subsurface energetics of the gulf stream near the charleston bump abstract the energy budgets of the eddies and the mean flow in the gulf stream near a topographic feature known as the charleston bump are computed first we consider these results in the context of the amplification hypothesis for the development of gulf stream meanders according to this hypothesis the finite amplitude gulf stream fluctuations observed offshore of onslow bay are the result of the destabilizing effect of the bump on the stream the present dataset was obtained both immediately upstream and downstream of the bump and the results of our analysis suggest 1 immediately south of the charleston bump the eddies perform net work on the gulf stream at a rate of 1 02 66 10 2 ergs cm 3 s 1 by transporting momentum offshore 2 the net work performed by the eddies south of the bump is not used locally to accelerate the mean rather it is exported to the rest of the ocean at a rate of 1 58 1 39 10 2 ergs cm 3 s 1 3 in spite of the net work performed by the eddies south of the bu

five years of florida current structure and transport from the royal caribbean cruise ship explorer of the seas 1 using ship of opportunity platform explorer of the seas five years of full depth velocity data have been collected across the florida straits at 26 n between may 2001 and may 2006 the mean transport of the florida current was 31 0 4 0 sv this compares to a mean transport of 32 4 3 2 sv inferred from cable voltages at 27 n over the same period implying an average 1 4 sv transport into the straits through the northwest providence channel the climatological core of the florida current is 170 cms 1 and is positioned at 79 8 w about 10 km east of the shelf break the largest variability in velocity occurs over the shelf and shelf break and is likely related to shelf waves a secondary maximum occurs across much of the straits over the top 100 m of the water column and may be associated with wind events the annual cycle of florida current transports has a range of 4 7 sv with a maximum in may june july and a minimum in january the difference between the summer and winter current structure appears as a first baroclinic mode with zero crossing at 150 m the maximum difference is about 15 cms 1 at the surface and is centered just offshore of the mean current core on interannual timescales low pass filtered explorer and cable transports show similar downward trends between 2002 and 2005 but diverge over the last year or so of the record

ocean and atmosphere storm tracks the role of eddy vorticity forcing abstract signatures of eddy variability and vorticity forcing are diagnosed in the atmosphere and ocean from weather center reanalysis and altimetric data broadly covering the same period 1992 2002 in the atmosphere there are localized regions of eddy variability referred to as storm tracks at the entrance of the storm track the eddies grow providing a downgradient heat flux and accelerating the mean flow eastward at the exit and downstream of the storm track the eddies decay and instead provide a westward acceleration in the ocean there are similar regions of enhanced eddy variability along the extension of midlatitude boundary currents and the antarctic circumpolar current within these regions of high eddy kinetic energy there are more localized signals of high eady growth rate and downgradient eddy heat fluxes as in the atmosphere there are localized regions in the southern ocean where ocean eddies provide statistically significant vorticity forcing which acts to accelerate the mean flow

effect of bathymetric curvature on gulf stream instability in the vicinity of the charleston bump abstract the effect of the isobathic curvature on the development and evolution of gulf stream frontal waves meanders and eddies in the vicinity of the charleston bump a topographic rise on the upper slope off charleston south carolina referred to as cb hereinafter is studied using the hybrid coordinate ocean model hycom baroclinic and barotropic energy transfers from the gulf stream to its meanders and eddies that appear as cold and warm anomalies are computed for four different cases in case i the curvature of the isobaths is artificially reduced and the cb is removed from the bathymetry in this simulation the simulated gulf stream meanders were barely noticeable in the study region energy transfer from the gulf stream to meanders and eddies was negligible in case ii the curvature of the isobaths was the same as in case i but a bump of the scale of the cb was added to the bathymetry in this simulation gulf stream meanders were amplified while passing over the cb in case iii the cb w

