vorticity flux through the yucatan channel and loop current variability in the gulf of mexico 1 recent observations the canek program candela et al 2002 suggest that potential vorticity pv flux anomaly vfa at yucatan channel may serve as a useful indicator of loop current variability including loop current extension retraction and eddy shedding intuitively anticyclonic vfa extends the loop current into the gulf of mexico and cyclonic vfa causes retraction or even shedding however this intuition is inconsistent with pv conservation the problem is reexamined here by careful analyses of the relation between vfa and loop current variability using 1 the results of a 15 year numerical simulation of shedding specified with simple forcing and 2 canek and satellite observations both model and observations indicate that loop current eddy shedding or retraction tends to occur shortly 1 2 months after the influx of vfa at yucatan has turned anticyclonic and that these events are sometimes preceded by a more prolonged period of influx of cyclonic vfa these findings suggest that contrary to intuition influx of cyclonic vfa tends to extend the loop current into the gulf thus making the loop current more susceptible to retract or shed an eddy and influx of anticyclonic vfa may then trigger retraction or eddy shedding however the loop current s behaviors are much more complex than can be prescribed by these simple rules a much longer observational data set coupled with more refined model experiments and sophisticated analyses is required to further quantify the phenomenon index terms 4520 oceanography physical eddies and mesoscale processes 4255 oceanography general numerical modeling 4576 oceanography physical western boundary currents 4243 oceanography general marginal and semienclosed seas keywords vorticity flux loop current yucatan channel citation oey l y 2004 vorticity flux through the yucatan channel and loop current variability in the gulf of mexico j geophys res 109 c10004 doi 10 1029 2004jc002400

adjoint sensitivity studies of loop current and eddy shedding in the gulf of mexico 1 adjoint model sensitivity analyses were applied for the loop current lc and its eddy shedding in the gulf of mexico gom using the mit general circulation model mitgcm the circulation in the gom is mainly driven by the energetic lc and subsequent lc eddy separation in order to understand which ocean regions and features control the evolution of the lc including anticyclonic warm core eddy shedding in the gom forward and adjoint sensitivities with respect to previous model state and atmospheric forcing were computed using the mitgcm and its adjoint since the validity of the adjoint model sensitivities depends on the capability of the forward model to simulate the real lc system and the eddy shedding processes a 5 year 2004 2008 forward model simulation was performed for the gom using realistic atmospheric forcing initial and boundary conditions this forward model simulation was compared to satellite measurements of sea surface height ssh and sea surface temperature sst and observed transport variability despite realistic mean state standard deviations and lc eddy shedding period the simulated lc extension shows less variability and more regularity than the observations however the model is suitable for studying the lc system and can be utilized for examining the ocean influences leading to a simple and hopefully generic lc eddy separation in the gom the adjoint sensitivities of the lc show influences from the yucatan channel yc flow and loop current frontal eddy lcfe on both lc extension and eddy separation as suggested by earlier work some of the processes that control lc extension after eddy separation differ from those controlling eddy shedding but include yc through flow the sensitivity remains stable for more than 30 days and moves generally upstream entering the caribbean sea the sensitivities of the lc for sst generally remain closer to the surface and move at speeds consistent with advection by the high speed core of the current while sensitivities to ssh generally extend to deeper layers and propagate more slowly the adjoint sensitivity to relative vorticity deduced from the sensitivities to velocity fields suggests that advection of cyclonic positive relative vorticity anomalies from the yc or the lcfes accelerate the lc eddy separation forward model perturbation experiments were performed to complement and check the adjoint sensitivity analysis as well as sampling the predictability and nonlinearity of the lc evolution the model and its adjoint can be used in four dimensional variational assimilation 4d var to produce dynamically consistent ocean state estimates for analysis and forecasts of the circulation of the gom

