geographic and seasonal distributions of brunt vaisala frequency and rossby radii in the north pacific and north atlantic abstract long term mean temperature and salinity profiles computed from an edited set of historical hydrographic data have been used to calculate mean profiles of density and brunt vaisala seasonal variations in internal rossby radii are everywhere surprisingly small

concurrent altimeter and infrared observations of rossby wave propagation near 34 n in the northeast atlantic we present observations of long wavelength baroclinic rossby waves near 34 n in the northeast atlantic ocean east of the mid atlantic ridge using both topex poseidon sea surface height ssh altimeter data and ers 1 along track scanning radiometer sea surface temperature sst measurements using the fourier transforms of longitude time diagrams of the zonal gradients of sst and ssh we locate the spectral components corresponding to westward wave propagation and estimate wavelength period and propagation speed the energy associated with the propagating waves in that region is distinctly higher than in the surrounding areas the similarities between the properties of the sst and ssh zonal gradients are remarkable with the same propagating signals clearly observed in both fields it is believed that the interaction between the rossby waves and the azores current could play a major role in the amplification of the waves themselves

a numerical study on the influence of the mid atlantic ridge on nonlinear first mode baroclinic rossby waves generated by seasonal winds abstract a numerical model simulation investigates the influence of the mid atlantic ridge on nonlinear first mode baroclinic rossby waves generated by seasonal wind fluctuations the north atlantic is simulated by a square box two layer quasi geostrophic qg model the bottom topography is ridge like and compromises the qg approximation and the actual shape of the ridge sponge layers protect all boundaries except the eastern one from wave reflection and eliminate the build up of the western boundary current the model is forced by a purely fluctuating wind stress curl derived from the most significant eofs of the fgge winds a flat bottom and a ridge experiment are compared in both experiments the eastern boundary is an important source of annual period baroclinic rossby waves wave trains having a wavelength of about 1060 km and a westward phase speed around 3 4 cm s 1 propagate energy westward at 3 cm s 1 in the flat bottom experiment a source of directly wind forced baroclinic waves of annual per

propagation characteristics of extratropical planetary waves observed in the atsr global sea surface temperature record this paper examines the characteristics of planetary wave signatures that have been found in the along track scanning radiometer averaged sea surface temperature asst record for 1991 1996 longitude time plots for every latitude between 5 and 50 north and south reveal westward propagating wave like patterns at many locations whose speed decreases with latitude like baroclinic rossby waves a two dimensional radon transform method is used to measure the wave speed and its variation with location and time which broadly matches the rossby wave speeds predicted by the most recent theory and those measured by topex altimetry although there are some discrepancies at low latitudes the thermally detected speeds are slower than expected a possible consequence of sampling limitations wave signatures are clearest between 25 and 40 s where the meridional temperature gradient is strongest here observed speeds are 20 30 greater than theoretical predictions planetary wave speed varies considerably with longitude in general it increases toward the west of ocean basins and distinct differences between ocean basins are evident the propagation characteristics of the waves appear to change abruptly at locations consistent with latitudinal variations in seafloor bathymetry particularly midocean ridges in addition eastward propagating signatures are found in the southern ocean the results demonstrate the value of the asst data set as a tool for studying basin scale wave processes as a complement to the use of altimetry by observing the thermal signature of rossby waves the method has the potential to clarify their influence on air sea interaction processes and to contribute to climate modeling studies

on the joint distribution of surface elevation and slopes for a nonlinear random sea with an application to radar altimetry the work of longuet higgins 1963 on the effects of wave nonlinearity on the statistics of the sea surface is extended here to obtain the joint distribution of surface elevation and slopes for a nonlinear random sea the results are used to examine the effect of wave nonlinearity on the form of a radar altimeter pulse which is reflected from the sea surface it is shown how wave information may be derived from the return pulse and how this can be used to correct errors in the altimeter mean sea level estimate a problem known as sea state bias

