west florida continental shelf response to upwelling favorable wind forcing 2 dynamics dynamics analyses are presented for the west florida continental shelf response to upwelling favorable alongshore or offshore winds using a three dimensional time dependent primitive equation model these analyses complement the kinematics analyses of li and weisberg 1999 results are provided on four topics 1 the response evolutions to quasi steady states 2 the across shelf distributions of the vertically integrated alongshore and across shelf momentum balances 3 the three dimensional structures of the terms composing the momentum balance closures and 4 the model sensitivity to vertical friction parameterization the response evolution starts with a local wind driven acceleration and it transitions over the inner shelf into a primary balance between the pressure gradient coriolis and vertical friction terms thus the inner shelf spin up takes a classical ekman geostrophic route the middle shelf takes longer because it also depends on coastal boundary effects notably the partial closure of the domain in the south by the florida keys the outer shelf never achieves a steady state because of topographic wave effects coastline and isobath geometries result in fully three dimensional flow fields thus a two dimensional model that ignores alongshore variations cannot account for the results obtained the inner shelf is the transition region between ekman and ekman geostrophic balances where the surface slope results from mass adjustments through overlapping surface and bottom ekman layers across the inner shelf the vertically integrated momentum balance shows a gradual trade off between the coriolis pressure gradient and bottom friction terms and with the inner shelf frictionally determined its scale is sensitive to vertical friction parameterization

the role of ocean dynamics in the optimal growth of tropical sst anomalies the role of ocean dynamics in optimally exciting interannual variability of tropical sea surface temperature sst anomalies is investigated using an idealized geometry ocean general circulation model initial temperature and salinity perturbations leading to an optimal growth of tropical sst anomalies typically arising from the nonnormal dynamics are evaluated the structure of the optimal perturbations is characterized by relatively strong deep salinity anomalies near the western boundary generating a transient amplification of equatorial sst anomalies in less than four years theassociatedgrowthmechanismislinkedtotheexcitationofcoastalandequatorialkelvinwavesnearthe westernboundaryfollowingarapidgeostrophicadjustmentowingtotheoptimalinitialtemperatureandsalinity perturbations the results suggest that the nonnormality of the ocean dynamics may efficiently create large tropical sst variability on interannual time scales in the atlantic without the participation of air sea processes or the meridional overturning circulation an optimal deep initial salinity perturbation of 0 1 ppt located near the western boundary can result in a tropical sst anomaly of approximately 0 458c after nearly four years assuming the dynamics are linear possible mechanisms for exciting such deep perturbations are discussed while this study is motivated by tropical atlantic sst variability its relevance to other basins is not excluded the optimal initial conditions leading to the tropical sst anomalies growth are obtained by solving a generalized eigenvalue problem the evaluation of the optimals is achieved by using the massachusetts institute of technology general circulation model mitgcm tangent linear and adjoint models as well the the arnoldi package arpack software for solving large scale eigenvalue problems

break up of the atlantic deep western boundary current into eddies at 8 s the existence in the ocean of deep western boundary currents which connect the high latitude regions where deep water is formed with upwelling regions as part of the global ocean circulation was postulated more than 40 years ago1 these ocean currents have been found adjacent to the continental slopes of all ocean basins and have core depths between 1 500 and 4 000 m in the atlantic ocean the deep western boundary current is estimated to carry 10 40 times 106 m3 s 1 of water2 3 4 5 transporting north atlantic deep water from the overflow regions between greenland and scotland and from the labrador sea into the south atlantic and the antarctic circumpolar current here we present direct velocity and water mass observations obtained in the period 2000 to 2003 as well as results from a numerical ocean circulation model showing that the atlantic deep western boundary current breaks up at 8 s southward of this latitude the transport of north atlantic deep water into the south atlantic ocean is accomplished by migrating eddies rather than by a continuous flow our model simulation indicates that the deep western boundary current breaks up into eddies at the present intensity of meridional overturning circulation for weaker overturning continuation as a stable laminar boundary flow seems possible

the frictional nearshore response to forcing by synoptic scale winds abstract an analytic barotropic model was used to study the nearshore frictional response to synoptic scale wind forcing the results depend only on the region where the surface and bottom ekman layers interact strongly and the water is consequently well mixed thus the conclusions apply even to shelves where baroclinic effects are not negligible father offshore the main findings are as follows i the blocking of the surface ekman flux which drives the shelf flow is a consequence of the interaction of ekwan layers in the nearshore region the interaction transfers progressively more of the surface stress directly to bottom stress as the depth decreases the consequent decrease in ekman flux toward the shore creates an ekman flux divergence which drives the interior flow ii the region over which the shelf is effectively forced is narrow it extends approximately from where the depth divided by the ekman layer e folding scale is 0 2 to where it is 2 5 iii simple equations for pressure and the

adjustment of the ocean under buoyancy forces part i the role of kelvin waves abstract the early stages of the adjustment of an ocean toward equilibrium is examined using an ocean general circulation model the initial state is one with uniform meridional potential temperature gradients yielding density gradients representative of those observed in the north atlantic the main adjustment in the time examined here the first few months is by coastal kelvin waves the first baroclinic mode dominates so the behavior proves to be very similar to that in a shallow water model also the dynamics is locally close to that for an f plane but account must be taken of the way f varies with latitude the essential result of the coastal adjustment is to reduce the temperature gradients around the perimeter of the basin especially at the level where the first mode has the maximum effect this study also examines the way this adjustment process is distorted in models due to the constraints imposed by computer limitations namely in a model with too coarse a horizontal resolution and an artif

a model of the thermal bar circulation in a long basin a thermal bar is defined here as a zone of descending water at or near the fresh water temperature of maximum density in the present study we model physical properties such as velocity temperature turbulent fluxes time of onset and migration speed of the thermal bar in an idealized basin unlike models using prescribed eddy viscosity and diffusivity coefficients our model uses a second order turbulence closure scheme to model mixing due to turbulence the only inputs in the calculation are the surface wind the surface heat flux and the initial state of the fluid numerical simulations of the resulting circulation are presented for flow in a long rotating basin under prescribed surface heat and wind conditions the results show the influence of the relative magnitudes of mechanical and thermal forcing on the circulation a comparison with field observations shows reasonable agreement between computed and measured bar migration speeds the time necessary for the formation of the bar is computed and is found to depend on the surface forcing

