comparison of topex sea surface heights and tide gauge sea levels topex sea surface height data from the first 300 days of the mission are compared to sea level data from 71 tide gauges the initial comparison uses sea surface height data processed according to standard procedures as defined in the users handbook it is found that the median correlations for island and for coastal tide gauges are 0 53 and 0 42 respectively the analogous rms differences between the two data sets are 7 9 and 10 4 cm the comparisons improve significantly when a 60 day harmonic is fit to the differences and removed this period captures aliased m2 and s2 tidal energy that is not removed by the tide model making this correction and smoothing the sea surface height data over 25 km along track segments results in median correlations of 0 58 and 0 46 for the islands and coastal stations and median rms differences of 5 8 and 7 7 cm respectively removing once per revolution signals from the sea surface heights results in degraded comparisons with the sea levels it is also found that a number of stations have poor comparisons due to propagating signals that introduce temporal lags between the altimeter and tide gauge time series a final comparison is made by eliminating stations where this propagation effect is large discarding two stations that are suspected to have problems with the sea level data smoothing over 10 day intervals and restricting attention to island gauges this results in a set of 552 data pairs that have a correlation of 0 66 and a rms difference of 4 3 cm the conclusion is that on timescales longer than about 10 days the rms sea surface height errors are less than or of the order of several centimeters

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

new altimetric estimates of mode 1 m2 internal tides in the central north pacific ocean abstract new estimates of mode 1 m2 internal tide energy flux are computed from an extended ocean topography experiment topex poseidon t p altimeter dataset that includes both the original and tandem tracks improving spatial resolution over previous estimates from o 500 km to o 250 km additionally a new technique is developed that allows separate resolution of northward and southward components half wavelength features previously seen in unseparated estimates are shown to be due to the superposition of northward and southward wave trains the new technique and higher spatial resolution afford a new view of mode 1 m2 internal tides in the central north pacific ocean as with all altimetric estimates only the coherent or phase locked signals are detectable owing to the long repeat period of the tracks emanating from specific generation sites consistent with predictions from numerical models internal tidal beams 1 are as narrow as 200 km and 2 propagate a longer distance than previously observ

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

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

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

chlorophyll anomalies along the critical latitude at 30 n in the ne pacific 1 the dissipation of surface tidal energy into internal tides plays a critical role in ocean mixing however quantifying the spatial distribution of this energy flux which is required for ocean and climate modeling has been largely based on modeling efforts and there is a need for validating observations the summer development of large blooms of chlorophyll along 30 n in the e pacific is presented as evidence of enhanced tidal mixing the region near 30 is a double critical latitude with a transformation of internal waves occurring at both diurnal and semidiurnal frequencies the breakdown at the critical latitude of internal waves generated at hawaii could provide the physical mechanism to explain these blooms the blooms develop in a region characterized by a weak summer surface stratification which is therefore more susceptible to mixing

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

temporal variability of internal tides in the northeast south china sea 1 the northeast south china sea is perhaps the largest internal tide energy source in the world the temporal variability of internal tides was investigated on the basis of 8 month moored acoustic doppler current profiler observations on the continental slope at the dongsha plateau the daily amplitude and phase of diurnal and semidiurnal internal tides were determined from complex demodulation and the dominant spatial and temporal patterns were extracted with empirical orthogonal function eof analysis the eof modal structures showed good agreement with the normal mode solution although vertical phase propagations were apparent the first semidiurnal eof mode corresponded to the first normal mode and the first two diurnal eof modes corresponded to the second and third normal modes respectively the modal structure and energy flux also were consistent with previous observations near the shelf break from the asian seas international acoustic experiment on the other hand the amplitudes of diurnal and semidiurnal eof modes both indicated large irregular fortnightly variations that were not phase locked incoherent with astronomical forcing the study highlighted the importance of incoherent internal tidal motion which accounted for about three fourths of the observed tidal energy

arsenic enrichment in groundwater of the alluvial aquifers in bangladesh an overview arsenic in the groundwater of bangladesh is a serious natural calamity and a public health hazard most groundwater from the shallow alluvial aquifers 150 m particularly in the holocene plai

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

distribution of arsenic and other trace elements in the holocene sediments of the meghna river delta bangladesh geochemical study of the holocene sediments of the meghna river delta chandpur bangladesh was conducted to investigate the distribution of arsenic and related trace and major elements the work carried out includes analyses of core sediments and provenance study by rare earth element ree analysis results showed that the cores pass downward from silty clays and clays into fine to medium sands the uppermost 3 m of the core sediments are oxidized average oxidation reduction potential orp 230 mv and the orp values gradually become negative with depths 45 to 170 mv indicating anoxic conditions prevail in the meghna sediments the ree patterns of all lithotypes in the study areas are similar and are comparable to the average upper continental crust arsenic and other trace elements pb zn cu ni and cr have greater concentrations in the silts and clays compared to those in the sands positive correlation between as and fe was found in the sediments indicating as may be adsorbed on fe oxides in aquifer sediments

