the unpredictable nature of internal tides on continental shelves abstractpackets of nonlinear internal waves nliws in a small area of the mid atlantic bight were 10 times more energetic during a local neap tide than during the preceding spring tide this counterintuitive result cannot be explained if the waves are generated near the shelf break by the local barotropic tide since changes in shelfbreak stratification explain only a small fraction of the variability in barotropic to baroclinic conversion instead this study suggests that the occurrence of strong nliws was caused by the shoaling of distantly generated internal tides with amplitudes that are uncorrelated with the local spring neap cycle an extensive set of moored observations show that nliws are correlated with the internal tide but uncorrelated with barotropic tide using harmonic analysis of a 40 day record this study associates steady phase motions at the shelf break with waves generated by the local barotropic tide and variable phase motions with the shoaling of distantly generated internal tides

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

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

small and mesoscale processes and their impact on the large scale an introduction abstract great progress has been made in understanding the role of small and mesoscale processes on the large scale structure and circulation of the oceans however many questions remain regarding the sensitivity of the large scale ocean circulation and hence the earth s climate to rates of stirring mixing and dissipation supported by ocean eddies internal waves and boundary layers although such relatively small scale oceanic phenomena are ubiquitous we lack detailed knowledge about their interaction with the large scale motions as well as their interactions amongst themselves contributions are presented from observational theoretical and modeling studies that focus on small and mesoscale ocean processes and some parameterizations of these processes for use in studies of the large scale circulation the range of topics is relatively broad with most focus on internal wave generation flow topography interaction and small and mesoscale processes involved in ocean mixing general conclusions emphasize the notion of localized mixing and the importance of interaction between waves eddies and topography and the importance of interactions between oceanic motions and the background density stratification

observations of the semidiurnal internal tide on the southern california slope and shelf 1 we give a detailed description of the semidiurnal band current and temperature variability observed during the internal waves on the continental margin iwaves field experiments of 1996 and 1997 off of mission beach california this variability was dominated by the internal tide and the structure of the internal tide on the slope and shelfbreak region was different from that on the narrow shelf on the slope and shelfbreak the internal tide was dominated by alongshore propagating coastal trapped waves in this region semidiurnal band currents were predominantly oriented in the alongshore direction in the lower half of the water column at a water depth h of 350 m current and temperature variability were consonant with a short wavelength 8 km bottom trapped wave propagating in the alongshore direction to the north in the upper 120 m of the water column above the depth of the shelfbreak slope and shelfbreak currents were highly coherent with a zero phase lag that is there was no phase propagation in the cross shore direction on the narrow 10 km shelf cross shore currents u were much more energetic than on the slope and had the structure of a mode one internal wave the alongshore currents v decreased monotonically from the surface to the bottom of the water column with a phase that did not change with depth the near bottom u signal propagated toward the coast during all mooring deployments faster in the summer than in the fall the near bottom u and mid column temperature relative phase was neither consistent with a purely progressive nor a purely standing mode one internal wave we conclude that the internal tide on the shelf was partially reflected

the impact of subtidal circulation on internal tide generation and propagation in the philippine sea abstractthis study examines the effects of the subtidal circulation on the generation and propagation of the m2 internal tide in the philippine sea using a primitive equation model barotropic to baroclinic conversion at the luzon strait is found to vary due to the background circulation changes over the generation site and the changing influence of remotely generated internal tides from the mariana arc the varying effect of remotely generated waves results from both changing generation energy levels at the mariana arc and variability in the propagation of the internal tides across the philippine sea the magnitude and direction of the depth integrated baroclinic energy fluxes vary temporally due to a combination of changing generation propagation and dissipation spatial patterns of internal tide propagation near the luzon strait are influenced by the locations of mesoscale eddies to the east and west of the strait the results provide insight into the mechanisms of variability of the baroclinic tide

incoherent signature of internal tides on sea level in idealized numerical simulations the nonpersistent phase relationship between internal tides and astronomical forcings also known as incoherence has been identified as a major question in the context of future wide swath satellite altimetry this study addresses this issue using a novel set of numerical experiments where a plane wave low mode internal tide propagates through a turbulent mesoscale eddy field these experiments demonstrate the emergence of internal tide incoherence as the eddy turbulence is strengthened in strongly turbulent situations the internal tide signature on sea level forms complex interference patterns with large amplifications of the initial internal wave these patterns evolve more rapidly than the signature of the turbulent eddy field on sea level the implications of such idealized numerical simulations for wide swath altimetry are discussed

role of mesoscale eddies in modulating the semidiurnal internal tide observation results in the northern south china sea abstractthe role of mesoscale eddies in modulating the semidiurnal internal tide sit in the northern south china sea scs is examined using the data from a cross shaped mooring array from novem

