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

internal tide coherence and decay over a wide shelf sea 1 a quasi synoptic hydrography and velocity section is used to determine the structure and the decay rate of the internal tide it across the broad continental shelf of the celtic sea in these observations the it is coherent over more than 170 km about five wavelengths with an estimated shoreward energy decay scale of 42 km the inferred it wavelength averaged dissipation rate near the shelf edge is estimated as 2 08 10 7 wkg 1 in close agreement with tidally and vertically averaged measurements from the region these results provide the firstin situ evidence of it coherence over many wavelengths in a shelf sea

m2 baroclinic tide variability modulated by the ocean circulation south of japan we analyze a concurrent simulation result of the ocean circulation and tidal currents using a data assimilative ocean general circulation model covering the western north pacific with horizontal resolution of 1 36 to investigate possible interactions between them four sites of active m2 internal tide variability in open ocean hot spots such as tokara strait izu ridge luzon strait and ogasawara ridge are detected from both the satellite observation and the simulation energy cycle analysis of the simulated m2 baroclinic tide indicates two types of the hot spots dissipation tokara strait and izu ridge and radiation luzon strait and ogasawara ridge dominant sites energy conversion from barotropic to baroclinic m2 tides at the hot spots is modulated considerably by the lower frequency changes in the density field modulation at the two spots tokara strait and izu ridge is affected by the kuroshio path variation together with the seasonal variation of the shallow thermocline at the other two sites influence from changes in the relatively deep stratification through the kuroshio intrusion into south china sea luzon strat and mesoscale eddy activity ogasawara ridge is dominant in the modulation

deformation of the oceanic crust between the north american and south american plates fracture zone trends and magnetic anomalies in the atlantic ocean indicate that the north american plate must have moved with respect to the south american plate during the opening of the atlantic a comparison of plate tectonic flow lines with fracture zones identified from geosat and seasat altimeter data suggests that the north american south american plate boundary migrated northward from die guinea demarara shear margin to the vema fracture zone before chron 34 84 ma to north of the doldrums fracture zone before chron 22 51 9 ma and to north of the mercurius fracture zone between chron 32 72 5 ma and chron 13 35 5 ma the paleoridge offset through time identified from magnetic anomalies and the computed cumulative strike slip motion in the plate boundary area indicate that the triple junction may have been located between the mercurius and the fifteen twenty fracture zones after 67 ma chron 30 plate reconstructions indicate a late cretaceous phase of transtension followed by transpression in the tertiary for the tiburon barracuda ridge area south of the fifteen twenty fracture zone the ocean floor in this area is characterized by a series of ridges and troughs with large bouguer gravity anomalies up to 135 mgal we use smoothing spline estimation to invert bouguer anomalies for crustal layer structure our model results suggest that the moho is uplifted 2 4 km over short wavelengths 70 km at the barracuda and tiburon ridges and imply large anelastic strains the severely thinned crust at the two ridges implies that crustal extension must have taken place before they were uplifted we propose that the north south american plate boundary migrated to the latitude of the tiburon ridge bounded by the vema and marathon fracture zones before chron 34 84 ma post chron 34 crustal thinning during a transtensional tectonic regime may have been localized at preexisting structural weaknesses such as the vema marathon mercurius and fifteen twenty fracture zone troughs but reaching the fifteen twenty fracture zone and future barracuda ridge area only after chron 32 72 5 ma this interpretation concurs with our crustal structural model which shows stronger crustal thinning underneath the tiburon ridge than at the barracuda ridge subsequent transpression may have continued along the existing zones of weakness in the tertiary creating the presently observed crustal deformation and uplift of the moho accompanied by anelastic failure of the crust middle eocene upper oligocene turbidites on the slope of the tiburon ridge now located 800 m above the abyssal plain suggest that most of its uplift occurred at post oligocene times the unusually shallow moho underneath the tiburon and barracuda ridges represents an unstable density distribution which may indicate that compressive stresses are still present to maintain these anomalies and that the north american south american plate boundary may still be located in this area

tidal mixing events on the deep flanks of kaena ridge hawaii abstract a 3 month mooring deployment august november 2002 was made in 2425 m depth on the south flank of kaena ridge hawaii to examine tidal variations within 200 m of the steeply sloping bottom horizontal currents and vertical displacements inferred from temperature fluctuations are dominated by the semidiurnal internal tide with amplitudes of 0 1 m s 1 and 100 m respectively a series of temperature sensors detected tidally driven overturns with vertical scales of 100 m a thorpe scale analysis of the overturns yields a time averaged dissipation near the bottom of 1 2 10 8 w kg 1 10 100 times that at similar depths in the ocean interior 50 km from the ridge dissipation events much larger than the overall mean up to 10 6 w kg 1 occur predominantly during two phases of the semidiurnal tide 1 at peak downslope flows when the tidal stratification is minimum n 5 10 4 s 1 and 2 at the flow reversal from downslope to upslope flow when the tidal stratification is ordinarily increasi

parameterizing tidal dissipation over rough topography the traditional model of tidal dissipation is based on a frictional bottom boundary layer in which the work done by bottom drag is proportional to a drag coefficient and the velocity cubed however away from shallow coastal regions the tidal velocities are small and the work done by the bottom boundary layer can account for only weak levels of dissipation in the deep ocean the energy flux carried by internal waves generated over rough topography dominates the energy transfer away from barotropic flow a parameterization for the internal wave drag over rough topography is included as a dissipative mechanism in a model for the barotropic tides model results suggest that the inclusion of this dissipation mechanism improves hydro dynamical models of the ocean tide it also substantially increases the amount of modeled tidal dissipation in the deep ocean bringing dissipation levels there into agreement with recent estimates from topex poseidon altimetry data

