tidal modeling of an ancient tide dominated seaway part 1 model validation and application to global early cretaceous aptian tides abstract the utility of deep time global paleotidal modeling is evaluated with a series of modeling experiments focused on the early cretaceous aptian the results from a series of paleobathymetry sensitivity experiments indicate that despite paleogeographic and paleobathymetric uncertainty appropriate use of global paleotidal models complements and enhances stratigraphic and sedimentological methods before being applied to global paleotidal modeling the imperial college ocean model icom is validated for the computation of modern global tides the icom results only deviate slightly from a state of the art published model and were achieved with considerably less computational expense and without data assimilation the results from global paleotidal modeling of the early cretaceous aptian were assessed by comparison with the published geological record icom predicts high mesotidal to macrotidal ranges on the arabian platform around india especially to the north and west along the pacific coast between north and south america northeast of australia and around southeast asia the model predicts low microtidal ranges in the proto south atlantic ocean and weddell sea a further validation test assessed the ability of the model to predict the dominant tidal constituents diurnal or semidiurnal in the aptian lower greensand seaway of southeastern england and northern france during the aptian this region was connected to the boreal proto atlantic and neotethys oceans and now preserves superbly documented tidal deposits the model predicts low microtidal ranges in the proto central atlantic ocean and boreal ocean suggesting that they had little impact on tides in the lower greensand seaway higher tidal amplitudes especially of diurnal once daily tides are predicted in the northwestern neotethys ocean suggesting that this ocean was an important source of tidal energy to the lower greensand seaway sensitivity tests to paleogeographic and paleobathymetric uncertainty indicate that the model predictions are robust the prediction of predominantly diurnal tides is supported by published analyses of large dune scale deposits in the lower greensand of southeast england

shallow and deep water global ocean tides from altimetry and numerical modeling 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

tidal corrections in the topex poseidon geophysical data records the aim of this paper is to give an assessment to topex poseidon data users of the two available oceanic tidal corrections which are based on the schwiderski model sch and the cartwright and ray model cr respectively large instantaneous differences are observed between the two corrections and use of either model may sometimes lead to inadequate understanding of the remaining oceanic signals in this paper we give an objective comparison of sch and cr models and point out the major features of both models our methodology is applicable to the validating and testing of future tide models that will soon be appearing

sea surface height determination in the arctic ocean from ers altimetry 1 accurate sea surface height measurements have been extracted from ers altimeter data in sea ice covered regions for the first time the data have been used to construct a mean sea surface of the arctic ocean between the latitudes of 60 degreesn and 81 5 degreesn based on 4 years of ers 2 data an rms value for the crossover differences of mean sea surface profiles of 4 2 cm was observed in the ice covered canada basin compared with 3 8 cm in the ice free greenland iceland norwegian seas comparisons are made with an existing global mean sea surface osumss95 highlighting significant differences between the two surfaces in permanently ice covered seas in addition we present the first altimeter derived sea surface height variability map of the arctic ocean comparisons with a high resolution coupled ocean sea ice general circulation model reveal a good qualitative agreement in the spatial distribution of variability quantitatively we found that the observed variability was on average a factor of 3 4 greater than model predictions

influence of the yangtze river and grain size on the spatial variations of heavy metals and organic carbon in the east china sea continental shelf sediments abstract bulk heavy metal fe mn zn cu pb cd al organic carbon and carbonate concentrations grain sizes and c13 of the organic carbon distributions were studied in sediments collected throughout the east china sea continental shelf and the yangtze river delta the results demonstrated that terrigenous sediments from the yangtze river is a dominating factor controlling the spatial variations of heavy metals and organic carbon concentrations on the east china sea continental shelf in addition grain size and recent anthropogenic influences are also major factors modifying the spatial and vertical variations of heavy metals large spatial variations with a band type distribution of heavy metals grain size organic carbon and carbonate were observed higher concentrations of heavy metal and light c13 of the organic carbon were found primarily in the deltaic and inner shelf sediments the band type distribution generally followed the coastline with little variations in the north south direction away from the delta and inner shelf west east direction most heavy metal concentrations decreased rapidly with the exception of cd where high concentrations of cd were also found in the carbonate rich shelf break sediments coarse grained relict sediments and biogenic carbonate are two primary diluting agents for the fine grained aluminosilicate sediments from the yangtze river with high concentrations of heavy metals unusually high concentrations of cu pb and cd showed both spatially and vertically that more pollution prevention measures are needed in the yangtze river drainage basin in order to prevent further heavy metal pollution of the east china sea inner continental shelf

ocean tide model obtained from topex poseidon altimetry data tidal corrections are very important for oceanographic study of altimetry because tidal signals contaminate the low frequency part of raw altimetric signals accurate tidal predictions are also necessary for geophysical research such as with the superconducting gravimeter scg which needs to distinguish very weak signals from the overwhelming tidal signals the aim of this paper is to derive accurate global ocean tide models from the topex poseidon sea surface height data of 5 cm accuracy more accurate than any other previous altimeter data topex geophysical data records of cycles 9 94 were processed and analyzed we describe response analysis of tidal waves at crossover points and application of hydrodynamical interpolation the tidal solutions with 0 5 grid system are obtained for eight major constituents i e m2 s2 n2 k2 k1 o1 p1 and q1 and compared with the schwiderski 1980a b c model the cartwright and ray 1991 model and the eight constituent version of the egbert et al 1994 model or tpxo 2 the accuracy of the models is checked using island and bottom tide gauge data in open ocean and using scg data in antarctica and japan

diurnal and semidiurnal variations in the earth s rotation rate induced by oceanic tides recent space geodetic observations have revealed daily and subdaily variations in the earth s rotation rate although spectral analysis suggests that the variations are primarily of tidal origin comparisons to previous theoretical predictions based on various ocean models have been less than satisfactory this disagreement is partly caused by deficiencies in physical modeling rotation predictions based on a reliable tidal height model with corresponding tidal currents inferred from a modified form of laplace s momentum equations yield predictions of tidal variations in universal time that agree with very long baseline interferometer observations to 2 microseconds this agreement resolves a major discrepancy between theory and observation and establishes the dominant role of oceanic tides for inducing variation in the earth s rotation at these frequencies

evidence for sea level and monsoonally driven variations in terrigenous input to the northern east china sea during the last 24 3 ka geochemical and sedimentological analyses of core pc 1 recovered from the northern east china sea ecs provide insights into variations in terrigenous input associated with sea level and climate changes over the past 24 3 ka based on high resolution multiproxy records our results suggest that the competing processes of sea level and monsoonally driven precipitation determined terrigenous input to the northern ecs dominance of terrigenous material along with relatively light globigerinoides ruber 18o indicates that the last glacial maximum lgm lowstand of sea level has occurred during the period 21 5 19 6 ka not suggesting an early slow rise but supporting the conventional lgm age of 21 ka this lgm lowstand was terminated by the rapid sea level rise of 19 ka meltwater pulse mwp which is well expressed by the nearly synchronous decreases in both terrigenous detritus and mean grain size from 19 6 to 18 9 ka mwp 1a is clearly marked in our records by a sharp reduction in terrigenous input and pronounced maxima of g ruber 18o at 15 3 14 8 ka given the considerable age uncertainties of deglacial marine radiocarbon samples a slightly increasing input of terrigenous matter is noted after 13 4 ka potentially pointing to a sea level fall following the inter allerod cooling period which was seldom reported previously although mwp 1b did not leave robust signatures in terrigenous input it is explicitly captured by the heavy 18o of g ruber and decline in mean grain size at 11 5 10 9 ka mwp 1c probably occurred in a broad millennial interval with multiple peaks which are robustly marked by the abrupt variations in terrigenous input and marine organic matter at 9 7 9 3 and 9 1 ka respectively during the late holocene the effect of continuously weakening monsoon precipitation overwhelmed that of stable sea level resulting in a uniform increase in the proportion of marine derived organic matter after 5 5 ka

energy budget of the tidal hydrodynamic model fes94 1 this paper presents a detailed energy budget of the m2 tide over the world ocean based on the hydrodynamic solution fes94 1 the global energy input by the astronomical forcing deduced from the 2 2 spherical harmonics of the m2 fes94 1 solution is 2 35 tw a quarter of this input takes place over the south atlantic ocean this energy is dissipated by bottom friction over the main continental shelves among which 40 over the north atlantic ocean the pacific ocean the indian ocean and the south atlantic ocean receive more energy than they dissipate by contrast the atlantic ocean and the arctic ocean show a large deficit compensated by a net influx of energy coming from the other basins one third of the total m2 energy input by astronomical forcing over the world ocean flows northward through the equatorial atlantic detailed energy dissipation estimates are computed over the different areas of dissipation and compared to the previous estimates

