Diurnal Constituents Research Articles

Tidal variation and flow dynamics in Indian Sundarban based on field observation and numerical models

Sundarban is made up of a mesh of macrotidal estuarine systems that contain the world's largest mangroves, the eco-geomorphic environment of which is heavily influenced by tidal behaviour and flow characteristics. The present study aimed to identify the tidal attributes and document the flow character of Indian Sundarban throughout a fortnightly tidal cycle. As such, seven tide monitoring stations were installed across the Saptamukhi-Hariabhanga and connected river system to monitor tidal water levels. Based on this data, the Institute of Ocean Sciences' (IOS) method was used to extract 17-major tidal harmonic components to study the links between various oceanic and shallow-water tidal constituents that may contribute to tidal asymmetry. A Mike-21-flow model was also run to simulate the tidal flow of the regime. Result shows that the progression and convergence of tidal waves in the funnel-shaped estuarine system causes notable lag between the southern and northern limits (avg. 45 min over a 52 km-long stretch of Thakuran estuary). The harmonic components indicate that semi-diurnal M2, S2; over tide 2MS6; and diurnal O1, K1 are the major forces, shaping the tidal amplitude in this region. The third, fourth, and sixth diurnal constituents represent additional tidal components, although with relatively minor amplitudes. The transition from coastal to headward stations sees a shift in the relative phase from 93.73° to 96.17°, suggesting a flood dominance and minimal dissipation of energy within the system. Mike-21FM found that the spring flood-current speed with an average value of 0.42–0.56 m/s is significantly higher than the ebb current of averaging 0.25–0.32 m/s. The nature of neap tidal current speed in the Sundarban region generally mirrors that of the spring condition, although with much less intensity. We assume that since any bi-weekly hydraulic analysis has not yet been conducted in Sundarban, it may be highly valuable for future studies.

Localized Tidal Energy Extraction in Puget Sound Can Adjust Estuary Reflection and Friction, Modifying Barotropic Tides System‐Wide

AbstractHarvesting energy via tidal stream turbines is being increasingly considered as a renewable energy resource in estuaries with strong tidal currents. It remains unclear how localized energy extraction changes basic tidal physics throughout real systems. Here, we analyze the influence of an extensive synthetic tidal turbine array on barotropic tides in the Salish Sea, a complex, tidally energetic estuary, using a realistic numerical model. Tidal energy fluxes are calculated at 15 sections throughout the system and decomposed into incident and reflected components, as well as by frequency. Results show the dominant semidiurnal constituent, M2, controls the total tidal energy flux everywhere. When turbines are placed in Tacoma Narrows, the M2 energy flux is enhanced at sections seaward of the array in Puget Sound and reduced landward. The principal diurnal constituent, K1, contributes little to the total energy flux, but behaves similarly. Changes to each constituent are primarily attributed to turbine enhanced frictional dissipation which reduces the estuary's natural resonant period (∼10 hr) amplification. Being close to the semidiurnal frequencies, the resonance adjustment reduces M2 tidal reflection seaward of the turbines and free surface amplitude (particularly landward of the turbines) thereby increasing (decreasing) tidal energy fluxes at seaward (landward) locations. K1 is further from the natural frequency and insensitive to resonance changes. We hypothesize K1 is directly sensitive to increased frictional dissipation which acts to reduce reflection and tidal amplitude, regardless of the estuary natural frequency. Spatial variability in dynamics is discussed, as well as potential environmental implications.

Tidal Analysis and Implementasion of an Internet of Things (IoT) Sea Level Monitoring Device in Coastal Region

