malvinas current volume transport at 41 s a 24 yearlong time series consistent with mooring data from 3 decades and satellite altimetry fil artana camila indira instituto franco argentino sobre estudios del clima y sus impactos argentina centre national de la recherche scientifique francia universite pierre et marie curie francia

satellite altimetry and current meter velocities in the malvinas current at 41 s comparisons and modes of variations three year long current meter arrays were deployed in the malvinas current at 41 s below a satellite altimeter track at about 10 years intervals surface geostrophic velocities sgv derived from satellite altimetric data are compared with the in situ velocities at the upper current meter 300 m multisatellite gridded sgv compare better with in situ observations than along track sgv in spite of the proximity of the moorings to the complex brazil malvinas confluence bmc region satellite sgv are significantly correlated with the 20 day low passed in situ velocities 0 85 for along isobaths velocities 0 8 for cross isobaths velocities the recent in situ measurement period 2014 2015 stands out in the altimetry record with a long lasting 4 months high level of eddy kinetic energy at the mooring site and a southernmost location of the subantarctic front saf the first two modes of variations of sea level anomaly sla over the bmc remarkably match the first two modes of the low passed in situ velocities the first mode is associated with a latitudinal migration of the saf and the second with a longitudinal displacement of the brazil current overshoot the two modes dominate the 24 year long record of sla in the bmc with energy peaks at the annual and semiannual periods for the first mode and at 3 5 months for the second mode the sla over the southwest atlantic was regressed onto the two confluence modes of sla variations and showed remarkable standing wave train like structures in the argentine basin

scaling and connectivity of joint systems in sandstones from western norway abstract the scaling properties of a joint system in devonian sandstones in western norway have been investigated using seven maps covering areas from 18 to 720 m across which were generated by mapping in the field and from low level aerial photography taken from different heights each map represent a scale window on the fracture population bounded by resolution at small scales and the sample size at large scales a power law relationship between fracture trace length and critical observation height maximum height at which a trace can be identified is derived and used to create a statistical model for the resolution effects the model indicates that a continuous smooth curve without a straight line segment on a log log cumulative frequency distribution plot does not necessarily rule out a power law as the underlying population distribution together the maps indicate a powerlaw trace length distribution with an exponent of 2 1 this power law may be valid over four or more orders of magnitude with natural lower cut off of around 1 m the exponent is significantly different from 2 0 strictly selfsimilar case and is reflected in a decrease in the abundance of fractures with length comparable to map size as map scale decreases the fracture trace length distribution results in a decrease in apparent connectivity with decreasing scale high resolution large scale maps are well connected while the lowest resolution map smallest scale is unconnected fractures in the smallest scale map are however connected by small fractures below the limit of resolution represented by the largest scale map the variation in apparent connectivity with scale has implications for fluid flow when fractures are open to fluid flow the scaling properties of apparent connectivity imply that beyond a certain scale the size of fracture controlling flow will be scale independent in this fracture system this appears to occur in sample areas of around 300 m across

pathways of eddies in the south atlantic ocean revealed from satellite altimeter observations 1 the majority of the kinetic energy of ocean currents is contained in the mesoscale eddies the pathways of ocean eddies which are the weather of ocean circulation are mapped from space using a decade long record of sea surface height measured by two simultaneously flying satellite radar altimeters the speed and direction of the propagation of eddies in the south atlantic ocean are presented in the paper the patterns of the eddy propagation velocity reveal the effects of the interaction between mean flow and eddies with strong influence of bottom topography the information describes a unique property of the ocean general circulation and serves as a basis for testing ocean models

characterization of westward propagating signals in the south atlantic from altimeter and radiometer records abstract radar altimeter data from topex poseidon and jason 1 and microwave radiometer data from trmm tmi are used to investigate the large scale variability between 10 5 s and 35 5 s in the south atlantic ocean the proposed method for the analysis of the longitude time diagrams of the cross correlation between ssh and sst anomalies shows that the variability in mid latitudes is a blend of first mode baroclinic rossby waves and propagating mesoscale eddy like structures the estimated phase speed of the wave cp and propagation speed of the eddies cv are similar in 70 of the cases the absolute difference between cp and cv is less than 11 in 40 of the cases this difference is less than 5 statistical results indicate that in the case of eddies as the thermocline deepens the sea surface temperature rises and vice versa however planetary waves show more complex yet self consistent results in lower latitudes 10 5 s 15 5 s the shallower thermocline and the weak thermal gradients impose a zero phase lag between temperature and height similar to eddies poleward of those latitudes sea surface temperature and height are in quadrature of phase this indicates that geostrophic advection of the relatively stronger thermal gradient is performed by rossby waves