gulf stream meander propagation past cape hatteras the propagation and growth characteristics of gulf stream meanders past the stream s separation point at cape hatteras are analyzed using yearlong time series from a mooring program sponsored by the minerals management service which included moorings imbedded in the gulf stream cyclonic flank both upstream south and downstream north of cape hatteras in the upstream region energetic meanders of 3 8 day period 180 380 km wavelength propagate downstream along the gulf stream at speeds of 40 55 km day 21 this variability decays almost completely across the gulf stream separation with growth in lower frequency variability 30 120 day in the downstream direction wavelength and phase speed in the 3 8 day band are strong functions of frequency with increasing phase speed for increasing wavenumber phase speeds upstream from cape hatteras and across the gulf stream separation point are faster for a given wavenumber than downstream from cape hatteras in keeping with prior published estimates at the upstream end of the study site both baroclinic and barotropic mechanisms contribute to the decay of 3 8 day meanders and growth of lower frequency 30 120day variability in the downstream direction at the downstream end of the study region the reverse holds with both baroclinic and barotropic mechanisms contributing to growth of 3 8 day meanders and decay of lowerfrequency 30 120 day variability

observations of gulf stream induced and wind driven upwelling in the georgia bight using ocean color and infrared imagery ocean color and infrared imagery from aircraft and satellite sensors are combined with in situ measurements of currents chlorophyll temperature salinity coastal winds and sea level to study upwelling events in the georgia bight where the gulf stream and continental shelf waters strongly interact these interactions were observed over an 8 day period in april 1980 during which five independent upwellings occurred the upwellings included a nearshore wind driven upwelling enhanced by topographic effects three gulf stream filament induced upwellings and what appears to have been a gulf stream meander induced event the chlorophyll distributions as inferred from the imagery are found to be reliable tracers which indicate filamentary circulation and propagation and advective routes by which nearshore water moves offshore the propagation of two of the filaments and the meander are studied in detail using the imagery and mooring array temperature time series both techniques yield nearly identical results for the phase speeds of each event there is evidence that one of the filaments accelerated as it entered into the charleston bump area where the gulf stream deflects offshore the other filament exhibited a steady deceleration as it moved past cape canaveral and eventually lost any semblance of wave motion also includedmore are data from april 1979 which offer corroborating evidence of filamentary structure and circulation intercomparisons of field measurements and the nimbus 7 coastal zone color scanner estimates of surface pigment concentrations show excellent agreement over the range of 0 1 7 0 mg m sup 3 54 references 22 figures 6 tables less

subsurface energetics of the gulf stream cyclonic frontal zone off onslow bay north carolina it has been shown with the use of 4 month long time series of velocity temperature and conductivity that fluctuating kinetic and potential energy was converted into kinetic and potential energy of the mean flow following a fluid particle in the subsurface gulf stream cyclonic frontal zone off onslow bay north carolina during early 1979 this result agrees well with earlier measurements made in the surface layer off onslow bay these flux calculations represent an important step in verifying the direction of the net cross stream energy flux within the stream off onslow bay according to an hypothesis presented for the growth and decay of gulf stream meanders along the continental margin of the southeastern united states onslow bay is an area of decreasing meander amplitude the direction of the energy conversion from meanders to the mean flow determined from our calculations is consistent with this hypothesis relatively low velocity covariances were found to be associated with relatively small transfers of kinetic energy during a period of low meander activity this finding supports the notion that meanders play a significant role in the energy transformation processes the presence of such quiet periods may indicate a low frequency modulation of gulf stream meander activity

the average distribution of volume transport and potential vorticity with temperature at three sections across the gulf stream abstract average cross sections of downstream velocity and temperature obtained using pegasus current profiles at three locations along the gulf stream have been partitioned into 2 5 c temperature intervals to examine the distribution of transport increase versus temperature between the two southern sections 27 and 29 n and off cape hatters 73 w between 27 and 29 n the total transport of the florida current over the sections increased only by about 3 106 m3 s 1 3 sv but the current broadens by about 50 by cape hatteras the transport has increased nearly three fold to 93 7 sv of which two thirds of the increase is contained in the 19 5 17 0 c 18 layer and in water colder than the 7 c still temperature found at 27 n cross stream distributions of layer transport potential vorticity and thickness are estimated at each section the 10 10 7 m 1 s 1 contour tends to be a boundary independent of temperature between the region of relatively uniform layer potential vorticity on the a

