energy levels phase and amplitude modulation of the baroclinic tide off hawaii abstract inverted echo sounder data from station aloha north of oahu hawaii are used to determine the absolute energy levels and time varying nature of the first mode baroclinic tide north of hawaii the semidiurnal tide amplitude and phase are modulated with 60 120 day periodicity which indicates interaction between the baroclinic tide and intra annual mesoscale variability seen off hawaii close to the presumed generation site there is less phase modulation and amplitude modulation is uncorrelated with the far field variability these results are consistent with a model of phase locked generation together with phase and amplitude distortion during propagation the sense of the amplitude modulation is opposite to that previously observed at decadal timescales semidiurnal energy flux at station aloha ranges from 2 2 to 8 0 kw m 1 with a mean value of 4 4 kw m 1

implementation of s band marine radar for surface wave measurement under precipitation abstract civil marine radar which operates at a low grazing incidence angle and with horizontal polarization in transmitting and receiving can be modified and used as a primary tool for surface wave monitoring the high spatial resolutions of sea clutter image sequences from x band radar offer a means of deriving individual waves and wave field at low cost however the performance of x band radar is impaired under rainy conditions which are usually accompanied by the severe weather at sea in the present study we examine the effectiveness of s band radar for wave measurements under precipitation the results of comprehensive comparative studies with sea truth data show that s band radar is capable of carrying out wave measurements in rainy conditions although the longer wavelength of the s band leads to a coarser resolution of radar imagery the s band radar features at least the equivalent performance of the x band system in non rainy conditions in terms of wave height measurement the results suggest that the s band and x band could be complementary systems in rainy conditions the s band is more efficient but in the non rainy periods the x band gives more confident results the relationship of significant wave height with radar signal to noise ratio snr and the modulation transfer function mtf between radar spectrum and wave spectrum for the used x band and s band radars are established and discussed in this paper

a deep eddy in the antarctic intermediate water north of the chatham rise in mid 1996 a hydrographic survey was made over the chatham rise near new zealand a deep isolated eddy of antarctic intermediate water was found north of the rise between 1200 and 1800 dbar it was widest on a potential density surface s1 of 32 1 potential temperature salinity and potential temperature oxygen characteristics identify the eddy as having a source south of the chatham rise this eddy was too deep to have passed over the chatham rise and the only way it could have reached this position was by flowing around the eastern end of the chatham rise the authors hypothesize that the intrusion may have been generated by a similar mechanism to that proposed for mediterranean eddies so that eddies are formed by separation of a frictional boundary layer at the end of the chatham rise once the intrusion is formed it was most likely advected to its observed position 500 km from the generation region by recirculation within a much largerscale permanent eddy found off the south east of the north island the wairarapa eddy

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

intra annual oscillations at station aloha north of oahu hawaii inverted echo sounders have been used to make continuous measurements of dynamic height at a site chosen to be representative of the central pacific subtropical gyre these show that the dominant features in dynamic height are fluctuations having peak to peak amplitudes of up to 27 dyn cm and timescales of about 100 days empirical orthogonal function analyses of temperature and salinity profiles suggest that if the oscillations are due to vertical motion within the water column the motion is not that of first baroclinic mode but has much higher vertical wavenumber structure zonal wavenumbers associated with the oscillations indicate westward phase propagation and meridional wavenumbers are close to zero the dominant periods are too short for freely propagating rossby waves two explanations of these observations are that the waves could be doppler shifted by the mean flow or that the region could be an area of active forcing

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

surface current measurements using x band marine radar with vertical polarization in this paper the retrieval of sea surface current velocity from vertically polarized v pol x band marine radar data is presented three different methods including the iterative least square approach the normalized scalar product method and the polar current shell algorithm that have been used for horizontally polarized data are employed here a comprehensive comparison of the performance of the three methods is conducted using the radar images collected by the v pol radar deployed on the forschungsplattformen in nord und ostsee no 3 fino3 offshore research platform and the acoustic doppler current profiler adcp data in the north sea the results indicate that all three methods are capable of providing reliable current speed and direction measurements from v pol data with similar performance based on the experimental data for which the current magnitude is less than 0 5 m s the radar derived results agree best with the adcp data at a depth of 6 8 m with the root mean square difference for current velocity x and y components being 7 2 8 9 cm s the correlation coefficients between the radar derived and adcp measured current velocity components are as high as 0 87 0 93

