altimeter observations of the peru chile countercurrent data from geosat and topex altimeters are used to infer the structure of the peru chile countercurrent a jet that flows from at least as far north as 10 s historical data suggests 7 s to 35 40 s maintaining its position between approximately 100 300 km offshore although the annual mean current cannot be determined from altimeter observations the nearly antisymmetric patterns in spring and fall combined with historical observations suggest that the countercurrent is poleward at most times and is maximum in spring and minimum in fall previous studies have linked the offshore countercurrent at 7 s to the equatorial undercurrent west of the galapagos islands suggesting that the countercurrent is part of a continuous flow that extends from the western equatorial pacific to the region off chile between 35 40 s

circulation and low frequency variability near the chilean coast remotely forced fluctuations during the 1991 92 el nino results are reported from the first long recording current meter observations over the slope off chile these observations at 308s during the 1991 92 el nino event are analyzed together with observations of currents at a local deep sea site local wind and sea level sea level from the peru and chile coasts and wind temperature and currents from the equatorial pacific mean poleward flow of 12 cm s21 was observed within the peru chile undercurrent over the slope mean flow in the depth range of antarctic intermediate water was not distinguishable from zero in the presence of strong low frequency lf variability which dominated slope currents at all depths the strongest lf fluctuations had periods of about 50 days but periods of 10 and about 5 days were also observed significant local wind forcing of slope currents was only found in the period band 6 10 days and may be related to coastal trapped waves in the atmosphere our analysis shows that free coastal trapped waves in the ocean arriving from the north dominated the lf variability over the shelf and slope off northern and central chile during the 1991 92 el nino event strong 50 day period fluctuations there started their journey about two months earlier and 15 000 km farther up the coastal equatorial waveguide near the date line in the equatorial pacific as equatorial kelvin waves forced by westerly wind events of similar period upon reaching the south american coast these waves forced coastal trapped waves which propagated along the peru coast into the study region likewise a scenario of equatorial trapped waves forcing coastal trapped waves may explain 10 day as well as 6 day and 4 5 day period coastal trapped waves off chile stemming from mixed rossby gravity and inertia gravity waves trapped at the equator since the large 50 day period coastal trapped waves may strongly modify coastal upwelling source water such remotely forced waves may have a significant influence on the pelagic ecosystem off chile at least during el nino events

a linear stratified ocean model of the coastal undercurrent the linear stratified ocean model of mccreary 1981 is used to study the wind driven response of the ocean near an eastern coast the model can be regarded as an extension of the inviscid models of lighthill 1969 and of gill clarke 1974 that allows the vertical diffusion of heat and momentum into the deep ocean solutions are still found as expansions of vertical normal modes vertical mixing affects each mode as a linear drag with a drag coefficient that increases rapidly with mode number n a zonally uniform band of steady equatorward winds forces the ocean and the resulting flow field has many features in common with observations at eastern boundaries there is a surface equatorward jet and a poleward coastal undercurrent confined within 10 20 km of the coast both currents extend well poleward of the wind band upwelling does not reach great depths but occurs only above the core of the undercurrent weak downwelling occurs at greater depths there is offshore ekman drift in the surface mixed layer and return flow at a depth slightly above the core of the undercurrent the baroclinic alongshore pressure gradient field and the vertical mixing of heat and momentum are essential elements of the model dynamics but the beta and horizontal mixing are not low order vertical modes n 6 tend toward a two dimensional balance they generate the transverse circulation pattern associated with coastal ekman pumping

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

subsurface connections in the eastern tropical pacific during la nina 1999 2001 and el nino 2002 2003 1 the subsurface connections between the equatorial current system ecs and the peru current system pcs between 1999 and 2005 are investigated with a primitive equation eddy resolving regional model that is forced with realistic atmospheric and lateral oceanic conditions specific attention is given to the 1999 2000 la nina and the 2002 2003 el nino the model s skill is assessed through a comparison with satellite derived sea level anomalies and in situ sea surface temperature time series the model reproduces fairly well the known dynamics of the region for climatological conditions and the numerical solution obtained for the particular 1999 2000 and 2002 2003 events presents patterns rather typical of cold and warm phases of el nino southern oscillation enso eulerian and lagrangian diagnoses are used to derive relevant information about the density and velocity vertical structures of the ecs and the pcs the transports of the major currents in the region are shown to differ a lot between the 1999 2000 la nina and the 2002 2003 el nino the equatorial subsurface currents transfer significantly more water into the eastern tropical pacific during la nina than during el nino whereas the peru chile undercurrent pcuc carries more water during el nino the equatorial subsurface currents and especially the primary southern subsurface countercurrent contribute to 80 of the pcuc transport during the 1999 2000 cold phase this ratio falls down to only 20 during the 2002 2003 warm phase

