mixed layer shear generated by wind stress in the central equatorial pacific abstract sixteen months of wind and current profile observations in the central equatorial pacific show the response of the upper ocean shear to local wind forcing the shear at the ocean surface is significantly correlated with the wind stress in direction but not in magnitude implying that the vertical eddy viscosity coefficient is proportional to the square of the wind speed or to the stress using this variable eddy viscosity coefficient in stommel s model of the equatorial undercurrent we calculate shears in the mixed layer that compare well with the observations the flow is downwind on the equator and tends toward and ekman spiral off the equator

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

a comparison of measured and wind derived ekman transport at 11 n in the atlantic ocean abstract a comparison of measured and wind derived ageostrophic transport is presented from a zonal transect spanning the atlantic ocean along 11 n the transport per unit depth shows a striking surface maximum that decays to nearly zero at a depth of approximately 100 m we identify this flow in the upper 100 m as the ekman transport the sustained values of wind stress and the penetration depth of the ekman transport reported here are considerably greater than in previous observations which were made in conditions of light winds the transport of 12 0 5 5 106 m3 s 1 calculated from the difference of geostrophic shear and shear measured by an acoustic doppler current profiler is in good agreement with that estimated from the shipboard winds 8 8 1 9 106 m3 s 1 and from climatology 13 5 0 3 106 m3 s 1 qualitatively the horizontal distribution of the wind driven flow was best predicted by the shipboard winds the cumulative transport increased linearly over the western three fourths of t

direct evidence for an ekman balance in the california current moored acoustic doppler current profiler velocity estimates and buoy wind observations made during a period of moderate southward winds were used to test the ekman balance at a site in the california current as in prior studies the wind driven flow was separated from the total flow by subtraction of a deep reference current the wind driven flow was shown to be in an ekman balance on daily timescales over a period of several months the mean observed transport was to the right of the wind and agreed to within 3 in magnitude and 4 in phase with the predicted ekman transport although the error bar was about 20 the mean velocity profile was a smooth spiral qualitatively similar although flatter than the theoretical ekman spiral prom the observed mean momentum balance profiles of the turbulent stress and eddy viscosity were inferred eddy viscosity estimates within the wind mixed layer were o 100 cm2 s 1

wind driven currents in the tropical pacific abstract an analysis is made of the ensemble mean ageostrophic near surface circulation measured by 1503 lagrangian drifters drogued to 15 m depth in the tropical pacific between 1987 and 1994 it was found that the physical model of the wind driven currents in a weakly stratified upper layer in which the richardson number remains near unity accounts for 40 of the vector variance of the observations in such a model the amplitude of the current is proportional to u n f 1 2 and the depth scale of the wind driven layer is proportional to u n f 1 2 when the ageostrophic currents at 15 m depth are binned by the scaled ekman depth a net rotation of 0 87 radians was observed through the layer depth these measurements suggest that the vertical austausch coefficient of the upper ocean is proportional to u2 n ekman proposed such a model based on two reports of wind driven currents in 1905 at widely separated latitudes

direct observations of the ekman balance at 10 n in the pacific abstract the wind driven transport and velocity structure are estimated from direct current measurements and geostrophic shears along a transpacific section at 10 n the total velocity field is dominated by the north equatorial current and its eddies while the shear features near inertial oscillations and a wind driven current spiral the section averaged cross track ageostrophic shear can be approximated as a slab layer 30 40 m thick with a velocity of 0 05 m s 1 overlying a sheared layer in which the velocity goes to zero below 80 m the resulting zonally integrated ageostrophic mass transport is 62 10 109 kg s 1 northward similar to the estimate of 52 10 109 kg s 1 predicted by the ekman balance using winds measured from the ship climatological winds yield similar transport the zonally averaged velocity relative to the top of the thermocline forms a clockwise spiral decaying with depth as has been found at higher latitudes this mean wind driven spiral results from the diurnal cycling o

high resolution dynamic ocean topography in the southern ocean from goce a mean dynamic ocean topography mdt has been computed using a high resolution goce gravity field and steady state ocean circulation explorer gravity model and a new mean sea surface obtained from a combination of satellite altimetry covering the period 1992 october till 2010 april the considered gravity model is go cons gcf 2 tim r3 which computes geoid using 12 months of goce gravity field data the goce gravity data allow for more detailed and accurate estimates of mdt this is illustrated in the southern ocean where the commission error is reduced from 20 to 5cm compared to the mdt computed using the grace gravity field model itg grace2010 as a result of the more detailed and accurate mdt the calculation of geostrophic velocities from the mdt is now possible with higher accuracy and spatial resolution and the error estimate is about 7 cms 1 for the southern ocean