Monitoring the sea level is crucial for the protection of coastal communities and infrastructure. Instruments that can record and transmit the sea level in real time are essential for preventing potential disasters. This study presents the design, construction, and evaluation of an instrument for measuring sea level using a pressure sensor, a microcontroller, and a GSM module. The sea level analyzed using T Tide analysis. The instrument's accuracy was established through a calibration process, resulting in a sensor reading accuracy of 96.76% and a low root mean square error of 3.24 cm. The linear regression model confirmed the strong correlation between sensor readings and actual water depth, with a coefficient of determination of 0.999. The instrument achieved an accuracy of 96.76% and a low root mean square error of 3.24 cm. Field testing over three days showed the instrument's reliability in measuring sea levels, with an accuracy rate of 91.93% and an root mean square error of 8.07 cm with a packet loss of 7.86%. The study area had mixed semidiurnal characteristics, with water levels ranging from 60.1 cm to 209.55 cm. Significant constituents such as principal lunar diurnal constituent (K1) and Principal lunar semidiurnal (M2) dominate the tidal patterns, each with distinct frequencies, amplitudes, and signal-to-noise ratios. This research provides a precise and cost-effective instrument for measuring water depth, which is suitable for coastal management, environmental monitoring, and scientific investigation.

Analysis and Prediction of Tidal Measurement Data from Temporary Stations using the Least Squares Method

This research was conducted by equipping three temporary tidal stations located in three places inside Palu Bay with pressure-type tidal gauges. The stations recorded tidal series fluctuations for 4 months with a 5-minute sampling interval (Dt). Moreover, the simple and widely used least squares method (LSM) was applied to separate the harmonic constants of constituents, including amplitudes (Hi) and phases (gi), from the observed tidal series. A total of 11 dominant constituents were selected based on the largest magnitudes of tidal generating potential (CE), and these include M2, K1, S2, O1, P1, N2, Mf, K2, Mm, Q1, and Msf, which were diurnal, semidiurnal, and long-period constituents. The results showed that the semidiurnal constituents generated higher amplitudes than the diurnal constituents, while the long-period constituents produced quite small amplitudes. Furthermore, the ratios of amplitudes recorded showed that tidal in Palu Bay was mainly mixed with semidiurnal constituents. The difference between the observed and predicted values was quite small, and this showed the validity of the measurement conducted at the temporary tidal stations. The performance indicators applied also showed that LSM had acceptable accuracy compared to other methods. Moreover, tidal datums were calculated using the peak approach, and the average tidal range (RA) of Palu Bay was found to be 2.39 m. Doi: 10.28991/CEJ-2024-010-02-03 Full Text: PDF

Multi-constellation GNSS interferometric reflectometry for tidal analysis: mitigations for K1 and K2 biases due to GPS geometrical errors

It has been observed that when using sea levels derived from GPS (Global Positioning System) signal-to-noise ratio (SNR) data to perform tidal analysis, the luni-solar semidiurnal (K2) and the luni-solar diurnal (K1) constituents are biased due to geometrical errors in the reflection data, which result from their periods coinciding with the GPS orbital period and revisit period. In this work, we use 18 months of GNSS SNR data from multiple frequencies and multiple constellations at three sites to further investigate the biases and how to mitigate them. We first estimate sea levels using SNR data from the GPS, GLONASS, and Galileo signals, both individually and by combination. Secondly, we conduct tidal harmonic analysis using these sea-level estimates. By comparing the eight major tidal constituents estimated from SNR data with those estimated from the co-located tide-gauge records, we find that the biases in the K1 and K2 amplitudes from GPS S1C, S2X and S5X SNR data can reach 5 cm, and they can be mitigated by supplementing GLONASS- and Galileo-based sea-level estimates. With a proper combination of sea-level estimates from GPS, GLONASS, and Galileo, SNR-based tidal constituents can reach agreement at the millimeter level with those from tide gauges.

Propagation Features of Diurnal Internal Tides West of the Luzon Strait Revealed by a Large PIES Array