energetics of m2 barotropic to baroclinic tidal conversion at the hawaiian islands abstract a high resolution primitive equation model simulation is used to form an energy budget for the principal semidiurnal tide m2 over a region of the hawaiian ridge from niihau to maui this region includes the kaena ridge one of the three main internal tide generation sites along the hawaiian ridge and the main study site of the hawaii ocean mixing experiment the 0 01 horizontal resolution simulation has a high level of skill when compared to satellite and in situ sea level observations moored adcp currents and notably reasonable agreement with microstructure data barotropic and baroclinic energy equations are derived from the model s sigma coordinate governing equations and are evaluated from the model simulation to form an energy budget the m2 barotropic tide loses 2 7 gw of energy over the study region of this 163 mw 6 is dissipated by bottom friction and 2 3 gw 85 is converted into internal tides internal tide generation primarily occurs along the flanks of the kaena ridge and

on the choice of orbits for an altimetric satellite to study ocean circulation and tides the choice of an orbit for satellite altimetric studies of the ocean s circulation and tides requires an understanding of the orbital characteristics that influence the accuracy of the satellite s measurements of sea level and the temporal and spatial distribution of the measurements three orbital parameters determine the temporal and spatial sampling characteristics of the satellite the orbital altitude the inclination of the orbit and the repetition period the eccentricity of the chosen orbit should be less than 0 001 to minimize altimeter errors caused by uncertainty in determining the time of each altimeter measurement and to maintain the rate of height variation over the oceans within the limits of the altimeter tracker the choice of the satellite s orbital altitude is constrained by the influences of atmospheric drag and errors in models of the gravity field which decrease with height and the required complexity of the altimeter e g the power and or antenna size required and the effect on satellite systems of radiation from earth s radiation belts which increase with height the choice of inclination is constrained by a desire to measure sea level over all the ocean by the requirement that the acute angle between intersections of the subsatellite track be as large as possible and by the time phasing of the repeat of the satellite s ground track as a function of inclination which determines the aliased frequencies of the measurements of the oceanic tides the choice of repetition period is constrained by tradeoffs between temporal and spatial coverage and by the aliasing of tidal constituents combining the above constraints leads to a set of orbits in a narrow range of altitude and inclination called here the topex poseidon window this window extends from 1100 to 1500 km altitude and 62 to 66 inclination for a 10 day repeat period and consists of three subwindows following lines of equal orbit plane precession there are four choices of orbits within these subwindows that overfly the planned calibration sites at bermuda and dakar these are at 64 80 and 1335 km 62 01 and 1252 km 65 84 and 1255 km and 62 69 and 1173 km these choices have a minimum separation between the aliased frequencies of the eight largest diurnal and semidiurnal tides of one cycle per 4 71 years one cycle per 4 86 years one cycle per 4 87 years and one cycle per 4 27 years respectively thus there will be less than one cycle separation over the nominal 3 years mission of these four choices the first at 64 8 and 1335 km is preferable because it is less sensitive to error in estimating the upcoming solar cycle which will be a maximum during the mission and because it is more nearly centered in terms of inclination than the other choices for other calibration sites other choices would have to be made additional work beyond the scope of this paper will also be necessary to determine if the topex poseidon mission requires a frozen orbit i e an orbit for which there are no long term variations in the eccentricity and argument of perigee of the orbit if a frozen orbit is required then the first and third choices listed above have frozen orbits with an eccentricity that is acceptable for topex poseidon

internal tides around the hawaiian ridge estimated from multisatellite altimetry 1 satellite altimetric sea surface height anomaly ssha data from geosat follow on gfo and european remote sensing ers as well as topex poseidon t p are merged to estimate m2 internal tides around the hawaiian ridge with higher spatial resolution than possible with single satellite altimetry the new estimates are compared with numerical model runs along track analyses show that m2 internal tides can be resolved from both 8 years of gfo and 15 5 years of ers ssha data comparisons at crossover points reveal that the m2 estimates from t p gfo and ers agree well multisatellite altimetry improves spatial resolution due to its denser ground tracks thus m2 internal tides can be plane wave fitted in 120 km 120 km regions compared to previous single satellite estimates in 4 lon 3 lat or 250 km 250 km regions in such small fitting regions the weaker and smaller scale mode 2 m2 internal tides can also be estimated the higher spatial resolution leads to a clearer view of the m2 internal tide field around the hawaiian ridge discrete generation sites and internal tidal beams are clearly distinguishable and consistent with the numerical model runs more importantly multisatellite altimetry produces larger m2 internal tidal energy fluxes which agree better with model results than previous single satellite estimates this study confirms that previous altimetric underestimates are partly due to the more widely spaced ground tracks and consequently larger fitting region multisatellite altimetry largely overcomes this limitation

internal tide energy over topography 1 the method used to separate surface and internal tides ultimately defines properties such as internal tide generation and the depth structure of internal tide energy flux here we provide a detailed analysis of several surface internal tide decompositions over arbitrary topography in all decompositions surface tide velocity is expressed as the depth average of total velocity analysis indicates that surface tide pressure is best expressed as the depth average of total pressure plus a new depth dependent profile of pressure which is due to isopycnal heaving by movement of the free surface internal tide velocity and pressure are defined as total variables minus the surface tide components corresponding surface and internal tide energy equations are derived that contain energy conversion solely through topographic internal tide generation the depth structure of internal tide energy flux produced by the new decomposition is unambiguous and differs from that of past decompositions numerical simulations over steep topography reveal that the decomposition is self consistent and physically relevant analysis of observations over kaena ridge hawaii and the oregon continental slope indicate o 50 w m 1 error in depth integrated energy fluxes when internal tide pressure is computed as the residual of pressure from its depth average while these errors are small at major internal tide generation sites they may be significant where surface tides are larger and depth integrated fluxes are weaker e g over continental shelves