buoyant eddies entering the labrador sea observed with gliders and altimetry abstract intense buoyant anticyclonic eddies spawned from the west greenland boundary current were observed with high resolution autonomous seaglider hydrography and satellite altimetry as they entered the labrador sea interior surveys of their internal structure establish the transport of both low salinity water in the upper ocean and warm saline irminger water at depth the observed eddies can contribute significantly to the rapid restratification of the labrador sea interior following wintertime deep convection these eddies have saline cores between 200 and 1000 m low salinity cores above 200 m and a velocity field that penetrates to at least 1000 m with 0 1000 m average speeds exceeding 40 cm s 1 their trajectory together with earlier estimates of the gyre circulation suggests why the observed region of deep convection is so small and does not occur where wintertime cooling by the atmosphere is most intense the cyclostrophic surface velocity field of the anticylones from satellite altimetry

vertical structure of eddies and rossby waves and their effect on the atlantic meridional overturning circulation at 26 5 n the meridional overturning circulation moc at inline image in the atlantic has a standard deviation of 4 9 sv and contains large fluctuations at subannual periods the geostrophic component of the moc is believed to be influenced on subannual time scales by eddies and rossby waves to quantify this effect the vertical structure and surface characteristics of westward propagating signals are studied using altimetric data and full depth mooring measurements from the rapid array at inline image westward propagating features are observed in the western north atlantic in both data sets and have periods of 80 250 days in the first baroclinic mode these features are still observed by the rapid moorings 20 km offshore of the western boundary the western boundary also exhibits deep variability characterized by enhanced energy in higher baroclinic modes the effect of eddies and rossby waves on the geostrophic transport is quantified by representing their vertical structure with the first baroclinic mode in total 42 of the variance of the transbasin thermocline transport inferred from geostrophic calculations at inline image can be attributed to first mode variability which is associated with eddies and rossby waves at periods of 80 250 days the standard deviation of the transbasin thermocline transport due to eddies and rossby waves is estimated to be 2 6 sv

uncertainties in the mean ocean dynamic topography before the launch of the gravity field and steady state ocean circulation explorer goce 1 in anticipation of the future observations of the gravity mission gravity field and steady state ocean circulation explorer goce the present day accuracy of mean dynamic topography mdt is estimated from both observations and models a comparison of five observational estimates illustrates that rms differences in mdt vary from 4 2 to 10 5 cm after low pass filtering the fields with a hamming window with wavenumber n 120 corresponding to an effective resolution of 167 km rms differences in observational mdt reduce to 2 4 8 3 cm for n 15 1334 km differences in data sources geoid model in situ data are mostly visible in the small scale oceanic features while differences in processing filtering inverse modeling techniques are reflected at larger scales a comparison of seven different numerical ocean models demonstrates that model estimates differ mostly in western boundary currents and in the antarctic circumpolar current rms differences between modeled and observed mdt are at best 8 8 cm for n 120 and reduce to 6 4 cm for n 15 for models with data assimilation a minimal rms difference of 6 6 cm n 120 to 3 4 cm n 15 is obtained with respect to the observational mdts the reduction of differences between mdts with increasing filtering scales is smaller than expected while it is expected that goce will improve mdt estimates at small spatial scales improvement of mean sea surface estimates from satellite altimetry may be needed to improve mdt estimates at larger scales

an objective method for computing advective surface velocities from sequential infrared satellite images using cross correlations between sequential infrared satellite images an objective technique is developed to compute advective sea surface velocities cross correlations are computed in 32 x 32 pixel search second image and 22 x 22 template first image windows from gradients of sea surface temperature computed from the satellite images velocity vectors computed from sequential images of the british columbia coastal ocean generally appear coherent and consistent with the seasonal surface current in the region during periods of strong wind forcing as indicated by maps of sea level pressure the image advective velocities are stronger and more coherent spatially and appear to cross surface temperature gradients when winds are weaker the advective velocities correspond better with the infrared temperature patterns suggesting the increased contribution of the geostrophic current to the surface flow velocities determined from coincident near surface drogued 5 10 m buoys positioned every half hour by internal loran c units in mid june show excellent agreement with the image advective velocities in addition conductivity temperature and depth ctd measurements taken during the buoy tracking confirm the homogeneity of the upper 10 m and ctd derived geostrophic currents are consistent with