wind driven motions in the northeast pacific as measured by lagrangian drifters abstract analysis is presented of the time dependent motion of 47 surface drifters in the northeast pacific during fall 1987 and 16 drifters in fall and winter 1989 90 the drifters were designed at 15 m depth and were designed to have wind produced slips less than 2 cm s 1 for wind speeds up to 20 m s 1 the coherence of velocity and local wind is presented for motions with periods between 1 day and 40 days for periods between 5 and 20 days drogue motion at 15 m depth is found to be highly coherent with local wind with an average phase of 70 to the right of the rotating wind vector these results differ from analyses of fgge type drifters as reported by mcnally et al and niiler in the same area a model of wind produced slip as a function of drifter design is used to provide a possible explanation of the differences a linear regression which accounts for 20 40 of the current variance gives water motion al 0 5 of wind speed and 68 to the right of the wind vector assuming an ekman type balance

anomalous surface currents in the tropical indian ocean an anomalous climate event occurred in 1997 in the indian ocean with severe consequences for the surrounding continental areas in response to an intensification of the trade winds a westward gradient of sst and an anomalous reversal of the eastward surface currents with peak velocity anomalies exceeding 1 m s were evident in boreal autumn a similar but weaker event took place in 1994 in this study we examine the observational record during the 1990s including surface drifter velocities sst and altimeter sea level to confirm these dramatic changes we examine the key momentum balance between wind induced momentum flux and the pressure gradient force as well as the important role of horizontal temperature advection in the mixed layer heat response

interannual variability of the surface summertime eastward jet in the south china sea the summertime eastward jet sej located around 12 n 110 e 113 e as the offshore extension of the vietnam coastal current is an important feature of the south china sea scs surface circulation in boreal summer analysis of satellite derived sea level and sea surface wind data during 1992 2012 reveals pronounced interannual variations in its surface strength ssej and latitudinal position ysej in most of these years the jas july august and september mean ssej fluctuates between 0 17 and 0 55 m s 1 while ysej shifts between 10 7 n and 14 3 n these variations of the sej are predominantly contributed from the geostrophic current component that is linked to a meridional dipole pattern of sea level variations this sea level dipole pattern is primarily induced by local wind changes within the scs associated with the el nino southern oscillation enso enhanced weakened southwest monsoon at the developing decaying stage of an el nino event causes a stronger weaker sej located south north of its mean position remote wind forcing from the tropical pacific can also affect the sea level in the scs via energy transmission through the philippine archipelago but its effect on the sej is small the impact of the oceanic internal variability such as eddy current interaction is assessed using an ocean general circulation model ogcm such impact can lead to considerable year to year changes of sea level and the sej equivalent to 20 of the observed variation this implies the complexity and prediction difficulty of the upper ocean circulation in this region

lagrangian study of the panama bight and surrounding regions near surface circulation of the panama bight and surrounding regions 0 9 n 73 w 90 w was studied using satellite tracked drifter trajectories from 1979 2004 this region encompasses three major currents showing typical velocities of 30 cm s 1 1 the eastward north equatorial counter current necc 2 the near circular panama bight cyclonic gyre pbcg and 3 the westward south equatorial current sec we do not observe significant modification of the mean surface circulation during el nino southern oscillation events even if the sec is slightly reinforced during relatively warm el nino periods at seasonal scales the circulation is strongly controlled by the activity of the panama wind jet in boreal winter the currents are stronger and an anticyclonic cell is present west of the pbcg this dipole leads to a strong 200 km wide southward current which then disappears during the rest of the year in summer the three major currents have reduced intensity by 30 40 large scale current vorticity shows that the upwelling associated with the pbcg is also 3 4 times stronger in winter than during summer months the kinetic energy is largely dominated by eddy activity and its intensity is double in winter than during summer ageostrophic motions and eddy activity appear to have a substantial impact on the energy spatial distribution in the necc and sec regions lagrangian scales are anisotropic and zonally enhanced in the direction of the mean currents the typical integral time and length scales of these regions are 2 5 days and 50 60 km in the zonal direction and 1 5 days and 25 30 km in the meridional direction lateral eddy diffusivity coefficients are on the order of 11 14 107 cm2 s 1 zonally and 5 6 107 cm2 s 1 meridionally in contrast in the pbcg region the lagrangian characteristics are isotropic with typical timescales of 1 7 days space scales of 30 km and eddy diffusivity coefficients of 6 107 cm2 s 1 in both directions