long range propagation of the semidiurnal internal tide from the hawaiian ridge abstract the northeastward progression of the semidiurnal internal tide from french frigate shoals ffs hawaii is studied with an array of six simultaneous profiling moorings spanning 25 5 37 1 n 1400 km and 13 yr long ocean topography experiment topex poseidon t p altimeter data processed by a new technique the moorings have excellent temporal and vertical resolutions while the altimeter offers broad spatial coverage of the surface manifestation of the internal tide s coherent portion together these two approaches provide a unique view of the internal tide s long range propagation in a complex ocean environment the moored observations reveal a rich time variable and multimodal internal tide field with higher mode motions contributing significantly to velocity displacement and energy in spite of these contributions the coherent mode 1 internal tide dominates the northeastward energy flux and is detectable in both moored and altimetric data over the entire array phase and group prop

andean growth and the deceleration of south american subduction time evolution of a coupled orogen subduction system article i nfo present day orography at the andean margin is a result of isostasy tectonic accretion and erosional processes the resulting excess mass of the andes gives rise to frictional stresses on the seismogenic plate interface that resist the sinking of the subducting slab into the upper mantle thus subduction rates should be sensitive to the time dependent dynamics of a back arc orogen as well as erosional or accretional processes that affect orogen growth here we develop a two dimensional coupled orogen slab model that allows for the prediction of orogen size and plate motion in response to both tectonic and erosional forcing we find that the frictional force exerted by the orogen on the subducting slab grows quadratically with orogen width and that the frictional resistance typically balances 10 50 of the slab pull force the time evolution of the coupled orogen subduction zone system is largely controlled by the rate of orogen growth which is controlled by the rate of convergence and the erosivity of the climate state in the case of the andean margin our models show that miocene aridification leads to reduced erosion increased orogen growth greater frictional resistance to subduction and ultimately to a 50 reduction in the convergence rate between the nazca and south american plates

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

the generation of internal tides at the hawaiian ridge previous analyses of altimeter and acoustic data indicate that the hawaiian ridge is a significant generation site for semidiurnal m2 period internal waves owing to tidal flow over topography such waves likely play an important role connecting the dissipation of tidal energy to ocean mixing here a primitive equation numerical model with realistic stratification bathymetry and tidal forcing is used to simulate the generation of these waves in a manner consistent with altimeter sea surface observations the highest amplitude waves originate at three generation sites located at both the island and seamount portions of the chain these sites have in common both enhanced flows across ridge shaped topography and maxima in model calculated body force which couples barotropic and baroclinic motions the model vertical structure suggests the presence of multiple dynamical modes within 100 km of the ridge and not just the lowest modes that have been detected at the sea surface

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

contributions of floodplain stratigraphy and evolution to the spatial patterns of groundwater arsenic in araihazar bangladesh extreme spatial heterogeneity has emerged as a salient characteristic of groundwater arsenic in many complex fluviodeltaic environments here we examine patterns of arsenic heterogeneity in the shallow 1 10 3 m in the 25 km 2 area indicate that the concentration of arsenic in shallow groundwater largely varies with the grain size thickness and distribution of fine grained 63 m sediments that overlie buried aquifer sands the overall pattern shows that lower arsenic concentrations are typically found where aquifer sands outcrop at or near the surface whereas higher arsenic levels typically underlie or are adjacent to thicker fine grained deposits furthermore chronostratigraphic reconstructions of aquifer sediments indicate that sediment distribution and consequently the patterning of dissolved arsenic is readily explained in the context of local river history and flood plain development within the past 1000 yr an important implication is that complex patterns of groundwater arsenic in afflicted fluviodeltaic settings can be better understood through reconstructions of local aquifer history this finding is especially relevant because the village and tube well locations are closely linked with surface landforms such as former levees and bars an additional and worrisome finding is that the artificial filling of villages to protect from flooding can mimic the natural fine grained stratigraphy commonly associated with high concentrations of arsenic

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

estimates of internal tide energy fluxes from topex poseidon altimetry central north pacific energy fluxes for first mode m2 internal tides are deduced throughout the central north pacific ocean from topex poseidon satellite altimeter data temporally coherent internal tide signals in the altimetry combined with climatological hydrographic data determine the tidal displacements pressures and currents at depth which yield power transmission rates for a variety of reasons the deduced rates should be considered lower bounds internal tides are found to emanate from several large bathymetric structures especially the hawaiian ridge where the integrated flux amounts to about 6 gigawatts internal tides are generated at the aleutian trench near 172 w and propagate southwards nearly 2000 km

validating satellite altimeter measurements of internal tides with long term tao triton buoy observations at 2 s 156 e satellite altimetry is regularly used to map the global distribution of mode 1 internal tides validating altimeter measurements of internal tides with in situ data is difficult as the mooring observations typically are too short compared with the altimetry here taking advantage of the long term since 1999 tropical atmosphere ocean triangle trans ocean buoy network tao triton buoy observations at 2 s 156 e located at a topex poseidon crossover in a region of strong internal tides direct comparisons are made between altimeter and in situ measurements over a common 15 year period the hourly buoy data are decimated every 9 9 day to emulate altimeter measurements the altimeter and decimated buoy data are highly coherent at the aliased semidiurnal period 60 day and they agree well for the stationary semidiurnal internal tide for the nonstationary internal tide which consists of a significant annual cycle the demodulated amplitude from the altimeter appears to be contaminated by nontidal signals the demodulated amplitude from the decimated buoy data on the other hand is capable of resolving the temporal variability this suggests the potential of mapping nonstationary internal tides from satellites