Tidal Residuals Research Articles

The importance of coastal altimetry retracking and detiding: a case study around the Great Barrier Reef, Australia

A new approach for improving the accuracy of altimetry-derived sea level anomalies (SLAs) near the coast is presented. Estimation of SLAs is optimized using optimal waveform retracking through a fuzzy multiple retracking system and the most appropriate detiding method. With the retracking system, fuzzy-retracked SLAs become available within 5 km of the coast; meanwhile it becomes more important to use pointwise tide modelling rather than state-of-the-art global tidal models, as the latter leave residual ocean tide signals in retracked SLAs. These improvements are demonstrated for Jason-2 waveforms in the area of the Great Barrier Reef, Australia. Comparing the retrieved SLAs with in situ tide gauge data from Townsville and Bundaberg stations showed that the SLAs from this study generally outperform those from conventional methods, demonstrating that adequate waveform retracking and detiding are equally important in bringing altimetry SLAs closer to the coast.

Enhancing water level prediction through model residual correction based on Chaos theory and Kriging

SUMMARYHydrodynamic models based on the physical processes are indispensable tools for predicting water levels in ocean environment. Nonetheless, their accuracies are limited by various factors such as simplifying assumptions, complex ocean bathymetry, and so on. Residual correction, as one of the data assimilation techniques, can extract information from observation and assimilate it into a numerical model to correct the model output directly. Such correction is often performed in two steps: prediction of the model residuals at measured stations followed by spatial distribution at non‐measured locations. For long‐term residual forecast, the accuracy of prediction usually deteriorates with the forecast horizon. In addition to the residual correction at measurement locations, in this paper, we address the critical question as to how to effectively update outputs for computational points without measurements. We develop a hybrid data assimilation procedure, which combines a modified local model (MLM) and an approximated ordinary kriging (AOK). This technique improves the forecasts over a long horizon over the entire computational domain. Using the proposed residual correction technique, the hybrid procedure is examined on a case study of Singapore Regional Model for correcting the water level outputs at locations with and without measurements. In order to provide a comparison, the analysis is carried out throughout prediction horizon of model residuals, tidal residuals, and sea level anomaly, respectively. The comparisons show that the proposed method can successfully assimilate and forecast all variables. Results indicate that resulting prediction accuracy can be significantly improved for all locations of interest independently of the forecast horizon. Copyright © 2014 John Wiley & Sons, Ltd.

Sea level variation from a remote river in the Gulf of Paria, Trinidad

Short-term sea level variability is investigated by analytical methods to ascertain whether there is a link between peak tidal residuals in the Gulf of Paria (GoP), Trinidad, and peak river outflow from the Orinoco on the Venezuelan mainland. Analysis of tidal data suggests that although the Orinoco delta fronts the Atlantic ocean, significant volumes of this river runoff enter into the GoP and play a role in seasonal sea level variation on the western coastline of the southernmost Caribbean island of Trinidad. The indications from various statistical analyses including harmonic, spectral and time series analyses of tide gauge data are that mean seasonal variations in water level in the north of the GoP exhibit a positive temporal correlation between the tidal residuals and the peak river discharge associated with the Orinoco's seasonal cycle. The maximal de-tided residuals are strongly correlated with maximal values of the river runoff, as well as the discharge trend, with the residual values at initial average estimates of about 12–15 cm/year.

웨이블릿방법을 이용한 조위편차 성분의 중·장주기 특성 분석

Fourier analysis and a wavelet method were carried out to elucidate the characteristics of tidal residual components in coastal waters. The result of Fourier analysis shows tide-induced and monsoon-induced residuals are conspicuous at the short period and mid period, respectively. The tidal residuals were decomposed by period from 3 hours to 8 months and the characteristics of their components were shown by reconstituting them with short periods less than 24 hours, mid-periods between 1 day and 16 days and long periods longer than 1 month. The tidal residuals in the short period, i.e., tide-induced components, being based on the tidal elevation prediction errors, appear in the West Sea with high tidal ranges and do not have much seasonal fluctuation. Additionally, the period of typhoon induced surge ranges more or less than 12 hours. The mid-period components were clearly generated mainly in the West Sea during the winter and largely affected by monsoon. Accordingly, the pure surge height components were concentrated on the mid-period and had clear features for each coastal waters. The long period components show similar characteristics at all stations and are considered to stem from variations of mean sea levels.

