern Bight which influences bed-stress distributions and hence bed-load sediment transport in the area. Besides changes in shallow regions, the distribution of tides at the shelf edge is affected. A discussion of the limitations of the present coarse-grid model in shelf-edge regions and how it can be used to provide boundary conditions for limited-area three-dimensional models that can include stratification is presented. Also the importance of stratification for sediment movement at the shelf edge is briefly discussed.Responsible Editor: Phil Dyke     

中国东西重力潮汐剖面

为了检验体潮与海潮的理论模型,分析了中国东西重力潮汐剖面（1981年9月-1985年1月）。同时,为研究LaCoste ET-20和ET-21重力仪的格值系统,建立了一条由17台LaCoste G型和2台LaCoste D型重力仪观测的重力垂直基线。在基线上标定的结果表明,ET-21重力仪的格值大了1％。由标定得到的格值计算剖面上各测站的潮汐因子,经海潮改正后,接近Wahr模型值,振幅因子的残差:O₁波小于0.3μGal,M₂波小于0.4μGal。但是上海和拉萨的观测经海潮改正后,相位迟后有很大的改善,振幅因子却更偏离于模型值,其潮汐异常主要是近海的海潮模型不完善,以及在海潮计算中,所采用的地球模型未考虑地壳与上地幔的横向不均匀性所引起。     

Modeling the formation of undulations of the coastline: The role of tides

An idealized model is developed and analyzed to investigate the relevance of tidal motion for the emergence of undulations of a sandy coastline. The model describes feedbacks between tidal and steady flow on the inner shelf, sand transport in the nearshore zone and an irregular coastline. It is demonstrated that an initially straight coastline can become unstable with respect to perturbations with a rhythmic structure in the alongshore direction. The mechanism causing the growth of these perturbations is explained in terms of vorticity concepts. The relative importance of tide-related and wave-driven sediment fluxes in generating undulations of the coastline is investigated for the Dutch coast. Using parameter values that are appropriate for the Dutch coast it is found that tides can render a straight coastline unstable. The model predicts a fastest growing mode (FGM) with a wavelength that is in the order of the observed length of barrier islands. The mode grows on a time scale of 50 yr and it migrates 200 m per year. The wavelength of the FGM decreases with increasing amplitude of the tidal currents. This result is consistent with data of tides, waves and the lengths of barrier islands that are located along the Dutch and German Wadden coast.