cyclonic eddies in the gulf of mexico observations by underwater gliders and simulations by numerical model abstractcirculation in the gulf of mexico gom is dominated by the loop current lc and by loop current eddies lces that form at irregular multimonth intervals by separation from the lc comparatively small cyclonic eddies ces are thought to have a controlling influence on the lce including its separation from the lc because the ces are so dynamic and short lived lasting only a few weeks they have proved a challenge to observe this study addresses that challenge using underwater gliders these gliders data and satellite sea surface height ssh are used in a four dimensional variational 4dvar assimilation in the massachusetts institute of technology mit general circulation model mitgcm the model serves two purposes first the model s estimate of ocean state allows the analysis of four dimensional fields and second the model forecasts are examined to determine the value of glider data ces have a rossby number of about 0 2 implying that the effects of flow curvature cyclostrophy to

physical connectivity between pulley ridge and dry tortugas coral reefs under the influence of the loop current florida current system abstract the pulley ridge and dry tortugas coral reefs are among the most pristine but also fragile marine ecosystems of the continental united states understanding connectivity processes between them and with surrounding shelf and deep areas is fundamental for their management this study focuses on the physical processes related to the connectivity of these reefs unprecedented in situ time series were used at these specific reef locations together with satellite observations and numerical simulations to investigate the dynamics controlling local circulation on the southwestern florida shelf swfs under oceanic influence the approach of the loop current and florida current lc fc system to the swfs slope can induce 0 5 to 1 m s offshore flows impacting the pulley ridge and dry tortugas reefs on the other hand when the lc fc system retreats from the slope onshore flows can carry open sea waters over the coral reefs local formation of cyclonic eddies is possible near the dry tortugas reefs in the lc approach case and passage of upstream lc frontal eddies is possible in the lc retreat case offshore currents 1 m s over the swfs slope were also found during periods of anticyclonic lc eddy separation a novel finding is the shedding and northward propagation of mesoscale anticyclonic eddies from the core of the lc along the west florida shelf eddy shedding may have a broader effect on the dynamics of the shelf around the study reef areas long periods of lc fc domination over these coral reefs reaching several weeks to months are characterized by strong 1 m s along shelf currents and continuous upwelling processes which may weaken the slope stratification and bring colder deeper waters over the shelf break and toward the shallower shelf region

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

loop current frontal eddies formation along the campeche bank and impact of coastally trapped waves abstractvelocity data from a mooring array deployed northeast of the campeche bank cb show the presence of subinertial high frequency below 15 days velocity fluctuations within the core of the northward flowing loop current these fluctuations are associated with the presence of surface intensified loop current frontal eddies lcfes with cyclonic vorticity and diameter 30 days that have been linked to caribbean eddies and the lc separation process model results show that wind variability associated with winter cold surges are responsible for the emergence

numerical studies of eddy shedding in the gulf of mexico we model the eddy shedding phenomenon in the gulf of mexico using the sandia ocean modeling system in the first part of the study a parameter sensitivity study is performed using a rectangular basin two level model in particular the sensitivity of the model eddy shedding to inflow outflow conditions horizontal resolution 80 40 and 20 km and reduced gravity is examined the results are interpreted in terms of the quasi geostrophic vertical motion equation and vorticity conservation in the second part of the paper we include realistic coastlines and bathymetry in the model a horizontal resolution of 20 km is used together with 16 vertical levels various observed features of the eddy shedding are simulated by the model a boundary current which follows topographic contours is generated around the gulf because of the splitting of the flows associated with the loop current and the shed eddy this current is likely to be important in the dissipative stages of the eddies in the western gulf in addition our results suggest that higher order baroclinic modes are important in the dissipation of loop current eddies