Controls on the initiation and development of blooms of the dinoflagellate Cochlodinium polykrikoides Margalef in lower Chesapeake Bay and its tributaries

Massive blooms of the dinoflagellate Cochlodinium polykrikoides occur annually in the Chesapeake Bay and its tributaries. The initiation of blooms and their physical transport has been documented and the location of bloom initiation was identified during the 2007 and 2008 blooms. In the present study we combined daily sampling of nutrient concentrations and phytoplankton abundance at a fixed station to determine physical and chemical controls on bloom formation and enhanced underway water quality monitoring (DATAFLOW) during periods when blooms are known to occur. While C. polykrikoides did not reach bloom concentrations until late June during 2009, vegetative cells were present at low concentrations in the Elizabeth River (4cellsml−1) as early as May 27. Subsequent samples collected from the Lafayette River documented the increase in C. polykrikoides abundance in the upper branches of the Lafayette River from mid-June to early July, when discolored waters were first observed. The 2009 C. polykrikoides bloom began in the Lafayette River when water temperatures were consistently above 25°C and during a period of calm winds, neap tides, high positive tidal residuals, low nutrient concentrations, and a low dissolved inorganic nitrogen (DIN) to dissolved inorganic phosphorous (DIP) ratio. The pulsing of nutrients associated with intense but highly localized storm activity during the summer months when water temperatures are above 25°C may play a role in the initiation of C. polykrikoides blooms. The upper Lafayette River appears to be an important area for initiation of algal blooms that then spread to other connected waterways.

Relationship between the Earth tidal factor and phase lag of groundwater levels in confined aquifers and the Wenchuan M s8.0 earthquake of 2008

This work focuses on variations of the Earth tidal factor and phase lag derived from groundwater observations before and after major earthquakes. It is based on an analysis of the data from four observational wells at boundaries between distinct active blocks of China mainland. These wells are also situated on several active fault zones and have exhibited considerable responses to the Wenchuan Ms8.0 earthquake of 2008 in China. We collected hourly records of water levels of these wells from 2007 to 2009 and processed these data for analysis. The tidal factors, phase lags, and phase-difference changes of tidal residuals of each well were calculated. We found that when the Wenchuan quake happened, the tidal factors of the 4 wells were changing rapidly, while their phase lags and phase differences of tidal residuals declined swiftly, which may reflect the stress and strain changes of the well-aquifer system during the seismic generation.

웨이블릿방법을 이용한 조위편차 성분 분리 및 단주기 특성 분석

The fact that tidal residuals are detected greatly at the tide-dominated region implies that tide component has still remained in the tidal residual. Auto-correlation function analysis also show that the auto-correlation coefficients are conspicuous near tidal periods at the Western Coast. A wavelet method was used to analyze characteristics of the short period or tide-relevant residuals. Considering the results that tidal period is prominent at the tide-dominated region, that seasonal variation is trivial at the short periods, and that shallow tidal period is conspicuous at Mokpo, the short period can be considered to be correlated with tide modulated surge. The result also shows short period components stem mainly from tide-forecasting error and tide-surge interaction. Thus tide modulated surge must be distinguished from meteorological surge.