baroclinic energy flux at the hawaiian ridge observations from the r p flip abstract estimates of baroclinic energy flux are made in the immediate nearfield september october 2002 and 450 km offshore farfield october november 2001 of the kaena ridge an active barotropic to baroclinic conversion site the flux estimates are based on repeated profiles of velocity and density obtained from the research platform floating instrument platform flip as an aspect of the hawaii ocean mixing experiment energetic beams associated with both semidiurnal and diurnal internal waves are observed in the kauai channel beam depths and orientations are consistent with generation along the upper flanks of the ridge at the far field site the baroclinic energy flux is borne primarily by first mode semidiurnal waves the energy flux associated with the entire spectrum of internal waves is computed by cross spectral analysis significant energy fluxes are found in the inertial diurnal semidiurnal and twice semidiurnal frequency bands the semidiurnal energy flux strongly dominates the s

global m 2 internal tide and its seasonal variability from high resolution ocean circulation and tide modeling 1 the present study describes a model simulation where ocean tide dynamics are simulated simultaneously with the ocean circulation the model is forced by a lunisolar tidal forcing described by ephemerides and by daily climatological wind stress heat and fresh water fluxes the horizontal resolution is about 0 1 and thus the model implicitly resolves meso scale eddies and internal waves in this model simulation the global m2 barotropic to baroclinic tidal energy conversion amounts to 1 2 tw we show global maps of the surface signature of the m2 baroclinic tide and compare it with an estimate obtained from 19 years of satellite altimeter data further the simulated seasonality in the low mode internal tide field is presented and as an example the physical mechanisms causing the non stationarity of the internal tide generated in luzon strait are discussed in general this study reveals the impact of inter annual changes of the solar radiative forcing and wind forced ocean circulation on the generation and propagation of the low mode internal tides the model is able to simulate non stationary signals in the internal tide field on global scales which have important implications for future satellite altimeter missions citation muller m j y cherniawsky m g g foreman and j s von storch 2012 global m2 internal tide and its seasonal variability from highresolution ocean circulation and tide modeling geophys res lett 39 l19607 doi 10 1029 2012gl053320

mapping shallow soil moisture profiles at the field scale using full waveform inversion of ground penetrating radar data full waveform inversions were applied to retrieve surface two layered and continuous soil moisture profiles from ground penetrating radar gpr data acquired in an 11 ha agricultural field situated in the loess belt area in central belgium the radar system consisted of a vector network analyzer combined with an off ground horn antenna operating in the frequency range 200 2000 mhz the gpr system was computer controlled and synchronized with a differential gps for real time data acquisition several inversion strategies were also tested using numerical experiments which in particular demonstrated the potentiality to reconstruct simplified two layered configurations from more complex continuous dielectric profiles as prevalent in the environment the surface soil moisture map obtained assuming a one layered model showed a global moisture pattern mainly explained by the topography while local moisture patterns indicated a line effect two layered and profile inversions provided consistent estimates with respect to each other and field observations showing significant moisture increases with depth however some discrepancies were observed between the measured and modeled gpr data in the higher frequency ranges mainly due to surface roughness effects which were not accounted for the proposed gpr method and inversion strategies showed great promise for high resolution real time mapping of soil moisture at the field scale

internal tide generation and destruction by shoaling internal tides 1 internal tide generation is usually predicted from local topography surface tides and stratification however internal tides are often observed to be unrelated to local spring neap forcing appearing intermittently in 3 5 day bursts here we suggest a source of this intermittency by illustrating how remotely generated shoaling internal tides induce first order changes in local internal tide generation theory numerical simulations and observations show that pressure perturbations associated with shoaling internal tides can correlate with surface tide velocities to generate or destroy internal tides where shoaling internal tides have random phase such as on the new jersey slope time averaged internal tide generation is unaffected but instantaneous internal tide generation varies rapidly altering internal tide energy and possibly affecting nonlinear internal waves across shelf transport and mixing where shoaling internal tides are phase locked to the local surface tide such as in double ridge systems time averaged internal tide generation is affected and may result in resonance

incoherent nature of m2 internal tides at the hawaiian ridge abstractmoored current temperature and conductivity measurements are used to study the temporal variability of m2 internal tide generation above the kaena ridge between the hawaiian islands of oahu and kauai the energy conversion from the barotropic to baroclinic tide measured near the ridge crest varies by a factor of 2 over the 6 month mooring deployment 0 5 1 1 w m 2 the energy flux measured just off the ridge undergoes a similar modulation as the ridge conversion the energy conversion varies largely because of changes in the phase of the perturbation pressure suggesting variable work done on remotely generated internal tides during the mooring deployment low frequency current and stratification fluctuations occur on and off the ridge model simulations suggest that these variations are due to two mesoscale eddies that passed through the region the impact of these eddies on low mode internal tide propagation over the ridge crest is considered it appears that eddy related changes in stratif

focusing of internal tides by near inertial waves the refraction of internal waves by lower frequency near inertial waves has been predicted theoretically but never observed before here we report observations of semi diurnal internal tides generated by the rough topography of the central indian ridge in the presence of a strong lower frequency near inertial wave field generated by a tropical storm the semi diurnal internal tide energy is trapped within upward propagating bands with a periodicity close to the inertial period a ray tracing model suggests that this trapping results from the internal tide refraction by the shear associated with near inertial waves this yields a strong increase of the internal tide energy and shear in space time regions where the background flow focuses the rays leading to the formation of caustics this mechanism may increase vertical mixing generated by baroclinic tides in the vicinity of mid ocean ridges in tropical regions