treating strong adjoint sensitivities in tropical eddy permitting variational data assimilation a variational data assimilation system has been implemented for the tropical pacific ocean using an eddy permitting regional implementation of the mitgcm the adjoint assimilation system was developed by the estimation of the circulation and the climate of the ocean consortium and has been extended to deal with open boundaries this system is used to adjust the model to match observations in the tropical pacific region using control parameters which include initial conditions open boundaries and time dependent surface fluxes this paper focuses on problems related to strong adjoint sensitivities that may impede the model fit to the observations a decomposition of the velocities at the open boundaries into barotropic and baroclinic modes is introduced to deal with very strong sensitivities of the model sea surface height to the barotropic component of the inflow increased viscosity and diffusivity terms are used in the adjoint model to reduce exponentially growing sensitivities in the backward run associated with nonlinearity of the forward model simplified experiments in which the model was constrained with levitus temperature and salinity data reynolds sea surface temperature data and topex poseidon altimeter data were performed to demonstrate the controllability of this assimilation system and to study its sensitivity to the starting guesses for forcing and initial conditions

flow structure and transport in the yucatan channel 1 the direct ocean current observations across the yucatan channel collected during the canek program allow the best description to date of the exchange between the caribbean sea and the gulf of mexico a net transport of 23 8 1 sv 1 sv 106m3s 1 95 confidence interval flowed through the yucatan channel from the caribbean sea into the gulf of mexico during the period between september 1999 and june 2000 this is about 20 percent less than the 30 sv accepted as the nominal transport of the florida current and less also than the 28 sv assumed for yucatan in closing the transport budgets for caribbean passages the discrepancy may be an imbalance due to fluctuations in the transports through other passages of the system especially the old bahama and northwest providence channels which remain poorly known our data corroborate the principal features of the flow through the yucatan channel the northerly surface yucatan current and its southerly under current off mexico and the southerly surface cuban counter current near cuba but previously unobserved mean currents are found to exist at depth especially on the eastern side of the channel fluctuations seen in the deep flows are related to volume anomalies over the gulf of mexico a transport through the yucatan channel smaller than previously thought has significant implications for the dynamics of the gulf of mexico and its modeling since this transport is the principal forcing of its circulation the circulation budgets in the western subtropical atlantic should be revised considering these new results

dynamic transfer of simulated altimeter data into subsurface information by a numerical ocean model a global eddy resolving capability to predict the ocean circulation is technologically feasible within the next decade for this purpose the satellite altimeter is the most promising operational source of oceanic data with global coverage but only at the surface a comparable source of subsurface data is not on the horizon this investigation demonstrates the ability of a numerical ocean model to dynamically transfer simulated altimeter data into subsurface information this was done for a variety of dynamical regimes with 1 barotropic baroclinic mixed and episodic instabilities 2 flat bottoms or large amplitude topography 3 relatively vigorous or gentle exchange of energy between the layers and 4 major time scales that are short 60 days long 1 year or both in all cases the pattern of the deep pressure field is much different from the one for the current related variations in the sea surface elevation and sometimes not obviously related to it the model was able to reconstruct the deep pressure field even in situations with energetic shallow and deep circulations baroclinic instability and a vigorous vertical exchange of energy however in such experiments the frequency of updating for the free surface elevation was critical in this study the maximum update interval that allowed successful dynamic surface to subsurface transfer was about half the shortest major time scale smts e g 50 60 days in the experiments with baroclinic instability without knowledge of the deep pressure field numerical predictions of the surface pressure field and the depth of the pycnocline typically were better than climatology for 1 4 to 1 2 the smts but with successful dynamic surface to subsurface transfer forecasts without updating were better than climatology for the smts or more the time scale for predictive skill can be substantially longer than the maximum update interval permitted because the update interval must be short enough to allow decreasing error in the deep pressure field from one free surface update to the next until the error asymptotes at some acceptable level approximately 30 50 in these results forecasts of nondispersive isolated eddies with beta rossby number o 1 demonstrated predictive skill for 3 months or more even when the subsurface initial state was unknown a serendipitous result of the study is some progress in understanding the generation of cyclonic eddies associated with the loop current in the eastern gulf of mexico section 5 5

anticyclonic rings in the gulf of mexico abstract using the historical data set this study describes the anticyclonic rings that separated from the loop current in the eastern gulf of mexico six quasi synoptic data sets are used to describe the evolving circulation of the gulf of mexico from october 1966 to september 1967 showing the separation and movement into the western gulf of three anticyclonic rings the historical data are used to determine that these rings typically translate to the west at a mean speed of 2 1 km day 1 their length scale as defined by their rms radii is 183 km an estimate of ring life span as defined by an e folding time is one year within the context of the gulf s water property distributions these rings appear as warm salty bodies the heat and salt added by one of these rings after separation are estimated to be 7 109 j m 2 and 17 g cm 2 respectively the heat and salt added by one of these features play an important role in the heat and salt budget of the western gulf the latter indicates that about one r