barotropic tides in the global oceans from a nonlinear tidal model assimilating altimetric tides 1 model description and results in this first part of a two part paper we present results from a high resolution data assimilative fully nonlinear barotropic tidal model of the global oceans that excludes the arctic the model assimilates in waters deeper than 1000 m altimetric tides derived from the analysis of 2 years of topex altimetric data it also assimilates tide gage data from coastal tide gages the model domain includes that covered by the altimeter and extends to the antarctic in the first part we present tidal results for the primary semidiurnal m2 s2 n2 and k2 and diurnal k1 o1 p1 and q1 constituents the second part deals with applications kantha et al this issue the model results are compared with observational data from pelagic gages these comparisons show that overall in the open ocean in deep waters away from the margins of the primary basins the model performance is comparable to other tidal models derived using topex data except for m2 and s2 however one advantage of this model compared with those based solely on the analysis of altimetric data is that the altimetry derived tides are subjected to dynamical constraints by the model this results in reduction of subtidal variability often folded into tidal signals by topex data analysis it is also shown that in shallow waters along the margins especially in east asian marginal seas the model differs substantially from these other models in addition to sea surface heights we also present dynamically consistent barotropic currents in the form of tidal ellipses for m2 and k1 constituents since the goal of this research is a global tidal model uniformly valid in both deep and shallow waters we finally present tidal elevations and currents on two well known shallow water areas the northwest european shelf and the northeast american shelf and a semienclosed western pacific marginal sea the bering sea the model results are compared with independent observations and where possible with results from other numerical models the results highlight the importance of bottom topography on the northwest european shelf where accurate bottom topography was included in the model the results are much better than on the northeast american shelf where the digital bathymetric data base 5 dbdb5 topographic database has significant errors results from the bering sea where the topography is more accurate than the dbdb5 compare well with known tides in the region

a 6 year record of baroclinic transport variability of the antarctic circumpolar current at 140 e derived from expendable bathythermograph and altimeter measurements 1 repeat hydrographic sections across the antarctic circumpolar current are used to derive an empirical relationship between upper ocean temperature and the baroclinic transport stream function cross validation shows this relationship can be used to infer baroclinic transport above and relative to 2500 dbar from temperature measurements with an error of a few per cent the mean transport distribution derived from 31 austral summer expendable bathythermograph xbt sections over a 6 year period consists of westward flow immediately south of tasmania a broad band of strong eastward flow between 50 and 55 s and three cores of eastward flow south of 55 s by defining a second empirical relationship between surface dynamic height and cumulative transport a continuous time series of baroclinic transport is derived from altimeter measurements of sea surface height transports derived from altimetry in this way agree well with simultaneous in situ estimates root mean square error in net transport is 4 106 m3 s 1 suggesting sea level anomalies largely reflect baroclinic changes above 2500 dbar the 10 day sampling of the altimeter transport time series shows the irregular xbt sampling aliases variability at unresolved timescales the standard deviation of net transport above and relative to 2500 m is 4 3 106 m3 s 1 the variability in net transport is largest 2 7 106 m3 s 1 in the quasi annual band periods of 4 months to 1 5 years slightly smaller 2 3 106 m3 s 1 in the mesoscale band 1 5 years 1 5 106 m3 s 1 changes in transport are correlated with local changes in both wind stress and wind stress curl in the quasi annual and interannual bands but the transport time series is too short to draw significant conclusions

intercomparison of recent ocean tide models one of the tremendous achievements of the topex poseidon t p satellite mission is the release of 12 new global ocean tide models during 1994 virtually all of these models are based on the high precision altimetry obtainable from the t p satellite and all of the models are superior to both the cartwright and ray 1990 1991 model as well as to the schwiderski 1980a b model when compared to tide gauges in the present intercomparison only global ocean tide models released during 1994 have been tested as t p continues to operate new ocean tide models will continue to be released and existing ocean models will be updated hence this intercomparison can only present a snapshot of the state of the art within ocean tide modeling however the intercomparison demonstrates the high accuracy and consistency of all these recent ocean tide models from a comparison with a common 104 tide gauge data set compiled by le provost and others unpublished data the general result is that six of the new ocean tide models have rms agreement better than 3 cm the obtainable accuracy with different tide gauge types raises the question about the accuracy of ground truth as ocean tide models become increasingly more accurate the accuracy of the harmonic constants derived from the tide gauge recordings becomes significant generally the rms agreement between models based on 2 years of t p altimetry is significantly better than the agreement between models based on 1 year of t p altimetry for models based on two years of t p altimetry the rms agreement has values around 2 0 1 4 1 0 and 0 7 cm for the m2 s2 k1 and o1 constituents respectively as a preliminary evaluation these values might be taken as a measure of the consistency of ocean tides estimated from the first part of the t p mission which is extremely promising for future ocean tide models derived from t p altimetry using 3 or more years of data this also suggests that further improvement using 3 or more years of data will only be marginal the differences arise when studying the ocean tides on continental shelves surrounding the ocean major differences are seen especially on the patagonian shelf as the continental shelves are critical for tidal dissipation it will be very important to improve tide models on the shelves in future global ocean tide models

accuracy assessment of recent ocean tide models over 20 global ocean tide models have been developed since 1994 primarily as a consequence of analysis of the precise altimetric measurements from topex poseidon and as a result of parallel developments in numerical tidal modeling and data assimilation this paper provides an accuracy assessment of 10 such tide models and discusses their benefits in many fields including geodesy oceanography and geophysics a variety of tests indicate that all these tide models agree within 2 3 cm in the deep ocean and they represent a significant improvement over the classical schwiderski 1980 model by approximately 5 cm rms as a result two tide models were selected for the reprocessing of topex poseidon geophysical data records in late 1995 current ocean tide models allow an improved observation of deep ocean surface dynamic topography using satellite altimetry other significant contributions include theft applications in an improved orbit computation for topex poseidon and other geodetic satellites to yield accurate predictions of earth rotation excitations and improved estimates of ocean loading corrections for geodetic observatories and to allow better separation of astronomical tides from phenomena with meteorological and geophysical origins the largest differences between these tide models occur in shallow waters indicating that the current models are still problematic in these areas future improvement of global tide models is anticipated with additional high quality altimeter data and with advances in numerical techniques to assimilate data into high resolution hydrodynamic models

the evolution of deep ocean pressure measurements in the uk abstract this paper is a brief review of the work carried out by the proudman oceanographic laboratory pol in measuring tides and sub surface pressure variations in the deep water of the ocean basins using bottom pressure recorders bprs it deals particularly with the work of david cartwright which he began in the early 1970s and carried out until he left pol in 1986 but is continued by his co workers of that time the paper mentions the early work in the north atlantic when instrument deployments were limited to one month duration and describes what was achieved from the measurements it concentrates mainly on measurements that were made since the early 1980s when it became possible because of developments in instrument technology to achieve individual measurements lasting for one year or more the results obtained from these measurements are described and some interesting features of the spectrum of the pelagic sub surface pressure are discussed as instrument technology further improved it became possible to study low frequency variations in sub surface pressure the contributions made by pol to studies of the atlantic and indian oceans and the contribution to ocean circulation studies during the world ocean circulation experiment are discussed this led to the development of an instrument capable of operating continuously at ocean depths for five years the preliminary results from a four year deployment of this instrument which was completed in november 1996 are included

a barotropic inverse tidal model for the arctic ocean 1 we describe high resolution 5 km grid linear dynamics and inverse models of arctic ocean barotropic tides obtained with the osu tidal inversion software otis package the 8 constituent dynamics based model uses the latest ibcao bathymetry and open boundary forcing from the recent tpxo 6 2 global barotropic tidal solution this model performs significantly better than the present benchmark arctic tidal model 14 km grid by z kowalik and a proshutinsky as judged by comparisons with 300 coastal tide gauges the greatest improvements are found in the canadian arctic archipelago nares strait and the baffin bay and labrador sea and can be explained by the higher resolution of the new model in these topographically complex regions the new arctic inverse model assimilates coastal and benthic tide gauges and topex poseidon and ers altimetry for further improvements of the 4 dominant constituents m2 s2 k1 and o1

a comparison of tidal ocean loading models using superconducting gravimeter data 1 errors in global ocean models have been shown to be larger than the accuracy of surface gravity measurements baker and bos 2001 and also new space gravity missions ray et al 2001 in this paper we compare the tidal loading estimated using 10 different ocean tide models to the surface gravity variations observed with 12 superconducting gravimeters sg belonging to the global geodynamics project crossley et al 1999 worldwide network ocean tidal gravity variations are shown to be mostly dependent on tidal sea height variations within a radius of 5000 km precise surface gravity measurements are therefore another tool for validating ocean tidal models from short to long wavelengths in addition for example to tide gauge data in this study we also compute the tidal loading using several different available computer codes as for ocean tidal models we show that the differences between tidal loading programs are frequently larger than the error estimates of sg measurements compared to previous models both recent hydrodynamical and topex poseidon derived tidal models allow a significant reduction of discrepancies between ocean tidal observations using sg and tidal loading estimates there still remains however a nonnegligible in phase discrepancy between ocean tidal loading estimates and surface gravity observations whereas the out of phase component is much smaller we have shown that the in phase disagreement does not seem to be caused by an inaccurate determination of the sg calibration

accuracy assessment of global barotropic ocean tide models the accuracy of state of the art global barotropic tide models is assessed using bottom pressure data coastal tide gauges satellite altimetry various geodetic data on antarctic ice shelves and independent tracked satellite orbit perturbations tide models under review include empirical purely hydrodynamic forward and assimilative dynamical i e constrained by observations ten dominant tidal constituents in the diurnal semidiurnal and quarter diurnal bands are considered since the last major model comparison project in 1997 models have improved markedly especially in shallow water regions and also in the deep ocean the root sum square differences between tide observations and the best models for eight major constituents are approximately 0 9 5 0 and 6 5 cm for pelagic shelf and coastal conditions respectively large intermodel discrepancies occur in high latitudes but testing in those regions is impeded by the paucity of high quality in situ tide records long wavelength components of models tested by analyzing satellite laser ranging measurements suggest that several models are comparably accurate for use in precise orbit determination but analyses of grace intersatellite ranging data show that all models are still imperfect on basin and subbasin scales especially near antarctica for the m2 constituent errors in purely hydrodynamic models are now almost comparable to the 1980 era schwiderski empirical solution indicating marked advancement in dynamical modeling assessing model accuracy using tidal currents remains problematic owing to uncertainties in in situ current meter estimates and the inability to isolate the barotropic mode velocity tests against both acoustic tomography and current meters do confirm that assimilative models perform better than purely hydrodynamic models