in situ measured current structures of the eddy field in the mozambique channel abstract circulation and the related biological production have been studied during five cruises conducted in the mozambique channel mzc between 2005 and 2010 the circulation in the mzc is known to be highly turbulent favouring enhanced primary production as a result of mesoscale eddy dynamics and connectivity throughout the channel due to the variable currents associated with migrating eddies this paper presents the results of in situ measurements that characterize the horizontal and vertical currents in the surface and subsurface layers 0 500 m the in situ data were analysed together with the geostrophic eddy field observed from satellite altimeter measurements different circulation regimes were investigated including the classical anticyclonic eddy generated at the channel narrows 16 s the enhancement of southward migrating eddies by merging with structures both cyclonic and anticyclonic formed in the east of the channel and the presence of a fully developed cyclonic eddy at the channel narrows comparison between in situ measurements s adcp and velocities derived from surface drifters and the geostrophic current derived from sea surface height measurements indicated that the latter can provide a reliable quantitative description of eddy driven circulation in the mzc with the exception that these currents are weaker by as much 30 it is also suggested from in situ observation drifters that the departure from geostrophy of the surface circulation might be linked to strong wind conditions finally our observations highlight that a geostrophic currents need to be considered in future research to facilitate a more comprehensive description of the circulation in this area

the physical environment of the peruvian upwelling system abstract knowledge of the characteristics of the physical environment of the peru coastal upwelling zone has increased greatly during the past decade observations made during 1976 and 1977 many made as part of the coastal upwelling ecosystem analysis joint ii expedition provide the basis for an interpretative description of the physical processes and phenomena occurring in peru coastal waters four important phenomena are discussed wind driven upwelling the poleward undercurrent surface mixed layer deepening and low frequency coastal trapped waves the coastal winds were invariably favorable for coastal upwelling even during the 1976 el nino the agreement between the offshore transport in the relatively shallow 30 m surface layer and the ekman transport deduced from the local wind was good for both the mean and variable state the agreement with the deeper onshore transport was less good consistent with the marked three dimensionally and spatial variability of the upwelling the poleward undercurrent was apparently continuous from 5 s to at least 15 s flowing just below the surface layer over the continental shelf and slope and supplying the upwelling water the variability in the alongshore velocity field was dominated by baroclinic free coastal trapped waves with periods of 5 20 days although there is appreciable temporal and spatial variability in the peru coastal upwelling system the upwelling the undercurrent and the low frequency coastal trapped waves were ubiquitous

long range inversions for ocean acoustic tomography ocean acoustic tomography was proposed by munk and wunsch 1979 as a method for making measurements of ocean variability over large areas after the successful demonstration of the feasibility of the idea in the 1981 three dimensional mesoscale experiment ocean tomography group 1982 the tomography group has proposed a new experiment to be carried out in 1986 in the eastern pacific ocean on ranges as long as the subtropical gyre scale in this paper the gyre scale experiment is simulated in the model ocean using holland s eddy resolving general circulation quasi geostrophic model the paper addresses the following issues 1 measurement of the heat content vertical profile horizontally averaged along the tomographic section 2 adequacy of the linearized inverse over very long ranges and the need for its improvement 3 possible improvements in the specification of the field statistics to obtain more accurate estimates and to measure properties like average pycnocline trends 4 relationship of possible range dependent information from the inversion to the assigned noise level the results of the modeling simulation can be summarized as follows 1 the linearized stochastic inversion needs to be improved for gyre scale ranges providing estimates of the average heat content that have warm or cold biases iteration is used and shown to provide good estimates of the average heat content 2 a smaller number of iterations is necessary if the initial estimate is improved this can be done by including a spatial mean in the horizontal covariance function for regions of the ocean where the energy level in the mean and in the long length scales may be even more important than the mesoscale energy peak 3 general trends like average pycnocline slopes can be estimated very well by including an inhomogeneous covariance in the inversion 4 the estimates of the mean heat content values and of the average slopes are rather insensitive to the specified noise level 5 the type and number of eigenrays used is not a critical factor in the inversion estimates as long as the eigenrays provide a good sampling of the interior water mass increasing the number of eigenrays does not significantly improve the estimate of the average values 6 range dependent information is primarily a function of the assigned noise for too high a noise the basic quantities that can be measured are the mean value and the average trend