generation of annual period rossby waves in the south atlantic ocean by the wind stress curl abstract the properties of first mode annual period baroclinic rossby waves generated by the observed wind stress curl in a numerical model of the south atlantic and southwest indian oceans are presented the forcing wind field for the area 15 51 s 45 w 41 e was obtained from a harmonic analysis at the annual period of the monthly mean wind stress curl values derived from hellerman and rosenstein s data and was used to drive a linear reduced gravity model of the south atlantic and southwest indian oceans bounded by 15 and 51 s 46 w and 50 e in the south atlantic ocean the response consists of long rossby waves which generally propagte their phase southwestward across the ocean and which exhibit refraction of wave energy towards the equator short rossby waves with eastward energy propagation are generated in the small area of the indian ocean included in the model domain medium to short waves generated to the southeast of africa reflect their energy off this landmass into the indian ocean slown

observational evidence of salt lens formation in the iberian basin the quasi synoptic picture of the mesoscale eddy field off portugal is presented on the basis of recent hydrographic measurements the dynamic topography and the salinity field at middepths 900 1300 m is shown to be dominated by several isolated meddy structures superimposed on a general east west gradient deduced from the actual dynamical situation there is evidence for meddy generation in this region numerical process studies demonstrate the possibility of vortex formation by baroclinic instability of a northward middepth jet of mediterranean water and by fragmentation of larger scale mediterranean water blobs

the near surface flow in the subtropical gyre south of the azores this study presents evidence that the azores current azc is a permanent feature of the north atlantic subtropical gyre and that it feeds the north equatorial current nec the azc path is located south of the azores its velocity is mostly geostrophic and the energy level in the mesoscale range is higher than in the nec the nec velocity appears to be mostly ageostrophic and the wind driven surface velocity is at about 15 to the right of the mean wind field

two dimensional modelling of the within field variation in rill and gully geometry and location related to topography abstract the topography rill pattern and geometry were surveyed within a small agricultural field the rill network and dimensions were converted to a grid based system and used to calculate the slope gradient and contributing area for each grid cell a strong correlation was found between the rill cross sections and a power function of slope gradient and contributing area the slope and area exponents were 1 28 and 0 89 respectively for all rill points and 1 02 and 0 87 respectively for the rill points not lying in the depositional area these exponents are within the range reported for field studies in a one dimensional context our data confirmed the potential of an inverse slope area relationship with an area exponent of 0 5 to predict areas prone to rilling and the location of ephemeral gullies however the prediction of individual rill starting points was not possible because of the major influence of small local variations in topography on overland flow discharge both the prediction of the rill cross sections and the prediction of the location of the two ephemeral gullies in the field were significantly improved when the tillage direction was taken into account in calculating the contributing area therefore tillage patterns should be given more attention when developing routing procedures for hydrological and erosion models

large scale propagating disturbances approximation by vertical normal modes abstract propagating features and waves occur everywhere in the ocean this paper derives a concise description of how such small amplitude large scale oceanic internal disturbances propagate dynamically against a slowly varying background mean flow and stratification computed using oceanic data for a flat bottomed ocean assumed here the linear internal modes computed using the local stratification form a useful basis for expanding the oceanic shear modes of propagation remarkably the shear modal structure is largely independent of orientation of the flow the resulting advective velocities which are termed pseudovelocities comprise background flow decomposed onto normal modes and westward planetary wave propagation velocities the diagonal entries of the matrix of pseudovelocities prove to be reasonably accurate descriptors of the speed and direction of propagation of the shear modes which thus respond as if simply advected by this diagonal entry velocity field the complicated three dimensi

