path and variability of the agulhas return current the combined analysis of hydrographic kinematic and dynamic data collected during the 1997 1999 kapex cape of good hope experiments reveals a quasi stationary meandering pattern of the agulhas retroflection current east and upstream of the southwest indian ridge the current meanders between 38 s and 40 s in a spatially and temporally continuous fashion and has a core width of approximately full size image 1 k with an associated transport of full size image 1 k in the upper full size image 1 k peak surface velocities decrease from full size image 1 k near the agulhas retroflection to full size image 1 k around 32 e meander troughs northward extremes are found predominantly near 26 8 e 32 6 e and 38 9 e while crests southward extremes are located with high probability near 29 7 e 35 5 e and 42 9 e resulting in a typical wavelength of full size image 1 k cold eddies are shed along the northern boundary of the current from meander troughs into the recirculation regime between the agulhas current proper and the agulhas return current strongest cyclonic eddies are preferably shed in austral autumn the cyclonic eddies so formed propagate westward at an average phase speed of full size image 1 k with however a variability of at least the same magnitude subsequently the cyclones are absorbed by the next meander trough located upstream and to the west of the shedding trough

eddy activity and mixing in upwelling systems a comparative study of northwest africa and california regions a comparative modeling approach is used to study the mesoscale dynamics of coastal transition zones in the upwelling systems of western sahara and central california it is shown that large differences in eddy activity and mixing exist between the two systems since upwelling favorable winds off central california and western sahara have similar amplitudes we suggest that observed and modeled differences in eddy activity are due to differences in configuration parameters it is argued that two of these parameters stratification and topography eventually affect the energy available for the mesoscales through baroclinic instability the large difference in stratification appears to be linked to the salinity structure formed by the large scale circulation and is directly related to available potential energy the shape of the continental shelf affects the position structure and scale of the ekman divergence hence upwelling intensity and frontal formation the potential impact of mesoscale eddy mixing and its variability on upwelling ecosystems is discussed

lagrangian exploration of the california undercurrent 1992 95 abstract during the period 1992 95 nineteen isobaric rafos floats placed in the california undercurrent at intermediate depths 150 600 m off monterey and san francisco california reveal a region of varying width of subsurface poleward flow adjacent to the continental margin the float trajectories exhibit three patterns poleward flow in the undercurrent reversing but predominately alongshore flow adjacent to the continental margin and farther offshore anticyclonic motion accompanied by slow westward drift flow continuity of the undercurrent exists between pt reyes and at least cape mendocino with an average speed dependent on the float depth speeds were variable but common features were acceleration occurring to the south of pt arena and deceleration to the north of cape mendocino an important mechanism for floats and water to enter the ocean interior from the undercurrent is through the formation of submesoscale coherent vortices

subsurface fine scale patterns in an anticyclonic eddy off cap vert peninsula observed from glider measurements glider measurements acquired along four transects between cap vert peninsula and thecape verde archipelago in the eastern tropical north atlantic during march april 2014 were used to investigate fine scale stirring in an anticyclonic eddy the anticyclone was formed near 12 n off the continental shelf and propagated northwest toward the cape verde islands at depth between 100 and 400 m the isolated anticyclone core contained relatively oxygenated low salinity south atlantic centralwater while the surrounding water masses were saltier and poorly oxygenated the dynamical and thermohaline subsurface environment favored the generation offine scale horizontal and vertical temperature and salinity structures in and around the core of the anticyclone these features exhibited horizontal scales of o 10 30 km relatively small with respect to the eddy radius of o 150 km the vertical scales of o 5 100 m were associated to density compensated gradient spectra of salinity and oxygen along isopycnals revealed a slope of around k 2in the 10 to 100 km horizontal scale range further analyses suggest that the fine scale structures are likely related to tracer stirring processes such mesoscale anticyclonic eddies and the embedded fine scale tracers in and around them could play a major role in the transport of south atlantic central water masses and ventilation of the north atlantic oxygen minimum zone

pacific bidecadal climate variability regulated by tidal mixing around the kuril islands 1 18 6 year period variability has been detected in various aspects of the climate especially in and around the pacific ocean although it is believed to be caused by 18 6 year period tidal cycle no study has directly shown how the tidal cycle regulates such variability using a state of the art climate model we show that the 18 6 year cycle in strong tidal mixing localized around the kuril islands induces 18 6 year periodicity in el nino southern oscillation like pacific climate variability influence of the tidal mixing propagates along the pacific western rim as coastally trapped waves temperature anomaly is generated in the subsurface western equatorial pacific which propagates along the equatorial thermocline and eventually excites 18 6 year periodicity in the equatorial sea surface temperature

characteristics and formation of eastern south pacific intermediate water 1 newly gathered hydrographic data from the eastern south pacific is combined with other high quality data mainly woce to reassess the properties and boundaries of the eastern south pacific intermediate water espiw to date the espiw has been only poorly described the espiw core is found off central and northern chile between the coast and 90 w and 20 38 s located at 50 400 m of depth its temperature varies between 11 13 c salinity ranges from 34 1 34 3 and its sigma t lies between 25 75 26 25 kgm 3 espiw spreads with the subtropical gyre circulation and can be traced to at least 150 w formed through the process of subduction southeastward of the wind driven gyre circulation the espiw communicates surface properties of the waters off central chile to tropical latitudes

impact of a coastal trapped wave on the near coastal circulation of the peru upwelling system from glider data alongshore velocity data from a glider repetitive section off the coast of peru 14 s are used to study the cross shore structure and temporal variability of the peru current system during a 5 week period in april may 2010 besides providing substantial information on the surface frontal jet associated with the peru coastal current and the surfacing peru chile undercurrent that flows poleward trapped on the continental shelf and slope the glider data reveal the presence of an intense deep equatorward current which transports up to 2 5 sv the dynamics of this current are investigated using an eddy resolving regional model the variability of the vertically sheared alongshore flow is shown to be related to the passage of a poleward propagating coastal trapped wave likely of equatorial origin solutions from a two dimensional linear coastal wave model suggest that the alongshore current observed vertical structure is associated with the second and third baroclinic modes of the coastal trapped wave

mass fluxes in the canary basin abstract ocean studies in the 1970s provided an improved knowledge of the coastal upwelling region off nw africa while in the 1980s and 1990s they led to a good description of the open ocean flow patterns in the canary basin it was not until the late 1990s that major research addressed the open coastal ocean coupled response here we examine the mean and seasonal circulation patterns in the canary basin with data from four hydrographic cruises carried out in the region between cape ghir madeira island and the canary islands we apply an inverse box model to an ocean divided into 14 layers with several layers representing each water mass or stratum to obtain mass fluxes consistent with the thermal wind equation an optimum flow description is obtained using conservation of mass salt and heat anomaly biologically corrected oxygen and silicate and allowing for ekman transport in the surface layer and dianeutral mixing between adjacent layers the deep waters show no predominant flow direction while the intermediate waters display localized southward flowing mediterranean water far from shore and northward flowing antarctic intermediate water near the continental slope specially in the passage between the eastern canary islands and the african slope the mean upper thermocline canary current composed of north atlantic central water flows south with an open ocean branch transporting about 3 1 sv 1 sv 10 6 m 3 s 1 10 9 kg s 1 and an upwelling related branch near the continental slope carrying 1 0 3 sv the seasonal transport by the open ocean branch intensifies and moves offshore from spring to fall 2 8 1 2 sv in spring 2 9 1 1 sv in summer and 4 5 1 2 sv in fall while it carries its lowest southward mass flux in winter 1 7 1 0 sv possibly as a result of a migration offshore the sampled region upwelling related southward flow is present in spring and summer 1 9 0 1 sv and 2 4 0 1 sv respectively while in fall and winter it merges with the offshore southward branch this westward migration allows a northward mass flux between the canary islands and the african coast 1 8 0 1 sv that by winter reaches cape ghir 0 5 0 2 sv seasonal air sea heat fluxes fit well with the climatological values the net phosphate transport in the surface layer indicates that primary production was negligible in this region during january 1997 and april 1998 though in this last month production was probably starting as a result of significant nutrient supply

