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Richard D. Ray - One of the best experts on this subject based on the ideXlab platform.
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First global observations of third-degree Ocean Tides
Science advances, 2020Co-Authors: Richard D. RayAbstract:The Moon’s tidal potential is slightly asymmetric, giving rise to so-called third-degree Ocean Tides, which are small and never before observed on a global scale. High-precision satellite altimeters have collected sea level records for almost three decades, providing a massive database from which tiny, time-coherent signals can be extracted. Here, four third-degree Tides are mapped: one diurnal, two semidiurnal, and one terdiurnal. Aside from practical benefits, such as improved tide prediction for geodesy and Oceanography, the new maps reveal unique ways the Ocean responds to a precisely known, but hitherto unexplored, force. An unexpected example involves the two semidiurnals, where the smaller lunar force is seen to generate the larger Ocean tide, especially in the South Pacific. An explanation leads to new information about an Ocean normal mode that spatially correlates with the third-degree astronomical potential. The maps also highlight previously unknown shelf resonances in all three tidal bands.
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Consideration of tidal variations in the geocenter on satellite altimeter observations of Ocean Tides
Geophysical Research Letters, 2014Co-Authors: Shailen D. Desai, Richard D. RayAbstract:Tidal geocenter motion has been previously ignored when developing Ocean tide models from satellite altimetry. Accounting for tidal geocenter motion is necessary because the best orbit determinations for altimetric satellites position sea-surface heights relative to the center of mass of the total Earth system, including the Ocean Tides. But the Ocean Tides are presumed relative to the Earth's crust and thus are effectively relative to the center of figure. By accounting for this effect, we find improved agreement between an altimeter-based Ocean tide model and bottom pressure recorder observations. The variance of differences between these two observations is reduced by 31% and 43% for the two tidal constituents with the largest contributions to geocenter variations, O1 and K1, respectively. With this accommodation the predicted contribution from altimeter-based Ocean tide models to geocenter variations is amplified by 15–22%, providing improved agreement with observations, especially for the K1 component.
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Precise comparisons of bottom‐pressure and altimetric Ocean Tides
Journal of Geophysical Research: Oceans, 2013Co-Authors: Richard D. RayAbstract:[1] A new set of pelagic tide determinations is constructed from seafloor pressure measurements obtained at 151 sites in the deep Ocean. To maximize precision of estimated Tides, only stations with long time series are used; median time series length is 567 days. Geographical coverage is considerably improved by use of the international tsunami network, but coverage in the Indian Ocean and South Pacific is still weak. As a tool for assessing global Ocean tide models, the data set is considerably more reliable than older data sets: the root-mean-square difference with a recent altimetric tide model is approximately 5 mm for the M2 constituent. Precision is sufficiently high to allow secondary effects in altimetric and bottom-pressure tide differences to be studied. The atmospheric tide in bottom pressure is clearly detected at the S1, S2, and T2 frequencies. The altimetric tide model is improved if satellite altimetry is corrected for crustal loading by the atmospheric tide. Models of the solid body tide can also be constrained. The free core-nutation effect in the K1 Love number is easily detected, but the overall estimates are not as accurate as a recent determination with very long baseline interferometry.
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precise comparisons of bottom pressure and altimetric Ocean Tides
Journal of Geophysical Research, 2013Co-Authors: Richard D. RayAbstract:[1] A new set of pelagic tide determinations is constructed from seafloor pressure measurements obtained at 151 sites in the deep Ocean. To maximize precision of estimated Tides, only stations with long time series are used; median time series length is 567 days. Geographical coverage is considerably improved by use of the international tsunami network, but coverage in the Indian Ocean and South Pacific is still weak. As a tool for assessing global Ocean tide models, the data set is considerably more reliable than older data sets: the root-mean-square difference with a recent altimetric tide model is approximately 5 mm for the M2 constituent. Precision is sufficiently high to allow secondary effects in altimetric and bottom-pressure tide differences to be studied. The atmospheric tide in bottom pressure is clearly detected at the S1, S2, and T2 frequencies. The altimetric tide model is improved if satellite altimetry is corrected for crustal loading by the atmospheric tide. Models of the solid body tide can also be constrained. The free core-nutation effect in the K1 Love number is easily detected, but the overall estimates are not as accurate as a recent determination with very long baseline interferometry.