empirical cotidal charts of the bohai yellow and east china seas from 10 years of topex poseidon altimetry 1 harmonic analysis of 10 years of topex poseidon tp along track altimetry is performed to derive the semidiurnal diurnal long period and quarter diurnal tides in the bohai yellow and east china seas the tp solutions are evaluated through intercomparison for crossover points and comparison with the ground truth showing that the accuracy of tp solutions in the study area has achieved levels of 2 4 cm in amplitudes and 5degrees in phase lags for principal constituents m 2 s 2 k 1 o 1 and s a the tp derived s a amplitudes have a systematic bias of about 10 as compared with the ground truth indicating the possible importance of loading effect of this constituent in the study area which is generally not considered in geodetic surveys the tidal harmonics from tp altimetry and at coastal and island stations are used to give a new set of empirical cotidal charts for principal constituents m 2 s 2 k 1 o 1 and s a the accuracy of these new charts is believed to be significantly higher than the previous charts for the offshore area

global charts of ocean tide loading effects global ocean tide loading charts of the radial displacement the potential divided by g gravity acceleration and the gravity effect have been computed using the 11 constituents m2 s2 n2 k2 k1 o1 p1 q1 mf mm ssa of schwiderski s tidal model these new charts have a resolution of 1 1 on the continents as well as on the oceanic area a description of farrell s convolution method to compute the loading effects is given and an estimate of the numerical errors leads to the conclusion that these global charts have a precision better than 2 5 independent of the accuracy of schwiderski s maps the current approximation of the loading effects by a proportionality relation with the local oceanic tides is also compared with farrell s convolution method departures of several centimeters systematically appear in particular over the continental shelves we then show that the maps of the oceanic tides deduced from satellite altimetry could be corrected for the loading effect by an iterative computational procedure based on our algorithm of farrell s convolution

oceanic tidal angular momentum and earth s rotation variations abstract luni solar tides affect earth s rotation in a variety of ways we give an overview of the physics and focus on the excitation of earth rotational variations by ocean tides under the conservation of angular momentum various models for diurnal and semidiurnal tidal height and tidal current fields have been derived following a legacy of a number of theoretical tide models from the topex poseidon t p ocean altimetry data we review the oceanic tidal angular momenta otam predicted by these t p models for the eight major tides q1 o1 p1 k1 n2 m2 s2 k2 and their excitations on both earth s rotational speed variation in terms of length of day or ut1 and polar motion prograde diurnal semidiurnal components and retrograde semidiurnal components these small high frequency effects have been unambiguously observed in recent years by precise earth rotation measurements via space geodetic techniques here we review the comparison of the very long baseline interferometry vlbi data with the t p otam predictions the agreement is good with discrepancies typically within 1 2 microseconds for ut1 and 10 30 microarcseconds for polar motion the eight tides collectively explain the majority of subdaily earth rotation variance during the intensive vlbi campaign cont94 this establishes the dominant role of otam in exciting the diurnal semidiurnal polar motion and paves the way for detailed studies of short period non otam excitations such as atmospheric and oceanic angular momentum variations earthquakes the atmospheric thermal tides earth librations and the response of the mantle lateral inhomogeneities to tidal forcing these studies await further improvements in tide models and earth rotation measurements

surface manifestation of internal tides in the deep ocean observations from altimetry and island gauges the sea surface height signatures of internal tides in the deep ocean amounting to a few centimeters or less are studied using two complementary measurement types satellite altimetry and island tide gauges altimetry can detect internal tides that maintain coherence with the astronomical forcing island gauges can monitor temporal variability which in some circumstances is due to internal tides varying in response to changes in the oceanic medium this latter mechanism is at work at hilo and other stations on the northern coasts of the hawaiian islands by detecting spatially coherent low frequency internal tide modulations the tide gauges along with inverted echo sounders at sea suggest that the mean internal tide is also spatially coherent satellite altimetry confirms this at hawaii and in many other places topex poseidon altimetry detects mean surface waves spatially coherent and propagating great distances 1000 km before decaying below background noise when temporal variability is small the altimetry plus information on ocean density sets useful constraints on energy fluxes into internal tides at the hawaiian ridge 15 gw of tidal power is being converted from barotropic to first mode baroclinic motion examples elsewhere warn that a simplistic interpretation of the altimetry without regard to variability noise or in situ information may be highly misleading with such uncertainties extension of the hawaiian results into a usefully realistic estimate of the global internal tide energy balance appears premature at this time

classification of the australian continental shelf based on predicted sediment threshold exceedance from tidal currents and swell waves abstract estimates of significant wave height and period together with tidal current speed over a semi lunar cycle were used to predict the area on the australian continental shelf over which unconsolidated sediment was mobilised threshold exceedance these sediment entraining processes were examined independently to quantify their relative importance on the continental shelf using observed grain size data mobilisation from swell waves occurred on 31 and tidal currents on 41 of the continental shelf swell wave energy is sufficient to mobilise fine sand 0 1 mm diameter to a water depth of 142 m on the otway shelf near the western entrance to bass strait tidal currents in king sound northwest shelf are capable of mobilising large areas of medium sand 0 35 mm diameter 100 of the time superimposing the distribution of threshold exceedance by wave and tidal currents indicates that there are areas on the shelf where either wave induced or tidal currents dominate some areas where waves and tides are of relatively equal importance and still other areas where neither is significant we define six shelf regions of relative wave and tidal energy zero no mobility waves only wave dominated mixed tide dominated and tides only our results provide a predictive process based understanding of the shelf sedimentary system that has applications to marine engineering projects and to regional studies of pollution dispersal and accumulation where significant shelf sediment mobilisation is a factor

interannual to interdecadal changes in the bering sea and concurrent 1998 99 changes over the north pacific abstract sea surface temperatures ssts upper water heat storage hs sea level displacements slds sea ice concentration sics in the bering seas and associated atmospheric circulations are analyzed to identify dominant interannual to interdecadal variations as a representative time series of the sst variations principal component pc of the first mode of a seasonally combined empirical orthogonal function eof is employed the corresponding eof spatial pattern exhibits the smallest amplitudes in winter and largest in summer pc1 is characterized by a warming trend throughout the record 1921 2001 with the warmest year in 1997 which is followed by rapid cooling until 1999 the warming from 1995 1997 and cooling from 1997 1999 are commonly found in hs along the southern rim of the bering sea and also accompanied by sld rise and fall respectively the sic variability corresponding to sst pc1 is prominent in the eastern bering sea in spring with correlations as high as 0 7 but good correlations were mainly observed prior to 1990 the correlations between the sst pc1 and sea level pressures slps also suggest that the spring atmospheric circulation anomalies play an important role in the variations of the sst and sea ice in the bering sea the cooling and sld fall in the late 1990s in the bering sea might be related with a possible major regime shift in 1998 1999 which was discussed by minobe 2000 hare and mantua 2000 and schwing and moore 2000 in the 1998 99 change over the north pacific ssts and hs increased abruptly both in the kuroshio oyashio extension region and the central north pacific accompanied by cooling in the eastern north pacific at the same time slds rose from japan to 160 w roughly along kuroshio extension path with a tongue like structure the tongue like sld rise is likely forced by wintertime atmospheric anomalies associated with slp increase in the eastern north pacific

altimeter sampling characteristics using a single satellite altimetric satellites have characteristic sampling patterns in both space and time based on their repeat period and orbit inclination aliased phenomena measured by altimetric measurements can appear as propagating waves with both wavelength and direction of propagation different from the underlying phenomena all signals that contribute to the altimetric measurement can be aliased and produce such patterns not just tidal signals for example mesoscale energy will be aliased as will unmodeled atmospheric variations past discussions of aliasing have only considered spatially homogeneous signals this paper extends this work to phenomena with finite wavelengths and considers both the north south and east west components of the resulting aliases

deviation of long period tides from equilibrium kinematics and geostrophy new empirical estimates of the long period fortnightly mf tide obtained from topex poseidon t p altimeter data confirm significant basin scale deviations from equilibrium elevations in the low latitude pacific have reduced amplitude and lag those in the atlantic by 308 or more these interbasin amplitude and phase variations are robust features that are reproduced by numerical solutions of the shallow water equations even for a constant depth ocean with schematic interconnected rectangular basins a simplified analytical model for cooscillating connected basins also reproduces the principal features observed in the empirical solutions this simple model is largely kinematic zonally averaged elevations within a simple closed basin would be nearly in equilibrium with the gravitational potential except for a constant offset required to conserve mass with connected basins these offsets are mostly eliminated by interbasin mass flux because of rotation this flux occurs mostly in a narrow boundary layer across the mouth and at the western edge of each basin and geostrophic balance in this zone supports small residual offsets and phase shifts between basins the simple model predicts that this effect should decrease roughly linearly with frequency a result that is confirmed by numerical modeling and empirical t p estimates of the monthly mm tidal constituent this model also explains some aspects of the anomalous nonisostatic response of the ocean to atmospheric pressure forcing at periods of around 5 days

