the normality of el nino the amplitude of the el nino southern oscillation enso would be normally distributed if the coupled pacific ocean atmosphere were a linear system forced by gaussian weather noise moment estimates of skewness and kurtosis demonstrate that this is not the case for monthly mean anomalies in pacific sea surface temperatures during 1950 97 the noted predominance of el nino events compared to la nina events is related to the high skewness in the eastern pacific skewness and kurtosis both exhibit an intriguing geographical variation from positive in the eastern to negative in the western pacific we have also examined nino 3 indices generated by three climate models having widely different complexity these exhibit a wide range of skewness and kurtosis values rather different from those found for the observations skewness and kurtosis can be used to diagnose non linear processes and provide powerful tools for validating models and for testing observed sea surface temperatures for the presence of possible climate change

wind driven effects on the yellow sea warm current the yellow sea is a shallow basin writh an average depth of 44 m located between china and the korean peninsula one of the dominant ocean circulation features of the yellow sea is a warm wrater intrusion known as the yellow sea warm current this feature is present throughout the year but reaches its farthest northward extension in winter the circulation of the yellow east china and bohai seas was modeled using the princeton ocean model to better understand the dynamics of the yellow sea warm current the horizontal resolution of the model varies from 8 km in the yellow sea to 25 km in the east china sea twenty four sigma levels are used to define the vertical structure the model uses daily atmospheric forcing from the navy operational global atmospheric prediction system for 1993 open boundary conditions are applied at the taiwan strait the tsushima korea strait an area south of taiwan and the tokara strait with a closed boundary south of the ryukyu islands the model results are examined to determine the effect of the wind on the northward extension of the warm water intrusion using both water mass characteristics and northward velocity components sensitivity tests and spectrum analyses performed to study the influence of the wind on the yellow sea warm current show that winds modify the pathway and extent of the yellow sea warm current the current s origin however appears to be due to external forcing from the current systems developed in the east china sea

the effects of channels and shoals on exchange between the chesapeake bay and the adjacent ocean the role of bathymetric changes in determining the transport of water and salt in the lower chesapeake bay lcb was investigated using high resolution acoustic doppler current profiler adcp and conductivity temperature depth profiles a cross channel transect was repeated eight times during neap tides on october 6 7 1993 which illustrated the lateral structure of the longitudinal and transverse flow fields and the intratidal variations in the flow structure across the lcb amplitude and phase of the m2 tidal component as well as the mean flow velocity were calculated using least squares fitting at every point of a uniform grid obtained from the adcp data the results differ from the classical two layer pattern of estuarine circulation modified by coriolis effects but are consistent with recent hydrographic observations semidiurnal flow was highest over the navigational channels and lateral gradients were strongest in regions of sharp bathymetric changes the phase lag of the semidiurnal flow also showed lateral and vertical gradients that represented advances at the bottom with respect to the surface and over the shoals in relation to the channels the section of the water column measured indicated a mean outflow of 0 7 104 m3 s and a mean inflow of 1 3 104 m3 s the apparent gain of water by the estuary during the period of observation can be explained by meteorologically forced net barotropic inflow the depth averaged mean longitudinal flow consisted of inflow in the navigational channels and outflow over the shoals the mean transverse flow showed near surface convergence over the channels we propose a possible explanation for the observed flow and density structure as follows the barotropic and baroclinic forcing interact with the bathymetry to extend the inflow from the bottom to the surface thereby inducing a transverse circulation that yields near surface convergence over the channels

shield like lithosphere of the lower indus basin evaluated from observations of surface wave dispersion abstract the lithospheric velocity structure of the lower indus basin has been evaluated through inversion of fundamental modes of both love and rayleigh wave group velocities from the broadband records of a seismic network maintained by the institute of seismological research gujarat india we have considered three clusters of wave paths a b and c that mainly cross the lower indus basin from south to north the wave paths of a mainly cross the continental shelf and the wave paths of b and c pass through the lower indus basin the measured group velocities correspond to periods of 5 to 90 s for rayleigh waves and 5 to 115 s for love waves these data sets resolve the structure of the lithosphere through a nonlinear inversion based on a genetic algorithm with a wide solution space the mean and standard deviation s d of the 70 accepted solutions for each of these three clusters provide the 2d structure for the lower indus basin from south to north the sediment consists of two layers with total thickness from 5 7 to 6 6 km increasing northward the crustal thickness also increases northward from 32 9 cluster a to 39 7 km cluster c in the lower indus region the s wave velocity below the crust varies from 4 55 to 4 59 km s which is close to the corresponding velocity of 4 60 km s of the indian shield region to the east of the aravalli range the thicknesses of the lithosphere as well as the velocities of the uppermost mantle of the lower indus plain are similar to that of the indian shield