non stationary internal tides observed with satellite altimetry 1 temporal variability of the internal tide is inferred from a 17 year combined record of topex poseidon and jason satellite altimeters a global sampling of along track sea surface height wavenumber spectra finds that non stationary variance is generally 25 or less of the average variance at wavenumbers characteristic of mode 1 tidal internal waves with some exceptions the non stationary variance does not exceed 0 25 cm2 the mode 2 signal where detectable contains a larger fraction of non stationary variance typically 50 or more temporal subsetting of the data reveals interannual variability barely significant compared with tidal estimation error from 3 year records comparison of summer vs winter conditions shows only one region of noteworthy seasonal changes the northern south china sea implications for the anticipated swot altimeter mission are briefly discussed

propagation of low mode internal waves through the ocean abstract the baroclinic tides play a significant role in the energy budget of the abyssal ocean although the basic principles of generation and propagation are known a clear understanding of these phenomena in the complex ocean environment is only now emerging to advance this effort a ray model is developed that quantifies the effects of spatially variable topography stratification and planetary vorticity on the horizontal propagation of internal gravity modes the objective is to identify baroclinic shoals where wave energy is spatially concentrated and enhanced dissipation might be expected the model is then extended to investigate the propagation of internal waves through a barotropic mesoscale current field the refraction of tidally generated internal waves at the hawaiian ridge is examined using an ensemble of mesoscale background realizations derived from weekly ocean topography experiment topex poseidon altimetric measurements the path of mode 1 is only slightly affected by typical cur

internal tides in the southwestern japan east sea abstract this paper investigates the internal tidal energy distribution in the southwestern japan east sea using vertical round trip travel time data from 23 pressure sensor equipped inverted echo sounders pies the records are analyzed by bandpass filtering to separate time dependent variability of the semidiurnal and diurnal bands the semidiurnal internal tides exhibit a horizontal beam pattern of high energy propagating into the open basin they originate from a restricted portion of the shelf break where the korea strait enters the ulleung basin the generation appears to occur at 200 m water depth near 35 5 35 7 n and 130 131 e where the slope of bottom topography matches that of the wave characteristics coinciding with the location where the semidiurnal barotropic cross slope tidal currents are strongest maximum vertical displacement of the thermocline interpreted as a long wave first baroclinic mode from the measured is about 25 m near the generation region annual and monthly var

inferring dynamics from the wavenumber spectra of an eddying global ocean model with embedded tides 1 the slopes of the wavenumber spectra of sea surface height ssh and kinetic energy ke have been used to infer interior or surface quasi geostrophic qg or sqg dynamics of the ocean however inspection of spectral slopes for altimeter ssh in the mesoscale band of 70 to 250 km shows much flatter slopes than the qg or sqg predictions over most of the ocean comparison of altimeter wavenumber spectra with spectra from an eddy resolving global ocean circulation model the hybrid coordinate ocean model hycom at 1 12 5 equatorial resolution which has embedded tides suggests that the flatter slopes of the altimeter ssh may arise from three possible sources 1 presence of strong internal tides 2 shift of the inertial sub range to smaller scales and 3 altimeter noise artificially adding noise to the model tends to flatten the spectra for low ke regions near internal tide generating regions spectral slopes in the presence of internal waves are much flatter than qg or sqg predictions separating the variability into high and low frequency around periods of 2 days then a different pattern emerges with a flat high frequency wavenumber spectrum and a steeper low frequency wavenumber spectrum for low mesoscale ke the inertial sub range defined by the nearly flat enstrophy band moves to smaller scales and the mesoscale band of 70 to 250 km no longer represents the inertial sub range the model wavenumber spectra are consistent with qg and sqg theory when internal waves and inertial sub range shifts are taken into consideration

the surface expression of semidiurnal internal tides near a strong source at hawaii part ii interactions with mesoscale currents abstract observations of semidiurnal surface currents in the kauai channel hawaii are interpreted in the light of the interaction of internal tides with energetic surface intensified mesoscale currents the impacts on internal tide propagation of a cyclone of 55 km diameter and 100 m vertical decay scale as well as of vorticity waves of 100 km wavelength and 100 200 m vertical decay scales are investigated using 3d ray tracing the doppler shifted intrinsic frequency is assumed to satisfy the classic hydrostatic internal wave dispersion relation using the local buoyancy frequency associated with the background currents through thermal wind or gradient wind balance the m2 internal tide rays with initial horizontal wavelength of 50 km and vertical wavelength of o 1000 m are propagated from possible generation locations at critical topographic slopes through idealized mesoscale currents approximating the observed currents despite the lack of scale separation between the internal waves and backgroun

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

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