Abstract Energetic internal tides (ITs) are generated from the Luzon Strait (LS) and propagate westward into the South China Sea (SCS). Owing to the lack of large-scale synchronous measurements, the propagation features and seasonal variations of diurnal ITs remain unclear. From 2018 to 2019, mode-1 diurnal ITs west of the LS were continuously observed using a large-scale moored array of 27 pressure-recording inverted echo sounders (PIESs) and a thermistor chain. Measurements confirmed that diurnal ITs radiate from the LS with a north–south asymmetrical pattern, with the most energetic channel located in the middle and south of the LS. The total energy radiated into the SCS across 120°E is 2.67 GW for the K1 ITs and 1.54 GW for the O1 ITs, approximately 2 times larger than those inferred from satellite observations. K1 dominates among the diurnal ITs, with its maximum isopycnal displacement (amplitude) and energy input to the SCS being the strongest in summer (i.e., 16.3 m and 2.81 GW, respectively). The propagation speed of K1 is higher in summer and autumn along the main channel (i.e., 4.33and 4.36 m s−1, respectively). Seasonal stratification and circulation play important roles in the seasonal variation of amplitude and propagation speed of the K1 ITs. The seasonal variability of diurnal-band ITs, which includes all diurnal constituents, is location-dependent and primarily results from the superposition of the K1 and P1 ITs. In particular, vertical displacement is strong in summer and winter along the main channel of the K1 and P1 ITs. The seasonal amplitude of K1 can modulate this seasonal feature. Significance Statement Internal tides (ITs) are internal waves at tidal frequencies. The Luzon Strait (LS) is one of the most energetic sites to generate large-amplitude ITs. The ITs propagate into the South China Sea (SCS), interact with mesoscale eddies, large-scale circulations, etc., and influence local hydrodynamics as well as ecosystem and sediment transport. This motivated an observation plan to investigate the ITs at the western entrance of the LS. From June 2018 to August 2019, an array of 28 PIESs was deployed in the northeastern SCS, almost covering the western entrance of the LS, to investigate the propagation properties of ITs including their amplitude, phase speed, wavelength, propagation direction, and energy fluxes and their annual and seasonal variations. Here, we primarily focus on the mode-1 diurnal ITs. The new insights enrich our understanding of IT dynamics and seasonal variations and support further improvements in numerical simulations.

Late Pleistocene Evolution of Tides and Tidal Dissipation

AbstractStudies of the Last Glacial Maximum (LGM; 26.5–19 ka) tides showed strong enhancements in open ocean tidal amplitudes and dissipation rates; however, changes prior to the LGM remain largely unexplored. Using two different ice sheet and sea level reconstructions, we explicitly simulate the evolution of the leading semi‐diurnal and diurnal tidal constituents (M2, S2, K1, and O1) over the last glacial cycle with a global tide model. Both sets of simulations show that global changes, dominated by the Atlantic, take place for the semi‐diurnal constituents, while changes for the diurnal constituents are mainly regional. Irrespective of the reconstruction, open ocean dissipation peaks during the sea level lowstands of MIS 2 (∼20 ka) and MIS 4 (∼60 ka), although dissipation values prior to MIS 2 are sensitive to differences in reconstructed ice sheet extent. Using the statistically significant relationship between global mean sea level and dissipation, we apply regression analysis to infer open ocean and shelf dissipation, respectively, over the last four glacial cycles back to 430 ka. Our analysis shows that open ocean tidal energy was probably increased for most of this period, peaking during glacial maxima, and returning to near‐present‐day values during interglacials. Due to tidal resonance during glacial phases, small changes in bathymetry could have caused large changes in tidal amplitudes and dissipation, emphasizing the need for accurate ice margin reconstructions. During glacial phases, once global mean sea level decreased by more than ∼100 m, the amount of open ocean tidal energy available for ocean mixing approximately doubled.

Polar Ocean Tides—Revisited Using Cryosat-2

With the availability of more than 9 years of Cryosat-2, it is possible to revisit polar ocean tides, which have traditionally been difficult to determine from satellite altimetry. The SAMOSA+ physical retracker is a stable retracker developed particularly for Cryosat-2. Being a physical retracker, it enables the determination of the sea state bias. Correcting for the sea state bias enables more reliable sea level estimates compared with traditional empirical retrackers used before. Cryosat-2 data have been analyzed for residual ocean tides to the FES2014 ocean tide model in the Arctic Ocean and Antarctic Ocean using the response formalism. We utilize data from the sub-cycle of Cryosat-2, which follows a repeating pattern of approximately 28.33 days. This sub-repeat period makes it an advantageous alias period for the majority of significant constituents. This allowed for the estimation and mapping of the major tidal constituents in the open ocean and also in floating ice shelves from data extracted from leads in the sea ice. A novel empirical ocean tide model designed specifically for the polar region, DTU22, is introduced. Our findings reveal substantial enhancements in semi-diurnal tides within the Arctic Ocean and improvement in diurnal constituents within the Southern Ocean. In the Southern Ocean, the diurnal constituents are particularly improved using the empirical model by more than a factor of two to around 3 cm for both constituents compared with FES2014b. These outcomes underscore the significance of incorporating the reprocessed and retracted Cryosat-2 data into tidal modeling, highlighting its pivotal role in advancing the field.

