validating earth and ocean tide models using tidal gravity measurements summary o1 and m2 observations from well calibrated spring gravimeters and superconducting gravimeters from the global geodynamics project ggp are used to test models of the earth s body tide and 10 ocean tide models it is shown that some of the ocean tide models give anomalous results in various parts of the world for example the schwiderski ocean tide model gives discrepancies in several areas and the fes series of ocean tide models have problems in the western pacific china japan and australia the majority of the high quality tidal gravity measurements in europe are in close agreement with the dehant defraigne and wahr ddw elastic and inelastic body tide models the gravimetric factors for the ddw elastic and inelastic models only differ by 0 12 per cent and the present calibration accuracy does not allow us to distinguish between these models but does reduce the previous upper bound on inelastic gravimetric factors the european observations give a phase lag of a few hundredths of a degree for the o1 body gravity tide which is consistent with the mathews inelastic body tide model at some european and worldwide stations the gravimetric factors differ by up to 0 3 per cent from the ddw model and it is suggested that further checks on the gravimeter calibrations are required accurate determinations of instrumental phase lags are now easier to achieve and the imaginary out of phase component of tidal gravity can be used for accurate tests of this component of ocean tide models

new transfer functions for nutations of a nonrigid earth there are differences between the observed values of nutation and the computed ones based on the international astronomical union iau 1980 adopted nutation series these differences can be expressed in the frequency domain where they may reach several milliarc seconds a level that is too large for practical use this paper aims to resolve part of these differences by computing a new theoretical model accounting for additional geophysical effects a new transfer function is computed based on an earth initially in a nonhydrostatic equilibrium corresponding to the steady state associated with the present mantle convection the mantle mass anomalies are deduced from seismic tomography data and the flow induced boundary deformations are computed from internal loading for an earth made up of a viscous inner core a liquid outer core a viscous mantle and a solid lithosphere in this way a new core mantle boundary cmb flattening is obtained which gives the observed free core nutation fcn period furthermore the global earth dynamical flattening induced by the mass anomalies in the mantle associated with tomography and by the mass anomalies due to the computed boundary deformations is in agreement with the j2 form factor or the observed precession constant in addition to this nonhydrostatic initial state the rheology of the mantle is considered as inelastic the transfer function for nutation is then obtained by numerical integration of motion equations from the earth s center up to the surface to provide a model which is completely self consistent in order to validate our model the transfer function is convolved with new rigid earth nutations ocean corrections are applied and the final results are then compared with the observed nutations or with the international earth rotation service iers nutation series the residuals between our model and the observation are about 3 times smaller than those between the iau 1980 adopted model and the observation however our model still presents residuals above the observational error this is particularly true for the out of phase part of the residuals while the in phase part gives very small residuals improvement of about 1 order of magnitude a further step in this study is a refinement of the modeling of geophysical fluids core ocean and atmosphere

bayesian chronological analyses consistent with synchronous age of 12 835 12 735 cal b p for younger dryas boundary on four continents the younger dryas impact hypothesis posits that a cosmic impact across much of the northern hemisphere deposited the younger dryas boundary ydb layer containing peak abundances in a variable assemblage of proxies including magnetic and glassy impact related spherules high temperature minerals and melt glass nanodiamonds carbon spherules aciniform carbon platinum and osmium bayesian chronological modeling was applied to 354 dates from 23 stratigraphic sections in 12 countries on four continents to establish a modeled ydb age range for this event of 12 835 12 735 cal b p at 95 probability this range overlaps that of a peak in extraterrestrial platinum in the greenland ice sheet and of the earliest age of the younger dryas climate episode in six proxy records suggesting a causal connection between the ydb impact event and the younger dryas two statistical tests indicate that both modeled and unmodeled ages in the 30 records are consistent with synchronous deposition of the ydb layer within the limits of dating uncertainty 100 y the widespread distribution of the ydb layer suggests that it may serve as a datum layer

body tides on a 3 d elastic earth toward a tidal tomography abstract the deformational and gravitational response of the earth to the tide generating potential has generally involved 1 d i e depth varying earth models progressive improvement in observational constraints on body tides generated from both ground and space based surveys suggests that an examination of the potential impact of lateral variations in earth structure is warranted we present a suite of predictions of the body tide response within the semi diurnal diurnal and long period tidal bands computed using a finite volume numerical code the calculations adopt 3 d density and elastic structure taken from seismic inferences and in a subset of the calculations dynamic topography on the surface and internal interfaces we find that perturbations in the radial displacement and surface gravity within the semi diurnal band reach 1 mm and 0 15 gal respectively the perturbations in the diurnal band are comparable to these values and within the long period band they are a factor of 3 5 smaller we also demonstrate that lateral variations in the elastic moduli which have been ignored in recent work contribute greater than 50 of the total perturbation the level of perturbation associated with 3 d structure exceeds the current observational uncertainty obtainable using space geodetic methods and this suggests the possibility of performing tidal tomographic inversions of such data