lower continental slope cyclonic eddies in the central gulf of mexico current meters an inverted echo sounder hydrography drifters and satellite imagery are used to characterize relatively small 100 to 150 km diameter cold cyclonic eddies in the central basin and on the lower louisiana slope of the gulf of mexico these cyclones are shown to be long lived 6 months or more have limited movements when compared with loop current anticyclones and be fairly vigorous with upper layer currents of 30 50 cm s 1 they usually have only small temperature differences with surrounding water masses in the upper 50 to 100 m of the water column and are therefore not readily apparent in satellite thermal imagery the largest isotherm displacements occur over depths of 200 800 m in one case a cyclone was traced from the deep basin near 92 w to the northern slope as a major anticyclone propagated southwestward through the gulf the presence of cyclones and anticyclones on the louisiana slope is consistent with observed current meter measurements in the upper half of the water column that have long several months periods and approximately equal variances in the cross slope and along slope directions

simulating the dynamics and intensification of cyclonic loop current frontal eddies in the gulf of mexico 1 the dynamics associated with the loop current lc variability in the gulf of mexico gom are studied using a 5 year free running numerical simulation with the hybrid coordinate ocean model hycom the dynamics of major gom circulation features are represented the extension of the lc and the associated anticyclonic warm core loop current eddies lces and cyclonic loop current frontal eddies lcfes the study focuses on the dynamics of the lcfes and their role during the lces shedding which dramatically affects the gom circulation we analyze several characteristics of the lc frontal dynamics modeled lcfes have a coherent vertical structure which extends to the deep layers of the gom they may split in two separate upper and lower layer eddies deep and surface remnants from different frontal eddies are able to align to form new coherent structures lcfes intensify along the extended lc northern edge when flowing over the deep northern gom shelf slope that forms the mississippi fan through a promontory effect in which the incoming cyclone aggregates positive potential vorticity anomalies in lower layers leading to the intensification of the whole vortex structure lcfes may also expand further along the lc path by horizontal vortex merging when they are blocked between the lc and the northeast corner of the continental shelf in the gom the intensification and merging due to topographic effects explain the enlarged frontal eddies observed on the eastern side of the loop current these larger eddies further migrate along the lc front and may play a role in the shedding sequence

deep flows in the yucatan channel and their relation to changes in the loop current extension 1 the first attempt to establish a relation between the loop current extension and deep flows in yucatan channel was made by maul et al 1985 it was unsuccessful probably because of the low spatial resolution of their observations from september 8 1999 to june 17 2000 eight moorings with acoustic doppler current profilers current meters and thermometers were deployed across the yucatan channel the data from these arrays were used to compute time series of the transports below the level of the deepest isotherm observed in the florida straits as required by a simple box model that restricts deep exchanges with the gulf of mexico to the yucatan channel the surface extension of the loop current was inferred from 3 day advanced very high resolution radiometer imagery from october to may when temperature gradients were sufficient to map the warm water unambiguously the deep transports appear at first unrelated to the rate of change of the loop current extension but filtering the series with a 20 day running mean increases the correlation between the low pass series to 0 62 and up to 0 83 with a lag of 8 5 days with loop current changes leading the deep flows the cumulative deep transport a quantity that favors lower frequencies is very well related correlations 0 9 to the surface extension of the loop current also with a lag of about a week these lags are not statistically significant but suggest a timescale for internal adjustment processes in the gulf of mexico the empirical orthogonal function of the current best related to the area extension of the loop current represents a unidirectional flow across the entire deep section flowing either toward or from the gulf of mexico and includes a strong expression of the yucatan undercurrent