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

low mode internal tides and balanced dynamics disentanglement in altimetric observations synergy with surface density observations the performance of a tentative method that disentangles the contributions of a low mode internal tide on sea level from that of the balanced mesoscale eddies is examined using an idealized high resolution numerical simulation this disentanglement is essential for proper estimation from sea level of the ocean circulation related to balanced motions the method relies on an independent observation of the sea surface water density whose variations are 1 dominated by the balanced dynamics and 2 correlate with variations of potential vorticity at depth for the chosen regime of surface intensified turbulence the surface density therefore leads via potential vorticity inversion to an estimate of the balanced contribution to sea level fluctuations the difference between instantaneous sea level presumably observed with altimetry and the balanced estimate compares moderately well with the contribution from the low mode tide application to realistic configurations remains to be tested these results aim at motivating further developments of reconstruction methods of the ocean dynamics based on potential vorticity dynamics arguments in that context they are particularly relevant for the upcoming wide swath high resolution altimetric missions swot

a regional model of the semidiurnal internal tide on the australian north west shelf a fully three dimensional nonlinear primitive equation model is applied to a study of the semidiurnal internal tide on the australian north west shelf a region of strong barotropic and baroclinic tide the model shows a significant internal tide over most of the continental slope region predominantly between 100 and 1000 m depths energy flux is highly variable with regions of onshore flux and regions of offshore flux corresponding to regions of subcritical and supercritical seabed slopes a comparison between the model and detailed observations from one region shows reasonable agreement in vertical displacement currents and depth integrated energy flux the comparison also highlights the difficulty in obtaining appropriate observations to provide a rigorous verification of internal tide models the m2 and s2 internal tides show similar patterns of flow with energy in the s2 internal tide about 25 of that in the m2 constituent estimates of the total baroclinic m2 energy are about 2 2 gw for the north west shelf nearly an order of magnitude larger than suggested by earlier studies this represents about 5 of the dissipation of the m2 barotropic tide in the model domain the seasonal variability in the baroclinic energy flux is about 20 from the mean the baroclinic energy extracted from the tide is expected to make a significant contribution to mixing in the region

internal tide generation at the continental shelf modeled using a modal decomposition two dimensional results abstract stratified flow over topography is studied with oceanic applications in mind a model is developed for a fluid with arbitrary vertical stratification and a free surface flowing over three dimensional topography of arbitrary size and steepness with background rotation in the linear hydrostatic regime the model uses an expansion of the flow fields in terms of a set of basis functions which efficiently capture the vertical dependence of the flow the horizontal structure may then be found by solving a set of coupled partial differential equations in two horizontal directions and time subject to simple boundary conditions in some cases these equations may be solved analytically but in general simple numerical procedures are required using this formulation the internal tide generated by a time periodic barotropic tidal flow over a continental shelf and slope is calculated in various idealized configurations the topography and fluid motion are taken to be independent of one coordinate di

propagation of internal tides generated near luzon strait observations from autonomous gliders 1 the vertical isopycnal displacements associated with internal waves generated by the barotropic tidal currents in the vicinity of luzon strait are estimated using measurements collected by autonomous underwater gliders nearly 23 000 profiles from seagliders and spray gliders collected during 29 different missions since 2007 are used to estimate the amplitude and phase of the linear semidiurnal and diurnal internal waves in this energetic region particularly in the previously poorly sampled area near the eastern ridge and on the pacific side of luzon strait the mean and variability of the internal wave field in the upper 1000 m of the water column are described the phase progression of internal waves as they propagate away from their generation sites is captured directly the glider based observations are used to map the mode 1 semidiurnal and diurnal internal wave fields providing the baroclinic energy flux over a roughly 600 km 800 km region based strictly on in situ observations

energetics of internal tides around the kerguelen plateau from modeling and altimetry a barotropic tidal model with a parameterization term to account for the internal wave drag energy dissipation is used to examine areas of possible m2 internal tide generation in the kerguelen plateau region barotropic energy flux and a distribution of wave drag dissipation are computed the results suggest important conversion of barotropic energy into baroclinic tide generation over the northern kerguelen plateau shelf break consistent with a theoretical criterion based on ocean stratification tidal forcing frequency and bathymetric gradients the sea surface height signatures of time coherent internal tides are studied using topex poseidon and jason 1 altimeter data whose ascending tracks cross nearly perpendicular to the eastern and western kerguelen plateau shelf break oscillations of a few centimeters associated with phase locked internal tides propagate away fromthe plateau over distances of several hundred kilometers with a 110 km wavelength when reaching the frontal area of the antarctic circumpolar current the internal tide cannot be identified because of the aliasing of mesoscale variability into the same alias band as m2 finally using altimeter data we estimate the m2 barotropic tidal power converted through the internal tide generation process we find consistent values with the barotropic model parameterization estimation which is also in good agreement with global internal tide model estimates combined with modeling this study has shown that altimetry can be used to estimate internal tide dissipation

barotropic and baroclinic tides in the central north pacific ocean determined from long range reciprocal acoustic transmissions abstract travel times of reciprocal 1000 km range acoustic transmissions determined from the 1987 reciprocal tomography experiment are used to study barotropic tidal currents and a large scale coherent baroclinic tide in the central north pacific ocean the difference in reciprocal travel times determines the tidal currents while the sum of reciprocal travel times determines the baroclinic tide displacement of isotachs or equivalently isotherms the barotropic tidal current accounts for 90 of the observed differential travel time variance the measured harmonic constants of the eight major tidal constituents of the barotropic tide and the constants determined from current meter measurements agree well with the empirical numerical tidal models of schwiderski and cartwright et al the amplitudes and phases of the first mode baroclinic tide determined from sum travel times agree with those determined from moored thermistors and current meters the baroclinic tidal signals are consistent with a large