A modified tidal harmonic analysis model for short-term water level observations

Tidal constants of major semi-diurnal and diurnal constituents are essential for understanding tidal features and long-term tidal prediction. Widely-used classical harmonic analysis (CHA) model requires at least half-year hourly sea level records to resolve eight major semi-diurnal and diurnal constituents based on the Rayleigh criterion. When the analyzed records are short (typically shorter than one month), most previous studies adopt tidal inference method to infer more constituents in the CHA model. The performance of tidal inference method depends on the accuracy of given inference relationships. In this paper, we propose a modified harmonic analysis model on the basis of the credo of smoothness (i.e. MHACS) which indicates inherent natural links between major astronomical diurnal and semi-diurnal constituents. In the CHA, tidal constituents are independent of each other and estimated individually. However, in the MHACS, major constituents are connected via smooth functions of frequency (linear or quadratic functions) indicated by the credo of smoothness. MHACS aims to determine such smooth functions via least squares and then calculate all major tides simultaneously. A series of ideal and practical experiments are conducted to examine the effectiveness of MHACS. It is found that MHACS can derive relatively accurate tidal constants of eight major tides from short-term hourly tide gauge records and satellite altimeter observations. As a general and understandable method, MHACS is easy to realize and can be widely used to analyze diverse tidal signals in the global ocean except diurnal resonant regions where semi-diurnal tidal admittances may be distorted by nonlinear interactions. Furthermore, it should be noted that widely-used tidal inference method can be considered as a special case of MHACS when tidal admittances are assumed as constant functions of frequency.

Numerical simulation of tidal hydrodynamics in the Arabian Gulf

A vertically 2-D numerical model based on the Delft3D modelling system is set up, calibrated, and validated to simulate the tidal hydrodynamics in the Arabian Gulf. The model is a barotropic solution, controlled by 13 tidal components at open boundaries. The performance of the numerical model was evaluated using the hourly water level observations and the TOPEX/Poseidon altimetry data. Statistical analysis showed a good agreement between the simulated and observed water levels. RMS error was found to be ranged from 0.07 to 0.23 m, with maximum discrepancies observed at Ras Tanura and Mina Sulman stations. However, the IOA between the simulated and observed water levels was significant (0.95–0.99). On average, the errors for the tidal constituents considered in the analysis are in the order of <0.02 m (4%). The M2, S2, K1 and O1 tidal waves represent the largest among other constituents, where the amplitude of S2 represents almost 30% of the M2, and the O1 tidal wave represents about 50% of the K1 tide. The co-tidal charts of the semidiurnal tides show the existence of two anticlockwise amphidromic systems in the north and south ends (centred around 28.25° and 24.5°N respectively) close to the western side, while the diurnal constituents form only a single amphidromic point in the central part, centred around 26.8°N (North Bahrain). On the other hand, the velocity amplitudes of the U and V components of the numerical model were compared with a previous observational study and found to be agreed well.

Comparison of GPS-derived ocean tide loading displacements with models in New Zealand

ABSTRACT We investigate the tidal displacement signals of two principle semidiurnal () and diurnal () tidal constituents in New Zealand. We calculate the predicted loading displacements using the latest ocean tide models and Earth models. The results show that, for the constituent, the tide models FES2014b and TPXO9-Atlas have subtle differences, and the vector differences between the Earth models shows that the regularity of the influence of the Earth model is weak. The vector difference of constituent have significant spatial coherence (about 0.2 mm). The residuals of constituent in the up component subtract about 0.2 mm across the entire areas after considering the anelastic dispersion. We find that the clear regional-scale spatial coherence of the residuals exists in both constituents in all models even if spatial water density and compressibility have been considered. However, the spatial coherence of residuals disappears when the network-mean value removed, and the reduction of RMS for constituent is close to the theoretical error of body tide (about 0.5 mm). We also find that for the different ocean tide models, part of the differences in residuals between the observations and predictions would be attributed to the choice of geocentric reference frame.