the signature of mesoscale eddies on the air sea turbulent heat fluxes in the south atlantic ocean abstract by collocating 10 years 1999 2009 of remotely sensed surface turbulent heat uxes withsatellite altimetry data we investigate the impact of oceanic mesoscale eddies on the latent and sensibleheat uxesinthesouthatlanticocean instronglyenergeticregions suchasthebrazil malvinascon uenceand the agulhas current retro ection eddies explain up to 20 of the total variance in the surfaceturbulent heat uxes with averaged anomalies of 10 20 w m 2 cyclonic anticyclonic respectively eddies are associated with negative positive heat ux anomalies that tend to cool warm the marineatmospheric boundary layer a composite analysis of the turbulent heat ux anomalies inside the eddiesrevealsadirectrelationshipbetweeneddyamplitudeandtheintensityofsuchanomalies inaddition theseanomaliesarestrongerneartheeddycenter decayingradiallytoreachminimumvaluesoutsidetheeddies 1 introduction the ocean atmosphere system is primarily turbulent in the mesoscale band oceanic eddies play a crucialrole in transporting heat salt momentum and biogeochemical tr acersalongtheirtrajectories signi cantlyimpactingtheoceandynamicsand uxes olson 1991 wunsch 1999 morrowetal 2003 mesoscaleeddiesare coherent rotating features with typical horizontal scales of 50 300 km and time scales ranging fromweeks to months cheltonetal 2011a theyalsoexhibitparticularthermohalineverticalstructuresassoci ated with strong dynamical perturbations of the density and pressure elds olson 1991 chaigneau et al 2011 kurian et al 2011 zhang et al 2013 roullet et al 2014 these perturbations extend up to the seasurface leadingtoanomaliesonseasurfaceheight seasurfacetemperature sst andwindstress amongothers frengeretal 2013 souzaetal 2014 asaresult itisexpectedthateddiesimpacttheair sea uxesandtheoverlayingatmosphericcirculation frengeretal 2013 the turbulent latent lhf and sensible shf heat uxes are the primary processes by which the oceanreleases heat to the atmosphere cayan 1992 both the lhf and shf can be derived from bulk formulaelinking oceanic and atmospheric parameters such as air speci c humidity sst and wind speed to theheat exchanged at the air sea interface liu et al 1979 fairall et al 2003 large and yeager 2009 theanomalies caused by mesoscale eddies in some of these parameters have been recently investigated e g white and annis 2003 hausmann and czaja 2012 frenger et al 2013 souza et al 2014 chelton and xie 2010 although there is ample evidence that oceanic mesoscale features have a signi cant impact onair seaproperties thereisstillalackofknowledgeabouttheirsignatureonthesurfaceturbulentheat uxesandtheirpotentialcontributionstothenetsurfaceheatbudget the recent release of daily satellite based data from the french research institute for exploitation of thesea ifremer bentamy et al 2013 has su cient resolution to estimate the lhf and shf associatedwith mesoscale processes the present work merges satellite altimetry sea level anomaly sla data withremotely sensed surface heat uxes to investigate the impact of mesoscale ocean eddies on the lhf andshfinthesouthatlanticocean sa the sa encompasses both quiescent areas and two regions of intense energetic variability associated withthe presence of large mesoscale eddies figure 1a namely the agulhas current retro ection agr olsonand evans 1986 goni et al 1997 andthebrazil malvinascon uence bmc garzoli and garra o 1989 olson et al 1988 more speci cally we aim i to assess the mean lhf and shf anomalies induced bycyclonicandanticycloniceddiesinthesa ii todescribethespatialvariationsoftheheat uxanomaliesinvillasboasetal

mesoscale eddies in the northeastern pacific tropical subtropical transition zone statistical characterization from satellite altimetry 1 mesoscale eddies in the northeastern pacific tropical subtropical transition zone 16 n 30 n 130 w 102 w are analyzed using nearly 18 years of satellite altimetry and an automated eddy identification algorithm eddies that lasted more than 10 weeks are described based on the analysis of 465 anticyclonic and 529 cyclonic eddy trajectories we found three near coastal eddy prolific areas 1 punta eugenia 2 cabo san lucas and 3 cabo corrientes these three areas are located in places where the coastal morphology changes abruptly and strong surface current intensification occurs at some phase of the seasonal cycle although mesoscale eddies in these areas have been previously reported this study provides their first statistically supported characterization punta eugenia showed the highest eddy production with more cyclones generated followed by cabo corrientes also with more cyclones and cabo san lucas with more anticyclones cabo corrientes eddies showed the highest mean values in propagation speed swirling speed and eddy kinetic energy whereas punta eugenia eddies showed the lowest values cyclonic eddies increased their distance traveled and duration from south to north in contrast anticyclonic eddies increased from north to south in average anticyclones tend to travel faster than cyclones in all the subregions these long lived eddies were mainly nonlinear and therefore can redistribute coastal waters relatively far into the open ocean the peaks in the seasonal signal of eddy generation can be associated with the peaks in the strength of the offshore currents and or in the coastal upwelling index no clear relationship could be established between el nino events and eddy generation

ocean climate of the south east atlantic observed from satellite data and wind models the near coastal south east atlantic ocean off africa is a unique and highly dynamic environment comprising the cool benguela current warm angola current and warm agulhas current strong coastal upwelling and the congo river strongly influence primary production much of the present knowledge of the south east atlantic has been derived from ship borne measurements and in situ sensors which cannot generally provide extensive spatial and temporal coverage similarly previous satellite studies of the region have often focused on small spatial areas and limited time periods this paper provides an improved understanding of seasonal and interannual variability in ocean dynamics along the south east atlantic coast of africa using time series of satellite and model derived data products eighteen years of satellite sea surface temperature data are complimented by 7 years of sea level data three years of chlorophyll a data illustrate the seasonal biological response but the time series is not of sufficient length for investigating interannual variability in chlorophyll biomass modelled wind fields are used to describe atmospheric forcing of the surface ocean this is the first synoptic scale description of the south east atlantic from a suite of large spatial coverage long time series products previous studies of seasonal and interannual variability in the region are reviewed and used to interpret key oceanographic features and processes identified in the satellite data key findings of this study are 1 descriptions of seasonal and interannual variability from these data show climate forcing of the south east atlantic coast of africa from both the northern and southern boundaries bimodal seasonal signals of equatorial origin propagate poleward along the angolan coast while the trade winds and events in the agulhas region dominate the agulhas bank and southern benguela the northern benguela is a mixed regime under the influence of forcing from both directions 2 the benguela nino years of 1984 and 1995 are clearly observed in sea surface temperature and sea level anomalies and correspond to anomalously weak southerly winds at the equator these conditions were also observed in 1999 suggesting this too may have been a benguela nino year 3 consideration of putative nino type events in the equatorial atlantic from this and other studies suggests that the frequency of these events is much higher than previously estimated and may be similar to the frequency of el nino southern oscillation enso events in the pacific ocean furthermore years of anomalously strong southerly winds at the equator occur during pacific enso years c 2003 elsevier ltd all rights reserved

vertical structure of mesoscale eddies in the eastern south pacific ocean a composite analysis from altimetry and argo profiling floats 1 the mean vertical structure of mesoscale eddies in the peru chile current system is investigated by combining the historical records of argo float profiles and satellite altimetry data a composite average of 420 526 profiles acquired by argo floats that surfaced into cyclonic anticyclonic mesoscale eddies allowed constructing the mean three dimensional eddy structure of the eastern south pacific ocean key differences in their thermohaline vertical structure were revealed the core of cyclonic eddies ces is centered at 150 m depth within the 25 2 26 0 kg m 3 potential density layer corresponding to the thermocline in contrast the core of the anticyclonic eddies aes is located below the thermocline at 400 m depth impacting the 26 0 26 8 kg m 3 density layer this difference was attributed to the mechanisms involved in the eddy formation while intrathermocline ces would be formed by instabilities of the surface equatorward coastal currents the subthermocline aes are likely to be shed by the subsurface poleward peru chile undercurrent in the eddy core maximum temperature and salinity anomalies are of 1 c and 0 1 with positive negative values for aes ces this study also provides new insight into the potential impact of mesoscale eddies for the cross shore transport of heat and salt in the eastern south pacific considering only the fraction of the water column associated with the fluid trapped within the eddies each ce and ae has a typical volume anomaly flux of 0 1 sv and yields to a heat and salt transport anomaly of 1 3 1011 w and 3 8 103 kg s 1 respectively

three dimensional circulation in the nw africa coastal transition zone abstract high resolution data collected southeast of the canary islands during late winter 2006 are analyzed to describe the hydrography and three dimensional circulation in the coastal transition zone off nw africa the data are optimally interpolated over a regular grid the geostrophic velocity field is calculated and the q vector formulation of the omega equation is used to compute the quasi geostrophic qg mesoscale vertical velocity the coastal transition zone is divided into upwelling frontal and offshore regions with distinct physical and dynamic characteristics the upwelling region is characterized by cold and weakly stratified waters flowing towards the equator with a poleward undercurrent of approximately 0 05 m s 1 over the continental slope the frontal region exhibits a southwestward baroclinic jet associated with cross shore raising isopycnals the jet transport is close to 1 sv with maximum velocities of 0 18 m s 1 at surface decreasing to 0 05 m s 1 at 300 db vertical sections across the frontal region show the presence of deep eddies probably generated by the topographic blocking of the islands to the southward current as well as much shallower eddies that likely have arisen as instabilities of the baroclinic upwelling jet the qg mesoscale vertical velocity field is patchy estimated to range from 18 to 12 m day 1 with the largest absolute values corresponding to an anticyclonic eddy located south of fuerteventura island these values are significantly larger than estimates for other vertical velocities diapycnal vertical velocities associated with mixing in the frontal region a few meters per day and wind induced vertical velocities non linear ekman pumping arising from the interaction between the wind stress and the background vorticity maximum values of a few meters per day linear ekman pumping due to the divergence of ekman transport a fraction of a meter per day or the coastal constraint in the upwelling region about 0 7 m day 1 however the patchiness in both the qg mesoscale vertical velocity and the non linear ekman pumping velocity cause their integrated vertical transports to be one order of magnitude smaller than either coastal ekman transport 0 08 sv integrated linear ekman pumping 0 05 sv or diapycnal transfer about 0 1 0 2 sv the pattern of the near surface fluorescence field is a good indicator of these different contributions with large homogeneous values in the coastal upwelling region and a patchy structure associated with the offshore mesoscale structures