experimental and modeled chlorine solubilities in aluminosilicate melts at 1 to 7000 bars and 700 to 1250 c applications to magmas of augustine volcano alaska hydrothermal experiments were conducted at ca 1 to 7000 bars and 700 to 1250 c in 121 rhyolitic to basaltic systems to determine cl solubility in silicate melts i e the maximum cl concentration in melts that are saturated in a hydrosaline liquid with or without an aqueous or aqueous carbonic vapor the cl concentration of melts increases with the cl contents of the fluid unless the melt coexists with vapor plus hydrosaline liquid at fixed pressure and temperature this phase assemblage buffers the cl content of each phase with increasing cl in the system the cl content of fluid s saturated melts is independent of the co 2 concentration of the saline liquid vapor with up to 21 wt co 2 in the fluid s the experiments show that cl dissolution in aluminosilicate melts increases with temperature and pressure chlorine solubility is also a function of melt composition it increases with the molar al 1 2 ca 1 2 mg 1 2 na si of the melt these experimental data have been integrated with results involving 41 other experiments webster and de vivo 2002 to develop a broadly expanded model that supports calculation of cl solubility in 163 aluminosilicate melts this empirical model applies to cl dissolution in melts of most silicate magmas at depths as great as 25 km it determines the exsolution of hydrosaline liquid with or without a coexisting vapor as magmas ascend from depth cool crystallize and differentiate from mafic to felsic compositions in combination with h 2 o solubility models our model supports determination of h 2 o cl solubility relations for most aluminosilicate magmas and is useful for barometric estimations based on silicate melt inclusions containing low co 2 and moderate to high cl concentrations the model is applied to the phase relations of fluids in volatile enriched magmas of augustine volcano alaska the cl and h 2 o concentrations of melt inclusions from 14 basaltic to dacitic eruptive units are compared with modeled solubilities of cl and h 2 o in augustine melts the majority of these eruptions involved magmas that first exsolved aqueous to aqueous carbonic vapors when the melts were dacitic in composition i e before the residual melts in these magmas had evolved to felsic compositions and well prior to the eruptions hydrosaline liquid with or without a vapor phase exsolved from other more felsic fractions of augustine melts at low near surface pressures of several tens of bars

transports through the straits of florida abstract transports were calculated for four sections of the florida current from key west to jupiter florida using a moored current meter array and voltages from cross channel telephone cables at the western and northern ends of the straits of florida in addition moored arrays were used to estimate transport through the northwest providence santaren and old bahama channels that connect the florida current to the southwestern part of the north atlantic ocean transport measurements were obtained for an 11 month period from december 1990 to november 1991 mean transports of 25 sv 1 sv 106 m3 s 1 for the flow across the western ends of the straits which agree quite well with recent estimates of 23 8 1 sv entering the gulf of mexico through the yucatan channel were obtained from both the key west to havana cable and the moored array this estimate is about 5 sv less than the generally accepted transport through the northern end of the straits at 27 n this difference was partially accounted fo

an adjoint sensitivity study of chlorofluorocarbons in the north atlantic 1 adjoint sensitivities of cfc 11 concentrations and cfc 11 cfc 12 ratio ages in a north atlantic general circulation model are analyzed these sensitivities are compared with those of spiciness t s where are the thermal and haline expansion coefficients respectively high sensitivity fields are candidates for providing the most powerful constraints in the corresponding inverse problems in the dual adjoint solutions all three variables exhibit the major ventilation pathways and define the associated timescales in the model overall however spiciness shows the highest sensitivity to the flow field in the north atlantic deep water sensitivities of cfc properties and spiciness to the isopycnal mixing and thickness diffusion are of the same order of magnitude in the lower subtropical thermocline sensitivities of cfc properties to the isopycnal mixing and thickness diffusion are higher the utility of this sensitivity is undermined by the need to reconstruct their boundary conditions given the influence of t s measurements on the density field they produce the most powerful constraints on the model on the large scale it still remains possible however that transient tracers can provide a larger relative information content concerning the mixing process between the near surface boundary layer and the thermocline but dependent upon the ability to reconstruct accurate initial and boundary conditions

loop current boundary variations the periodicity of warm ring separation from the loop current and the characteristics of cold perturbations found along the loop current boundary were studied using a long term data set made up of noaa satellite infrared images the results showed that the period between separation of warm rings from the loop current was highly variable the average period was about 10 9 months the minimum period was 6 months and the maximum period was 17 months for the data set used ring separations occurred most often in the winter the study of the cold perturbations indicated that these perturbations were most pronounced along the northern and eastern portions of the loop current boundary and were less pronounced south of 27 n along the western boundary the data suggested that the perturbations either formed or intensified in the northwestern portions of the boundary the large effects along the eastern boundary of the loop current were thought to be associated with the movement of the intense perturbations that are initially found along the northwestern portions of the boundary