mesoscale eddy detection in satellite imagery of the oceans using the radon transform abstract the present study proposes a new methodology to identify mesoscale eddies that are ubiquitous in the ocean and can be observed in a variety of satellite images our focus is on eddies with mean diameter of 100 500 km the proposed methodology uses an algorithm based on the radon transform the basic premise is that the inverse radon transform of a circularly symmetric feature is angle independent therefore the more constant the radon transform of an image is with respect to the rotation angle the more circularly symmetric the image is although our method is based on circular symmetry it is able to detect non symmetric eddies using a sensitivity parameter that quantifies the deformation our method is effective to determine how circular a feature observed in a satellite image is and suggest whether it is an eddy or not based on geometric criteria a series of tests with synthetic data were performed to assess the sensitivity to spectral content and aspect ratio detectable by the method another sequence of tests was carried out with images of chlorophyll a concentration sea surface temperature and sea surface height in the three cases five areas of 100 50 pixels were selected and filtered with exactly the same algorithm and parameters the two sets of tests indicate that the proposed method was able to identify eddies in a single time series of satellite images and in multiple series of different variables the main advantage of this method in comparison with either automatic ones based on dynamics and geometry or manual methods is its ability to observe eddies in multiple data sets of different variables

bottom currents derived from a shipborne adcp on woce cruise a11 in the south atlantic abstract this paper is divided into two parts the first describing an enhancement of the shipborne adcp system and the second describing information about bottom currents that have been obtained therefrom on woce cruise a11 in the south atlantic punta arenas to cape town rrs discovery has been fitted with a gps3df receiver and an array of antennas about its bridge which determine the instantaneous attitude of the ship the heading record from this instrument has been compared with the ship s gyrocompass throughout the 40 day cruise differences have been calculated and examined according to heading speed and movements underway differences are found insensitive to heading except in a southerly sector but on station differences exhibit a sinusoidal dependence on heading with range 3 steaming from a station led to transient behavior with recognizable effects for 1 hour the results are generally consistent with earlier reports and are attributed to gyro error an improved heading measurement has a

global rate and spectral characteristics of internal gravity wave generation by geostrophic flow over topography the rate of generation of internal gravity waves in the lee of small length scale topography by geostrophic flow in the world ocean was estimated using linear theory with corrections for finite amplitude topography several global data sets were combined for the calculation including an ocean circulation model for the near bottom geostrophic flow statistics over 500 abyssal current meter records historical climatological data for the buoyancy frequency and two independent estimates of the small scale topographic statistical properties the first topography estimate was based on an empirically derived relationship between paleo spreading rates and abyssal hill roughness with corrections for sedimentation the second estimate was based on small scale 100 km roughness of satellite altimetry derived gravity field using upward continuation relationships to derive estimates of abyssal hill roughness at the seafloor at scales less than approximately 20 km the lee wave generation rate was found to be between 0 34 to 0 49 tw the southern hemisphere produced 92 of the lee wave energy with the southern ocean dominating strength of the bottom flow was the most important factor in producing the global pattern of generation rate except in the indian ocean where extremely rough topography produced strong lee wave generation despite only moderate bottom flows the results imply about one half of the mechanical power input to the ocean general circulation from the extra equatorial wind stress of the world ocean results from abyssal lee wave generation topographic length scales between 176 m and 2 5 km horizontal wavelengths between 1 and 16 km accounted for 90 of the globally integrated generation

mafic ultramafic and quartz rich rock indices deduced from aster thermal infrared data using a linear approximation to the planck function abstract aster thermal infrared tir data are widely used to detect mafic ultramafic rock and quartz rich rock and several rock indices have been proposed based on emissivity features however aster tir bands of radiance data correlate highly with each other which indicates that the independent information derived from different bands may be limited what s more aster tir radiance at sensor data contain atmospheric effect and temperature information thus interfering with the availability of these previously proposed indices in this study we aim to explain the correlation using a linear approximation of the planck function and deduce a linear equation that represents the relationship of the radiance between two tir bands theoretical difference indices were deduced based on the linear equation and regression residual characteristics for any two aster tir radiance bands the study area is located in qinghai province china and belongs to the qinghai tibet plateau where the average elevation is approximately 4200 m a scatter plot of radiance derived from the aster image that overlaps the study area indicates that mafic ultramafic rock and quartz rich rock can be distinguished from other surface objects well two mafic ultramafic rock indices mi1 b13 0 9147 b10 1 4366 and mi2 b13 0 8945 b11 1 2404 and two quartz rich rock indices qi1 b13 0 9261 b12 1 4623 and qi2 b14 0 844 b12 1 8971 were proposed they satisfactorily map these rock units the atmospheric effect on the indices is weak in arid or high elevation region so it will not interfere with the indices obviously in these regions one way variance analysis was performed to discuss the stability of the indices with respect to temperature the mafic ultramafic rock indices are found to be independent of temperature whereas the values of quartz rich rock indices increase with the rising of temperature we thus conclude that the quartz rich rock indices are suitable for the high elevation region only while the mafic ultramafic rock indices may be capable of detecting these rocks in regions with different natural conditions

