improved global surface currents from the merging of altimetry and sea surface temperature data abstract six years of surface velocities have been calculated over the global ocean by combining altimeter derived geostrophic velocities and sea surface temperature sst data the method is based on the inversion for the velocity of the heat conservation equation using the altimeter velocities as background by accurately prescribing the error both on the background velocities and on the forcing term heat fluxes the altimeter background velocities are successfully improved in areas characterized by strong sst gradients and remain unchanged in low sst gradient regions where by construction no additional information may be brought by the sst field this allows us to provide for the first time a global field of surface velocities from the merging of altimetry and sst both the spatial and temporal resolution of the altimeter derived velocities is enhanced by the sst information validation is performed through comparison to in situ drifting buoy velocities major improvements 10 20 globally up to 35 locally are obtained on the meridional component of the velocity and in the equatorial band due to the large uncertainty on the heat fluxes and the spatio temporal resolution of the input datasets the high frequency ageostrophic components of the circulation is hardly resolved by the method and outside the equatorial band improvements are mainly on the geostrophic component it is shown that the level of accuracy obtained by combining altimeter velocities based on a two satellite configuration and microwave sst data is equivalent or higher to the one from a four altimeter constellation in western boundary currents this opens the perspective for a systematic use of the method to improve the altimeter derived surface velocities over the 1993 2001 period for which only 2 altimeters have been flying simultaneously finally over the recent years the use of higher resolution sst products based on both microwave and infrared measurements leads to further enhancement of the accuracy of the altimeter velocities on both the zonal and the meridional component in strong sst gradients areas

surface circulation in the solomon sea derived from lagrangian drifter observations abstractvelocity measurements from satellite tracked surface drifters collected between 1994 and 2010 are used to map the surface circulation in the solomon sea the last passageway for waters of subtropical origin flowing northward toward the equator where they replenish the pacific warm pool pseudo eulerian statistics of the drifter observations show a strong seasonal cycle in both the mean circulation and the eddy kinetic energy in the region the circulation is characterized by a strong northward flow from june to november the season of strong southeasterly trade winds over the solomon sea and a mostly southward flow with increased variability from december to may when the winds over the sea are weak the seasonal velocity signal has the largest magnitude narrowly along the double western boundary formed by the eastern coastlines of new guinea and the solomon islands suggesting that direct wind driving with its much larger spatial scales is not the main influence in addition the surface circu

the southwest pacific ocean circulation and climate experiment spice the southwest pacific ocean circulation and climate experiment spice is an international research program under the auspices of clivar the key objectives are to understand the southwest pacific ocean circulation and the south pacific convergence zone spcz dynamics as well as their influence on regional and basin scale climate patterns south pacific thermocline waters are transported in the westward flowing south equatorial current sec toward australia and papua new guinea on its way the sec encounters the numerous islands and straits of the southwest pacific and forms boundary currents and jets that eventually redistribute water to the equator and high latitudes the transit in the coral solomon and tasman seas is of great importance to the climate system because changes in either the temperature or the amount of water arriving at the equator have the capability to modulate the el nino southern oscillation while the southward transports influence the climate and biodiversity in the tasman sea after 7 years of substantial in situ oceanic observational and modeling efforts our understanding of the region has much improved we have a refined description of the spcz behavior boundary currents pathways and water mass transformation including the previously undocumented solomon sea the transports are large and vary substantially in a counter intuitive way with asymmetries and gating effects that depend on time scales this paper provides a review of recent advancements and discusses our current knowledge gaps and important emerging research directions