dissolved inorganic carbon in the xijiang river concentration and stable isotopic composition dissolved inorganic carbon dic is one the major products of chemical weathering of the land and it is also one of the most active components in the riverine carbon species concentration and stable isotopic composition of dic in the mainstream of the xijiang river xjr and its two tributaries the guijiang and hejiang rivers were investigated during a hydrological year and a massive flooding dic concentration of most selected sections of the xjr system varied from 750 to 2 400 m with an average of 1 630 390 m dic was significantly diluted in the massive flooding period the stable isotopic composition of dic 13cdic varied from 14 75 to 8 25 with an average of 11 19 1 18 from 17 22 to 10 65 with an average of 13 00 1 86 and from 15 94 to 9 71 with an average of 12 68 1 28 in the mainstream of the xjr the guijiang river and the hejiang river respectively this is jointly determined by the outcrop area of carbonate rocks and the properties of soil organic carbon within the catchments 13cdic is less negative in the dry season because of the increasing contribution from karst groundwater and more negative in the wet season because of the increasing contribution from surface soil water calcite was saturated sometimes at the mainstream sections of the xjr carbonate sourced dic contributes 10 32 43 95 with an average of about 27 69 6 03 of the riverine dic for the xjr the xjr exports about 4 27 1012 g of dic in the surveyed year of which about 83 occurred in the wet season

evidence for the existence of a north hawaiian ridge current abstract two different datasets are examined for information about the existence and characteristics of the north hawaiian ridge current nhrc the pan pacific drifter dataset shows a mean nhrc to be confined to within about 100 km of the northern side of the hawaiian ridge a close look at the distribution of the data shows that the current is mostly confined in time to a two month period in the fall of 1991 mbt data from the trade wind zone oceanography pilot study conducted in the mid 1960s were also examined of the 14 cruises with sections north of the hawaiian ridge 5 showed evidence of northwestward flow along the ridge of those 5 one was associated with northward meandering of the north equatorial current it is thus suggested that the nhrc is highly intermittent there are three related hypotheses for the formation of the nhrc 1 propagation of rossby waves westward into the ridge 2 forking of the north equatorial current and 3 as a western boundary current for the eastern pacific north

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

global patterns of low mode internal wave propagation part i energy and energy flux abstract extending an earlier attempt to understand long range propagation of the global internal wave field the energy e and horizontal energy flux f are computed for the two gravest baroclinic modes at 80 historical moorings around the globe with bandpass filtering the calculation is performed for the semidiurnal band emphasizing m2 internal tides generated by flow over sloping topography and for the near inertial band emphasizing wind generated waves near the coriolis frequency the time dependence of semidiurnal e and f is first examined at six locations north of the hawaiian ridge e and f typically rise and fall together and can vary by over an order of magnitude at each site this variability typically has a strong spring neap component in addition to longer time scales the observed spring tides at sites northwest of the hawaiian ridge are coherent with barotropic forcing at the ridge but lagged by times consistent with travel at the theoretical mode 1 group speed from the ridge phase c

numerical modeling of internal tide generation along the hawaiian ridge internal m2 tides near hawaii are investigated with a two dimensional two layer numerical model it is seen that along the hawaiian ridge barotropic tidal energy is transformed into baroclinic internal tides that propagate in both northeast and southwest directions as previously hypothesized the internal tide for a certain beam is seen to propagate well over 1000 km with an approximate decay scale of 1000 km an asymmetric pattern in the baroclinic energy flux is observed to the north and south of the hawaiian ridge due to the spatially inhomogeneous baroclinic energy sources the surface manifestation of the m2 internal tide in the model is compared with analysis results from topex poseidon satellite altimetry the baroclinic short wave variation of a few centimeters amplitude superposed on the barotropic surface amplitude agrees well with the altimeter analyses this together with snapshots of the interfacial disturbance allows the authors to sketch the propagation pattern of internal waves emanating northward and southward from the hawaiian ridge tidal current ellipses in the upper layer are dominated by the baroclinic internal tide with large spatial variability in their magnitude compared to the barotropic tidal ellipses the m2 baroclinic energy flux is over 10 kw m 21 for the strongest energy beam propagating toward the northeast along the western hawaiian ridge about 3 8 gw of tidal power is converted from barotropic to baroclinic motion the average northward or southward flux density for the first baroclinic mode is about 1 35 kw m21 in the western hawaiian ridge also if 2 7 kw m21 1 35 kw m21 to each direction is assumed for the whole 2000 km long hawaiian ridge a total of 5 4 gw is obtained this value indicates that there is still a large uncertainty in the rate of barotropic to radiating baroclinic energy conversion along the hawaiian 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