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

circulation of the pacific ocean seen in a global ocean model ocean circulation and climate advanced modelling project occam this paper compares observations made in the pacific ocean and the 8 12 year climatology of a global numerical model meridional mass and heat transports and their divergences are calculated and zonal averages compared with the air sea exchange values of doney et al 1998 with mixed success the large scale distribution of sea surface height and near surface currents are shown to be well reproduced by the model but their variance is underestimated severely so in areas of weak variability synoptic wind forcing enhances the latter though only slightly while higher model resolution improves agreement in areas of strong variability model mean transports in the east australian current in the vitiaz strait and in the kuroshio exceed measurements by 10 0 18 sv respectively and variability is underestimated by factors between 2 and 4 near 1000 m and in strong currents the flow is overestimated but over most of the ocean model output does not match either the magnitude or the spatial variability of the observations in contrast the inflow of bottom water and its spreading path throughout both south and north pacific is well described good agreement is found with measured transport through the samoan passage but at 32 s east of the tonga kermadec ridge the model yields only 60 of the observed value the sverdrup balance is shown to hold widely in the model interior utilizing the complete depth integrated vorticity equation it is found that bottom pressure torques balance the advection of planetary vorticity in both surface and bottom intensified western boundary currents

the termination of the equatorial undercurrent in the eastern pacific abstract the termination of the equatorial undercurrent euc in the eastern tropical pacific has been studied through analysis of the historical hydrographic station data in the region bounded by 5 n 10 s 80 w and 100 w three distinctive hydrographic features associated with the euc are used along with dynamic topography to trace the mean path of the euc and to investigate aspects of its seasonal variation these features are 1 the 13 c thermostad 2 the high salinity core and 3 the high dissolved oxygen concentration tongue the thermostad is thickest just south of the equator to the west of the galapagos islands with a decreasing maximum extending southeast to the coast of south america near 7 s the thermostad is poorly developed in the mean near the equator east of the galapagos islands this pattern appears to be produced by convergence of eastward flow in the euc and in the southern subsurface countercurrent as the euc flows southeastward from the galapagos this interpretation is supported by the geostrophic flow calculated from the mean dynamic topography the isolated high salinity core is found to the south of the equator and is traced all the way to the coast of south america the high oxygen tongue associated with the euc splits at the galapagos with the southward projecting branch disappearing rapidly as an identifiable feature the other branch of the tongue continues around the islands to the north and along the equator to the coast of ecuador some evidence of recirculation of euc water in the south equatorial current is seen to the northwest of the galapagos a strong seasonal pulsation of the euc affects these features in a consistent way with the pulse occurring first west of the galapagos and later along the coast the thermostad first reaches maximum development and then a pronounced downwelling of the thermocline occurs rapidly leading to minimum thermostad extent associated wtih this downwelling is an eastward protruding high salinity tongue near the equator which is later seen as an isolated core along the coast at 4 s and 6 s pressure gradients along the equator and the coast inferred from dynamic topography suggest that this pulse is associated with an increase in the flow of the euc and ultimately the peru chile undercurrent the pressure gradient reversal along the equator occurs prior to the annual wind reversal suggesting that remote forcing plays a role in the seasonal pulse of the euc in the eastern pacific

numerical simulation of flow around a tall isolated seamount part i problem formulation and model accuracy abstract a sigma coordinate ocean circulation model is employed to study flow trapped to a tall seamount in a periodic f plane channel in part i errors arising from the pressure gradient formulation in the steep topography strong stratification limit are examined to illustrate the error properties a linearized adiabatic version of the model is considered both with and without forcing and starting from a resting state with level isopycnals the systematic discretization errors from the horizontal pressure gradient terms are shown analytically to increase with steeper topography relative to a fixed horizontal grid and for stronger stratification as measured by the burger number for an initially quiescent unforced ocean the pressure gradient errors produce a spurious oscillating current that at the end of 10 days is approximately 1 cm s 1 in amplitude the period of the spurious oscillation about 0 5 days is shown to be a consequence of the particular form of the pressure gradient terms in th