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

study of harmonic site position variations determined by very long baseline interferometry 1 position variations of 40 very long baseline interferometry vlbi stations at 32 tidal frequencies were obtained from analysis of 3 million measurements of group delays from 1980 to 2002 residual displacements after the removal of the effect of solid earth tides were studied the purpose of this study is to investigate a harmonic signal at any frequency where it is expected and to assess quantitatively whether the models of vertical and horizontal site position variations agree with the observations it was found that the estimates of station displacements are generally in good agreement with the ocean loading computed on the basis of ocean tide models for the main diurnal and semidiurnal tides moreover vlbi results allow us to discriminate between different ocean tide models however discrepancies between vlbi results and all models of ocean loading for k1 k2 and s2 tides exceed both the errors of the vlbi estimates and the errors of ocean loading displacements based on the reported formal uncertainties of ocean tide models it was found that there is a significant nontidal signal at diurnal and annual frequencies applying a model of hydrological loading reduces the variance of the residual vertical displacements at the annual frequency by 30 using an empirical model of harmonic site position variations in vlbi processing provides a better fit and improves the baseline length repeatability

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

atmospheric effects and spurious signals in gps analyses improvements in the analyses of global positioning system gps obser vations yield resolvable mm to sub mm di erences in coordinate estimates thus provid ing su cient resolution to distinguish subtle di erences in analysis methodologies here we investigate the e ects on site coordinates of using di erent approaches to modelling atmospheric loading deformation atml and handling of tropospheric delays the rig orous approach of using the time varying vmf1 mapping function yields solutions with lower noise at a range of frequencies compared with solutions generated using empiri cal mapping functions this is particularly evident when atml is accounted for some improvement also arises from using improved a priori zenith hydrostatic delays zhd with the combined e ect being site speci c importantly inadequacies in both mapping functions and a priori zhds not only introduce time correlated noise but signi cant pe riodic terms at solar annual and semi annual periods we nd no signi cant di erence between solutions where non tidal atml is applied at the observation level rather than as a daily averaged value but failing to model diurnal and semi diurnal tidal atml at the observation level can introduce anomalous propagated signals with periods that closely match the gps draconitic annual 351 4 d and semi annual period 175 7 d ex acerbated by not xing ambiguities these signals are evident in both stacked and sin gle site power spectra with each tide contributing roughly equally to the dominant semi annual peak the amplitude of the propagated signal reaches a maximum of 0 8 mm with a clear latitudinal dependence that is not correlated directly with locations of maximum tidal amplitude this is the first evidence of aliased signals being produced from tidal atml deformations

tides for a convective earth in this paper we give values of the tidal gravimetric factor as well as of the love numbers for the tidal surface displacement and for the tidal mass redistribution potential that are consistent with the presently adopted definitions we present analytical expressions for these quantities and compute numerical values for two rotating nonspherical earth models in the first model the earth is everywhere in hydrostatic equilibrium and the inner core and mantle are both elastic in the second model the earth is ellipsoidal with an inelastic mantle and with a nonhydrostatic initial state for which the effects of mantle convection and its associated boundary deformations are considered this latter model is constrained to reproduce the observed free core nutation period and global earth dynamical flattening

static response of monopile to lateral load in overconsolidated dense sand abstractlarge diameter rigid monopile foundations have been extensively used in the fast growing offshore wind energy industry over the last two decades in view of the offshore environment later

nloadf a program for computing ocean tide loading the loading of the earth by the ocean tides produces several kinds of signals which can be measured by geodetic technique in order to compute these most accurately a combination of global and local models of the ocean tides may be needed the program nloadf convolves the green functions for loading with ocean tide models using a station centered grid with fixed dimensions making it easy to combine different ocean models without overlap in the convolution the program computes all the quantities of interest gravity displacement tilt and strain and includes the case where measurements are made beneath the surface of the ocean

analysis of tidal signals in surface displacement measured by a dense continuous gps array abstract we analyze the tidal displacement signals for the eight major diurnal and semidiurnal tides from global positioning system gps measurements made at the western united states over the past 16 years with 1075 independent stations by careful examinations among inland versus coastal gps data we are able to demonstrate that estimated precisions down to the level of 0 1 mm horizontal and 0 3 mm vertical have been reached for the tidal signals and that at such precisions coherent spatial patterns are revealed in the residual tidal amplitudes and phases after the removal of a priori modeled effects of body tides and ocean tidal loading otl we demonstrate the facility of modern precise gps data in not only constraining the ocean tide models but more significantly in providing source data in terms of regional complex love numbers for geophysical inference of the heterogeneities of elastic and inelastic structures in the solid earth s deep interior on tidal timescales