extraction of tidal streams from a ship borne acoustic doppler current profiler using a statistical dynamical model we present a method for extracting the barotropic tide directly from the time space series of horizontal velocity obtained by a ship borne acoustic doppler current profiler adcp the method is conceptually straightforward easy to implement and suitable for operational use it involves fitting a limited area tidal model based on the linearized depth averaged shallow water equations to the adcp record the flows across the open boundaries of the model domain are assumed periodic in time with known frequencies corresponding to the tidal constituents of interest the unknown tidal amplitudes and phases at the boundary are estimated from interior adcp velocities using an inverse method the solution of the shallow water equations is posed as a boundary value problem in the frequency domain and the estimation procedure is based on generalized least squares regression results obtained include tidal maps a tidal residual series and associated error estimates an application of the method to ship adcp data collected on a cruise to the western bank region of the scotian shelf off the east coast of canada is described the tidal estimates and the residual field obtained are verified by comparison to other data collected during the cruise the residual circulation shows an anticyclonic gyre centered on the crest of western bank and a northward current to the west of this region

an advective reflective conceptual model for the oscillatory nature of the enso recent findings about zonal displacements of the pacific warm pool required a notable modification of the delayed action oscillator theory the current leading theory for the el nino southern oscillation enso simulations with a linearized coupled ocean atmosphere model resulted in 3 to 6 year enso like oscillations with many of the variable model parameters found to be very close to their observed values this simple model suggests that ocean processes that are ignored or underestimated in the delayed action oscillator theory such as zonal current convergence zonal advection of sea surface temperature and equatorial wave reflection from the eastern ocean boundary are fundamental to the development of the enso in particular to its manifestations in the central equatorial pacific

high resolution observations of the intensity of secondary circulation along a curved tidal channel 1 high horizontal resolution moving vessel acoustic doppler current profiler adcp observations of the spatial pattern of cross stream velocities in a curved tidal channel show radially outward surface velocities up to 10 cm s 1 which are maximum midchannel consistent with helical secondary flow in a vertical plane normal to the depth averaged velocity the 30 m cross and 150 m along channel resolution observations are from a 2700 m long section of a 350 m wide horizontally and vertically well mixed tidal channel with a radius of curvature 1 5 km the along channel resolution allows the intensity of the curvature induced secondary flow to be estimated from the linear correlation between the observed cross channel component of vertical shear and the shear estimated from the streamwise velocity and its varying curvature using an existing analytic model the two shears are highly correlated and the regression line slope demonstrates that the observed curvature induced secondary flow is 30 more intense than that predicted by the model for a typical bottom drag coefficient the secondary flow is 50 more intense than that predicted using the drag coefficient which best fits the streamwise velocity profile numerical solutions demonstrate that the intensity of the secondary flow is sensitive to small changes in the shape of the eddy viscosity profile hence intensity may be sensitive to the way turbulence is modeled lagged correlation of the observations showed that the secondary flow adapts to changes in curvature and primary flow over a 300 m length scale or 20 water depths consistent with the existing model and laboratory studies

