pacific equatorial subsurface countercurrent velocity transport and potential vorticity concurrent shipboard adcp and ctd sections are used to calculate the mean velocity transport and potential vorticity fields associated with the pacific equatorial subsurface countercurrents sccs averaged in stream coordinates the core eastward velocity of the sccs is a factor of 2 higher than previously reported means but the estimated transports are unchanged the meridional profile of zonal velocity along isopycnals is sharply peaked and nearly linear on each flank of the current the sharp and strong reversal of relative vorticity over a distance of 20 km at the jet core sharpens the coincident potential vorticity front this front separates a region of very low homogeneous potential vorticity on the equatorward side from a homogeneous high potential vorticity region on the poleward side each potential vorticity pool extends well beyond the edges of the scc into regions of westward flow on the equatorward sides of the sccs this westward flow is the equatorial intermediate current in the western pacific but in the central and eastern parts of the basin it is off the equator in deep extensions of the south equatorial current in the central and eastern regions the net westward transport in an isopycnal layer between the sccs exceeds the combined eastward scc transport in that layer the net zonal transport between the scc cores is highly divergent in the east and convergent in the west this pattern together with downstream changes in scc density indicates that neither they nor the westward return flows are simple inertial recirculations strong diapycnal processes must be involved

equatorial subthermocline currents across the pacific recent sections crossing the equator at nine longitudes from 146 e to 86 w show zonal currents below 400 m similar to those found in a 16 month mean section on 159 w from the pacific equatorial ocean dynamics pequod program in 1982 1983 most of the new measurements were made with a lowered acoustic doppler current profiler eastward current extrema north and south intermediate countercurrents are found in all sections about 2 from the equator in the depth range 500 1500 m with the possible exceptions of 146 e where topography complicates the picture south of the equator and 150 e where the sections extend only from 1 s to 2 n poleward of the intermediate countercurrents westward flow is found near 3 from the equator in most of the sections on the equator from 250 500 m depth a westward equatorial intermediate current is found in many but not all of the sections similarly it is present in the pequod mean but not in all synoptic sections below the intermediate currents and countercurrents an eastward current near 3000 m was found at and south of the equator in the pequod mean and in the new sections from 150 e to 110 w near 4000 m there is westward flow south of the equator in the pequod mean and near the equator in the new sections from 179 e to 135 w geostrophic currents calculated from an 8 year mean hydrographic section at 165 e also resemble the pequod mean although not conclusive the evidence presented here indicates that these currents are basin scale components of the general circulation perhaps involving vigorous horizontal recirculation in a set of basin wide elongated gyres within a few degrees of the equator

observations of the equatorial intermediate current in the western pacific ocean 165 e abstract direct current measurements 0 600 m re 600 m were carried out every six months from january 1984 to june 1986 in the western tropical pacific ocean 165 e from 20 s to 10 n the equatorial intermediate current eic occurred beneath the equatorial undercurrent euc in the 300 500 m depth range between 20 s and 2 n at 165 e the mean i e the average of six cruiser eic flow has a characteristic reversed u shape centered at the equator its associated hydrological features are i the eic transport water of salinity 34 6 34 9 ii its upper and lower limits correspond to the 26 4 and 27 0 sigma t surfaces and ifi its velocity core is located in the 1 1 140c water the average transport of the eic is 7 0 4 8 106 m3 s 1 i e 35 of the mean euc transport computed for the same cruises individual cruises exhibit little variability in the vertical 250 500 m and meridional 2 s 2 n eic structure the eic velocity core during these cruises is thinnest at the equator and ranges in

water mass and transport variability at 110 w in the equatorial pacific abstract an analysis of nine hydrographic sections collected in 1979 81 along 110 w in the equatorial pacific ocean is presented sections typically sampled the upper 500 m of the water column from 10 n to 3 s analysis concentrated on the repeated sections north of the equator examination of the variability of eastward transport indicates that the north equatorial countercurrent necc and the northern subsurface countercurrent nscc cannot be distinguished solely on the basis of water mass structure however using a potential density surface 25 0 as a current boundary we find that on average the nscc transports 13 7 106 m3 s 1 compared to only 8 3 106 m3 s 1 for the necc the nscc flow is sufficiently stable so that meridional surface dynamic height gradient remains a good index of zonal transport fluctuations variations in surface dynamic height observed in our data and in the eastropac data indicate a seasonal cycle to the surface topography with large values for the equatorial and coun