tidal conversion at a submarine ridge the radiative flux of internal wave energy the tidal conversion powered by the oscillating flow of a uniformly stratified fluid over a two dimensional submarine ridge is computed using an integral equation method the problem is characterized by two nondimensional parameters a and b the first parameter a is the ridge half width scaled by h where h is the uniform depth of the ocean far from the ridge and is the inverse slope of internal tidal rays horizontal run over vertical rise the second parameter b i s the ridge height scaled by h two topographic profiles are considered a triangular or tent shaped ridge and a polynomial ridge with continuous topographic slope for both profiles complete coverage of the a b parameter space is obtained by reducing the problem to an integral equation which is then discretized and solved numerically it is shown that in the supercritical regime ray slopes steeper than topographic slopes the radiated power increases monotonically with b and decreases monotonically with a in the subcritical regime the radiated power has a complicated and nonmonotonic dependence on these parameters as a 0 recent results are recovered for the tidal conversion produced by a knife edge barrier it is shown analytically that the a 0 limit is regular if a 1 the reduction in tidal conversion below that at a 0 is proportional to a 2 further the knife edge model is shown to be indicative of both conversion rates and the structure of the radiated wave field over a broad region of the supercritical parameter space as a increases the topographic slopes become gentler and at a certain value of a the ridge becomes critical that is there is a single point on the flanks at which the topographic slope is equal to the slope of an internal tidal beam the conversion decreases continuously as a increases through this transition visualization of the disturbed buoyancy field shows prominent singular lines tidal beams in the case of a triangular ridge these beams originate at the crest of the triangle in the case of a supercritical polynomial ridge the beams originate at the shallowest point on the flank at which the topographic slope equals the ray slope

prediction of m2 tidal surface currents by a global baroclinic ocean model and evaluation using observed drifter trajectories global m2 tidal surface currents are predicted using a global baroclinic ocean model with horizontal grid spacing of 1 12 and 19 z levels in the vertical after first showing the predicted tidal elevations are in reasonable agreement with observations made by bottom pressure recorders and altimeters the predicted tidal surface currents are evaluated by comparing them with independent estimates based on observed drifter trajectories both predicted and observed tidal surface currents can exceed 0 1 m s 1 in the deep ocean internal tides are shown to make a significant contribution to the predicted tidal surface currents phase locking of the surface and internal tides causes spatial changes in the predicted tidal surface currents that vary with approximately the same wavenumber as that of the lowest mode internal tide qualitatively similar small scale variations are also detected in the observed estimates but the variations do not line up exactly with the predictions possible explanations for the mismatch are given the seasonal variation of m2 tidal surface currents and the energy conversion rate from surface to internal tides is also predicted by initializing and restoring the model to an observed seasonal climatology of temperature and salinity compared to tidal elevation the seasonal change of tidal surface current can be large order 10 for each hemisphere it is caused by seasonal variations in the vertical structure of the baroclinic modes and the energy conversion rate in the vicinity of major bathymetric features the seasonal variation of second and higher order modes can be much larger up to 50

observations of strong mid pacific internal tides above horizon guyot abstract large semidiurnal current and isotherm oscillations were observed by one current meter continuously for 9 months in the waters above horizon guyot a seamount located in the central pacific the m2 tides dominated the current meter record the m2 current ellipse was oriented along 142 the semi major amplitude was 7 6 cm s 1 and the currents rotated in a clockwise direction the m2 isotherm deflection amplitude was 20 m the m2 currents observed above the guyot were two to three times larger than m2 currents either observed in or predicted for this region of the mid pacific evidence suggests that the semidiurnal tide was predominantly an internal tide that was generated at the guyot the observed internal tide had a narrow bandwidth and a constant amplitude and phase for 9 months and had characteristics similar to a vertically propagating rather than a vertically standing internal wave

scattering of low mode internal tides at a continental shelf abstracta series of laboratory experiments are performed to investigate the scattering of low mode internal tides at a continental shelf by varying the criticality parameter and normalized topograp

baroclinic tidal sea level from exact repeat mission altimetry abstracta near global model for the sea surface expression of the baroclinic tide has been developed using exact repeat mission altimetry the methodology used differs in detail from other altimetr

first results from a marine controlled source electromagnetic survey to detect gas hydrates offshore oregon 1 submarine gas hydrate is a hazard to drilling a potential hydrocarbon resource and has been implicated as a factor in both submarine slope stability and climate change bulk in situ electrical resistivities evaluated from electromagnetic surveys have the potential to provide an estimate of the total hydrate volume fraction more directly than by using seismic and well log data we conducted a marine controlled source electromagnetic sounding at hydrate ridge oregon usa in august 2004 electromagnetic fields transmitted by a deep towed horizontal electric dipole source were measured by a linear array of 25 seafloor electromagnetic receivers positioned 600 m apart to produce a dense coverage in the recorded electric field data results are presented in simple form by apparent resistivity pseudosections which produce an approximate image of lateral resistivity variations across the study region resistivity values are consistent with those from well logs collected in the area and pseudosection features are correlated with seismic reflectors archie s law based on pseudosection apparent resistivities predicts volumetric hydrate concentrations vary from 0 30 across the ridge

global baroclinic tides an approximate estimate of the energy in the first mode m2 baroclinic tide has been made from satellite observations results based on topex poseidon t p precision altimetry indicate that the internal tide patterns are similar to those expected from mid ocean topographic features in the global oceans both the orthotide and harmonic analyses indicate that the total energy in global m2 baroclinic tide is approximately 50 pj for a variety of reasons m2 is the only component that can be obtained reliably from altimetric measurements even then the energy value may be an underestimate and the energy flux the dissipation rate cannot be deduced from altimetry since it is the tidal currents flowing over mid ocean topographic features that are responsible for generating internal tides a model calibrated by m2 observations is a plausible alternative currents from a high resolution 15 barotropic tidal model have therefore been used to obtain an estimate of both the energy and the dissipation rate in m2 s2 and k1 baroclinic tides a simple model of baroclinic tide generation has been used and the unknown constant in this model has been selected to yield a total energy of 50 pj in the first mode m2 baroclinic tide based on this calibration the total energy is 8 pj in s2 first mode baroclinic tide and 15 pj in k1 the total in all first mode baroclinic tides is 90 pj about 16 of the total energy 580 pj in barotropic tides the model results also suggest that about 360 gw of tidal energy are dissipated in m2 baroclinic tides alone and 520 gw are dissipated in all first mode baroclinic tides the latter value is approximately 15 of the power input into barotropic ocean tides 3490 gw by the lunisolar tidal forces we have preferred to be conservative and hence these are likely to be underestimates especially since the altimetric tracks do not often intersect mid ocean topographic features at optimum angles while these values are very much within the range of earlier estimates in literature they should be regarded as still uncertain to perhaps a factor of two the dissipation rate could be anywhere from 400 gw to 800 gw the most likely value being about 600 gw the small signal to noise ratio involved in altimetric measurements of the surface manifestation of internal tides and potential contamination by mesoscale signals are serious problems in situ measurements at least a few locations underneath altimetric tracks are essential for confirmation and or refinement of these preliminary estimates hopefully these very first estimates of the energy and dissipation rate in global baroclinic tides though rather crude will serve as a catalyst for a better estimation in the future since internal tides are likely to be a prominent source of mixing in the deep oceans and important to thermocline maintenance