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

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

removal of ambiguity of two dimensional power spectra obtained by processing ship radar images of ocean waves the usual spatial power spectra of ocean wave images taken from ppi of a ship radar show an ambiguity in the wave propagation direction a simple numerical procedure is suggested and realized to remove this ambiguity it makes use of the data from two consecutive turns of the radar antenna as well as of the wave dispersion law the results obtained show a good agreement with the ground truth

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

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

altimeter and current meter observations of internal tides do they agree abstract baroclinic tides can be observed both remotely from the ocean topography experiment topex poseidon t p altimeter and in situ using current meters however it is rare that current meter moorings have high vertical resolution and are located under t p ground tracks so that a direct comparison can be made between the two methods of observations here data from a current meter mooring directly under a t p ground track off the bounty plateau new zealand are used to obtain energy estimates of the first baroclinic mode these estimates are compared with those calculated from the t p surface elevation the two methods return estimates of the internal tide that are in agreement in phase and direction but have about a factor of 2 difference in amplitude and a factor of 4 difference in energy the flux estimates are 787 and 170 w m 1 respectively uncertainties in these estimates are relatively large and there is a low but not negligible probability that the differences are entirely due to measu

wind direction estimation from rain contaminated marine radar data using the ensemble empirical mode decomposition method two ensemble empirical mode decomposition eemd based methods are presented to retrieve wind direction from rain contaminated x band nautical radar sea surface images each radar image is first decomposed into disparate intrinsic mode function imf components using 1 d eemd or 2 d eemd then the standard deviation of one imf component or the combination of several imf components as a function of azimuth is least squares fitted to a harmonic function to determine the wind direction tests of the proposed algorithms are conducted by employing radar and anemometer data collected in a sea trial during rain events off the east coast of canada the results show that compared with the 1 d discrete fourier transform based method both the 1 d and 2 d eemd based algorithms improve the wind direction results in rain events showing a reduction of 7 4 and 8 7 respectively in the root mean square difference with respect to the reference

low frequency modulation of turbulent diapycnal mixing by anticyclonic eddies inferred from the hot time series profiles of potential density obtained from ctd measurements during the hawaii ocean time series hot programin thevicinityoftheislandofoahu hawaii areusedtoevaluatelow frequencyvariabilityof turbulent kinetic dissipation rates based on a finescale parameterization method a distinct seasonal cycle as well asan increasingtrendofdissipationrates is foundin the upper300 600 m thetrendis mainlydueto the much weaker diapycnal mixing in the first four years of the record that is 1988 92 in the upper 300 600 m enhanced diapycnal mixing is found under anticyclonic eddies with the mean dissipation rate about 53 larger than that under eddy free conditions the modulation of dissipation rates by anticyclonic eddies becomes more evident with increasing eddy strength the role of cyclonic eddies in modulating diapycnal mixing is almost negligible compared with that of anticyclonic eddies the mean dissipation rate under cyclonic eddies is comparable to that under eddy free conditions with a difference of less than 10 seasonality of the dissipation rates is partly modulated by the seasonal variation of anticyclonic eddies

observation and intercomparison of wave motion and wave measurement using shore based coherent microwave radar and hf radar shore based coherent microwave radar and high frequency hf surface wave radar are two components of a rapidly emerging set of technologies suitable for ocean wave remote sensing to investigate their differences this paper describes and analyzes the relationship between the water particle velocity and the wave height spectrum based on linear wave theory which underpins the algorithms developed for the analysis of data collected by coherent microwave radar the backscatter mechanism which addresses the interaction of the hf radio waves with the ocean surface waves as well as the empirical method adopted in our hf radar is also presented the wave characteristics observed by the shore based coherent s band radar microwave ocean remote sensor morse are analyzed a multifrequency hf mhf radar based on a circular receiving array which is capable of sensing waves up to 100 km offshore is also introduced an intercomparison of the wave height measurements obtained from the morse mhf radar and wave buoy is made the comparison indicates that the wave heights measured by the morse and the mhf radar are consistent with the buoy derived wave heights with the root mean square differences rmsds of 0 27 and 0 37 m respectively

