surface geostrophic currents across the antarctic circumpolar current in drake passage from 1992 to 2004 the southern ocean plays an important role in the global overturning circulation as a significant proportion of deep water is converted into intermediate and deeper water masses in this region recently a secular trend has been reported in wind stress around the southern ocean and it is thought theoretically that the strength of the acc is closely related to wind stress so one consequence should be a corresponding increase in acc transport and hence changes in the rate of the global overturning there are no long term data sets of acc transport and so we must examine other data that may also respond to changing wind stress here we calculate surface currents in drake passage every seven days over 11 25 years from 1992 to 2004 we combine surface velocity anomalies calculated from satellite altimeter sea surface heights with measured surface currents since 1992 the uk has regularly occupied woce hydrographic section sr1b across the acc in drake passage from seven hydrographic sections surface currents are estimated by referencing relative geostrophic velocities from ctd sections with current measurements made by shipboard and lowered acoustic doppler current profilers combining the seven estimates of surface currents with the altimeter data reduces bias in the estimates of average currents over time through drake passage and we show that surface current anomalies estimated by satellite and in situ observations are in good agreement the strongest surface currents are found in the subantarctic and polar fronts with average speeds of 50 cm s and 35 cm s respectively and are inversely correlated so that maximum westward flow in one corresponds to minimum westward flow in the other the average cross sectional weighted surface velocity from 1992 to 2004 is 16 7 0 2 cm s a spectral analysis of the average surface current has only weakly increasing energy at higher frequencies and there is no dominant mode of variability the standard deviation of the seven day currents is 0 68 cm s and a running 12 month average has only a slightly smaller standard deviation of 0 52 0 16 cm s the southern annular mode sam measures the circumpolar average of wind stress and like the surface currents its spectrum has slightly increased energy at frequencies greater than 1 cpy a cospectral analysis of these averaging cospectra of five slightly overlapping 36 month segments improve statistical reliability suggests that there is coherence between them at 1 cpy with the currents leading changes in the southern annular mode we conclude that the sam and average drake passage surface currents are weakly correlated with no dominant co varying modes and hence predicting southern ocean transport variability from the sam is not likely to give significant results and that secular trends in surface currents are likely to be masked by weekly and interannual variability

interannual variability in the north atlantic ocean s temperature field and its association with the wind stress forcing abstractspectral analyses of the north atlantic temperature field in the simple ocean data analysis soda reanalysis identify prominent and statistically significant interannual oscillations along the gulf stream front and in large regions of the north atlantic a 7 8 yr oscillatory mode is characterized by a basinwide southwest to northeast oriented propagation pattern in the sea surface temperature sst field this pattern is found to be linked to a seesaw in the meridional dipole structure of the zonal wind stress forcing taux in the subpolar gyre the sst and taux fields of this mode are shown to be in phase opposition which suggests a cooling effect of the wind stress on the upper ocean layer over all this mode s temperature field is characterized by a strong equivalent barotropic component as shown by covariations in ssts and sea surface heights and by phase coherent behavior of temperature layers at depth with the sst field recent improvements of multivariate singular spectrum analysis

near surface dynamical structure of the kuroshio extension 1 lagrangian data from 657 svp drifters cnes aviso archiving validation and interpretation of satellite oceanographic data time variable satellite altimeter sea level anomaly and levitus 98 hydrographic data are used to develop 0 25 spatial resolution maps of the mean and eddy circulations in the northwestern pacific during the 1990s drifter velocities at 15 m depth and 200 m temperature data clearly indicate in the kuroshio extension ke jet two prominent meanders that culminate in a 300 km northward deflection east of the shatsky rise at 160 e the interannual trends of aviso mesoscale variance are absent along the path of the meandering ke jet three anticyclonic recirculations can be identified south or southeast of the kuroshio the southernmost around daito island being a new discovery about 3 of the drifters with drogues attached crossed the kuroshio front the aviso currents are correlated at 0 8 with drifter geostrophic velocity the aviso geostrophic currents are adjusted in amplitude to the contemporaneous drifter observations and are further used to compute an unbiased mean geostrophic circulation and the quasi geostrophic reynolds stresses in the ke region the principal axes of the eddy reynolds stresses are oriented along the unbiased mean velocity vectors within the meandering ke jet the time mean horizontal momentum balance that includes both the mean and eddy momentum convergences is used to compute absolute sea level map and its uncertainty at 145 e the 2000 m depth absolute dynamic height referenced to the sea level reveals a heretofore unknown 70 dynamic cm drop from 25 to 42 n

decadal sea level variability along the coast of japan in response to ocean circulation changes 1 decadal sea level variability along the coast of japan and its relation to large scale ocean circulation changes from 1993 to 2010 was investigated using tide gauge and satellite derived sea level data a singular value decomposition svd analysis is performed between coastal sea levels of japan and sea levels in the western north pacific the first svd mode reveals that the northward shifts of the kuroshio extension ke jet and the kuroshio southeast of japan accompany the coastal sea level rise in the early 2000s and 2010 and their southward shifts accompany the coastal sea level fall in the late 1990s and the late 2000s the shifts of the ke jet are induced by westward propagating rossby wave from the eastern north pacific which is concentrated along the ke jet axis as jet trapped rossby waves the resulting sea level changes along the coast of japan show a strong spatial contrast the sea level fluctuation is quite large along the southeastern coast of japan that is under the direct influence of the jet trapped rossby waves and also large in the western coast of japan probably due to coastal waves that are excited by the incoming rossby waves but is small north of the ke jet latitude hence the nature of the wave trapped by the ke jet produces an active zone and a shadow zone of coastal sea level variability of japan our results indicate that the correct representation of western boundary currents is necessary for reliable prediction of future coastal sea level changes

small mesoscale features at a meandering upper ocean front in the western ionian sea mediterranean sea vertical motion and potential vorticity analysis abstract transient mesoscale and submesoscale processes such as small eddies and filaments could play a fundamental role in the marine ecosystem especially in oligotrophic seas like the mediterranean however very little is known about the biological and physical dynamics characterizing such structures in this work the 8 km horizontal resolution data collected during the symplex 1998 survey are analyzed to describe the physical dynamics of small mesoscale features along the atlantic ionian stream western ionian sea the data were optimally interpolated over a regular grid and used to compute the 3d ageostrophic circulation by solution of the q vector formulation of the omega equation the relative importance of stratification relative vorticity and twisting terms in the rossby ertel potential vorticity is thus examined along selected isopycnals together with the associated vertical motions and vortex stretching a surface cyclonic eddy 15 km of radius was observed near a meander of the atlanti

synoptic flow structures in the confluence region of the kuroshio and the ryukyu current 1 in the southeastern region of kyushu japan the kuroshio from the east china sea encounters the ryukyu current from the east of the ryukyu islands by analyzing synoptic sections of water properties and geostrophic velocity in august 2004 and october 2005 we distinguished the waters in the kuroshio southeast of kyushu to be separated into an offshore region and a shallow onshore one the onshore water is derived from the east china sea while the offshore water originates from both the east of amami oshima island and the interior region of the north pacific the water mass transport from the east of amami oshima island may become equivalent to that of the kuroshio in the east china sea as in october 2005 the volume transport averaged temperature of the kuroshio southeast of kyushu is significantly lower than that in the east china sea because of the confluence with the colder ryukyu current east of the amami oshima island