internal tides observed at 2 s 156 e by in situ and topex poseidon data during the coupled ocean atmosphere response experiment coare during the enhanced monitoring phase of the coupled ocean atmosphere experiment coare semidiurnal baroclinic tides were observed at 2 s 156 e 1739 m depth the tropical atmosphere ocean tao mooring outfitted with additional sensors from surface to bottom provides an interesting tool for describing the internal tides m2 s2 and n2 baroclinic components were detected explaining 59 of the semidiurnal variance on surface dynamic height at the semidiurnal frequency vertical displacements of isopycnals highly variable in time can reach 30 m and are mostly a combination of the m2 s2 and n2 internal waves the two first baroclinic modes explain 70 of the variance in vertical displacement m2 and s2 internal waves have different vertical structure m2 resembles the first baroclinic mode and s2 resembles the second baroclinic mode the m2 and s2 internal waves projected on their respective baroclinic mode are highly related to the modeled barotropic tide two topex poseidon tracks cross over the mooring every 10 days and the internal wave signature can be expected in sea level along the tracks despite the weakness of the signal sea level spectra along both ascending and descending tracks show the existence of energy around the 250 km and the 120 km wavelength respectively which is in accordance with a first baroclinic wave propagating northeastward as suggested in previous studies from wavelet transform the baroclinic tide signatures on the ascending descending track are centered around 2 5 s 3 5 s with a 1 2 latitudinal extension respectively limited to the ontong java plateau we confirm the northeastward propagation of the baroclinic tides and their source could be a series of islands parallel to the kilinailau trench or the large sloping topography between the kilinailau trench and the ontong java plateau

mapping low mode internal tides near hawaii using topex poseidon altimeter data 1 objective maps of m2 internal tide variability are derived from topex poseidon altimeter data obtained near the hawaiian ridge an estimate of the wavenumber spectrum shows that the radiation is dominated by a few spectral peaks at wavenumbers consistent with the theoretically expected value for mode 1 internal tides the data are not always consistent with the traveling wave model because the spacing of the altimeter tracks is larger than the internal tide wavelength the objective map underestimates the energy between the altimeter tracks with this caveat the maps are used to determine that 2 6 gw of power is radiated from a 1700 km section of the hawaiian ridge time series of hydrographic data obtained at the hot site north of oahu hawaii show that changes in mode 1 phase speed caused by variations in stratification have only a small effect on the propagation of the mode 1 internal tides

can oceanic submesoscale processes be observed with satellite altimetry high resolution 2 km and hourly observations of surface currents from high frequency radars are analyzed in terms of sea level anomalies sla and compared with data from two satellite altimeter ground tracks purpose is to investigate whether ocean submesoscale processes can be observed with satellite altimetry our results highlight two major problems that must be overcome before being able to resolve submesoscale processes with altimetry i signal contamination from high frequency motions and in particular from incoherent internal tides near inertial oscillations have no effect on sla and ii measurement noise which prevents the computation of accurate cross track currents on scales o 10 km the latter may be overcome by future satellite altimeter missions but the former will require taking into account the effect of mesoscale variability on internal tide propagation in regions where internal tides are significant citation chavanne c p and p klein 2010 can oceanic submesoscale processes be observed with satellite altimetry geophys res lett 37 l22602 doi 10 1029 2010gl045057

surface manifestation of internal tides generated near hawaii analysis of topex poseidon satellite altimetry reveals short wavelength fluctuations in the ocean surface tide that are attributable to internal tides a significant fraction of the semidiurnal internal tide generated at the hawaiian ridge is evidently phase locked to the astronomical potential and can modulate the amplitude of the surface tide by 5 cm the internal tide is thus easily mapped along satellite groundtracks and it is found to be spatially coherent over great distances with waves propagating well over 1000 km from the hawaiian ridge before decaying below noise level both first and second baroclinic modes are observed in both the m 2 lunar and s 2 solar tides the high space time coherence is in sharp contrast to what is often inferred from current meter observations but it confirms recent speculations from an acoustic experiment north of hawaii

global observations of open ocean mode 1 m2internal tides abstracta global map of open ocean mode 1 m2 internal tides is constructed using sea surface height ssh measurements from multiple satellite altimeters during 1992 2012 representing a 20 yr coherent internal tide field a two dimensional plane wave fit method is employed to 1 suppress mesoscale contamination by extracting internal tides with both spatial and temporal coherence and 2 separately resolve multiple internal tidal waves global maps of amplitude phase energy and flux of mode 1 m2 internal tides are presented the m2 internal tides are mainly generated over topographic features including continental slopes midocean ridges and seamounts internal tidal beams of 100 300 km width are observed to propagate hundreds to thousands of kilometers multiwave interference of some degree is widespread because of the m2 internal tide s numerous generation sites and long range propagation the m2 internal tide propagates across the critical latitudes for parametric subharmonic instability 28 8 s n