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

mooring observations of equatorial currents in the upper 1000 m of the western pacific ocean during 2014 time depth variations of the equatorial currents over the upper 1000 m depth in the western pacific ocean were directly measured by acoustic doppler current profiler moorings at 2 degrees n 140 degrees e and 4 7 degrees n 140 degrees e during january august 2014 intraseasonal variations of the equatorial currents with periods of 37 73 days were observed encompassing the north equatorial countercurrent necc northern branch of the south equatorial current sec equatorial undercurrent euc equatorial intermediate current eic north intermediate countercurrent nicc and north equatorial subsurface current nesc compared with previous studies based mainly on shipboard synoptic surveys the 8 month time series of velocity profiles provided direct evidence for the existence of nesc captured reversals of the eic in may and the nesc in june from westward to eastward direction and revealed larger vertical extensions of the sec and nesc and greater depths of the eic and nicc than previously thought according to a global analysis product of ocean surface current during january april 2014 the necc was located around its southernmost position and with its the weakest intensity over the past 20 years some of the anomalous characteristics of these flows may be related to the fickle el nino of 2014

subthermocline and intermediate zonal currents in the tropical pacific ocean paths and vertical structure abstractthe mean subthermocline and intermediate zonal circulation in the tropical pacific is investigated using a compilation of shipboard adcp measurements and absolute geostrophic velocities constructed from a high resolution 0 2000 m argo climatology referenced to a 1000 m velocity field derived from argo float drifts this reference field is dominated by basinwide alternating zonal jets with a meridional wavelength of about 3 in regions where the sampling of sadcp data is sufficient the consistency between the two independent datasets is striking using the argo drift reference is crucial to capture the current structures two apparently distinct systems of alternating westward and eastward zonal jets are seen in both datasets equatorward of 10 a series of low latitude subthermocline currents llscs below the thermocline extending from about 200 to 800 m including the eastward tsuchiya jets and a series of low latitude intermediate currents llics extending from about 700 to at least 2000

equatorial undercurrent disappears during 1982 1983 el nino the equatorial undercurrent at 159 w decayed during august 1982 partially reversed during september and rapidly reappeared in january 1983 the virtual disappearance is consistent with the basin wide adjustment of sea surface slope to the strong westerly winds in the western and central pacific that caused the 1982 1983 el nino event

intermediate zonal jets in the tropical pacific ocean observed by argo floats abstractargo float data in the tropical pacific ocean during january 2003 august 2011 are analyzed to obtain lagrangian subsurface velocities at their parking depths maps of mean zonal velocities at 1000 and 1500 m are presented at both depths a series of alternating westward and eastward zonal jets with a meridional scale of 1 5 is seen at the basin scale from 10 s to 10 n these alternating jets with mean speeds about 5 cm s 1 are clearly present in the western and central parts of the basin but weaken and disappear approaching the eastern coast they are stronger in the southern hemisphere along the equator at both 1000 and 1500 m a westward jet is seen the jets closer to the equator are remarkably zonally coherent across the basin but the jets farther poleward appear broken in several segments in the western half of the basin the 1000 m zonal jets appear to slant slightly poleward from east to west at the western boundary in the south east of solomon islands and papua new guinea the al

upper and intermediate circulation in the western equatorial pacific ocean in october 1999 and april 2000 1 the upper and intermediate circulation 0 1200 m in the western equatorial pacific ocean is examined thanks to lowered acoustic doppler current profiler ladcp measurements carried out during two cruises in october 1999 and april 2000 several new features of the equatorial circulation are discussed it is shown that the secondary south subsurface countercurrent ssscc laying at 6 s 400 m depth had a deep extension at 165 e with a maximum core velocity around 5 s 1000 m furthermore the equatorial intermediate current eic and the lower eic leic displayed a strong temporal variability between 165 e and 180 as these two westward currents were replaced by eastward flow along the equator on the second cruise finally during the april 2000 cruise the zonal velocity profile carried out at the equator east of the gilbert island around 175 e broke into small vertical scales possibly reflecting topographic effect and or destabilization mechanism that leads to the formation of long zonal jet like structures