global ocean mean wave period data validation and description a global comparison of altimeter and era 40 mean wave period data is performed for the first time altimeter and era 40 mean wave period are shown to compare well in non swell dominated conditions triply collocated altimeter buoy and era 40 data show that the variance of the random errors is bigger for the era 40 data and smaller for the buoy data a new expression is given to relate altimeter data to wave period in wind dominated conditions provided this correction is applied altimeter data are adequate for the most needed validation of global model mean wave period data in non swell dominated conditions triply collocated altimeter buoy and era 40 also reveal that altimeter mean wave period is reliable even in swell conditions for moderate to high winds in contrast to previous suggestions which limited its validity to wind dominated seas

upper ocean inertial currents forced by a strong storm part i data and comparisons with linear theory abstract a strong isolated october storm generated 0 35 0 7 m s 1 inertia frequency currents in the 40 m deep mixed layer of a 300 km 300 km region of the northeast pacific ocean the authors describe the evolution of these currents and the background flow in which they evolve for nearly a month following the storm instruments included ctd profilers 36 surface drifters an array of 7 moorings and air deployed velocity profilers the authors then test whether the theory of linear internal waves propagating in a homogeneous ocean can explain the observed evolution of the inertial frequency currents the subinertial frequency flow is weak with typical currents of 5 cm s 1 and steady over the period of interest the storm generates inertial frequency currents in and somewhat below the mixed layer with a horizontal scale much larger than the rossby radius of deformation reflecting the large scale and rapid translation speed of the storm this scale is too large for significant linear propagation of the

variations of zonal currents in the central tropical pacific during 1970 to 1987 sea level and dynamic height measurements the annual and interannual variations of the major zonal currents of the central tropical pacific for the period 1970 1987 are described by analyzing two data sets sea level data from a few selected island stations and ship of opportunity expendable bathythermograph xbt observations the annual cycles of geostrophic surface current indices dynamic height or sea level difference between the ridge and the trough defining the current in the north equatorial current nec and north equatorial countercurrent necc are found to be in phase maxima in november to be strong and to explain about 50 of the total variance the annual cycle of volume transport relative to 400 dbar in the necc is also strong but nec volume transport has a weak annual cycle the discrepancy between the nec surface current and the transport is due to the variation of the surface current being larger than that of the deep currents the annual cycle of the transport of the south equatorial current sec is 6 months out of phase with that of the nec and necc phases of the annual cycles of the sea level and dynamic height indices of flow agree well in general but there are significant differences between the annual amplitudes of the two types of measurements these differences arise from a variety of sources dynamic height reference level assumptions longitudinal spacing of sea level gauges meridional resolution of sea level array and different signal to noise ratios for the two sets of indices the necc shows marked flow maxima during the peaks of the strong ninos of 1972 and 1982 which were followed by near disappearance of the current the following year these fluctuations are clearly present in both the surface current indices and the volume transport in 1976 and 1986 1987 moderate ninos the same pattern is not marked the el nino signal in nec transport is weak there was a strong rise of equatorial sea level during the early phases of the 1972 and 1982 ninos followed by a fall the next year this resulted in a decrease of the transport of the sec in the first year followed by an increase to a maximum during the second year the maximum coincides with a minimum in necc transport

interannual to decadal changes in the western south atlantic s surface circulation 1 a combination of surface drifters and altimetry is used to analyze the seasonal to interannual variability of the surface velocity field in the brazil malvinas confluence of the western south atlantic ocean longer term changes are inferred from wind and sea surface temperature fields during the period october 1992 to december 2007 a southward shift of 0 6 to 0 9 decade 1 is found in the confluence latitude of the brazil and malvinas currents a comparable trend is found in the latitude of the maximum wind stress curl averaged across the south atlantic basin allowing a proxy for the confluence latitude to be calculated for the prealtimeter time period this longer time series suggests that the recent trend may be part of a longer term oscillation which has returned to values last sustained in the early 1980s this variation does not appear to be related to the multidecadal trend in the southern annular mode but instead is inversely related to long term variations in the sea surface temperature anomaly in the agulhas benguela pathway of the eastern south atlantic subtropical basin