a study of the thermal bar in lake ladoga using water surface temperature data from satellite images during spring and autumn a special thermohydrodynamic phenomenon called a thermal bar can be observed in dimictic lakes a dimictic lake is a lake where a complete turnover of the water occurs twice a year in spring and autumn the thermal bar is a zone of mixing that separates waters with temperatures above and below 4 c its practical importance is due to the possibility that it might isolate the nearshore region from the offshore region as seen from the thermal bar which may cause a serious pollution problem along the beach this article presents a study of the thermal bar and its temporal behavior in lake ladoga russia using noaa avhrr ch4 ch5 data as the thermal bar is associated with a rather characteristic temperature pattern that is relatively large temperature changes from the shore to the bar and weak gradients beyond implying almost isothermal conditions satellite data can provide a good means of detecting the existence of a thermal bar the satellite derived water surface temperature distributions calibrated with some in situ temperature data show that the thermal bar progresses from the shallow southern region to the deep northern part of the lake the thermal bar progression during spring obtained from sequences of satellite images is also compared with predictions from a simple theoretical model the model assumes that the heat entering through the surface of a water column remains within the column i e horizontal heat fluxes are neglected and that complete vertical mixing takes place by convective water movements the comparison shows a good agreement between satellite derived and model predicted thermal bar locations although there are uncertainties as to certain inputs to the model this indicates that advective and diffusive horizontal heat fluxes are not of primary importance for the thermal bar displacement and that the model is a good first approximation for predictions of the thermal bar location

an upwelling case study on florida s west coast using a combination of satellite sea surface temperature imagery in situ currents temperature and sea level data and a numerical circulation model we describe an upwelling event observed along florida s west coast although ubiquitous features of continental shelves descriptions of coastal upwellings or downwellings are generally complicated by the continuum of processes in which they occur for the case study presented the winds were light and the baroclinic background currents were steady for several days prior to the event these conditions allow the evolution of a specific winddriven upwelling event to be viewed as an initial value problem the data and the numerical model analysis show that the route of adjustment by the sea level and currents is a classical ekman geostrophic one sea level drops due to an offshore ekman transport causing a geostrophic alongshore jet and the associated onshore flow within the bottom ekman layer accounts for the appearance of cold water at the surface this surface manifestation occurs as an elongated feature centered about the 25 m isobath that spans roughly half of the florida peninsula from just north of tampa bay to key west the coldest water is observed offshore from tampa bay and we explain this region of locally maximum upwelling on the basis of the coastline and isobath geometries

west florida shelf response to upwelling favorable wind forcing kinematics the barotropic responses of the west florida continental shelf to idealized upwelling favorable alongshore and offshore wind stresses are studied using the three dimensional time dependent primitive equation princeton ocean model pom when forced with uniform winds the shelf circulation evolves quickly to a quasi steady state a southeastward alongshore wind lowers sea level along the coast and drives a southeastward coastal jet with a relatively weak northwestward return flow farther offshore a southwestward offshore wind lowers sea level along the west florida coast and raises sea level along the panhandle coast two independent circulation gyres are set up in association with these regionally different sea level distributions an anticyclonic gyre off the west florida coast consisting of a southeastward coastal jet and a broad return flow over the middle shelf and a cyclonic gyre off the panhandle coast consisting of a strong northwestward coastal jet and an adjacent narrow southeastward undercurrent these gyres are separated by the big bend region in both cases alongshore and offshore wind forcing the circulations are fully three dimensional with opposing surface and bottom boundary layer flows accounting for the across shelf transports the shapes of the coastline and the isobaths are important determinants of the shelf wide responses several locally maximum upwelling regions are identified for geometrical reasons these include the panhandle coast south of apalachicola bay the west florida coast south of tampa bay along the florida keys and at the shelf break where topographic rossby waves are evident

optimal excitation of interannual atlantic meridional overturning circulation variability the optimal excitation of atlantic meridional overturning circulation moc anomalies is investigated in an ocean general circulation model with an idealized configuration the optimal three dimensional spatial structure of temperature and salinity perturbations defined as the leading singular vector and generating the maximum amplification of moc anomalies is evaluated by solving a generalized eigenvalue problem using tangent linear and adjoint models despite the stable linearized dynamics a large amplification of moc anomalies mostly due to the interference of nonnormal modes is initiated by the optimal perturbations the largest amplification of moc anomalies found to be excited by high latitude deep density perturbations in the northern part of the basin is achieved after about 7 5 years the anomalies grow as a result of a conversion of mean available potential energy into potential and kinetic energy of the perturbations reminiscent of baroclinic instability the time scale of growth of moc anomalies can be understood by examining the time evolution of deep zonal density gradients which are related to the moc via the thermal wind relation the velocity of propagation of the density anomalies found to depend on the horizontal component of the mean flow velocity and the mean density gradient determines the growth time scale of the moc anomalies and therefore provides an upper bound on the moc predictability time the results suggest that the nonnormal linearized ocean dynamics can give rise to enhanced moc variability if for instance overflows eddies and or deep convection can excite high latitude density anomalies in the ocean interior with a structure resembling that of the optimal perturbations found in this study the findings also indicate that errors in ocean initial conditions or in model parameterizations or processes particularly at depth may significantly reduce the atlantic moc predictability time to less than a decade

the response of stratified frictional flow of shelf and slope waters to fluctuating large scale low frequency wind forcing abstract numerical and analytical models are developed to discuss large scale low frequency wind driven fluctuations over the continental shelf and slope in the presence of realistic density stratification and bottom friction the models employ the long wave assumption that frequencies are small relative to the inertial frequency and that alongshore scales are large relative to cross cross shelf scales an attempt is made to make the effect of bottom friction on the flow as realistic as possible by taking into account the influence of surface gravity waves on bottom stress the results were obtained for sinusoidal wind forcing having frequency and alongshore wavenumber l and are described below a general criterion for barotropic shelf water response for wind forcing frequencies in the weather band 2 few weeks to 2 few days can be derived for the purpose of rapid calculation this criterion reduces approximately tohere ns2 is a shelf averaged value of the buoyancy frequency squared is

