secular changes in the solar semidiurnal tide of the western north atlantic ocean 1 an analysis of twentieth century tide gauge records reveals that the solar semidiurnal tide s2 has been decreasing in amplitude along the eastern coast of north america and at the mid ocean site bermuda in relative terms the observed rates are unusually large of order 10 per century periods of greatest change however are inconsistent among the stations and roughly half the stations show increasing amplitude since the late 1990s excepting the gulf of maine lunar tides are either static or slightly increasing in amplitude a few stations show decreases large changes in solar but not lunar tides suggest causes related to variable radiational forcing but the hypothesis is at present unproven

the limiting pressure on a circular pile loaded laterally in cohesive soil in the analysis of the undrained loading of laterally loaded piles an important quantity is the ultimate lateral resistance at depth to purely horizontal movement if the soil is modelled as a perfectly plastic cohesive material then the calculation of this quantity reduces to a plane strain problem in plasticity theory in which the load is calculated on a long cylinder which moves laterally through an infinite medium an exact calculation of the load on such a cylinder is presented if this load is non dimensionalized with respect to the soil strength and the diameter of the pile it is found that the load factor varies between for a perfectly smooth pile and for a perfectly rough pile this result is discussed in the context of previous calculations for the lateral load capacity of piles and is compared with approximate calculations using cavity expansion theory and a wedge failure near the soil surface la resistance laterale limite en profondeur au seul mouvement horizontal represente un parametre im

a numerical study on the influence of the mid atlantic ridge on nonlinear first mode baroclinic rossby waves generated by seasonal winds abstract a numerical model simulation investigates the influence of the mid atlantic ridge on nonlinear first mode baroclinic rossby waves generated by seasonal wind fluctuations the north atlantic is simulated by a square box two layer quasi geostrophic qg model the bottom topography is ridge like and compromises the qg approximation and the actual shape of the ridge sponge layers protect all boundaries except the eastern one from wave reflection and eliminate the build up of the western boundary current the model is forced by a purely fluctuating wind stress curl derived from the most significant eofs of the fgge winds a flat bottom and a ridge experiment are compared in both experiments the eastern boundary is an important source of annual period baroclinic rossby waves wave trains having a wavelength of about 1060 km and a westward phase speed around 3 4 cm s 1 propagate energy westward at 3 cm s 1 in the flat bottom experiment a source of directly wind forced baroclinic waves of annual per

the zonal currents and transports at 35 w in the tropical atlantic the total of 13 existing cross equatorial shipboard current profiling sections taken during the woce period between 1990 and 2002 along 35 w are used to determine the mean meridional structure of the zonal top to bottom circulation between the brazilian coast near 5 s and 5 n and to estimate mean transports of the individual identified shallow intermediate and deep current branches one of the results is that on the equator a mean westward equatorial intermediate current below the equatorial undercurrent exists

a plasticity model for predicting the vertical and lateral behaviour of pipelines in clay soils a complete theoretical model for predicting the undrained behaviour of a rigid pipe in clay soils when subjected to combined vertical and horizontal loading is described physical modelling of a pipe on soft lightly overconsolidated kaolin clay was conducted with the experimental test programme specifically designed to establish the model parameters the testing was conducted within the university of western australia s geotechnical drum centrifuge using an element of pipe 10 mm in diameter and 50 mm long at an acceleration of 50 times the earth s gravity the model presented is expressed by the force resultants on the pipe and the corresponding displacements and allows predictions of response to be made for various vertical and horizontal load or displacement combinations however it is limited to monotonic loading and does not account for the influence of berms created by repetitive large lateral displacements the model is verified in this paper by retrospectively simulating a selection of combined

settlements of shallow foundations on sand a method to evaluate settlements and rotations of rigid shallow foundations on sand under the combined action of inclined and eccentric loads is presented experimental results obtained on a model strip foundation are shown first next a mathematical model is formulated which is based on the hypotheses that a the foundation and the soil can be considered as a macro element for which the loadings act as generalized stress variables while the displacements and rotation of the foundation are the corresponding generalized strain variables and b the constitutive law of the macro element that is the relationship between generalized stress and strain rates is rigid plastic strain hardening with a non associated flow rule constitutive functions and parameters are determined by means of simple calibration tests predictions of the theory are then compared with experimental results in tests where loadings vary in a complex way up to foundation failure it is shown that experimental evidence is well matched

lagrangian circulation of antarctic intermediate water in the subtropical south atlantic this study combines float data from different projects collected between 1991 and 2003 in the south atlantic to describe the flow of antarctic intermediate water aaiw velocity space time averages are calculated for various grid resolutions and with cells deformed to match the bathymetry f h or f h with h being the water depth and h being the thickness of the aaiw layer when judged by the degree of alignment between respective isolines and the resulting average velocity fields the best grid is based on a nominal cell size of 3o latitude by 4o longitude with cell shapes deformed according to f h using this grid objectively estimated mean currents and their associated errors as well as meridional and zonal volume transports are estimated results show an anticyclonic subtropical gyre centred near 36os and spanning from 23o 1 s to 46 1os the south atlantic current meanders from 33os to 46os and shows a mean speed of 9 6 7 8 cm s 1 8 5 sv 3 5 sv 1 sv 1 106 m3 s 1 the northern branch of the subtropical gyre is located between 22os and 32os and flows westward with a mean speed of 4 7 3 3 cm s 1 9 3 sv 3 4 sv evidence of a cyclonic tropical gyre divided in two sub cells is visible on the stream function

oxygen tongues and zonal currents in the equatorial atlantic 1 equatorial zonal currents and associated oxygen distributions are studied using shipboard hydrographic data trajectories from isopycnic floats drifting at about 300 m depth and velocity time series from the upper 1100 m obtained at two equatorial moorings located at 35 w and 23 w mean profiles of zonal velocity measured by moored acoustic doppler current profilers yielded a westward flowing equatorial intermediate current eic below the equatorial undercurrent euc at both locations the eic consists of two westward current cores at about 250 and 450 m the upper core of the eic deepens by about 30 m from 23 w where it has a mean velocity of 6 2 cm s 1 to 35 w where the mean is 5 3 cm s 1 the lower core of the eic is about twice as strong with 12 1 cm s 1 at 23 w and 9 2 cm s 1 at 35 w the flow below the euc is characterized by substantial interannual variability from may to december 2005 a strong zonally coherent eastward jet occurred at 300 to 350 m depth found to be an expression of shallow stacked jets superimposed on the mean eic shipboard hydrographic observations in june july 2006 revealed the existence of a high oxygen tongue that can be traced from 35 w to 10 w in the depth range of the eastward jet prevailing during the preceding year on the basis of an advection diffusion balance it is suggested that the oxygen decrease from 35 w to 10 w within the oxygen tongue is mainly balanced by lateral eddy diffusivity and oxygen consumption with diapycnal turbulent diffusivity playing only a minor role

experimental measurement of monotonic and cyclic lateral resistance of risers and pipelines in gulf of mexico clays the location near the touchdown zone tdz of a steel catenary riser scr at the seabed is a primary hot spot for fatigue assessment with seabed stiffness having a major influence on the predic

combined loading of spudcan foundations on clay laboratory tests recent research has shown that work hardening plasticity theory provides a suitable framework for interpreting and predicting the load displacement behaviour of rigid shallow foundations under combined vertical moment and horizontal loading most previous work has however been restricted to footings on granular soils this paper describes a series of laboratory tests conducted at unit gravity using a small circular footing and specimens of reconstituted kaolin the results indicate that work hardening plasticity concepts can also be applied to the modelling of shallow foundation behaviour on undrained clay the footing shape chosen for the experiments is representative of the spudcan foundations which support the legs of jack up drilling platforms a novel testing apparatus allows independent control of the vertical rotational and horizontal footing displacements within a single vertical plane tests conducted at constant vertical penetration are used to investigate the shape and size of the combine

coupling of sea level rise tidal amplification and inundation abstractwith the global sea level rising it is imperative to quantify how the dynamics of tidal estuaries and embayments will respond to increased depth and newly inundated perimeter regions with increased depth comes a decrease in frictional effects in the basin interior and altered tidal amplification inundation due to higher sea level also causes an increase in planform area tidal prism and frictional effects in the newly inundated areas to investigate the coupling between ocean forcing tidal dynamics and inundation the authors employ a high resolution hydrodynamic model of san francisco bay california comprising two basins with distinct tidal characteristics multiple shoreline scenarios are simulated ranging from a leveed scenario in which tidal flows are limited to present day shorelines to a simulation in which all topography is allowed to flood simulating increased mean sea level while preserving original shorelines produces additional tidal amplification however flooding of adj