sea level variabilities in the gulf stream between cape hatteras and 50 w a geosat study sea level residuals relative to a 2 year mean sea level in the gulf stream downstream of cape hatteras between 80 w and 50 w longitude are studied using geosat altimetry between november 1986 and december 1988 spectral slopes computed at four nominal locations along the gulf stream 72 w 65 w 60 w and 55 w range between 1 5 and 0 9 significantly less steep than the 2 5 spectral slope found at bermuda because of increased short wavelength energy the spectra tend to become more white going eastward but this trend is not statistically significant energy at the annual cycle decreases eastward from around 40 of the total variance at 72 w to 20 of the total variance at 55 w maximum residual geostrophic sea surface velocities associated with the annual cycle were of the order of 70 cm s comparison between the gulf stream path from sea level residual maps and the north wall edge observed from noaa infrared ir imagery shows an rms difference of 49 km between 75 w and 60 w longitude but not all sea level maps show a clearly defined gulf stream using the ir estimates for gulf stream position sea level residuals were modeled as the meandering of a sea level front shaped as 0 5 m tanh x x0 50 km sin with the angle between the geosat track and the gulf stream edge and x0 is based on the observed ir north wall positions this showed that the annual signal in terms of the location and phase of its maxima is dominated by the meandering of the gulf stream

currents fronts and eddy fluxes in the canary basin hydrographic data from two cruises in the canary basin meteor 57 july 1981 poseidon 86 april 1982 are analysed with respect to current distribution and lateral heat flux in the azores madeira region the first part of the data base consists of long transects of xbt and g e k measurements between cape finisterre north west spain and the northern canary basin where several year long current meter records exist further information is obtained by thermosalinograph surface data and by expendable current profilers xcp geostrophic currents are derived from xbt profiles using the tight temperature salinity relationship in the depth range of the warmwassersphare the results compare well with the g e k and xcp current observations the second part consists of ctd data from an eddy resolving box shaped ctd survey 500 500 km2 centered at the mooring location 33 n 22 w the observations are supplemented by satellite buoy trajectories horizontal parameter distribution is shown in terms of objectively contoured maps bands of spatially enhanced energetic structures seen in the long transects are further resolved by the box survey as a deep jet like current system cross the canary basin in a west east direction associated with this azores current is a frontal zone with near surface temperature and salinity steps of order 2 k and 0 3 practical salinity units the dynamic topography field can be decomposed into a linear background field a rossby wave and a mesoscale eddy field we find that major contributions to the meridional eddy heat flux are confined to the vicinity of the azores current frontal zone it is shown that the principal balance in the temperature equation is between heating by the mean horizontal advection terms and cooling by the eddy flux divergence

aliased tidal errors in topex poseidon sea surface height data alias periods and wavelengths for the m2 s2 n2 k1 o1 and p1 tidal constituents are calculated for topex poseidon alias wavelengths calculated in previous studies are shown to be in error and a correct method is presented with the exception of the k1 constituent all of these tidal aliases for topex poseidon have periods shorter than 90 days and are unlikely to be confounded with long period sea surface height signals associated with real ocean processes in particular the correspondence between the periods and wavelengths of the m2 alias and annual baroclinic rossby waves that plagued geosat sea surface height data is avoided the potential for aliasing residual tidal errors in smoothed estimates of sea surface height is calculated for the six tidal constituents the potential for aliasing the lunar tidal constituents m2 n2 and o1 fluctuates with latitude and is different for estimates made at the crossovers of ascending and descending ground tracks than for estimates at points midway between crossovers the potential for aliasing the solar tidal constituents s2 k1 and p1 varies smoothly with latitude s2 is strongly aliased for latitudes within 50 degrees of the equator while k1 and p1 are only weakly aliased in that range a weighted least squares method for estimating and removing residual tidal errors from topex poseidon sea surface height data is presented a clear understanding of the nature of aliased tidal error in topex poseidon data aids the unambiguous identification of real propagating sea surface height signals unequivocal evidence of annual period westward propagating waves in the north atlantic is presented