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Fortnightly Ocean Tides, Earth Rotation, and Mantle Anelasticity
2012Co-Authors: Richard D. Ray, Gary D EgbertAbstract:The fortnightly Mf Ocean tide is the largest of the long-period Tides (periods between 1 week and 18.6 years), but Mf is still very small, generally 2 cm or less. All long-period Tides are thought to be near equilibrium with the astronomical tidal potential, with an almost pure zonal structure. However, several lines of evidence point to Mf having a significant dynamic response to forcing. We use a combination of numerical modeling, satellite altimetry, and observations of polar motion to determine the Mf Ocean tide and to place constraints on certain global properties, such as angular momentum. Polar motion provides the only constraints on Mf tidal currents. With a model of the Mf Ocean tide in hand, we use it to remove the effects of the Ocean from estimates of fortnightly variations in length-of-day. The latter is dominated by the earth's body tide, but a small residual allows us to place new constraints on the anelasticity of the earth's mantle. The result gives the first experimental confirmation of theoretical predictions made by Wahr and Bergen in 1986.
Ole Baltazar Andersen - One of the best experts on this subject based on the ideXlab platform.
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Extreme Southern Ocean Tide Modeling
International Association of Geodesy Symposia, 2003Co-Authors: C K Shum, Ole Baltazar Andersen, Per KnudsenAbstract:Predictability of barotropic Ocean Tides is significantly less accurate in the coastal regions, littoral and shallow seas, and Oceans not covered by TOPEX/POSEIDON (T/P) than in deep Oceans (>1000 m depth) within ±66° latitude. Barotropic Ocean tide models (mostly with spatial resolutions at 50 km or longer), benefited primarily from T/P altimetry and hydrodynamic modeling, allow predictions of deep Ocean tidal amplitudes with an estimated accuracy of 1-2 cm (1 σ). Even with the availability of most recent suite of available global tide models based primarily on T/P data, e.g., GOT00, NA099, Delft, FESOO, extreme Southern Ocean Tides below 60S are limited both in accuracy and resolutions, especially in regions near Antarctica where parts of Ocean surfaces are seasonally or permanently covered with ice. In our initial study with the objectives to improve Tides in Antarctic Oceans for accurate prediction of ground-line locations to enhance ice mass balance studies, we provide an assessment of accuracy of tide models in the region. In addition to global models, regional models such as the Padman models (Weddell Sea and Ross Sea) are currently available. Test models below 50S are presented using available T/P and ERS-2 altimeter data over Ocean surfaces as well as retracked ERS-2 data over sea surfaces covered with ice.