abyssal mixing where it is not abstract a parameterization based on internal wave wave interaction theory which infers turbulence production from finescale internal wave shear is applied to 114 full water depth velocity profiles in the sargasso sea an average eddy diffusivity of 0 1 10 4 m2 s 1 independent of depth is inferred this value is consistent with full water depth microstructure measurements from abyssal basins in the eastern north atlantic and eastern north pacific it is an order of magnitude smaller than the values inferred from a simple vertical advection diffusion balance or bulk budgets thus the mixing needed to close deep global water mass budgets does not appear to occur over midlatitude abyssal plains this suggests that ocean mixing is either i confined to boundary layers as in ideal thermocline theory or ii localized to hotspots such as over rough topography or restrictive passages abyssal diffusivities do not display any dependence on bottom slope for slopes less than 7 10 2 based on 5 10 km bathy

direct observations of the current structure east of the bahamas quasisynoptic absolute velocity sections were obtained in the western north atlantic to the east of the bahamas on five cruises from 1992 to 1994 showing complex spatial and temporal variability of the currents throughout the water column lowered acoustic doppler current profilers were used on all cruises for comparison an acoustically tracked free fall profiler was used on the august 1992 and june 1993 cruises where simultaneous profiles from both methods are available depth averaged differences are less than 0 01 m s 1 in the ensemble mean and standard deviation though small the mean difference appears to be statistically non zero for one of the two doppler profilers used no cause has been found the individual velocity sections show a banded structure of currents in the offshore direction with strong baroclinic and depth averaged components extending over the full sampling domain two sections show a picture of the southward flowing deep western boundary current dwbc differing from previous observations during august 1992 and june 1993 the mean dwbc core was located more than 100 km offshore in observations prior to 1990 it was usually near 50 km offshore net southward transport below 800 m integrated from the coast to 400 km offshore varied from 15 to 50 sv with a mean of about 40 sv 1 sv 1 106 m s 1 our mean is consistent with previous estimates our sections add new evidence that the transport is highly variable to at least 400 km offshore

nodal variations and long term changes in the main tides on the coasts of china the long term changes in the main tidal constituents o1 k1 m2 n2 and s2 along the coasts of china and in adjacent seas are investigated based on 17 tide gauge records covering the period 1954 2012 the observed 18 61 year nodal modulations of the diurnal constituents o1 and k1 are in agreement with the equilibrium tidal theory except in the south china sea the observed modulations of the m2 and n2 amplitudes are smaller than theoretically predicted at the northern stations and larger at the southern stations the discrepancies between the theoretically predicted nodal variations and the observations are discussed the 8 85 year perigean cycle is identifiable in the n2 parameters at most stations except those in the south china sea the radiational component of s2 contributes on average 16 of the observed s2 except in the gulf of tonkin on the south coast where it accounts for up to 65 we confirmed the existence of nodal modulation in s2 which is stronger on the north coast the semidiurnal tidal parameters show significant secular trends in the bohai and yellow seas on the north coast and in the taiwan strait the largest increase is found for m2 for which the amplitude increases by 4 7 mm yr in the yellow sea the potential causes for the linear trends in tidal constants are discussed

pacific equatorial turbulence abstract in january and february 1979 a free fall vehicle was deployed at 150 w near the equator to sample velocity and temperature microstructure airfoil shear probes on the vehicle are able to resolve the peak of the velocity gradient spectrum and permit computation of the rate of dissipation of turbulent energy these measurements indicate maximum values of of 10 7 w kg 1 10 3 cm2 s 3 to be within 0 5 of the equator above the velocity core of the undercurrent similar in location to the observed distribution in the atlantic crawford and osborn 1979a however a secondary maximum below the core of the undercurrent found in the atlantic was not observed in the pacific a comparison of profile averaged values of with the zonal current and density profiles suggests that temporal variations in are related to the strength of the zonal shear and the magnitude of the stable stratification above the 150 m deep core of the undercurrent the vertical eddy viscosity due to turbulence km

evaluation of elastic stiffness parameters for pipeline soil interaction abstractthis paper focuses on elastic stiffness parameters for axial horizontal and vertical motions of a pipeline relative to the seabed with the aim of expressing these parameters in terms of fundamental elastic properties of the soil limited information exists in the literature on the axial elastic response of on bottom pipelines particularly for nonhomogeneous soil therefore an approximate analytical approach was developed for axial stiffness focusing on the case of shear modulus proportional to depth the solution was then verified through numerical analysis further numerical analysis was carried out to obtain relationships for horizontal and vertical elastic stiffnesses of on bottom pipelines finally relationships among elastic stiffnesses were developed here recommendations are made for the selection of proper elastic stiffnesses in all three directions of motion these recommendations allow consistent and rigorous modeling of elastic pipe seabed interactions with application to the ana

a note on tidal asymmetry in the severn estuary a one dimensional non linear numerical model is used to investigate the tidally averaged frictional stress and set up of water level due to tidal asymmetry in the severn estuary these quantities depend on the overtides in the region a linearized model of the overtides is applied to calculations of the m4 currents in order to delineate the mechanisms responsible for their generation the relative importance of individual non linear mechanisms to the tidally averaged stress and set up is determined these mechanisms are interactions between tidal flow and changes in depth or breadth over a cross section frictional interaction between the tidal flow and stokes drift interaction between the tidal fluctuations in water depth and frictional retardation and non linear advection

the mean flow field of the tropical atlantic ocean the mean horizontal sow eld of the tropical atlantic ocean is described between 20in and 20is from observations and literature results for three layers of the upper ocean tropical surface water central water and antarctic intermediate water compared to the subtropical gyres the tropical circulation shows several zonal current and countercurrent bands of smaller meridional and vertical extent the wind driven ekman layer in the upper tens of meters of the ocean masks at some places the sow structure of the tropical surface water layer as is the case for the angola gyre in the eastern tropical south atlantic although there are regions with a strong seasonal cycle of the tropical surface water circulation such as the north equatorial countercurrent large regions of the tropics do not show a signi cant seasonal cycle in the central water layer below the eastward north and south equatorial undercurrents appear imbedded in the westward sowing south equatorial current the antarcic intermediate water layer contains several zonal current bands south of 3in but only weak sow exists north of 3in the sparse available data suggest that the equatorial intermediate current as well as the southern and northern intermediate countercurrents extend zonally across the entire equatorial basin due to the convergence of northern and southern water masses the western tropical atlantic north of the equator is an important site for the mixture of water masses but more work is needed to better understand the role of the various zonal under and countercurrents in cross equatorial water mass transfer 1999 elsevier science ltd all rights reserved

shallow equatorial jets when zonal velocity profiles from the central equatorial pacific are expanded into sums of vertical normal modes the peak amplitudes occur consistently near modes 1 5 12 and 18 the first two of these peaks sum to a recognizable equatorial undercurrent profile the two higher mode peaks blunt and thicken the equatorial undercurrent euc and add a westward extremum near 340 m during the 1982 1983 el nino the low mode component of the flow modes 1 10 was more variable than the residual component which was dominated by the modes near 12 and 18 the residuals below 120 m persisted as alternating westward and eastward current bands the shallow jets through the disappearance of the euc in the second half of 1982 and its reappearance in 1983 the shallow jets were nearly constant in depth until late 1982 and then gradually rose through the end of the time series in june 1983 differences in temporal behavior among the mode amplitude peaks indicate that these peaks are describing dynamically separate components of the flow which are not tightly coupled on time scales shorter than a few months