submesoscale instability and generation of mesoscale anticyclones near a separation of the california undercurrent abstractthe california undercurrent cuc flows poleward mostly along the continental slope it develops a narrow strip of large negative vertical vorticity through the turbulent boundary layer and bottom stress in several downstream locations the current separates aided by topographic curvature and flow inertia in particular near point sur ridge south of monterey bay when this happens the high vorticity strip undergoes rapid instability that appears to be mesoscale in eddy resolving simulations but is substantially submesoscale with a finer computational grid the negative relative vorticity in the cuc is larger than the background rotation f and ertel potential vorticity is negative this instigates ageostrophic centrifugal instability the submesoscale turbulence is partly unbalanced has elevated local dissipation and mixing and leads to dilution of the extreme vorticity values farther downstream the submesoscale activity abates and the remaining eddy motions exhibit an upscale organizati

steep shelf stabilization of the coastal bransfield current linear stability analysis abstractin situ measurements obtained during the 2010 coupling cruise were analyzed in order to fully characterize the velocity structure of the coastal bransfield current an idealized two layer shallow water model was used to investigate the various instability processes of the realistic current along the coastal shelf particularly studied is how the topographic parameter to ratio between the shelf slope and the isopycnal slope of the surface current impacts the growth and the wavelength of the unstable perturbations for small bottom slopes when the evolution of the coastal current is controlled by the baroclinic instability the increase of the topographic parameter to yields a selection of smaller unstable wavelengths the growth rates increase with small values of to for larger values of to to 10 which is relevant for the coastal bransfield current the baroclinic instability is strongly dampened and the horizontal shear instability becomes the dominant one in this steep shelf regime the

numerical simulation of flow around a tall isolated seamount part i problem formulation and model accuracy abstract a sigma coordinate ocean circulation model is employed to study flow trapped to a tall seamount in a periodic f plane channel in part i errors arising from the pressure gradient formulation in the steep topography strong stratification limit are examined to illustrate the error properties a linearized adiabatic version of the model is considered both with and without forcing and starting from a resting state with level isopycnals the systematic discretization errors from the horizontal pressure gradient terms are shown analytically to increase with steeper topography relative to a fixed horizontal grid and for stronger stratification as measured by the burger number for an initially quiescent unforced ocean the pressure gradient errors produce a spurious oscillating current that at the end of 10 days is approximately 1 cm s 1 in amplitude the period of the spurious oscillation about 0 5 days is shown to be a consequence of the particular form of the pressure gradient terms in th

decreased surface salinity in the sea of okhotsk during the last glacial period estimated from alkenones 1 studies of sediment cores from the sea of okhotsk which is characterized by seasonal sea ice have shown a large variability of sea ice indicators during the glacial interglacial cycles in this study we apply the relative abundance of the c37 4 alkenone to total c37 alkenones c37 4 as a molecular indicator of salinity and water masses to further investigate surface oceanographic condition in the sea of okhotsk in the glacial period we found a large fluctuation of c37 4 4 35 with higher values 20 35 during the last glacial period and lower values 8 during warm periods suggesting a decreased surface salinity in the glacial period the variation of c37 4 was found to be consistent with the ice rafted debris ird in the sediment core correlation coefficient r2 between c37 4 and ird 0 72 this suggests that the duration of seasonal sea ice was longer in the glacial period than today the lowered surface salinity in the glacial might also have been seriously affected by the close off of the shallow soya strait which currently transports massive volumes of saline water from the sea of japan to the sea of okhotsk

a note on the charleston gyre the deflection of the gulf stream caused by a topographic feature the charleston bump located offshore of savannah georgia results in a quasi stationary cyclonic eddy the charleston gyre which is situated over the continental slope east of charleston and cape romain occasionally the upwelling associated with this eddy produces an enhancement in the surface layer primary production that is great enough to be detected by the nimbus 7 coastal zone color scanner czcs in this note a czcs image with simultaneous hydrography current and wind observations is presented that documents an unusual manifestation of the gyre in addition to the czcs image a seasat synthetic aperture radar sar image is included that clearly indicates the presence of the eddy adjacent to the gulf stream front