Competition Between Atmospheric and Tidally Attenuated Forcing in an Elongated Coastal Lagoon

Water level measurements at four sub-basins of a highly dissipative coastal lagoon were used to study variability at tidal and subtidal scales and to determine whether atmospheric forcing influenced variations in water level at tidal scales. The amplitude of the main astronomic constituents, which were diurnal, attenuated quickly to <5% by the second sub-basin. The attenuation was represented well by an analytical solution that described a damped wave. The semidiurnal constituent with a period of 12 h (S2), however, decreased to 50% of the lagoon’s entrance amplitude and then increased to 60% by the fourth sub-basin. Reproduction of this S2 behavior by the analytical model required unrealistically low signal attenuation, much lower than for the other semidiurnal constituent (12.42 h, M2). This behavior suggested that the S2 amplification was non-gravitational and related to semidiurnal atmospheric forcing, which was dominated by barometric pressure. Such suggestion was confirmed by coherence and wavelet coherence analysis and by the fact that the largest overtide was related to the interaction between S2, instead of M2, and the diurnal constituent. This study documents that a highly dissipative coastal lagoon becomes forced semidiurnally by barometric pressure toward its head. Subtidal water levels were studied with empirical orthogonal functions, revealing 2 modes that explained ~85% of the variance. Mode 1 was related to northerly winds (‘Nortes’) and mode 2 was linked to the Trade winds that dominate the region.

Stepwise alterations in tidal hydrodynamics in a highly human-modified estuary: The roles of channel deepening and narrowing

With the rapid development of coastal cities, estuarine environments have been drastically changed by human interventions that considerably alter hydrodynamics (e.g., tidal amplitude) and water quality (e.g., salinity intrusion). In this study, we used a well-developed one-dimensional analytical model that accounts for the mutual nonlinear interactions between different tidal constituents to investigate the stepwise alterations in tidal hydrodynamics in Lingdingyang Bay of the Pearl River Estuary during 1965–2016, with a particular focus on the impacts of channel deepening and narrowing. The stepwise alterations in tidal hydrodynamics in Lingdingyang Bay can be divided into three distinct phases: the pre-human period (1965–1989), the transitional period (1990–2007), and the post-human period (2008–2016). It was shown that channel deepening and narrowing exert a dramatic influence on the tidal hydrodynamics in terms of increasing wave celerity, amplifying tidal waves, increasing the velocity amplitude and becoming more standing wave character. Furthermore, analytical results show that the responses of the semi-diurnal constituents (M2 and S2) to morphological changes are much more sensitive than those of the diurnal constituents (K1 and O1). In addition, based on the sensitivity analysis, we show that the effects of channel narrowing on tidal hydrodynamics are stronger than those of channel deepening. These results quantifying the effects of estuarine morphology on tidal hydrodynamics can provide scientific guidelines for sustainable water resources management in Lingdingyang Bay and other tide-dominated estuaries that are subject to intensive human interventions, especially regarding morphological changes.