structure of the atlantic ocean equatorial deep jets the equatorial deep jets in the atlantic ocean are described using vertical strain jz estimated from all available deep ctd stations in the region wavelet analysis reveals a distinct energy peak around 661 sdbar vertical wavelength 1232 dbar pressure and 61 58 latitude from the equator this high vertical wavenumber and off equatorial maximum coupled with previously published velocity data that show nodes in zonal velocity near 61 58 is grossly consistent with the structure of first meridional mode equatorial rossby waves however the meridional scale obtained from the observations exceeds by about 1 5 the theoretical meridional scale for these waves the jets are strong with zonal velocities similar in magnitude to the kelvin wave phase speed for their vertical wavelength harmonics of jz at vertical wavelengths of 1 2 1 4 and perhaps 1 8 that of the primary peak provide evidence of a large amplitude structure although sparse available phase data at the 661 sdbar vertical wavelength suggest downward and westward phase propagation assuming sinusoidal character in time and longitude gives estimates of a 5 61 yr period and a 708 6608 zonal wavelength these vertical temporal and zonal scales are roughly consistent with first meridional mode equatorial rossby wave dynamics however although vertical and zonal phase propagation are discernible there is no obvious signature of upward energy propagation in the variance vertical maxima which is problematic for a simple linear rossby wave interpretation

finescale velocity density characteristics and richardson number statistics of the eastern equatorial pacific abstract an analysis of finescale horizontal velocity shear and density data collected along 110 w longitude in the equatorial pacific is presented the measurements were made with the free fall velocity density profiler tops twenty five deployments are used to investigate the variability in the depth interval 150 900 m in this interval the shear and strain fields are dominated by finescale structures the extra equatorial latitude band 4 10 n exhibits shear and strain spectra as well as richardson number ri statistics that are consistent with midlatitude internal wave model predictions approaching the equator an enhancement of shear and strain variance is found along with an accompanying increase in the occurrence of ri less than consistent with previous studies the present measurement suggest that the 13 c thermostad is turbulently mixed a high occurrence of ri less than is also found below the thermostad and in the latitude range 2 4 s the implications of these observations are discussed

deep velocity measurements in the western equatorial indian ocean abstract vertical profiles of horizontal current collected in april and june 1979 in the western indian ocean revealed the presence of short vertical scale 150 300 m deep zonal jets trapped to within 1 of the equator meridional velocity records displayed in general higher temporal and spatial variability and significantly less energy at the larger vertical scales as compared with zonal records vertical wavenumber spectra of velocity showed no statistically significant peaks the conspicuous alternating zonal jets were identified with the slightly more energetic as compared to background levels 500 429 stretched meter sm wavelengths for most vertical wavenumbers zonal currents were not significantly coherent at distances greater than 400 km downstream at shorter zonal separations phase lags were indistinguishable from zero on the equator there is an indication of upward shift of approximately 100 sm over the 500 429 sm band also on the equator zonal current u and vertical displacement

equatorial deep jets and abyssal mixing in the indian ocean abstract vertical profiles of horizontal currents and hydrographic measurements from three cruises along 80 5 e from the coast of sri lanka to 6 s between december 1990 and september 1994 are used to investigate the scales of the indian ocean deep jets as well as internal wave parameters and dissipation at the equator the deep jets at 80 5 e have a vertical wavelength of 660 sm stretched meters and amplitudes exceeding 10 cm s 1 in zonal velocity they are observed throughout the water column and their flow direction reverses at 2 off the equator the vertical positions of the jets differ among the cruises and are consistent with a flow reversal between the data collected in winter and summer during september 1994 the jets were less pronounced due to the meridional distribution of their zonal velocity and the phase relationship between zonal velocity and vertical displacement the jets are best described as nondispersive first mode equatorial rossby waves the hydrographic data revealed thick layer

impact of the equatorial deep jets on estimates of zonal transports in the atlantic the structure and variability of the zonal equatorial flow in the atlantic is studied on the basis of velocity profiles obtained with lowered acoustic doppler current profilers during multiple surveys the vertical extent of the zonal currents is found to vary considerably it can be as small as 100 m or as large as 1000 m in the atlantic vertical scales of 400 600 m have been associated with the equatorial deep jets they are also frequently called deep jets or stacked jets typical amplitudes of the zonal velocity are about 20 cm s 1 an analysis of quasi synoptic surveys indicates that the zonal extent of most jets is likely to be at least 27d they can rise or deepen from west to east although the deepening was observed more often and is often more pronounced the west to east deepening can be as large as 320 m 10d basin wide mean depth changes of the jets are mostly on the order of 50 m 10d and the largest depth changes are typically observed between 35d and 23d w the existence of these changes indicates that vertically propagating equatorially trapped waves might be one cause for the jet structure however the dependence of the slope on the longitude indicates that other processes must be involved as well the typical vertical extent of the jets is small enough to result in several direction changes of the zonal flow in the antarctic intermediate water aaiw and the north atlantic deep water nadw layer from transport estimates for 14 meridional sections it is found that the transport for the westward component of the flow within the aaiw layer 500 1000 m can be as large as 24 sv 1 sv 10 6 m s 1 within 1d of the equator for the eastward component of the flow in the aaiw layer the transport can be as large as 8 sv adding the transport components for each section results in a range of total aaiw transports from 24 to 7 sv this suggest that the annual mean transport of aaiw is westward the only months with eastward total transports are june and july this is consistent with earlier lagrangian and some other observations that indicated that the aaiw flow along the equator is governed by an annual cycle in the nadw layer 1200 3900 m the transport for the westward eastward flow can be as large as 25 sv 23 sv within 1d of the equator this results in a range of total nadw transports from 10 to 18 sv the variations of the total transports of aaiw and nadw are anti correlated with a correlation coefficient of 0 86 since only eight sections reached deep enough to allow transport estimates in the nadw layer it is more difficult to come to a conclusion about the mean transport in this layer than for the transport in the aaiw layer for the latter layer 14 sections were available nevertheless the obtained estimates suggest that the total nadw transport may be eastward

basin wavelength equatorial deep jet signals across three oceans equatorial deep jets edjs are equatorially trapped stacked zonal currents that reverse direction every few hundred meters in depth throughout much of the water column this study evaluates their structure observationally in all three oceans using new high vertical resolution argo float conductivity temperature depth ctd instrument profiles from 2010 to 2014 augmented with historical shipboard ctd data from 1972 to 2014 and lower vertical resolution argo float profiles from 2007 to 2014 the vertical strain of density is calculated from the profiles and analyzed in a stretched vertical coordinate system determined from the mean vertical density structure the power spectra of vertical strain in each basin are analyzed using wavelet decomposition in the indian and pacific oceans there are two distinct peaks in the power spectra one kelvin wave like and the other entirely consistent with the dispersion relation of a linear first meridional mode equatorial rossby wave in the atlantic ocean the first meridional mode rossby wave signature is very strong and dominates in all three ocean basins rossby wave like signatures are coherent across the basin width and appear to have wavelengths the scale of the basin width with periods of about 5 yr in the indian and atlantic oceans and about 12 yr in the pacific ocean their observed meridional scales are about 1 5 times the linear theoretical values their phase propagation is downward with time implying upward energy propagation if linear wave dynamics hold

abyssal circulation in the somali basin the bottom and deep circulation in the somali basin are investigated on the basis of hydrographic and direct velocity profiles from three shipboard surveys carried out during the southwest monsoon in 1995 and of velocity time series from the woce mooring array icm7 the inflow of bottom water into the somali basin through the amirante passage drives a thermohaline circulation which may be modulated by the monsoon wind forcing details of the abyssal circulation have been discussed controversially deep velocity records from the mooring array in the northern somali basin are dominated by fluctuations with periods of 30 50 days and amplitudes above full size image 1 k despite this strong variability annual record averages indicate the existence of a deep western boundary current dwbc below full size image 1 k at the base of the continental slope south of socotra island as part of a cyclonic bottom circulation the southwestward dwbc transport off socotra island is estimated to full size image 1 k the bottom and deep water exchange between the somali and arabian basin north of 7 n is estimated from two cross basin geostrophic velocity sections referenced by vertically averaged ladcp currents for the bottom water an eastward transport into the arabian basin of full size image 1 k and full size image 1 k was determined in june and august respectively while for the deep water layer above full size image 1 k eastward transports of full size image 1 k in june and full size image 1 k in august were obtained

pacific equatorial turbulence revisited abstract turbulence measurements from the central equatorial pacific in february 1982 have been analyzed and compared to synoptic ctd and current velocity profiles and current meter data these suggest considerably more time if not space variability than had previously been anticipated above 300 m at the equator the turbulence levels were greater but less than previous equatorial measurements and turbulent patches occurred more frequently than elsewhere in the open ocean below 300 m the occurrence of turbulent patches was less frequent than in other regions of the ocean except for the persistence of a patch at 500 m