The tidal displacement field at Earth's surface determined using global GPS observations

AbstractWe investigate the 3‐D tidal displacement field on Earth's surface recorded globally by 456 continuous global positioning system (GPS) stations of IGS spanning 1996–2011, for eight principal diurnal and semidiurnal tidal constituents. In‐phase and quadrature amplitudes of the residual tidal displacements, after removal of an a priori body tide model, are estimated using the precise point positioning (PPP) technique on the daily GPS data; the resultant daily estimates are combined to derive final estimates for each tide at each station. The results are compared with the predictions of eight recent global ocean tide models, separately for coastal (307) and inland (149) stations. We show that GPS can provide tidal displacement estimates accurate to the level of 0.12 mm (horizontal) and 0.24 mm (vertical) for the lunar‐only constituents (M2, N2, O1, and Q1) and less favorably for solar‐related tidal constituents (S2, K2, K1, and P1), although improved by ambiguity resolution. Most recent ocean tide models fit the GPS estimates equally well on the global scale but do not agree well between them in certain coastal areas, especially for the vertical displacements, suggesting the existence of model uncertainties near shallow seas. The tidal residuals for the inland stations after removing both body tides and ocean tidal loading (OTL) furthermore show clear continental‐scale spatial coherence, implying deficiencies of the a priori body tide modeling in catching lateral heterogeneity in elastic as well as inelastic properties in the Earth's deep interior. We assert that the GPS tidal displacement estimates now achieve sufficient accuracy to potentially provide constraints on the Earth's structure.

한반도 연안 조위편차의 확률밀도함수

Tidal residual is being an important factor by the influence of the climate change in terms of the coastal safety and defense. It is one of the most important factor for the determination of the reference sea level in order to check the safety and performance of the coastal structures in company with the typhoon intensity variation. The probability density function (pdf) of tidal residuals in the Korean coasts have a non-ignorable skewness and high kurtosis. It is highly restricted to the application of the normal pdf assumption as an approximated pdf of tidal residuals. In this study, the pdf of tidal residuals estimated using the Kernel function is suggested as a more reliable and accurate pdf of tidal residuals than the normal function. This suggested pdf shows a good agreement with the empirical cumulative distribution function and histogram. It also gives the more accurate estimation result on the extreme values in comparison with the results based on the normal pdf assumption.

Multimission empirical ocean tide modeling for shallow waters and polar seas

A new global ocean tide model named DTU10 (developed at Technical University of Denmark) representing all major diurnal and semidiurnal tidal constituents is proposed based on an empirical correction to the global tide model FES2004 (Finite Element Solutions), with residual tides determined using the response method. The improvements are achieved by introducing 4 years of TOPEX–Jason 1 interleaved mission into existing 18 years (1993–2010) of primary joint TOPEX, Jason 1, and Jason 2 mission time series. Hereby the spatial distribution of observations are doubled and satellite altimetry should be able to recover twice the spatial variations of the tidal signal which is particularly important in shallow waters where the spatial scale of the tidal signal is scaled down. Outside the ±66° parallel combined Envisat, GEOSAT Follow‐On, and ERS‐2, data sets have been included to solve for the tides up to the ±82° parallel. A new approach to removing the annual sea level variations prior to estimating the residual tides significantly improved tidal determination of diurnal constituents from the Sun‐synchronous satellites (e.g., ERS‐2 and Envisat) in the polar seas. Extensive evaluations with six tide gauge sets show that the new tide model fits the tide gauge measurements favorably to other state of the art global ocean tide models in both the deep and shallow waters, especially in the Arctic Ocean and the Southern Ocean. One example is a comparison with 207 tide gauge data in the East Asian marginal seas where the root‐mean‐square agreement improved by 35.12%, 22.61%, 27.07%, and 22.65% (M2, S2, K1, and O1) for the DTU10 tide model compared with the FES2004 tide model. A similar comparison in the Arctic Ocean with 151 gauge data improved by 9.93%, 0.34%, 7.46%, and 9.52% for the M2, S2, K1, and O1 constituents, respectively.