a model of gulf stream frontal instabilities meanders and eddies along the continental slope abstract for a simplified model of the gulf stream front along a vertical walled continental slope of a constant depth ocean basin the dynamics governing frontal instabilities meanders and eddies depend primarily on i l0 r0 the ratio of the cross stream distance of the stream axis from the slope l0 to the roosby radius of deformation l0 and ii h0 h the ratio of the depth l0 of upper layer of light water to ocean basin depth h a nonlinear time dependent three dimensional model is used to study this interdependency two different types of meander solutions are found depending on the value of the nondimensionalized initial available potential energy per unit alongfront length and per unit rossby area hr0 ape l0 r0 h0 h 2 for small ape the meanders and their associated cyclones are slope bounded as they propagate downstream this solution has characteristics similar to observed gulf stream meanders south of a topographic feature at 31 5 n the so called charleston bump on

submesoscale cold filaments in the gulf stream abstracta set of realistic very high resolution simulations is made for the gulf stream region using the oceanic model regional oceanic modeling system roms to study the life cycle of the intense submesoscale cold filaments that form on the subtropical gyre interior wall of the gulf stream the surface buoyancy gradients and ageostrophic secondary circulations intensify in response to the mesoscale strain field as predicted by the theory of filamentogenesis it can be understood in terms of a dual frontogenetic process along the lines understood for a single front there is however a stronger secondary circulation due to the amplification at the center of a cold filament filament dynamics in the presence of a mixed layer are not adequately described by the classical thermal wind balance the effect of vertical mixing of momentum due to turbulence in the surface layer is of the same order of magnitude as the pressure gradient and coriolis force and contributes equally to a so called turbulent therm

shelf impact on buoyant coastal current instabilities abstractthe impact of shelf slope on the linear stability of buoyant coastal currents and on the nonlinear formation of coastal meanders and eddies is investigated the authors consider a simplified two layer stratification in cylindrical geometry where a buoyant surface current flows along the coast above a denser water with a flat bottom or steep shelves simulations were performed using the nucleus for european modelling of the ocean nemo ocean global circulation model the initial state of these simulations was defined according to laboratory experiments performed in the same configuration comparisons between laboratory and numerical results highlight the role of momentum diffusion and of the initial perturbations amplitude the authors results confirm that the topographic parameter to ratio between the shelf slope and the isopycnal slope of the current is the relevant parameter to quantify the shelf impact on the linear and nonlinear dynamics of the surface current when the evolution of the b

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

mixed layer instabilities and restratification abstract the restratification of the oceanic surface mixed layer that results from lateral gradients in the surface density field is studied the lateral gradients are shown to be unstable to ageostrophic baroclinic instabilities and slump from the horizontal to the vertical these instabilities which are referred to as mixed layer instabilities mlis differ from instabilities in the ocean interior because of the weak surface stratification spatial scales are o 1 10 km and growth time scales are on the order of a day linear stability analysis and fully nonlinear simulations are used to study mlis and their impact on mixed layer restratification the main result is that mlis are a leading order process in the ml heat budget acting to constantly restratify the surface ocean climate and regional ocean models do not resolve the scales associated with mlis and are likely to underestimate the rate of ml restratification and consequently suffer from a bias in sea surface temperatures and ml depths in a

topographic control of basin and channel flows the role of bottom pressure torques and friction the topographical control of western boundary currents within a basin and zonal jets in a channel is investigated in terms of the potential vorticity pv and barotropic vorticity bv the curl of the depth integrated velocity budgets using isopycnic adiabatic wind driven experiments along the western boundary the wind driven transport is returned across latitude lines by the bottom pressure torque while friction is only important in altering the pv within an isopycnic layer and in allowing a closed circulation these contrasting balances constrain the geometry of the flow through integral relationships for the bv and pv for both homogenous and stratified basins with sloping sidewalls the northward subtropical jet separates from the western wall and has opposing frictional torques on either side of the jet which cancel in a zonal integral for bv but alter the pv within a layer streamline in a channel with partial topographic barriers the bottom pressure torque is again important in returning wind driven flows along western boundaries and in transferring bv from neighboring wind driven gyres into a zonal jet the depth integrated flow steered by topography controls where the bottom friction alters the pv which can lead to different pv states being attained for separate subbasins along a channel