middepth equatorial tracer tongues in a model of the atlantic ocean 1 observational estimates of middepth tracer tongues in the equatorial atlantic are reviewed and are compared with results from several eddy resolving model simulations local maxima of chlorofluorocarbon cfc concentrations along the equator at around 1500 m depth are related to mean eastward jet structures in the models at similar depth ranges and can also be identified in several simulated tracer distributions similar to the observations strong eastward jets are located in the simulations 1 2 north and south of the equator the model simulations show in addition consistent with the cfc observations weaker jets at around 4 6 n s and 8 10 n s suggestive of a large scale alternating eastward westward current system in the western tropical atlantic in this depth range lagrangian transport estimates in the model using float diagnostics show a transport of 1 3 sv in each of the eastward jets 1 2 n s off the equator compared to 3 12 sv throughflow into the south atlantic with no seasonal cycle apparent in the transport fractioning comparing different model solutions reveals the choice of the subgrid scale mixing parameterization as important for the amplitudes of the jets enhanced reduced diapycnal mixing is related to stronger weaker jets

internal wave interactions with equatorial deep jets part ii acceleration of the jets abstract what drives the equatorial deep jets is a puzzle because of their isolation from surface forcing by the intervening main pycnocline and the equatorial undercurrent and from lateral boundaries by distances of tens of thousands of kilometers it would take decades for energy to propagate to the jets midbasin location from boundary sources their persistence points to some mechanism maintaining them in situ the authors hypothesize that the ambient internal wave field deposits momentum fluxes at critical layers within the deep jets and using calculated momentum and energy flux divergences as forcing estimate acceleration of the mean zonal flow in the deep jets internal wave momentum flux divergences are more than sufficient to sustain the jets acting to sharpen the shear between the jets on timescales of months to years predicted energy flux divergences produce turbulent dissipation rates compatible with those observed

rapid change in semi diurnal tides in the north atlantic since 1980 1 an anomalously large trend of m2 and s2 amplitudes and phases beginning in the early 1980s is observed in the north atlantic harmonic analysis of long term sea level records from tide gauge stations along the north american atlantic coast and european atlantic coast shows a large decrease in m2 and s2 amplitudes and an increase in phase lag the characteristics of the evolution of m2 and s2 tides are similar but not fully conclusive which may suggesting different causes in general the trends may be due to global warming which significantly increased in the early 1980s in the north atlantic region several climate related driving mechanisms for the observed changes in tides are discussed

the atlantic deep western boundary current water masses and transports near the equator the distributions and transports of deepwater masses at the western boundary in the tropical atlantic off brazil have been studied on three surveys along 35 degrees w and 5 degrees s and one at 10 degrees s transports are obtained from direct measurements of the velocity fields pegasus profiling system and lowered acoustic doppler current profiler and from geostrophic computations using chlorofluoromethane cfm and hydrographic distributions four water masses could be identified forming the north atlantic deep water nadw system two of these have a high cfm content the shallow upper nadw sunadw and the overflow lower nadw olnadw these exhibit the highest velocity signals at 35 degrees w where distinct flow cores seem to exist most of the southeastward flow of the sunadw centered around 1600 m occurs 320 km offshore between 3 degrees 09 s and 1 degrees 50 s 9 7 3 3 sv farther north in that section a highly variable reversing flow is found in a second velocity maximum the transport of olnadw centered around 3800 m of 4 6 2 6 sv is guided by the parnaiba ridge at 1 degrees 45 s 35 degrees w the water masses located between the two cfm maxima the labrador sea water lsw and the lnadw old water mass lnadw old did not show any persistent flow features however a rather constant transport of 11 1 2 6 sv was observed for these two layers the total southeastward flow of the nadw at 35 degrees w showed a transport of 26 8 7 0 sv if one neglects the reversing sunadw north of 1 degrees 50 s at 5 degrees s the flow of all deepwater masses shows vertically aligned cores the main southward transport occurred near the coast 19 5 5 3 sv the boundary current is limited offshore by a flow reversal present in all three surveys but located at different longitudes at 10 degrees s a southward transport of 4 7 sv was observed in november 1992 however the section extended only to 32 degrees 30 w so that probably a significant part of the flow has been missed an important result is the large transport variability between single cruises as well as variability of the spatial distribution of the flow at 35 degrees w which could lead to large uncertainties in the interpretation of single cruise observations despite these uncertainties we suggest a circulation pattern of the various deepwater masses near the equator by combining our mean transport estimates with other observations

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

on the resonance and shelf open ocean coupling of the global diurnal tides abstractthe resonance of diurnal tidal elevations is investigated with a forward ocean tide model run in a realistic near global domain and a synthesis of free oscillations normal modes computed for realistic global ocean geometries and ocean physics as a prelude to performing the forward ocean tide simulations the topographic wave drag which is now commonly employed in forward ocean tide models is tuned specifically for diurnal tides the synthesis of global free oscillations predicts reasonably well the forward ocean diurnal tide model sensitivity to changes in the frequency zonal structure and meridional structure of the astronomical diurnal tidal forcing three global free oscillations that are important for understanding diurnal tides as a superposition of forced damped resonant free oscillations are identified an admittance analysis of the frequency sweep experiments demonstrates that some coastal locations such as the sea of okhotsk are resonant to diurnal tidal forcing as in earlier wo

crossing of the equator by the deep western boundary current in the western atlantic ocean abstract property distributions and geostrophic shear from a hydrographic section near 37 w in the atlantic ocean show the deep western boundary current dwbc in the north atlantic deep water nadw established against the western boundary of the brazil basin immediately south of the equator between 2 and 5 s the dwbc thus has directly crossed the equator to the south atlantic following the east southeast trend of the continental slope isobaths the estimated dwbc transport of nadw is 35 106 m3 s 1 similar to other estimates from the tropics discussed here these large dwbc transports are opposed by flow of deep water to the north atlantic immediately offshore of the dwbc with as much as two thirds of the dwbc transport being returned as these recirculations one recirculation center is the guiana basin north of the equator but extends at least a few hundred kilometers south of the equator another is visible at 11 s in the brazil basin the degree of connection of these two observed recirculatio

extended deep equatorial layering as a possible imprint of inertial instability the deep equatorial track of the world ocean is subject to intense zonal flow fields that still remain to be better understood inertial instability has been invoked to explain some of its features here we present possible in situ imprints of such a mechanism in the equatorial atlantic ocean below the thermocline we analyse the observed pattern of homogeneous density layers of 50 100 m vertical scale which are characterized by a large meridional coherency up to 2degrees of latitude a concentration in the vicinity of the equator and foremost a vertical localization within regions of well mixed angular momentum westward jets these distinctive properties suggest inertial instability to be a plausible mechanism for this extended layering numerical simulations forced by a time oscillating shear reproduce the observed density layering characteristics the prescription of deep jets in the background flow controls the vertical localization of the layering inside westward jets

shear and strain in santa monica basin by injecting a cloud of sf6 into santa monica basin at a depth of 790 m and observing its vertical spread ledwell and watson 1991 estimate the average diapycnal diffusivity between 750 and 850 m as kp 2 5 10 5 m2 m 1 this diffusivity is higher than inferred from microstructure measurements in the open ocean thermocline for typical internal wave levels gregg and sanford 1988 to examine shear and strain in the basin we dropped expendable current profilers xcps and calculated strain from conductivity temperature and depth ctd casts shear and strain are above the gm76 model spectrum garrett and munk 1975 cairns and williams 1976 and comparisons with published parameterizations indicate more than enough shear variance to account for the high diffusivity reported by ledwell and watson thus the eddy diffusivity in santa monica basin is not at odds with lower values estimated from microstructure measurements in the open ocean but is due to an elevated internal wave field the spectral shapes however differ from typical open ocean spectra

temporal and spatial structure of the equatorial deep jets in the pacific ocean abstract the spatial and temporal structure of the equatorial deep jets edjs in the pacific ocean is investigated using ctd station data taken on the equator from 1979 through 2001 the edjs are revealed in profiles of vertical strain z estimated from the ctd data in a stretched vertical coordinate system the majority of synoptic meridional sections were occupied over an 8 yr span west of the date line two decade equatorial time series are available at both 110 w and 140 w analysis shows the expected equatorial trapping of z but yields little new detailed information about the edj meridional structure analysis of the equatorial data yields novel results the edjs are most easily seen in the eastern pacific at and east of 140 w there they may be isolated from the influence of higher frequency rossby waves generated by surface forcing spectral analysis of equatorial z profiles shows a significant and coherent peak at 400 sdbar vertical wavelength with no 1 56 10 3 s 1 from 95 w to 142