on the spring neap variability and age of the internal tide at the hawaiian ridge 1 observations and modeling have shown that an energetic m2 internal tide is generated by tidal flow over the hawaiian ridge this paper presents numerical results that explore the variability of the internal tide over the spring neap cycle resulting from the combination of m2 and s2 constituents the spring neap cycle is simulated from a superposition of separate model runs for m2 and s2 and from longer model runs with combined m2 and s2 forcing there are only small differences between the two methods indicating that at tidal frequencies and the 4 km model resolution the system is approximately linear energy fluxes at spring tides are substantially stronger than the sum of m2 and s2 fluxes suggesting strong contrast from spring to neap tides in energy available for mixing the baroclinic currents vary in amplitude over the spring neap cycle by approximately 50 but tidal beams maintain their overall structure the time of maximum spring amplitudes relative to the astronomical forcing is examined in terms of the age of the tide near the ridge where the internal tide is generated the age is the same as that of the barotropic tidal currents which is approximately 1 day older than the barotropic surface elevation the age of the internal tide is approximately 1 day along the ridge and increases moving away from the ridge consistent with the group velocity of the internal waves hence away from the ridge spring internal tides may occur 2 or 3 days after spring tidal elevations at the ridge

arecibo s thermospheric gravity waves and the case for an ocean source 1 wave like disturbances in electron density ne have been observed in the thermosphere above arecibo observatory puerto rico throughout its 45 year history however only recently has it become evident that these waves are continuously present in the arecibo thermosphere the wave characteristics are fairly constant between day and night and from season to season high resolution electron density measurements obtained by applying the coded long pulse radar technique to photoelectron enhanced langmuir waves are presented these new observations strongly suggest that the perturbations in electron density are the result of internal acoustic gravity waves agws propagating through the arecibo thermosphere the agws appear to be broadbanded in wave number space the downward phase trajectories of ne ne between 400 and 120 km combined with the low horizontal phase velocities obtained from airglow measurements support the idea that the agws are not ducted but rather are locally produced in addition the altitudes at which major peaks in ne ne are observed follow theoretical estimates for nonducted waves the nominal period of the agws is 60 min at 250 km altitude but periods of 20 min are also evident at lower attitudes classic sources of agws do not appear to be consistent with the arecibo observations of a continuous flux of background agws ray tracing of the agws combined with 630 0 nm airglow observations point to a source location in the atlantic ocean that is roughly 2100 km east northeast of arecibo internal ocean waves generated in response to the internal tide at the mid atlantic ridge are the most likely source of arecibo s thermospheric agws

structure and variability of semidiurnal internal tides in mamala bay hawaii 1 moored current meter and temperature observations and results from a three dimensional primitive equation model are used to examine the energetic semidiurnal internal tides present in mamala bay on the south coast of oahu hawaii the steady harmonic component of the internal tide is characterized by large vertical displacements in the central region of the bay 35 m amplitude for the m2 constituent and enhanced alongshelf baroclinic currents at the headlands on either end of the bay 0 27 m s 1 seasonal changes in amplitude and phase are observed the model captures the qualitative spatial structure of the observations baroclinic energy flux estimates from the mooring observations and the numerical simulations suggest that internal tide energy propagates into the bay and does not originate within the bay the model indicates that internal wave generation occurs over the flanks 500 1000 m depth of the ridge predominantly on the east side with perhaps some additional contribution on the west from an energetic internal tide generated north of oahu wave superposition is believed to account for the alongshelf spatial structure of currents and displacements incoherent modulations of the internal tide occur that are not related to local changes in stratification at least on superannual timescales factors contributing to this signal may include stratification variations at the deep generation sites mesoscale activity and or the shoaling of a random internal wave field into the bay from the open ocean

model estimates of m2 internal tide energetics at the hawaiian ridge 1 a primitive equation model is used to examine the structure and energetics of m 2 internal tides generated at the hawaiian ridge recent estimates based on altimeter data suggest that 20 gw of barotropic tidal dissipation occurs at the ridge with conversion to internal tides believed to be the dominant dissipation mechanism the model simulates an internal tide that accounts for 9 7 gw of radiated energy away from the ridge in the northeast and southwest directions the strongest generation occurs at three sites where enhanced barotropic currents flow across elongated topographic features the depth integrated baroclinic energy flux and energy densities at these sites are on the order of 10 4 w m 1 and 10 4 j m 2 respectively a modal decomposition indicates that 62 of the outgoing energy flux is accounted for by the first internal mode 15 is accounted for by the second mode and less than 5 is accounted for by each subsequent higher mode the tidal dissipation due to bottom friction along the ridge is estimated to be 0 1 gw the level of turbulent dissipation near the ridge owing to tidal energy conversion remains to be determined to assess fully the barotropic baroclinic energy budget

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

the surface expression of semidiurnal internal tides near a strong source at hawaii part i observations and numerical predictions abstract observations of semidiurnal currents from high frequency radio doppler current meters and moored acoustic doppler current profilers adcps in the kauai channel hawaii are described and compared with two primitive equation numerical models of the tides the kauai channel separating the islands of oahu and kauai is a site of strong internal tide generation by the barotropic tides flowing over kaena ridge the subsurface extension of oahu the nature and impacts of internal tide generation in the kauai channel were intensively studied during the 2002 03 near field component of the hawaii ocean mixing experiment comparisons of observed coherent i e phase locked to the astronomical forcing m2 and s2 surface currents with model predictions show good agreement for the phases indicating propagation of internal tides away from the ridge although the predicted m2 and s2 surface currents are similar except for their magnitudes as expected for internal waves at periods closer to each other 12