departures from the local inverse barometer model observed in altimeter and tide gauge data and in a global barotropic numerical model sea level data from the topex poseidon altimeter satellite and from subsets of the global tide gauge and bottom pressure recorder networks have been employed to study the worldwide distribution of departures from the simple local inverse barometer lib model from a combination of measurement techniques the lib model was found to provide a reasonable representation of the data within 5 10 outside of the tropics for timescales from several days to several weeks for most locations however several parts of the southern ocean and other higher latitude areas were seen from the altimetry to contain significant departures across the range of timescales accessible for study by the technique within the tropics the response of sea level to air pressure forcing was observed to be typically 50 of that of the lib model at timescales of several days with considerable spatial variation and to approximate the lib model more closely at timescales of several weeks a coarse grid global barotropic numerical model was found to reproduce qualitatively the global average response as a function of frequency to simulate many of the characteristics of the spatial variation of the response and to demonstrate the relative importance of air pressure and wind forcing at different timescales data sets from the permanent service for mean sea level and u k meteorological office were used to investigate lib departures at intraseasonal and longer timescales along continental coastlines and at ocean islands increasingly large departures were observed along many parts of the world coastline as timescales increased from months to seasons

icesat over arctic sea ice interpretation of altimetric and reflectivity profiles 1 we provide an assessment of the icesat altimeter for studying the arctic ocean and examine the magnitude of the large and small scale expressions of geophysical processes embedded in the elevation profiles this analysis includes data from six surveys at the large scale the response of the ice covered ocean to atmospheric loading is near ideal i e approximately 1 cm hpa after removal of the inverted barometer effects and best available geoid the elevation signal is still dominated by unresolved geoid residuals 0 4 m that can be seen in the similarity of the remaining spatial patterns seasonal differences in elevations over multiyear ice are consistent with snow depth climatology the broad differential spatial patterns are indicative of interannual differences in multiyear ice coverage associated with advection patterns in the derived surface roughness fields correspond to the seasonal and perennial ice zones seen in quikscat data at the small scale near coincident radarsat imagery provides a spatial context for understanding the signature of the observed elevations waveforms and reflectivity in particular those associated with thin ice open water multiyear ice and ridges the precision of the elevation estimates measured over relatively flat sea ice identified in synthetic aperture radar sar imagery is 2 cm the unambiguous identification of ridged areas in coupled icesat radarsat analysis could be used to enhance the utility of sar imagery for examining ridge distributions over a 20 day period we monitored the evolution of the reflectivity of a newly opened lead the steep increase in reflectivity due to snow coverage suggests that dips in icesat reflectivity are likely areas of thin ice and could serve as a basis for selection of tie points for use as sea level reference identification of these tie points is crucial for accurate estimation of sea ice freeboard

early miocene benthic foraminifera and biostratigraphy of the qom formation deh namak central iran abstract a total of 165 samples were collected from the qom formation investigated in a stratigraphic section north of deh namak in central iran from these 35 genera and 47 species of benthic foraminifera were identified the age of the studied section is early miocene aquitanian to early burdigalian based on the occurrence of borelis melo curdica meandropsina anahensis meandropsina iranica elphidium sp 14 peneroplis farsensis and triloculina tricarinata the thickness of the qom formation is 401 m of which 161 2 m is early burdigalian in age foraminiferal assemblages in the deh namak section are referable to the borelis melo group meandropsina iranica assemblage zone and miogypsinoides archaias valvulinid assemblage zone of adams t d bourgeois f 1967 asmari biostratigraphy iranian oil operating companies geological and exploration division report1074 unpublished 1 37 described originally from the asmari formation

anomalous ocean load tide signal observed in lake level variations in tierra del fuego 1 we demonstrate the application of a 100 km long lake as a sensor for studying the tidal effects on tierra del fuego main island the lake level variations observed in lago fagnano reflect both the direct response to the tidal potential and the indirect effect of the ocean tidal loading modeling both contributions explains the observed tidal signal in the lake to about 70 underestimated model load tide amplitudes are found to be probably responsible for the remaining difference we interpret this discrepancy as a hint for regional elastic lithosphere properties differing substantially from those represented by currently available global models

testing ocean tide models in the nordic seas with tidal gravity observations summary tidal gravity observations at ny alesund on spitzbergen made with a lacoste romberg gravimeter with electrostatic feedback have been used to assess the accuracy of ocean tide models in the nordic seas eight ocean tide models have been used to compute the ocean tide loading at ny alesund the station is very close to the coast and therefore experiences a significant direct gravitational attraction of the nearby tidal water mass for the bay adjacent to the station the model values have been replaced by the tide gauge values and a special effort has been made to fit the models correctly to the coastline the ocean tide models for m2 and o1 have also been compared with observations made over 30 years ago at longyearbyen spitzbergen with askania gravimeters the comparisons of the tidal gravity observations with computed ocean tide loading show that for the harmonic m2 the phase lag of the ocean tide model of schwiderski and the local tide model of gjevik et al are wrong by 15 and 5 in the norwegian basin for the harmonic s2 the models fes94 1 got00 2 and schwiderski give a poor fit to the observed tidal loading at ny alesund because of phase lags that are too large in the norwegian basin by 10 fes94 1 and got00 2 also have s2 amplitudes that are 5 cm too large in the norwegian basin for n2 fes94 1 fes95 2 got00 2 and schwiderski have phase lags that are 10 too large in the norwegian basin and fes94 1 and 95 2 also have n2 amplitudes that are 2 4 cm too large in that region overall for these three harmonics the global model fes99 gives the best fit to the tidal gravity observations at ny alesund and this agreement is even closer than that obtained using regional arctic ocean tide models

aliased tidal errors in topex poseidon sea surface height data alias periods and wavelengths for the m2 s2 n2 k1 o1 and p1 tidal constituents are calculated for topex poseidon alias wavelengths calculated in previous studies are shown to be in error and a correct method is presented with the exception of the k1 constituent all of these tidal aliases for topex poseidon have periods shorter than 90 days and are unlikely to be confounded with long period sea surface height signals associated with real ocean processes in particular the correspondence between the periods and wavelengths of the m2 alias and annual baroclinic rossby waves that plagued geosat sea surface height data is avoided the potential for aliasing residual tidal errors in smoothed estimates of sea surface height is calculated for the six tidal constituents the potential for aliasing the lunar tidal constituents m2 n2 and o1 fluctuates with latitude and is different for estimates made at the crossovers of ascending and descending ground tracks than for estimates at points midway between crossovers the potential for aliasing the solar tidal constituents s2 k1 and p1 varies smoothly with latitude s2 is strongly aliased for latitudes within 50 degrees of the equator while k1 and p1 are only weakly aliased in that range a weighted least squares method for estimating and removing residual tidal errors from topex poseidon sea surface height data is presented a clear understanding of the nature of aliased tidal error in topex poseidon data aids the unambiguous identification of real propagating sea surface height signals unequivocal evidence of annual period westward propagating waves in the north atlantic is presented

the global structure of the annual and semiannual sea surface height variability from geosat altimeter data the global structure of the annual and semiannual sea surface height variability is constructed from the first 2 years of the geosat exact repeat mission erm altimeter data the gem t2 orbits available for the first 2 years of the erm have an accuracy of 40 cm rms residual orbit error is modeled as one cycle per orbital revolution and is removed from collinear differences of arcs made of data from one full orbital revolution of the satellite the error in the schwiderski m2 tidal model must be estimated due to the fact that the tidal variability aliases to 1 15 cycles per year cpy and this frequency is not separable from 1 cpy with the 2 years of data an estimate of the m2 tidal error is made based on the particular temporal and spatial aliasing of the tide with this error removed a least squares fit of sine and cosine waves with annual and semiannual frequencies is made to the time series at every point along the ground track of the satellite this produces sine and cosine coefficients at the ground track points which are interpolated to a regularly spaced grid over the globe from the sine and cosine maps amplitude and phase may be obtained interpolation of the sine and cosine coefficients using different spatial scales is done to better observe the large scale phase changes and to remove small scale noise results show the phase relationships between major current systems large scale variations near the equator in the intertropical convergence zone itcz a 180 phase difference between the northern and southern hemispheres for the annual variability large scale westward propagating waves and other large scale gyre features

enrichment and toxicity of trace metals in near shore bottom sediments of cuddalore se coast of india in order to identify contaminating trace metals and their sources studies on trace metals are often included in routine environmental monitoring programs twenty five near shore bottom sediment samples from the inner shelf region near cuddalore of the bay of bengal were analysed for sediment texture organic matter carbonate caco3 concentrations and total trace metal concentrations ttms fe mn cr cu ni co pb zn and cd in order to evaluate geochemical processes such as enrichment and their origin the presence of carbonates 2 5 5 8 indicates the dominance of calcareous shells in the region a relatively high percentage of organic matter 0 2 3 9 is attributed to the predominance of finer sediments entering through the minor rivers high concentrations of ttms in fine and organic rich sediments are influenced by municipal and industrial sources which contention is well supported by correlations of ttms concentrations with fe mn fractions geoaccumulation index igeo calculations indicate that cr cu ni pb and cd concentrations are above the values expected from their presence in the discharge of effluents from the industrial zones bordering the shoreline comparing the findings of the present study with those from different parts of the world cr cu ni pb appear to be enriched in the sediments of the region