separation of tidal and subtidal currents in ship mounted acoustic doppler current profiler observations a simple method is developed to analyze current measurements obtained from a moving platform the need for this is motivated by the now common use of the ship mounted acoustic doppler current profiler adcp to acquire absolute velocity data during an oceanographic survey of a given region the full potential of this new measurement technique is severely hindered when the presence of high frequency phenomena e g tidal or inertial motions prevents a clear visualization of the lower frequency current structure of interest our analysis method is based on a spatial interpolation scheme using arbitrary functions that allows for the tidal current time variability which then permits the tide induced motions to be subtracted from the adcp data to yield the subtidal current field the method also allows nearby moored and drifter current measurements if available to be combined with the shipboard adcp observations in a single analysis to obtain the best description of the tidal and subtidal currents to illustrate this method we present results from the analysis of adcp data taken during oceanographic surveys in two different continental shelf regions the east china sea and the amazon shelf a 5 day conductivity temperature depth ctd and adcp survey was made in the east china sea near the mouth of the yellow sea during january 1986 there the currents were essentially barotropic and dominated by the semidiurnal tide the adcp derived cotidal chart for the m2 12 42 hours component agrees well with existing charts derived empirically from sea level observations or from regional numerical models the adcp derived steady flow is also consistent with the observed density field and indicates little flow in or out of the yellow sea and a transport of about 1 sv toward the tsushima strait two ctd adcp surveys lasting 21 and 23 days were conducted over the amazon shelf during march and may 1990 simultaneously moored current observations were also obtained at three locations along a cross shelf array 200 km north of the amazon river mouth for a common period of at least 2 months february 12 to april 13 over the shelf tidal and subtidal currents were comparable in magnitude our analysis indicates that the tidal currents were essentially barotropic semidiurnal and polarized in the cross shelf direction increasing in magnitude toward the inner shelf where current values of more than 2 m s are common the adcp derived steady currents were aligned in the along shelf direction and strongly influenced by the north brazil current nbc during both adcp surveys the northwestward flowing nbc was transporting more than 2 sv over the shelf at depths shallower than 100 m

direct velocity observations of volume flux between iceland and the shetland islands atlantic waters flowing northward into the nordic seas are important for their role as an early indicator of changes to deepwater formation as such this requires a fundamental understanding of the pathways and volume fluxes through the primary passageways from the atlantic into the nordic seas a mean annual volume transport of 6 1 0 3 sv was observed flowing in above the t 27 8 isopycnal a proxy for the lower limit of atlantic water depth through the faroe shetland channel fsc and over the iceland faroes ridge ifr from march 2008 to june 2012 using repeat velocity sections obtained from a vessel mounted acoustic doppler current profiler adcp a new vessel route has expanded the spatial coverage of fsc observations and reveals a difference in average inflow transport which most likely results from an interannual variation in the total transport through the fsc which in turn is tied to a weakening of the southerly flow over the western slope of the channel this interannual variability has increased the mean transport through the fsc from 0 9 sv observed over the first 2 years of this program by rossby and flagg 2012 to a 4 5 year mean of 1 7 0 2 sv which emphasizes the importance of knowing the flow along the faroese shelf interannual fluctuations in transport observed over the ifr are related to the width of the inflow over the faroese half of the ridge

change of el nino and la nina amplitude asymmetry around 1980 amplitude of el nino and la nina was significantly different during 1980 2016 but almost same during 1958 1979 the cause of this interdecadal change is investigated through an oceanic mixed layer heat budget analysis it was found that this interdecadal change was primarily attributed to the distinctive effects of nonlinear zonal temperature advection between the two periods during 1980 2016 nonlinear zonal advection working together with nonlinear meridional advection contributes to the el nino and la nina amplitude asymmetry during 1958 1979 the nonlinear zonal advection had an opposite effect the difference in the nonlinear zonal advection between the two interdecadal periods was caused by distinctive longitudinal locations of el nino centers maximum sst anomaly ssta centers were confined near the coast of south america east of 90 w during the first period but appear near 110 w during the second period because of this difference an anomalous eastward ocean surface current caused by a positive thermocline depth anomaly during el nino would generate a negative positive nonlinear zonal advection before after 1980 the distinctive longitudinal locations of el nino centers are possibly caused by the interdecadal changes of mean thermocline and high frequency wind variability over the equatorial western central pacific a hypothesis was put forth to understand distinctive initiation locations between el nino and la nina