equatorial pacific 13 c water eddies in the eastern subtropical south pacific ocean abstract argo float profile data are used to analyze warm salty weakly stratified subthermocline eddies of tropical origin in the eastern subtropical south pacific ocean these eddies contain anomalous signatures of the equatorial pacific 13 c water that is carried poleward within the peru chile undercurrent pcu as it flows along the west coast of south america from their source along the chilean coast between 29 and 39 s the eddies spread westward and slightly northward likely at least partly advected by the subtropical gyre the eddy water properties contrast strongly with the colder fresher more strongly stratified waters of subantarctic origin being carried northward then westward by the gyre near the eddy source about 6 of argo profiles sample eddies that are above selected thresholds for both salinity and potential vorticity anomalies relative to maps of the mean distributions of these properties on and around the core isopycnal for the eddies the proportion of such profiles dimini

topex poseidon observations of mesoscale eddies over the subtropical countercurrent kinematic characteristics of an anticyclonic eddy and a cyclonic eddy 1 relative dynamic heights and geostrophic fields were derived from topex poseidon altimetry data and then used to track mesoscale eddies over the subtropical countercurrent stcc the radii centers vorticities shearing deformation rates stretching deformation rates divergences and center velocities of all identified eddies over the stcc were determined using a model that assumes constant velocity gradients most eddies are concentrated in a zonal band near 22 n and there is an interannual variation in the number of eddies a case study was made for a cyclonic eddy and an anticyclonic eddy with time series of eddy kinematic parameters computed both eddies survive for 220 days and propagate westward along over 22 n 24 n to reach the kuroshio current east coast of taiwan where the eddies were dissipated and in turn affected the kuroshio current in many ways sea surface temperature data and drifter data confirm the existence of these two eddies the radii of both eddies vary and their shapes are mostly elliptical during propagation the anticyclonic eddy propagated almost westward with oscillating north south components and the mean speed is 8 3 km day the cyclonic eddy moved southwestward before reaching 130 e and then moved northwestward with a mean speed of 7 6 km day the propagations of these two eddies are basically consistent with the standard theory of eddy propagation but with larger speeds the propagating direction could be altered while passing steep bottom topography or merging with the other eddies index terms 4520 oceanography physical eddies and mesoscale processes 4576 oceanography physical western boundary currents 4512 oceanography physical currents 4594 oceanography physical instruments and techniques 4556 oceanography physical sea level variations

geostrophic and ageostrophic circulation of a shallow anticyclonic eddy off cape bojador a shallow mesoscale anticyclonic eddy observed south of the canary islands with satellite altimetry has been intensively studied with multiparametric sampling hydrographic data from a ctd installed on an undulating nu shuttle platform reveal the presence of a mesoscale anticyclonic eddy of 125 km diameter the difference in sea level anomaly sla between the interior and the edge of the eddy as determined from altimetry is 15 cm which compares well with the maximum dynamic height differences as inferred using a very shallow reference level 130 m further the associated surface geostrophic velocities of about 35 cm s 1 in the northeast and southwest edges of the eddy are in good agreement with direct velocity measurements from the ship deep rosette ctd casts confirm that the structure is a shallow eddy extending no deeper than 250 m before the fusion with another anticyclone the sla tendency temporal rate of change of sea surface height indicates a clear northwestward migration during the two first weeks of november 2008 applying an eddy ssh based tracker the eddy s velocity propagation is estimated as 4 km d 1 use of the qg omega equation diagnoses maximum downward upward velocities of about 2 m d 1 the instability of the canary coastal jet appears to be the mechanism responsible for the generation of the shallow anticyclonic eddy

origins and variability of the benguela current a subset of the benguela sources and transports best 1992 1993 data is analyzed to study the magnitude and variability of the large scale transports in the area the data consist of inverted echo sounder series and conductivity temperature depth stations the mean 16 month transport values for the upper 1000 m indicate that of the 13 sv northward transport within the benguela current 50 is derived from the central atlantic which from geometry may be chiefly south atlantic water 25 comes from the indian ocean which may be chiefly agulhas water and the remaining 25 may be a blend of agulhas and tropical atlantic water a simple schematic of the transport pattern with a somewhat restricted corridor for agulhas eddies translation is envisioned to the west of the eddy corridor flows the south atlantic source for the benguela current to the east is the agulhas indian ocean source the corridor is breached by south atlantic and indian water as the transient eddy field stirs these water masses

a mesoscale eddy dipole in the offshore california current there is a transition zone in the california current system between inshore coastal and offshore oceanic flow this transition zone is associated with the main core of the california current and is populated with offshore mesoscale eddies the structure of isolated eddies and dipole eddy pairs found within the transition zone is examined using water mass analysis spiciness and dissolved oxygen the analyses show that these offshore mesoscale eddies have cores which contain california undercurrent water these observations and independent observations of the sitka eddy near sitka alaska support the conclusion that a bathymetrically induced instability of the california undercurrent is a likely generation mechanism for the offshore eddies this conclusion also is consistent with mathematical models of eddy generation in a subsurface poleward baroclinic current the similarity between long term mean conditions caicofi conditions observed during january 1981 and july 1985 and those of the sitka eddy coupled with the bathymetric effects provides a plausible explanation for the recurrence of offshore mesoscale eddies at preferred locations within the transition zone

water masses in the humboldt current system properties distribution and the nitrate deficit as a chemical water mass tracer for equatorial subsurface water off chile abstract three sections are used to analyze the physical and chemical characteristics of the water masses in the eastern south pacific and their distributions oceanographic data were taken from the scorpio may june 1967 piquero may june 1969 and krill june 1974 cruises vertical sections of temperature salinity dissolved oxygen nitrate nitrite phosphate and silicate were used to analyze the water column structure five water masses were identified in the zone through t s diagrams subantarctic water subtropical water equatorial subsurface water antarctic intermediate water and pacific deep water their proportions in the sea water mixture are calculated using the mixing triangle method vertical sections were used to describe the geographical distributions of the water mass cores in the upper 1500 m several characteristic oceanographic features in the study area were analyzed the shallow salinity minimum displacement towards the equator the equatorial subsurface salinity maximum associated with a dissolved oxygen minimum zone and a high nutrient content displacement towards the south and the equatorward intermediate antarctic salinity minimum associated with a dissolved oxygen maximum the nitrate deficit generated in the denitrification area off peru and northern chile is proposed as a conservative chemical tracer for the equatorial subsurface waters off the coast of chile south of 25 s

continuity of the poleward undercurrent along the eastern boundary of the mid latitude north pacific abstract several recent data sets improve our view of the poleward undercurrent of the california current system as part of a triennial national marine fisheries service nmfs survey of pacific whiting a series of 105 shipboard acoustic doppler current profiler adcp velocity sections across the shelf break from 33 to 51 n at about 18 km meridional spacing were collected from july to august 1995 significant 0 05 m s 1 subsurface poleward flow occurred in 91 of the sections a mean cross shelf section using the entire data set has statistical significance revealing an undercurrent core 0 1 m s 1 from 200 275 m depth 20 25 km off the shelf break the mean poleward volume transport in a 125 325 m layer is 0 8 0 2 10 6 m 3 s 1 we focus particular attention on the cape blanco to cape mendocino region and the nmfs results are compared with shipboard adcp three weeks later from a study of coastal upwelling processes near cape blanco adcp streamfunction maps are derived and strongly suggest that one portion of flow is continuous over the 440 km meridional extent of the analysis region other portions of the flow show evidence of offshore turning separation and the formation of anti cyclonic eddies we also note that isopycnic potential vorticity from alongslope ctd stations during the nmfs survey appears to be a tracer for the poleward flow

cross shore transport variability in the california current ekman upwelling vs eddy dynamics abstract the low frequency dynamics of coastal upwelling and cross shelf transport in the central and southern california current system ccs are investigated using the regional ocean modeling system roms over the period 1965 2008 an ensemble of passive tracers released in the numerical model is used to characterize the effects of linear ekman upwelling and non linear mesoscale eddies circulation dynamics on the statistics of advection of coastal waters the statistics of passive tracers released in the subsurface show that the low frequency variability of coastal upwelling and cross shelf transport of the upwelled water mass are strongly correlated with the alongshore wind stress and are coherent between the central and southern ccs however the offshore transport of tracers released at the surface is not coherent between the two regions and is modulated by intrinsic mesoscale eddy activity in particular cyclonic eddies the transport of cyclonic eddies extends with depth and entrains water masses of southern origin advected by the poleward california undercurrent cuc the cuc water masses are not only entrained by eddies but also constitute a source for the central california upwelling system the interplay between intrinsic eddy activity and deterministic ekman upwelling dynamics in controlling the cross shelf exchanges in the ccs may provide an improved framework to understand and interpret nutrients and ecosystem variability

the canary islands coastal transition zone upwelling eddies and filaments 3 pages printed version published in issue aug sep 2004 issue title the canary islands coastal transition zone upwelling eddies and filaments

finescale vertical structure of the upwelling system off southern peru as observed from glider data abstractthe upwelling system off southern peru has been observed using an autonomous underwater vehicle a slocum glider during october november 2008 nine cross front sections have been carried out across an intense upwelling cell near 14 s during almost two months profiles of temperature salinity and fluorescence were collected at less than 1 km resolution between the surface and 200 m depth estimates of alongshore absolute geostrophic velocities were inferred from the density field and the glider drift between two surfacings in the frontal region salinity and biogeochemical fields displayed cross shore submesoscale filamentary structures throughout the mission those features presented a width of 10 20 km a vertical extent of 150 m and appeared to propagate toward the shore they were steeper than isopycnals and kept an aspect ratio close to f n the inverse of the prandtl ratio these filamentary structures may be interpreted mainly as a manifestation of submesoscale turbulence through sti