anisotropic response of surface currents to the wind in a coastal region analysis of coastal surface currents measured off the coast of san diego for two years suggests an anisotropic and asymmetric response to the wind probably as a result of bottom coastline boundary effects including pressure gradients in a linear regression the statistically estimated anisotropic response explains approximately 20 more surface current variance than an isotropic wind ocean response model after steady wind forcing for three days the isotropic surface current response veers 42 86 28 to the right of the wind regardless of wind direction whereas the anisotropic analysis suggests that the upcoast onshore wind stress generates surface currents with 10 86 48 71 86 38 to the right of the wind direction the anisotropic response thus reflects the dominance of alongshore currents in this coastal region both analyses yield winddriven currents with 3 5 of the wind speed as expected in addition nonlinear isotropic and anisotropic response functions are considered and the asymmetric current responses to the wind are examined these results provide a comprehensive statistical model of the wind driven currents in the coastal region which has not been well identified in previous field studies but is qualitatively consistent with descriptions of the current response in coastal ocean models

dynamics of wind driven upwelling off the northeastern coast of hainan island both observational and reanalysis sea surface temperature data reveal that upwelling occurs frequently off the northeastern coast of hainan island downstream of the change in topography off tongluo cape which cannot be attributed to the along shelf wind alone to identify dynamics of the upwelling we conduct a numerical experiment using an idealized topography that is simplified from the actual topography off the eastern and northeastern coasts of hainan island the result indicates that the upwelling downstream of the change in topography is associated with onshore cross isobath transport analysis of the vertically integrated momentum balance shows that the upwelling linked onshore transport is primarily intensified by the along isobath barotropic pressure gradient force pgt but is weakened by the along isobath baroclinic pressure gradient force pgc the along isobath pgt is linked to the advection of relative vorticity the bottom stress curl and the gradient of momentum flux in vorticity equation on the other hand the pgc related process is diagnosed by potential vorticity pv balance similar to the negative pv term from wind stress the negative pv terms of the joint effect of baroclinicity and relief and the baroclinic bottom pressure torque weaken the upwelling linked onshore transport downstream of the change in topography the onshore transport is enhanced by the positive pv from bottom stress in addition the cross isobath forces play an important role in upwelling intensification in the shallow nearshore region

prediction of tropical atlantic sea surface temperatures using linear inverse modeling the predictability of tropical atlantic sea surface temperature on seasonal to interannual timescales by linear inverse modeling is quantified the authors find that predictability of caribbean sea and north tropical atlantic sea surface temperature anomalies sstas is enhanced when one uses global tropical sstas as predictors compared with using only tropical atlantic predictors this predictability advantage does not carry over into the equatorial and south tropical atlantic indeed persistence is a competitive predictor in those regions to help resolve the issue of whether or not the dipole structure found by applying empirical orthogonal function analysis to tropical atlantic ssts is an artifact of the technique or a physically real structure the authors combine empirically derived normal modes and their adjoints to form influence functions maps highlighting the geographical areas to which the north tropical atlantic and the south tropical atlantic ssts are most sensitive at specified lead times when the analysis is confined to the atlantic basin the 6 month influence functions in the north and south tropical atlantic tend to be of the opposite sign and evolve into clear dipoles within 6 months when the analysis is performed on global tropical ssts the 6 month influence functions are connected

upper ocean singular vectors of the north atlantic climate with implications for linear predictability and variability the limits of predictability of the meridional overturning circulation moc and upper ocean temperatures due to errors in ocean initial conditions and model parametrizations are investigated in an idealized configuration of an ocean general circulation model gcm singular vectors optimal perturbations are calculated using the gcm its tangent linear and adjoint models to determine an upper bound on the predictability of north atlantic climate the maximum growth time scales of moc and upper ocean temperature anomalies excited by the singular vectors are 18 5 and 13 years respectively and in part explained by the westward propagation of upper ocean anomalies against the mean flow as a result of the linear interference of non orthogonal eigenmodes of the non normal dynamics the ocean dynamics are found to actively participate in the significant growth of the anomalies an initial density perturbation of merely 0 02 kg m 3 is found to lead to a 1 7 sv moc anomaly after 18 5 years in addition northern hemisphere upper ocean temperature perturbations can be amplified by a factor of 2 after 13 years the growth of upper ocean temperature and moc anomalies is slower and weaker when excited by the upper ocean singular vectors than when the deep ocean is perturbed this leads to the conclusion that predictability experiments perturbing only the atmospheric initial state may overestimate the predictability time interestingly optimal moc and upper ocean temperature excitations are only weakly correlated thus limiting the utility of sst observations to infer moc variability the excitation of anomalies in this model might have a crucial impact on the variability and predictability of atlantic climate the limit of predictability of the moc is found to be different from that of the upper ocean heat content emphasizing that errors in ocean initial conditions will affect various measures differently and such uncertainties should be carefully considered in decadal prediction experiments copyright c

momentum balances on the north carolina inner shelf four months of moored current pressure temperature conductivity wave and wind observations on the north carolina shelf indicate three dynamically distinct regions the surf zone the inner shelf between the surf zone and the 13 m isobath and the midshelf in the surf zone the along shelf momentum balance is between the cross shelf gradient of the wave radiation stress and the bottom stress the linear drag coefficient in the surf zone is about 10 times larger than seaward of the surf zone on the inner shelf the along shelf momentum balance is also frictional the along shelf wind stress and pressure gradient are balanced by bottom stress in the cross shelf momentum balance the pressure gradient is the superposition of roughly equal contributions from the coriolis force geostrophy and wave setdown from shoaling unbroken surface gravity waves at midshelf the along shelf momentum balance is less frictional and hence flow accelerations are important the cross shelf momentum balance is predominantly geostrophic because the greater depth and smaller bottom slope at midshelf reduce the importance of wave setdown the cross shelf density gradient is in thermal wind balance with the vertical shear in the along shelf flow in depths as shallow as 10 m the dominant along shelf momentum balances provide a simple estimate of the depth averaged along shelf current in terms of the measured forcing i e wind stress wave radiation stress divergence and along shelf pressure gradient that reproduces accurately the observed cross shelf variation of the depth averaged along shelf current between the surf zone and midshelf