antarctic intermediate water circulation in the tropical and subtropical south atlantic recent hydrographic data from the south atlantic ventilation experiment cruises and others are combined with historical data and used to map the isopycnal properties corresponding to the antarctic intermediate water aaiw in the atlantic ocean the low salinity of the aaiw extends eastward across the south atlantic just south of the equator 3 4 s evidence of a weak eastward flow just north of the equator 1 2 n is also shown lateral and vertical homogenization of properties in the aaiw is found at the equator between 2 s and 2 n there is no clear zonal gradient in salinity just along the equator these observations suggest enhanced mixing within the equatorial baroclinic deformation radius the south atlantic tropical gyre is shown to consist of the following three cells one cyclonic cell centered at about 7 s another centered at about 19 s in the west and 23 s in the east and one anticyclonic cell centered at about 13 s these cells are associated with a westward extension at 10 s of high salinity and low oxygen which originates in the eastern tropical south atlantic and a front in these properties at about 15 s in the west and about 20 s in the east

a composite spectrum of vertical shear in the upper ocean abstract results from three separate velocity profilers operated nearly simultaneously in the northwest atlantic in 1975 are used to form a composite shear spectrum over vertical wavelengths from 100 m down to a few centimeters this exercise constitutes an intercomparison of the three different measurement techniques and reveals a shear spectrum which is approximately fiat at a wkb scaled level from k 0 01 cpm through k0 0 1 cpm then falls as k 1 to a buoyancy wavenumber k0 n3 1 2 determined by the local average vaisala frequency n and the volume averaged dissipation rate various consequences of the observed shear spectral shape are explored

energy and heat fluxes due to vertically propagating yanai waves observed in the equatorial indian ocean shipboard current measurements in the equatorial indian ocean in october and november of 2011 revealed oscillations in the meridional velocity with amplitude 0 10m s these were clearest in a layer extending from 300 to 600 m depth and had periods near 3 weeks phase propagation was upward measurements from two sequential time series at the equator four meridional transects and one zonal transect are used to identify the oscillation as a yanai wave packet and to establish its dominant frequency and vertical wavelength the doppler shift is accounted for so that measured wave properties are translated into the reference frame of the mean zonal flow we take advantage of the fact that in the depth range where the wave signal was clearest the time averaged current and buoyancy frequency were nearly uniform with depth allowing application of the classical theoretical representation of vertically propagating plane waves using the theory we estimate wave properties that are not directly measured such as the group velocity and the zonal wavelength and phase speed the theory predicts a vertical energy flux that is comparable to that carried by midlatitude near inertial waves we also quantify the wave driven meridional heat flux and the stokes drift

low frequency variability in the equatorial atlantic abstract low frequency v and u component oscillations in the eastern equatorial atlantic are addressed using lime series of up to 1 5 years duration from the lower portion of the main thermocline a distinct frequency separation is observed with characteristic time scales of 1 month for v and 4 8 months for u the principal v component oscillations correspond to seasonally modulated linear equatorially trapped rossby gravity waves apparently generated at the surface in the central equatorial atlantic by shear instability between the south equatorial current and the north equatorial countercurrent their length and time scales are well defined and they agree with theoretical predictions the principal u component oscillations correspond to the deep zonal jets observed by recent profiling experiments in the indian and pacific oceans the vertical scales found here agree with the results from the other oceans however insufficient data are available anywhere to ascertain zonal scales linear theory would

atlantic equatorial deep jets space time structure and cross equatorial fluxes the so called equatorial stacked jets are analyzed with ship board observations and moored time series from the atlantic ocean the features are identified and isolated by comparing vertical wavenumber spectra at the equator with those a few degrees from the equator mode filtering gives clear views of the jets in meridional sections the typical extent being 618 in latitude the vertical structure can be well described explaining 82 of the variance by n21 stretched cosines with a gaussian amplitude tapering in the vertical the stretched wavelengths are somewhat variable fitting jets of a fixed stretched wavelength to four moored sensors in the depth range 1300 1900 m allows one to track the vertical phase of the jets with an rms error of 308 458 the resulting fit from a 20 month moored time series shows long periods of unchanging jet conditions and intermittent times of high variability there is no significant vertical propagation on these timescales nor a seasonal reversal using a composite from many different experiments interannual variability is visible however a possible mechanism for the stacked jets is inertial instability resulting from background meridional shears at the equator a condition is that the ertel potential vorticity becomes zero somewhere due to meridional asymmetries in the zonal flows the ship board observations show that this may be approximately fulfilled by the instantaneous zonal low mode flows at various depths resulting from an excess of zonal momentum south of the equator most of the time inertial instability should act to redistribute this zonal momentum and our mooring data show indeed persistent northward momentum flux but not at the depth levels expected the momentum transport might suggest that the jets can also flux or mix other properties across the equator

a 20th century acceleration in global sea level rise 1 multi century sea level records and climate models indicate an acceleration of sea level rise but no 20th century acceleration has previously been detected a reconstruction of global sea level using tide gauge data from 1950 to 2000 indicates a larger rate of rise after 1993 and other periods of rapid sea level rise but no significant acceleration over this period here we extend the reconstruction of global mean sea level back to 1870 and find a sea level rise from january 1870 to december 2004 of 195 mm a 20th century rate of sea level rise of 1 7 0 3 mm yr 1 and a significant acceleration of sea level rise of 0 013 0 006 mm yr 2 this acceleration is an important confirmation of climate change simulations which show an acceleration not previously observed if this acceleration remained constant then the 1990 to 2100 rise would range from 280 to 340 mm consistent with projections in the ipcc tar

the deep currents in the eastern equatorial atlantic ocean 1 in the atlantic ocean equatorial deep jets have been observed in the central and western equatorial basin here we present three meridional velocity sections carried out in boreal summer 2000 in the eastern equatorial atlantic at that time the deep equatorial jets were observed to weaken or to vanish in the gulf of guinea toward the african coast at 10 w the comparison with currents measured one year before in boreal summer 1999 along with tracer distributions confirm the existence of an eastward route along the equator of part of the north atlantic deep water

on the width of the equatorial deep jets the equatorial deep jets edj are a striking feature of the equatorial ocean circulation in the atlantic ocean the edj are associated with a vertical scale of between 300 and 700 m a time scale of roughly 4 5 years and upward energy propagation to the surface it has been found that the meridional width of the edj is roughly 1 5 times larger than expected based on their vertical scale here we use a shallow water model for a high order baroclinic vertical normal mode to argue that mixing of momentum along isopycnals can explain the enhanced width a lateral eddy viscosity of 300 m2 s 1 10 is found to be sufficient to account for the width implied by observations

modelling the embedment process during offshore pipe laying on fine grained soils subsea pipelines are becoming an increasingly significant element of offshore hydrocarbon developments as exploration moves into deep water environments further from shore during the lay process pipelines are subject to small amplitude vertical and horizontal oscillations driven by the sea state and lay vessel motions centrifuge model tests have been used to simulate these small amplitude lay effects with varying degrees of idealization relative to the real lay process in the soft soils found in deep water pipe embedment can exceed a diameter or more thus significantly affecting the lateral pipe soil interaction axial resistance and thermal insulation in this paper results from centrifuge model tests are used to calibrate a model for calculating the dynamic embedment of a subsea pipeline the model uses elements of plasticity theory to capture the effects of combined vertical and horizontal loading and incorporates the softening of the surrounding soil as it is remoulded due to the pipelinemotions influences from the lay rate lay geometry and sea state are included in the calculation process the model is compared with observed as laid pipeline embedment data fromfield surveys at three different offshore sites using site specific soil parameters obtained from in situ testing and idealized pipe loads and motions to represent the load and displacement patterns during offshore pipe laying respectively the model is shown to capture well the final as laid embedment measured in the field surveys

pipe soil interaction on free span shoulder subject to vortex induced vibration free span refers to a subsea pipeline section that is suspended over the seabed such a pipe section is vulnerable to vortex induced vibration leading to possible fatigue pipe damage existing stud