results from a velocity transect along the equator from 125 to 159 w abstract during march april 1980 a velocity and ctd transect was made in the pacific along the equator from 110 to 180 w the horizontal baroclinic pressure gradient was observed to be primary confined between 160 and 130 w direct velocity profiles between 125 and 159 w showed the equatorial undercurrent to be a continuous feature maximum eastward transport per unit width in the undercurrent was 2 5 108 cm2 s 1 at 150 w and decreased both westward and eastward to about 1 5 108 cm2 s 1 at 159 w and at 125 w despite these variations the maximum speeds along the transect remained 150 cm s 1 beneath the undercurrent the velocities decreased and were of the order of 25 cm s 1 they exhibited small scale variation in the vertical as has recently been observed at other equatorial locations above 1600 m the vertical wavelength of these variations in the zonal component was 300 m small scale features in these zonal velocities were identifiable over 10 of longitude 1000 km the small vertical an

direct measurements of upper ocean currents and water properties across the tropical pacific during the 1990s abstract meridional sections of upper ocean zonal currents potential temperature and salinity are estimated at ten longitudes from 143 e to 95 w using conductivity temperature depth and acoustic doppler current profiler data from 172 synoptic sections taken in the tropical pacific between 138 e and 86 w mostly in the 1990s data reduction is carried out in a potential isopycnal and mixed layer framework to preserve a sharp pycnocline a mixed layer water property extrema and velocity extrema mean zonal currents potential temperatures and salinities are produced at each longitude the seasonal cycles of these fields are also estimated as well as a simple el nino southern oscillation enso cycle zonal sections along the equator are also presented properties of the near equatorial zonal currents including transports temperatures and salinities are estimated separately from the synoptic sections the seasonal cycles of these quantities and their correlations with the southern oscillation index are investigated the work is distinguished from most existing literature in that direct estimates of zonal velocity are combined with contemporaneous temperature and salinity data allowing trans pacific estimates of near equatorial current transports and properties including those of the northern branch of the south equatorial current the new guinea coastal undercurrent and the equatorial undercurrent

upper ocean water masses and transports in the western tropical pacific 165 e abstract as part of the international toga program the orstom center in noumea new caledonia initiated in january 1984 a series of semi annual cruises along the 165 e meridian from 20 s to 10 n across the equatorial current system of the western pacific this paper presents an analysis of the first six hydrographic 0 1000 m and current 0 600 m sections a detailed description of typical january 1986 vertical structures of temperature salinity and zonal measured velocity is offered differences are noted with structures previously obtained in the tropical pacific compared to the central and eastern pacific the 165 e dataset evidences a much weaker equatorial upwelling and deeper surface isothermal layer and subsurface currents compared to the few western pacific measurements the two speed cores of the equatorial undercurrent euc previously reported at 100 and 200 m are not observed here special attention is given to the eastward equatorial jet 2 s 2 n 0 75 m measured in january 1985 wh

from the subtropics to the central equatorial pacific ocean neodymium isotopic composition and rare earth element concentration variations 1 neodymium isotopic compositions end and rare earth element ree concentrations were measured for filtered surface to deep waters 112 samples in the southern tropical pacific the relatively detailed picture of these tracer distributions allowed us to refine the areas where oceanic end variations occur end values increase for most of the water masses flowing from samoa to the solomon sea and in the papua new guinea png area as already observed furthermore water masses arriving from the eastern equatorial pacific 200 550 m depth also revealed radiogenic values possibly acquired in the vicinity of the south american coasts and galapagos islands these end variations affect the whole water column the most likely process causing such variations is boundary exchange between the numerous radiogenic slopes margins located in this area and seawater flowing past dissolution of atmospheric deposition and or diffuse streaming of volcanic ash are also suggested to explain the radiogenic end observed at the surface in the png area interestingly a positive europium eu anomaly characterizes the normalized ree patterns of most of the studied water masses this anomaly is consistent with the ree patterns of sediment and rock samples that are potential sources for the local waters such consistency reinforces the hypothesis that lithogenic sources play a major role in the oceanic ree budget thanks to boundary exchange the data set presented here is a good basis for further sampling that will be realized in the framework of the ongoing geotraces program www geotraces org