semidiurnal tides observed in the western equatorial pacific during the tropical ocean global atmosphere coupled ocean atmosphere response experiment the semidiurnal tide within a 100 km square region of the western equatorial pacific centered at 1 8 s 156 1 e is examined using shipboard survey and mooring data collected during the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare baroclinic and barotropic tidal amplitudes and phases are estimated from the survey and mooring observations in the upper 300 m of the 1800 m deep ocean by specifying their horizontal and vertical structures the barotropic tide is assumed to have zero horizontal wavenumber over the domain while a component of the baroclinic tide that is phase locked to the barotropic tide is determined by a searching method using plane wave fits to the data the estimated barotropic tidal current is in good agreement with tide models derived from topex poseidon observations the plane wave analysis indicates a dominant mode one baroclinic wave propagating toward the northeast the second vertical mode can also be detected given the phase differences between the m2 and s2 constituents in the barotropic and baroclinic tides the source of the baroclinic tidal signal is determined to be about 320 km southwest of the observing region at a series of islands and shallow ridges the combined estimates of the barotropic and baroclinic tides typically account for only 40 60 of the observed semidiurnal band current variance in the mooring data indicating the high degree of temporal and spatial variability of the baroclinic tide in this region the results of this study suggest however that coherent barotropic and baroclinic tidal signals can be successfully distinguished in the deep ocean using shipboard survey data even when the data are limited to the upper 300 m

tidal currents on the central oregon shelf models data and assimilation 1 measurements of tidal currents on the central oregon shelf are available from several sources including recent high frequency hf coastal radar and acoustic doppler profiler adp deployments and historical current moorings in this paper we use a generalized inverse gi approach to compare these data to and then assimilate them into numerical models for the barotropic tides harmonic analysis of the data in short time windows using a modified admittance approach reveals that tidal currents on the oregon shelf are highly variable in time and can contain significant baroclinic components data from the winter months when waters on the shelf are only weakly stratified are found to be most nearly barotropic and thus most reasonable for assimilation into the shallow water equations model the various data sources are used in several different combinations for assimilation and validation forcing the prior forward model with normal flow open boundary conditions obtained from a regional barotropic inverse model results in semidiurnal barotropic currents that are consistent within estimated error limits with all available data in contrast diurnal currents on the shelf are very sensitive to details of the model configuration and are significantly improved by data assimilation very similar solutions result from assimilation of either the hf radar or adp data sets the high sensitivity of the diurnal band currents can be understood dynamically in terms of trapped shelf waves a short 85 km long section of shelf off the central oregon coast is wide enough to allow first mode barotropic shelf waves at the subinertial diurnal frequencies this results in locally resonant large amplitude diurnal tidal currents that are very sensitive to details in the local forcing and hence quite variable in time

the north south tilt in the australian height datum is explained by the ocean s mean dynamic topography 1 using geodetic and oceanographic data we show that the apparent north south slope between the australian height datum ahd and the geoid is caused almost completely by the ocean s time mean dynamic topography mdt this is because the ahd was constrained to zero height at local mean sea level at multiple tide gauges around the australian continent using mdt models and corrected leveling data almost all of the apparent north south slope can be removed from the ahd an auxiliary observation is that a satellite only mdt model based on only around one year of goce data generates results commensurate with geodetic oceanographic and combined mdt models

estimates of m2 tidal energy dissipation from topex poseidon altimeter data most of the tidal energy dissipation in the ocean occurs in shallow seas as has long been recognized however recent work has suggested that a significant fraction of the dissipation perhaps 1 tw or more occurs in the deep ocean this paper builds further evidence for that conclusion more than 6 years of data from the topex poseidon satellite altimeter are used to map the tidal dissipation rate throughout the world ocean the dissipation rate is estimated as a balance between the rate of working by tidal forces and the energy flux divergence computed using currents derived by least squares fitting of the altimeter data and the shallow water equations such calculations require dynamical assumptions in particular about the nature of dissipation to assess sensitivity of dissipation estimates to input assumptions a large suite of tidal inversions based on a wide range of drag parameterizations and employing both real and synthetic altimeter data are compared these experiments and monte carlo error fields from a generalized inverse model are used to establish error uncertainties for the dissipation estimates owing to the tight constraints on tidal elevation fields provided by the altimeter area integrals of the energy balance are remarkably insensitive to required dynamical assumptions tidal energy dissipation is estimated for all major shallow seas excluding individual polar seas and compared with previous model and data based estimates dissipation in the open ocean is significantly enhanced around major bathymetric features in a manner consistent with simple theories for the generation of baroclinic tides

tidal observations on floating ice using a single gps receiver 1 we measure ocean tides as experienced by sea ice or ice shelves using a single gps receiver such a method allows for tidal measurements to be made with the same precision regardless of its distance from a gps base station since such a base station is not required single epoch observations are shown to be accurate to about 50 mm when compared with concurrent bottom pressure gauge bpg observations the differences between the gps and bpg observations are largely free from power at tidal frequencies furthermore harmonic tidal analyses show that these gps observations allow the correct determination of diurnal and semi diurnal tidal constituents meaning that observations of this type can be assimilated into numerical tide models

ice shelf tidal motion derived from ers altimetry 1 ocean tides beneath floating ice shelves can affect heat and water circulations within the subshelf cavity which may influence patterns of basal melting accurate tidal predictions are essential to eliminate vertical tide motions when mapping the flow speeds and thickness changes of floating ice global ocean tide solutions are typically accurate to 2 3 cm in amplitude however their coarse resolution limits their utility in coastal regions moreover the absence of satellite and extensive gauge station data in the polar regions has resulted in significant differences between recent tide model solutions around the antarctic continent we use 9 years of high resolution european remote sensing ers satellite radar altimeter range measurements and a modified form of the orthotide method to generate tidal solutions for a series of ice shelves around the antarctic peninsula we compare our tidal solution at george vi ice shelf on the western coast of the antarctic peninsula to direct measurements from british antarctic survey tide gauge records and contrast the results with solutions from the fes99 and kantha2 0 global and the cats01 02 antarctic ocean tide models the average root mean square vector difference between the tide gauge and tide model predictions of amplitude and phase was 10 9 17 1 4 2 and 15 4 cm for the ers ice shelf kantha2 0 cats01 02 and fes99 models respectively tidal predictions derived from the ers ice shelf model are closer to the tide gauge recordings than those of the global models and the inclusion of ers altimeter data may lead to improved global model performance

ocean load tides at the south pole a validation of recent ocean tide models small diurnal and semidiurnal gravity tides are seen at the south pole because of the loading by and attraction of the ocean tides these data provide a check on the quality of ocean tide models especially in the southernmost ocean which has historically been the most lacking in tidal data ocean tide models developed in the 1980 s did not predict the gravity tides at this location very well recently developed models based on the topex poseidon altimetric data and improved hydrodynamical modeling agree much better with the observations provided that the tides beneath the ice shelves are included the level of agreement at this remote location suggests that loads from very local tides aside the new generation of ocean tide models can predict the loading tides to very high accuracy

satellite altimetry the marine geoid and the oceanic general circulation for technical reasons the general circulation of the ocean has historically been treated as a steady laminar flow field the recent availability of extremely highaccuracy and high precision satellite altimetry has provided a graphic demonstration that the ocean is actually a rapidly time evolving turbulent flow field to render the observations quantitatively useful for oceanographic purposes has required order of magnitude improvements in a number of fields including orbit dynamics gravity field estimation and atmospheric variability with five years of very high quality data now available the nature of oceanic variability on all space and time scales is emerging including new findings about such diverse and important phenomena as mixing coefficients the frequency wavenumber spectrum and turbulent cascades because the surface elevation is both a cause and consequence of motions deep within the water column oceanographers soon will be able to provide general circulation numerical models tested against and then combined with the altimeter data these will be complete three dimensional timeevolving estimates of the ocean circulation permitting greatly improved estimates of oceanic heat carbon and other property fluxes

a preliminary tidal analysis of topex poseidon altimetry approximately 12 months of data from the topex poseidon satellite altimeter mission are analyzed for the major short period oceanic tides a harmonic analysis is performed on data captured within bins defined on a deep ocean grid which owing to tidal aliasing considerations must have a relatively coarse spatial resolution our analysis is in terms of corrections to the schwiderski and cartwright ray models and it confirms many of the schwiderski differences previously reported by cartwright and ray our differences with respect to the geosat based cartwright and ray model form a sectorial pattern in m2 with high low differences separated roughly 180 in longitude we suggest that these sectorial errors were most likely induced by geosat s relatively large orbit error comparisons to independent data validate the improved topex poseidon solutions in situ ground truth shows m2 rms differences of 4 10cm schwiderski 3 86cm cartwright and ray 2 63cm this paper global rates of energy dissipation confirm earlier estimates for m2 and show improved agreement with satellite tracking studies for k1 and s2 these preliminary exercises confirm that topex poseidon should result in a new generation of improved global tidal models

tides on filchner ronne ice shelf from ers radar altimetry 1 we use harmonic analysis of 8 years of ers satellite radar altimeter ra data at orbital crossovers to retrieve complex amplitude amplitude and phase coefficients for several major tidal harmonics over the filchner ronne ice shelf fris antarctica we describe a method for estimating the accuracy of this method which ranges from 2 to 8 cm per harmonic a comparison between m2 complex amplitude from a recent ocean model and from our ers ra analyses identifies two regions of the fris where the ra data are inconsistent with the model in both regions the differences can be attributed to incorrect specification of the grounding line location in the model our study demonstrates the value of ers ra data in antarctic ice shelf tide modeling and the potential for future altimeter satellites with high polar orbits to contribute to the definition of global tide height variations

a two dimensional tidal model for the mediterranean sea the tidal propagation in the mediterranean sea is described through a high resolution two dimensional hydrodynamic model forced by the equilibrium tide and the incoming tide at the strait of gibraltar the four most significant constituents m2 s2 k1 and o1 are included in the model good agreement with a set of 63 coastal gauges is achieved the significance of the equilibrium tide and the forcing at the open boundary is investigated the incoming wave from the strait of gibraltar is important in tuning the tides in the whole of the mediterranean for the north aegean sea the solution without the forcing at gibraltar results in a doubling of the amplitudes of the semidiurnal tides the estimated energy dissipation due to bottom friction is 8 8 108 w the major area of dissipation is the gulf of gabes energy fluxes through the major straits are calculated