observation of internal tidal currents in the kaoping canyon off southwestern taiwan abstract internal tidal currents and associated water mass displacements were investigated during multiple cruises in the kaoping submarine canyon off southwestern taiwan observations from both moored and shipboard acoustic doppler current profilers and hydrographic casts were conducted along the canyon the velocity data showed that in the lower layer the major axis of the tidal currents aligned with the orientation of the canyon and currents moved up canyon during flood and down canyon during ebb the vertical phase shift and amplitude of the currents indicated that the semidiurnal internal tide dominated with intensity increasing with depth toward the canyon head tidal energy was channeled from the shelf landward with a beamlike internal wave guided by bottom topography the estimated phase velocity was 1 4 1 7 m s 1 based on normal mode analysis and the phase lag between sampling stations empirical orthogonal function analysis of hydrographic profiles confirmed that the first mode m 2 internal tide explained 70 of the total variance the strong convergence of internal tidal currents near the canyon head during flood may play an important role in the daily migration of cherry shrimps which burrow along the canyon wall

a direct estimate of poleward volume heat and freshwater fluxes at 59 5 n between greenland and scotland the meridional overturning circulation moc in the north atlantic plays a major role in the transport of heat from low to high latitudes in this study we combine recent measurements of currents from the surface to 700 m from a shipboard acoustic doppler current profiler with argo profiles to 2000 m to estimate poleward volume heat and freshwater flux at 59 5 n between greenland and scotland this is made possible thanks to the vessel nuka arctica that operates on a 3 week schedule between greenland and denmark for the period late 2012 to early 2016 the de seasoned mean meridional overturning circulation reaches a 18 4 3 4 sv maximum at the 27 55 kg m 3 isopycnal which varies in depth from near the surface in the western irminger sea to 1000 m in rockall trough the total heat and fresh water fluxes across 59 5 n 399 74 tw and 0 20 0 04 sv where the uncertainties are principally due to that of the moc analysis of altimetric sea surface height variations along exactly the same route reveals a somewhat stronger geostrophic flow north during this period compared to the 23 year mean suggesting that for a long term mean the above flux estimates should be reduced slightly to 17 4 sv 377 tw and 0 19 sv respectively with the same estimate uncertainties the adcp program is ongoing

a western pacific oscillator paradigm for the el nino southern oscillation a data based hypothesis is presented on the mechanism of the el nino southern oscillation enso a major determinant of interannual global climate variability the hypothesis emphasizes the importance of off equator sea surface temperature and sea level pressure variations west of the dateline for initiating equatorial easterly winds over the far western pacific these winds compete with westerly winds over the equatorial central pacific enabling the coupled ocean atmosphere system to oscillate consistent with this hypothesis an analogical oscillator model is constructed that produces enso like oscillations the proposed mechanism differs from the delayed oscillator paradigm in that wave reflection at the western boundary is not a necessary condition for the coupled ocean atmosphere system to oscillate

morphology and sedimentation of sand bodies in the tidal shelf sea of eastern taiwan strait abstract changyun ridge located in the central eastern part of the taiwan strait consists of sand bodies the eastern changyun sand ridge 65 km long and 13 km wide a sand shoal 53 km long and 22 km wide and a sand sheet 60 km long 40 km wide and 22 m in height the eastern changyun sand ridge and the sand sheet are oriented parallel to the coastline but the sand shoal is perpendicular to the coast the eastern changyun sand ridge is oriented oblique to the narrow reciprocal tidal ellipses the sand shoal and sand sheet are normal and oblique to the broad rotary tidal ellipses respectively surface sediments of the changyun ridge are composed of very fine to coarse sands in a progressive seaward decrease in grain size the configuration and spatial distribution of these three sand bodies with corresponding decrease in tidal speed and in grain size together suggest that the sand bodies developed sequentially from the near shore to the offshore area presumably in response to westward shifting of the north flowing tidal currents sand waves occur widespreadly on the sand shoal and seldom appear on the eastern changyun sand ridge occurrences of sand waves suggest that the sand shoal is considered to be active and the sand ridge to be moribund chirp sonar profiles reveal the internal structures of the sand shoal showing a relatively flat basal reflector underlying the sand body the thickness of the sand accumulation is about 22 25 m and it is firstly determined by the depth difference between the modern sea bed and the basal reflector to better describe morphology and document dimensions of these sand bodies the presence of several short inclined reflectors dipping northeast and down lapping the basal flat reflector indicate that sands are most likely transported from south to north for the sand shoal the sand bodies of the changyun ridge rest upon a relative flat basal reflector suggesting a mainly hydrodynamically controlled origin the variations of the hydrodynamic conditions mainly tidal currents on the central eastern taiwan strait shelf seem to be the primary control on sedimentary facies shift morphological changes and sand ridge growth for the changyun ridge the changyun ridge is ongoing to receive sands from the south in a transitional development stage as long as the sand supply continues and over a longer time period the sand bodies eventually will develop into three individual linear sand ridges separated by swales oriented parallel to the peak currents