observing the galapagos euc interaction insights and challenges although sustained observations yield a description of the mean equatorial current system from the western pacific to the eastern terminus of the tropical atmosphere ocean tao array a comprehensive observational dataset suitable for describing the structure and pathways of the equatorial undercurrent euc east of 958w does not exist and therefore climate models are unconstrained in a region that plays acriticalroleinocean atmospherecoupling furthermore oceanmodelssuggestthattheinteractionbetween

how much energy propagates vertically in the equatorial oceans abstract vertically propagating linear wave calculations using realistic equatorial buoyancy profiles are presented which show the percentage of the downward surface energy flux that reaches the deep equatorial oceans the percentages vary widely depending upon the buoyancy profile and the equivalent depth but can be as low as 10 on average for equivalent depths between 1 cm and 1 m if the thermocline is sharp this means that models with constant or weak thermocline buoyancy profiles which allow all or most downward surface energy flux to reach the deep ocean are very unrealistic in this respect another conclusion is that the observed very low frequency small vertical scale deep jets cannot be explained by linear wave theory as caused by surface forcing it is also shown that a wkb analysis of observations can be misleading even if applied to a single vertically propagating wave in a region that excludes the main thermocline implications are that comparing estimates of the equivalent depth from th

vertically propagating annual and interannual variability in an ogcm simulation of the tropical pacific ocean in 1985 94 abstract the annual and interannual variability in the subthermocline equatorial pacific is studied in a simulation of the tropical pacific for the 1985 94 decade using a primitive equation high resolution model the study focuses on temperature variability and vertical energy fluxes similar to the observations made by w s kessler and j p mccreary the annual harmonic of vertical isotherm displacements presents phase lines sloping downward from east to west with off equatorial maxima estimates of zonal and vertical phase speeds the location of the maxima of isotherm displacements and an analysis of ernergy fluxes suggest the presence of l 1 rossby waves the simulated field is somewhat more trapped toward the equator than the observations a linear simulation is carried out for the vertical standing modes with characteristics derived from the ogcm simulation in the linear simulation high order meridional mode rossby waves are more prominent than in the ogcm simulation however the l 1 ros

annual reversal of the equatorial intermediate current in the pacific observations and model diagnostics abstract a large reversal of zonal transport below the thermocline was observed over a period of 6 months in the western pacific ocean between 2 s and the equator from 26 2 sv 1 sv 106 m3 s 1 eastward in october 1999 to 28 6 sv westward in april 2000 to document this reversal and assess its origin an unprecedented collection of adcp observations of zonal currents 2004 06 together with a realistic ogcm simulation of the tropical pacific was analyzed the results of this study indicate that this reversal is the signature of intense annual variability in the subsurface zonal circulation at the equator at the level of the equatorial intermediate current eic and the lower equatorial intermediate current l eic in this study the eic and the l eic are both shown to reverse seasonally to eastward currents in boreal spring and winter for the l eic over a large depth range extending from 300 m to at least 1200 m the peak to peak amplitude of the annual cycle of subthermocline zonal currents at

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

monitoring the 1979 1985 equatorial pacific current transports with expendable bathythermograph data geostrophic transports of the major equatorial currents including the equatorial undercurrent and the south equatorial current have been estimated on a bimonthly basis in the central and western pacific over the 1979 1985 period this was made possible by a collection of carefully checked expendable bathythermograph xbt data and a few hydrocast and conductivity temperature depth data this collection considerably improved the number and quality of temperature profiles of the original institut francais de recherche scientifique pour le developpement en cooperation orstom scripps institute of oceanography tropical pacific xbt ship of opportunity program the temperature profiles were first grouped independently of longitude in regions around mean xbt tracks dynamic heights were then calculated relative to 400 db through a t s relationship deduced from the climatological levitus file geostrophic currents were calculated along the roughly south north oriented fiji hawaii and new caledonia japan mean xbt tracks using a specific technique this technique which combines fourier filtering in the meridional direction and in time also ensures the continuity across the equator between geostrophic currents deduced from the first and second derivatives of the meridional pressure field the filter coefficients in the meridional direction were determined through an adjustment of geostrophic currents to directly measured currents using the mean of data collected along 165 e during six tropical ocean and global atmosphere toga orstom cruises finally transports of the main equatorial currents were computed in a subjective way between 20 n and 20 s 0 400 m using monthly charts of geostrophic currents along the two mean xbt tracks the transports in the central pacific were compared to the transports derived from the semicontinuous direct current measurements taken during the hawaii tahiti shuttle experiment in 1979 1980 and during the line island profiling project pacific equatorial ocean dynamics experiment in 1982 1983 reasonable agreement demonstrates that it is possible to use xbt data for transport indexes of the major equatorial currents in the central and western pacific