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

oceanographic variability off ecuador associated with an el nino event in 1982 1983 the development of the 1982 1983 el nino event is described by reference to the oceanographic conditions prevailing off ecuador during the period 1982 1984 the first signs of the anomaly s onset off the ecuadorian coast were observed in august 1982 the 16 c isotherm was found some 50 m deeper than normal along 82 30 w this observation preceded by approximately 2 months the rapid rise in sea level the appearance of warm sea surface temperature sst anomalies and heavy rainfalls by february 1983 the whole area off ecuador was covered by very warm 29 30 c and low salinity less than 33 0 parts per thousand surface water two mechanisms seemed to be involved in the formation of the low salinity water advection of northern water and dilution by local rainfall although the ocean surface was 4 c warmer than normal the most notable changes took place throughout the water column a strong depression of the thermocline and all the isotherms down to 15 c the largest anomalies being observed over the 100 m water column up to 9 c at 50 m depth during the subsequent months ssts continued to increase thus the highest sst anomalies 6 3 c were observed in may and june recovery from the 1982 1983 anomaly started in july 1983 with a general uprising of the isotherms and a fall in sea level by october the warm sst anomalies had dropped to 1 5 c in november 1983 the presence of the equatorial front also attested to the return to normal of the oceanographic conditions in the region

dynamics of an equatorial river plume theory and numerical experiments applied to the congo plume case abstractthe congo river has the second largest rate of flow in the world and is mainly responsible for the broad tongue of low salinity water that is observed in the gulf of guinea despite their importance near equatorial river plumes have not been studied as thoroughly as midlatitude plumes and their dynamics remain unclear using both theory and idealized numerical experiments that reproduce the major characteristics of the region the authors have investigated the dynamics of the congo river plume and examine its sensitivity to different forcing mechanisms it is found that near equatorial plumes are more likely to be surface trapped than midlatitude plumes and the importance of the effect in describing the strong offshore extent of the low salinity tongue during most of the year is demonstrated it is shown that the buoyant plume constrained by the geomorphology is subject to the pulling of nonlinear structures and wavelike equatorial dynamics the wind is found to strengthen the intrinsic buoy

on the cross shelf exchange driven by frontal eddies along a western boundary current during austral winter 2007 western boundary currents are characterized by high mesoscale eddy activity including that of cyclonic frontal eddies cfes these form frequently adjacent to the shelf break export coastal water and affect biological productivity here we study the physical properties of eddies identified within the intensification zone of the east australian current eac through the analysis of remotely sensed data the application of an ocean circulation model and the evaluation of lagrangian simulations during austral winter 2007 we examine the spatial and temporal evolution of identified eddies investigate their formation mechanism and quantify the contribution made to cross shelf exchanges the mesoscale eddies are tracked from generation to decay using an eddy detection and tracking method in this case study we identify two cfes referred to as c1 and c2 with lifetimes of 11 and 38 days and radii of 45 and 70 km respectively and one anticyclonic eddy ace with a lifetime of 62 days and a radius of 60 km both cfes interact with the ace leading to quasi stationary dipole eddies located in the vicinity of the shelf this is the first time dipole eddies are reported for the intensification zone of the eac the location of cfes characterised by negative sea surface height anomaly ssha and clockwise rotation coincides with remotely sensed sea surface temperature sst and chlorophyll a chl a anomalies cfes c1 and c2 appear to contribute in different ways to the cross shelf transport along the shelf break cfe c1 drives a stronger onshore transport while cfe c2 appears to enhance the offshore transport the estimated daily cross shelf export of shelf water associated with cfe c2 is estimated with about 1 23 sv 106 km3 day 1 it renews the regional shelf water in about 7 days the lifetime of cfe c2 is about 38 days thus the eddy had the potential to flush the shelf at least five times the transient cfes were found for the first time to intensify the cross shelf exchange that is due to the wind driven cyclonic circulation of the fraser gyre this seasonally occurring gyre dominates the local shelf during austral autumn and winter the results from this study demonstrate the importance of cfes in exporting cooler and chl a enriched shelf water into the warmer and oligotrophic waters of the southward flowing eac