implications of refined altimetry on estimates of mesoscale activity and eddy driven offshore transport in the eastern boundary upwelling systems we investigate the extent to which the recently upgraded version of the ssalto duacs sea level anomaly product affects the description of mesoscale activity in the eastern boundary upwelling systems ebus drifter observations confirm that the new data set released by archiving validation and inter pretation of satellite oceanographic data aviso in april 2014 dt14 offers an enhanced description of mesoscale activity for the four ebus dt14 returns significantly higher eddy kinetic energy levels 80 within a 300 km coastal band where mesoscale structures are known to induce important lateral phys ical and biogeochemical fluxes when applied to dt14 an automatic eddy detection algorithm detects more eddies in the ebus 37 and lower eddy radius estimates in comparison with results using the for mer altimetry product dt10 we show that despite higher eddy densities the smaller eddy radii result in westward eddy transport estimates that are smaller than those obtained from dt10 12

an offshore eddy in the california current system part i interior dynamics abstract from january 9 to 17 1981 detailed observations of the horizontal and vertical structure beneath one of the quasi permanent semi stationary mesoscale offshore eddy signatures in the california current system ccs discussed by bernstein breaker and whritner 1977 burkov and pavlova 1980 and simpson 1982 were made the vertical sections of temperature and density show the presence of three layer system a subsurface warm core eddy whose diameter is about 150 km at the 7 c isotherm is the dominant feature a warm surface layer which extends to a depth of 75 m lies over the eddy between the warm surface layer and the subsurface warm core eddy there is a cold core region which extends to a depth of about 200 m there is a high degree of symmetry about the vertical axis of rotation vertical sections of salinity and dissolved oxygen are entirely different from sections of temperature and density diagrams of water mass characteristics confirm that the core of the eddy found between 250 600 m consists of inshore water from the california undercurrent cu below about 700 m local waters from the deep poleward flow dpf have been incorporated into the eddy the observed distributions of properties t s o 2 are inconsistent with a single local generation process for the eddy system radial distributions of angular velocity normalized gradient velocity and relative vorticity support the use of a gaussian radial height field as an initial condition in eddy models possible reasons why ccs eddies may differ dynamically from gulf stream rings are given in the text at the time the observations were made the system as a whole was in near geostrophic balance local geostrophic balance however cannot explain the observed distribution of properties and structure the observed symmetry in the structure of the eddy system chemical evidence simpson 1984 biological distributions haury 1984 and satellite images of the cc koblinsky simpson and dickey 1984 suggest that lateral entrainment of warm oceanic and cold coastal water into the upper two layers of the three layer system by the subsurface eddy is a likely generation mechanism for the cold core region the coastal origin of the frontal structure along the northeastern quadrant and the oceanic origin of the frontal structure along the southwestern quadrant of the eddy system further support lateral entrainment as a generation mechanism for the cold core this entrainment makes the ccs eddy system different from cold core rings in the gulf stream and rather similar to some warm core eddies found in the east australian current the presence of cu water in the core of this eddy raises the question of how cu water was transported from the continental slope eddy generation mechanisms other than baroclinic instability of the cc may be required to explain the distribution persistence and core composition of offshore mesoscale eddies in the ccs there is evidence that barotropic in addition to baroclinic processes may be important

upwelling filaments off cap blanc interaction of the nw african upwelling current and the cape verde frontal zone eddy field 1 the hydrographical and dynamical properties of the upwelling filaments forming off cap blanc mauritania are investigated using remotely sensed and in situ data collected in april may 2009 during the strongest upwelling season the area is situated at the southern edge of the nw african upwelling system where the cape verde frontal zone cvfz separates warmer saltier north atlantic central water nacw and cooler fresher south atlantic central water sacw sea surface temperature images indicated the presence of an upwelling filament extending 280 km offshore rooted over the cap blanc promontory and entrained around a warm core anticyclonic eddy after this filament started to decay a new cold filament developed at the approximate same location high resolution moving vessel profiler mvp and acoustic doppler current profiler adcp surveys of these mesoscale structures revealed that both filaments were carrying south atlantic central water sacw offshore through an intense jet like flow similarity of the relative vorticity structure across the filament with that of the tangent eddy suggested that the latter was responsible for the offshore current tracking of this eddy in altimetric data demonstrated that it originated from the cvfz as implied by its hydrographic structure altimetric data also revealed that another anticyclonic structure centered over the cap blanc promontory was responsible for the northwestward advection of sacw into the base of the filament the results support the idea that some upwelling filaments can be produced by the interaction of an external eddy field including topographic eddies with the upwelled water

interactions between mesoscale eddies and synoptic oscillations in the bay of bengal during the strong monsoon of 2019

eddy properties in the california current system 1 eddy detection and tracking algorithms are applied to both satellite altimetry and a high resolution dx 5 km climatological model solution of the u s west coast to study the properties of surface and undercurrent eddies in the california current system eddy properties show remarkable similarity in space and time and even somewhat in polarity summer and fall are the most active seasons for undercurrent eddy generation while there is less seasonal variation at surface most of the eddies have radii in the range of 25 100 km sea level anomaly amplitudes of 1 4 cm and vorticity normalized by f amplitudes of 0 025 0 2 many of the eddies formed near the coast travel considerable distance westward with speeds about 2 km day consistent with the effect anticyclones and cyclones show equatorward and poleward displacements respectively long lived surface eddies show a cyclonic dominance the subsurface california undercurrent generates more long lived anticyclones than cyclones through instabilities and topographic coastline effects in contrast surface eddies and subsurface cyclones have much more widely distributed birth sites the majority of the identified eddies have lifetimes less than a season eddies extend to 800 1500 m depth and have distinctive vertical structures for cyclones and anticyclones eddies show high nonlinearity rotation speed higher than propagation speed and hence can be efficient in transporting materials offshore

three agulhas rings observed during the benguela current experiment a field program to study the circulation of the benguela current and its extension into the southeastern atlantic ocean has completed the survey and instrument deployment phase we report here new observations of three agulhas rings north and west of cape town south africa three mesoscale anticyclonic rings initially identified by means of topex poseidon altimetry were surveyed with expendable bathythermographs conductivity temperature depth oxygen profiles direct current measurements from a lowered acoustic doppler current profiler a hull mounted acoustic doppler current profiler and satellite tracked surface drifters characteristics of the rings are presented and their origins are discussed two are typical agulhas rings surveyed at different times after their generation the third agulhas ring has an anomalous water mass structure whose most likely origin is the subtropical front

the upwelling area off northwest africa a description of phenomena related to coastal upwelling abstract this paper presents a brief review of the oceanography along the upwelling coast of northwest africa the description contains information on seasonal variations of large scale winds ocean circulation and some gross of features of the hydrography characteristic meso scale patterns of currents during the upwelling season between 16 n and 26 n air and water temperature differences during upwelling season diurnal and semi diurnal variations of temperature atmospheric pressure wind and current regional peculiarities canyons and the banc d arguin

upper ocean water mass characteristics of the california current summer 1993 abstract two large high resolution upper ocean surveys of the california current region were conducted in the summer of 1993 temperature and salinity were measured from a seasoar vehicle and velocity was measured by a ship borne acoustic doppler current profiler both surveys extended from the continental margin to 128 w and consisted of zonal sections 28 km apart the first survey 7 28 june extended from 39 5 n to 36 25 n and the second 16 august to 1 september extended from 39 0 n to 37 0 n the current field was fairly simple in june showing an equatorward surface jet with only one gentle meander a nearly continuous poleward california undercurrent near the continental margin and two anticyclonic subsurface eddies offshore of the jet by august meanders in the surface jet had strengthened and eddies dominated the flow field large scale trends in the water mass characteristics spiciness along three isopycnal surfaces 26 4 26 0 and 25 6 kg m 3 show that temperature and salinity tend to increase towards the equator and towards shore consistent with poleward advection along the continental margin local minima in spiciness tend to coincide with the equatorward surface jet local maxima in spiciness are associated with subsurface anticyclonic eddies which have a core depth of about 150 m and seem to originate in the california undercurrent over the continental slope at local latitudes we identified several different anticyclonic eddies each with different water mass characteristics all of the eddies we observed had diameters larger than the baroclinic radius of deformation water mass characteristics and migration rates are consistent with formation over the continental margin within the preceding 6 8 months

ocean science eddy effects on biogeochemistry ocean eddies tens of kilometres in radius can delineate local ecosystems and contribute to biogeochemical budgets the characterization of three such eddies in a coastal upwelling region provides insight into these wonders of nature

eddy activity in the four major upwelling systems from satellite altimetry 1992 2007 eddy activity in the four major eastern boundary upwelling systems ebus is investigated using 15 years of satellite altimetry data based on the analysis of more than 4000 long lived eddy trajectories in every ebus we show that mesoscale structures are mainly generated along the continental coasts and south of the main archipelagos and propagate westward with velocities increasing toward the equator these mesoscale eddies having radii of 70 160 km are then frequently observed along the coastal transition zones and frontal regions and some large oceanic areas are preferentially populated by cyclonic or anticyclonic eddies temporal variations of the number of newly formed eddies and the associated eddy activity index defined as the mean eddy energy density are finally examined at seasonal and interannual scales the strongest seasonal interannual respectively variations are observed in the california benguela upwelling systems the proposed indices also exhibit contrasted long term trends in each ebus which suggests that eddy activity might be sensitive to a warming climate