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global Ocean Tides from ers 1 and topex poseidon altimetry
Journal of Geophysical Research, 1995Co-Authors: Ole Baltazar AndersenAbstract:Ocean tide models representing all major diurnal and semidiurnal tidal constituents with a spatial resolution of 0.75°×0.75° have been estimated using the first 1.5 years of ERS 1 and TOPEX/POSEIDON altimetry. The Ocean tide model was derived from the combined use of ERS 1 and TOPEX/POSEIDON data by using a modified orthotide formulation that simultaneously solves for all diurnal and semidiurnal constituents as well as the annual signal. An additional adjustment of the solar semidiurnal harmonic of the gravitational potential was applied in order to account for radiational forcing, particularly in the S2 constituent. TOPEX/POSEIDON provides excellent Ocean tide estimates in the open Ocean. However, especially in coastal regions, the track spacing of TOPEX/POSEIDON (315 km at the equator) is too coarse to determine large parts of the Ocean tide signal. For these regions the inclusion of data from the ERS 1 35-day repeat mission provides a valuable supplement, as the ERS 1 satellite has a track spacing which is around 3.6 times better than that of the TOPEX/POSEIDON satellite. The combined ERS 1 and TOPEX/POSEIDON Ocean tide solution exhibits distinct sectoral geographical pattern of highs and lows when compared with the Cartwright and Ray (1990, 1991) Ocean tide model. This indicates the presence of small but fundamental orbit errors present in the Cartwright and Ray Ocean tide solution. Compared with a new set of 104 tide gauge readings compiled by Le Provost, the RMS differences of the combined ERS 1 and TOPEX solution are 2.51, 1.67, 1.58, and 1.13 cm for the M2, S2, K1, and O1 constituents, respectively. The increased spatial resolution of the combined ERS 1 and TOPEX model as compared to a TOPEX-alone model is seen to reduce RMS differences from 37 to 22 cm for the M2 constituent, when compared to a selection of 90 pelagic and coastal tide gauges in the northwest European shelf region.
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Global Ocean Tides from ERS 1 and TOPEX/POSEIDON altimetry
Journal of Geophysical Research, 1995Co-Authors: Ole Baltazar AndersenAbstract:Ocean tide models representing all major diurnal and semidiurnal tidal constituents with a spatial resolution of 0.75°×0.75° have been estimated using the first 1.5 years of ERS 1 and TOPEX/POSEIDON altimetry. The Ocean tide model was derived from the combined use of ERS 1 and TOPEX/POSEIDON data by using a modified orthotide formulation that simultaneously solves for all diurnal and semidiurnal constituents as well as the annual signal. An additional adjustment of the solar semidiurnal harmonic of the gravitational potential was applied in order to account for radiational forcing, particularly in the S2 constituent. TOPEX/POSEIDON provides excellent Ocean tide estimates in the open Ocean. However, especially in coastal regions, the track spacing of TOPEX/POSEIDON (315 km at the equator) is too coarse to determine large parts of the Ocean tide signal. For these regions the inclusion of data from the ERS 1 35-day repeat mission provides a valuable supplement, as the ERS 1 satellite has a track spacing which is around 3.6 times better than that of the TOPEX/POSEIDON satellite. The combined ERS 1 and TOPEX/POSEIDON Ocean tide solution exhibits distinct sectoral geographical pattern of highs and lows when compared with the Cartwright and Ray (1990, 1991) Ocean tide model. This indicates the presence of small but fundamental orbit errors present in the Cartwright and Ray Ocean tide solution. Compared with a new set of 104 tide gauge readings compiled by Le Provost, the RMS differences of the combined ERS 1 and TOPEX solution are 2.51, 1.67, 1.58, and 1.13 cm for the M2, S2, K1, and O1 constituents, respectively. The increased spatial resolution of the combined ERS 1 and TOPEX model as compared to a TOPEX-alone model is seen to reduce RMS differences from 37 to 22 cm for the M2 constituent, when compared to a selection of 90 pelagic and coastal tide gauges in the northwest European shelf region.
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Ocean Tides in the northern north atlantic and adjacent seas from ers 1 altimetry
Journal of Geophysical Research, 1994Co-Authors: Ole Baltazar AndersenAbstract:Twenty months of ERS 1 35-day repeat altimeter data containing 18 repeat cycles have been used to estimate the major diurnal and semidiurnal Ocean tide signals in the northern parts of the North Atlantic and adjacent seas. ERS 1 provides valuable information when investigating Ocean Tides, owing to the repeated dense spatial sampling. However, several tidal constituents are extremely difficult to resolve using conventional harmonic analysis with the chosen sun syncronous orbit. Instead, temporal analysis at each crossover location is applied using a modified form of the orthotide formulation, which simultaneously solves for the diurnal and semidiurnal species as well as for the annual signal. The use of the response formalism ensures that the sun syncronous component S2 can be resolved, although this component is “frozen” in the orbit. Maps of the M2, S2 and K1 tidal amplitudes and phases in 0.5°×0.5° grids are presented and are seen to compare favorably with measurements at 68 pelagic tide gauges provided by the International Association for Physical Sciences of the Ocean. The major tidal constituents of the ERS 1 derived model are also in close agreement with the improved Flather (1981) Ocean tide model for the northwest European continental shelf area, as well as a numerical model for the Arctic and Nordic Seas by Gjevik and Straume (1989).