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

evolution and kinematics of a loop current eddy in the gulf of mexico during 1985 the large eddy that broke off from the loop current in july 1985 was the most extensively studied eddy ever to appear in the gulf of mexico other investigators have described its early evolution based on lagrangian drifters and its later evolution using moored current meters in the western gulf this paper provides additional insight on the early evolution of the eddy using results from air dropped expendable bathythermographs and air dropped expendable current profilers in early may a hydrographic ship survey in mid july and a detailed ship survey in august using expendable bathythermographs and a current profiler the may survey established a center of circulation at about 26 n but showed that the eddy had not separated from the loop current a maximum velocity of 171 cm s was observed near the northern edge of the feature the evidence suggests that a large elongated eddy then separated from the loop current and later split into two smaller eddies the july hydrographic cruise showed a clear separation of the large eddy from the loop current to the southeast two weeks later the august survey showed an asymmetric eddy with the maximum surface current 178 cm s south of the center of circulation and 132 cm s to the north a western eddy named ghost eddy then separated from an eastern eddy named fast eddy using the current profiles and data from the drifters we constructed a simple kinematic feature model for eddies in the gulf of mexico

eddy energy and shelf interactions in the gulf of mexico sea surface height anomaly data from satellite are continuously available for the entire gulf of mexico surface current velocities derived from these remotely sensed data are compared with surface velocities from drifting buoys the comparison shows that satellite altimetry does an excellent job resolving gulf eddies over the shelf rise depths between 200 and 2000 m if the proper length scale is used correlations between altimeter and drifter derived velocities are statistically significant r 0 5 when the surface slope is computed over 125 km indicating that remotely sensed sea surface height anomaly data can be used to aid the understanding of circulation over the shelf rise velocity variance over the shelf rise from the altimetry data shows regions of pronounced eddy energy south of the mississippi outflow south of the texas louisiana shelf and in the northwest and northeast corners of the gulf these are the same locations where surface drifters are most likely to cross the shelf rise suggesting gulf eddies promote cross shore flows this is clearly exemplified with both warm and cold eddies finally the contribution of gulf eddies and wind stress to changes in the mean circulation are compared results indicate that the eddy generated vorticity flux to the mean flow is greater than the contribution from the surface wind stress curl especially in the region of the loop current and along the shelf rise base in the western gulf future modeling efforts must not neglect the role of eddies in driving gulf circulation over the shelf rise

an adjoint sensitivity study of buoyancy and wind driven circulation on the new jersey inner shelf adjoint sensitivity analysis is used to study the new york bight circulation for three idealized situations an unforced buoyant river plume and upwelling and downwelling wind forcing a derivation of adjoint sensitivity is presented that clarifies how the method simultaneously addresses initial boundary and forcing sensitivities considerations of interpretation and appropriate definitions of sensitivity scalar indices are discussed the adjoint method identifies the oceanic conditions and forcing that are dynamically upstream to a region or feature of interest as well as the relative roles of the prior ocean state forcing and dynamical influences to illustrate the method which is quite general the authors consider coastal sea surface temperature sst variability and define the adjoint scalar index as the temporal spatial mean squared sst anomaly on a segment of the new jersey coast at the conclusion of a 3 day period in the absence of wind surface temperature advection dominates the sst anomaly with two sources of surface water identified downwelling winds amplify upstream advective influence sensitivity to temperature is separated into direct advection and the dynamic effect on density stratification and mixing for upwelling conditions this decomposition shows that coastal sst is controlled by both advection from the south and subsurface but above the 5 m depth and temperature related density stratification between 5 and 15 m to 10 km offshore by identifying the timing and location of ocean conditions crucial to subsequent prediction of specific circulation features the adjoint sensitivity method has application to quantitative evaluation of observational sampling strategies