main eddy vertical structures observed in the four major eastern boundary upwelling systems in the four major eastern boundary upwelling systems ebus mesoscale eddies are known to modulate the biological productivity and transport near coastal seawater properties toward the offshore ocean however little is known about their main characteristics and vertical structure this study combines 10 years of satellite altimetry data and argo float profiles of temperature and salinity and our main goals are i to describe the main surface characteristics of long lived eddies formed in each ebus and their evolution and ii to depict the main vertical structure of the eddy types that coexist in these regions a clustering analysis of the argo profiles surfacing within the long lived eddies of each ebus allows us to determine the proportion of surface and subsurface intensified eddies in each region and to describe their vertical structure in terms of temperature salinity and dynamic height anomalies in the peru chile upwelling system 55 of the sampled anticyclonic eddies aes have subsurface intensified maximum temperature and salinity anomalies below the seasonal pycnocline whereas 88 of the cyclonic eddies ces are surface intensified in the california upwelling system only 30 of the aes are subsurface intensified and all of the ces show maximum anomalies above the pycnocline in the canary upwelling system 40 of the aes and 60 of the ces are subsurface intensified with maximum anomalies extending down to 800 m depth finally the benguela upwelling system tends to generate 40 50 of weak surface intensified eddies and 50 60 of much stronger subsurface intensified eddies with a clear geographical distribution the mechanisms involved in the observed eddy vertical shapes are discussed

eddy induced sea surface temperature gradients in eastern boundary current systems many processes are known to influence the distribution of sea surface temperature sst fronts in eastern boundary current systems ebcs including wind forcing mesoscale activity flow instabilities and flow topography interactions here we used satellite observations to quantify the relative importance of one of these processes mesoscale eddy activity on the distribution of sst gradients in ebcs eddies are characterized by large sst and sst gradient anomalies in all ebcs at the end of the upwelling season eddy induced sst gradients are dominant components of the full sst gradient offshore of 300 km from the coast especially in regions of high eddy activity comparisons between eddy induced and full sst gradients in the california current system indicate that the offshore migration of mesoscale eddies plays a significant role on the seasonal widening of the region of high frontal activity sst gradients associated with anticyclonic eddies are largest within 400 km from shore while the signature of cyclones can extend for up to 700 km from the coast

on the pathways of the equatorial subsurface currents in the eastern equatorial pacific and their contributions to the peru chile undercurrent 1 theconnections between theequatorial currentsystem andtheperu currentsystem in the eastern tropical pacific etp are examined with a primitive equations eddy resolving regional model the quasi equilibrium solutions reproduce three eastward equatorial subsurface currents of interest the equatorial undercurrent euc located between 1 n and 1 s the primary southern subsurface countercurrent psscc between 3 and 4 s and farther south the secondary southern subsurface countercurrent ssscc between 7 and 8 s using a lagrangian tracking procedure the fate of these currents in the etp and their contribution to the peru chile undercurrent pcuc are studied lagrangian diagnostics show that for the most part the euc water contributes to westward flows including the south equatorial current and deeper flows below it and strikingly only a very little fraction feeds the pcuc while a significant part of both ssccs contribute substantially mesoscale eddies are shown to exert an effect on these connections in addition about 30 of the pcuc is fed by the three subsurface equatorial flows euc psscc ssscc the remaining part of the pcuc comes from an alongshore recirculation associated with flows below it and from the southern part of the domain south of 9 s

structure and surface properties of eddies in the southeast pacific ocean 1 a number of studies have posited that coastally generated eddies could cool the southeast pacific ocean sep by advecting cool upwelled waters offshore we examine this mechanism by characterizing the upper ocean properties of mesoscale eddies in the sep with a variety of observations and by estimating the surface layer eddy heat flux divergence with satellite data cyclonic and anticyclonic eddies observed during two cruises featured deep positive salinity anomalies along the 26 5 kg m 3isopycnal indicating that the eddies had likely trapped and transported coastal waters offshore the cyclonic eddies observed during the cruises were characterized by shoaling isopycnals in the upper 200 m and cool near surface temperature anomalies whereas the upper ocean structure of anticyclonic eddies was more variable using a variety of large scale observations including argo float profiles drifter records and satellite sea surface temperature fields we show that relative to mean conditions cyclonic eddies are associated with cooler surface temperatures and that anticyclonic eddies are associated with warmer surface temperatures within each data set the mean eddy surface temperature anomalies are small and of approximately equal magnitude but opposite sign eddy statistics drawn from satellite altimetry data reveal that cyclonic and anticyclonic eddies occur with similar frequency and have similar average radii in the sep a satellite based estimate of the surface layer eddy heat flux divergence while large in coastal regions is small when averaged over the sep suggesting that eddies do not substantially contribute to cooling the surface layer of the sep

near coastal circulation in the northern humboldt current system from shipboard adcp data the near coastal circulation of the northern humboldt current system is described analyzing 8700 velocity profiles acquired by a shipboard acoustic doppler current profiler sadcp during 21 surveys realized between 2008 and 2012 along the peruvian coast this data set permits observation of i part of the peru coastal current and the peru oceanic current that flow equatorward in near surface layers close to the coast and farther than 150 km from the coast respectively ii the peru chile undercurrent pcuc flowing poleward in subsurface layers along the outer continental shelf and inner slope iii the near surfacing equatorial undercurrent renamed as ecuador peru coastal current that feeds the pcuc and iv a deep equatorward current referred to as the chile peru deep coastal current flowing below the pcuc a focus in the pcuc core layer shows that this current exhibits typical velocities of 5 10 cm s 1 the pcuc deepens with an increasing thickness poleward consistent with the alongshore conservation of potential vorticity the pcuc mass transport increases from 1 8 sv at 5 s to a maximum value of 5 2 sv at 15 s partly explained by the sverdrup balance the pcuc experiences relatively weak seasonal variability and the confluence of eddy like structures and coastal currents strongly complicates the circulation the pcuc intensity is also affected by the southward propagation of coastally trapped waves as revealed by a strong pcuc intensification in march 2010 coincident with the passage of a downwelling coastal wave associated with a weak el nino event

evolution movement and decay of warm core leeuwin current eddies abstract characteristics of eddies originating in the leeuwin current lc have been investigated using 10 day sea level anomaly maps of combined topex poseidon and ers altimeter data for the period 1995 2000 during these 6 years 37 long lived anticyclonic eddies were tracked from the west coast of australian to 90 e between three and nine eddies were spawned each year and their trajectories are described in detail most long lived eddies are generated in may june when the lc is most intense and at three preferred locations 20 21 5 s 24 25 s and 28 31 s the temporal evolution and latitudinal variations of the sea level anomalies and their radius and drift speed are discussed topography plays an important role in the evolution and structure of the eddies interactions with topography can induce splitting or merging of eddies which further affects the eddy decay

looping rafos floats in the california current system abstract looping motions of rafos floats deployed off the central california coast between 1992 and 2010 are described most floats were deployed in the california undercurrent floats at 300 m were observed to loop 26 of the time with anticyclonic rotation observed about twice as often as cyclonic rotation characteristics of anticyclonic rotation at 300 m included median swirl speeds of 14 cm s for diameters of 59 km and 14 day periods long lived 70 days and at least 8 consecutive loops anticyclonic loopers are identified as california undercurrent eddies or cuddies one cuddy was observed to move southwestward 1650 km over a period of 520 days before observations ended kinematically cuddies are similar to mediterranean water eddies meddies in the iberian basin except that meddies are somewhat stronger larger and deeper over the slope most cuddies were formed between either pt sur and pt reyes or cape mendocino and cape blanco the region north of cape mendocino is estimated to generate six cuddies each year these eddies form from waters on the inshore side of the california undercurrent as they move past cape mendocino topographic drag is the most likely formation mechanism two of eight deep floats were observed to loop one anticyclonically 1545 m for 279 days and the other cyclonically 1167 m for 192 days looping for these floats ended near taney seamounts

an observational study of oceanic eddy generation mechanisms by tall deep water islands gran canaria 1 oceanic eddy generation by tall deep water islands is common phenomenon it is recognized that these eddies may have a significant impact on the marine system and related biogeochemical fluxes hence it is important to establish favourable conditions for their generation with this objective we present an observational study on eddy generation mechanisms by tall deep water islands using as a case study the island of gran canaria observations show that the main generation mechanism is topographic forcing which leads to eddy generation when the incident oceanic flow is sufficiently intense wind shear at the island wake may acts only as an additional eddy generation trigger mechanism when the impinging oceanic flow is not sufficiently intense for the case of the island of gran canaria we have observed a mean of ten generated cyclonic eddies per year eddies are more frequently generated in summer coinciding with intense trade winds and canary current