estimated location of the seafloor sources of marine natural oil seeps from sea surface outbreaks a new source path procedure applied to the northern gulf of mexico abstract marine oil reservoirs are generally characterized on the sea surface by the presence of natural oil seeps sea surface outbreaks hereafter sso the latter are easily evidenced with synthetic aperture radar sar images because of the dampening effect that oil has on the capillary and associated small gravity waves bragg waves the sea surface outbreaks of oil seeps are offset from their source on the seabed seafloor sources sfs by hundreds meters or even kilometres this displacement all along the sea water column is a function of the upward velocity of the oil droplet size and the presence of lateral marine currents this paper proposes a vertical drift model vdm that combines both sar images to get the sso and the hydrodynamic model hycom function of the oil droplet size to estimate the sfs after oil seeps detection from sar images the vdm proceeds to a regression in time and space based on the upward velocity of the oil based on stokes law and the hydrodynamic conditions hycom to estimate the location of the seep source on the seafloor the upward velocity depends strongly on the unknown droplet size we propose herein a new vdm method named sources paths that allows to estimate the oil seeps sources on the seafloor without a priori knowledge of the oil droplet size by finding for each oil seep the seafloor sources corresponding to different diameters we call sources path the line that joins the seafloor sources for an oil seep the seafloor sources ought to be at the intersection of the maximum sources paths the methodology has been applied to the northern gulf of mexico where the locations of many prolific oil seep sites are well known a first validation of the source path procedure is that the obtained sfss correspond to the seafloor sources of oil droplets having the same diameter and seeped at different times another validation has been performed through the comparison of sfs locations and those of the outcropping shallow salt this comparison shows a good correlation and suggests that the oil seeps may be situated above the allochtonous toward autochthonous salt connections

evolution of a deep water carbonate platform upper cretaceous to pleistocene sedimentary environments on the west florida margin abstract deep water carbonates have been accumulating on the west florida margin since the early late cretaceous although the depositional style and sediment types have changed through time seven coreholes drilled by exxon record the establishment of two gently dipping aggradational ramps the first in the late cretaceous to oligocene and the second in the middle to late miocene to the present these dominantly pelagic depositional environments followed episodes of downslope transport of shallow water grains diluting background pelagic sedimentation and producing progradational ramps that built seaward this study traces the evolution of the deep water west florida sedimentary systems and contrasts the older aggradational ramp characterized by both foraminiferal and radiolarian oozes as well as volcanic ash with the late neogene ramp whose biogenic components are mainly foraminifera and coccoliths the cycles of progradation separated by periods of ramp aggradation developed as eustasy interacted with prolonged subsidence of the margin early late cretaceous as well as oceanographic changes caused by closure of the suwannee strait late oligocene to early miocene and of the isthmus of panama middle to late miocene the major transitions in environments recorded in the west florida ramp platform thus resulted from the superposition of climatic tectonic and oceanographic events on global sea level changes

instabilities and multiscale interactions underlying the loop current eddy shedding in the gulf of mexico abstracta recently developed tool the multiscale window transform along with the theory of canonical energy transfer is used to investigate the roles of multiscale interactions and instabilities

gulf of mexico circulation within a high resolution numerical simulation of the north atlantic ocean 1 the gulf of mexico circulation is examined from the results of a high resolution 1 12 north atlantic simulation using the miami isopycnic coordinate ocean model the motivation for this paper is twofold first we validate the model s performance in the gulf of mexico by comparing the model fields to past and recent observations and second given the good agreement with the observed gulf of mexico surface circulation and loop current variability we expand the discussion and analysis of the model circulation to areas that have not been extensively observed analyzed such as the vertical structure of the loop current and associated eddies especially the deep circulation below 1500 m the interval between successive model eddy sheddings is 3 to 15 months the eddy diameters range between 140 and 500 km the life span is about 1 year and the translational speeds are 2 3 km d 1 in good agreement with observations areas of high cyclonic eddy occurrence in the model are southwest of florida the loop current boundary and the western campeche bay area the cyclonic eddy diameters range between 50 and 375 km the orbital speeds range between 1 and 55 cm s 1 the translational speeds range between 0 5 and 14 km d 1 and the eddy life spans range between 1 and 3 months the vertical structure of the temperature and salinity of each modeled eddy from the moment it is shed until it disintegrates in the western gulf of mexico is in agreement with the few available observations below 1500 m deep cyclonic eddies are associated with the surface loop current anticyclones the eddy variability is consistent with rossby waves propagating westward and there is bottom intensification of the flow close to steep topography overall we show that this very high horizontal resolution isopycnic coordinate ocean model which is able to produce a quite realistic surface circulation for the north and equatorial atlantic is also able to reproduce well the smaller scale basin wide intricate dynamics such as the gulf of mexico variability