sensitivity of the northern humboldt current system nearshore modeled circulation to initial and boundary conditions 1 the influence of the eastern pacific equatorial circulation on the dynamics of the northern humboldt current system is studied using an eddy resolving regional circulation model forced by boundary conditions from three distinct ocean general circulation models the seasonal variability of the modeled nearshore circulation and the mesoscale activity are contrasted in order to evaluate the role of the density forcing the seasonal variability of the surface and subsurface alongshore currents strongly depends on the amplitude and timing of the seasonal eastward propagating equatorial waves the equatorward flow and upwelling intensity are also impacted by nonlinear processes such as the seasonal generation of nearshore mesoscale eddies which create alongshore pressure gradients modulating the surface current boundary conditions affect differently the intensity and phase of the eddy kinetic energy as baroclinic instability is triggered by coastal waves during austral summer and fall whereas it is sustained by the wind driven upwelling during austral winter

central south pacific thermocline water circulation from a high resolution ocean model validated against satellite data seasonal variability and el nino 1997 1998 influence 1 the oceanic circulation in french polynesia central south pacific is investigated based on a high resolution model validated with satellite data we focus on the upper 500 m where ocean current variability has been barely documented due to a lack of in situ measurements seasonal and el nino southern oscillation 1997 1999 variability of surface and subsurface currents are characterized in the north the south equatorial current sec follows a seasonal cycle with winter enhancement corresponding to trade wind strengthening during summer the sec slows and the eastward south equatorial countercurrent secc appears across the domain north of an upward ekman pumping region related to the south pacific convergence zone development in the area around the marquesas islands a wind curl dipole is suspected to create westward and eastward marquesas countercurrent mcc jets the eastward subtropical countercurrent stcc is found south of 20 s it is disturbed by eddies and broken into westward and eastward branches during el nino 1997 1998 due to the reversed winds in the equatorial band the sec weakened while eastward countercurrents appeared the secc reinforced and moved northeastward in summer 1998 during la nina 1998 1999 following the trade wind enhancement the sec strengthened the countercurrents weakened or disappeared and the secc moved southwestward in summer 1999 during both el nino and la nina events the stcc eddy activity strengthened while the mcc and associated westward jet were absent these variations and their dynamical origins are discussed and a coherent picture of the french polynesian current system and its variations is proposed

equilibrium structure and dynamics of the california current system this paper addresses the structure and dynamical mechanisms of regional and mesoscale physical variability in the subtropical northeast pacific ocean using the regional oceanic modeling system roms the model is configured with a u s west coast domain that spans the california current system ccs with a mesoscale horizontal resolution up to as fine as 3 5 km its mean seasonal forcing is by momentum heat and water fluxes at the surface and adaptive nudging to gyre scale fields at the open water boundaries its equilibrium solutions show realistic mean and seasonal states and vigorous mesoscale eddies fronts and filaments the level of eddy kinetic energy eke in the model is comparable to drifter and altimeter estimates in the solutions with sufficiently fine resolution because the model lacks nonseasonal transient forcing the authors conclude that the dominant mesoscale variability in the ccs is intrinsic rather than transiently forced the primary eddy generation mechanism is the baroclinic instability of upwelling alongshore currents there is progressive movement of meanseasonal currents and eddy energy offshore and downward into the oceanic interior in an annually recurrent cycle the associated offshore eddy heat fluxes provide the principal balance against nearshore cooling by mean ekman transport and upwelling the currents are highly nonuniform along the coast with important influences by capes and ridges in both maintaining mean standing eddies and launching transient filaments and fronts

impact of nearshore wind stress curl on coastal circulation and primary productivity in the peru upwelling system 1 coastal upwelling dynamics are strongly affected by alongshore wind stress and nearshore wind stress curl a coupled physical biogeochemical regional model and lagrangian diagnostics are used in the peru current system to determine how the upwelling of nutrients and the primary productivity are impacted by the spatial structure of the nearshore wind stress three wind stress products derived from the ers and quikscat scatterometers and a smoothed quikscat field mainly differing in nearshore wind stress curl patterns were used simulations are found to produce significantly different mean surface chlorophyll distributions and show that strong upwelling favorable nearshore wind stress curl may locally induce a wide coastal productive zone through upwelling of nutrient replete waters brought by a shoaling coastal undercurrent using wind stress products with realistic nearshore patterns is therefore crucial for the modeling of coupled physical biogeochemical coastal processes