spatial scales of mesoscale variability in the north atlantic as deduced from geosat data two years of geosat data were used to systematically investigate the mesoscale variability and spatial scales of the north atlantic we first calculated sea surface height variability and eddy kinetic energy these compare well with the eddy kinetic energy obtained with surface drifters then the spatial scales of mesoscale variability were characterized in 10 latitude 10 longitude areas by their wave number spectra and autocorrelation functions comparison with existing in situ data shows good agreement and it is believed that the total error budget is globally below that of the oceanic signal the wave number spectra show significant differences as a function of latitude and longitude and these can be related to different types of forcing instability of a mean current or fluctuating wind scales typically decrease from west to east and south to north simple proportionality with respect to the first internal rossby radii does not apply everywhere

barotropic and baroclinic tidal currents in the eastern basins of the north atlantic data from a large scale moored array in the iberian and canary basins are used to determine the energies of barotropic and baroclinic m2 and s2 tides an analysis of time varying dynamical modes is performed the results for barotropic modes confirm the global surface tide model results of schwiderski 1980 for this region the barotropic modes dominate in the deep basins but increased baroclinic contributions are usually found over rough topography at three locations near the continental slope in the southern canary basin the baroclinic modes dominate the barotropic mode results from an array of three moorings at the northern part of the cape verde rise show an inverse behavior of barotropic and baroclinic energies such that the baroclinic energy is steadily enhanced while the barotropic energy is reduced towards the continental margin the increase in baroclinic energy is consistent with a generation of internal tides close to the shelf by surface tidal forcing over topography further evidence for this process is provided by the 2 week periodicity of the first order baroclinic mode at the slope corresponding to the spring neap cycle of the barotropic tide

large scale sea level variations and associated atmospheric forcing in the subtropical north east atlantic ocean abstract the large scale sea level variations in the subtropical north eastern atlantic ocean are characterised by a predominant seasonal fluctuation analysis of 6 years 1993 98 of combined topex poseidon and ers 1 2 altimetric data together with data of concurrent oceanic surface geophysical fields ecmwf net heat fluxes ecmwf winds and reynolds sea surface temperature reveals that the dominant physical forcing of sea level variations on an annual timescale is the air sea net heat fluxes this local forcing generates a seasonal ocean steric response whose amplitude of the order of 4 5 cm varies spatially within the studied area and temporally over the 6 year period the residual variability is mainly characterised by a non seasonal signal which is observed northwards of the azores current 34 n and its time variation resembles that of the north atlantic oscillation nao a combination of steric effects wind induced heat fluxes and wind effects barotropic sverdrup response appear to explain this signal some evidence of a local ekman pumping response is also found regionally both in the seasonal and non seasonal variations of the observed sea level at the interannual timescale an overall sea level trend with a mean rate of 0 5 cm year is detected however the magnitude of the trend varies locally so that the entire sea surface appears to undergo a general tilt which extends beyond the studied area superimposed on this long term trend a sharp temporal sea level rise occurs in 1995 mainly between the azores and madeira islands all together these low frequency sea level variations seem to co vary with the large scale sea surface temperature sst variations this implies a comparable evolution of the sea level with the upper ocean thermal content which suggests a contribution from steric effects a weaker situation is observed in the northern area indicating a possible low frequency wind forcing enhanced contribution

nonlinear rossby waves off california 1 a new interpretation of ssh anomalies propagating in the california current system as weakly nonlinear rossby waves rws is suggested satellite altimetry and float data were used to extract annual and semi annual components of rws from a multi scale altimetry signal and estimate their kinematic characteristics different propagation regimes for the waves were identified by propagation speed wave steepness and length of spatial phase coherence spc a transition from a ssh field dominated by waves to a turbulent like field was detected in the saturation regime the recurrence period for wave behavior was estimated as about 105 120 195 210 days for the semiannual annual component the propagation speed and length of spc decreased when wave steepness increased and westward propagation halted during the saturation regime