global ocean tides from ers 1 and topex poseidon altimetry 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

variability of tidal constants in the rio de la plata estuary associated to the natural cycles of the runoff abstract we analyze the only long term 47 years long hourly tide gauge record available for the rio de la plata estuary for variability in the amplitude and phase of the dominant principal lunar semi diurnal m 2 constituent the tidal record was first filtered to isolate the signal at the frequency of m 2 then harmonic analysis was applied to the filtered data for periods of one year with progressive lags of one month this way monthly time series of m 2 amplitude and phase were obtained which were then analyzed by means of several spectral techniques both m 2 amplitude and phase present a long term trend inter decadal cycles and significant pseudo periodicities at frequencies which are known as typical of the el nino southern oscillation enso cycles a joint multi channel singular spectral analysis of the tidal constants and the runoff to the estuary which variability is dominated by the enso cycles effect on precipitation over southern south america reveals co movements at periods around 2 5 3 5 and 6 5 years as well as long term trends inter decadal cycles positive negative runoff anomalies are associated with negative positive amplitude anomalies and negative positive phase anomalies the detected variability in the tidal constants seems to be the result of the interaction between the tidal wave propagating upstream and the downstream currents due to the runoff rather than a result of the variability in the mean sea level caused by the runoff

improving the quality of satellite altimetry data over continental shelves 1 satellite altimetry has proven to be a useful tool to study oceanic processes in the deep ocean over continental shelves however the aliasing of unresolved high frequency signals of tidal and wind induced origin is the source of long wavelength errors that corrupt altimetry measurements and limit their use in shallow waters in 2005 ssalto duacs performed a complete reanalysis of altimeter data to accommodate the latest tidal model got2000 and a correction for the aliased high frequency signals using a hydrodynamic model mog2d g this paper examines the quality and the performance of the newly released altimetry data over the northwest european shelf this region is known for complex tides and for frequent storm surges the newly corrected maps of sea level anomalies were compared with a previous altimetry product residual tidal aliasing was analyzed and the impact of mog2d g and got2000 models was assessed altimeter records were compared with tide gauge measurements this research showed a significant reduction in the contamination of data by high frequency aliasing achieved through the use of the aforementioned models however aliased shallow water tidal constituents pose a serious problem and it is obvious that future tidal corrections should feature local tides nonaliased physical sea level variability was also studied focusing on interannual seasonal and intra annual periods from 20 days to 1 year modes the magnitudes and the contributions of each mode to the total variance were estimated it was demonstrated that the newly corrected data can successfully be used to study the variability of sea level over continental shelves

a topex poseidon global tidal model tpxo 2 and barotropic tidal currents determined from long range acoustic transmissions abstract tidal currents derived from the tpxo 2 global tidal model of egbert bennett and foreman are compared with those determined from long range reciprocal acoustic transmissions amplitudes and phases of tidal constituents in the western north atlantic are derived from acoustic data obtained in 1991 1992 using a pentagonal array of transceivers small spatially coherent differences between the measured and modeled tidal harmonic constants mostly result from smoothing assumptions made in the model and errors caused in the model currents by complicated topography to the southwest of the acoustical array acoustically measured harmonic constants amplitude phase of m2 tidal vorticity 3 8 10 9s 1 210 310 agree with those derived from the tpxo 2 model 2 5 10 9s 1 250 300 whereas harmonic constants of about 1 2 10 9s 1 350 360 are theoretically expected from the equations of motion harmonic constants in the north pacific ocean are determined using acoustic data from a triangular transceiver array deployed in 1987 these constants are consistent with those given by the tpxo 2 tidal model within the uncertainties tidal current harmonic constants determined from current meters do not generally provide a critical test of tidal models the tidal currents have been estimated to high accuracy using long range reciprocal acoustic transmissions these estimates will be useful constraints on future global tidal models

gps estimates of ocean tide loading in nw france determination of ocean tide loading constituents and comparison with a recent ocean tide model summary ocean loading effects cause 3 d displacements large enough to affect space geodesy measurements either at the subdiurnal periods or at longer time scales by the means of spurious signals gps measurements in turn could provide local improvements of the models in coastal areas if their ability to precisely monitor such rapid displacements is assessed in this paper we use 105 days of continuous gps measurements collected in 2004 in the french brittany and cotentin region to investigate 1 the precision achieved by the gps analysis on measuring 3 d subdiurnal displacements and amplitude and phase of the tidal constituents 2 the quality of the most recent ocean tide model fes2004 in such a complex coastal context indeed in this area tide amplitudes are among the largest in the world up to 16 cm of loading displacements on the vertical component and are believed to show strong shallow water tides from a state of the art gps analysis using the scientific gamit software over 2 h sessions we test two independent strategies for the realization of the reference frame the position time series are then compared with the displacements predicted by the fes2004 model applied on an elastic earth model the two sets of results are consistent with each other at the same level of agreement than with the predicted displacements namely 3 5 mm on the horizontal components 10 mm on the vertical this assesses the capability of this technique for measuring 3 d ocean tide loading deformation we validate the fes2004 model in the brittany area even though it slightly 2 7 mm underestimates the three components amplitudes with a harmonic analysis of the observed position time series we obtain nevertheless an agreement at a submillimetre level for the m2 n2 o1 q1 tidal constituents and at a millimetre level for the k1 and s2 tidal constituents moreover we can extract a significant m4 load signal at the 95 per cent confidence level from the gps time series at the stations located in the mont st michel area the detection of other shallow water constituents would be helpful to understand the amplitude deficit between the fes2004 predicted and gps observed displacements

estimate of tidal constituents in nearshore waters using x band marine radar image sequences the accurate observation and prediction of tides are important in coastal waters a new method is proposed to estimate tidal constituents in nearshore waters from x band marine radar image sequences based on the modulation of wave height by tide the relative wave height is retrieved from the first principal component of the x band marine radar image sequence and a self adaption method is used to remove the low quality data under very low sea state to eliminate the influence of atmospheric planetary waves a type i chebyshev bandpass filter is applied to the time series of the derived wave heights relative tidal amplitudes and phases are then obtained through harmonic analysis of the filtered wave heights and true tidal amplitudes are derived through a linear relation while true tidal phases are obtained by cross spectral analysis the errors of the amplitudes of m2 s2 k1 and o1 tides retrieved from x band marine radar image sequences are 0 15 1 12 2 22 3 83 3 06 4 29 and 4 50 9 47 cm respectively as compared with those predicted by a numerical model the errors of m2 tidal phase are 3 27 4 59 it shows that the proposed method is appropriate for long and continuous observations of x band marine radar

tidal corrections for topex altimetry in the coral sea and great barrier reef lagoon comparisons with long term tide gauge records 1 the well known capability of topex poseidon altimetry to map sea levels precisely in the deep oceans motivates its application to the topographically complex coral sea and ne australian continental margin we assess several global tidal models for correcting topex altimetry in the coral sea and find csr3 0 offers good overall performance based on comparisons of model predicted and tide gauge harmonic constituents using csr3 0 tidal corrections we evaluate residual sea surface height ssh root mean square rms variability and residual m2 tidal alias errors away from large reefs and islands csr3 0 amplitude and phase errors for m2 are typically less than 5 cm and 8 deg respectively with rms tidal errors of 5 cm or less and rms ssh residuals approximating 10 cm since model deficiencies appear in the macro tidal region of the southern great barrier reef lagoon near broad sound we employ a high resolution hydrodynamic model in this area to compute the tidal corrections predicted m2 amplitude and phase in this region are within 3 cm and 5 deg of observations rms errors are mostly under 4 cm and coastal rms ssh residuals are as low as 15 cm in spite of coastal trapped waves and submesocale eddies in the lagoon daily and monthly smoothed ssh residual time series respectively yield optimal lagged correlations with in situ sea level data in the range 0 3 0 9 and 0 6 0 9 for locations spanning the coral sea and in the lagoon lag correlations of monthly smoothed geostrophic current anomalies derived from topex ssh gradients with long term currents from the continental slope yield optimal correlations of 0 5 and 0 8 respectively near jewell lat 14 deg s and myrmidon reef 19 deg s our results demonstrate that low frequency sea level and geostrophic current variations can be reliably observed using altimetry over the coral sea and ne australian continental slope and for selected locations on the continental shelf if appropriate tide correction models are employed

estimation of main tidal constituents from topex altimetry using a proudman function expansion tidal models for the main diurnal and semidiurnal constituents have been computed from topex altimeter data and a set of proudman functions computed numerically in the space defined by the ocean basins the accurate modeling of the ocean tides is necessary in order to interpret the height measurements of the ocean surface obtained from satellite altimeters it is also an interesting dynamical problem in its own right the surface height field due to any tidal constituent can be expanded in terms of the eigenfunctions of the velocity potential proudman functions with coefficients estimated in a least squares sense from a field of discrete data points obtained from altimetry tide gauges bottom pressure sensors etc the proudman functions constitute a mass conserving orthogonal basis their computation does not require any assumption concerning friction or energy dissipation only a numerical grid expressing the shape of coastline and the bathymetry of the ocean basins they have the space structure of standing waves and can be identified as the zero rotation gravitational normal modes they have to be evaluated numerically only once for each particular grid resolution in this investigation the proudman functions were computed by means of finite differences in spherical coordinates over a 2ox2 o grid covering most of the world s oceans for a total of 8608 degrees of freedom the data field used in this study consists of approximately 15 months of topex altimetry in the form of collinear differences results for the major semidiurnal and diurnal constituents m2 s2 n2 k2 k1 o1 p 1 and q1 have been obtained in terms of corrections to a priori values obtained by fitting schwiderski s 1980 models the new models goddard space flight center gsfc94a are tested at a set of ground truth data points these tests indicate substantial improvement for most of the constituents as compared with schwiderski s solutions use of gsfc94a results in a 7 8 cm reduction in the rms overlap difference of 15 5 cm the gsfc94a model yielded a mean rms sea surface variability of 7 9 cm compared with the 9 4 cm obtained when using schwiderski s model