a modeling study of the coastal eastern boundary current system off iberia and morocco to investigate the northern canary current system nccs results from four numerical experiments of increasing complexity are examined experiment 1 which uses seasonal wind forcing only shows that as expected wind forcing is the key generative mechanism for the current upwelling meander eddy and filament structures experiments 2 and 3 which have the additional effects of irregular coastline geometry show the following capes are areas for enhanced upwelling extensive filaments maximum current velocities and enhanced growth of cyclonic meanders and eddies an embayment like the gulf of cadiz is a primary region for anticyclonic meander and eddy development the results from the complex flow regime of experiment 4 which has the additional effects of thermohaline gradients and mediterranean outflow highlights the major characteristics and unique features such as the generation of meddies of the nccs with relatively close similarities to field observations

characteristics of intermediate water flow in the benguela current as measured with rafos floats abstract seven floats not launched in rings crossed over the mid atlantic ridge in the benguela extension with a mean westward velocity of around 2 cm s between 22s and 35s two agulhas rings crossed over the mid atlantic ridge with a mean velocity of 5 7 cm s toward 285 this implies they translated at around 3 8 cm s through the background velocity field near 750 m the boundaries of the benguela current extension were clearly defined from the observations at 750 m the benguela extension was bounded on the south by 35s and the north by an eastward current located between 18s and 21s other recent float measurements suggest that this eastward current originates near the trindade ridge close to the western boundary and extends across most of the south atlantic limiting the benguela extension from flowing north of around 20s the westward transport of the benguela extension was estimated to be 15 sv by integrating the mean westward velocities from 22s to 35s and multiplying by the 500 m estimated thickness of intermediate water roughly 1 5 sv of this are transported by the 3 agulhas rings that cross the mid atlantic ridge each year as observed with altimetry this value of the benguela extension transport is the first one to have been obtained from long term two year observations and across the full width of the benguela extension

dynamics and evolution of a northern meddy abstract a meddy was discovered in april 1997 off the northwestern corner of spain near 45 n 11 30 w it was tracked during 18 months with lagrangian floats and deep drogued buoys and several cruises were set to collect further hydrological and lowered adcp measurements on it the meddy named ulla was a one core lens with maximum values of temperature and salinity of 11 5 c and 36 17 psu near 1000 m depth yielding anomalies above 2 5 c and 0 5 psu compared to its environment its rotation frequency was close to 1 loop every 5 days the maximum azimuthal velocities of 15 20 cm s 1 were reached near a 15 km radius the meddy had a wide remote influence notably up to the surface and was associated with a total azimuthal volume transport of around 10 sv sv 106 m3 s 1 of which around 2 sv was trapped in the core a widening of the radial structure with decreasing depth was notable in august 1997 meddy ulla was significantly elliptic for most of the time and depending on the periods the main el

basin to mesoscale surface circulation of the western mediterranean manifested by satellite derived data products abstract in this article there is an overview of the potential of different mostly altimetry derived products for manifesting features of basin and mesoscale circulation of the western mediterranean basin in terms of detection of mesoscale eddies and larger gyres the comparison was performed between eddy statistics extracted directly from fields of sea surface temperature sst on the one hand and reconstructed from different scalar and vector altimetry derived fields on the other hand among the products being analysed there are fields of i sea level anomaly sla ii geostrophic currents and iii finite size lyapunov exponents fsle comparison of the eddy statistics provided by such different data sources revealed that altimetry based techniques tended to overestimate the number of big cyclones and thus failed to reproduce cyclonic anticyclonic eddy asymmetry which was shown by fields of sst defining the spatial scale of eddies via altimetry based techniques seemed particularly problematic fsle product analysed in the study showed significant disagreements with vortical structures observed in fields of sst both in terms of the spatial scale and the sign of rotation in order to scrutinize basin scale features of surface circulation in the region of interest fields of i geostrophic currents ii total currents reconstructed by the globcurrent project and iii surface currents provided by the reanalysis technique were analysed as a result of the comparison performed a conclusion was made on the complementarity of the datasets analysed

mesoscale variability and nutrient phytoplankton distributions off central southern chile during the upwelling season the influence of mesoscale eddies abstract mesoscale features are recurrently found in the coastal transition zone ctz off central southern chile 35 40 s a region characterized by seasonal wind driven coastal upwelling in this study oceanographic data from two consecutive cruises carried out during the upwelling season january 2009 were combined with satellite time series data in order to characterize the structure and evolution of mesoscale eddies and to explore their influence on phytoplankton structure and nutrient distribution in the context of organic carbon exchanges between the coastal upwelling zone and the ctz two coastally generated contiguous mesoscale eddies 2 months old were characterized a surface cyclonic eddy cc1 and a subsurface anticyclonic eddy aa1 the distributions of salinity and dissolved oxygen together with nutrients suggested that both eddies were sites of vertical injection of high nutrient concentrations from the equatorial subsurface water mass essw into the upper layer in the ctz in addition eddy aa1 in combination with an upwelling plume was involved in the offshore advection of nutrients from the core of the essw located in the coastal zone at shallow depths

meridional heat and salt transport across the subantarctic front by cold core eddies mesoscale eddies are ubiquitous in the southern ocean particularly in regions where the antarctic circumpolar current interacts with topography eddies play a critical role in the meridional transport of heat and salt across the antarctic circumpolar current however observations of the heat and salt content of eddies are extremely rare here we present new observations that characterize the three dimensional structure of a cyclonic cold core eddy generated at the subantarctic front south of tasmania automated detection software is used with satellite altimetry to follow the eddy through the subantarctic zone the physical properties at the center of the eddy are substantially modified from those near the formation region indicating a strong transformation during the eddy s lifetime the eddy carried heat and salt content anomalies relative to surrounding subantarctic zone waters of 0 5 0 1 1020 j and 2 1 0 4 1012 kg respectively previous studies have not captured the full heat and salt content of eddies due to limited observations and have underestimated their content by a factor of 2 to 3 south of tasmania applying the observed correlation between eddy elevated volume and eddy heat and salt content to the history of cyclonic eddies in the satellite altimeter record leads us to propose that about 21 of the heat carried across the subantarctic front south of tasmania is achieved by cyclonic eddies entering the subantarctic zone the freshwater contribution to the subantarctic zone by long lived cold core eddies is of the same order of magnitude as the ekman flux in this region

the transition zone of the canary current upwelling region abstract like all the major upwelling regions the canary current is characterised by intense mesoscale structure in the transition zone between the cool nutrient rich waters of the coastal upwelling regime and the warmer oligotrophic waters of the open ocean the canary island archipelago which straddles the transition introduces a second source of variability by perturbing the general southwestward flow of both ocean currents and trade winds the combined effects of the flow disturbance and the eddying and meandering of the boundary between upwelled and oceanic waters produce a complex pattern of regional variability on the basis of historical data and a series of interdisciplinary field studies the principal features of the region are described these include a prominent upwelling filament originating near 28 n off the african coast cyclonic and anti cyclonic eddies downstream of the archipelago and warm wake regions protected from the trade winds by the high volcanic peaks of the islands the filament is shown to be a recurrent feature apparently arising from the interaction of a topographically trapped cyclonic eddy with the outer edge of the coastal upwelling zone its role in the transport and exchange of biogenic material including fish larvae is considered strong cyclonic eddies observed throughout the year drift slowly southwestward from gran canaria one sampled in late summer was characterised by large vertical isopycnal displacements apparent surface divergence and strong upwelling producing a fourfold increase in chlorophyll concentrations over background values such intense eddies can be responsible for a major contribution to the vertical flux of nitrogen the lee region of gran canaria is shown to be a location of strong pycnocline deformation resulting from ekman pumping on the wind shear boundaries which may contribute to the eddy formation process

lee region of gran canaria the mountainous canary islancls present obstacles to the trade wincls ancl to the canary current flowing equatorwarc past them in situ observations of hydrographic properties ancl surface wincls south of gran canaria together with advancecl very high resolution racliometer ancl synthetic aperture racial images e uring 2 weeks in summer 1995 are analyzecl a cyclonic edcly shecl l rom the west of the islancl c1riftecl southwestwarcl at 5 s j while the southeast coast was approachecl by an upwelling filament originating off nw africa a wincllee region bounclecl by intense horizontal shear lines hacl a weak return islandwarcl wincl in its center the lee formee a triangulai c1iurnally varying war111 water 001 with two sea surface temperature maxima separatecl by lower temperatures below the return wincl shallow temperature stratification occurrecl behincl the islancl in contrast to the l1niform surface mixecllayer in exposecl regions upwelling ancl clownwelling of 10 20 111 were indicatecl on the cyclonic ancl anticyclonic sicles of the lee region in the sar la u lines of strong current shear along a temperature front between the cyclonic eclcly the upwelling filament were iclentifiable i iowever the racial images were clominatecl atmospheric phenomena including mountain lee wave paclcets winclrows and wincl lines estimation of the wincl field l rom the sar backscatter intensity revealed ex structure and intensification on the eclges of the warm lee

subthermocline eddies over the washington continental slope as observed by seagliders 2003 09 abstractin the california current system subthermocline lenslike anticyclonic eddies generated within the california undercurrent cu are one mechanism for lateral transport of the warm saline waters of the cu garfield et al established the name cuddies for eddies of this type and hypothesized that they account for a significant fraction of the offshore transport of cu water this study presents observations of subthermocline eddies collected from a time series of seaglider surveys in the northern california current system gliders made 46 crossings of subthermocline anticyclones and 17 crossings of subthermocline cyclones over 5 5 yr close inspection grouped these into 20 distinct anticyclones and 10 distinct cyclones water properties at the core of anticyclonic eddies were similar to those in the core of the cu over the continental slope these anticyclones are examples of cuddies anticyclonic cyclonic eddies had average radii of 20 4 20 6 km peak azimuthal current speeds of 0 25 0 23