acceleration creation and depletion of wind driven baroclinic rossby waves over an ocean ridge the influences of topography on the propagation spatial patterns and amplitude variations of long baroclinic rossby waves are investigated with a wind forced two layer model above a midocean ridge with steep topography the evolution equation for the baroclinic mode is shown to differ from that for a flat bottom in several ways 1 the phase speed is systematically faster by the factor h h2 where h is the total ocean depth and h2 is the lower layer thickness though the propagation remains westward and nearly nondispersive 2 an effectively dissipative transfer to the barotropic mode occurs whenever the baroclinic mode is locally parallel to f h contours where f is the coriolis frequency and 3 the wind forced response is amplified in proportion to the topographic steepness f h dh dx df dy for a longitudinally varying topography which can be a large factor but the amplification is only by the modest factor h h2 for a latitudinally varying topography effects 2 and 3 are the result of energy exchanges to and from the barotropic mode respectively effect 3 causes freely propagating baroclinic rossby waves to be generated west of the ridge these effects collectively cause distortions of the baroclinic wave pattern as it traverses the ridge these effects account qualitatively for several features seen in altimetric measurements in the vicinity of major topographic features an increase in variance of baroclinic signals on the west side an enhanced phase speed overall compared to flat bottom waves and an abrupt change in the phase speed at midocean ridges

the effect of the degree of wave development on the sea state bias in radar altimetry measurement the effect of the degree of wave development on the sea state bias ssb in geosat altimeter height measurement is evaluated theoretical considerations suggest that the altimetric ssb is generally not a linear function of significant wave height but depends also on other factors of wave development of particular interest is its dependence on wave age defined as the ratio of the phase speed of the dominant ocean waves to ocean wind speed we estimate wave age rather crudely on the basis of the significant wave height h and wind speed measured by the altimeter under general conditions when the sea is not in equilibrium with the wind this estimate may not correspond to the wave age in a strict sense and hence is called pseudo wave age in this paper nevertheless the pseudo wave age is a rough indicator for the degree of wave development the general trend in the dependence of the ssb on pseudo wave age as found by analyzing 2 7 years worth of geosat data agrees well with the theoretical prediction for a given h the ssb decreases as the degree of the wave development measured by the pseudo wave age increases this empirical trend is modeled as ssb a m m h where and m are the pseudo wave age and its average value respectively a 0 013 0 005 and m 0 88 0 37 statistically this model performs slightly better than a standard model i e ssb h with being a constant in terms of the global rms error the improvement is by 1 6 cm however because the degree of wave development varies with the season and geographical location this small improvement could become important for more accurate altimetric missions in the future when the centimetric basin scale signals are the focus of the study

can meddies be detected by satellite altimetry geosat exact repeat mission altimeter data have been used to estimate the sea surface height anomaly relative to a 2 year mean reference surface in the eastern north atlantic ocean horizontal maps of the sea surface height anomaly for various periods were constructed by means of an objective analysis procedure the mean sea level was approximated by the dynamic topography from climatological hydrographic data results were compared to the dynamic topography calculated from hydrographic ground truth data sampled during march 1988 on an eddy resolving station network in the iberian basin despite the low signal to noise ratio of the altimeter data in this part of the ocean the agreement of the altimeter signal with hydrographic measurements is found to be significant individual cyclonic and anticyclonic eddies in the mediterranean outflow are identified in the altimetric maps the information visible in the sea surface height is significantly correlated with the dynamic topography of the layer 500 3000 dbar containing the core of the mediterranean outflow and maximum velocities of the baroclinic eddies the successive development of the identified eddies as studied from a sequence of sea surface height maps indicates a slight westward drift of the most pronounced feature with approximately 1 9 cm s propagation velocity the inferred path of that feature is consistent with additional information from moored current meter data