Robert H. Tyler - One of the best experts on this subject based on the ideXlab platform.
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heating of enceladus due to the dissipation of Ocean Tides
Icarus, 2020Co-Authors: Robert H. TylerAbstract:Abstract Given Cassini observations of a large and unexplained endogenic heat source, the subsurface Ocean on Enceladus is an important test bed for modeling icy-satellite Ocean Tides and the dissipative heat generated. Here we revisit and expand estimates of the Ocean tidal power (heating rate) to describe how the power depends on input parameter and process assumptions. The approach taken in this (and previous) work by this author is that the dissipation process in Enceladus' Ocean is unknown and cannot be reliably modeled from first principles. Considered instead are generic dissipation forms that cover specific physical dissipation processes as special cases (specific cases described here include linear/nonlinear drag, eddy viscosity, viscoelastic ice coupling, and vertical wave damping). The justification for basing conclusions primarily on the generic (rather than specific) dissipation forms is that whatever the Ocean dissipation process, it must draw from the stored energy (kinetic or potential) in the Ocean tidal response, and this process must have an associated time scale for the dissipation to take place. By treating this time scale (as well as the Lamb number/wave speed) as free parameters, millions of tidal solutions are calculated to sample the full domain of tidal scenarios that arrive from different combinations of these two parameters, as well as the assumed dissipation form. Conclusions drawn from the general behavior in this larger solution domain are then considered to be more robust than conclusions drawn from the subdomain that assumes the validity of a specific physical dissipation process. The results show plausible states whereby the Ocean Tides (even if Enceladus is covered with thick ice) generate the observed heat flux. While the same results show that low-power, non-resonant states are also allowed, an argument is presented that these low-power states may not be stable in the presence of secular trends (e.g. cooling, stratification). Rather, self-tuned resonance stabilizes the tidal configuration in a near-resonant forced state with high power and dissipative heat.
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comparative estimates of the heat generated by Ocean Tides on icy satellites in the outer solar system
Icarus, 2014Co-Authors: Robert H. TylerAbstract:Abstract This study illuminates scenarios whereby the heat produced by the dissipation of Ocean Tides is significant in the heat budgets maintaining liquid Oceans on icy satellites in the outer Solar System. It has been shown in previous work that Ocean Tides, if resonantly forced, can supply heat at or exceeding the rates necessary for maintaining these Oceans. It has also been shown that because of feedbacks these resonant configurations may be unavoidable under typical situations. This study extends from the previous work and seeks to examine the full set of dynamically-consistent Ocean tidal solutions to describe the parameter dependencies that may cause one Ocean to become trapped in such a vigorous Ocean state while allowing another to freeze—why do some of these satellites have Oceans, and others do not? It is found that even with no other sources of heat, a liquid Ocean on many of these satellites would be maintained by Ocean tidal heat because the process of freezing (which changes the thickness of the remaining liquid Ocean and thereby the eigenmodes) would push the Ocean into a resonant configuration, with the associated increase in heat production preventing further freezing and stabilizing the configuration. An Ocean on Io or Mimas would suffer extreme Tides (with heat generated exceeding 1 W/m 2 ) unless an implausibly large volume of water were present to lift the eigenmodes of the configuration out of resonance with the tidal forces. Europa can maintain a thick (∼100 km) Ocean due to an obliquity-forced tidal resonance, while parameters for most other satellites suggest eccentricity-driven resonance scenarios involving much thinner Ocean thicknesses (1–10s km). But these thin Ocean thickness in the latter scenarios will be altered by ice cover: as the ice cover damps the Ocean tidal response, significant heat is still generated which would stall freezing but the Ocean thicknesses are modified to larger values than would be expected without ice cover.