equatorial pacific thermostad response to el nino el ninos are characterized by a shift of warm surface water from the western to eastern equatorial pacific due to weakening of easterly trade winds this shift is associated with the pycnocline or thermocline the large vertical density gradient beneath the surface mixed layer shoaling in the west and deepening in the east inducing a redistribution of ocean heat with global impacts here the response of the pacific equatorial thermostad a layer of low vertical stratification below the pycnocline to el nino is investigated using a monthly argo float climatology and argo float deep velocity data a mean seasonal cycle trend and time lagged linear response to the nino3 4 index are fit by least squares to temperature and salinity at each gridpoint as well as to deep float velocities omitting the trend the results of these fits are used to characterize the response of physical properties in the thermostad including layer thickness and velocity to el nino by comparing the mean properties following neutral conditions nino3 4 0 c versus those following a moderate el nino nino3 4 1 c following an el nino a strengthening of the westward flowing equatorial intermediate current of about 2 7 106 m3 s 1 shifts about 97 1012 m3 of thermostad water from the east to the west allowing conservation of volume within the thermostad as the pycnocline above deepens in the east and shoals in the west this transport and volume change imply a 14 month time scale consistent with el nino this article is protected by copyright all rights reserved

observed tracer fields structuration by middepth zonal jets in the tropical pacific abstractthe middepth ocean circulation in the tropical pacific is dominated by sets of alternating eastward and westward jets the origin and transport properties of these flow features remain in m

a stochastic ground motion model for switzerland abstract we present a stochastic ground motion model for switzerland a model for the far field fourier amplitude spectra of earthquakes is first proposed constrained by ground motions observed from small local and regional earthquakes in addition to macroseismic intensities observed from large damaging events in switzerland we then use this model in a stochastic simulation technique to generate predictions of peak ground acceleration and velocity and 5 damped response pseudo spectral acceleration we facilitate the prediction of ground motions from finite fault sources through the use of the r eff distance metric and show that magnitude and distance scaling behavior of events up to m w 7 5 is broadly consistent with next generation attenuation and japanese models ground motion prediction uncertainty is described in terms of between and within event uncertainties through residual analysis of response spectra finally single station sigma is derived accounting for the prediction uncertainty at a given site without the ergodic assumption consistency of the model is emphasized through its compatibility with other seismic hazard products the model is referenced to a generic rock profile that was developed by utilizing velocity profiles of the sites of seismic stations and is calibrated at higher magnitudes to the swiss regional macroseismic intensity prediction model furthermore the model is based on moment magnitudes from the recently developed earthquake catalogue of switzerland 2009 ecos09 the well defined reference for the model means that it can easily be adapted for a site specific application for instance through the use of proxies such as quarter wavelength velocity and travel time average shear wave velocity in the upper 30 m v s 30

the equatorial undercurrent and its origin in the region between mindanao and new guinea herein the spatial characteristics of the equatorial undercurrent euc in the region between mindanao and new guinea and the origins of the euc and the north equatorial countercurrent necc were investigated using a combination of high resolution argo hydrographic data and numerical modeling the mindanao current mc results in the formation of a strong euc depth eastward current that splits into two branches near the halmahera eddy west of 132 degrees e with one branch directly flowing eastward without experiencing the halmahera eddy rotation effect and the other branch flowing southwestward and then turning northeastward the euc and necc were difficult to distinguish between 132 degrees e and 136 degrees e since the former combined with the latter to form a continuous equator tilted current at similar to 137 degrees e the euc axis started turning toward the equator and an isolated euc core was observed at 143 degrees e and similar to 200 m depth the pacific euc was shown to originate at similar to 130 degrees e where it featured an isolated current core with a maximum velocity of 5 10cm s at similar to 1 degrees n and 200 to 400 m depth the euc and necc in the western tropical pacific were found to have the same water sources namely the mc and the new guinea coastal undercurrent with the shallow parts centered at similar to 100 m depth of mc and new guinea coastal undercurrent finally reaching the necc and their deeper parts centered at similar to 200 m depth finally reaching the euc