kinematic elements of antarctic intermediate water in the western south atlantic the northward flowing antarctic intermediate water aaiw is a major contributor to the large scale meridional circulation of water masses in the atlantic together with bottom and thermocline water aaiw replaces north atlantic deep water that penetrates into the south atlantic from the north on the northbound propagation of aaiw from its formation area in the south western region of the argentine basin the aaiw progresses through a complex spreading pattern at the base of the main thermocline this paper presents trajectories of 75 subsurface floats seeded at aaiw depth the floats were acoustically tracked covering a period from december 1992 to october 1996 discussions of selected trajectories focus on mesoscale kinematic elements that contribute to the spreading of aaiw in the equatorial region intermittent westward and eastward currents were observed suggesting a seasonal cycle of the aaiw flow direction at tropical latitudes just offshore the intermediate western boundary current the southward advection of an anticyclonic eddy was observed between 5 degrees s and 11 degrees s farther offshore the flow lacks an advective pattern and is governed by eddy diffusion the westward subtropical gyre return current at about 28 degrees s shows considerable stability with the mean kinetic energy to eddy kinetic energy ratio being around one farther south the eastward deeper south atlantic current is dominated by large scale meanders with particle velocities in excess of 60 cm s 1 at the brazil falkland current confluence zone a cyclonic eddy near 40 degrees s 50 degrees w seems to act as injector of freshly mixed aaiw into the subtropical gyre in general much of the mixing of the various blends of aaiw is due to the activity of mesoscale eddies which frequently reoccupy similar positions c 1999 elsevier science ltd all rights reserved

pipe soil interaction model for current induced pipeline instability on a sloping sandy seabed as offshore exploitation moves to deeper waters ocean currents become the prevailing hydrodynamic loads on pipelines and at the same time a sloping seabed is always encountered the prediction of lateral soil resistance is vital in evaluating pipeline on bottom stability unlike previous pipe soil interaction models used mainly for horizontal seabed conditions a pipe soil interaction model for current induced downslope and upslope instabilities is proposed by using the limit equilibrium approach the coulomb s theory of passive earth pressure for the sloping seabed is incorporated in the derivation the model verification with existing full scale tests shows good agreement between the experimental results and predicted ones parametric study indicates that the effect of slope angle on pipeline lateral soil resistance is significant in the examined range of slope angle from 15 to 15 the critical pipeline embedment and corresponding passive pressure decrease approximately linearly with increasing slo

deep jets in the equatorial atlantic ocean deep velocity profiles taken in the equatorial atlantic ocean show equatorially trapped deep jets with similar features to those of the indian and pacific oceans a zonal velocity of the order of 10 to 20 cm s 1 and a meridional scale of 1 in the pacific and indian oceans the zonal extent of the jets is at least 15 of longitude owing to the lack of synoptic measurements we have no information on the zonal scale in the atlantic ocean but we present here zonal velocity profiles made at a 16 month interval that have identical baroclinic structure in the western 35 w and central basin 13 w the atlantic jets have a vertical scale larger 400 600 m than those observed in the pacific ocean 250 400 m our measurements confirm the opposite directions of the jets for different seasons in the atlantic ocean furthermore for a given season the vertical profiles of zonal velocity at 35 w 0 are astonishingly similar at a 5 year interval as in the pacific and indian oceans the jets are embedded in a large vertical scale current that changes direction with time the few profiles available in the equatorial atlantic ocean suggest a seasonal reversal of the jets but neither this nor the temporal variability of the large scale current has been adequately resolved

forcing of the atlantic equatorial deep jets derived from observations the equatorial deep jets edjs are an ubiquitous feature of the equatorial oceans in the atlantic ocean they are the dominant mode of interannual variability of the zonal flow at intermediate depth on the basis of more than 10 years of moored observations of zonal velocity at 23 w the vertically propagating edjs are best described as superimposed oscillations of the 13th to the 23th baroclinic modes with a dominant oscillation period for all modes of 1650 days this period is close to the resonance period of the respective gravest equatorial basin mode for the dominant vertical modes 16 and 17 it is argued that since the equatorial basin mode is composed of linear equatorial waves a linear reduced gravity model can be employed for each baroclinic mode driven by spatially homogeneous zonal forcing oscillating with the edj period the fit of the model solutions to observations at 23 w yields a basin wide reconstruction of the edjs and the associated vertical structure of their forcing from the resulting vertical profile of mean power input and vertical energy flux on the equator it follows that the edjs are locally maintained over a considerable depth range from 500 2500 m with the maximum power input and vertical energy flux at 1300 m the strong dissipation closely ties the apparent vertical propagation of energy to the vertical distribution of power input and together with the edjs prevailing downward phase propagation require the phase of the forcing of the edjs to propagate downward

variability at intermediate depths at the equator in the atlantic ocean in 2000 06 annual cycle equatorial deep jets and intraseasonal meridional velocity fluctuations time series of high vertical resolution current meter measurements between 600 m and 1800 m depths on the equator in the atlantic were obtained at two locations 10 and 23 w the measurements have a time span of almost 7 years 2000 06 and provide insights into the temporal scales and vertical structure of variability at intermediate depths variability in the zonal velocity component records is dominated by semiannual annual and interannual fluctuations at semiannual and annual periodicities vertical scales are large on the order of 2000 stretched meters sm and show upward phase propagation in contrast interannual variability is associated with small vertical scale flows called equatorial deep jets edjs presenting downward phase propagation most of the time fitting a plane wave to these small vertical scale flows leads to velocity amplitude vertical scale and temporal scale estimates of 8 normalized cm s 1 440 sm and 4 4 yr however this plane wave cannot explain all the variability presenting small vertical scales indeed the data suggest that along with a seasonal cycle of much larger vertical scale different features with edj vertical scale coexist with the possibility of a semipermanent eastward jet at around 1500 sm variability in the meridional velocity component is dominated by intraseasonal fluctuations in addition at 23 w the meridional component shows low frequency flows that may be due to the interaction of zonal fluctuations with the mid atlantic ridge

observations of shear and vertical stability from a neutrally buoyant float measurements of 1 to 5 m shear and strain from a neutrally buoyant float are used to examine the statistics and causes of shear instability in a 9 day record unstable conditions defined as vz n 2 where vz vz are due to higher than average shear rather than lower than average buoyancy frequency and there are no instances of unstable buoyancy frequency or overturns on the 0 5 m spacing of the thermistors shear is dominated by upward propagating near inertial motions unstable events were more frequent when a near inertial wave packet occupied the water parcel tracked by the float groups of unstable events occur roughly every 5 7 hours at scales 2 5 m and much less often at larger scales events typically last 10 min one buoyancy period or longer these time scales appear to be controlled by vertical advection of 1 m fine structure past the float sensors so do not represent the intrinsic time scales of instability turbulent and mixing quantities are estimated from these fine scale measurements giving a dissipation rate of e 2 3 16 10 10 w kg and an eddy diffusivity of k 3 10 6 m2 s in agreement with direct microstructure estimates therefore the float adequately resolves those quantities needed to estimate turbulent dissipation and could be used to monitor turbulent mixing in the ocean

deep currents and their interpretation as equatorial waves in the western pacific ocean abstract vertical profiles of current and density made within 5 latitude of the equator along longitudes 168 and 179 e the vicinity of the gilbert islands reveal multiple deep current reversals which are confined to the equator these current jets have amplitudes of roughly 5 20 cm s 1 vertical scales of order hundreds of meters and time scales longer than the one month of measurements during the cruise spectral analysis of profiles indicates that 1 meridional trapping varies roughly as the square root of the vertical scale 2 both east and north currents are coherent over meridional separations of 0 45 within roughly 1 30 of the equator and 3 zonal current lags vertical displacement by 4 in depth within 0 45 of the equator zonal coherence scales are smaller than the smallest separation of 3 30 along the equator kinetic energy decreases near the island chain current meter records taken over nearly two years near the islands suggest strong quasi annual variability in deep currents near t

subtropical catastrophe significant loss of low mode tidal energy at 28 9 1 an idealized numerical study of a northward propagating internal tide reveals a dramatic loss of energy to small scale subharmonic instabilities near 28 9 n inspired by observations of the internal tide radiating northward from the hawaiian ridge a three dimensional numerical model is initialized with a northward baroclinic tidal flux of approximately 1 7 kw m after an initial spinup period energy is quickly transferred from the baroclinic tide to subharmonic motions with half the horizontal tidal wavenumber and small vertical scales through nonlinear advection of horizontal tidal velocity gradients potential oceanic implications are twofold first once a steady state has been reached the instability acts as a partial filter of northward tidal flux between 27 5 and 29 5 n in rough agreement with some altimetric tidal observations second elevated shear of the subharmonic motions suggests the potential for elevated near surface dissipation rates near the critical latitude that may be important for upper ocean mixing