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

an index to distinguish surface and subsurface intensified vortices from surface observations in this study the authors first show that it is difficult to reconstruct the vertical structure of vortices using only surface observations in particular they show that the recent surface quasigeostrophy sqg and interior and surface quasigeostrophy isqg methods systematically lead to surface intensified vortices and those subsurface intensified vortices are thus not correctly modeled the authors then investigate the possibility of distinguishing between surface and subsurface intensified eddies from surface data only using the sea surface height and the sea surface temperature available from satellite observations a simple index based on the ratio of the sea surface temperature anomaly and the sea level anomaly is proposed while the index is expected to give perfect results for isolated vortices the authors show that in a complex environment errors can be expected in particular when strong currents exist in the vicinity of the vortex the validity of the index is then analyzed using results from a realistic regional circulation model of the peru chile upwelling system where both surface and subsurface eddies coexist the authors find that errors are mostly associated with double core eddies aligned surface and subsurface cores and that the index can be useful to determine the nature of mesoscale eddies surface or subsurface intensified from surface satellite observations however the errors reach 24 and some possible improvements of the index calculations are discussed

a model investigation of internal variability in the angola benguela frontal zone 1 in this study a regional ocean model is applied to the tropical southeast atlantic ocean with the aim of investigating internal variability of the angola benguela front the model is forced at the upper boundary with monthly climatologies of windstress heat and freshwater fluxes the model results suggest that anomalous northward southward positions of the angola benguela frontal zone are connected to anomalous intensities of the front anomalous northward shifts of the angola benguela frontal zone appear to be associated with an anticyclonic circulation pattern in the area that shifts the frontal system toward the north this anomalous circulation also forces changes in coastal upwelling that in turn alter upper ocean temperatures such as to enhance the meridional temperature gradient across the front this mechanism is seasonally dependent and most clearly established during austral spring and summer a comparison between model variability near the angola benguela frontal zone and other modes of variability suggests that variability resulting from the monthly climatological forcing could at times account for the same amount of variability as that induced by the el nino southern oscillation and for up to 20 of the variability apparent during major warm events in the southeast atlantic such as benguela ninos

a comparison of long coastal trapped wave theory with observations off peru abstract the agreement between coastal trapped wave theory and observation is studied for the case of observations made off peru during the 1977 cuea joint ii experiment wave properties are calculated using a numerical model with realistic horizontally uniform stratification and realistic bottom topography these properties are then explored as a function of the ratio of the first internal rossby radius of deformation to the shelf slope width the agreement of observed and calculated first mode free wave phase speeds 230 cm s 1 is excellent while modal structures agree more poorly a forced wave calculation using observed winds and currents as input is used to hindcast alongshore currents and sea level in the frequency band where smith 1978 observed free coastal trapped waves during 1977 the model suggests that most of the observed sea level and alongshore velocity fluctuations in the 5 10 day period band are due to free waves originating equatorward of 5 deg s while winds between 5 deg s and

subsurface circulation and mesoscale variability in the algerian subbasin from altimeter derived eddy trajectories algerian eddies are the strongest and largest propagating mesoscale structures in the western mediterranean sea they have a large influence on the mean circulation water masses and biological processes over 20 years of satellite altimeter data have been analyzed to characterize the propagation of these eddies using automatic detection methods and cross correlation analysis we found that on average algerian eddy trajectories form two subbasin scale anticlockwise gyres that coincide with the two algerian gyres which were described in the literature as the barotropic circulation in the area this result suggests that altimetry sea surface observations can provide information on subsurface currents and their variability through the study of the propagation of deep mesoscale eddies in semienclosed seas the analysis of eddy sea level anomalies along the mean pathways reveals three preferred areas of formation eddies are usually formed at a specific time of the year in these areas with a strong interannual variability over the last 20 years

a model study of the angola benguela frontal zone sensitivity to atmospheric forcing 1 a regional ocean model is applied to the tropical south east atlantic ocean in order to investigate the sensitivity of the intensity and position of the angola benguela frontal zone the results suggest that the position of the angola benguela frontal zone is mainly determined by opposing northward and southward flow within 2 degrees off the coast the windstress curl plays a major role in altering the position of the angola benguela frontal zone as it controls the southeastward flow of the south equatorial counter current the opposing northward flow is mainly the result of geostrophic adjustment to coastal upwelling driven by the meridional windstress the strength of the frontal zone is found to be related to the strength of the southerly windstress that controls the coastal upwelling