Estimating ocean tide loading displacements with GPS and GLONASS

Abstract. Ground displacements due to ocean tide loading have previously been successfully observed using Global Positioning System (GPS) data, and such estimates for the principal lunar M2 constituent have been used to infer the rheology and structure of the asthenosphere. The GPS orbital repeat period is close to that of several other major tidal constituents (K1, K2, S2); thus, GPS estimates of ground displacement at these frequencies are subject to GPS systematic errors. We assess the addition of GLONASS (GLObal NAvigation Satellite System) to increase the accuracy and reliability of eight major ocean tide loading constituents: four semi-diurnal (M2, S2, N2, K2) and four diurnal constituents (K1, O1, P1, Q1). We revisit a previous GPS study, focusing on 21 sites in the UK and western Europe, expanding it with an assessment of GLONASS and GPS+GLONASS estimates. In the region, both GPS and GLONASS data have been abundant since 2010.0. We therefore focus on the period 2010.0–2014.0, a span considered long enough to reliably estimate the major constituents. Data were processed with a kinematic precise point positioning (PPP) strategy to produce site coordinate time series for each of three different modes: GPS, GLONASS and GPS+GLONASS. The GPS solution with ambiguities resolved was used as a baseline for performance assessment of the additional modes. GPS+GLONASS shows very close agreement with ambiguity resolved GPS for lunar constituents (M2, N2, O1, Q1) but with substantial differences for solar-related constituents (S2, K2, K1, P1), with solutions including GLONASS being generally closer to model estimates. While no single constellation mode performs best for all constituents and components, we propose to use a combination of constellation modes to recover tidal parameters: GPS+GLONASS for most constituents, except for K2 and K1 where GLONASS (north and up) and GPS with ambiguities resolved (east) perform best.

Trends in Tidal Levels and Mean Sea Level in the Gulf of Thailand

Astronomical tides have a major impact on coastal sediment distribution, seawater levels, coastal navigation, and other coastal dynamics. Any significant change to tides could have impacts on coastal ecosystems. This study explored the hourly water level from 11 tidal gauge stations along the Gulf of Thailand over different periods using harmonic analysis. Secular trends of tidal levels, tidal range, mean sea level and tidal constituents were assessed using a linear regression model. We found changes in all the tidal levels assessed. Increasing trends were observed for almost all tidal levels and the mean sea level at all locations. At most of the locations, the trends in tidal levels were similar to the mean sea level. Widespread increasing trends were observed in relation to the tidal levels, and in most cases, the trends were consistent with the mean sea level. Analysis of the tidal harmonic constituents showed significant trends for the luni-solar diurnal constituent (K1) at most stations. However, the magnitude of the trends in the harmonic constituents was less pronounced compared to the trends in water levels. Coastal management policies should take into account these widespread changes in tides.

Arctic tidal current atlas

Tidal and wind-driven near-inertial currents play a vital role in the changing Arctic climate and the marine ecosystems. We compiled 429 available moored current observations taken over the last two decades throughout the Arctic to assemble a pan-Arctic atlas of tidal band currents. The atlas contains different tidal current products designed for the analysis of tidal parameters from monthly to inter-annual time scales. On shorter time scales, wind-driven inertial currents cannot be analytically separated from semidiurnal tidal constituents. Thus, we include 10–30 h band-pass filtered currents, which include all semidiurnal and diurnal tidal constituents as well as wind-driven inertial currents for the analysis of high-frequency variability of ocean dynamics. This allows for a wide range of possible uses, including local case studies of baroclinic tidal currents, assessment of long-term trends in tidal band kinetic energy and Arctic-wide validation of ocean circulation models. This atlas may also be a valuable tool for resource management and industrial applications such as fisheries, navigation and offshore construction.

CM6: a comprehensive geomagnetic field model derived from both CHAMP and Swarm satellite observations

From the launch of the Ørsted satellite in 1999, through the CHAMP mission from 2000 to 2010, and now with the Swarm constellation mission starting in 2013, satellite magnetometry has provided excellent monitoring of the near-Earth magnetic field regime. The advanced Comprehensive Inversion scheme has been applied to data before Swarm and to the Swarm data itself, but now for the first time to all the satellite data in this new era, culminating in the CM6 model. The highlights of this model include not only a continuous core magnetic field description over the entire time period 1999 to 2019.5 in good agreement with the CHAOS model series, but the addition of two new oceanic tidal magnetic sources: the larger lunar elliptic semi-diurnal constituent N_2 and the lunar diurnal constituent O_1. CM6 is also the parent model of the NASA/GSFC candidates for the DGRF2015 and IGRF2020 in response to the IGRF-13 call. This paper provides a full report on the development of CM6.