spatially broad observations of internal waves in the upper ocean at the hawaiian ridge abstract the density and current structure at the hawaiian ridge was observed using seasoar and doppler sonar during a survey extending from oahu to brooks banks across and along ridge changes in internal wave statistics in the upper ocean within 200 km of the ridge are investigated internal waves with trough to crest amplitude as large as 60 m and horizontal wavelength of about 50 km are observed repeatedly in across ridge sections of potential density within 150 km of the ridge kinetic and potential energy density exceed open ocean values with maxima about 10 times garrett munk levels in the kauai channel kc the kinetic energy density is largest along an m2 internal tide ray the ray originates at the northern edge of the ridge peak at a large across ridge change in topographic slope and terminates at the ocean surface about 30 40 km south of the ridge peak kinetic and potential energy density are larger on the south side of the ridge at kc the side with larger topographic slope energy densi

the island scale internal wave climate of moorea french polynesia 1 analysis of five year records of temperatures and currents collected at moorea reveal strong internal wave activity at predominantly semi diurnal frequencies impacting reef slopes at depths 30 m around the entire island temperature changes of 1 5 c to 3 c are accompanied by surges of upward and onshore flow and vertical shear in onshore currents superimposed on annual temperature changes of approximately 3 c internal wave activity is high from oct may and markedly lower from jun sep the offshore pycnocline is broadly distributed with continuous stratification to at least 500 m depth and a subsurface fluorescence maximum above the strong nutricline at approximately 200 m minimum buoyancy periods range from 4 8 to 6 min with the maximum density gradient occurring at 50 to 60 m depth in summer and deepening to approximately 150 to 200 m in winter the bottom slope angle around all of moorea is super critical relative to the vertical stratification angle suggesting that energy propagating into shallow water is only a portion of total incident internal wave energy vertical gradient richardson numbers indicate dominance by density stability relative to current shear with relatively limited diapycnal mixing coherence and lagged cross correlation of semi diurnal temperature variation indicate complex patterns of inter site arrival of internal waves and no clear coherence or lagged correlation relationships among island sides semi diurnal and high frequency internal wave packets likely arrive on moorea from a combination of local and distant sources and may have important impacts for nutrient and particle fluxes in deep reef environments

regional synchrony of temperature variation and internal wave forcing along the florida keys reef tract 1 analysis of 10 year temperature records collected along the florida keys reef tract flkrt reveals strong regional scale synchrony in high frequency temperature variation suggestive of internal wave forcing at predominately semidiurnal frequencies in each year and at all sites the amplitude of semidiurnal temperature variation was greatest from march to september and markedly lower from october to february comparisons of the semidiurnal component of the temperature variation among sites suggest complex patterns in the arrival of internal waves with highest cross correlation among closely spaced sites and synchrony in periods of enhanced internal wave activity across the length of the flkrt particularly in summer the periods of enhanced semidiurnal temperature variation at the 20 and 30 m isobaths on the reef slopes appear to be associated with the dynamics of the florida current and the onshore movement of warm fronts preceding the passage of florida current frontal eddies regional scale satellite altimetry observations suggest temporal linkages to sea surface height anomalies in the loop current upstream of the florida current and setup of the tortugas gyre the synchronized forcing of cool water onto the reef slope sites across the flkrt is likely to affect physiological responses to temperature variation in corals and other ectothermic organisms as well as larval transport and nutrient dynamics with the potential for regionally coherent pulses of larvae and nutrients arriving on reef slopes across the flkrt

coherence of internal tide modulations along the hawaiian ridge long time series of sea level from tide gauges along the north side of the hawaiian ridge and shorter series of dynamic heights inferred from inverted echo sounders moored just north of the main hawaiian islands are examined for evidence of internal tides at the m2 frequency we find that the amplitudes and phases of the m2 tidal components have low frequency variability which is consistent with a superposition of an internal tide with the larger barotropic tide further the low frequency variability is correlated with low frequency changes in the depth of the pycnocline which suggests a simple physical mechanism to account for the low frequency modulations in the internal tidal amplitude these modulations are coherent for long distances along the hawaiian ridge indicating a coherent generation of the internal tide that is consistent with acoustic observations in the north pacific and with recent analyses of sea surface heights from satellite altimetry

an algorithm for estimation of wave height from shadowing in x band radar sea surface images directional wave spectra and integrated wave parameters can be derived from x band radar sea surface images the calibration of such spectra has until now depended on various empirical and semiempirical methods which also require an external reference increasing the total expenses of operation a novel algorithm which is fully based on theory producing reasonable estimates of the significant wave height based on shadowing in the images has been now developed the method does not require any reference measurements and with that enables automatic calibration of spectra from radar sea surface images as well as the potential for reduced operational cost and increased accuracy of such wave monitoring systems promising results are obtained with data acquired at a test site in the north sea further work is however required to refine the algorithm and to test it under varying circumstances at various sites