the role of vorticity fluxes in the dynamics of the zapiola anticyclone 1 the argentine basin in the south atlantic ocean is one of the most energetic regions in the ocean with complicated dynamics which plays an important role in the global climate a number of observations have discovered an intense anticyclonic gyre of barotropic circulation around the zapiola rise in the center of the basin theoretical studies have shown that the zapiola anticyclone represents an eddy driven flow controlled by bottom friction recent advances in high resolution global ocean data syntheses performed using nasa supercomputing facilities provide realistic simulations of the circulation and the variability in the argentine basin using these simulations and satellite altimeter observations we analyzed the vorticity balance of the zapiola anticyclone our results suggest the dominance of vorticity fluxes and the advection of the potential vorticity over a nonuniform bottom topography in determining the variability of the gyre while the impact of the local wind stress is small the divergence of the relative vorticity anomaly advection by eddies is found to be the most important contributor to the relative vorticity flux divergence influencing the variability of the zapiola anticyclone our results demonstrate that the relative vorticity influencing the variability of the anticyclone is mainly advected from the south where the northern branch of the antarctic circumpolar current at the subpolar front is located

on the origins of the variability of the malvinas current in a global eddy permitting numerical simulation 1 this article investigates the origins of the variability of the malvinas current mc transport using the results of an eddy permitting ocean general circulation model first the dynamical links between the variabilities of the mc and the antarctic circumpolar current acc transports at the drake passage are established time series analyses indicate that the connection between the transport variations of the acc and the mc is masked by high frequency oscillations although a substantial portion of this highfrequency variability is produced and dissipated locally there are also anomalies that propagate between those regions the most conspicuous of these signals has an average speed of 6 7 cm s 1 and a period of 150 days second the contribution of the wind forcing to the variability of the acc and the mc is determined from principal estimator patterns analysis the analysis indicates that the variance of the transport of both currents is more directly related to the variability of the wind stress than to the wind stress curl the transport variability is particularly sensitive to zonal wind stress anomalies in the latitudinal range of the drake passage that extends farther north over the south indian ocean a rather counterintuitive result of our analysis is that the wind stress forcing over the south atlantic ocean is unimportant to the variability of the mc transport

dynamically balanced absolute sea level of the global ocean derived from near surface velocity observations 1 the 1992 2002 time mean absolute sea level distribution of the global ocean is computed for the first time from observations of near surface velocity for this computation we use the near surface horizontal momentum balance the velocity observed by drifters is used to compute the coriolis force and the force due to acceleration of water parcels the anomaly of horizontal pressure gradient is derived from satellite altimetry and corrects the temporal bias in drifter data distribution ncep reanalysis winds are used to compute the force due to ekman currents the mean sea level gradient force which closes the momentum balance is integrated for mean sea level we find that our computation agrees within uncertainties with the sea level computed from the geostrophic hydrostatic momentum balance using historical mean density except in the antarctic circumpolar current a consistent horizontally and vertically dynamically balanced near surface global pressure field has now been derived from observations

a new eulerian method to estimate spicy agulhas leakage in climate models the agulhas leakage brings warm and saline water from the indian ocean into the south atlantic forming part of the returning branch of the global thermohaline circulation an important component of climate we develop a new method using the passive tracer spice to estimate agulhas leakage transport in an ocean eddy resolving climate model that properly captures agulhas retroflection and leakage we identify agulhas leakage waters as positive spice anomalies 0 1 and are able to trace leakage to depths greater than 1000 m spice based eulerian agulhas leakage captures spikes in lagrangian leakage transport which coincide with the passage of agulhas rings yielding a statistically significant correlation 0 47 on interannual times scales differences between eulerian and lagrangian transports are reduced and correlation increases to 0 77 we obtain a mean spice based eulerian agulhas leakage of 17 4 sverdrup sv and lagrangian agulhas leakage of 18 2 sv which are within the range of observational estimates