east west asymmetry in nonlinear internal waves from luzon strait the nonhydrostatic regional ocean modeling system is applied to study the effects of thermocline shoaling deepening bathymetry and asymmetric modulated tides on the soliton growth to the west and east of luzon strait in the south china sea and western pacific ocean luzon strait comprises a shallow east ridge and a deep west ridge and its interaction with barotropic tidal currents yields strong westward internal tides that disperse into solitons satellite imagery indicates that the westward solitons are more numerous and better defined than the eastward solitons the model results show that the eastward solitons are 45 39 28 and 23 smaller than the westward solitons due to asymmetric modulated barotropic tides at the east ridge a deeper pacific ocean westward thermocline shoaling related to the kuroshio current and internal tide resonance in a double ridge configuration respectively due to the westward location of the kuroshio little thermocline deepening occurs east of the east ridge hence the influence of thermocline deepening on counteracting eastward soliton growth is small the kuroshio mainly enhances westward soliton growth the dispersion of internal tides into solitons is governed by the balance between the nonlinearity parameter on the one hand and the nonhydrostatic and coriolis dispersions on the other it is shown that this balance favors soliton growth for thermocline shoaling while it counters it for a deeper ocean a series of double ridge experiments is performed in which the distance between the ridges and the height of the west ridge are varied for a semidiurnal tidal forcing and two gaussian ridges separated by 100 km barotropic to baroclinic energy conversion is enhanced at both ridges causing larger westward internal tides and solitons the combination of coriolis forcing thermocline shoaling and a double ridge configuration enhances the distinctiveness of the so called type a and b solitons when a modulated tide occurs

the northeastward current southeast of the ryukyu islands in late fall of 2000 estimated by an inverse technique 1 the northeastward current nc southeast of the ryukyu islands is estimated using an inverse technique with hydrographic section data collected in december 2000 the inversion results show the nc flowing over the continental slope with a subsurface maximum velocity of 34 cm s 1 at 270 dbar depth southeast of okinawa and 67 cm s 1 at 400 dbar depth east of amami ohshima the nc volume transports are nearly equal at the two lines 15 sv and their vertical profiles exhibit similar subsurface maximum structure at both lines these results strongly suggest that the nc off amami ohshima originates from the nc off okinawa during our observation period

kuroshio extension variability and forcing of the pacific decadal oscillations responses and potential feedback abstract a forcing mechanism is sought for the large scale circulation changes in the kuroshio extension region of the western north pacific ocean as inferred by topex poseidon sea surface height ssh data the low frequency signal of the kuroshio extension over the last decade was characterized by a modulation in its zonal mean flow intensity the mean kuroshio extension jet weakened progressively from 1993 to 1996 and this trend reversed after 1997 the ability to simulate the major trends in the observed ssh signals with linear vorticity dynamics leads the authors to conclude that the modulation in the zonal mean jet was remotely forced by wind stress curl anomalies in the eastern north pacific ocean related to the pacific decadal oscillations pdos to be specific the weakening strengthening trend in 1993 96 1997 2001 was caused by westward expansions of negative positive ssh anomalies south of the kuroshio extension and positive negative ssh anomalies north of the kuroshio extension emerg

sea surface height signals as indicators for oceanic meridional mass transports numerical models are used to test whether the sea surface height ssh can be used as an indicator for the variability of atlantic meridional oceanic mass transports the results suggest that if the transports over the western boundary current region and those in the eastern part of the basin are considered separately significant correlations 0 3 0 9 are found between zonal ssh differences and the meridional transports in the top 1100 m much weaker correlations are found for the basinwide transport which corresponds to the surface branch of the meridional overturning circulation moc for the eastern and western branches of the meridional transport combining the ssh signal with the baroclinic structure obtained from rossby wave theory enables calculation of a quantitative estimate of the transport variability in the top 1100 m the results of the method are less convincing for the variability of the moc the reason for this is that even small relative errors in the variability of the eastern and western branches can be large compared with the moc variability these errors project onto the sum of the eastern and western transports and therefore onto the surface branch of the moc nevertheless being able to infer transport anomalies from ssh signals in the eastern and western parts of the atlantic might prove useful in interpreting moc observations from the u k natural environment research council rapid climate change rapid mooring array at 268n which show a large subannual variability that is mainly due to changes at the western boundary transports inferred from the ssh could help to identify the origin of this variability and whether transport anomalies propagate into the western boundary region from the basin interior or from other latitudes

effects of large scale wind on the kuroshio path south of japan in a 60 year historical ogcm simulation the effects of large scale wind forcing on the bimodality of the kuroshio path south of japan the large meander lm and non large meander nlm were studied by using a historical simulation 1948 2007 with a high resolution ocean general circulation models ogcm the kuroshio in this simulation spent much time in the nlm state and reproduced several aspects of its long term path variability for the first time in historical ogcm simulation presumably because the eddy kinetic energy was kept at a moderate level by using the simulated fields the relationships between wind forcing or kuroshio transport and path variation proposed by past studies were tested and specific roles of eddies in those variations were investigated the long term variation of the simulated net kuroshio transport south of japan was largely explained by the linear baroclinic rossby wave adjustment to wind forcing in the simulated lm events a triggering meander originated from the interaction of a wind induced positive sea surface height ssh anomaly with the upstream kuroshio and was enlarged by cyclonic eddies from the recirculation gyre the cyclonic eddy of the trigger meander was followed by a sizable anticyclonic eddy on the upstream side subsequently a weak strong kuroshio favored the lm nlm the lm tended to be maintained when the kuroshio transport off southern japan was small and increasing kuroshio transport promoted decay of an existing lm the supply of disturbances from upstream which is related to the wind induced ssh variability at low latitudes contributed to the maintenance of an existing lm

a direct determination of the world ocean barotropic circulation abstractthe time mean argo float displacements and the world ocean atlas 2009 temperature salinity climatology are used to obtain the total top to bottom mass transports outside of an equatorial band the total transports are the sum of the vertical integrals of geostrophic and wind driven ekman currents however these transports are generally divergent and to obtain a mass conserving circulation a poisson equation is solved for the streamfunction with dirichlet boundary conditions at solid boundaries the value of the streamfunction on islands is also part of the unknowns this study presents and discusses an energetic circulation in three basins the north atlantic the north pacific and the southern ocean this global method leads to new estimations of the time mean western eulerian boundary current transports maxima of 97 sverdrups sv 1 sv 106 m3 s 1 at 60 w for the gulf stream 84 sv at 157 e for the kuroshio 80 sv for the agulhas current between 32 and 36 s and finally 175 sv for the