why western boundary currents in realistic oceans are inviscid a link between form stress and bottom pressure torques it is shown that wind stress curl is balanced by bottom pressure torque in a zonal integral over any strip wide enough to smooth out the effect of nonlinear terms typically about 3 of latitude the derivation is completely general as long as the zonal wind stress is balanced by form stress at each latitude as is known to be the case in the ocean this implies that viscous torques are not important in western boundary currents their place being taken by bottom pressure torques the prediction is confirmed in the context of a global eddy permitting numerical ocean model this link between form stress and bottom pressure torques makes it easier to consider southern ocean dynamics and subtropical gyre dynamics in the same conceptual framework with topographic interactions being important in both cases

a comparison of surface eddy kinetic energy and reynolds stresses in the gulf stream and the kuroshio current systems from merged topex poseidon and ers 1 2 altimetric data analyses of surface eddy kinetic energy eke inferred from 5 years of merged topex poseidon and ers 1 2 altimetric data are presented in the gulf stream gs and the kuroshio ks current systems focusing on anisotropy and eke seasonal interannual and long term variations as well as reynolds stresses for both gs and ks a descriptive analysis of the eke field shows that it is anisotropic along the path of the currents and assesses the close relationship between the spatial distribution of eke high levels and bottom topography a striking ocean feature is found in the gs shaped as a zonal double blade structure in the eke field centered at 37 n 71 5 w that likely corresponds to a regular and permanent lateral displacement of the mean path of the current at this geographical location maps of eke seasonal means for years 1993 1996 and 1997 provide a detailed description of the surface variability meanders pinched off eddies etc and show strong interannual variations in the ks eke monthly mean changes in the ks reveal a well marked seasonal cycle during the first 3 years 1993 1995 with eke peaking in july august this is followed by a constant increase of its level from the beginning of year 1996 till the beginning of 1997 during this increase the zonal velocity variance u 2 is up to 30 higher than its meridional counterpart suggesting a zonal acceleration of the eastward flow eke seasonal changes are also found in the ks current 30 35 n 130 140 e and also show a regular annual cycle during the first 3 years which precedes by 2 months the eke seasonal cycle in the ks extension maximum in may june the maximum in eke in both regions precedes by 2 months the maximum surface transport found by qiu et al 1991 and zlotnicki 1991 occurring in july and late september respectively no such annual cycle is found in the gs region during the first 3 years year 1996 is anomalous in both current systems with mean eke level that increases by more than 20 compared to the other years also eke monthly mean changes in the ks reveal a well marked positive tendency in the eastern part of the current of more than 300 cm2 s 2 yr 1 and a negative tendency both in its eastern part and in the ks current this feature is absent from the gs at last eddy mean flow interaction is presented both the spatial averaging of turbulent quantities and the relative contribution of the different terms of the horizontal momentum fluxes are discussed a tentative explanation is given for the anomalously large u 2 at the end of 1996 in the ks extension

symmetric instability in the gulf stream abstract analyses of wintertime surveys of the gulf stream gs conducted as part of the clivar mode water dynamic experiment climode reveal that water with negative potential vorticity pv is commonly found within the surface boundary layer sbl of the current the lowest values of pv are found within the north wall of the gs on the isopycnal layer occupied by eighteen degree water suggesting that processes within the gs may contribute to the formation of this low pv water mass in spite of large heat loss the generation of negative pv was primarily attributable to cross front advection of dense water over light by ekman flow driven by winds with a down front component beneath a critical depth the sbl was stably stratified yet the pv remained negative due to the strong baroclinicity of the current suggesting that the flow was symmetrically unstable a large eddy simulation configured with forcing and flow parameters based on the observations confirms that the observed structure of the sbl is consistent with the dynamics of symmetric instability si forced by wind and surface cooling the simulation shows that both strong turbulence and vertical gradients in density momentum and tracers coexist in the sbl of symmetrically unstable fronts si is a shear instability that draws its energy from geostrophic flows a parameterization for the rate of kinetic energy ke extraction by si applied to the observations suggests that si could result in a net dissipation of 33 mw m 2 and 1 mw m 2 for surveys with strong and weak fronts respectively the surveys also showed signs of baroclinic instability bci in the sbl namely thermally direct vertical circulations that advect biomass and pv the vertical circulation was inferred using the omega equation and used to estimate the rate of release of available potential energy ape by bci the rate of ape release was found to be comparable in magnitude to the net dissipation associated with si this result points to an energy pathway where the gs s reservoir of ape is drained by bci converted to ke and then dissipated by si and its secondary instabilities similar dynamics are likely to be found at other strong fronts forced by winds and or cooling and could play an important role in the energy balance of the ocean circulation