intrathermocline eddies in the coastal transition zone off central chile 31 41 s 1 the three dimensional structure and the origin of mesoscale anticyclonic intrathermocline eddies ites in the coastal transition zone ctz off central chile 31 41 s were analyzed through the combination of data from oceanographic cruises and satellite altimetry and the application of an eddy resolving primitive equation ocean model coupled with a numerical experiment using a passive tracer in this region ites are represented by subsurface lenses 100 km diameter 500 m thickness or vertical extension of nearly homogeneous salinity 34 5 and oxygen deficient 1 0 ml l 1 waters properties which are linked to the equatorial subsurface water mass essw transported poleward by the peru chile undercurrent pcuc in the coastal band at least five to seven ites were observed simultaneously in the area between 31 and 38 s during winter cruises in 1997 and 2009 satellite data indicated that the ites identified from in situ data moved westward each at a mean speed of 2 km d 1 and transported a total volume of 1 106 m3 s 1 1 sv the lifespan of each ite ranged from a few months to 1 year model results indicate that ites become detached from the pcuc under summer upwelling conditions in the coastal zone

westward motion of mesoscale eddies abstract since the pioneering work of nof the determination of the westward drift of mesoscale eddies under the planetary beta effect has been a recurrent theme in mesoscale oceanography and several different formulae have been proposed in the literature here recpatiulation is sought and within the confines of a single layer model a generalized formula is derived although it is similar to nof s the present formula is established from a modified definition and with fewer assumptions it also recaptiulates all other formulae for the one layer model and applies to a wide variety of situations including cases when the vortex develops a wake of rossby waves or undergoes axismmetrization following the derivation of the formula a physical interpretation clarifies the migration mechanism which can be divided between a self induced propulsion and a reaction from the displaced ambient fluid numerical simulations with primitive and geostrophic equations validate the formula for a variety of length sc

mesoscale eddies in the northwestern subtropical pacific ocean statistical characteristics and three dimensional structures mesoscale eddy properties in the northwestern subtropical pacific ocean are investigated by analyzing 22 567 cyclonic eddies ces and 26 365 anticyclonic eddies aes detected from 19 year altimetric sea level records eddy occurrence frequency and kinetic energy are prevailingly high in the subtropical countercurrent zonal band between 19 degrees n and 26 degrees n and further elevated near the luzon taiwan coast a general superiority of aes is observed at most latitudes except between 19 degrees n and 22 degrees n where the ce number is larger the modal radius and mean lifespan of the ces aes are 134km and 11 2weeks 121km and 10 9weeks respectively after generation most eddies propagate westward with a mean speed of 7 2cms 1 and deflect northward following the kuroshio along the luzon taiwan coast three dimensional eddy structures are further explored with composite eddy images in five subregions constructed by surfacing argo temperature salinity data into altimeter detected eddy areas due to the existence of mode waters in the main thermocline eddy induced temperature anomaly exhibits a double core vertical structure which is especially evident in ce images because of the vertical water mass distribution salinity anomaly features a sandwich like pattern which is more evident in ae images also revealed is the significant structure difference in these five subregions eddies are greatly intensified as they approach the western boundary inducing larger temperature and salinity anomalies and influencing deeper ocean along the luzon taiwan coast aes are preferentially strengthened by the northward background flow

global observations of large oceanic eddies 1 ten years of sea surface height ssh fields constructed from the merged topex poseidon t p and ers 1 2 altimeter datasets are analyzed to investigate mesoscale variability in the global ocean the higher resolution of the merged dataset reveals that more than 50 of the variability over much of the world ocean is accounted for by eddies with amplitudes of 5 25 cm and diameters of 100 200 km these eddies propagate nearly due west at approximately the phase speed of nondispersive baroclinic rossby waves with preferences for slight poleward and equatorward deflection of cyclonic and anticyclonic eddies respectively the vast majority of the eddies are found to be nonlinear

mesoscale eddy activity in the southern benguela upwelling system from satellite altimetry and model data we characterize eddy activity in the southern benguela upwelling system with absolute sea level data deduced from remote sensing measurements and numerical simulations run with a regional model using a wavelet based technique for identification and tracking of coherent structures statistics on eddy count size type and location are obtained along the continental slope of the upwelling system for a common period of interest shared by model and satellite data we draw a comparison between mesoscale variability calculated by the regional model and ground truth accounted by satellite altimetry we show that the presence of cyclonic eddies along the upwelling front over the south benguela slope is recurrent throughout the year moreover the agreement between model and observations is fair and validates the modeling approach tracking in the model of volume properties of continental slope cyclonic eddies on their way toward the open ocean suggests that these eddies play a significant role in coastal open ocean exchanges with lifetimes of several months these eddies can export significant volumes of nutrient rich waters far from the coastal upwelling

a shallow subtropical subducting westward propagating eddy swesty swesty is a shallow subtropical subducting westward propagating eddy that was observed to move across the eastern basin of the north atlantic at a latitude near 25 n the eddy was first detected by the movement and temperature of a drogued argos buoy near 23 w 26 n in february 1993 by december 1993 the drogued buoy had moved 1000 km westward to 33 w and a winter eddy survey was made from rrs charles darwin the eddy was about 100 km in diameter and had a centre water mass core at a depth of 190 m with characteristic temperature 19 9 c and salinity 37 06 psu but was best resolved by properties related to vertical gradient structure e g brunt vaisala frequency temperature perturbation structure the eddy was particularly flat with a height to width aspect ratio of only ca 0 14 and a vertical decay scale of ca 250 m for temperature displacements maximum azimuthal currents were ca 16 cm s 1 at a depth of 175 m and the eddy azimuthal transport was only 3 sv however the potential vorticity in the eddy core was 1 5 x 10 11 rad ms 1 comparable with other deep anticyclonic lenses and lower than background values by a factor of ten the eddy appeared slightly elliptical with a detectable sea surface cooling ca 0 2 c over its centre three argos buoys with drogues set at a depth of 200 m were deployed near the centre of the eddy and one buoy continued looping westward for a further ca 800 km the drogued argos buoy results showed that the eddy moved westward at ca 100 km month 1 and about half this westward rate was attributed to self propagation during this ca 1650 km continuously drogued journey the eddy only slipped southward by about one degree of latitude and so was perhaps resisting the southward component of flow of the subtropical gyre the buoy results suggested that the central rotation rate increased with time but the eddy became smaller the initial rotation period of the central core was ca 8 d giving a corresponding normalized relative vorticity of 0 3 about 400 d later the period of core rotation was ca 5 d with normalized relative vorticity of 0 5 some of the increase in central rotation rate was attributed to subduction effects variance spectra and filtered components of velocity were derived from the buoy positions kinetic energy levels in the eddy ca 73 cm 2 s 2 were markedly elevated with respect to background levels ca 29 cm 2 s 2 the core properties of the eddy indicated a winter formation near 27 n 22 w and hydrographic sections showed that the eddy would be sinking at a rate of about 40 m a 1 by the second year the subducted water parcel the eddy core was sufficiently deep below the surface of the ocean to escape further effects of winter mixing

the 3 d structure of mesoscale eddies in the lofoten basin of the norwegian sea a composite analysis from altimetry and in situ data

a subsurface warm eddy off northern baja california in july 2004 1 upper ocean eddies are commonly observed from remote sensing but submerged eddies are more difficult to detect during july 2004 a 21 day hydrographic survey in the southern region of the california current was carried out to investigate the mesoscale variability we observed for the first time a subsurface anticyclonic eddy off northern baja california with the same water mass characteristics as the california undercurrent the core of the eddy was quasi circular with radii of 35 km and thickness of 250 m the maximum swirl velocity was 3 cms 1 the water mass of the core of the eddy was characterized by potential temperature of 11 c salinity of 34 5 and dissolved oxygen of 1 4 mll 1 the eddy propagated westward the subsurface warm eddy could transport relatively saline water into the north pacific subtropical gyre

observations of mesoscale eddies in the south atlantic cape basin baroclinic and deep barotropic eddy variability 1 anticyclones and cyclones in the eastern south atlantic are characterized based on data collected during january 2003 to march 2005 along a jason 1 satellite altimeter ground track as part of the agulhas south atlantic thermohaline transport experiment large and small cyclones and anticyclones were ubiquitous in the deep ocean of the eastern south atlantic as well as in the upper ocean eddy structures jointly corotating in the upper and deep water column were common most of the time 94 these were not axially aligned as they copropagated the agulhas rings and cyclones that populate the region generally carry both a steric component baroclinic and a mass loading component deep barotropic structure average translation speeds were 7 5 cm s 1 for baroclinic eddies and twice as fast for barotropic eddies irrespective of polarity translation speeds were higher than advection by the mean background flow field in addition large mixed baroclinic barotropic rings crashed into the agulhas ridge and nearby seamounts and split into two or more parts some ring parts were also observed to fuse together deep cyclones as well as interactions with topography were observed to play a role in the fission process of agulhas rings these processes can increase the population of agulhas rings and their remnant eddies which took three pathways from the agulhas and into the cape basin 1 a deep pathway between the continental slope and erica seamount 2 a shallower pathway over or near the agulhas ridge and schmitt otto seamount and 3 a deep seaward pathway around the agulhas ridge