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Magnetic remote sensing of Europa’s Ocean Tides
Icarus, 2011Co-Authors: Robert H. TylerAbstract:Abstract Recent analyses of Galileo magnetometer and gravity data justifies approximations that allow estimates of the magnetic fields generated by Europa’s Ocean Tides to be made even though some of the Ocean parameters that would generally be required are unavailable. We show solutions for the magnetic fields generated by published estimates of Ocean Tides on Europa and provide simple scaling formulas that can be used to estimate the magnetic-field amplitudes for other choices for the Ocean tidal state. Because of the distinguished spatial/temporal form of these fields, it is expected that Europa’s Ocean Tides can be inferred from remote magnetic sensing by an orbiter of sufficient duration.
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Ocean Tides heat enceladus
Geophysical Research Letters, 2009Co-Authors: Robert H. TylerAbstract:[1] With a young, highly reflective surface and vigorous geological activity, Saturn's tiny moon Enceladus has been one of the most mysterious planetary bodies in the solar system. Recent observations from the Cassini spacecraft show vast plumes of vapor erupting from geysers near the south pole, and inferred heat fluxes of about 100 mW/m2 for the same region have helped consolidate the essential enigma of Enceladus: there must be a relatively large and unidentified source of heat in the tiny moon. Here we present a case for heating from dissipation by tidal flow in an ice-covered Ocean. We show that if the spin axis of Enceladus is tilted with respect to its orbital plane by at least 0.05 degree then strong tidal flow will be generated with enough dissipative heating to explain the observed heat flux. In an alternative case of a shallow (10 km or less) Ocean, comparable flow velocities and heating may be obtained by eccentricity tidal forces.
Brian K Arbic - One of the best experts on this subject based on the ideXlab platform.
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secular trends in Ocean Tides observations and model results
Journal of Geophysical Research, 2011Co-Authors: Malte Muller, Brian K Arbic, Jerry X. MitrovicaAbstract:[1] During the last century the response of the Oceans to tidal forces has changed significantly. This study focuses on an analysis of long-term sea level records located in the Atlantic and Pacific, primarily in the Northern Hemisphere. It shows that changes of tidal amplitude and/or phase have taken place over large scales. The principal solar semidiurnal (S2) tide shows the largest trends. At some locations, the change in the mean tidal range due to tidal trends is significant compared with the trend in mean sea level. Thus, it might be advisable to consider these changes in studies of the impact of rising sea level. Numerical simulations of the principal lunar semidiurnal tide (M2) demonstrate a model sensitivity in the North Atlantic to changes in glacial isostatic adjustment and sea level rise, which captures 30–40% of the magnitude of the trends in observations. However, the spatial patterns do not agree well with those inferred from observations, suggesting that forward global models are currently useful for qualitative but not quantitative understanding of the observed trends. A global free oscillation synthesis indicates that sea level rise due to glacial isostatic adjustment leads to decreasing global resonant periods and increasing damping in the system and a coupled oscillator model shows that changes in sea level on the shelf are much more effective at perturbing shelf and Ocean Tides than sea level changes in the deep Ocean.
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a coupled oscillator model of shelf and Ocean Tides
Continental Shelf Research, 2010Co-Authors: Brian K Arbic, Chris GarrettAbstract:Abstract 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 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.