contributions of thermal expansion of monuments and nearby bedrock to observed gps height changes 1 long term continuous global positioning system gps observations have become an important tool for studying the various geodynamic processes to fully study the geodynamic processes at gps stations the temporal movements of gps monuments and nearby bedrock induced by thermal expansion need to be considered in this paper we extend a theoretical model to estimate the thermal expansions of gps monuments and nearby bedrock for 86 globally distributed gps stations based upon measurements of surface air temperatures the results show that annual temperature variations are the dominant contributors for the thermal expansion of gps monuments and nearby bedrock the contributions of thermal expansion to gps height changes display largely spatial variations and can reach to a few millimeters citation yan h w chen y zhu w zhang and m zhong 2009 contributions of thermal expansion of monuments and nearby bedrock to observed gps height changes geophys res lett 36 l13301 doi 10 1029 2009gl038152

troposphere mapping functions for gps and very long baseline interferometry from european centre for medium range weather forecasts operational analysis data 1 in the analyses of geodetic very long baseline interferometry vlbi and gps data the analytic form used for mapping of the atmosphere delay from zenith to the line of site is most often a three parameter continued fraction in 1 sin elevation using the 40 years reanalysis era 40 data of the european centre for medium range weather forecasts for the year 2001 the b and c coefficients of the continued fraction form for the hydrostatic mapping functions have been redetermined unlike previous mapping functions based on data from numerical weather models isobaric mapping functions niell 2000 and vienna mapping functions vmf boehm and schuh 2004 the new c coefficients are dependent on the day of the year and unlike the niell mapping functions niell 1996 they are no longer symmetric with respect to the equator apart from the opposite phase for the two hemispheres compared to vmf this causes an effect on the vlbi or gps station heights that is constant and as large as 2 mm at the equator and that varies seasonally between 4 mm and 0 mm at the poles the updated vmf based on these new coefficients and called vmf1 hereinafter yields slightly better baseline length repeatabilities for vlbi data the hydrostatic and wet mapping functions are applied in various combinations with different kinds of a priori zenith delays in the analyses of all vlbi international vlbi service for geodesy and astrometry ivs r1 and ivs r4 24 hour sessions of 2002 and 2003 the investigations concentrate on baseline length repeatabilities as well as on absolute changes of station heights

carrier phase ambiguity resolution for the global positioning system applied to geodetic baselines up to 2000 km the global positioning system gps carrier phase data are biased by an integer number of cycles a successful strategy has been developed and demonstrated for resolving these integer ambiguities for geodetic baselines of up to 2000 km in length resulting in a factor of 3 improvement in baseline accuracy and giving centimeter level agreement with coordinates inferred by very long baseline interferometry in the western united states for this experiment a method using pseudorange data is shown to be more reliable than one using ionospheric constraints for baselines longer than 200 km an automated algorithm exploits the correlations between the many phase biases of a gps receiver network to enable the resolution of ambiguities for very long baselines a method called bias optimizing has been developed which unlike traditional bias fixing does not require an arbitrary confidence test bias optimizing is expected to be preferable to bias fixing for poorly configured networks in order to enable ambiguity resolution for long baselines it is recommended that future gps networks have a wide spectrum of baseline lengths ranging from 1000 km and that gps receivers be used which can acquire dual frequency p code data

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

the tidal displacement field at earth s surface determined using global gps observations 1 we investigate the 3 d tidal displacement field on earth s surface recorded globally by 456 continuous global positioning system gps stations of igs spanning 1996 2011 for eight principal diurnal and semidiurnal tidal constituents in phase and quadrature amplitudes of the residual tidal displacements after removal of an a priori body tide model are estimated using the precise point positioning ppp technique on the daily gps data the resultant daily estimates are combined to derive final estimates for each tide at each station the results are compared with the predictions of eight recent global ocean tide models separately for coastal 307 and inland 149 stations we show that gps can provide tidal displacement estimates accurate to the level of 0 12 mm horizontal and 0 24 mm vertical for the lunar only constituents m2 n2 o1 and q1 and less favorably for solar related tidal constituents s2 k2 k1 and p1 although improved by ambiguity resolution most recent ocean tide models fit the gps estimates equally well on the global scale but do not agree well between them in certain coastal areas especially for the vertical displacements suggesting the existence of model uncertainties near shallow seas the tidal residuals for the inland stations after removing both body tides and ocean tidal loading otl furthermore show clear continental scale spatial coherence implying deficiencies of the a priori body tide modeling in catching lateral heterogeneity in elastic as well as inelastic properties in the earth s deep interior we assert that the gps tidal displacement estimates now achieve sufficient accuracy to potentially provide constraints on the earth s structure