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

a test of ocean surface current mapping with over the horizon radar a two day test with a decametric over the horizon oth or ionospheric radar in virginia attempted to map the radial component of ocean surface currents over a 210 000 km sup 2 area that includes the florida straits and parts of the gulf of mexico as distant as 1500 km ionospheric motions distort and bias individual measurements but their effects are mitigated by a combination of strategies that take advantage of the different space and time scales of oceanic and ionospheric motions in addition nearby land echoes are used as zero doppler references to correct for ionospheric shifts the result is a composite picture of the florida current and ancillary surface flows with 10 15 km resolution the picture agrees quantitatively with known currents in the region but reveals dynamical features with new detail concurrent sea surface topography in the gulf of mexico derived using tandem altimetric observations from the topex poseidon and ers 1 satellites confirms that a region where the oth radar measures a southwestward current greater than 1 m s sup 1 coincides with the confluence of the tortugas gyre and the gulf of mexico loop current these results suggest that consistent surface current maps can be constructed by using oth radar to repeatedly interrogate a region of interest perhaps over several days

pliocene shallow water paleoceanography of the north atlantic ocean based on marine ostracodes abstract middle pliocene marine ostracodes from coastal and shelf deposits of north and central america and iceland were studied to reconstruct paleotemperatures of shelf waters bordering portions of the western boundary current system including the gulf loop current florida current gulf stream and north atlantic drift factor analytic transfer functions provided pliocene august and february bottom water temperatures of eight regions from the tropics to the subfrigid the results indicate 1 meridional temperature gradients in the western north atlantic were less steep during the pliocene than either today or during late pleistocene isotope stage 5e 2 tropical and subtropical shelf waters during the middle pliocene were as warm as or slightly cooler than today 3 slightly cooler water was on the outer shelf off the southeastern and mid atlantic coast of the u s possibly due to summer upwelling of gulf stream water 4 the shelf north of cape hatteras north carolina may have been influenced by warm water incursions from the western edge of the gulf stream especially in summer 5 the northeast branch of the north atlantic drift brought warm water to northern iceland between 4 and 3 ma evidence from the iceland record indicates that cold east greenland current water did not affect coastal iceland between 4 and 3 ma 6 middle pliocene north atlantic circulation may have been intensified transporting more heat from the tropics to the arctic than it does today

an analysis of loop current frontal eddies in a atlantic ocean model simulation abstractthe loop current frontal eddies lcfes refer to cyclonic cold eddies moving downstream along the outside edge of the loop current in the eastern gulf of mexico they have been observed by in situ measurements and satellite imagery mostly downstream of the campeche bank continental shelf their evolution simulated by a primitive equation and 37 level atlantic ocean general circulation numerical model is described in detail in this study some of the simulated lcfes arise with the passage through the yucatan channel of a caribbean anticyclonic eddy as weak cyclones with diameters less than 100 km near the yucatan channel they then grow to fully developed eddies with diameters on the order of 150 200 km while moving along the loop current edge modeled lcfes have a very coherent vertical structure with isotherm doming seen from 50 to 1000 m depth the caribbean anticyclone and lcfe are two predominant features in this numerical model simulation which account for 22 and 10 respectively

climatology of ocean features in the gulf of mexico using satellite remote sensing data a climatology of various ocean features in the gulf of mexico gom was developed using the combination of satellite remote sensing and in situ data that spanned periods as long as 32 years twelve separate statistics were created some of which described characteristics of the loop current while others are involved with warm core rings that separate from the loop current and cold core rings these statistics examined the frequency with which the loop current was found in the gom the orientation of the loop current the frequency of intrusion of loop current water onto the west florida shelf and into the gom common water region ring separation period from the loop current ring dissipation ring speed ring path frequency of ring water in the western gom and the frequency of warm and cold core rings wcrs and ccrs respectively in the gom the results indicate that ccrs were principally responsible for mass and heat redistribution in the eastern gom egom and wcrs are responsible for mass and heat redistribution in the western gom wgom the average period for wcr separation from the loop current was 11 months and the range from 5 to 19 months wcrs moved through the wgom most often using the central path i e their trajectory was found between 24 and 26 n latitude and they decreased to about 55 of their initial size when they reach the western wall of the gom ccrs were most often found in the egom and their frequency of occurrence in the egom surpassed that of wcrs anywhere in the gom