estimation of source parameters quality factor qs and site characteristics using accelerograms uttarakhand himalaya region abstract a study of source path and site characteristics was conducted for the uttarakhand himalaya region using accelerogram data from 15 earthquakes m l 3 5 these earthquakes were recorded at the 16 station accelerograph network operated by the indian institute of technology roorkee during 2005 2011 the average seismic moment m 0 of the studied earthquakes ranges between 1 20 10 22 and 1 02 10 24 dyn cm and the average moment magnitude m w is between 4 0 and 5 3 the estimated corner frequency f c varies from 1 1 to 3 3 hz radius of rupture r d from 0 5 to 1 4 km and stress drop from 6 to 172 bars indicating continuous seismic energy release in the uttarakhand region the interdependence between estimated source parameters is shown by determining scaling laws for the studied region the constant q 0 of the shear wave quality factor q s q 0 f n varies between 40 and 300 and exponent n varies between 0 85 and 1 5 providing an average relation of q s 174 f 1 27 however least square fitting of the observed data set in the frequency range 0 1 20 hz gives q s as 159 f 1 16 the value of q s demonstrates that the region is heterogeneous seismically active and attenuative the high frequency spectral fall off factor varies from 1 3 to 2 1 and the upper crustal attenuation factor from 0 023 to 0 07 s at different sites with an average of 0 044 s the site response characteristics are estimated by horizontal to vertical spectral ratio hvsr and generalized inversion ginv techniques results obtained from both the techniques show 1 1 correspondence the site amplification factor varies between 2 3 and 9 4 using hvsr and between 2 6 and 10 9 using ginv among different stations the predominant frequency ranges from 1 3 to 8 3 hz with hvsr and from 1 3 to and 9 0 hz with ginv online material tables of source path and site parameters with associated errors at different sites for the earthquakes recorded from december 2005 to march 2011 figures represent accelerogram records source spectra matching and site amplification patterns

gulf stream bimodality and variability downstream of the charleston bump gulf stream mean flow and variability have been studied in the gulf stream deflection and meander energetics experiment damex this study was conducted between september 1981 and april 1982 in the area of the charleston bump off the coast of the southeastern united states using data from an array of current meters and satellite imagery it has been shown that the seaward deflection of the gulf stream by the bump has a bimodal character and that the gulf stream meander field downstream of the bump differs between the two states of deflection the two deflection conditions have been termed the weakly deflected state and the strongly deflected state in this paper a weakly deflected gulf stream flows past the charleston bump and close enough to the edge of the continental shelf that its shoreward sea surface temperature sst front remains inshore of the 600 m isobath between charleston and cape hatteras a strongly deflected gulf stream turns sharply eastward at the bump and flows seaward far enough to have its shoreward sst front offshore of the 600 m isobath for several tens of kilometers along the continental slope downstream of the bump the transitions between deflection states may occur very rapidly and once in a strongly deflected state the gulf stream may remain so for up to several months two transitions were observed during damex one from a weakly to a strongly deflected state and one in the other direction the transition from weakly to strongly deflected state took only a few days at a given site while the signatures of the other transition were not as definite in the data records the strongly deflected state occurred during the fall and winter in damex october through january and satellite observations from earlier years suggest that it is this time of year in which the strongly deflected state preferentially occurs it was not clear from the damex data alone how the transition from a weakly deflected to a strongly deflected state may be induced but path or transport changes in the gulf stream as it approaches the bump and interactions between the current and rings or eddies are candidate mechanisms the bimodal character of the stream s path affects the low frequency variability of the current between the charleston bump and cape hatteras in the following manner typical meander frontal eddy patterns dominate the mesoscale fluctuation field during times of weak deflection while larger amplitude meanders of the gulf stream jet which can have very sharp curvature and strong anticyclonic circulations in their crests exist during times of strong deflection furthermore these larger amplitude meanders which we call the damex biweekly meanders have generally slower phase propagation speeds than do the typical meander frontal eddy events about 20 25 km day compared with 35 60 km day as well as longer periods about 16 days compared to 1 week