west florida shelf mean circulation observed with long term moorings 1 the mean circulation on the west florida continental shelf is described using long term current measurements bounded by the florida peninsula to the east and the gulf of mexico to the west the west florida continental shelf mean flow is oriented approximately along isobath and southward the mean velocity vectors veer systematically with depth shoreward over shallow water and seaward over deeper water this polarization change implies that the mean flow is upwelling over shallow water and downwelling seaward from the inner shelf such a well organized three dimensional coastal ocean circulation pattern revealed by an unprecedented set of observations and explained on the basis of wind forcing and density field adjustment has important implications for both fisheries and red tide occurrences

optimal excitation of amoc decadal variability links to the subpolar ocean this study describes the excitation of variability of the atlantic meridional overturning circulation amoc by optimal perturbations in surface temperature and salinity our approach is based on a generalized stability analysis within a realistic ocean general circulation model which extends the conventional linear stability analysis to transient growth unlike methods based on singular value decomposition our analysis invokes an optimization procedure using lagrangian multipliers which is a more general approach allowing us to impose relevant constraints on the perturbations and use linear measures of the amoc meridional volume and heat transports we find that the structure of the optimal perturbations is characterized by anomalies in surface temperature or salinity centered in the subpolar regions of the north atlantic off the east coasts of greenland and canada south of the denmark strait the maximum impact of such perturbations on the amoc is reached after 7 9 yr this is a robust result independent of the perturbations type the optimization measures the model surface boundary conditions or other constraints the transient growth involves the following mechanism after the initial positive surface density perturbation reaches the deep ocean it generates a cyclonic geostrophic flow that extracts a zonally varying temperature anomaly from the mean temperature field in the upper ocean in turn the anomalous zonal temperature gradient induces by thermal wind balance a northward flow in the upper ocean and a southward flow in the deep ocean thus strengthening the amoc subsequently the transient growth gives way to a decaying oscillation corresponding to a damped oceanic eigenmode with a period of about 24 yr this mode is controlled by westward propagating large scale thermal rossby waves modifying the density field in the north atlantic and hence the amoc simple estimates show that realistic changes in salinity or temperature in the upper ocean such as those due to the great salinity anomaly can induce amoc variations of several sverdups via this mechanism or 10 20 of the mean overturning an idealized model is formulated to investigate the transient growth and highlight the role of mean convection in communicating surface density anomalies to the deep ocean 2014 published by elsevier ltd

momentum balances on the inner continental shelf at martha s vineyard coastal observatory 1 the subtidal depth average momentum balances in 12 m and 27 m water depth are investigated using observations from 2001 to 2007 of water velocity temperature and density bottom pressure surface gravity waves and wind stress in the fluctuating across shelf momentum budget the dominant terms are surface wind stress pressure gradient and coriolis acceleration the balance is a combination of 1 the geostrophic balance expected at midshelf sites and 2 the coastal setup and setdown balance driven by the across shelf wind stress expected where surface and bottom boundary layers overlap at the 12 m site the estimated wave radiation stress gradient due to surface gravity wave shoaling is also large but is uncorrelated with the observed pressure gradient a simple model suggests the wave radiation stress gradient is balanced by an across shelf pressure gradient with a spatial scale too small to resolve with this mooring array in the fluctuating along shelf momentum balance the dominant terms are surface wind stress pressure gradient and bottom stress at the shallower site but the other estimated terms are not negligible our results support the grant and madsen 1986 formulation for wave induced bottom stress the fluctuating along shelf pressure gradient is mainly a local sea level response to wind forcing not a remotely generated pressure gradient a strong correlation between along shelf velocity and along shelf wind stress at the shallower site is captured by a simple steady model of imbalance between wind stress and pressure gradient balanced by linear bottom drag

kinematics of inner shelf motions during the summer stratified season off new jersey subinertial currents on a wide 100 km shallow 20 m but nevertheless vertically stratified shelf off the atlantic seaboard of the united states are investigated at spatial scales of about 20 km in the alongshore and 10 km in the across shore direction during the summer of 1996 the inner shelf off new jersey was stratified due to both temperature and salinity that varied vertically by more than 128c and 4 psu respectively upwelling favorable winds and an intermittent buoyancy driven hudson coastal current impact this stratification inshore of the 15 m isobath waters offshore were always stratified except during the passage of tropical storm bertha mean currents are weak because wind forced upwelling and buoyancy forced downwelling events occurred about evenly during the observational study period at monthly to daily timescales currents always veered counterclockwise with depth in a bottom ekman layer sense by more than 308 inshore and 508 offshore complex empirical orthogonal function ceof analyses revealed that these veering angles are contained in the first mode that explains 80 85 of the total variance at individual locations it also explains 72 of the variance of 44 current time series of an across shore section the veering constitutes a robust feature that cannot be rationalized by ekman dynamics in shallow water alone the authors hypothesize that the veering represents a frictional response common to both upwelling and downwelling events the ceof analysis does not separate wind from buoyancy forcing the two forcing mechanisms thus appear to be dynamically coupled nevertheless the first two ceofs suggest distinctly different circulation regimes for positive and negative temporal amplitudes mode 1 represents a wind forced upwelling and a buoyancy forced downwelling circulation while mode 2 represents the lateral shear of the flow field synoptic maps of surface currents from ocean surface current radar reveal realizations of these event types

did deepwater horizon hydrocarbons transit to the west florida continental shelf abstract hydrocarbons that originated from deepwater horizon were observed at the surface along west florida s northern coastline in june 2010 the farthest eastward advance nearly to cape san blas occurred during the last week of june before the surface oil retreated back westward and dissipated surface oil was not observed on the portion of the west florida continental shelf wfs situated to the southeast of cape san blas nevertheless there were numerous anecdotal occurrences of reef fish caught on the wfs with lesions and other deformities subsequent systematic sampling of wfs reef fish provided additional evidence for damage that extended as far south as the dry tortugas here we examine the possibility that hydrocarbons of deepwater horizon origin transited to the wfs beneath the surface we use a numerical circulation model simulation run for the entirety of 2010 and quantitatively gauged against in situ observations a passive tracer is introduced into the model to mimic the movement of subsurface hydrocarbons either dissolved or of sufficiently small particle size to effectively be dissolved the tracer driven primarily by an anomalously strong and persistent upwelling circulation eventually covered most of the wfs using reasonable estimates of what the initial tracer concentration may have been with respect to hydrocarbons we conclude that the transport of subsurface hydrocarbons to the wfs is both plausible and consistent with the observed distribution of fish lesions fish liver chemistry and other chemical and ecological evidence