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

an investigation of the circulation of the gulf of mexico empirical search and inverse techniques were used to reanalyze historical hydrographic data obtained in the gulf of mexico february 12 to march 31 1962 from these data eight transects which provide basin wide coverage of the gulf were constructed on the basis of water properties the circulation of the gulf of mexico was characterized as a three layer mass conservative system along most sections an empirical search in density coordinates was sufficient to obtain an optimum reference level that balanced the transport in the three layers an inverse correction was necessary to obtain a mass balance for those sections that crossed the loop current and mesoscale eddies the density of the optimum reference level 1 32 17 obtained from this analysis corresponds approximately to the bottom of the antarctic intermediate water layer that exists in the gulf of mexico by using this optimum reference level total velocity profiles at specific locations in the gulf of mexico were obtained taken together these yielded a description of the winter circulation of this region in general the large scale circulation consists of a clockwise anticyclonic gyre which is most prominent in the upper 500 m eastward and westward transports associated with the gyre are approximately equal at about 5 106 m3 s 1 variations to this flow are provided by the loop current in the eastern gulf and a cyclonic eddy in the northwestern gulf transports obtained for these circulation features are approximately 30 106 and 8 106 m3 s 1 respectively which are in agreement with values obtained from other hydrographic surveys in the gulf of mexico

eddy statistics from lagrangian drifters and hydrography for the northern gulf of mexico slope 1 cyclones and anticyclones on the northern gulf of mexico slope have been statistically characterized using upper layer drifter orbits and repeated hydrographic surveys a total of 243 slope eddy drifter orbits 151 cyclones and 92 anticyclones were analyzed in terms of size mean radius and eccentricity and rotation period orbits in large loop current anticyclones were excluded eddies of both signs scale approximately as the baroclinic radius of deformation with relatively smaller radii on the upper slope where water depths are less than 1000 m the median radius for all eddies was 30 km and median periods were 12 and 13 5 days for cyclones and anticyclones respectively anticyclones also tend to be more circular than cyclones relative vorticity maps were constructed for seven hydrographic surveys which mapped the slope at 4 5 month intervals a total of 26 cyclones and 15 anticyclones had statistics that were consistent with drifter orbit analyses the surveys indicate that at any one time between 2 and 5 cyclones and 1 and 3 anticyclones may be present both drifters and surveys indicate that cyclones have a slight numerical dominance

carbonate mineral cycles generated by foraminiferal and pteropod response to pleistocene climate west florida ramp slope carbonate ramps are gently sloping depositional surfaces where shallow water coarse grained facies pass basinward into fine grained deep water sediments with no abrupt change in slope the objectives of this study are i to integrate the depositional processes recorded in the pleistocene stratigraphy of the west florida outer ramp into a palaeoclimatic and palaeoceanographic framework for the eastern gulf of mexico and ii to examine the origin of mineralogical and sedimentary cycles in the light of pteropod and planktonic foraminiferal populations corresponding to climatic oscillations aragonitic pteropod rich sediments with large amounts of insoluble residue occur in sediments deposited during glacial intervals sandy calcitic sediments with abundant planktonic foraminifera accumulate during interglacials these cycles reflect variations in biological productivity of pelagic pteropods and planktonic foraminifera rather than preferential dissolution of either aragonitic or calcitic fractions species assemblages suggest that the productivity cycles are linked to changes in upwelling intensity at the margins of the loop current and variations in water mass salinities as well as terrigenous dilution from the mississippi delta these cycles are the response to pleistocene glacial interglacial oscillations controlled by milankovitch orbital parameters although the organisms contributing to deep water carbonate environments have changed through geological time facies patterns as well as sedimentary textures and structures identified in the west florida sediments provide criteria for recognition of ancient ramps an understanding of the processes on a modern ramp slope such as west florida may prove valuable in palaeoclimatic and palaeoenvironmental analysis of epicontinental carbonate sequences and ramps in the rock record

morphology of pyroclastic cones and tectonics the relationships between morphology and spatial distribution of 1315 quaternary pyroclastic cones and coeval faulting of the volcanic substrate are analyzed in the following regions with different structural settings tepic rift mexico ethiopian rift mexican volcanic belt canary archipelago and mount etna field data and analog experiments of tephra cone emplacement and collapse enable the definition of a number of parameters which can be used to infer the geometry of the fracture feeding the magma to a pyroclastic cone the strike of the feeding plane is directly related to 1 the elongation of cone base and crater 2 the location of depressions on the crater rim and 3 the alignment of pyroclastic cones in relation to a given vent spacing in addition the strike and dip of faults affect the direction of cone breaching these relationships are valid for volcanic substrate topographic surfaces with an inclination of less than 9 and are especially sensitive to fault escarpment and cone height lava and cone density and fault orientation with respect to the dip of the volcanic substrate topography relations 1 and 2 become more pronounced for regions undergoing extensional tectonics where edifices also have a larger dimension whereas breaching in the direction of the fault dip is more widespread in regions under extension breaching along the fault strike as well as the coincidence between fault strike and vent alignment are more frequent in regions with transcurrent or transtensional tectonics