new cnes cls09 global mean dynamic topography computed from the combination of grace data altimetry and in situ measurements 1 an accurate knowledge of the ocean mean dynamic topography mdt is mandatory for the optimal use of altimetric data including their assimilation into operational ocean forecasting systems a new global 1 4 resolution mdt was computed for the 1993 1999 time period with improved data and methodology compared to the previous rio05 mdt field first a large scale mdt is obtained from the cls01 altimetric mean sea surface and a recent geoid model computed from 4 5 years of grace gravity recovery and climate experiment data altimetric sea level anomalies and in situ measurements are then combined to compute synthetic estimates of the mdt and the corresponding mean currents while the rio05 mdt was based on 10 years of in situ dynamic heights and drifting buoy velocities the new field benefits from an enlarged data set of in situ measurements ranging from 1993 to 2008 and includes all hydrological profiles from the argo array moreover the processing of the in situ data has been updated a new ekman model was developed to extract the geostrophic velocity component from the drifting buoy measurements the handling of hydrologic measurements has also been revisited compared to the previous rio05 solution the new global mdt resolves much stronger gradients in western boundary currents with mean velocities being doubled in some places moreover in comparison to several other recent mdt estimates we find that the new cnes cls09 mdt is in better agreement with independent in situ observations

gulf stream dynamics along the southeastern u s seaboard abstractthe gulf stream strongly interacts with the topography along the southeastern u s seaboard between the straits of florida and cape hatteras the dynamics of the gulf stream in this region is investigated with a set of realistic very high resolution simulations using the regional ocean modeling system roms the mean path is strongly influenced by the topography and in particular the charleston bump there are significant local pressure anomalies and topographic form stresses exerted by the bump that retard the mean flow and steer the mean current pathway seaward the topography provides through bottom pressure torque the positive input of barotropic vorticity necessary to balance the meridional transport of fluid and close the gyre scale vorticity balance the effect of the topography on the development of meanders and eddies is studied by computing energy budgets of the eddies and the mean flow the baroclinic instability is stabilized by the slope everywhere except past the bump the flow

cyclogenesis in the deep ocean beneath the gulf stream 2 dynamics strong cyclones in the deep ocean beneath the gulf stream have been observed during the period june 13 1988 to august 7 1990 near 68 w 37 n in data from the synoptic ocean prediction synop experiment these cyclones developed in association with the evolution of large amplitude quasi stationary meander troughs in the gulf stream it is likely that baroclinic instability is responsible for cyclone spin up the dynamical analysis of these cyclones indicates the process is analogous with atmospheric cyclogenesis from the perspectives of divergence and conservation of potential vorticity but not in terms of the density field evolution large positive vertical velocities in the thermocline over developing low pressure centers at 3500 m are consistent with convergence at depth and divergence in the upper ocean and with stretching of the lower water column and shortening of the upper water column the stretching of the lower water column accounts for the generation of positive relative vorticity there however the evolution of the density field in the oceanic case does not resemble the atmospheric case in the atmosphere density field adjustments in the air column above the low pressure center at the earth s surface are in the correct sense to account for decreasing pressure there in the ocean density field adjustments in the water column fail to account for the developing low pressure centers so sea surface height depressions must be responsible these depressions must have an approximate magnitude of 0 5 m depth over a 250 km horizontal extent the cyclone s diameter