properties of rossby waves in the north atlantic estimated from satellite data this study uses satellite observations of sea surface height ssh to detect westward propagating anomalies presumably baroclinic rossby waves in the north atlantic and to estimate their period wavelength amplitude and phase speed detection involved a nonlinear fit of the theoretical dispersion relation for rossby waves to the time longitude spectrum at a given latitude estimates of period wavelength and phase speed resulted directly from the detection process based on these a filter was designed and applied to extract the rossby wave signal from the data this allowed a mapping of the spatial variability of the rossby wave amplitude for the north atlantic results showed the familiar larger speed of observed rossby waves relative to that expected from theory with the largest differences occurring at shorter periods the data also show that the dominant rossby waves those with periods that are less than annual propagated with almost uniform speed in the western part of the north atlantic between 308 and 408n in agreement with previous studies the amplitude of the rossby wave field was higher in the western part of the north atlantic than in the eastern part this is often attributed to the influence of the mid atlantic ridge by contrast this study through an analysis of the wave spatial structure suggests that the source of the baroclinic rossby waves at midlatitudes in the western north atlantic is located southeast of the grand banks where the gulf stream and the deep western boundary current interact with the newfoundland ridge the spatial structure of the waves in the eastern north atlantic is consistent with the formation of these waves along the basin s eastern boundary

long baroclinic rossby waves detected by topex poseidon residual sea surface height anomaly fields are obtained over the north atlantic basin from topex poseidon altimeter data evidence of westward propagating anomalies characterized as first mode baroclinic rossby waves is presented the phase speeds are obtained from the analysis of the autocorrelation matrices of the residual surface height anomaly in three dimensions on a 5 5 grid periods are calculated by least squares fitting a sinusoidal function to the time series at each grid point zonal and meridional wavelengths are obtained from the phase speed and period and are least squares fit to the data as a consistency check zonally averaged westward phase speeds vary between 1 and 27 km d between 50 and 5 n increasing southward phase speeds are directed to the southwest north of approximately 25 n and to the northwest south of this latitude the sea surface height signal is divided into two spectral bands the first with periods between 280 and 450 days and the second with periods between 120 and 280 days for the first band the average of the periods taken over the whole basin is 370 days in the second band a signal of period between 6 and 7 months is evident also throughout the basin the zonally averaged zonal wavelengths associated with the first band are in the range of 400 4600 km between 50 and 5 n and for the second band are in the range 270 2500 km between 45 and 5 n longer wavelengths are found close to the southern boundaries shorter wavelengths are found in the northern portion of the basin comparison with results from numerical models suggests that the baroclinic waves observed at midlatitudes are generated at the eastern boundary by fluctuations of the wind stress curl waves observed south of 20 n support the hypothesis of direct wind forcing

sea level response to pressure forcing in a barotropic numerical model abstract a barotropic shallow water model is used to study the large scale sea level response to realistic barometric forcing at periods ranging from 1 day to 1 year results are presented from coarse resolution open ocean experiments i e no shallow continental shelf regions or marginal seas with coastal geometries and bottom topography representative of the north atlantic and pacific basins the validity of the inverted barometer ib approximation is examined in detail including nonlocal effects which result from taking into account the constant volume of the ocean these effects are found to be important at low latitudes where a considerable part of the sea level variability is related to pressure forcing over higher latitudes root mean square deviations from an ib response in the range of 1 3 cm are typical with most of the variance occurring at high frequencies basin averaged estimates yield ib deviations of only a few percent at time scales longer than 1 week increasing to 5 20 over the

persistent westward flow in the azores current as seen from altimetry and hydrography temporal and spatial variability of the eastward flowing jet like azores current is investigated by applying a new method for combining altimetry with hydrography in order to produce absolute surface geostrophic currents challenor et al 1996 the altimeter surface measurements contain information about both the geoid and the geostrophic ocean circulation the geoid signal dominates and is generally not sufficiently well known at the small length scales required to identify the mesoscale ocean signal in this study hydrography is used to distinguish the mean ocean signal from the geoid along an ers 1 satellite track south of the azores during both 3 day repeat phases and thereby determine cross stream absolute dynamic topography of the azores current at high temporal resolution hydrographic data collected near 28 w in march 1992 is combined with ers 1 altimeter data from january march 1992 and january to early april 1994 time series of 3 day repeat profiles of absolute surface geostrophic velocity perpendicular to the altimeter cruise track are examined the azores current absolute velocity profile along this track is rather coherent the current variability is less than the mean surprisingly a persistent westward flow of 25 cm s 1 is observed near 35 n 28 w this flow appears to be a retroflection from the main eastward flowing current an isopycnal analysis reveals the westward flow to be cooler by 0 5 c and fresher by 0 15 practical salinity units than the main body of the azores current the flow appears to persist throughout each of the above 3 month periods in late winter early spring but the question of whether this is a seasonal feature or more permanent remains open it is suggested that the westward flow is topographically controlled