estimated global hydrographic variability an estimate is made of the three dimensional global oceanic temperature and salinity variability omitting the seasonal cycle both as a major descriptive element of the ocean circulation and for use in the error estimates of state estimation historical hydrography recent data from the world ocean circulation experiment and argo profile data are all used root mean square vertical displacements in the upper 300 m of the ocean are generally smaller than 50 m except in energetic boundary currents and in the north atlantic subpolar gyre variability in temperature and salinity is strongly correlated below the top 100 m salinity contributions to sea surface height variability appear more significant at low latitudes than expected possibly resulting from advective and diffusive processes results are generally consistent with altimetric variability under two simple kinematic hypotheses and much of the observed structure coincides with known dynamical features a large fraction of the sea surface height variability is consistent with the hypothesis of dominance of the first baroclinic mode

wind driven currents on the west florida shelf abstract three weeks of current meter wind and sea level data off cedar key florida are analyzed currents and sea level are found to be coherent with alongshore wind stress in the synoptic band 0 05 0 25 cycle per day and to lag it by approximately half a day little coherence is found with cross shelf wind stress at the inshore mooring 22 m depth currents are nearly barotropic for these winter 1978 data a linear parameterization of bottom stress in the barotropic alongshore current leads to a bottom friction parameter r of 0 01 0 02 cm s 1 using coastal wind stress no significant steady alongshore slope is found during this short interval the dominant momentum balance in the alongshore direction is between wind and bottom stress the offshore frictional length scale csanady 1978 is estimated to be 75 100 km which implies a seaward extent to a depth of about 30 m at the offshore mooring 44 m depth there is vertical shear between the currents at 9 and 39 m the upper cross shelf compon

decadal and interannual sst variability in the tropical atlantic ocean abstract the mechanisms regulating interannual and decadal variations of sea surface temperature sst in the tropical atlantic are examined observed variations of sea surface temperature are typically in the range of 0 3 0 5 c and are linked to fluctuations in rainfall on both the african and south american continents the authors use a numerical model to simulate the observed time series of sea surface temperature for the period 1960 1989 based on the results experiments are conducted to determine the relative importance of heat flux and momentum forcing two dominant timescales for variability of sst are identified a decadal timescale that is controlled by latent heat flux anomalies and is primarily responsible for sst anomalies off the equator and an equatorial mode with a timescale of 2 5 years that is dominated by dynamical processes the interhemispheric gradient of anomalous sst the sst dipole is primarily linked to the former process and thus results from the gradual strengthening and weak

coastal boundary conditions and the baroclinic structure of wind driven continental shelf currents abstract the generation of continental shelf currents by wind forcing is investigated by analytical and numerical methods the investigation is motivated by observations from the coastal ocean dynamics experiment a central assumption is that the vertical structure of the response over the inshore half of the shelf is controlled by the vertical distribution of the turbulent stress this suggests a two layer model of the wind driven circulation in which the upper layer represents a surface wind mixed layer and the lower layer represents the remainder of the fluid the response of this idealized dynamical model to wind forcing is examined and compared with observations in the 2 7 day period band for the alongshore velocity gain relative to local wind stress an onshore surface maximum and an offshore interior maximum are robustly reproduced by the model these features are evidently related to a dynamical transition over the inner half of the shelf in which the alongshore wind stress is balanced more by

oceanic isopycnal mixing by coordinate rotation abstract current numerical models of oceanic circulation differentiate between the eddy diffusion and viscosity transport along the geopotential horizontal and vertical directions only in order to model the effect of anisotropic turbulence as diffusive transport along and across density surfaces the isopycnal mixing tensor has been transformed from a diagonal second rank tensor in the isopycnal coordinate system to a tensor containing off diagonal elements in the geopotential coordinate system

construction of the adjoint mit ocean general circulation model and application to atlantic heat transport sensitivity we first describe the principles and practical considerations behind the computer generation of the adjoint to the massachusetts institute of technology ocean general circulation model gcm using r giering s software tool tangent linear and adjoint model compiler tamc the tamc s recipe for fortran line by line generation of adjoint code is explained by interpreting an adjoint model strictly as the operator that gives the sensitivity of the output of a model to its input then the sensitivity of 1993 annual mean heat transport across 29on in the atlantic to the hydrography on january 1 1993 is calculated from a global solution of the gcm the kinematic sensitivity to initial temperature variations is isolated showing how the latter would influence heat transport if they did not affect the density and hence the flow over 1 year the heat transport at 29on is influenced kinematically from regions up to 20 o upstream in the western boundary current and up to 5 o upstream in the interior in contrast the dynamical influences of initial temperature and salinity perturbations spread from as far as the rim of the labrador sea to the 29on section along the western boundary the sensitivities calculated with the adjoint compare excellently to those from a perturbation calculation with the dynamical model perturbations in initial interior salinity influence meridional overturning and heat transport when they have propagated to the western boundary and can thus influence the integrated east west density difference our results support the notion that boundary monitoring of meridional mass and heat transports is feasible

seasonal modulation of the west florida continental shelf circulation velocity data from 28 n 84 w on the west florida continental shelf are presented the data were sampled from october 1993 through january 1995 at 1 m intervals between 3 m and 42 m in a total water depth of 47 m their monthly means suggest an annual cycle hypothesized to be driven by a seasonally varying shelf wide baroclinic structure motions at semi diurnal diurnal and synoptic time scales are seasonally modulated both by wind forcing and stratification that decouples fluid motions from the damping effects of bottom friction these motions are presented in the form of progressive vector plots with 16 months of data probability density and distribution functions for along shore and across shore particle displacements over specific time intervals are constructed for daily intervals particles are equally likely to travel approximately 5 km depending upon confidence interval in any direction for monthly intervals particles may travel a few hundred km primarily along shore

assimilation of high frequency radar currents in a nested model of the west florida shelf 1 high frequency radar currents are assimilated in a west florida shelf wfs model based on the regional ocean model system roms which is nested in the atlantic hybrid coordinate ocean model hycom for the purpose of including both local and deep ocean forcing particularly the gulf of mexico loop current tides are not included in this model an ensemble simulation of the wfs model is carried out under different wind forcings in order to estimate the error covariance of the model state vector and the covariance between ocean currents and winds radial currents measured by high frequency radar antennas near saint petersburg and venice florida usa are assimilated using this ensemble based error covariance different assimilation techniques using a time average ensemble a filter to reduce surface gravity waves and an extended state vector including wind stress were tested results of the wfs model assimilating surface currents show an improvement of the model currents not only at the surface but also at depth