improving ocean tide predictions by using additional semidiurnal constituents from spline interpolation in the frequency domain the improvement in accuracy that can be obtained by increasing the number of constituents in the model at present used for tidal height corrections in the gdrs of satellite altimetric measurements is analysed by referring to the performance of the harmonic method in predicting tides at a selected number of locations in the world where observations of sea level variations are available given the interest in such improvements a way of extending the existing data set is proposed without the need to run a new model of the world s oceans the method relies on the concept of admittance world s oceans maps are derived for five additional constituents and the differences in predicted heights resulting from these improvements are evaluated

tidal data inversion interpolation and inference initial efforts in applying inverse methods to studies of ocean tides have focused on making the best use of a small number of observations to map tidal fields in a large area as such inversion can be viewed as an objective analysis scheme which uses a dynamically appropriate spatial covariance derived from the shallow water equations to interpolate and smooth a sparse data set data from recent altimetry missions are not sparsely distributed relative to tidal wavelengths in the open ocean apparently reducing the need for complicated dynamically based interpolation schemes altimetric data sets are also quite large making application of rigorous inversion methods to global tidal modeling a challenging computational problem we describe here a new iterative solution scheme which allows us for the first time to fit the full set of topex poseidon cross over differences the resulting solution tpxo 3 fits validation tide gauges significantly better than previous inverse solutions tpxo 3 also reduces residual cross over variances relative to other recent inverse and empirical solutions particularly in shallow water where improvements are dramatic with the new solution approach very significant improvements in global tidal models should be possible in shallow areas and in the vicinity of complex bathymetry where high accuracy tidal modeling remains a challenging problem with the recent improvements in the definition of tidal elevations in the open ocean it should now also be possible to resolve some long unanswered questions about tidal energetics and dynamics inverse methods provide a natural framework for addressing these issues and making inferences about tidal dynamics in particular by bringing data and dynamics together in a single solution we can rigorously test the consistency of the two we present results of global and local inversions which suggest that over elongated bathymetric features oriented perpendicular to tidal flows energy dissipation in the open ocean is significantly enhanced presumably due to conversion of barotropic tidal motions into baroclinic modes for the m2 tide our preliminary results suggest that perhaps as much as 0 5 tw of energy is dissipated in this manner however due to the simplified linear dynamics and limited spatial resolution used for our inversion there are significant uncertainties associated with these results a more careful application of inverse methods to make more rigorous inferences about tidal energetics including use of more reasonable prior dynamics and the highest possible spatial resolution should allow for closure of the tidal energy budget within the next few years

global marine gravity field from the ers 1 and geosat geodetic mission altimetry satellite altimetry from the geosat and the ers i geodetic missions provide altimeter data with very dense spatial coverage therefore the gravity field may be recovered in great detail as neighboring ground tracks are very closely distributed cross track variations in the sea surface heights are extremely sensitive to sea surface variability to avoid errors in the gravity field caused by such effects sea surface variability needs to be carefully eliminated from the observations initially a careful removal of gross errors and outliers was performed and the tracks were fitted individually to a geoid model and crossover adjusted using bias and tilt subsequently sea surface heights were gridded using local collocation in which residual ocean variability was considered the conversion of the heights into gravity anomalies was carried out using the fast fourier transform fft in this process filtering was done in the spectral domain to avoid the so called orange skin characteristics comparison with marine gravity was finally carried out in three different regions of the earth to evaluate the accuracy of the global marine gravity field from ers 1 and geosat

empirical ocean tide models estimated from topex poseidon altimetry three empirical ocean tide models are determined from repeat cycles 10 to 78 of the topex poseidon t p altimeter mission the three models investigate the effects of the satellite orbit ephemeris on the ocean tides determined from t p altimetry and the effect of extracting the free core nutation resonance in the definition of the diurnal ocean tide admittance the altimetric data series use the joint gravity model jgm 2 geopotential orbit ephemeris and the preliminary jgm 3 orbit ephemeris computed at the university of texas center for space research the altimetric data from the t p mission are shown to have the precision necessary to estimate the monthly and fortnightly ocean tides in each bin inclusion of existing models of the ocean tides in the polar latitudes not sampled by the altimeter demonstrates the importance of these latitudes on spherical harmonic representations of the ocean tides the ocean tides are first estimated in bins of size 2 834 in longitude by 1 in latitude and then smoothed to 1 by 1 grids within 66 latitude the orthotide response formalism of groves and reynolds 1975 is used to represent the diurnal and semidiurnal ocean tides while a constant admittance is assumed across narrow bandwidths around each of the monthly mm fortnightly mf and termensual mt tidal components comparisons of the t p ocean tide models to tide gauge observations indicate their accuracies to be of the order of 2 3 cm the t p derived ocean tide models remove approximately 20 cm2 more of the t p measured sea surface variance than the cartwright and ray 1991 tide model and show a 19 cm2 and 15 cm2 improvement over the schwiderski 1980a b and cartwright and ray 1991 tide models respectively when compared to tide gauge estimates of the ocean tides

an investigation of ocean tides derived from along track altimetry 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

the tides in the arctic ocean from a finite element model the two main diurnal i e k1 and o1 and semidiurnal i e m2 and s2 tidal waves have been computed from a hydrodynamic finite element spectral model the spatial resolution of the model varies from a few kilometers at the coastline to 100 km in the deepest regions an optimization of the open boundary conditions has been performed to improve the solution accuracy the bottom topography used in this model has been originally extracted from the earth topography 5 minutes grid etopo5 and corrected from various sources of data the impact of the input parameters like the friction coefficient the loading effects and the parameterisation of the additional friction due to the arctic ice cover is investigated the tidal elevations are compared to a set of in situ observations and validated they also are compared to the kowalik and proshutinsky 1993 model these comparisons mainly show good agreement between the two models nevertheless significant differences are observed where small wavelength structures are produced by the topographic trapping of the tidal energy the velocities associated with the elevations are also presented the potential rate of work the dissipation and the energy fluxes are computed from these elevations and velocities because of the uncertainties of the velocities at the open boundaries we are restricted to a qualitative analysis of the energy equation terms which appears to be consistent with the previous studies on arctic tides

gps height time series short period origins of spurious long period signals gps height time series used in geophysical studies are often formed from discrete continuous nonoverlapping 24 hour processing sessions with such a strategy unmodeled periodic ground displacements with approximately semidiurnal and diurnal periods have often been assumed to average close to zero by analyzing several years of continuous gps data from globally distributed sites at which controlled errors were not modeled this paper shows such an assumption to be erroneous it is shown that each unmodeled sub daily periodic displacement can propagate to several spurious long wavelength features in a gps height time series ranging in period from about 2 weeks to 1 year admittances ratio of amplitude of spurious long wavelength output signal in the gps height time series to amplitude of unmodeled periodic ground displacement depend on the coordinate component and the tidal constituent considered for example it is shown that an unmodeled s2 north component periodic ground displacement can propagate to a semiannual height signal with admittance of greater than 100 whereas the height admittance is around 5 10 since model errors in ocean tide loading atmospheric pressure loading and solid earth tide displacement amplitudes can be several millimeters long wavelength spurious signals of up to these amplitudes may be expected to appear in gps height time series this paper provides an indication of how such errors will propagate where such errors are greatest and hence how spurious fortnightly semiannual and in some cases annual effects may be present at some sites copyright 2007 by the american geophysical union

diurnal semidiurnal oceanic tidal angular momentum topex poseidon models in comparison with earth s rotation rate the oceanic tidal angular momentum otam has been demonstrated to be the primary cause for the diurnal and semidiurnal variations in the earth s rotational rate or aut1 three ocean tide models derived from the topex poseidon altimetry mission are employed to yield predictions of aut1 for eight major diurnal semidiurnal fides the predictions are compared with geodetic determinations of aut1 from the very long baseline interferometry data both for long term observations and during intensive campaigns the agreement is good with discrepancies typically within 2 3 gs systematic discrepancies observed for the well determined m 2 tide clearly reveal the contribution of the earth s spin libration