mean circulation and eddy kinetic energy in the eastern north atlantic sixty two satellite tracked buoys have been released in the northern part of the western and central north atlantic during 1981 and 1982 by the institut fur meereskunde universitat kiel federal republic of germany additionally six buoys deployed in spring 1980 by the bedford institute have been taken over mean values and variances about the mean have been calculated for 3 by 3 areas the mean velocities confirm the large scale gyre circulation as deduced from hydrographie data and numerical models the center of the gyre is located at about 33 n eddy kinetic energy decreases east and southward and is concentrated along the north atlantic current it appears that the north atlantic current polar front is the main source of eddy kinetic energy for the northern north atlantic whereas the mid atlantic ridge is no source of eddy energy eddy kinetic energy along the north atlantic current decreases from about 1000 cm2 s 2 near newfoundland to 300 cm2 s 2 west of scotland a homogeneous pool of low eddy kinetic energy less than 100 cm2 s 2 appears in the central north atlantic east of the mid atlantic ridge the level increases towards the european and african shelf where the mean southward flow also becomes stronger the results concern the upper ocean

on the reasons for the formation and variability of the azores current abstract recent studies have shown that the formation of the well defined zonally oriented azores current may be the result of water mass transformation associated with the mediterranean outflow in the gulf of cadiz as the denser mediterranean water descends down the continental slope it entrains overlying north atlantic central water it is believed that the azores current then forms as part of the horizontal recirculating gyre generated through the plume mechanism in this study the authors further explore this hypothesis by performing a series of numerical experiments these experiments are based on a high resolution general circulation model that includes the mediterranean sea and that realistically simulates the water mass exchange through the strait of gibraltar and the transport and variability of the azores current the authors show that the divergence of the relative vorticity flux and the planetary vorticity flux associated with planetary waves are the main factors determining the variab

on the origin of the azores current the azores current south of the azores archipelago is part of the subtropical north atlantic gyre using an international hydrographic data set we analyze mean and seasonal geostrophic transport fields in the upper 800 m of the ocean in order to determine the origin of the azores current in the western basin and seasonal changes in the related flow geostrophic currents are obtained by using the method applied by stramma 1984 in the eastern basin the azores current is found to originate in the area of the southwest newfoundland rise figure 10 in winter an almost uniform current connects this region of origin with the azores current while a branching into two current bands is observed in summer with the southern band forming a marked cyclonic loop within the upper 800 m all of the transport in the northern band and about 70 of the transport in the southern band recirculates in the eastern basin additionally expendable bathythermograph data from the azores current region indicate an increase of eddy potential energy from winter to summer

physical oceanography of the azores front abstract there is a considerable body of evidence for the existence of a permanent front sw of the azores surveys in the summer of 1981 show the structure to penetrate to a depth of 2 000 m and suggest that its meandering is related to the alignment of the atlantis gt meteor seamount chain the total volume transport above 2 000 m is between 10 and 12 106 m3 s 1 towards the east the main water mass contrasts across the front are confined to the upper 400 m of the water column only a small change in mediterranean water strength was seen across the front satellite tracked drogued buoys seeded into the front showed surface speeds of up to 40 cm sec 1 and revealed the formation of a closed cold core eddy some 100 115 km in diameter which propagated westward at 2 2 km day 1 over a 200 day period sea surface temperature contrasts across the frontal boundary are small and together with frequent cloud cover prevent the detection of the front and associated eddies by satellite infra red imagery the front apparently marks the eastward extension of the southern branch of the gulf stream recirculation and the northern limit of the 18 c water mass eddies formed at the front could propagate westward into the interior of the sargasso sea but have not yet been observed to cross the mid atlantic ridge