on the structure and motions of cyclones in the northern gulf of mexico 1 the eddy field on the northern slope of the gulf of mexico has been investigated using high resolution axbt and axcp aircraft surveys and argos tracked drifters a number of vigorous cyclones were mapped their vertical structures showed solid body rotation with radii of 50 75 km with a subsurface maximum 40 cm s 1 at the outer edge at about 150 m flows had little shear in the upper 400 m and only weak currents below depths of 800 to 1000 m cyclones were observed to move on and off the slope under the influence of swirl velocities of larger warm core eddies including loop current lc anticyclones rotational periods range from about 7 to 18 days the mapped eddy fields contained both cyclones and anticyclones with a range of diameters from about 40 to 150 km the presence of many relatively small scale features along the upper slope strongly affects features of the shelf break velocity field that were measured by a moored current meter array the directions and vertical shears of the moored currents were consistent with flows caused by the northern edges of cyclones and anticyclones these eddies can cause persistent events and strong cross isobath fluctuations of the currents counterrotating pairs of eddies on the upper slope seem to be a mechanism for the transport of material on and off the louisiana and east texas shelves coherences between moorings 74 km apart were generally not significant as might be expected when the currents are dominated by small scale eddies however an eof analysis of the shelf break array indicates that about 40 of the along slope current variances could be attributed to westward propagating continental shelf waves

lagrangian observations of an anticyclonic ring in the western gulf of mexico this analysis documents for the first time the movement and velocity characteristics of an anticyclonic ring the ring was pinched off from the loop current in the fall of 1980 and moved into the western gulf of mexico lagrangian measurements obtained from satellite tracked drifters show that typical speeds of the near surface currents associated with this ring are about 50 cm s there is also a surprising amount of higher frequency current fluctuations these include diurnal and semidiurnal tides a basin tidal resonance and a free gravity mode

adjoint sensitivity of an ocean general circulation model to bottom topography abstract bottom topography or more generally the geometry of the ocean basins is an important ingredient in numerical ocean modeling with the help of an adjoint model it is shown that scalar diagnostics or objective functions in a coarse resolution model such as the transport through drake passage the strength of the atlantic ocean meridional overturning circulation the deacon cell and the meridional heat transport across 32 s are sensitive to bottom topography as much as they are to surface boundary conditions for example adjoint topography sensitivities of the transport through drake passage are large in choke point areas such as the crozet kerguelen plateau and south of new zealand the atlantic meridional overturning circulation is sensitive to topography in the western boundary region of the north atlantic ocean and along the scotland iceland ridge many sensitivities are connected to steep topography and can be interpreted in terms of bottom form stress that is the product of bottom pre

analysis of flow variability in the yucatan channel 1 the structure and variability of the velocity and temperature fields in yucatan channel are analyzed using data from an eight mooring array deployed from august 1999 to june 2000 the area averaged kinetic energy and transport fluctuations spectra show that the extrema of these quantities do not coincide and that flow variability is dominated by highly energetic processes with weak transport contributions transport fluctuations peak in the 20 40 and 5 10 day period bands but show no clear correlation with the local wind stress forcing empirical orthogonal function eof analysis of the along channel velocity component shows that approximately 55 of the total velocity variance is retained in the first two eofs which depict tripolar the center of the channel is out of phase with the sides and dipolar structures a multivariate complex eof analysis of low passed temperature and velocity components suggests the tripole dipole structures are the components of irregular oscillations of the flow related to the northwestward propagation of anticyclones and cyclones through the channel the weak transport signal in these modes is consistent with the eddies being advected by the mean flow in contrast to other western boundary current regions the passage of eddies provides the predominant explanation for the variability in the yucatan channel however the processes controlling transport variability remain unclear

cyclonic eddies in the eastern gulf of mexico abstract cold domed cyclonic eddies juxtaposed to the cyclonic shear side of the gulf loop current are observed in simultaneously obtained hydrographic current meter mooring and satellite infrared data the cyclones are initially observed in the satellite data as cold perturbations on the northern extreme of the current and grow either into a cold tongue or a quasi stable meander off the dry tortugas florida areal shipboard surveys show closed isopleths of temperature and salinity and surface geostrophic current speeds relative to 1000 db are in excess of 100 cm s 1 the diameter of the cold domes varied from 80 to 120 km separation of large anticyclonic rings is always observed to be preceded by cyclonic eddies in the transition zone between campeche bank and the west florida shelf but only on the eastern side not every cyclonic eddy off dry tortups is associated with the separation of an anticyclonic ring some are eroded away by the florida current but they have never been observed in 10 years