gulf stream meanders in the south atlantic bight 1 scaling and energetics as the gulf stream flows along the outer edge of the southeastern united states continental shelf it meanders on and offshore creating frontal eddies which influence the exchange of water between the shelf and the adjacent atlantic ocean on weekly timescales the dynamics controlling the development of such features in this region the open quotes south atlantic bight close quotes or sab is the subject of this pair of papers in the present paper the authors provide the background on the subject summarize the length time and velocity scales associated with these features and discuss meander energetics as simulated by a numerical model the scaling indicates that significant ageostgrophic dynamics may be crucial to the development of these flows and that the semigeostrophic equations may provide the simplest description of the system these nonlinear dynamics may permit complex interactions among meander modes and with topography resulting in the observed behavior of the gulf stream in the sab the princeton ocean model was tuned for conditions which prevail in the southern south atlantic bight and idealized numerical simulations of gulf stream meanders and associated frontal eddies were performed the system was found to be sensitive to both the amplitude and period of a small perturbationmore applied at the southern boundary the energetics indicate that the development of these features is controlled by a mixture of both baroclinic and barotropic instabilities of the mean gulf stream flow tantalizing hints of a period doubling phenomenon are present in the energy conversion time series 47 refs 12 figs 4 tabs less

near surface currents in desoto canyon 1997 99 comparison of current meters satellite observation and model simulation this study evaluates a data assimilated model simulation of near surface circulation in desoto canyon dsc gulf of mexico with emphasis on analyzing moored current meter observations and comparing them with satellite data and model results the study period is for two years from april 1997 to april 1999 the model results are from a high resolution gulf of mexico model forced by analyzed wind and surface heat flux two types of data are used to deduce near surface circulation moored current meters at 13 locations in the dsc and satellite sea level anomaly the moored currents are mapped through multivariate objective analysis to produce surface currents and surface geopotentials against which satellite and model derived sea surface heights and geostrophic currents are compared coupled patterns between the observations model results and satellite data are obtained using the singular value decomposition svd analysis there are two dominant modes a single eddy mode in which currents are concentrated at the foot of the canyon and an eddy pair mode in which one eddy is at the foot of the canyon and the other a counterrotating eddy is over the head of canyon mode 1 appears to be associated with the mesoscale eddy traveling around the loop current crest and trough and mode 2 is associated with the intrusion of loop current crest and trough over the west florida shelf the observed and model currents are in good agreement about the means and variances the model currents also appear to be well constrained by the steep topography however the model velocity field contains only the first mode the satellite derived velocity field on the other hand contains both the first and second modes though the satellite field does not adequately resolve the velocity structures over the slope

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

altimeter data and geoid error in mesoscale ocean prediction some results from a primitive equation model a primitive equation ocean model has been applied to the study of mesoscale ocean dynamics and prediction using sea surface height information derived from a satellite borne altimeter results from a model of the gulf of mexico were directly compared with the altimeter data from geos 3 and seasat reported by marsh et al 1984 and in situ hydrographic data analyzed by maul and herman 1985 in the eastern gulf the amplitude and position of relative maxima of sea surface height variability were found to be similar for model altimeter and in situ data in the central gulf the model and the altimeter derived sea surface height variability maps were similar but differed considerably from the in situ results the mean sea surface in the model and from the in situ data also agreed well in the eastern gulf but there was little agreement in the central gulf while there is no geoid adequate for determining an independent altimetric estimate of the mean dynamic height of the sea surface in the gulf by differencing the geoid with the altimeter derived mean sea surface the model dynamic mean sea surface can be subtracted from the mean surface of marsh et al 1984 to obtain a new estimate of the gulf geoid which may be the best geoid available in that region for several years a benchmark experiment truth was integrated to statistical equilibrium and compared with results from four experiments in which the model was initialized with fields modified from archived benchmark data the experiments differed only in the initialization fields each experiment was integrated for 100 days with inflow transport remaining constant throughout the integration the idealized experiments were initialized geostrophically 1 with the exact sea surface and pycnocline height fields 2 with only the exact sea surface heights and a pycnocline assumed to compensate it such that the deep pressure perturbations vanished 3 just as in case 2 but with a geoid error component added on small spatial scales and 4 just as in case 3 except the geoid error model included an additional contribution in strong geoid gradient regions the sequence of four numerical experiments showed that 1 geostrophic initialization with exact sea surface and pycnocline height information provided accurate forecasts to 100 days 2 even when only the sea surface height information was provided to the numerical model for geostrophic initialization and deep pressure perturbations assumed to vanish at the initial time the forecasts were superior to persistence or climatology over the 100 day forecast period and 3 errors in the geoid on spatial scales comparable to the grid resolution of the model did not seriously degrade the forecast even in dynamically active regions with large gradients in the geoid height where instability processes were observed to occur