Gravity measurements in southeastern Alaska reveal negative gravity rate of change caused by glacial isostatic adjustment

For the past 300 years, southeastern Alaska has undergone rapid ice‐melting and land uplift attributable to global warming. Corresponding crustal deformation (3 cm/yr) caused by the Little Ice Age retreat is detectable with modern geodetic techniques such as GPS and tidal gauge measurements. Geodetic deformation provides useful information for assessing ice‐melting rates, global warming effects, and subcrustal viscosity. Nevertheless, integrated geodetic observations, including gravity measurements, are important. To detect crustal deformation caused by glacial isostatic adjustment and to elucidate the viscosity structure in southeastern Alaska, Japanese and U.S. researchers began a joint 3‐year project in 2006 using GPS, Earth tide, and absolute gravity measurements. A new absolute gravity network was established, comprising five sites around Glacier Bay, near Juneau, Alaska. This paper reports the network's gravity measurements during 2006–2008. The bad ocean model in this area hindered ocean loading correction: Large tidal residuals remain in the observations. Accurate tidal correction necessitated on‐site tidal observation. Results show high observation precision for all five stations: <1 μGal. The gravity rate of change was found to be −3.5 to −5.6 μGal/yr in the gravity network. Furthermore, gravity results obtained during the 3 years indicate a similar gravity change rate. These gravity data are anticipated for application in geophysical studies of southeastern Alaska. Using gravity and vertical displacement data, we constructed a quantity to remove viscoelastic effects. The observations are thus useful to constrain present‐day ice thickness changes. A gravity bias of about −13.2 ± 0.1 mGal exists between the Potsdam and current FG5 gravity data.

Tidal gravity variations revisited at Vostok Station, Antarctica

In 1969, prior to the discovery of the subglacial Lake Vostok, an Askania Gs-11 gravimeter was operated at Vostok Station (78.466°S, 106.832°E; 3478 m asl) to observe tidal gravity variations. To gain a better understanding of the lake's tidal dynamics, we reanalyzed these data using a Bayesian Tidal Analysis Program Grouping method (BAYTAP-G and -L programs). The obtained phase leads for the semidiurnal waves M2 (6.6 ± 2.1°) and S2 (10.1 ± 4.2°) are more pronounced than those of the diurnal waves, among which the largest phase lead (for K1) was 5.0 ± 0.5°. The obtained δ factor for M2 was 0.890 ± 0.032, significantly less than the theoretical value of 1.16. For three global ocean tide models (NAO99b, FES2004, and TPXO6.2), the estimated load tides on waves Q1, O1, P1, K1, M2, and S2 range from 0.1–0.2 μGal (Q1 and S2) to 0.6–0.7 μGal (K1). The difference in amplitude among the three models is less than 0.14 μGal (M2), and the difference in phase is generally less than 10°. In calculating the residual tide vectors using the ocean models, the TPXO6.2 model generally gave the smallest residual amplitudes. Our result for the K1 wave was anomalously large (1.36 ± 0.25 μGal), while that for the M2 wave was sufficiently small (0.37 ± 0.17 μGal). The associated uncertainty is half that reported in previous studies. It is interesting that the residual K1 tide is approximately 90° phase-leaded, while the M2 tide is approximately 180° phase-leaded (delayed). Importantly, a similar reanalysis of data collected at Asuka Station (71.5°S, 24.1°E) gave residual tides within 0.2–0.3 μGal for all major diurnal and semidiurnal waves, including the K1 wave. Therefore, the anomalous K1 residual tide observed at Vostok Station must be linked to the existence of the subglacial lake and the nature of solid–ice–water dynamics in the region.

Sea level extremes in southern Europe

Knowledge of sea level extremes is important for coastal planning purposes. Temporal changes in the extremes may indicate changes in the forcing parameters, most probably the storm surges. Sea level extremes and their spatial and temporal variability in southern Europe are explored on the basis of 73 tide gauge records from 1940. This study uses all data available to infer risks at the coast caused by extreme sea levels. Extreme values of 250 cm are observed at the Atlantic coasts with smaller values in the Mediterranean where, with the exception of the Strait of Gibraltar and the Adriatic Sea, the extreme values are less than 60 cm. At the Adriatic Sea values of up to 200 cm are found. When the tidal contribution is removed the differences between the various areas reduce. The spatial distribution of the extremes of the tidal residuals is well represented by the hindcast of a two‐dimensional hydrodynamic model forced by the atmospheric pressure and the wind, although the model underestimates the extremes. Higher return levels (200–300 cm for the 50‐year return level) are observed in the Atlantic stations due to the larger tides. In the Mediterranean, higher values are found in the northern Adriatic (between 150 and 200 cm) while in the rest of the domain they vary between 20 and 60 cm. The nonlinear interaction between tides and surges is negligible in the Mediterranean, thus the joint tides‐surges distribution can be applied. The interannual and decadal variability in time of extremes is caused by mean sea level changes.