on the spatial structure and temporal variability of poleward transport between scotland and greenland 1 the flow north of warm subtropical water though the northeastern atlantic is known to have many pathways that vary over time here we use a combination of upper ocean current measurements betwe

direct measurement of volume flux in the faroe shetland channel and over the iceland faroe ridge 1 determining the exchange of water across the iceland faroe scotland ridge is of fundamental interest because it measures the rate of transformation of north atlantic water into dense water and thus the strength of the meridional overturning circulation moc here we study this exchange by monitoring all water flowing through the area east of iceland to near the bottom or 600 m depth using a 75 khz acoustic doppler current profiler adcp mounted on the high seas ferry m f norrona starting in march 2008 currents have been measured in the faroe shetland channel fsc and along the iceland faroe ridge ifr on the ferry s weekly round trips between iceland and denmark the detided average transports to the north across the two sections are 4 1 0 1 sv 106 m2s 1 through the fsc and 4 4 0 25 sv across the ifr this excludes 1 6 sv circulating around the faroes the norrona program is ongoing

sedimentation dynamics in the east china sea elucidated from and sedimentation dynamics in the east china sea was investigated based on profiles and inventories of 210 pb 137 cs and ex 239 240 pu in sediment cores collected from various settings in this marginal sea the derived sedimentation rates vary by two orders of magnitude from 2 to 0 02 cm yr y1 and generally decrease southward along the inner shelf and eastward offshore this pattern is consistent with the dispersal of yangtze river derived sediments by the current and tidal systems y2 y1 the weighted mean sedimentation rate over the shelf ca 0 3 g cm yr appears to be higher than fluvial inputs from the y2 y1 yangtze river and taiwan 0 14 g cm yr the discrepancy can be reduced by considering the effect of sediment mixing which renders sedimentation rates overestimated and the possibility of additional sediment input from the yellow river s dispersal system spatial variations of the observed nuclide inventories in sediments suggest extensive sediment redistribution boundary scavenging of 210 pb and large inputs of 137 cs and 239 240 pu from yangtze river s drainage basin

a comparison of techniques for tide removal from ship mounted acoustic doppler measurements along the southwest coast of vancouver island two approaches are examined for the removal of tidal currents from acoustic doppler current profiler henceforth adcp measurements the first uses predictions from a numerical model foreman and walters 1990 whose domain includes the measurement region although the numerical model is barotropic adjustments are made to correct for baroclinicity in accordance with historical observations from stationary current meters in the region the second approach originally proposed by candela et al 1990 performs a least squares polynomial or biharmonic spline fit to the adcp data in order to determine the spatially varying amplitudes and phases of major tidal constituents and the magnitude of the residual flow both tide removal techniques are applied to adcp data taken during a 3 day cruise off the southwest coast of vancouver island and their relative effectiveness is compared some of the detided currents are seen to compare well with geopotential surfaces and clearly show the juan de fuca eddy freeland and denman 1982 a discussion of the results and limitations of each technique is also presented

analysis of flow at the gate of taiwan strait 1 a field survey with ship borne acoustic doppler current profiler was carried out across the penghu channel the gate of taiwan strait from 17 to 20 of may 1999 a new method of least squares interpolation is used to separate the mean flow from tidal currents the technique uses gaussian interpolation functions with local support which also take into consideration the anisotropic nature of the flow structure optimal solution is obtained by determining the tradeoff between the misfit and the model order the analysis indicates that the currents in the penghu channel are essentially barotropic and characterized by strong semidiurnal tides and mean flow the along channel averaged tidal velocity amplitudes are 1 2 m s 1 and 0 32 m s 1 for semidiurnal and diurnal tides respectively the mean current is uniform with an average northward velocity of 0 73 m s 1 the total transport is about 1 6 sv which represents a significant mass and material flux into the east china sea