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

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 high resolution assimilating tidal model for the northeast pacific ocean a high resolution nonlinear barotropic finite element tidal model is developed for removing tidal elevations from satellite altimeter observations in the northeast pacific ocean surface elevations and currents for the constitutents m2 s2 n2 k2 k1 o1 p1 and q1 are computed using boundary forcing from the oregon state university global tidal model tpxo 3 and the effects of the tidal potential earth tide and ocean self attraction and loading amplitudes and phases computed from the harmonic analyses of altimeter time series at crossover locations along the tracks of the topex poseidon satellite are assimilated into the model and the corrected harmonics are compared with pelagic and coastal tide and pressure gauge measurements and with the tpxo 3 and fes95 2 1 global models diurnal tidal currents along the british columbia and alaska continental shelves are shown to be strongly influenced by the presence of continental shelf waves the surface manifestation of these waves is clearly evident in k1 coamplitude plots k1 and m2 energy fluxes are calculated along these shelves and the potential generation of internal tides is discussed barotropic tidal dissipation is estimated in several key subregions and the m2 total for the gulf of alaska is found to be approximately half that of previous estimates

a perfect focus of the internal tide from the mariana arc 1 the mariana arc of ridges and islands forms an 1300 km long arc of a circle 630 km in radius centered at 17 n 139 6 e the hypothesis that the westward propagating internal tides originating from the arc converge in a focal region is tested by examining the dominant m2 internal tides observed with air launched expendable bathythermographs axbts and altimetric data from multiple satellites the altimetric and axbt observations agree well though they measure different aspects of the internal tidal motion m2 internal tides radiate both westward and eastward from the mariana arc with isophase lines parallel to the arc and sharing the same center the westward propagating m2 internal tides converge in a focal region and diverge beyond the focus the focusing leads to energetic m2 internal tides in the focal region the spatially smoothed energy flux is about 6 5 kw m about four times the mean value at the arc the spatially un smoothed energy flux may reach up to 17 kw m the size of the focus is close to the rayleigh estimate it is thus a perfect focus

vertical structure of the baroclinic tides in the central north pacific subtropical gyre abstract cruises are made monthly to the world ocean circulation experiment deep water station about 100 km north of oahu hawaii during these cruises the principal causes of variability in dynamic height are the internal tides having a range about 30 of the annual range in dynamic height the internal tides have peak to peak vertical displacements of up to 30 dbar but show little vertical coherence at the diurnal frequencies modal fits typically require 6 8 baroclinic modes to account for 90 of the variance suggesting that the diurnal tide should not be described in terms of dynamic modes the semidiurnal tide has about two to three times the amplitude of the diurnal tide and shows more vertical phase coherence but still requires three or four modes to describe it generally the dominant mode is the second or third mode

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

internal tide generation along the south scotia ridge abstract the generation of semidiurnal internal tides along the south scotia ridge ssr the boundary between the northern weddell sea and the scotia sea is investigated using a fully three dimensional primitive equation numerical model the sensitivity of the model to changes in horizontal and vertical grid spacing stratification and choice of bathymetric data set is discussed the highest resolution model 1 16 1 25 41 levels with realistic stratification produces an average along ridge lateral baroclinic m2 energy flux magnitude j m2 160 w m 1 for the section of the ssr between the tip of the antarctic peninsula and the south orkney plateau this value is 10 to time averaged open water fraction thus baroclinic tides may play a significant role in setting mean heat and freshwater exchange and ice formation in the northern weddell sea

indirect evidence for substantial damping of low mode internal tides in the open ocean a global high resolution ocean circulation model forced by atmospheric fields and the m2 tidal constituent is used to explore plausible scenarios for the damping of low mode internal tides the plausibility of different damping scenarios is tested by comparing the modeled barotropic tides with tpxo8 a highly accurate satellite altimetry constrained tide model and by comparing the modeled coherent baroclinic tide amplitudes against along track altimetry five scenarios are tested 1 a topographic internal wave drag argued here to represent the breaking of unresolved high vertical modes applied to the bottom flow default configuration 2 a wave drag applied to the barotropic flow 3 absence of wave drag 4 a substantial increase in quadratic bottom friction along the continental shelves with wave drag turned off and 5 application of wave drag to the barotropic flow at the same time that quadratic bottom friction is substantially increased along the shelves of the scenarios tested here the default configuration 1 yields the most accurate tides in all other scenarios 2 5 the lack of damping on open ocean baroclinic motions yields baroclinic tides that are too energetic and travel too far from their sources despite the presence of a vigorous mesoscale eddy field which can scatter and decohere internal tides in the model the barotropic tides are also less accurate in the absence of an open ocean damping on barotropic motions that is in scenarios 3 and 4 the results presented here suggest that low mode internal tides experience substantial damping in the open ocean

a coupled model for laplace s tidal equations in a fluid with one horizontal dimension and variable depth abstracttide topography interactions dominate the transfer of tidal energy from large to small scales at present it is poorly understood how low mode internal tides reflect and scatter along the continental margins here the coupling equations for linear tides model celt are derived to determine the independent modal solutions to laplace s tidal equations lte over stepwise topography in one horizontal dimension celt is i applicable to arbitrary one dimensional topography and realistic stratification without requiring numerically expensive simulations and ii formulated to quantify scattering because it implicitly separates incident and reflected waves energy fluxes and horizontal velocities obtained using celt are shown to converge to analytical solutions indicating that flat bottom modes which evolve according to lte are also relevant in describing tides over sloping topography the theoretical framework presented can then be used to quantify simultaneous incident and reflected energy fl

using an altimeter derived internal tide model to remove tides from in situ data internal waves at tidal frequencies i e the internal tides are a prominent source of variability in the ocean associated with significant vertical isopycnal displacements and currents because the isopycnal displacements are caused by ageostrophic dynamics they contribute uncertainty to geostrophic transport inferred from vertical profiles in the ocean here it is demonstrated that a newly developed model of the main semidiurnal m2 internal tide derived from satellite altimetry may be used to partially remove the tide from vertical profile data as measured by the reduction of steric height variance inferred from the profiles it is further demonstrated that the internal tide model can account for a component of the near surface velocity as measured by drogued drifters these comparisons represent a validation of the internal tide model using independent data and highlight its potential use in removing internal tide signals from in situ observations