estimation of heat and freshwater transports in the north pacific using high resolution expendable bathythermograph data 1 the mean heat and freshwater transports in the north pacific subtropical gyre during 1998 2002 are estimated high resolution expendable bathythermograph expendable conductivity temperature depth xbt xctd transects px 40 honolulu to japan px 37 san francisco to honolulu px 10 honolulu to guam px 44 guam to taiwan hong kong are used to calculate geostrophic transport across each of the ship tracks ekman transport is estimated from satellite scatterometer wind stress the mean heat and freshwater transport convergences into the northern box bounded by the px 40 37 transects and the tsushima and bering straits are 0 26 0 16 pw pw 1015 w and 0 26 0 11 sv sv 106 m3 s respectively heat and freshwater transport convergences into the western box bounded by the px 40 10 44 transects and the tsushima strait are estimated to be 0 32 0 17 pw and 0 08 0 07 sv respectively in both boxes warmer waters transported inward by the ekman flow and by the kuroshio are compensated by the export of waters at cooler temperatures whose peaks are found in the temperatures of the mode waters formed in the north pacific the salt budget is also described to consider the mechanisms of freshwater transport since the western box includes the region with the strongest heat loss to the atmosphere and is possibly a key region for climatic decadal variation it is necessary to continue the high resolution xbt xctd measurement and to make an effort at improving the estimation of heat and freshwater transports in order to contribute to advancing climate studies

the impact of subtidal circulation on internal tide generation and propagation in the philippine sea abstractthis study examines the effects of the subtidal circulation on the generation and propagation of the m2 internal tide in the philippine sea using a primitive equation model barotropic to baroclinic conversion at the luzon strait is found to vary due to the background circulation changes over the generation site and the changing influence of remotely generated internal tides from the mariana arc the varying effect of remotely generated waves results from both changing generation energy levels at the mariana arc and variability in the propagation of the internal tides across the philippine sea the magnitude and direction of the depth integrated baroclinic energy fluxes vary temporally due to a combination of changing generation propagation and dissipation spatial patterns of internal tide propagation near the luzon strait are influenced by the locations of mesoscale eddies to the east and west of the strait the results provide insight into the mechanisms of variability of the baroclinic tide

kuroshio temporal and spatial variations south of japan determined from inverted echo sounder measurements 1 the affiliated surveys of the kuroshio off ashizuri misaki asuka project is a collaboration between scientists in japan and the united states to improve our understanding of the structure and dynamics of the kuroshio off the coast of southwest japan in this project an array of nine inverted echo sounders and nine current meter moorings were deployed for 2 years 1993 1995 along a line extending 1000 km from shikoku numerous hydrographic profiles along this section were used to determine the regional gravest empirical modes gems which relate vertical profiles of temperature and specific volume anomaly to vertical acoustic echo time these gems were used in conjunction with the inverted echo sounder data to calculate 2 year time series of entire sections of relative geostrophic velocity and temperature current meter data provided absolute velocity references for the geostrophic velocity sections in addition a time series of kuroshio position was determined from the gem temperature sections it shows three big 80 km displacement and three little offshore meanders of the kuroshio occurring in february may june and october of both years this suggests a 4 month periodicity possibly phase locked to the annual cycle the meanders may be caused by mesoscale eddies arriving from the east the observed meanders were preceded by low kuroshio volume transport and were followed by high kuroshio volume transport the kuroshio volume and temperature transports were highly variable with respective means of 65 4 sv and 3 7 0 2 pw and standard deviations of 20 sv and 0 9 pw

nonlinear internal waves generated and trapped upstream of islands in the kuroshio nonlinear internal waves niws induce strong surface currents which are observable in synthetic aperture radar sar images sar images of the kuroshio show parabolic features around japan s izu islands implying possible niws most images were taken during the summer when the kuroshio approached the islands and the winds were relatively weak nonhydrostatic numerical simulations revealed that around the islands mode 1 internal waves are not trapped but higher modes with lower propagation speeds are trapped the surface convergence field predicted by the model reproduces prominent parabolic features observed in the sar images based on this agreement we suggest that the niws are generated around the izu islands by the kuroshio and the parabolic features detected by sar are surface manifestations of these niws specific atmospheric and oceanic conditions which are conducive for niw detection by sar are defined

evaluation of hycom in the kuroshio extension region using new metrics 1 a high resolution 0 08 at equator hybrid coordinate ocean model hycom simulation is evaluated using observations for the period 1993 2003 for a western pacific region containing the kuroshio extension ke 25 45 n and 135 180 e comparisons are made for the ke path and strength and for the upper ocean heat budget the mean strength and path agree well with observations except near the ke separation point where the jet is as much as 2 of latitude too far south however the model path variations are considerably more energetic than observed and this likely obscures the observed tendency for weaker meandering when the ke is strong the model accurately reproduces seasonal variations of upper ocean heat content but the long period about 10 yr variations of heat content and ke strength clearly differ in the region upstream of 150 e the long period variations in model ssh do not show the same relationship to wind forcing that is seen in the observations and in a low resolution ocean model simulation the hycom upper ocean heat budget is similar to a diagnostic heat budget inferred from observations in that the dominant contribution is from lateral fluxes advection however advection fluctuations again primarily in the upstream region are much larger in the model this evaluation of hycom shows realistic mean quantities and realistic variations away from the separation region however an overly energetic jet upstream of 150 e can obscure the longer period variability and its contribution to the upper ocean heat budget

the annual cycle of the japan sea throughflow abstractthe mechanism responsible for the annual cycle of the flow through the straits of the japan sea is investigated using a two layer model observations show maximum throughflow from summer to fall and minimum in winter occurring synchronously at the three major straits tsushima tsugaru and soya straits this study finds the subpolar winds located to the north of japan as the leading forcing agent which first affects the soya strait rather than the tsushima or tsugaru straits the subpolar winds generate baroclinic kelvin waves along the coastlines of the subpolar gyre affect the sea surface height at the soya strait and modify the flow through the strait this causes barotropic adjustment to occur inside the japan sea and thus affect the flow at the tsugaru and tsushima straits almost synchronously the barotropic adjustment mechanism explains well why the observations show a similar annual cycle at the three straits the annual cycle at the tsugaru strait is further shown to be weaker than t

satellite altimeter monitoring the kuroshio transport south of japan in 1993 1995 we carried out observations of the kuroshio south of japan including direct current measurements and repeated hydrographic surveys along a satellite track of the topex poseidon altimeter the velocity field of the kuroshio is determined by geostrophic calculation using the repeated hydrographic survey data referenced to velocities observed at mid and abyssal depths the volume transport of the kuroshio is estimated from this velocity field the estimated transports of the kuroshio have a high correlation with sea surface height differences across the kuroshio having this relationship and using the altimeter data we obtained a time series of the kuroshio transport over seven years at ten day intervals the kuroshio transport excluding contributions by local recirculations is estimated to be 42 106 m sec on average the correlation between sea surface height difference and transport provides a practical method of long term monitoring of the kuroshio transport using satellite altimetry