observations of inflow of philippine sea surface water into the south china sea through the luzon strait abstract velocity observations near the surface made with argos satellite tracked drifters between 1989 and 2002 provide evidence of seasonal currents entering the south china sea from the philippine sea through the luzon strait the drifters cross the strait and reach the interior of the south china sea only between october and january with ensemble mean speeds of 0 7 0 4 m s 1 and daily mean westward speeds that can exceed 1 65 m s 1 the majority of the drifters that continued to reside in the south china sea made the entry within a westward current system located at 20 n that crossed the prevailing northward kuroshio path in other seasons the drifters looped across the strait within the kuroshio and exited along the south coast of taiwan during one intrusion event satellite altimeters indicated that directly west of the strait anticyclonic and cyclonic eddies resided respectively north and south of the entering drifter track the surface currents measured by the crossing drifters were much

intense surface currents in the tropical pacific during 1996 1998 tropical pacific ocean near surface currents and their momentum and temperature balances are investigated using several data sets including drifting buoy velocities and topex poseidon altimetry the data sets are combined to produce monthly surface current estimates on a uniform grid for the 6 year period 1993 1998 using multivariate optimal interpolation the analysis shows dramatic changes in current from december 1996 through august 1998 in response to the recent el nino southern oscillation event eastward current anomalies of 1ms 21 were recorded in december 1996 in the western pacific generated by sporadic westerly wind bursts by april 1997 these equatorial anomalies reached the eastern boundary and in the summer of 1997 a band of strong eastward flow formed across the basin this circulation pattern persisted until the beginning of 1998 when a westward equatorial jet appeared in january april interestingly the reversal of flow occurred prior to the restoration of the trade winds the timing of these events as well as the results of previous dynamical studies raise questions about the relative importance of terms in the zonal momentum and temperature balances we address the first of these questions by examining the applicability of a three term linear zonal momentum balance on the equator in all cases we focus on anomalies from the time mean our results show that local acceleration is reasonably well balanced by the difference between zonal pressure gradient anomaly and wind induced momentum flux this three term balance displays significant basin wide variations and is consistent with the conclusion that the equatorial pacific is not in equilibrium with local wind forcing due to the presence of propagating waves examination of the temperature balance shows that at the beginning of el nino the warming in the central pacific is mainly supported by horizontal temperature transport while the vertical heat exchange and transport become important in the eastern half of the equatorial pacific during the transition from el nino to la nina

the ultimate fate of a synmagmatic shear zone interplay between rupturing and ductile flow in a cooling granite pluton abstract the neoarchean cundimurra pluton yilgarn craton western australia was emplaced incrementally along the transpressional cundimurra shear zone during syndeformational cooling discrete networks of cataclasites and ultramylonites developed in the narrowest segment of the shear zone showing the same kinematics as the earlier synmagmatic structures lithological boundaries between aplite pegmatite veins and host granitic gneiss show more intense pre cataclasite fabrics than homogeneous material and these boundaries later became the preferred sites of shear rupture and cataclasite nucleation transient ductile instabilities established along lithological boundaries culminated in shear rupture at relatively high temperature 500 600 c here tensile fractures at high angles from the fault plane formed asymmetrically on one side of the fault indicating development during seismic rupture establishing the oldest documented earthquake on earth tourmaline veins were emplaced during brittle shearing but fluid pressure probably played a minor role in brittle failure as cataclasites are in places tourmaline free subsequent ductile deformation localized in the rheologically weak tourmaline rich aggregates forming ultramylonites that deformed by grain size sensitive creep the shape and width of the pluton shear zone and the regime of strain partitioning induced by melt present deformation and established during pluton emplacement played a key role in controlling the local distribution of brittle and then ductile subsolidus structures

lagrangian observations of inner shelf motions in southern california can surface waves decelerate shoreward moving drifters just outside the surf zone abstractthis study explores eulerian and lagrangian circulation during weak winds at two inner shelf locations off the southern california coast where the shoreline shelf wind and wave characteristics differ from those in previous studies in agreement with recent observational studies wave driven eulerian offshore flow just outside the surf zone referred to as undertow is a substantial component of the net cross shore circulation during periods of weak winds drifter observations show onshore surface flow likely due to light onshore winds and a consistent decrease in onshore velocity of roughly 4 cm s 1 within a few hundred meters of the surf zone undertow is examined as a possible explanation for the observed lagrangian decelerations model results suggest that even when waves are small undertow can decrease the velocity of shoreward moving drifters by 2 cm s 1 roughly half the observed deceleration the coastal boundary condition also has the potential to contribute to the observed deceler