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

nonstationary internal tides observed using dual satellite altimetry abstractdual satellite crossover data from the jason 2 and cryosat 2 altimeter missions are used in a novel approach to quantify stationary and nonstationary tides from time lagged mean square sea surface height ssh differences computed for lags from 1 to 1440 h 60 days the approach is made feasible by removing independent estimates of the stationary tide and mesoscale ssh variance which greatly reduces the sampling error of the ssh statistics for the semidiurnal tidal band the stationary tidal variance is approximately 0 73 cm2 and the nonstationary variance is about 0 33 cm2 or 30 of the total the temporal correlation of the nonstationary tide is examined by complex demodulation and found to be oscillatory with first 0 crossing at 400 h 17 days because a significant fraction of the time variable mesoscale signal is resolved at time scales of roughly 150 h by the present constellation of satellite altimeters the results suggest that it may be feasible to predict the nonstationary tide fr

long range propagation and associated variability of internal tides in the south china sea the variability of internal tides during their generation and long range propagation in the south china sea scs is investigated by driving a high resolution numerical model the present study clarifies the notably different processes of generation propagation and dissipation between diurnal and semidiurnal internal tides internal tides in the scs originate from multiple source sites among which the luzon strait is dominant and contributes approximately 90 and 74 of the baroclinic energy for m2 and k1 respectively to the west of the luzon strait local generation of k1 internal tides inside the scs is more energetic than the m2 tides diurnal and semidiurnal internal tides from the luzon strait radiate into the scs in a north south asymmetry but with different patterns because of the complex two ridge system the tidal beams can travel across the deep basin and finally arrive at the vietnam coast and nansha island more than 1000 1500 km away during propagation m2 internal tides maintain a southwestward direction whereas k1 exhibit complicated wave fields because of the superposition of waves from local sources and island scattering effects after significant dissipation within the luzon strait the remaining energy travels into the scs and reduces by more than 90 over a distance of 1000 km inside the scs the k1 internal tides with long crests and flat beam angles are more influenced by seafloor topographical features and thus undergo apparent dissipation along the entire path whereas the prominent dissipation of m2 internal tides only occurs after their arrival at zhongsha island this article is protected by copyright all rights reserved

internal tide radiation from the luzon strait the m2 k1 and o1 internal tides originating in the luzon strait are investigated using the sea surface height measurements by multiple satellites ers 2 envisat topex poseidon jason 1 2 and geosat follow on a plane wave fit method is used to resolve multiple internal tides in arbitrary horizontal directions the luzon strait is an energetic internal tide generation site and radiates internal tides both westward into the south china sea scs and eastward into the western pacific wp in the scs the k1 and o1 internal tides propagate over 1600 km reaching the vietnam coast in the wp they propagate over 2500 km and arrive to the mariana ridge and guam the k1 and o1 internal tides refract toward the equator during propagation the m2 internal tides in the scs bifurcate into two beams the northwestward beam is coincident with the frequent occurrence of internal solitary waves in this region implying their causative relation the phase speeds inferred from the altimetric along beam propagation agree with the theoretical values due to the influence of the earth s rotation the k1 and o1 phase speeds decrease remarkably from high to low latitudes for the diurnal internal tides the eastward radiation is about 50 greater than the westward radiation for m2 the westward radiation is about two times the eastward radiation the altimetric energy fluxes are about 50 of those in numerical model simulations

oceanic tides from geosat altimetry direct tidal analysis of the altimetry from the geosat exact repeat mission s first year is used to derive estimates of the diurnal and semidiurnal oceanic tides the geoid is removed by collinear differences at 34 1 day separation and the orbit error is reduced by subtracting a slowly modulated 1 cycle revolution term a sequence of independent analyses at grid areas of 1 latitude 1 5 longitude using orthotide functions ensures complete definition of the diurnal and semidiurnal species global admittance maps for m2 and s2 within the latitudes 58 n and 59 s compare well with ground truth at 66 open ocean sites maps of differences between geosat and the naval surface weapons center model show important areas of the order of 10 15 cm the integral for the global power input from the moon gives 2 51 tw m2 0 44 tw s2 lower than many previous estimates but in agreement with figures deduced from a recent analysis of satellite orbits

time variable refraction of the internal tide at the hawaiian ridge abstractthe interaction of the dominant semidiurnal m2 internal tide with the large scale subtidal flow is examined in an ocean model by propagating the tide through an ensemble of background fields in a domain centered on the hawaiian ridge the background fields are taken from the simple ocean data assimilation soda ocean analysis at 2 month intervals from 1992 through 2001 tides are computed with the primitive equation z coordinate harmonic analysis of tides pez hat model by 14 day integrations using soda initial conditions and m2 tidal forcing variability of the tide is found to occur primarily as the result of propagation through the nonstationary background fields rather than via generation site variability generation of incoherent tidal variability is mapped and shown to occur mostly in association with waves generated at french frigate shoals scattering near the musicians seamounts to the north of the ridge the phase coherent internal tide loses energy at a domain average rate of 2 mw m

semidiurnal baroclinic wave momentum fluxes at kaena ridge hawaii abstractkaena ridge hawaii is a site of energetic conversion of the semidiurnal barotropic tide diffuse baroclinic wave beams emanate from the critical slope regions near the ridge crest directed upward and southward from the north flank of the ridge and upward and northward from the south flank here the momentum fluxes associated with generation at the ridge are estimated continuous vertical profiles of density and velocity from 80 to 800 m were obtained from the research platform floating instrument platform flip over the southern edge of the ridge as an aspect of the hawaii ocean mixing experiment data are used to estimate the reynolds stress eulerian buoyancy flux and the combined eliassen palm flux in the semidiurnal band an upward southward stress maximum of 0 5 10 4 m2 s 2 appears at depths of 300 500 m generally consistent with beam like behavior a strong off ridge buoyancy flux 0 3 10 4 m2 s 3 combines with large along ridge reynolds stresses to form an eliassen palm flux

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