Modeling of Salt Intrusion, Intertidal Mixing, and Circulation in a Braided Estuary

The Snohomish River is one of the largest rivers to discharge into to the Puget Sound estuarine system. The tidal circulation, mixing and salt intrusion processes in the Snohomish River estuary are complex due to the presence of a large intertidal region, multiple distributary channels, and a sharp gradient of bottom elevation from the estuary to the fjordal depths of Puget Sound. To accurately simulate the tidal mixing and salt intrusion in such a complex system, a high-resolution model grid in both horizontal and vertical directions is required to represent the details of the geometry and bathymetry changes in the study domain. In this paper, a finite volume, unstructured coastal ocean model, FVCOM, was used to simulate the estuarine physical processes specific to the current state of the Snohomish River estuary, which consists of a number of dike-trained channels forming a uniquely braided system. The model was calibrated against observed data for a neap-spring tidal cycle collected during fall of 2006. Model simulations were carried out to study the tidal mixing, baroclinic flow, tidal residuals, salinity stratification and intrusion in the Snohomish River. Model results demonstrated that successful simulation of the physical processes in a complex braided estuary are feasible with a finite volume, unstructured model such as FVCOM.

The seasonal circulation and volume transport on the northwest European continental shelf: A fine‐resolution model study

In this paper the circulation of the northwest European continental shelf is investigated using the first year‐long density‐evolving simulation at shelf wide scales and sub‐Rossby Radius resolution (∼1.8 km). A series of numerical experiments are conducted to distinguish between the wind‐, density‐, and oceanic‐driven components of the flow. These demonstrate that, while all components have a role throughout the year, the density‐driven component is particularly important during the summer and autumn months. The time evolution of the density field makes a significant contribution to the seasonal variation of volume transport on shelf wide scales and is persistent in direction; whereas the wind‐driven volume transport acts on much shorter timescales and is more variable in direction. The importance of the oceanic forcing is demonstrated, representing tidal residuals and large‐scale oceanic sea level (pressure) variation; this forcing drives a substantial component of the circulation throughout the year. Twenty six satellite tracked drifters deployed in the summer of 2001 are used for a direct validation of the model currents. The model current speeds are found to be accurate to ∼46% when averaged over ∼40 d, but tend to be too slow. The summer volume fluxes are compared with estimates in the literature showing good agreement, although there is a suggestion that the North Sea inflows are overestimated. Comparisons with the coarser resolution model used for boundary conditions demonstrate the importance of fine‐resolution to the details of the frontal currents with consequences for modeling exchange processes and biological activity in these regions.

A rapid response model for simulating radioactivity dispersion in the Strait of Gibraltar

GISPART (GIbraltar Strait PARticle Tracking model) is a three-dimensional particle-tracking code that simulates the dispersion of radionuclides in the Strait of Gibraltar. It consists of a hydrodynamic module that is run off-line to determine tidal constants and residuals in the domain. This information is stored in files that are read by the dispersion module to reconstruct water movements. A Lagrangian approach is used, thus, a radionuclide release is simulated by a number of particles, whose paths are computed individually. Radionuclide concentrations are obtained from the density of particles per water volume unit. Some examples of the results are shown. Matlab GUIs (graphical user interfaces) allow an easy application of the model and visualization of results.