mesoscale dynamics in the arabian sea and a focus on the great whirl life cycle a numerical investigation using roms the great whirl gw is a persistent anticyclonic mesoscale eddy that is observed seasonally in the arabian sea during a period embedding the 3 months of the southwest monsoon june july august at a quasi steady location its dynamics remain unclear despite it being one of the largest coherent vortices in the world ocean realistic regional numerical experiments using roms are performed to investigate the life cycle of the gw which is not well resolved by sparse available in situ measurements in the region using a set of sensitivity experiments and an accurate temporal characterization of the eddy properties including position radius depth and vorticity we i confirm the role of basin scale downwelling rossby waves in the gw generation ii clarify the role of the monsoonal strong anticyclonic wind in its maintenance and barotropization and iii suggest a connection between basin scale rossby wave dynamics and gw collapse

equatorward energy cascade critical latitude and the predominance of cyclonic vortices in geostrophic turbulence geostrophic turbulence exhibits features similar to those observed in the oceans a movement of energy toward the equator a critical latitude below which are alternating zonal flows and above which the flow is largely isotropic and a predominance of cyclonic vortices above the critical latitude these features arise in geostrophic turbulence when the latitude dependence of the deformation radius is taken into account with the aid of a quasigeostrophic one layer numerical model this paper proposes physical mechanisms giving rise to these features

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

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

atmospheric boundary layer modification drag coefficient and surface heat flux in the antarctic marginal ice zone during a traverse of the antarctic marginal ice zone miz near the greenwich meridian in october 1981 we launched a series of radiosondes along a 150 km track starting at the ice edge since the wind was from the north off the ocean these radiosonde profiles showed profound modification of the atmospheric boundary layer abl as the increasing surface roughness decelerated the flow the primary manifestation of this modification was a lifting of the inversion layer with increasing distance from the ice edge by the induced vertical velocity but there was also a cooling of the stably stratified mixed layer below the inversion and a consequent flux of sensible heat to the surface that averaged over 200 w m2 the magnitude of this flux suggests that atmospheric heat transport plays a significant role in the destruction of ice in the antarctic miz using the rising of the inversion and abl similarity theory we estimated the change in the neutral stability drag coefficient cd across the miz cd increased from its open ocean value 1 2 10 3 at the ice edge to 4 0 10 3 at 80 90 ice concentration we present an equation for this dependence of drag on ice concentration that should be useful for modeling the surface stress in marginal ice zones

the benguela a laboratory for comparative modeling studies abstract equilibrium dynamics of the benguela system is investigated using the holistic nature of the spatially and temporally cohesive output of a numerical model the regional ocean modeling system roms is used to simulate the benguela system in its entirety it successfully simulates the cool coastal upwelling regime and its division into seven distinctly separate cells as well as the large scale offshore regime and the respective seasonal fluctuations it does however present a cool bias at the coast due to an underestimation of the coastal wind drop off as well as a warm bias offshore in the southern benguela due to the overestimation of agulhas current input the benguela can be divided into northern and southern regimes based on dynamic as well as topographic differences topographically the division between the northern and southern regimes coincides with an abrupt narrowing of the continental shelf toward the north at 28 s the large scale depth integrated flow to the north of this feature is weak but distinctly poleward while to the south the flow regime is governed by the meandering nature of the equatorward benguela current and is the pathway for eddies that originate at the agulhas retroflection the poleward flowing regime of the northern benguela is tied to the sverdrup relation which links meridional transport with wind stress curl the luderitz upwelling cell at 27 s experiences the most vigorous upwelling throughout the year and as a result offshore volume fluxes in this region are extremely large this upwelling cell divides the northern and southern benguela coastal upwelling systems into separate regimes based on the fact that their seasonal signals are out of phase the offshore gradient of eddy kinetic energy eke is generally strong in the benguela system and exceptionally so in the southern benguela due to vigorous mesoscale activity offshore of the shelf edge originating from the agulhas retroflection area the juxtaposition between the steep offshore eke gradients in the south and much weaker offshore gradients of eke in the northern benguela has different implications for cross shore exchanges