three dimensional numerical simulation of m2 internal tides in the east china sea the east china sea and adjacent seas are one of the most significant generation regions of the m 2 internal tide in the world s oceans in the present study we investigate the distribution and energetics of the m 2 internal tide around the continental shelf edge in the east china sea using a three dimensional numerical model the numerical experiment shows that m 2 internal tides are effectively generated over prominent topographic features such as the subsurface ridges in the bashi luzon and tokara straits the ridges along the ryukyu island chain and the continental shelf slope in the east china sea the former particularly so all of these topographic features are characterized by steep slopes at the depth of the thermocline onto which the m 2 barotropic tide is almost normally incident the m 2 internal tides propagating away from these multiple source regions interfere with each other to create a complicated wave pattern it is found that the calculated pattern of the m 2 internal tide agrees well with topex poseidon altimeter observations the conversion rate from m 2 barotropic to baroclinic energy over the whole analyzed model domain is estimated to be 35 gw roughly 10 of the energy in the m 2 surface tide incident on the prominent topographic features is converted to the m 2 internal tide although about half of the m 2 internal tidal energy is subject to local dissipation in close proximity to the generation sites

circulation in the alboran sea as determined by quasi synoptic hydrographic observations part i three dimensional structure of the two anticyclonic gyres abstract the circulation and dynamics of the modified atlantic water have been studied using data from an intensive field experiment carried out between 22 september and 7 october 1992 data included 134 ctd casts adcp and satellite imagery a well defined wavelike front was observed with two significant anticyclonic gyres in the western and eastern alboran sea smaller scale cyclonic eddies were also observed the front separates the more saline older modified atlantic water s 38 in the northern region from the fresher more recent modified atlantic water s 36 8 in the south the associated baroclinic jet had a mean transport of 1 sv and maximum geostrophic velocities of 1 0 ms 1 the three dimensional structure and spatial scales of both gyres were similar that is 90 km long and 220 m deep in the eastern alboran northeast of oran the origin of the algerian current was also detected with an eastward transport of 1 8 sv the general picture can be presented as a structure formed by a wavelike

kuroshio stream path variation and its associated velocity structures south of shikoku japan during 1993 1995 twelve repeat observations of the kuroshio south of shikoku japan were carried out for obtaining a vertical velocity section of the upper 300m using a towed type acoustic doppler current profiler adcp among the twelve observations the kuroshio took the onshore path 9 times and the offshore path 3 times the cross stream velocity distribution around the kuroshio stream axis is asymmetric steeper on the onshore side than on the offshore side for the onshore path while it is symmetric for the offshore one the core with a maximum velocity is submerged to 100 200m depths for the onshore case and located at the near surface for the offshore case in the combined analysis with the rapid bulletin of ocean conditions the kuroshio mainly took an onshore path with stream axis positions less than 80km from cape ashizuri but the distance was increased over 150km at the frequency once a year

ageostrophic secondary circulation in a subtropical intrathermocline eddy abstractvertical motions play a key role in the enhancement of primary production within mesoscale eddies through the introduction of nutrients into the euphotic layer however the details of the vertical velocity field w driving these enhancements remain under discussion for the first time the mesoscale w associated with an intrathermocline eddy is computed and analyzed using in situ high resolution three dimensional 3d fields of density and horizontal velocity by resolving a generalized omega equation valid for high rossby numbers in the seasonal pycnocline the diagnosed w reveals a multipolar structure with upwelling and downwelling cells located at the eddy periphery in the main pycnocline w is characterized by a dipolar structure with downwelling velocities upstream of the propagation path and upwelling velocities downstream maximum values of w reach 6 4 m day 1 an observed enhancement of chlorophyll a at the eddy periphery coincides with the location of the upwelling and downwelling cells a

roles of mesoscale eddies in the kuroshio paths a high resolution ocean general circulation model is developed to simulate connections between the kuroshio path variations and mesoscale eddy activities as realistically as possible the climatological mean of the modeled kuroshio takes a nearshore nonlarge meander path it is found that the model is capable of simulating two types of nonlarge meander state and a possible version of the large meander state the offshore nonlarge meander is generated through interaction between the kuroshio and an anticyclonic eddy the large meander occurs just after significant intensification of the anticyclonic kuroshio recirculation successive intrusion of anticyclonic eddies from the upstream region is responsible for this process those anticyclonic eddies are advected by the kuroshio from the region northeast of luzon island and increase the upstream kuroshio volume transport on an interannual time scale the cyclonic eddies propagating from the kuroshio extension region on the other hand weaken the kuroshio meander after the merger the kuroshio path variations south of japan thus seem to be closely related to eddy activities in the subtropical gyre system

annual variation of the kuroshio transport in a two layer numerical model with a ridge abstract a two layer numerical model driven by the wind stress is used to explain the observed annual variation of the kuroshio transport south of japan special attention is given to the effect of a ridge representing the izu ogasawara ridge on the generation of the baroclinic activity through the coupling of the barotropic and baroclinic modes of motion for annual variation lower layer motion is found in areas surrounding the ridge because isostasy a state of no motion in the lower layer is not achieved within such a short timescale thus the lower layer flow impinges on the bottom slope this impinging process generates anomalies of the upper layer thickness especially on the eastern side of the ridge thereafter anomalies move westward with characteristic velocities composed of the vertically averaged flow and westward propagation of the long baroclinic rossby wave forced above the ridge as anomalies of the upper layer thickness move westward above the ridge isostasy is accomplished with res

on the generation and evolution of nonlinear internal waves in the south china sea the nonhydrostatic regional ocean modeling system is applied to the nonlinear internal waves or solitons that are generated at the luzon ridge in the south china sea the luzon ridge near the batan islands is represented by an idealized ridge with a height of 2 6 km on a flat bottom model runs are performed for various ridge shapes and a symmetric tidal forcings the model is in the mixed tidal lee wave regime the barotropic tide over the ridge generates first mode waves through the internal tide release mechanism westward traveling solitons emerge from these first mode waves through nonlinear steepening in the internal tide release mechanism asymmetric tides with strong eastward currents can generate strong westward solitons the eastward current creates an elevation wave with a higher energy density west of the ridge and as soon as the current slackens the wave is released westward on its backslope strong solitons develop the energy density is further enhanced by nonlinearities such as differences in phase speeds and energy fluxes related to lee waves a modal and harmonic decomposition shows the generation of vertical modes and higher temporal harmonics and indicates significant wave wave interaction e g triads in the mixed tidal lee wave regime more energy is contained in the first mode compared to the higher modes hence linear internal tide beams are less well defined and strong solitons develop