the influence of loop current perturbations on the formation and evolution of tortugas eddies in the southern straits of florida large cyclonic eddies on the northern edge of the florida current are the dominant mesoscale features within the southern straits of florida the most prominent of these features is a quasi stationary eddy that forms near the dry tortugas our observations compiled from 3 years of advanced very high resolution radiometer measurements in the straits of florida and gulf of mexico demonstrate a strong relationship between the generation of anticyclonic rings from the gulf of mexico loop current and the evolution of tortugas eddies within the southern straits of florida in six cases tortugas eddies evolve from cyclonic frontal eddies which form along the boundary of the loop current the eddies remain stationary near the dry tortugas until they are impacted by an approaching loop current frontal eddy the length of time an eddy spends near the dry tortugas is increased when the loop current sheds an anticyclonic ring the involvement of a loop current frontal eddy in the ring shedding process results in a delay in its and hence the tortugas eddy s downstream propagation results suggest that the lifetime of a tortugas eddy can be as long as 140 days when a ring shedding event occurs or as short as 50 days in the absence of any ring shedding events upon entering the straits of florida the tortugas eddies are deformed by the narrowing topography and shrink to approximately 55 of their original size as they propagated downstream the shrinking of these eddies is accompanied by an accelerated translation from 5 km d in the western straits of florida to 16 km d in the east

cyclonic activity in the eastern gulf of mexico characterization from along track altimetry and in situ drifter trajectories abstract the shedding sequence of the loop current lc inside the gulf of mexico gom is strongly influenced by cyclonic frontal eddies around its edge along track altimetry data analyzed based on a wavelet decomposition to provide estimates of individual cyclones diameter amplitude and relative vorticity and in situ surface drifter data from the global drifter program are used to investigate the cyclonic activity in the eastern gulf of mexico where the lc extends and retracts by analyzing this 20 year long 1992 2011 combined set of observation data records we were able to complement previous findings to confirm results from modeling studies and to provide new insights on the lc frontal dynamics drifter data indicate for the first time that loop current frontal eddies lcfes are in solid body rotation close to their core this property makes relative vorticity the most robust diagnostic from along track altimetry for characterizing lcfes in the eastern gom based on consistent comparisons with drifter data both data sets are complementary for describing the lcfes regional variability lcfes observed in the deep southeastern gom show intense relative vorticity but they are not frequently observed the study of an unprecedented long drifter trajectory suggests that they are not intensified locally this implies that among lcfes coming from the northern gom only intense ones reach the deep southeastern gom the observation datasets provide for the first time quantitative evidences of processes so far only identified with models lcfes are intensified when they are advected over the mississippi fan in the northern gom a small area north of campeche bank shows intense lcfe activity the altimetry and drifter data confirm and complement results from more limited datasets lcfes forming the tortugas eddies at the entrance of the straits of florida are the most intensely observed lcfes in altimetry coming from the gom interior they can be modified in size and intensity just before or during their stay in the dry tortugas area whereas they were long considered to be modified only after they were advected in the straits of florida a single drifter trajectory illustrates in detail the erosion of a lcfe in the southeastern gom presumably under the influence of the lc which leads to the re arrangement of vorticity and the formation of a distinct lcfe just upstream the dry tortugas area the study also confirms that lcfes have diameters of 80 120 km generally larger east and north of the lc they tend to stay for long periods in the northeastern gom and thus may undergo vortex merging with incoming eddies as previously noted on individual episodes altimetry reveals that the largest lcfes reside in the central eastern gom in a location where they are known to block the lc extension however our long altimetry dataset shows that these large eddies are not always involved in such lc blocking finally this study led to improvements in data treatment for both along track altimetry and drifter trajectories the wavelet approach used to derive eddy characteristics from along track altimetry allows robust estimates of the eddy relative vorticity the drifter dataset has been extended to include data from drifters even after they lost their drogue the latter data treatment can be applied in areas of moderate winds