probing asthenospheric density temperature and elastic moduli below the western united states periodic ocean tides continually provide a cyclic load on earth s surface the response to which can be exploited to provide new insights into earth s interior structure we used geodetic observations of surface displacements induced by ocean tidal loads to constrain a depth dependent model for the crust and uppermost mantle that provides independent estimates of density and elastic moduli below the western united states and nearby offshore regions our observations require strong gradients in both density and elastic shear moduli at the top and bottom of the asthenosphere but no discrete structural discontinuity at a depth of 220 kilometers the model indicates that the asthenosphere has a low density anomaly of 50 kilograms per cubic meter a temperature anomaly of 300 c can simultaneously explain this density anomaly and inferred colocated minima in elastic moduli

geochemical evidence of the presence of volcanic and meteoritic materials in late pleistocene lake sediments of lithuania abstract concentrations of trace elements in four late pleistocene lake sediment sequences across lithuania were studied using inductively coupled plasma mass spectrometry icp ms such elements as cr cu eu la ni zn zr and platinum group elements were used for constraints the studied sediments deposited during the time interval from bolling to allerod and to younger dryas material for sediments of the dengtiltis and krokslys sequences was delivered from the same or very similar source geochemical features of the sediments are consistent with the presence of extraterrestrial material in at least two horizons separated by 2000 years and resulted from two separate events the younger horizon is detected in all studied sequences and corresponds to the age of ca 11 0 11 5 ka bp its geochemical features are suggested to result from a local meteorite impact bolide explosion tentatively related to the velnio duob s meteorite crater the older horizon detected only for the la 2 sequence corresponds to the age of ca 13 5 ka bp and is due to the bolide airburst there is also suggested meteoritic material in sediments dated as ca 12 9 ka bp the presence of volcanic materials related to the volcanic activity in the french massif central a volcano of ca 15 3 ka bp and laacher see volcano in germany 12 88 ka bp are suggested for some sedimentary layers of the studied sequences

apparent stability of gps monumentation from short baseline time series 1 long running short 1 km gps baselines offer an insight into the accuracy budget of geophysical estimates inferred from gps coordinate time series in this paper we report on analysis of 10 short baselines using data spanning several years and examine deviations from a constant baseline length annual signals with amplitude 0 5 mm are evident in various coordinate components at 6 of the 10 sites with amplitudes exceeding 2 5 mm on two baselines these signals are largely invariant to elevation cutoff angle multipath and phase center model errors are shown to probably have negligible effects at most sites at annual periods they are therefore likely real monument motions although linear thermal expansion is negligible at most sites linear trends 0 25 mm yr 1 are evident on four baselines in at least one coordinate component subdaily signals are present at all sites at k1 and its higher harmonics time correlated noise possibly in the form of flicker noise dominates despite many common signals being eliminated as a result of the small baseline lengths although it is around 1 order of magnitude smaller than for single site ppp solutions we constrain monument random walk motion to be no more than 0 5 mm yr 1 2 if these baseline motion results were representative of the 300 currently active igs sites 180 would have annual signals 0 5 mm in at least one coordinate component 120 would have linear rates 0 25 mm yr 1 and almost all sites would have subdaily k1 k2 signals of 0 1 mm each solely due to local site effects

multimission empirical ocean tide modeling for shallow waters and polar seas 1 a new global ocean tide model named dtu10 developed at technical university of denmark representing all major diurnal and semidiurnal tidal constituents is proposed based on an empirical correction to the global tide model fes2004 finite element solutions with residual tides determined using the response method the improvements are achieved by introducing 4 years of topex jason 1 interleaved mission into existing 18 years 1993 2010 of primary joint topex jason 1 and jason 2 mission time series hereby the spatial distribution of observations are doubled and satellite altimetry should be able to recover twice the spatial variations of the tidal signal which is particularly important in shallow waters where the spatial scale of the tidal signal is scaled down outside the 66 parallel combined envisat geosat follow on and ers 2 data sets have been included to solve for the tides up to the 82 parallel a new approach to removing the annual sea level variations prior to estimating the residual tides significantly improved tidal determination of diurnal constituents from the sun synchronous satellites e g ers 2 and envisat in the polar seas extensive evaluations with six tide gauge sets show that the new tide model fits the tide gauge measurements favorably to other state of the art global ocean tide models in both the deep and shallow waters especially in the arctic ocean and the southern ocean one example is a comparison with 207 tide gauge data in the east asian marginal seas where the root mean square agreement improved by 35 12 22 61 27 07 and 22 65 m2 s2 k1 and o1 for the dtu10 tide model compared with the fes2004 tide model a similar comparison in the arctic ocean with 151 gauge data improved by 9 93 0 34 7 46 and 9 52 for the m2 s2 k1 and o1 constituents respectively

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