estimation of the sea level trend south of japan by combining satellite altimeter data with in situ hydrographic data 1 the sea level trend from1992 to 2006 was estimated by combining satellite altimeter data with in situ hydrographic data along the topex poseidon and jason 1 subsatellite track south of japan the sea level trend estimates from the altimeter data were consistent with those from the coastal tide gauge data the mean sea level trend along the hydrographic observation line was 4 2 0 8 mm a 1 by assuming that the sea level trend due to large scale deformation of ocean basins from glacial isostatic adjustment is 0 3 mm a 1 the sea level trend by the ocean mass change was estimated to be 1 3 0 4 mm a 1 and the steric height trend was estimated to be 3 2 0 9 mm a 1 2 8 0 9 mm a 1 between 0 and 1800 dbar plus 0 4 0 2 mm a 1 between 1800 and 4500 dbar steric height estimated from the altimeter data agreed well with that estimated from the conductivity temperature depth profiler and expendable bathythermograph data however steric height estimated from the argo float data over year 2004 2006 was significantly biased of about 10 mm on average with respect to that estimated from the altimeter data a systematic pressure error of about 2 dbar in the argo float profiles could account for this negative bias in steric height

tidal currents and kuroshio transport variations in the tokara strait estimated from ferryboat adcp data from 2003 through 2011 current surveys using an acoustic doppler current profiler adcp mounted on the ferry naminoue were conducted across the tokara strait tks 1 234 of the resulting velocity sections were used to estimate major tidal current constituents in the tks the semi diurnal m2 tidal current maximum amplitude 27 cm s 1 was dominant among all the tidal constituents and the diurnal k1 tidal current maximum amplitude 21 cm s 1 was the largest among all the diurnal tidal constituents over the section the ratios relative to m2 of averaged amplitudes of m2 s2 n2 k2 k1 o1 p1 and q1 tidal currents were 1 00 0 44 0 21 0 12 0 56 0 33 0 14 0 10 tidal currents estimated from the ship mounted adcp data were in good agreement with those from the mooring adcp data their root mean square difference for the m2 tidal current amplitude was 2 0 cm s 1 after removing the tidal currents the annual mean of the net volume transport nvt through the tks its standard derivation was 23 03 3 31 sv sv 106 m3 s 1 the maximum minimum monthly mean nvt occurred in july november with 24 60 21 47 sv nvt values from the ship mounted adcp were in good agreement with previous geostrophic volume transports calculated from conductivity temperature depth data but the former showed much finer temporal structure than those from the geostrophic calculation this article is protected by copyright all rights reserved

incoherent nature of m2 internal tides at the hawaiian ridge abstractmoored current temperature and conductivity measurements are used to study the temporal variability of m2 internal tide generation above the kaena ridge between the hawaiian islands of oahu and kauai the energy conversion from the barotropic to baroclinic tide measured near the ridge crest varies by a factor of 2 over the 6 month mooring deployment 0 5 1 1 w m 2 the energy flux measured just off the ridge undergoes a similar modulation as the ridge conversion the energy conversion varies largely because of changes in the phase of the perturbation pressure suggesting variable work done on remotely generated internal tides during the mooring deployment low frequency current and stratification fluctuations occur on and off the ridge model simulations suggest that these variations are due to two mesoscale eddies that passed through the region the impact of these eddies on low mode internal tide propagation over the ridge crest is considered it appears that eddy related changes in stratif

energy flux and dissipation in luzon strait two tales of two ridges abstractinternal tide generation propagation and dissipation are investigated in luzon strait a system of two quasi parallel ridges situated between taiwan and the philippines two profiling moorings deployed for about 20 days and a set of nineteen 36 h lowered adcp ctd time series stations allowed separate measurement of diurnal and semidiurnal internal tide signals measurements were concentrated on a northern line where the ridge spacing was approximately equal to the mode 1 wavelength for semidiurnal motions and a southern line where the spacing was approximately two thirds that the authors contrast the two sites to emphasize the potential importance of resonance between generation sites throughout luzon strait baroclinic energy energy fluxes and turbulent dissipation were some of the strongest ever measured peak to peak baroclinic velocity and vertical displacements often exceeded 2 m s 1 and 300 m respectively energy fluxes exceeding 60 kw m 1 were measured at spring tide at the wester

current system east of the ryukyu islands 1 the ryukyu current system rcs is a northeastward current southeast of the ryukyu islands the variation of current structure in the rcs region was investigated on the basis of the absolute geostrophic velocity estimated by inverse calculation using hydrographic data three realizations of the rcs are examined from cruises in may september and october 2002 it was found that the current structure in the rcs region is divided into upper and lower layers by an isopycnal surface of 26 the currents in both layers proceed northeastward along the eastern slope east of the ryukyu islands the current in the upper layer merges with the inflow from the interior region resulting in larger northeastward volume transport southeast of amami oshima island than southeast of okinawa island the volume transport from the east reaches more than 40 of that southeast of amami oshima island on the other hand the current in the lower layer is not affected by inflow from the east it is also found that the upper rcs gains heat mainly through the advection of warm water from the east resulting in an increase in the downstream temperature by about 0 5 c on average

stable volume and heat transports of the north pacific subtropical gyre revealed by identifying the kuroshio in synoptic hydrography south of japan 1 we conducted synoptic hydrographic surveys three times under distinctly different conditions of the kuroshio in the region off the southern coast of japan the large meander october 2004 and non large meander september 2005 and september 2006 states as a result of the water mass analysis we could separate the volume and heat transports of the north pacific subtropical gyre from the local recirculation gyre and mesoscale eddies despite the different flow conditions of the kuroshio the volume transport and the volume transport averaged temperature of the subtropical gyre fluctuate within the ranges of 23 3 29 0 106 m3 s 1 and 17 3 17 6 c respectively which are quite stable with respect to those for the kuroshio south of japan estimated in the past studies taking into account the decrease in the volume transport averaged temperature in the north pacific interior region the net heat transport of the subtropical gyre across the latitude of 30 n was estimated to be between 0 19 and 0 22 1015 w

a balanced approach to modelling rotating stably stratified geophysical flows we describe a new approach to modelling three dimensional rotating stratified flows under the boussinesq approximation this approach is based on the explicit conservation of potential vorticity and exploits the underlying leading order geostrophic and hydrostratic balances inherent in these equations in the limit of small froude and rossby numbers these balances are not imposed but instead are used to motivate the use of a pair of new variables expressing the departure from geostrophic and hydrostratic balance these new variables are the ageostrophic horizontal vorticity components i e the vorticity not directly associated with the displacement of isopycnal surfaces the use of potential vorticity and ageostrophic horizontal vorticity rather than the usual primitive variables of velocity and density reveals a deep mathematical structure and appears to have advantages numerically

upgradient and downgradient potential vorticity fluxes produced by forced rossby waves part i basic experiments abstractthe mean flow and potential vorticity pv flux produced by rossby waves are examined particularly by focusing on the effects of stratification and nonlinearity on upgradient and downgradi

estimates of the mean circulation in the deep 2 000m layer of the eastern north atlantic a total of 131 current meter records of between 6 and 24 month duration are analysed to describe the deep flow field of the eastern north atlantic from 19 to 54 n and from the continental slope to the mid atlantic ridge mean flows are weak and may be statistically indeterminate in some records and locations but appear to indicate cyclonic circulations around the iberia and porcupine abyssal plains with a generally southward flow along the mid atlantic ridge and a deep northward slope current where measurements exist along the eastern boundary the deepest inflow to the north eastern basin that has been identified to date takes place through the discovery gap of 4 700 m sill depth at 37 25 n 15 45 w in the azores portugal ridge south of that ridge observations are sparse and no systematic circulation is yet evident these observations are discussed in relation to recent geostrophic estimates of the deep circulation