spatiotemporal variation in cross shelf exchange across the inner shelf of monterey bay california abstractcross shelf exchange resulting from wind and wave driven flows across the inner shelf has been the focus of a considerable body of work this contribution extends recent analyses to the central california coastline using 5 yr of moored current observations acoustic doppler current profiler adcp data from stations across the monterey bay two in the northern bay and one in the southern bay in water depths of 20 m showed net offshore transport throughout the year for the northern bay sites cross shelf exchange was dominated by ekman transport driven by along shelf diurnal sea breezes during the upwelling season intense stratification in the northern bay leads to very shallow observed ekman layers 5 8 m and consequently no overlap between bottom and surface ekman layers within a few hundred meters of the coast the total transport is less than predicted by theory consistent with models of shallow water ekman transport the observed transport 42 of full ekman transport is shown to b

wind forced variability of the deep eastern north pacific observations of seafloor pressure and abyssal currents data from an array of bottom pressure gauges and a string of current meters in the vicinity of 47on 139ow are used to examine the deep ocean variability forced by ocean surface wind stress curl from august 1987 to june 1988 bottom geostrophic currents are computed from the pressure gauge array and these correspond well to the long period directly measured currents at 3000 m the supratidalperiod bottom pressure variations are coherent at 95 confidence with the wind stress curl in period bands of 3 4 days and 15 60 days but removed in distances of 400 and 700 km to the northwest and the southeast respectively a linear two layer hydrodynamic model is used to examine the theoretical forcing produced by random phased surface wind fields for the conditions of the eastern north pacific and the 15 to 60 day period observed response is reproduced credibly to model 3 to 15 day variations more realistic models are required currents are related to surface winds were derived from yearlong current meter records in a cluster of moorings north and east of barbados koblinsky and niiler 1982 showed that significant coherences existed between the 4 to 40 dayperiod east west pulsations of the trade winds r x above barbados and the north south currents v at all depths in the ocean at 15on 54ow the response amplitude of v to r x was depth and period dependent it decreased by a factor of 3 from 150 to 4000 m depths and increased by a factor of 5 from 8 to 40 day periods the interpretation of these data was that the deep ocean forcing was produced by large horizontal scale wind stress curl hereinafter referred to simply as curl due to westward propagating pulses in the trade winds with larger east west than north south scale the amplitude of the deep wind related currents was 1 3 cm s thus deep ocean forcing should be observable in many places where the mesoscale eddy energy is low theoretically wind forced deep ocean motions should depend upon wind stress curl mt iller and frankignoul 1981 using a model of randomly forced linear motions in a stratified infinite flat bottom beta plane ocean computed local coherences and showed that motions across the planetary vorticity gradient should exhibit the strongest coherence with the local wind stress curl niiler and koblinsky 1985 using current meter data demonstrated that such a dynamical link does in fact exist locally at 42on 152ow although at a shorter period than was predicted by milller and frankignoul both the amplitude and the phase of the currents that were forced across the planetary potential vorticity field orf h contours on a 150 km horizontal scale were predicted from the local surface wind stress computed from a similar 150 km scale wind field the 4000 m oscilla

ocean surface geostrophic circulation climatology and annual variations inferred from satellite altimetry and goce gravity data we have studied for the first time variations in absolute surface geostrophic currents sgc using satellite data only the proposed approach combines 18 years altimetry data which provide reliable measurements of absolute sea level asl with a gravity field and steady state ocean circulation explorer geoid model to obtain dynamic topography and achieves unprecedented precision and accuracy our proposal overcomes the main limitations of existing approaches based solely on altimetry data which suffer from lack of an independent reference for derivation of asl maps and approximations based on in situ data which are characterized by a sparse and inhomogeneous coverage in time and space features of annual variations of sgc are also addressed as a result of our study we provide new absolute sgc climatology in the form of a 52 week data set of surface current fields gridded at quarter degree longitude and latitude resolution and resolving spatial scales as short as 140 km for presentation this data set is averaged monthly and the results presented as monthly climatology are compared with climatology based on in situ observations from drifter data