On the interpretation of gravity tide residuals in the Iberian Peninsula

Abstract The interpretation of tidal gravity final residuals is an issue of high debate in geodesy. Whereas some authors suggest that final residuals are related to possible instrumental and measurement errors or to errors in the evaluation of the oceanic load computations, others propose certain empirical relationships between the gravity tidal residuals and the heat flow, or the tectonothermal age of the lithosphere which, in turn, reveals structural variations with respect to a homogeneous elastic model. We examine such relationships in the Iberian Peninsula by studying correlations between the cosine component of the final residual vector for the M 2 and O 1 waves of the gravity tide potential and different structural parameters for a total of 21 gravity tide stations. The selected parameters, which are related to the capability of the lithosphere to deform, include surface heat flow as the main parameter and, to a lesser extent, lithospheric strength, Moho temperature and tectonothermal age of the lithosphere. Our study agrees with previous results by other authors and does not demonstrate the existence of empirical relationships between the gravity residuals and structural parameters. Actually, when we consider the most precise observations and recent ocean tide models the final residuals are mostly uncorrelated noise. Our results also agree with theoretical studies proposing that the distortions of the tidal gravity field from spherical symmetry are very small and hardly to observe.

Modelling the hydrodynamics of offshore sandbanks

This paper describes the details of a quasi-three-dimensional model (3DBANK), which has been developed to investigate medium and long-term morphological evolution and development of offshore sandbanks. The model is based on a three-dimensional tidal module using the Galerkin-eigenfunction method, but also includes four sub-modules to compute: the instantaneous bedform characteristics from which the temporal and spatial variations of the shear stresses at the sea bed can be derived; the suspended sediment concentration through the water column; the bed-load and suspended sediment fluxes at a point-in-plan; and the resulting morphological changes, respectively. The model also includes the effects of the wind and waves at the sea surface, as well as the wave–current interaction (WCI), and operates with full hydrodynamic and morphodynamic interaction. The components of the model were tested against laboratory and field data, and the complete model was then applied to Middlekerke Bank off the Flemish coast where extensive field measurements were taken during the European Community (EC) funded Circulation and Sediment Transport Around Banks (CSTAB) Project using various advanced instrumentation including STABLE and HF OSCR. Comparisons of the model results with the field measurements and observations show that the model is capable of reproducing the current and wave-induced bedforms, bed roughness, tidal currents and tidal residuals around the sandbank satisfactorily, and can be used to study the long-term sandbank evolution under various offshore conditions. This paper, however, focuses on the hydrodynamic aspects of the model, while the details of the morphological components will be given in a companion paper.

Simple analytical results for bedload transport due to tides

Abstract Patterns of sediment erosion and deposition arising from tide induced bedload transport are explored using standard bedload formulae and a simple analytic approach. Decomposing the current into a principal M 2 tidal constituent, an M 4 first harmonic and a tidal residual, it is straightforward to derive an expression for the contribution each makes to the integrated tidal flux. The resulting expressions are applied to calculate the net change in bed level induced by bedload transport due to a superposition of a Kelvin tidal wave, a harmonic overtide and a residual tide.

On the sensitivity of tidal residuals off the west coast of Britain to mesh resolution

An irregular mesh model of the west coast of Britain is used to examine the sensitivity of tidal residuals to mesh resolution in the region. Computed residuals are compared with earlier published results determined with a high resolution (1 km grid) finite difference model of the eastern Irish Sea. Initial calculations show that tidal residuals are largest in nearshore regions particularly in the vicinity of headlands. Local refinement of the mesh in these regions leads to a more detailed picture of the flow field, particularly adjacent to the coast. Although large scale offshore features of the flow can be resolved using the high resolution finite difference model, such an approach leads to a “stair case” representation of the coastal boundary with an adjacent near coastal region of spurious tidal residuals. By using an irregular mesh that follows the coast, this effect is removed. In the Mersey river region the tidal residual is resolved with a mesh resolution of 120 m, although calculations show that its distribution is particularly sensitive to small scale features of the topography. A variable mesh that can accurately represent the lateral variations in river width and details of topography in both the nearshore and estuarine environment appears essential in modelling the coastal spread of freshwater plumes from rivers and pollutants discharged into the near coastal environment.