effects of kuroshio intrusions on nonlinear internal waves in the south china sea during winter 1 during winter the kuroshio tends to cross luzon strait penetrating the northeastern south china sea where it forms energetic mesoscale structures luzon strait is also a site where westward propagating large amplitude internal waves are generated we describe observations of these waves acquired in the deep basin of the south china sea during the winter of 2010 2011 with the goal of assessing the influence of mesoscale variability on their properties combining tidal current simulations with an internal wave generation and evolution model we obtain time series of deviations between our observations and the model simulations these deviations are analyzed in terms of mesoscale variability based on the data assimilated hybrid coordinate ocean model hycom simulations we find that simplified models of nonlinear internal wave response to changes in horizontal stratification gradients and vertical shear provide at best weak simulations of amplitude modulation in contrast to these results deviations of internal wave arrival time occurring up to 2 h early during kuroshio inflows are quite well simulated when derived from integration of the first internal mode phase speed along two dimensional ray traced paths using hycom simulations of velocity and density fields together with bathymetry refraction of the internal waves by kuroshio intrusions can lead to substantial distortion of the paths sufficient to provide a potential explanation for the apparent suppression of waves during previous winter measurements our results suggest that the internal wave field can be a sensitive indicator of mesoscale variability in luzon strait and the northeastern south china sea

sensitivity of internal tide generation in hawaii energy from the barotropic tide is transferred into the baroclinic tide over topographic gradients which provides a mechanism for the ocean boundaries to communicate with the deep ocean to close energy budgets and as a source of flux affecting nutrient supply and larval transport understanding the temporal variability of the conversion from barotropic to baroclinic tides is critical to our understanding of these processes using a numerical model and its adjoint we examine the sensitivity of tidal conversion at kaena ridge in hawaii we find a sensitivity to changes in the upper ocean due to a phase difference between the pressure anomaly and tidal velocity caused by internal waves generated on the opposite slope of the ridge however we also find that conversion is equally as sensitive to local deep stratification changes

deep variability in the atlantic western boundary current based on altimetric and expendable bathythermograph data 1 the deep variability in two areas of the atlantic western boundary is studied one site is located at 38 n inshore of the gulf stream the other is at 8 s off the brazilian coast analyses are centered on current time series estimated by a method that uses expendable bathythermograph derived dynamic heights to remove the near surface signal from altimetric sea surface height both series are approximately 6 years long currents are compared to scatterometer derived alongshore wind stress and basin wide wind stress curl in both areas current variability is correlated to basin averaged wind stress curl and also to alongshore wind stress the relationship between currents and wind curl is coherent with the western boundary currents response to interior sverdrup flow we propose that alongshore wind stress exerts control over the flow by divergence of the ekman flow at the coast in the north the variability is dominated by interannual oscillations of the wind curl the effects of the alongshore stress are secondary and have annual frequency in the southern site the alongshore effect appears to be the dominant forcing the main observed results are confirmed by data from a numerical model with 1 6 horizontal resolution

observed eastward progression of the fukushima 134cs signal across the north pacific radionuclide samples taken as part of hydrographic surveys at 30 n in the north pacific reveal that the easternmost edge of fukushima derived 134cs observed at 174 3 w in 2012 had progressed eastward across the basin to 160 6 w by 2013 the 2013 30 n observations indicate surface 134cs concentrations of 3 5 bq m3 between 160 e and 160 w slightly lower concentrations west of 160 e and no detectable signal east of 160 6 w profile samples show 134cs penetration to 500 m west of 180 with shoaling penetration depth toward to the east the near uniform vertical distribution of 137cs between 152 w and 121 3 w in the top 500 m is indicative of trace amounts of radionuclides remaining from weapons testing the physical processes responsible for the deep 134cs penetration in the western pacific appear to be related to distinct water mass subduction pathways however the timing and rapidity of deep penetration over the broad scales observed has yet to be clarified

numerical treatment of cross shelf open boundaries in a barotropic coastal ocean model abstract using a barotropic coastal ocean model with a straight coastline and uniform cross shelf bottom slope seven different cross shelf open boundary conditions four of which are applied in either implicit or explicit form are compared in three numerical experiments 1 a mound of water is allowed to collapse and radiate waves toward the open boundaries 2 a uniform alongshelf wind stress is applied at zero time over the entire shelf and held constant for the duration of the experiment 3 a uniform cross shelf wind stress is applied at zero time over the entire shelf and held constant for the duration of the experiment the boundary condition which is most transparent to waves consists of a sponge at the outer edge of the model domain with an orlanski radiation condition at the outer edge of the sponge several open boundary conditions perform adequately in the wind stress experiments but the orlanski radiation condition alone without a sponge appears to give the best total performance of thes

sea surface slope as a proxy for agulhas current strength the linear relation between the strength of the agulhas current at nominal latitude 34 s and the gradient in sea level height anomaly across the current is investigated in a 1 10 resolution regional numerical ocean model our results show that the strength of the current can be estimated with reasonable accuracy using altimeter data once it has been calibrated using in situ transport measurements three years of transport measurements provide a calibration with worst case correlation r 0 78 in that case the errors in proxy transport have a standard deviation of 9 8 sv compared to a 20 2 sv standard deviation of the transport time series itself from these results we conclude that the design of the agulhas current timeseries act experiment a three year deployment of moorings across the agulhas current and along a topex jason altimeter ground track will likely produce a good quality multi decadal time series of agulhas current strength

overturning circulation that ventilates the intermediate layer of the sea of okhotsk and the north pacific the role of salinity advection dense shelf water dsw formation in the northwestern continental shelf of the sea of okhotsk is the beginning of the lower limb of the overturning circulation that ventilates the intermediate layer of the north pacific ocean the upper limb consisting of surface currents in the okhotsk sea and the subarctic gyre has not been clarified using a high resolution north pacific ocean model with a curvilinear grid as fine as 3 km 3 km in the sea of okhotsk we succeeded in representing the three dimensional structure of the overturning circulation including the narrow boundary currents and flows through straits that constitute the upper limb as well as the lower limb consisting of dsw formation and ventilation in particular pathways and time scales from the bering sea to the intermediate layer via the ventilation in the sea of okhotsk were examined in detail using tracer experiments further we found that the overturning circulation that connects the surface and intermediate layer is sensitive to wind stress in the case of strong winds the coastal current under polynyas where dsw forms is intensified and consequently diapycnal transport from the surface layer to the intermediate layer increases strong winds also induce a positive sea surface salinity anomaly in the subarctic region causing a significant decrease in the density stratification and increase in the dsw salinity i e density these processes act together to produce intense overturning circulation and deep ventilation which may subduct even to the bottom of the sea of okhotsk if the wind is strong