A Tidal Hydrodynamic Model for Cook Inlet, Alaska, to Support Tidal Energy Resource Characterization

Cook Inlet in Alaska has been identified as a prime site in the U.S. for potential tidal energy development, because of its enormous tidal power potential that accounts for nearly one-third of the national total. As one important step to facilitate tidal energy development, a tidal hydrodynamic model based on the unstructured-grid, finite-volume community ocean model (FVCOM) was developed for Cook Inlet to characterize the tidal stream energy resource. The model has a grid resolution that varies from about 1000 m at the open boundary to 100–300 m inside the Inlet. Extensive model validation was achieved by comparing model predictions with field observations for tidal elevation and velocity at various locations in Cook Inlet. The error statistics confirmed the model performs reasonably well in capturing the tidal dynamics in the system, e.g., R2 &gt; 0.98 for tidal elevation and generally &gt; 0.9 for velocity. Model results suggest that tides in Cook Inlet evolve from progressive waves at the entrance to standing waves at the upper Inlet, and that semi-diurnal tidal constituents are amplified more rapidly than diurnal constituents. The model output was used to identify hotspots that have high energy potential and warrant additional velocity and turbulence measurements such as East Foreland, where averaged power density exceeds 5 kw/m2. Lastly, a tidal energy extraction simulation was conducted for a hypothetical turbine farm configuration at the Forelands cross section to evaluate tidal energy extraction and resulting changes in far-field hydrodynamics.

The amplitudes and phases of tidal constituents from Harmonic Analysis at two stations in the Gulf of Aden

Amplitudes and phases of the tidal constituents are computed from harmonic analysis for the ports of Aden and Djibouti from the hourly Sea Level data for the year 2008 at these locations. The analysis shows that the tides are of mixed nature in the area. The ratio F = K1 + O1/M2 +S2 gives a value of 0.87 and 0.85 for Aden and Djibouti stations. The high astronomical tide and low astronomical tides are respectively 1.138 m and − 1.681 m for Aden port and 1.144 m and − 1.671 m for Djibouti port. Tidal amplitudes and phases at both stations are found closely similar. The major constituents of semi-diurnal waves are M2, S2 and N2 tides with amplitudes of 0.476, 0.215 and 0.129 m. The dominant diurnal waves are K1, O1 and P1 tides with amplitudes of 0.401, 0.201 and 0.121 m respectively. Other tidal constituents represented by third, fourth and sixth diurnal constituents, they have small amplitudes. In these groups, the M3, M4 are the major components with amplitudes of 0.005 m, 0.003 m respectively.

Numerical modelling of the Caspian Sea tides

Abstract. The Caspian Sea is the largest enclosed basin on Earth and a unique subject for the analysis of tidal dynamics. Tides in the basin are produced directly by the tide-generating forces. Using the Princeton Ocean Model (POM), we examine details of the spatial and temporal features of the tidal dynamics in the Caspian Sea. We present tidal charts of the amplitudes and phase lags of the major tidal constituents, together with maps of the form factor, tidal range, and tidal current speed. Semi-diurnal tides in the Caspian Sea are determined by a Taylor amphidromic system with anticlockwise rotation. The largest M2 amplitude is 6 cm and is located in Türkmen Aylagy (called Turkmen Bay hereafter). For the diurnal constituents, the Absheron Peninsula separates two individual amphidromes with anticlockwise rotation in the north and in the south. The maximum K1 amplitudes (up to 0.7–0.8 cm) are located in (1) the south-eastern part of the basin, (2) Türkmenbaşy Gulf, (3) Mangyshlak Bay; and (4) Kizlyar Bay. As a result, the semi-diurnal tides prevail over diurnal tides in the Caspian Sea. The maximum tidal range, of up to 21 cm, has been found in Turkmen Bay. The strongest tidal currents have been located in the straits to the north and south of Ogurja Ada, where speeds reach 22 and 19 cm s−1, respectively. Numerical simulations of the tides using different mean sea levels (within a range of 5 m) indicate that spatial features of the Caspian Sea tides are strongly sensitive to changes in mean sea level.