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on tidal resonance in the global Ocean and the back effect of coastal Tides upon open Ocean Tides
Atmosphere-ocean, 2009Co-Authors: Brian K Arbic, Richard Karsten, Chris GarrettAbstract:Abstract The resonance of semi‐diurnal tidal elevations is investigated with a forward numerical forced damped global tide model and an analytical model of forced‐damped Tides in a deep Ocean basin coupled to a shelf. The analytical model contains the classical half‐wavelength and quarter‐wavelength resonances in the deep Ocean and shelf, respectively, as well as a forcing‐scale dependence which depends on the ratio of the phase speed of open‐Ocean gravity waves to that of the astronomical forcing. In the analytical model, when the deep Ocean and shelf resonate separately at the same frequency, the resonance in the coupled system shifts to frequencies slightly higher and lower than the original frequency, such that a ‘double bump’ is seen in plots of elevation amplitude versus frequency. The addition of a shelf to a resonant open Ocean tends to reduce open‐Ocean Tides, especially when the shelf is also near resonance. The magnitude of this ‘back‐effect’ is controlled by shelf friction. A weakly damped res...
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Ocean Tides and Heinrich events
Nature, 2004Co-Authors: Brian K Arbic, Douglas R Macayeal, Jerry X. Mitrovica, Glenn A. MilneAbstract:Climate varied enormously over the most recent ice age1 — for example, large pulses of ice-rafted debris2, originating mainly from the Labrador Sea3, were deposited into the North Atlantic at roughly 7,000-year intervals, with global climatic implications3. Here we show that Ocean Tides within the Labrador Sea were exceptionally large over the period spanning these huge, abrupt ice movements, which are known as Heinrich events. We propose that Tides played a catalytic role in liberating iceberg armadas during that time.
George H Born - One of the best experts on this subject based on the ideXlab platform.
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shallow and deep water global Ocean Tides from altimetry and numerical modeling
Journal of Geophysical Research, 2000Co-Authors: Craig C Tierney, Lakshmi Kantha, George H BornAbstract:We present here a 1/4° resolution near-global barotropic tidal model designed specifically to provide more accurate Tides in shallow water. The model assimilates Tides derived from 4 years of TOPEX/Poseidon (T/P) altimetric data. Procedures are used that tend to preserve the small spatial scales in the tidal structure in shallow water. Data from coastal tide gauges are also assimilated into the model. The result is a tidal model that is useful in most of the shallow and deep areas of the global Oceans. Some problems exist in regions where no data are available for assimilation, such as the Southern Ocean. Pelagic tide gauge comparisons show that in deep water the new model is comparable in accuracy to the best of the existing T/P-based global tidal models. Comparisons to crossover differences in shallow water suggest improved performance. We found that more accurate accounting of the load Tides in the Ocean tide model using an iterative technique based on the Green's function formalism does not yield Ocean Tides that are significantly different from the simpler approaches used thus far by Ocean tide modelers when data are assimilated. It is our hope that this tidal model will not only help advance our understanding of shallow water tidal processes around the globe but also extend the utility of altimetry to waters shallower than 1000 m.
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an investigation of Ocean Tides derived from along track altimetry
Journal of Geophysical Research, 1998Co-Authors: Craig C Tierney, Mike E Parke, George H BornAbstract:With the availability of a long data record of accurate sea surface height measurements, it is now possible to estimate the Ocean tide along the ground track of TOPEX/POSEIDON (T/P). This has been done from over 4.5 years of data using both response and harmonic analyses. These estimates agree well with each other, and with other gridded models over both long and short wavelengths in deep water, for those tidal components whose alias frequencies are separable by the Rayleigh criterion. Comparisons of along-track (AT) estimates to current tide models show shorter wavelength features not present in dynamical and empirical global models. AT estimates follow the general trends of empirical models far from sharp topographical changes, but near sharp changes, they tend to follow dynamical model results. Error estimates show that the T/P data are not significantly worse in shallow water than in deep water, suggesting that there is accurate information about Tides in shallow water in the T/P data. Tides at crossover locations are improved by computing estimates with both ascending and descending track data. Possible techniques to improve AT tidal estimates between crossover points are discussed. AT tidal estimation can be useful for studying local regions where resolution is more important than regular spacing, for studying tidal interactions over sharp topography, and for extending tidal models from deep to shallow waters through assimilation into a dynamical model.