subtropical coral reveals abrupt early twentieth century freshening in the western north pacific ocean instrumental climate observations provide robust records of global land and ocean temperatures during the twentieth century unlike for temperature continuous salinity observations in the surface ocean are scarce prior to 1970 and the magnitude of salinity changes during the twentieth century is largely unknown surface ocean salinity is a major component in climate dynamics as it influences ocean circulation and water mass formation here we present an annually resolved reconstruction of salinity variations in the surface waters of the western subtropical north pacific ocean since 1873 based on bimonthly records of 18o sr ca and u ca in a coral from the ogasawara islands the reconstruction indicates that an abrupt regime shift toward fresher surface ocean conditions occurred between 1905 and 1910 observational atmospheric data suggest that the abrupt freshening was associated with a weakening of the winds that drive the kuroshio current system and the associated subtropical gyre circulation we note that the abrupt early twentieth century freshening in the western subtropical north pacific precedes abrupt climate change in the northern north atlantic by a few years the potential for abrupt regime shifts in surface ocean salinity should be considered in climate predictions for the coming decades

the current system east of the ryukyu islands as revealed by a global ocean reanalysis abstract the structure and variability of the ryukyu current system rcs which forms the western boundary current along the eastern slope of the ryukyu islands are studied using results from a 32 layer 1 12 5 global hybrid coordinate ocean model hycom and navy coupled ocean data assimilation ncoda reanalysis for the period 1993 2012 it is confirmed that the reanalysis realistically reproduces salient features of the observed currents at three sections southeast of miyakojima okinawa and amami ohshima the mean velocity sections show well developed subsurface velocity maxima between 700 and 900 m the current core southeast of amami ohshima shows year to year variations with cyclonic anticyclonic circulation east of amami ohshima generating weak strong velocity cores interaction of the rcs with an anticyclonic eddy often produces a two core velocity structure with a surface core in the upper 300 m and a deeper core near 700 900 m the horizontal structure of the rcs at 15 m depth shows a well developed northeastward current northeast of okinawa which is partly fed by the southwestward extension of the anticyclonic recirculation gyre the rcs forms a continuous northeastward current from miyakojima to amami ohshima below 500 m with shoreward intensification the circulation at 2000 m shows a seasonal flow reversal which is northeastward from december to june and southwestward from august to october with july and november being the transition months the volume transports across these three sections have respective mean values of 0 6 6 2 and 12 4 sv 1 sv 106 m3 s 1 and standard deviations of 10 2 7 1 and 11 3 sv they have dominant seasonal variations with the maximum in winter and spring and the minimum in summer the interannual variation of the transport anomaly which co varies with the rcs core results from westward propagating mesoscale eddies arriving from the pacific interior

internal tides in the southwestern japan east sea abstract this paper investigates the internal tidal energy distribution in the southwestern japan east sea using vertical round trip travel time data from 23 pressure sensor equipped inverted echo sounders pies the records are analyzed by bandpass filtering to separate time dependent variability of the semidiurnal and diurnal bands the semidiurnal internal tides exhibit a horizontal beam pattern of high energy propagating into the open basin they originate from a restricted portion of the shelf break where the korea strait enters the ulleung basin the generation appears to occur at 200 m water depth near 35 5 35 7 n and 130 131 e where the slope of bottom topography matches that of the wave characteristics coinciding with the location where the semidiurnal barotropic cross slope tidal currents are strongest maximum vertical displacement of the thermocline interpreted as a long wave first baroclinic mode from the measured is about 25 m near the generation region annual and monthly var

propagation of low mode internal waves through the ocean abstract the baroclinic tides play a significant role in the energy budget of the abyssal ocean although the basic principles of generation and propagation are known a clear understanding of these phenomena in the complex ocean environment is only now emerging to advance this effort a ray model is developed that quantifies the effects of spatially variable topography stratification and planetary vorticity on the horizontal propagation of internal gravity modes the objective is to identify baroclinic shoals where wave energy is spatially concentrated and enhanced dissipation might be expected the model is then extended to investigate the propagation of internal waves through a barotropic mesoscale current field the refraction of tidally generated internal waves at the hawaiian ridge is examined using an ensemble of mesoscale background realizations derived from weekly ocean topography experiment topex poseidon altimetric measurements the path of mode 1 is only slightly affected by typical cur

the kuroshio east of taiwan moored transport observations from the woce pcm 1 array observations from the woce pcm 1 moored current meter array east of taiwan for the period september 1994 to may 1996 are used to derive estimates of the kuroshio transport at the entrance to the east china sea three different methods of calculating the kuroshio transport are employed and compared these methods include 1 a direct method that uses conventional interpolation of the measured currents and extrapolation to the surface and bottom to estimate the current structure 2 a dynamic height method in which moored temperature measurements from moorings on opposite sides of the channel are used to estimate dynamic height differences across the current and spatially averaged baroclinic transport profiles and 3 an adjusted geostrophic method in which all moored temperature measurements within the array are used to estimate a relative geostrophic velocity field that is referenced and adjusted by the available direct current measurements the first two methods are largely independent and are shown to produce very similar transport results the latter two methods are particularly useful in situations where direct current measurements may have marginal resolution for accurate transport estimates these methods should be generally applicable in other settings and illustrate the benefits of including a dynamic height measuring capability as a backup for conventional direct transport calculations the mean transport of the kuroshio over the 20 month duration of the experiment ranges from 20 7 to 22 1 sv 1 sv 106 m3 s 1 for the three methods or within 1 3 sv of each other the overall mean transport for the kuroshio is estimated to be 21 5 sv with an uncertainty of 2 5 sv all methods show a similar range of variability of 10 sv with dominant timescales of several months fluctuations in the transport are shown to have a robust vertical structure with over 90 of the transport variance explained by a single vertical mode the moored transports are used to determine the relationship between kuroshio transport and sea level difference between taiwan and the southern ryukyu islands allowing for long term monitoring of the kuroshio inflow to the east china sea

vertical velocity in mesoscale geophysical flows an analysis of the vertical velocity field using the full generalized omega equation equation in a single mesoscale baroclinic oceanic gyre is carried out the evolution of the gyre over 20 inertial periods is simulated using a new three dimensional numerical model which directly integrates the horizontal ageostrophic vorticity explicitly conserves the potential vorticity pv via contour advection on isopycnal surfaces and inverts the nonlinear pv definition via the solution of a three dimensional monge ampere equation in this framework the equation comes simply from the horizontal divergence of the horizontal ageostrophic vorticity prognostic equation the ageostrophic vorticity is written as the laplacian of a vector potential from which both the velocity and the density fields are recovered respectively from the curl and divergence of a new initialization technique based on the slow progressive growth of the pv field during an initial time interval is used to avoid the generation of internal gravity waves during the initialization of the gyre this method generates a nearly balanced baroclinic gyre for which the influence of internal gravity waves in the mesoscale vertical velocity field is negligible the numerical fields obtained are then used to carry out a first numerical analysis of the equation the analysis shows that for moderately high rossby numbers the local and the advective rates of change of the differential ageostrophic vertical vorticity z are of the same order of magnitude as the three largest terms in the w equation there is however a large cancellation between these two terms resulting in the approximate material conservation of z this might explain the over applicability of the quasi geostrophic qg equation for rossby numbers larger than 0 1 the qg vertical velocity is only 22 smaller than the total vertical velocity for the case studied having a rossby number of 0 5