ancient engineering geology projects in china a canal system in ganzu province and trenches along the great wall in ningxia hui autonomous region abstract two major construction projects of ancient times in china involved what todaywould be considered engineering geology we describe an ancient canal system in gaotai county gansu province that was possibly begun in the han dynasty 206 bc 220 ad the canal system heads at the dasha river and extends northwestward for about 55 km to the city of camels and xusanwan village four parallel canals are present at the local site we examined the canals were likely built primarily to transport water but may also have served as defensive military barriers a second project involves trenches and berms along the north side of the great wall dearly part of the great wall defensive system this site is in ningxia autonomous region near the town of shizuishan

mesoscale eddies off peru in altimeter records identification algorithms and eddy spatio temporal patterns relatively little is known about coherent vortices in the eastern south pacific along the peruvian coast even with regard to basic facts about their frequency of occurrence longevity and structure this study addresses these issues with nearly 15 years of relatively high resolution satellite altimetry measurements we first compare two distinct automated methods for eddy identification the objective validation protocol shows that the rarely used geometrical or winding angle method based on the curvature of the streamline functions is more accurate than the commonly used okubo weiss algorithm which defines a vortex as a simple connected region with values of okubo weiss parameter weaker than a given threshold we then investigate vortices off peru using more than 20 000 mesoscale eddies identified by the winding angle method coherent eddies characterized by a high ratio of vorticity to deformation rate are typically formed along the coast and propagate westward at 3 6 cm s 1 the vortices have a mean radius of 80 km increasing northward and are most frequently observed off of chimbote 9s and south of san juan 15s the mean eddy lifetime is about 1 month but if eddies survive at least 2 months the probability for surviving an additional week or month is constant at 90 or 67 anticyclonic eddies tend to propagate northwestward whereas cyclonic vortices migrate southwestward in general cyclones and anticyclones are similar except for eddies surviving at least 6 months in this case after a similar 3 4 months of radius and amplitude growth amplitudes or sizes decay particularly rapidly for anticyclonic or cyclonic eddies in terms of intensity cyclonic eddies show a rapid decay during the first 3 months before arriving at a quasi constant value whereas anticyclones exhibit steady decline finally eddy temporal variations were examined at seasonal and interannual scales in the coastal region favorable to the formation of energetic mesoscale structures on seasonal scales eddy activity is maximal in fall and minimum in spring at interannual scales the eddy activity index was maximal during the strong el nino of 1997 1998 but another strong maximum of eddy activity also occurred late in 2004 these temporal variations are probably associated with the intensification of the upwelling thermal front and with the passage of coastal trapped waves which generate baroclinic instabilities further investigation of the mechanisms involved on the eddy genesis is needed

eddy characteristics in the eastern south pacific 1 the main eddy characteristics length scales rotation period swirl and translation velocities are determined in the eastern south pacific region 10 35 s and 70 100 w based on surface drifter measurements satellite altimetry and hydrographic data from the woce p19 section the chile peru current eddies have a typical diameter of order of 30 km smaller than the typical rossby radii observed in the region they are principally formed near the south american coast and propagate seaward with a translation velocity varying from 3 cm s 1 in the southern part of the study domain to 6 cm s 1 north of 15 s long lived anticyclonic eddies propagate northwestward with a mean angle of around 333 t whereas cyclonic vortices propagate westward consistent with the vortices propagation theory on a plane the radial distribution of the swirl velocity shows that the chile peru current eddies have a maximum diameter of order 200 km with a swirl velocity of around 14 cm s 1 and a rotation period of 50 days hydrographic data reveal a vertical extent down to around 2000 m for energetic eddies no significant difference is observed between the tangential velocities of cyclonic and anticyclonic eddies geostrophic balance can be considered for large radii whereas ageostrophic dynamics may play an important role near the eddy centers

mesoscale eddies in the south china sea mean properties spatiotemporal variability and impact on thermohaline structure we investigated mean properties and the spatiotemporal variability of eddies in the south china sea scs by analyzing more than 7000 eddies corresponding to 827 eddy tracks identified using the winding angle method and 17 years of satellite altimetry data eddies are mainly generated in a northeast southwest direction and southwest of luzon strait there is no significant difference between the numbers of two types of eddies anticyclonic and cyclonic in most regions the mean radius and lifetime of eddies are 132 km and 8 8 weeks respectively both depending on where the eddies are formed anticyclonic and cyclonic eddies tend to deform during their lifetimes in different ways furthermore eddy propagation and evolution characteristics are examined in the northern scs eddies mainly propagate southwestward along the continental slope with velocities of 5 0 9 0 cm s 1 while in the central scs eddies tend to move with slight divergence but still in a quasi westward direction with velocities of 2 0 6 4 cm s 1 eddy propagation in the western basin to the east of vietnam is quite random with no uniform propagate direction investigation of 38 long lived eddies shows that eddies have a swift growing phase during the first 12 weeks and then a slow decaying phase that affects the eddy radii and eddy energy densities nevertheless vorticity has less variability in addition the effect of eddies on the thermocline and halocline is analyzed using 763 argo temperature profile data cyclonic eddies drive the thermocline shallower and thinner and significantly strengthen the thermocline intensity whereas anticyclonic eddies cause the thermocline to deepen and thicken and weaken the thermocline intensity to a certain degree the halocline impacted by cyclonic eddies is also shallower and thinner than that impacted by anticyclonic eddies finally eddy temporal variations are examined at seasonal and interannual scales eddy activity is sensitive to the wind stress curl and in the northern scs it is also related with the strength of the background flows

eddies in the tropical atlantic ocean and their seasonal variability we study mesoscale eddy characteristics in the tropical atlantic ocean using 23 yearsof daily altimetry sea level anomalies eddies are mainly generated in the eastern boundary up wellings and in the brazil current region they have westward propagating speed reaching 20 cms 1 in equatorial area decreasing with latitudes they present typical amplitudes of around 1 5 cm the largest and most energetic eddies are observed in the equatorial region in particular in theretroflection of the north brazil current nbc the seasonal cycle of the main eddy characteristicsshows a marked seasonal cycle along the nbc retroflection and along the western part of the northequatorial countercurrent necc we propose a criterion using altimetry to analyse the mecha nism responsible for eddy generation in the necc we argue that eddy generation is mainly due tobarotropic instability of mean surface currents whereas other mechanisms must be invoked for thenbc

mesoscale eddies in the south china sea observed with altimeter data 1 a composite time series 1993 2000 of sea surface height anomaly from several satellites is used to identify eddies in the south china sea scs the eddy lifetime radius strength and straight line travel distance are estimated altogether 58 anticyclonic eddies and 28 cyclonic eddies are identified for this period they are grouped into four geographical zones according to known eddy generation mechanisms and their statistics are discussed accordingly our geographical classification is a useful first step in gaining an overview of their generation

average circulation seasonal cycle and mesoscale dynamics of the peru current system a modeling approach h isolines the pccc appears to be directly forced by the cyclonic wind stress curl the model is able to produce the upwelling front the cold water tongue which extends toward the equator and the equatorial front as described in the literature model seasonal changes in sst and ssh are compared to measurements for the central pcs model eke is 10 to 30 lower than the observations the model eddy diameters follow a strong equatorward increase the injection length scales derived from the energy spectra strongly correlate to the rossby radius of deformation confirming the predominant role of baroclinic instability at 3 s the model solution appears to switch from a turbulent oceanic regime to an equatorial regime dominated by zonal currents

divergent pathways of cyclonic and anti cyclonic ocean eddies satellite altimetry is used to study the propagation pathways of warm and cold ocean eddies in different ocean basins we consider eddies that have a life span longer than 3 months and we present three regional studies in the southeast indian the southeast atlantic and the northeast pacific oceans the case studies show that simple theories for vortex propagation on a plane work in regions where energetic eddies propagate though a weak background flow under these conditions anticyclonic cyclonic eddies propagate westward and equatorward poleward this divergence in the eddy pathways implies a net equatorward eddy heat flux and has implications for the meridional transport of freshwater carbon nutrients etc

three dimensional oceanic eddy analysis in the southern california bight from a numerical product with eight islands complex coastlines and bottom topography strong wind curls and frequent upwelling fronts the southern california bight scb is an area with strong eddy activity by applying an automated eddy detection scheme to a 12 year high resolution numerical product of the oceanic circulation in the scb a three dimensional eddy data set is developed it includes information for each eddy s location polarity intensity size boundary and moving path at nine vertical levels through a series of statistical analyses applied to the eddy data set three dimensional statistical characteristics of mesoscale and submeoscale eddy variations in the scb are elucidated these shed light on how eddies are generated evolve and terminate a significant percentage of eddies is found to be generated around islands and headlands along the coastline which indicates that islands in the scb play a vital role in eddy generation three types of eddies based on shape are identified from the numerical product bowl lens and cone a dynamic analysis shows that some submesoscale eddies with finite local rossby numbers tend to be ageostrophic balanced while mesoscale eddies are in geostrophic balance the present research results are useful for the interpretation of data sets obtained during the interdisciplinary santa barbara channel radiance in a dynamic ocean radyo field experiment conducted on september 3 25 2008