evaluation of frictional wind forced long wave theory on the west florida shelf abstract clarke and van gorder have recently formulated a model describing the large scale low frequency response of continental shelf waters to synoptic scale wind stress in terms of a sum of forced waves the model includes realistic friction and time dependence and provides an efficient method for calculating the response evaluation of the model using wed florida shelf data gave the following results i the model successfully predicts both the coastal sea level and alongshore velocity component ii the west florida shelf coastal pressure field is dominated by the first mode and can be understood as the sum of a forced wave which travels with the southward propagating wind stress and a free wave generated at the florida keys iii almost all the wind induced energy on the wed florida shelf is due to the wind forcing acting on wed florida shelf waters however a small but significant energy flux appears to enter the west florida shelf from the caucus florida shelf wave guide

inner shelf circulation patterns and nearshore flow reversal under downwelling and stratified conditions off a curved coastline 1 the role of a curved coastline and associated bathymetry in the development of downwelling circulation in a stratified inner shelf is examined through a number of numerical experiments different scenarios include constant versus variable wind forcing and variations in bottom friction the three dimensional response of the shelf within the domain embayment enclosed by capes is associated with the generation of a velocity pycnocline disturbance at the upstream cape and its subsequent downstream advection this disturbance is more pronounced under variable wind conditions its downstream advection through the bay exhibits different patterns depending on the competition between inertia and bottom friction near the cape when inertia dominates the disturbance separates from the cape and travels downwind with an enhanced downstream flow offshore and a countercurrent inshore the separation occurs at a low rossby number ro 0 15 which is attributed to the positive curvature of the coastline forming the cape when friction dominates the advection path is constrained along the coastline resulting in an alongshore temperature gradient and a transient thermal front running almost perpendicular to the coast isobaths simulations with spatially variable bottom friction with higher friction toward the coast result in the generation of eddy like features the numerical results are in agreement with both observations and surface temperature imagery from long bay south carolina an embayment enclosed by two capes and emphasize the role that coastline and associated shelf morphology can play in enhancing cross shelf transport and exchange

local and deep ocean forcing contributions to anomalous water properties on the west florida shelf 1 material property distributions on continental shelves result from the mixing and modifications of estuarine and deep ocean source waters how this occurs depends on the momentum and buoyancy that are input either locally on the shelf or from the deep ocean at the shelf break we address this question of local versus deep ocean forcing for the west florida shelf wfs using in situ data and a numerical circulation model the spring and summer seasons of 1998 and 1999 show distinctively different water properties on the shelf and at the shelf break we account for these differences by a combination of local forcing independent of the adjacent gulf of mexico loop current and interactions of the loop current with the shelf the primary role of the deep ocean is to set the height of material isopleths along the shelf slope whether or not these material isopleths broach the shelf break is then a consequence of local shelf wide wind and buoyancy forcing the subsequent along and across shelf distributions are accomplished through a combination of local and deep ocean effects with the bottom ekman layer being the major conduit for the across shelf transport of ecologically important materials

coastal upwelling in summer 2000 in the northeastern south china sea using a combination of hydrographic tide gauge near bottom mooring and satellite observations and a numerical circulation model we investigate the coastal upwelling in the northeastern south china sea nscs off the coast of fujian and guangdong provinces china in the summer of 2000 subsurface upwelling phenomenon exists mainly near the bottom boundary in the whole region investigated it is closely related to the coastal sea level fluctuations which are evidently modulated by both the local wind forcing and the large scale circulation the northeastward interior flow following the bathymetry is accelerated by the drop of coastal sea level and leads to onshore transport and subsequent cooling in the bottom boundary layer bbl over the shelf west of shantou to the east of shantou the near bottom flow veers more eastward parallel to the coastline and transports the nearshore cold water mass farther to the southern fujian coast the cross shelf advected cold water does not always penetrate through the stratification and reach the surface the local wind exhibits considerable synoptic variability the decrease in sea surface temperature sst is mostly significant near dongshan shantou intermittent in time and intensifies preferably during weather events that bring southwesterly alongshore wind to the west a freshwater tongue originating from the pearl river forms a barrier layer which results in high surface temperature in the freshwater plume the observational evidences and modeled results shown in this study provide important information for further understanding the ecological effects associated with the upwelling processes in the nscs

intensified upwelling over a widened shelf in the northeastern south china sea 1 observational and three dimensional modeling studies reveal that the intensified upwelling in the northeastern south china sea nscs is formed as a result of intensified upslope advection of dense deep waters that cross the middle shelf toward the inner shelf over a distinctly eastward widened shelf the strongest advection occurs over the converging isobaths near the head of the widened shelf as these dense deep waters advance shoreward they are advected downstream by the quickly developed upwelling current over the inner shelf and eventually outcropped at the lee of a coastal cape dynamically the shoreward cross isobath transport over the widened shelf is geostrophically enhanced by a quasi barotropic negative westward along isobath pressure gradient force as a result of the net rate of the momentum influx and by an intensified bottom frictional transport owing to the flow confluence near the head of the widened shelf a negative pressure gradient also exists at the lee of the coastal cape over the inner shelf and locally amplifies shoreward motion induced by the respective widened shelf and the coastal promontory the along isobath variations of cross isobath transport in the water column over the middle and inner shelves interactively characterize intensified upwelling in the nscs

a loop current intrusion case study on the west florida shelf the gulf of mexico loop current intruded upon the west florida continental shelf in june 2000 in situ currents and hydrography along with satellite temperature and altimetry measurements are used to describe this event and its effects on the shelf a strong southward current is observed to flow along the shelf slope seaward of the intruded water boundary this current transported cold nutrient rich water from the north thereby producing anomalous hydrographic features near the shelf break 80 m isobath an array of moored velocity profilers reveals that the currents landward of the intruded water are independent of the loop current and primarily driven by local winds a series of idealized numerical model simulations inclusive of forcing by both the loop current and local winds confirm the observational findings that the shelfbreak currents are largely loop current controlled while the shelf currents are largely controlled by the local winds