investigating ground movements caused by the construction of multiple tunnels in soft ground using laboratory model tests the prediction of the ground movements above single tunnels in soft ground is well established and can be estimated using semi empirical methods based on the gaussian curve however the prediction

adjoint sensitivity of the nino 3 surface temperature to wind forcing theevolutionof sea surface temperature sst overthe easternequatorialpacific playsa significant rolein the intense tropicalair sea interaction there and is of central importance to the el nino southern oscillation enso phenomenon effects of atmospheric fields especially wind stress and ocean state on the eastern equatorial pacific sst variations are investigated using the massachusetts institute of technology general circulation model mitgcm and its adjoint model which can calculate the sensitivities of a cost function in this case the averaged 0 30 m temperature in the nino 3 region during an enso event peak to previous atmospheric forcing fields and ocean state going backward in time the sensitivity of the nino 3 surface temperature to monthly zonal wind stress in preceding months can be understood by invoking mixed layer heat balance ocean dynamics and especially linear equatorial wave dynamics the maximum positive sen sitivity of the nino 3 surface temperature to local wind forcing usually happens 1 2 months before the peak of the enso event and is hypothesized to be associated with the ekman pumping mechanism in model experiments itsmagnitudeiscloselyrelatedtothesubsurfaceverticaltemperaturegradient exhibitingstrong event to eventdifferenceswithstrong weak positivesensitivityduringla nina strongelnino events the adjoint sensitivity to remote wind forcing in the central and western equatorial pacific is consistent with the standardhypothesisthattheremotewindforcingaffectsthenino 3surfacetemperature indirectlybyexciting equatorial kelvin and rossby waves and modulating thermocline depth in the nino 3 region the current adjoint sensitivity study is consistent with a previous regression based sensitivity study derived from per turbation experiments finally implication for enso monitoring and prediction is also discussed

global ocean circulation during 1992 1997 estimated from ocean observations and a general circulation model 1 a three dimensional oceanic state is estimated for the period 1992 1997 as it results from combining large scale ocean data sets with a general circulation model at the cost of increased computational load the estimation assimilation method is chosen specifically so that the resulting state estimate is consistent with the model equations having no artificial sources or sinks to bring the model into close agreement with observations its initial temperature and salinity conditions are permitted to change as are the time dependent surface fluxes of momentum heat and freshwater resulting changes of these control vectors are largely consistent with accepted uncertainties in the hydrographic climatology and meteorological analyses the assimilation procedure is able to correct for many of the traditional shortcomings of the flow field by changing the surface boundary conditions changes in the resulting flow field are predominantly on the gyre scale and affect many features that are often poorly simulated in traditional numerical simulations such as the strengths of the gulf stream and its extension the azores current and the anticyclonic circulation associated with the labrador sea tests of the results and their consistency with prior error assumptions show that the constrained model has moved considerably closer to the observations imposed as constraints but has also moved closer to independent data from the world ocean circulation experiment not used in the assimilation procedure in some regions where the comparisons remain indeterminate not enough ocean observations are available and it is difficult to ascribe the residuals to either the model or the observations although problems remain a useful first solution to the global time dependent ocean state estimation problem has been found the estimates will continue to improve through the evolution of numerical models computer power increases more data and more efficient estimation methods

the potential vorticity flux through the yucatan channel and the loop current in the gulf of mexico 1 two year long time series of current and density structure measurements across the yucatan channel s main section allow the calculation of the time dependent potential vorticity flux between the gulf of mexico and the caribbean sea which is characterized by alternating periods of positive cyclonic and negative anti cyclonic vorticity influx periods of negative cumulative vorticity influx are related to the loop current extending into the gulf of mexico whereas periods of positive cumulative vorticity influx relate to a loop current retraction sometimes coincident with the shedding of an anti cyclonic eddy