agulhas eddies a synoptic view using geosat erm data abstract warm core rings formed in the agulhas retroflection transfer water from the indian ocean to the south atlantic in an attempt to measure the strength of this exchange a combination of satellite altimeter and hydrographic data are used to examine agulhas eddy paths and decay rates in the south atlantic because the surface dynamic height of a warm core eddy is higher than surrounding waters the rings are visible in satellite altimeter measurements over 20 agulhas eddies have been tracked from maps of anomalous sea surface height ssh derived from the geosat exact repeat mission erm dataset the correlation r2 of dynamic height referenced to 2000 dbar and anomaly ssh for one coincidentally sampled area is 97 within an agulhas eddy dropping to a fraction of that outside of it indicating that the ssh anomaly signal is a reliable measure for strong features like agulhas eddies the sizes and distribution of the agulhas eddies in the erm record compare favorably with those in recent hydrogr

on the dynamics of the zapiola anticyclone recent observations obtained in the south atlantic suggest the existence of a strong anticyclonic flow positioned over a major bottom topographic feature known as the zapiola drift here a numerical simulation of the south atlantic is described in which this anticyclone is reproduced and the model is used to diagnose the dynamics maintaining this flow with a mean barotropic transport of 140 sv and bottom velocities of 10 cm s 1 the simulated zapiola anticyclone compares well with in situ observations furthermore the model surface eddy kinetic energy shows a local minimum over the drift in agreement with observations from topex poseidon numerical experiments show that the circulation feature is sensitive to the intensity of the eddy field and to the particular value of the bottom friction both of these tendencies are in agreement with a theoretical explanation of the zapiola anticyclone that has recently appeared elsewhere thus we argue that the anticyclone is maintained by eddy driven potential vorticity fluxes accelerating flow within topographically closed ambient potential vorticity contours as far as we know this is the first south atlantic simulation to reproduce the zapiola anticyclone in a realistic fashion the quantitative success of this experiment is attributed to the use of a topography following sigma coordinate in a spatially well resolved model

puzzling over the dynamics of the lofoten basin a sub arctic hot spot of ocean variability 1 a sub arctic hot spot of intense synoptic scale variability is observed in the lofoten basin lb of the norwegian sea using ers 1 2 and envisat satellite altimetry measurements we discover a cyclonic propagation of the synoptic scale sea surface height anomalies around the center of the lb surface drifter trajectories do not reveal an associated coherent near surface cyclonic flow suggesting that the propagating signals have a wavelike nature we identify a dipole and a quadrupole wave modes rotating around the center of the lb obtain analytic dispersion relations for these modes and demonstrate that the observed propagation is a manifestation of topographic rossby waves most of the observed waves have a wavelength of about 500 km and phase speeds ranging from 2 to 10 km day we show that these waves are largely responsible for the localization and amplification of sea surface height variability in the center of the lb

subsurface circulation and mesoscale variability in the algerian subbasin from altimeter derived eddy trajectories algerian eddies are the strongest and largest propagating mesoscale structures in the western mediterranean sea they have a large influence on the mean circulation water masses and biological processes over 20 years of satellite altimeter data have been analyzed to characterize the propagation of these eddies using automatic detection methods and cross correlation analysis we found that on average algerian eddy trajectories form two subbasin scale anticlockwise gyres that coincide with the two algerian gyres which were described in the literature as the barotropic circulation in the area this result suggests that altimetry sea surface observations can provide information on subsurface currents and their variability through the study of the propagation of deep mesoscale eddies in semienclosed seas the analysis of eddy sea level anomalies along the mean pathways reveals three preferred areas of formation eddies are usually formed at a specific time of the year in these areas with a strong interannual variability over the last 20 years

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

divergent pathways of cyclonic and anti cyclonic ocean eddies satellite altimetry is used to study the propagation pathways of warm and cold ocean eddies in different ocean basins we consider eddies that have a life span longer than 3 months and we present three regional studies in the southeast indian the southeast atlantic and the northeast pacific oceans the case studies show that simple theories for vortex propagation on a plane work in regions where energetic eddies propagate though a weak background flow under these conditions anticyclonic cyclonic eddies propagate westward and equatorward poleward this divergence in the eddy pathways implies a net equatorward eddy heat flux and has implications for the meridional transport of freshwater carbon nutrients etc