tropical atlantic sea surface temperature variability and its relation to el nino southern oscillation past analyses of tropical atlantic sea surface temperature variability have suggested a dipole behavior between the northern and southern tropics across the intertropical convergence zone itcz by analyzing an improved 43 year 1950 1992 record of sst smith et al 1996 and other data derived from the comprehensive ocean atmosphere data set coads it is shown that the regions north and south of the itcz are statistically independent of each other at the seasonal to interannual timescales dominating the data confirming the conclusions of houghton and tourre 1992 some dipole behavior does develop weakly during the boreal spring season when there is a tendency for sst anomaly west of angola to be opposite of that in the tropical north atlantic it is further shown that tropical atlantic sst variability is corre lated with pacific e1 nifio southern oscillation enso variability in several regions the ma jor region affected is the north atlantic area of ne trades west of 40ow along 10on 20on and extending into the caribbean there about 50 80 of the anomalous sst variability is associ ated with the pacific enso with atlantic warmings occurring 4 5 months after the mature phases of pacific warm events an analysis of local surface flux fields derived from coads data shows that the enso related atlantic warmings occur as a result of reductions in the surface ne trade wind speeds which in turn reduce latent and sensible heat losses over the region in ques tion as well as cooling due to entrainment this enso connection is best developed during the boreal spring following the most frequent season of maximum enso anomalies in the pacific a region of secondary covariability with enso occurs along the northern edge of the mean itcz position and appears to be associated with northward migrations of the itcz when the north at lantic warmings occur although easterly winds are intensified in the western equatorial atlantic in response to pacific warm events they do not produce strong local changes in sst contrary to expectations from studies based on equatorial dynamics these teleconnected wind anomalies do not give rise to significant correlations of sst in the gulf of guinea with the pacific enso as the teleconnection sequence matures strong se trades at low southern latitudes follow the de velopment of the north atlantic sst anomaly and precede by several months the appearance of weak negative sst anomalies off angola and stronger positive anomalies extending eastward from southern brazil along 15o 30os

the wind driven shelf and slope water flow in terms of a local and a remote response abstract clarke and van gorder suggest that many coastally trapped wave modes are needed to describe the wind driven shelf and slope water alongshore velocity field calculations with an harmonic wind forcing confirm this and show that for example the alongshore velocity field is usually underestimated by using only three coastally trapped wave modes this is a serious drawback in the forced wave mode method since it is difficult to calculate the many needed higher order modes fortunately large mode number coastally trapped wave asymptotics also suggest that these higher order modes are effectively generated by just the local wind both computationally and physically it is therefore convenient to regard the velocity field as being due to a two dimensional local solution which depends only on local winds and a remote solution driven by the alongshore pressure gradient and depending on non local wind stress to compute such a local plus remote solution at a given coastal cross section the alongsh

investigation of the spring thermal regime in lake ladoga using field and satellite data we use a combination of field and satellite data to investigate the thermal regime in lake ladoga in spring 1992 the analysis concentrates mainly on the temperature structure in the convectively mixed region and the dynamics of a special thermo hydrodynamic phenomenon called thermal bar a zone of descending water with the temperature of maximum density equal to 4 c a theoretical model of the temperature distribution in the convectively mixed region temperatures 4 c and the thermal bar progression is also applied and compared with satellite data the study shows that the temperature offshore the 4 c isotherm in the convectively mixed region of the lake is almost depth constant because of strong convective mixing and that the horizontal heat flux seems to be of minor importance in this region the comparison between predictions from the simple theoretical model describing the temperature evolution and movement of the thermal bar with observations showed a fairly good agreement however calculations of the change of heat content in water columns along sections indicate heat transport from the nearshore stably stratified region toward the 4 c isotherm which will affect the movement of the thermal bar this effect has been incorporated in an improved model of the thermal bar progression a better agreement between predictions and observations was also obtained with this model

west florida shelf response to local wind forcing april 1998 we compare west florida shelf velocity and sea level data with a model simulation for april 1998 responses for three upwelling and three downwelling favorable wind events are documented along shelf jets accompanied by oppositely directed upper and lower layer across shelf flows with connecting vertical velocity comprise the fully three dimensional inner shelf responses which are sensitive to stratification with an initial density field representative of april 1998 the model simulates velocity and sea level variations in general agreement with the observations whereas substantial mismatches occur without stratification despite the winds being the primary motive agent for the inner shelf the stratification dependence requires that model density fields be maintained through a combination of adequate initial conditions surface offshore and land derived buoyancy inputs and data assimilation dynamical analyses define the inner shelf as the region where the surface and bottom boundary layers are important in the momentum balance kinematically this is where surface ekman layer divergence fed by the bottom ekman layer convergence or conversely sets up the across shelf pressure gradient stratification causes a response asymmetry wherein the offshore scale and magnitude of the upwelling responses are larger than those for the downwelling responses this asymmetry is attributed to thermal wind effects across the bottom ekman layer buoyancy torque by isopycnals bending into the bottom adds constructively destructively with planetary vorticity tilting under upwelling downwelling favorable winds and this may have important implications for nutrients and other material property distributions on the shelf

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

tides on the west florida shelf the principal semidiurnal m2 and s2 and diurnal k1 and o1 tidal constituents are described on the west florida continental shelf wfs using a combination of in situ measurements and a three dimensional primitive equation numerical model the measurements are of sea level and currents along the coastline and across the shelf respectively the model extends from west of the mississippi river to the florida keys with an open boundary arcing between it is along this open boundary that the regional model is forced by a global tide model standard barotropic tidal analyses are performed for both the data and the model and quantifiable metrics are provided for comparison based on these comparisons the authors present coamplitude and cophase charts for sea level and velocity hodographs for currents the semidiurnal constituents show marked spatial variability whereas the diurnal constituents are spatially more uniform apalachicola bay is a demarcation point for the semidiurnal tides that are well developed to the southeast along the wfs but are minimal to the west the largest semidiurnal tides are in the florida big bend and florida bay regions with a relative minimum in between just to the south of tampa bay these spatial distributions may be explained on the basis of local geometry a lagrangian stokes drift coherently directed toward the northwest is identified but is of relatively small magnitude when compared with the potential for particle transport by seasonal and synoptic scale forcing bottom stressinduced tidal mixing is examined and estimates are made of the bottom logarithmic layer height by the m2 tidal currents