equatorial currents at 1000 m in the atlantic ocean twenty seven profiling alace palace floats were deployed in the equatorial atlantic during july august 1997 the floats were ballasted to drift at 1000 m for 10 to 14 days return to the surface while obtaining a temperature profile transmit data via satellite and then after one day return to 1000 m one year float paths are now available floats deployed on the equator were launched into a deep westward jet the jet extends some 1 o 2 o north of the equator with eastward motion observed in floats to the north of 2 on the equatorial current reverses in the central basin to the east in mid october and then back to the west in mid february flow to the north also reverses the short space and time scales contrast with earlier work based on fewer floats that inferred space scales of some 5 o 10 o in latitude and time scales greater than one year the new results are consistent with models that indicate that equatorial rossby waves are the cause of the reversing currents

on perturbations of harmonic constants in the thames estuary summary a long series of southend sea level observations extending over a period of 51 years 1929 79 is analysed using the harmonic method of tidal analysis the harmonic method of tidal analysis and prediction works on the assumption that the relationship of nodal terms with their respective principal terms in the physical tide is the same as in the equilibrium tide it is concluded that although this assumption is very useful in accounting for those terms which are not separable from a given length of observations it is not always fully valid as a result a systematic error is introduced in tidal analysis and prediction it is observed that small secular trends are present in amplitudes and phase lags of some principal tidal constituents in the diurnal band amplitudes of o1 and k1 are almost constant but the phase lag of k1 is increasing and the phase lag of o1 is decreasing in the semi diurnal band amplitudes of m2 s2 and k2 are increasing while the phase lag of m2 is decreasing and the phase lag of k2 is increasing the influence of these secular trends in amplitudes is to increase the tidal range and extreme levels this is confirmed by increases in the range of tide in the last one and a half centuries statistically no significance can be attached to trends in phase lags because standard errors are large a comparison of old records with tides synthesized by modern constituents for london bridge suggests that the phase of the tide was almost stable there from 1683 to 1835 then a large change occurred after 1835 similar changes are noted in the tidal range the nature of these changes indicates that they are partly due to increased input at southend resulting from secular trends in tidal harmonics and partly due to man made alterations embankment bank raising and deepening of the estuary

exact solutions to kawase s linear model of deep ocean circulation abstract exact solutions are found for kawase s linear two layer model of mass driven deep ocean circulation it is demonstrated that for strong damping even though the deep western boundary current dwbc bifurcates at the equator as found in kawase s perturbation solution the equatorial flow is much weaker and has a much broader scale than the imposed dwbc it is found that the presence of an eastern boundary is not necessary for the dwbc to cross the equator in the weak damping case

moored observations of deep low frequency motions in the central pacific ocean vertical structure and interpretation as equatorial waves abstract two year time series of current and temperature collected in the deep equatorial central pacific 0cean as part of the pacific equatorial ocean dynamics pequod project indicate that motions with vertical scales comparable to those of low baroclinic modes dominate motions from annual to fortnightly frequencies properties of equatorial waves are consistent with many aspects of the observed spectra and coherences in particular the hypothesis of a spectrum of long rossby and kelvin waves at periods longer than about 40 days and rossby mixed rossby gravity and kelvin waves at periods between about 14 and 40 days is consistent with the observations neither vertically propagating rays nor randomly phased baroclinic modes can explain coherence phases uniformly but forced phase locked baroclinic modes provide a possible explanation sea level in the central pacific is coherent with deep motions at periods of months or shorter in particular the quasi annual sea level signal associated with the 19

evolution of tidal amplitudes in the eastern pacific ocean 1 global sea level gsl rise is well documented however changes in high waters including the tidal contribution are sometimes more relevant than gsl rise analysis of 34 long tidal records from the eastern pacific ocean shows that k1 and m2 amplitudes k1 and m2 are increasing except for m2 in the gulf of panama north of 18 n k1 and m2 are both growing at 2 2 century 1 the mean increase in total tidal amplitude 0 59 mmyr 1 is less than the present gsl rise 1 7 mmyr 1 however mean sea level is nearly constant in the ne pacific so tidal evolution plays a major regional role in changes in high water levels the spatial pattern of tidal evolution suggests the influence of large scale processes and the similarity in spatial patterns for k1 and m2 excludes mechanisms with strong frequency dependence increasing tidal amplitudes may impact ocean mixing nutrient supply primary production fisheries and coastal erosion

stacked jets in the deep equatorial atlantic ocean 1 middepth current measurements in the equatorial atlantic are characterized by elevated levels of energy contained in zonal flows of high baroclinic mode number these alternating zonal flows often called equatorial stacked jets have amplitudes up to 20 cm s 1 and vertical wavelengths of 600 m the jets are most pronounced in the depth range between 500 and 2500 m repeated direct velocity observations at 35 w indicate that the jets are coherent within 1 of the equator individual jets can persist for 1 2 years but they appear and decay rather irregularly the equatorial stacked jets are also found in realistic general circulation model simulations the features grow in amplitude with increasing horizontal and vertical model resolution however even at very high model resolutions their amplitudes are still underestimated in all model simulations high levels of energy related to the stacked jets are found in the vicinity of the western boundary currents wbcs depth range and strength of the wbcs in different experiments are related to depth range and strength of the jets in the interior stacked jets are characterized by eastward wave propagation suggesting that high baroclinic mode kelvin waves radiate energy generated in the wbc into the interior and form the stacked jets

effect of installation on the bearing capacity of a spudcan under combined loading in soft clay previous numerical analyses of the bearing capacity of embedded footing under combined vertical horizontal and moment loading have been based on the assumption that the foundation is wished in place surrounded by undisturbed soil under these conditions the large displacement and remolding of the soil during the footing installation are not accounted for this assumption results in an overestimation of the capacity this paper presents results of the size and shape of the bearing capacity surface of spudcan footing in soft clay that accounts for the effects of installation in the modeling results for soil sensitivities between one and five and for embedment depths up to three diameters are provided the findings have practical application in the site specific assessment of mobile jack up platforms in soft clay

a simple model for deep equatorial zonal currents forced at lateral boundaries abstract deep lateral boundary processes e g western boundary currents are hypothesized as an alternative energy source exciting the equatorial wave guide at long time scales a linear continuously stratified model is used to study the equatorial zonal currents generated by a time dependent short vertical scale deep zonal jet located at the meridional walls and centered at the equator examples of solutions with periodic transient and spectral forcing are presented for low frequency forcing at the western or eastern boundaries energy travels from the source along ray paths associated with kelvin and long rossby waves respectively linearly damped solutions look similar in both cases solutions show in general a rich baroclinic structure and a complex time dependence e g periodic solutions can exhibit both upward and downward phase propagation and standing mode oscillations at different depths in the water column with the vertical structure depending among other factors on the vertical sca

zonal intermediate currents in the equatorial atlantic ocean acoustic float data collected near 800 m depth are used to map zonal mean currents within the antarctic intermediate water aaiw tongue in the equatorial atlantic alternating zonal jets of 2 latitudinal width are revealed between 6 s and 6 n displacements from profiling floats drifting near 1000 m depth also reveal similar zonal jets at the base of the aaiw layer the strongest jets 15 cm s 1 peak are found at 4 s 2 s 0 2 n and 4 n they are coherent longitudinally over order of 3000 km and poleward of 1 s and 1 n generally coherent vertically between 800 m and 1000 m large seasonal fluctuations exist at both levels within 1 of equator aaiw at 800 m flows westward 8 cm s 1 mean in boreal summer and fall but eastward 3 cm s 1 mean in winter whereas the flow at 1000 m is eastward in late fall and winter

equatorial velocity profiles part ii zonal component abstract vertical profiles of horizontal velocity made along 53 e in the western indian ocean during and after he onset of the southwest monsoon in 1976 show features in zonal velocity of relatively small vertical scale persistence of the features over the month long observation period and over 2 degrees of longitude indicates long temporal and zonal scales the vertical structure is common to those profiles close to the equator with no appreciable variation in amplitude or depth between 1 30 n and 3 n the phase of the features reverses there is no evidence of similar features at 5 n the data suggest meridionally trapped equatorial waves similarities between the observed phenomena and the linear theory of equatorial waves are striking but quantitative comparisons lead us to question its naive application here equatorial intensification is apparent but it does not scale with the rossby radius of deformation indicating that kelvin waves are not dominant at any vertical scale the phase change and