the surface expression of semidiurnal internal tides near a strong source at hawaii part ii interactions with mesoscale currents abstract observations of semidiurnal surface currents in the kauai channel hawaii are interpreted in the light of the interaction of internal tides with energetic surface intensified mesoscale currents the impacts on internal tide propagation of a cyclone of 55 km diameter and 100 m vertical decay scale as well as of vorticity waves of 100 km wavelength and 100 200 m vertical decay scales are investigated using 3d ray tracing the doppler shifted intrinsic frequency is assumed to satisfy the classic hydrostatic internal wave dispersion relation using the local buoyancy frequency associated with the background currents through thermal wind or gradient wind balance the m2 internal tide rays with initial horizontal wavelength of 50 km and vertical wavelength of o 1000 m are propagated from possible generation locations at critical topographic slopes through idealized mesoscale currents approximating the observed currents despite the lack of scale separation between the internal waves and backgroun

mechanism of internal waves in the luzon strait 1 this study suggests a western boundary current instability generation mechanism for the ocean internal waves a linear model describing this instability is developed and an analytical solution is derived from a zero order complex frequency wavenumber relation the real part of the relation represents a dispersion relation of the generated internal waves and the imaginary part is an exponential growth rate the dispersion relation describes the wave propagation characteristics while the growth rate represents the instability properties the theoretical results are used for the case of the kuroshio east of the luzon strait based on the analysis it is found that for the westward propagating disturbance the kuroshio west wing is unstable and the east wing is stable while the reverse is true for the eastern propagating disturbance the results are used to interpret satellite sar images of the ocean internal waves which were generated in the luzon strait and propagated westward reasonable estimates for the growth rate and propagation velocity are derived from a scale analysis of the kuroshio east of the luzon strait

surface water hydrography of the kuroshio extension during the pliocene pleistocene climate transition abstract the pliocene pleistocene climate transition offers an opportunity to study the effect of glaciation on the ocean climate system we present a globigerinoides ruber 18 o record from ocean drilling program site 1208 kuroshio current extension kce this exclusively sub tropical foraminifer a summer fall mixed layer dweller at the kce affords the first long 3 0 ma to 1 8 ma orbital scale 2 5 kyr time step account of the sea surface in this area the section s temperature corrected benthic foraminiferal 18 o record constrains global changes in ice volume yielding a 18 o record that primarily reflects summer fall kce hydrography temperature and salinity a 0 3 decrease in 18 o values at 2 7 ma coincides with the onset of northern hemisphere glaciation indicating as much as 1 5 c warming during the summer fall to suggest that the subtropical north pacific sea surface provided heat and moisture for expanding ice sheets on the orbital scale the 41 kyr cycle that dominates high latitude climate is absent from the 18 o record indicating a stable surface water hydrographic regime on this time scale rather the 18 o record varies at and is coherent with the 19 kyr precessional component of the regional insolation curve supporting a direct response to subtropical insolation and insensitivity to extra regional forcing factors such as ice sheets

internal tide generation by seamounts ridges and islands a numerical investigation is made into the generation of semidiurnal internal tides by tidal flow over steep topographic features in the deep ocean a fully three dimensional free surface nonlinear hydrostatic model the princeton ocean model is used with real stratification representative tidal forcing and gaussian shaped seamounts ridges and islands for the topography the efficiencies of the different topographies in extracting energy from the barotropic tide and in generating an internal tide are considered each topography produces an internal tide characterized by signals propagating away from the feature as beams that follow internal wave characteristic paths the strength of the signals however varies markedly for different topographies this is largely attributed to the way in which the barotropic tide interacts with the three dimensional topography internal wave generation requires a significant vertical displacement of stratified water by the barotropic tide as it flows over topography it is found that for symmetric seamounts and islands the barotropic flow tends to go around the feature producing only a weak internal tide when elongated into a ridge barotropic flow is forced across isobaths generating an energetic internal tide changing the horizontal aspect ratio of the topography from 1 1 a seamount to 3 1 a ridge increases the resulting baroclinic energy flux by nearly an order of magnitude the slope of the topography relative to that of the internal wave characteristics is also shown to be important with strongest generation occurring at regions of critical or supercritical topographic slope

subregional characterization of mesoscale eddies across the brazil malvinas confluence horizontal and vertical motions associated with coherent mesoscale structures including eddies and meanders are responsible for significant global transports of many properties including heat and mass mesoscale vertical fluxes also influence upper ocean biological productivity by mediating the supply of nutrients into the euphotic layer with potential impacts on the global carbon cycle the brazil malvinas confluence bmc is a western boundary current region in the south atlantic with intense mesoscale activity this region has an active role in the genesis and transformation of water masses and thus is a critical component of the atlantic meridional overturning circulation the collision between the malvinas and brazil currents over the patagonian shelf slope creates an energetic front that translates offshore to form a vigorous eddy field recent improvements in gridded altimetric sea level anomaly fields allow us to track bmc mesoscale eddies with high spatial and temporal resolutions using an automated eddy tracker we characterize the eddies across fourteen 5 5 subregions eddy centric composites of tracers and geostrophic currents diagnosed from a global reanalysis of surface and in situ data reveal substantial subregional heterogeneity the in situ data are also used to compute the evolving quasi geostrophic vertical velocity qg associated with each instantaneous eddy instance the qg eddy composites have the expected dipole patterns of alternating upwelling downwelling however the magnitude and sign of azimuthally averaged vertical velocity varies among subregions maximum eddy values are found near fronts and sharp topographic gradients in comparison with regional eddy composites subregional composites provide refined information about mesoscale eddy heterogeneity this article is protected by copyright all rights reserved

time varying parametric subharmonic instability from repeat ctd surveys in the northwestern pacific ocean 1 time varying diapycnal diffusivity signals are estimated using the fine scale parameterization method from high resolution ctd data along three repeat sections in the northwestern pacific ocean indicative of the parametric subharmonic instability psi locally elevated diapycnal mixing is detected alongallthree sections within the 25 29 n band where bottom topography is relatively featureless due to their proximity to the semidiurnal internal tide generation sites the two sections along 137 e have a time mean diffusivity value 2 5 10 5 m2 s 1 in the 300 2 000 m upper ocean in contrast it is 1 2 10 5 m2 s 1along the 165 e section the time varying diffusivity along both sections is dominated by signals whose vertical structure resembles the local first dynamic normal mode profile at the 137 e site of 25 29 n the local spring neap modulated semidiurnal tidal current is found to lead the ctd derived diffusivity time series by 6 days and can alter the diffusivity level by 0 24 10 5 m2 s 1 similarly the concurrent surface wind work is found to modify the diffusivity level by 0 35 10 5 m2 s 1 the combined spring neap tide and wind work forcing explains 47 of the observed time varying diffusivity signals