a method for estimating wind driven frictional time dependent stratified shelf and slope water flow abstract friction the alongshore pressure gradient and time dependent effects are all of lowest order importance in the dynamics of wind driven fluctuating currents and sea levels on continental shelves previous work has shown that when all these effects are included the ocean response can be described by an infinite sum of coastal trapped waves whose amplitudes satisfy a fully coupled infinite set of forced first order wave equations we present a practical method for solving this coupled set of equations for general low frequency large scale wind stress forcing as input convergence properties of the solution are examined analytically for the same accuracy more modes are required to describe alongshore currents than sea level and fewer modes are required to describe barotropic than depth dependent motion as an example numerical calculations were carried out for a model of the west florida shelf the sea level field was effectively described by one mode but the alongshore velocity field was not

an adjoint analysis of the meridional overturning circulation in an ocean model abstract using the adjoint of a fully three dimensional primitive equation ocean model in an idealized geometry spatial variations in the sensitivity to surface boundary forcing of the meridional overturning circulation s strength are studied steady state sensitivities to diapycnal mixing wind stress freshwater and heat forcing are examined three different commonly used boundary forcing scenarios are studied both with and without wind forcing almost identical circulation is achieved in each scenario but the sensitivity patterns show major quantitative and qualitative differences sensitivities to surface forcing and diapycnal mixing are substantially larger under mixed boundary conditions in which fluxes of freshwater and heat are supplemented by a temperature relaxation term or under flux boundary conditions in which climatological fluxes alone drive the circulation than under restoring boundary conditions the sensitivity pattern to diapycnal mixing which peaks in the tropics is similar

multiyear subinertial and seasonal eulerian current observations near the florida big bend coast abstractmultiyear in situ eulerian acoustic doppler current profiler measurements were obtained at 5 10 and 19 m depths off the big bend coast and in 19 m off the florida peninsula to the south analysis on subinertial time scales dominated by weatherband frequencies led to the following conclusions at the 19 m big bend site k tower consistent with coastally trapped wave ctw theory the along isobath flow is not proportional to the local along isobath wind stress but rather to the alongshore wind stress to the south along the west florida shelf wfs at the southern 19 m site consistent with previous work the along isobath flow is driven by but is weakened by an alongshore pressure gradient brake via ctw dynamics this brake is due to the abrupt end of the wfs at the florida keys by contrast along isobath flow at the shallow 5 m site is driven by the local wind in a constant stress turbulent frictional layer because of the freshwater flux near the coast density usually increases s

ocean currents and sea surface heights estimated across the west florida shelf abstract the across shelf structures of the ocean circulation and the associated sea surface height ssh variability are examined on the west florida shelf wfs for the 3 yr interval from september 1998 to december 2001 five sets of characteristic circulation patterns are extracted from 2 day low pass filtered data using the self organizing map extreme upwelling and downwelling structures with strong currents asymmetric upwelling and downwelling structures with moderate currents and a set of transitional structures with weak currents the temporal variations of these structures are coherent with the local winds on synoptic weather time scales on seasonal time scales they are related to both the local winds and the water density variations the circulation is predominantly upwelling during autumn to spring months october april and downwelling during summer months june september coastal sea level fluctuations are related to both the dynamical responses of the inner shelf circulation to meteorol

decomposing observations of high frequency radar derived surface currents by their forcing mechanisms locally wind driven surface currents 1 the wind impulse response function and transfer function for high frequency radar derived surface currents off southern san diego are calculated using several local wind observations the spatial map of the transfer function reflects the influence of the coast on wind current dynamics near the coast within 20 km from the shoreline the amplitudes of the transfer function at inertial and diurnal frequencies are reduced due to effects of coastline and bottom bathymetry meanwhile the amplitude of low frequency currents increases near the coast which is attributed to the local geostrophic balance between cross shore pressure gradients against the coast and currents locally wind driven surface currents are estimated from the data derived response function and their power spectrum shows a strong diurnal peak superposed on a red spectrum similar to the spectra of observed winds current magnitudes and veering angles to a quasi steady wind are typically 2 5 of the wind speed and vary 50 90 to the right of the wind respectively a wind skill map is introduced to present the fractional variance of surface currents explained by local winds as a verification tool for wind data quality and relevance moreover the transfer functions in summer and winter are presented to examine the seasonal variation in ocean surface current response to the wind associated with stratification change

wind and topography influence on an upwelling system at the eastern hainan coast 1 during the summer monsoon an upwelling dominates east of hainan island which can be observed by means of field studies and satellite sea surface temperature images the centers of cold water at the surface always show a strong patchiness a 3 d high resolution model is applied to study the impact of the topography on the wind driven upwelling system the experiments show that the upwelling favoring wind is the main driving force and we concluded that the formation of the centers of cold water at the surface significantly depends on the strength of southwesterly and southerly winds moreover the internal waves are generated at the shelf break representing the most prominent interaction between inner shelf and open ocean the alongshore topographic variations play an important role in the distribution of the upwelling centers this combined effect of wind and topography leads to the following processes 1 when the southwesterly or southerly wind is strong enough topographic variations cause upwelling centers at the downstream side of topographic high and a downwelling center at the upstream side which in turn lead to density variations 2 these density variations cause additional pressure gradients which advect the upwelling centers toward the northeast 3 a longer period of upwelling favorable winds support the advection processes which cause an enlargement of the cold water centers all these processes together can explain the observed uneven distribution of upwelling centers

stochastic forcing of the north atlantic wind driven ocean circulation part i a diagnostic analysis of the ocean response to stochastic forcing abstract at midlatitudes the magnitude of stochastic wind stress forcing due to atmospheric weather is comparable to that associated with the seasonal cycle stochastic forcing is therefore likely to have a significant influence on the ocean circulation in this work the influence of the stochastic component of the wind stress forcing on the large scale wind driven circulation of the north atlantic ocean is examined to this end a quasigeostrophic model of the north atlantic was forced with estimates of the stochastic component of wind stress curl obtained from the ncar community climate model analysis reveals that much of the stochastically induced variability in the ocean circulation occurs in the vicinity of the western boundary and some major bathymetric features thus the response is localized even though the stochastic forcing occurs over most of the ocean basin using the ideas of generalized stability theory the stochastically induced response in the ocean circulation can be interpreted as