hindcast forecast of enso events based upon the redistribution of observed and model heat content in the western tropical pacific 1964 86 anomalous sea level anomalous observed dynamic height 0 400 db and anomalous model dynamic height are examined at the locations of 13 island sea level stations in the tropical pacific for each bimonth of the four year period 1979 to 1982 starting in 1981 the anomalous dynamic height data show off equatorial rossby waves propagated toward the w boundary of the pacific basin at the w boundary the model rossby wave activity was found to have excited coastally trapped kelvin munk waves which transmitted the anomalous dynamic height equatorward at the equator coastally trapped wave activity excited eastward propagating equatorial kelvin waves yielding a pair of anomalous peaks in dynamic height variability in the e equatorial pacific associated with the 1982 1983 enso event the evolution of the peaks in dynamic height associated with the rossby and kelvin wave activity reflects the redistribution of observed upper ocean heat content in the w tropical pacific providing a qualitative hindcast for the 1982 1983 enso event

oceanic tides from geosat altimetry direct tidal analysis of the altimetry from the geosat exact repeat mission s first year is used to derive estimates of the diurnal and semidiurnal oceanic tides the geoid is removed by collinear differences at 34 1 day separation and the orbit error is reduced by subtracting a slowly modulated 1 cycle revolution term a sequence of independent analyses at grid areas of 1 latitude 1 5 longitude using orthotide functions ensures complete definition of the diurnal and semidiurnal species global admittance maps for m2 and s2 within the latitudes 58 n and 59 s compare well with ground truth at 66 open ocean sites maps of differences between geosat and the naval surface weapons center model show important areas of the order of 10 15 cm the integral for the global power input from the moon gives 2 51 tw m2 0 44 tw s2 lower than many previous estimates but in agreement with figures deduced from a recent analysis of satellite orbits

observed variability of the south pacific westward sea level anomaly signal in the presence of bottom topography this study investigates the behavior of westward propagating sea level anomalies across the south pacific ocean with a focus on the long rossby wave signal determined from filtered topex poseidon and ers satellite altimeter data an evaluation of the energy variability of the signal using a two dimensional radon transform analysis suggests that rossby waves interact with both ridges and seamounts at various locations across the basin anomalously slow rossby wave phase speeds are found over steep isolated bathymetric features in the tropical south pacific and over the plateau around new zealand interaction with ridges increases the energetic variability range of dominant propagation speeds and meridional deviations in the rossby wave signal

observations in the canary basin and the azores frontal region using geosat data this paper discusses observations of the sea level in the azores frontal region and the canary basin as seen by the geosat altimeter frorn 5 to 45 w and 25 to 45 n two years of geosat exact repeat data were processed by colocating the data on a 0 06 grid then removing the mean by the along track difference method and removing the orbit error by a crossover analysis technique the data set was then interpolated by the successive correction method onto 15 day 0 5 maps to produce 47 residual height fields which were analyzed using complex empirical orthogonal functions eof and spectral analysis the results show that there is a region of high variability in the northwest corner reflecting the gulf stream extension and a region of medium variability at approximately 35 n reflecting the azores current the variability changes only slightly throughout the year with the winter season being the highest the data set also shows first mode baroclinic rossby waves between 30 and 35 n there is evidence that these rossby waves have different wavenumbers to the east and west of the mid atlantic ridge it is postulated that these waves have different generation mechanisms the mid atlantic ridge topography in the west and some other generation mechanism in the canary basin rossby waves are not apparent at 40 n