sediment pathway of the east china sea inferred from an r mode factor analysis of surface sediments in the okinawa trough major and trace elements loss on ignition loi and grain size distributions were determined on 190 surface sediment samples collected from the continental shelf slope and the north okinawa trough in the east china sea at water depths of 100 200 200 600 and more than 600 m respectively the sediments are composed mainly of sand and silt generally low clay contents average 10 5 increasing over the range of 0 12 53 6 from the shelf and slope to the trough sediments were sandier on the continental shelf particularly in the northern shelf sector spatial distributions in chemical compositions show that the contents of sio 2 cao sr and loi values were relatively high on the sandy continental shelf by contrast the contents of al 2 o 3 mgo na 2 o mno feo tio 2 cu zn co ni and cr were relatively high in the trough and along the central western shelf margin where the sediments were composed mainly of silt fe 2 o 3 p 2 o 5 and zr enrichment was highest in the slope sediments three factors were extracted by means of an r mode factor analysis of chemical composition factor 1 has two inversely correlated elemental assemblages 1 sio 2 k 2 o tio 2 al 2 o 3 and zr which can be associated with terrigenous debris input and show high positive factor scores in the southern sector of the shelf and 2 cao sr and loi which can be related with biogenic debris enrichment and show high negative factor scores in the northern shelf sector as well as in a more restricted area along the slope cao sio 2 k 2 o and sr represent the element assemblage of the shelf factor 2 comprises na 2 o feo al 2 o 3 tio 2 cu zn and ni and shows high scores in the trough sediments na 2 o cu zn and ni represent the elemental assemblage of the okinawa trough and can be associated with volcanic matter factor 3 comprises fe 2 o 3 mgo cr and co with high factor scores on the slope and along the central western shelf margin of the study area due to upwelling induced enrichments in nutrients and biogenic shells fe 2 o 3 and mgo are the slope elements based on the results of the distribution of the chemical compositions and the elemental assemblage of the surface sediment in the source to sink system the influence of the yellow river on the continental shelf is stronger than that of the yangtze river from the continental shelf and slope to the trough the influence of the yellow river decreased from north to south in the okinawa trough the sediment from the yellow river decreases and from the yangtze river increases and the chemical compositions changed c 2009 elsevier ltd and inqua all rights reserved

observability of the irminger sea circulation using variational data assimilation this paper explores the prospects for constraining circulation and stratification estimates in the irminger sea and denmark strait using variational data assimilation a regional circulation model with 9 km horizontal grid spacing seven vertical levels and open boundaries is used the circulation it simulates is realistic in several important respects and includes a chaotic mesoscale eddy field pulsation of the outflow of dense water through the denmark strait is also reasonably realistic although entrainment and mixing of this water downstream is crudely represented identical twin assimilation experiments are performed to address the observability of the system with the existing in situ and satellite observing network in the absence of systematic errors that is the constraints exerted on the circulation and stratification by the data assimilation system are quantified synthetic data come from a reasonably realistic observing network that includes in situ hydrographic and current measurements and remotely sensed surface temperature and sea level over a 15 day assimilation period in summer the system fits all the observations to the relevant noise level largely by correcting the initial conditions only modest changes in the time dependent surface forcing and negligible changes to the open boundary conditions are needed the system can accurately estimate sea surface height and sea surface temperature correcting errors in the locations of surface fronts and eddies the mid depth salinity is almost completely unconstrained however whereas the velocity fields are somewhat constrained by the assimilation especially by the remote sensing data assimilation of satellite data enables us to accurately track the phase and amplitude of the overflow variability at the exit of denmark strait in the identical twin experiments at other model outflow transects the assimilated solution is contaminated with spurious inertial oscillations this is true even at a section offshore of angmagssalik where a current meter mooring array exists in our experiments and in the real ocean nevertheless improvement of the model dense outflow near the moorings is significant and propagates several hundred kilometres upstream and downstream copyright 2006 royal meteorological society

reef parameterisation schemes with applications to tidal modelling a variety of analytical models is used to investigate the effects on tidal propagation of a barrier reef system these models specify reef geometry by two parameters they can accommodate cases where water flows over reefs as well as through inter reef gaps and also incorporate quadratic bottom friction although based on a one dimensional approach adaptations of a solution by huthnance are used to account for the additional blockage effects associated with two dimensional flow patterns near reef barriers the present work adopts the philosophy that only a numerical approach can cope with the wide variations in reef geometry that are encountered in areas such as the great barrier reef gbr region of australia moreover since typical model grids cannot resolve inter reef gaps and other features with sufficient accuracy a parameterised approach is needed to accommodate the conflicting demands of reef geometry and an economically feasible model resolution the formulation of the analytical models is such that they can be applied immediately to standard numerical algorithms numerical experiments for flow in a channel with a reef barrier across its centre are used to test the parameterisation schemes comparison of the results for parameterised reefs with those obtained using extremely fine grids shows convincing evidence of the success of the schemes a separate method for automatically generating reef parameters has simplified the task of applying the methodology to real reefal systems a tidal model of the southern gbr a region which exhibits unusual tidal behaviour but which also has ample field data available for model testing is used to demonstrate the accuracy that can be attained with the parameterised approach although tides are considered specifically in the present work the formulation should be applicable with equal ease to the many other significant classes of low frequency motions in the gbr

verification of the ellipsoidal earth model with an inelastic and convective mantle using tidal gravity variations revisited summary tidal gravity observations can be used to validate theoretical estimation for inelastic response of the earth and its latitude dependence using gravimetric factors we used superconducting gravimeter sg data at five sites mets ahovi strasbourg sutherland canberra and syowa to validate theoretical estimation based on an existing method for the correction of ocean loading effect we tested eight global ocean tide models four old csr4 0 got99 2b nao 99b and fes2004 and four new tpxo7 atlas eot11a dtu10 and hamtide11a were tested we selected an optimal ocean tide model based on the criterion of the smallest misfit for the three main waves o1 k1 and m2 at each station as determinedbytheresidualbetweentheobservedloadingeffectandthemodelledoceanloading effect large discrepancies among the results of ocean tide models remained at mets

regional identification in the tropical atlantic ocean of residual tide errors from an empirical orthogonal function analysis of topex poseidon altimetric data two years october 1992 to september 1994 of topex poseidon data have been processed over the tropical atlantic ocean to produce monthly sea level anomalies four different oceanic tide corrections have been applied in order to quantify the effect of this correction on the large scale altimetrically determined sea level variability and to identify potential residual tide errors two tide corrections are drawn from the u s university of texas tide model and two others are drawn from the french grenoble tide model comparison of the altimetric sea level anomalies with tide gauge data gives rms differences of between 2 and 5 cm equivalent to those already observed by several authors during recent topex poseidon studies however this paper demonstrates that the 2 monthly oscillations which were previously identified in investigations using old versions of tide corrections still remain to some extent independently of the new tide models being used these 2 monthly oscillations are not only located along the western boundary and therefore cannot be attributed to 40 to 60 day oscillations observed in several mooring records in that area an empirical orthogonal function analysis of the altimetric data clearly shows that these oscillations are due to tide aliasing this approach also emphasizes the improvement finalized by the more recent versions of the university of texas and the grenoble tide models however the most convincing result of this analysis is that it allows regional quantification of the impact of tidal residual error aliasing which persists even when the more sophisticated tide models are used

how stationary are the internal tides in a high resolution global ocean circulation model the stationarity of the internal tides generated in a global eddy resolving ocean circulation model forced by realistic atmospheric fluxes and the luni solar gravitational potential is explored the root mean square rms variability in the m2 internal tidal amplitude is approximately 2 mm or less over most of the ocean and exceeds 2 mm in regions with larger internal tidal amplitude the m2 rms variability approaches the mean amplitude in weaker tidal areas such as the tropical pacific and eastern indian ocean but is smaller than the mean amplitude near generation regions approximately 60 of the variance in the complex m2 tidal amplitude is due to amplitude weighted phase variations using the rms tidal amplitude variations normalized by the mean tidal amplitude normalized rms variability nrms as a metric for stationarity low mode m2 internal tides with nrms 0 5 are stationary over 25 of the deep ocean particularly near the generation regions the m2 rms variability tends to increase with increasing mean amplitude however the m2 nrms variability tends to decrease with increasing mean amplitude and regions with strong low mode internal tides are more stationary the internal tide beams radiating away from generation regions become less stationary with distance similar results are obtained for other tidal constituents with the overall stationarity of the constituent decreasing as the energy in the constituent decreases seasonal variations dominate the rms variability in the arabian sea and near equatorial oceans regions of high eddy kinetic energy are regions of higher internal tide nonstationarity

the global frequency wavenumber spectrum of oceanic variability estimated from topex poseidon altimetric measurements two years of altimetric data from the topex poseidon spacecraft have been used to produce preliminary estimates of the space and time spectra of global variability for both sea surface height and slope the results are expressed in terms of both degree variances from spherical harmonic expansions and in along track wavenumbers simple analytic approximations both in terms of piecewise power laws and pade fractions are provided for comparison with independent measurements and for easy use of the results a number of uses of such spectra exist including the possibility of combining the altimetric data with other observations predictions of spatial coherences and the estimation of the accuracy of apparent secular trends in sea level

validation of ocean tide models around antarctica using onshore gps and gravity data 1 ocean tide models around antarctica are presently only sparsely tested against independent data ocean tide modeling errors along with subsequent ocean tide loading otl displacement modeling errors alias into altimetry and time variable gravity e g gravity recovery and climate experiment grace time series for example to validate various ocean tide models around antarctica gps data from 15 sites have been used to derive three dimensional displacement estimates at eight diurnal and semidiurnal tidal frequencies using hundreds of days of gps data harmonic parameters were estimated on a daily basis then combined these were then compared with otl displacement estimates derived from global and regional ocean tide models in east antarctica where the tides are well defined submillimeter differences are demonstrated in each coordinate component with the lunar n2 and q1 constituents in closest agreement as found in other studies k1 and especially k2 agree less well the spatial variation in the misfits for these two constituents indicates a site dependency with the k2 errors also suggesting an interaction with satellite dependent effects in west antarctica where sites are nearer the largest ice shelves agreement with the older models csr3 and tpxo 2 and nao 99b is poor for all constituents modeled tidal gravity variations were also compared with gravity measurements at the south pole overall the gps and gravity data agree best with newer tide models namely tpxo 6 cada00 10 fes99 and cats02 01 however validation data are lacking at the southern extents of the large ice shelves and hence some uncertainty still exists in all ocean tide models in these regions