cyclonic eddies northeast of the campeche bank from altimetry data eight cyclonic eddies were identified near the western edge of the loop current at the northeast shelf break of the campeche bank through topex poseidon sea surface height anomaly data from january 1993 through march 2000 the eddies migration and their lifecycle are described the formation of the eddies appears to be related to the dynamics of the loop current because the timing of their generation corresponds to the last stage of the anticyclone shedding from the loop current the cyclones intensify while moving slightly to the northwest along the shelf break of the campeche bank later some cyclones are observed to move northward toward the mississippi shelf break the cyclones remain next to the campeche bank south of 268n from 1 3 to 9 6 months later some of them move northward and strengthen by merging with other eddies extending their life span the eddies vertical structure is analyzed with hydrographic data and the connection between the formation of the cyclones and the evolution of the loop current is further described using sea surface temperature images

morphological adjustments in a meandering reach of the middle yangtze river caused by severe human activities abstract in the past 50 years the shishou reach in the middle yangtze river underwent significant channel evolution owing to the implementation of an artificial cutoff the construction of bank revetment works and the operation of the three gorges project tgp based on the measured hydrological data and topographic data the processes of channel evolution in this reach were investigated mainly from the adjustments in planform and cross sectional geometries the variation in planform geometry obtained in this study indicates that i the artificial cutoff at zhongzhouzi caused the river regime to adjust drastically with the mean rate of thalweg migration at reach scale of 42 0 m a over the period 1966 1975 ii then the effect of this artificial cutoff reduced gradually with the mean migration rate decreasing to 40 m a owing to the occurrence of high water levels in 1993 1998 and iii the average annual rate of thalweg migration decreased to 29 3 m a because of the impacts of various bank protection engineering and the tgp operation during the period 2002 2015 however remarkable thalweg migration processes still occurred in local regions after the tgp operation which resulted in significant bankline migration in local reaches of beimenkou shijiatai and tiaoxiankou in addition the adjustments of bankfull channel geometry were investigated at section and reach scales after the tgp operation calculated results show that lateral channel migration in this reach was restricted by various river regulation works and that channel evolution was mainly characterized by an increase in bankfull depth and cross sectional area empirical relationships were developed between the reach scale bankfull dimensions depth and area the bankfull widths at specified sections and the previous 5 year average fluvial erosion intensity during flood seasons with high correlation degrees between them being obtained

feature modeling approach to simulating loop current frontal eddies abstract loop current frontal eddies lcfe in the gulf of mexico are simulated with a regional configuration of the princeton ocean model using a feature oriented initialization technique the initialization procedure is based on a prior investigation of stability characteristics of the loop current lc zonal channel experiments conducted with a multi layer intermediate equations model allowed to identify conditions necessary for formation and growth of frontal eddies the simulations were able to reproduce key features of lcfe topography interaction in the desoto canyon region observed during the eddy intrusion study

observations of intermittent deep currents and eddies in the gulf of mexico 1 intense currents having speeds between 10 and 40 cm s 1from 1000 m below the surface to the bottom have been measured in the loop current lc region and in the western gulf of mexico wgm the observations come from moored current meters sampling from the near surface to the bottom at 3300 3500 m and from august 2008 to august 2010 ten intermittent intensified currents are documented these events last 10 to 30 days and take place in the region just between the surface intensified anticyclonic cyclonic features as deduced from altimetry and measured currents in the wgm they occur between the cores of anticyclone cyclone pairs in the eastern gulf of mexico egm they occur in the loop current edge between its anticyclonic circulation and a neighboring cyclone during each event the analysis shows an increase in the barotropic contribution to the current in the loop current region these events are often associated with intensification of cyclonic vorticity in the deep layer