deep circulation in the equatorial atlantic ocean in the atlantic ocean the northward export of warm surface water is compensated by a southward flow of cold north atlantic deep water nadw the nadvv is transported southward along the american continental margin within the deep western boundary current dwbc some tracer and float observations have shown that part of the dwbc water flows eastward along the equator here we present three meridional velocity sections which give an instantaneous image of the lop to bottom zonal circulation along the equatorial atlantic they reveal the presence of equatorial deep jets edjs between 1 30 n and 1 30 s alternating eastward westward currents with short vertical scale surrounded by columns of eastward currents the extra equatorial jets or eejs at 2 n and 2 s in addition to direct velocity measurements tracer distributions give indications of water mass feeding of the edjs and eejs by the dwbc

the zonal dimension of the indian ocean meridional overturning circulation abstract the three dimensional structure of the meridional overturning circulation moc in the deep indian ocean is investigated with an eddy permitting ocean model the amplitude of the modeled deep indian ocean moc is 5 6 sv 1 sv 106 m3 s 1 a broadly realistic but somewhat weak overturning although the model parameterization of diapycnal mixing is inaccurate the model s short spinup allows the effective diapycnal velocity the sum of model drift and the explicitly modeled diapycnal velocity to resemble the true real ocean diapycnal velocity for this reason the model is able to recover the broad zonal asymmetry in the turbulent buoyancy flux that is suggested by observations the model features a substantial deep depth reversing zonal circulation of nearly 50 of the moc the existence of this circulation brought about by the zonally asymmetric distribution of diapycnal mixing implies a much slower ventilation of the deep indian ocean by a factor of 5 6 than would be in place without zon

pipe soil interaction model incorporating large lateral displacements in calcareous sand the use of the plasticity theory offers an attractive framework to encapsulate the behavior of a pipe and the underlying soil in terminology consistent with pipeline structural analysis models that express the pipe soil behavior purely in terms of the loads on a segment of pipe and the corresponding displacements have been suggested although verification with geotechnical centrifuge experiments has been limited to relatively small lateral displacements i e less than two pipe diameters over larger movements the berms that build up alongside the pipe affect the load displacement behavior with existing strain hardening plasticity models incapable of simulating this transition this technical note provides experimental evidence of pipe soil behavior for lateral displacements for up to five diameters it further presents observations from 20 centrifuge experiments of a prototype 1 m diameter pipe in calcareous sand the results are used to validate the modification of a pipe soil model to include the

some characteristics of internal gravity waves in the equatorial pacific one year moored current and temperature measurements made in the central equatorial pacific ocean at subthermocline depths display spectral characteristics at internal gravity wave frequencies which are distinct from those found at mid latitudes these characteristics are meridional orientation of current ellipses kinetic energy scaling proportional to buoyancy frequency 1 2 and coherence of zonal current and temperature at phases significantly different then 0 or 180 characteristics vary over as little as 100 m vertically but not over 40 km horizontally low frequency flow is predominantly zonal and shares similar spatial structure suggesting internal waves are influenced by it although horizontal internal wave fluxes cannot be calculated directly from the observations models provide a framework in which to interpret internal wave spectral characteristics models of internal waves near the equator in a resting ocean an ocean with a uniform zonal current and an ocean with depth dependent zonal current all require wave flux to be horizontally anisotropic in order to obtain current ellipses and zonal current temperatures similar to those observed the model with vertical shear is the most realistic of these three observed shears are sufficiently strong to allow the possibility of internal wave critical layers which in turn are a likely source of both horizontal anisotropy and vertical asymmetry of wave fluxes

deep cross equatorial flow in the atlantic measured with sofar floats neutrally buoyant sofar floats at nominal depths of 800 1800 and 3300 m were tracked for 21 months in the vicinity of tropical boundary currents in the atlantic near 6 n and at several sites near 11 n as well as along the equator trajectories at 1800 m show a swift 50 cm s narrow 100 km wide southward flowing deep western boundary current dwbc extending from 7 n to the equator the average transport per unit depth in the dwbc was estimated to be 13 8 103 m2 s coupling this value with mean velocities measured in the dwbc by current meters gave a volume transport of 15 106 m3 s between depths of 900 m and 2800 m approximately 6 106 m3 s recirculated northward between the dwbc and the mid atlantic ridge leaving 9 106 m3 s as cross equatorial transport no obvious dwbc nor swift equatorial current was observed by the 3300 m floats a low mean velocity at this depth lay between f 11 and higher velocity cores above and below the 1800 m trajectories also suggest that at times february march 1989 the north atlantic deep water in the dwbc turned eastward and flowed along the equator and at other times august september 1990 the dwbc crossed the equator and continued southward the velocity near the equator calculated by grouping floats in a box along the equator was eastward at 4 1 cm s from february 1989 to february 1990 and westward at 4 6 cm s from march 1990 to november 1990 thus the amount of cross equatorial flow in the dwbc appeared to be linked to low frequency variability of the structure of the equatorial current system floats in antarctic intermediate water at 800 m revealed a northwestward western boundary current although flow patterns were complicated three floats that significantly contributed to the northwestward flow looped in anticyclonic eddies that translated up the coast at 8 cm s six 800 m floats drifted eastward along the equator between 5 s and 6 n at a mean velocity of 11 cm s one reached 5 w in the gulf of guinea suggesting that the equatorial currents at this depth extended at least 35 40 along the equator three of these floats reversed direction near the end of the tracking period

evidence for seafloor intensified mixing by surface generated equatorial waves little is known about mixing in the abyssal equatorial oceans in spite of its inferred importance for upwelling dense water here we present full depth microstructure turbulence profiles obtained in the equatorial pacific that show evidence for intense wind generated abyssal mixing mixing was intensified over the bottom 700 m where the diffusivity reached 10 3 m2 s 1 of similar intensity to mixing driven by tidal flow over rough topography however here the mixing was found over smooth topography we suggest that the intense mixing could have been driven by surface generated equatorial waves through two possible mechanisms 1 near bottom wave trapping as a result of the horizontal component of the earth s rotation and 2 inertial instability the generation of lee waves over smooth topography at low latitudes and their subsequent breaking is another viable mechanism for the mixing

uplift tests on full scale pipe segment in lumpy soft clay backfill upheaval buckling of pipelines caused by thermal and pressure induced loading is an important issue in pipeline design the uplift capacity of pipelines is determined by the pipe soil interaction during pipeline upheaval in soil pipelines to be installed in soft clay are usually placed into trenches and then backfilled in this paper a set of test devices were developed and a series of full scale model tests were carried out on a pipe segment buried in lumpy soft clay backfill including backfilling tests load controlled uplift tests and a displacement controlled test eight total pressure transducers were embedded in the wall of the pipe segment to measure soil pressures on the pipe segment and five linear variable differential displacement transducers lvdts were arranged to record the vertical displacement of the pipe segment and the surface of the soft clay ground the stabilizing force keeping the pipe segment in place during the backfilling process was found to fit a nearly linear relationshi

secular trends in ocean tides observations and model results 1 during the last century the response of the oceans to tidal forces has changed significantly this study focuses on an analysis of long term sea level records located in the atlantic and pacific primarily in the northern hemisphere it shows that changes of tidal amplitude and or phase have taken place over large scales the principal solar semidiurnal s2 tide shows the largest trends at some locations the change in the mean tidal range due to tidal trends is significant compared with the trend in mean sea level thus it might be advisable to consider these changes in studies of the impact of rising sea level numerical simulations of the principal lunar semidiurnal tide m2 demonstrate a model sensitivity in the north atlantic to changes in glacial isostatic adjustment and sea level rise which captures 30 40 of the magnitude of the trends in observations however the spatial patterns do not agree well with those inferred from observations suggesting that forward global models are currently useful for qualitative but not quantitative understanding of the observed trends a global free oscillation synthesis indicates that sea level rise due to glacial isostatic adjustment leads to decreasing global resonant periods and increasing damping in the system and a coupled oscillator model shows that changes in sea level on the shelf are much more effective at perturbing shelf and ocean tides than sea level changes in the deep ocean