stirring of the northeast atlantic spring bloom a lagrangian analysis based on multisatellite data 1 the effect of the geostrophic stirring on phytoplankton variability during the northeast atlantic spring bloom is studied by analyzing satellite derived surface chlorophyll sea surface temperature and sea surface height the calculation of unstable manifolds is used as a diagnostic of the transport properties of the geostrophic velocity field calculated from the sea surface height we identify two mechanisms by which the geostrophic velocity field acts on chlorophyll patterns the first mechanism is a direct effect of the horizontal transport on already formed chlorophyll by acting as sticking transport barriers the unstable manifolds are shown to 1 modulate the fronts of already formed phytoplankton in lobular structures 2 create spiralling chlorophyll anomalies within eddies and 3 produce chlorophyll filaments the second mechanism is an indirect effect on in situ chlorophyll production mediated by nutrient upwelling supported by a recent study on the vertical velocities of the northeast atlantic legal et al 2006 we argue that the horizontal unstable manifolds also shape the filamentary vertical velocity cells and hence the patterns of in situ produced chlorophyll through submesoscale vertical nutrient injection

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

inversion of submesoscale patterns from a high resolution solomon sea model feasibility assessment a high resolution realistic numerical model of the solomon sea which exhibits a high level of variability at mesoscales and submesoscales is used to explore new avenues for data assimilation image data assimilation represents a powerful methodology to integrate information from high resolution observations such as satellite sea surface temperature or chlorophyll or high resolution altimetric sea surface height that will be observed in the forthcoming swot mission the present study investigates the feasibility and accuracy of the inversion of the dynamical submesoscale information contained in high resolution images of sea surface temperature sst or salinity sss to improve the estimation of oceanic surface currents the inversion method is tested in the context of twin experiments with sst and sss data provided by a model of the solomon sea for that purpose synthetic tracer images are built by binarizing the norm of the gradient of sst sss or spiciness the binarized tracer images are compared to the dynamical image which is derived from the finite size lyapunov exponents the adjustment of the dynamical image to the tracer image provides the optimal correction to be applied on the surface velocity field the method is evaluated by comparing the result of the inversion to the reference model solution the feasibility of the inversion of various images sst sss both sst and sss or spiciness is explored on two small areas of the solomon sea we show that errors in the surface velocity field can be substantially reduced through the inversion of tracer images

subsurface structure of the solfatara volcano campi flegrei caldera italy as deduced from joint seismic noise array volcanological and morphostructural analysis 1 the joint application of different seismological techniques for seismic noise analysis and the results of a volcanological and morphostructural survey have allowed us to obtain a detailed and well constrained image of the shallow crustal structure of the solfatara volcano campi flegrei caldera italy horizontal to vertical spectral ratios inversion of surface wave dispersion curves and polarization analysis provided resonance frequencies and peak amplitudes shear wave velocity profiles and polarization pattern of coherent ambient noise these results combined in a unique framework indicate that the volcanic edifice is characterized by lateral and vertical discontinuities and heterogeneities in terms of shear wave velocity lithological contrasts and structural setting the interpretation of the seismological results with the volcanological and morphostructural constraints supports the hypothesis that the volcano has been characterized by a complex and intense activity with the alternation of constructive and destructive phases during which magmatic and phreatomagmatic explosions built a complex tuff cone later reworked by atmospheric agents and altered by hydrothermal activity the differences in the velocity structure between the central and eastern parts of the crater have been interpreted as resulting from a possible eastward migration of the eruptive vent along the deformational features affecting the area and to the presence of viscous lava and lithified tuff bodies within the feeding conduits which are buried under a covering of reworked materials of variable thickness the observed fault and fracture systems partially inherited from regional structural setting and exhumed during volcanism and ground deformation episodes also seems to strongly control wave propagation affecting the noise polarization properties

seismic zonation of barcelona based on numerical simulation of site effects seismic responses of different sites of barcelona have been investigated through numerical modelling geological maps and geotechnical data available from drillings for buildings and infrastructures have been used to determine the dynamical properties of the soils through different correlations between standard geotechnical data and dynamical parameters obtained in other regions an estimation of the depth of the palaeozoic basement has been obtained through an inversion of a detailed gravity survey a 1 d equivalent linear method has been used to compute complete transfer functions and other spectral responses such as psa and psv for various damping values with the purpose of classifying zones with similar behaviour given the uncertainties associated with the input data a montecarlo s simulation process has been carried out four zones characterized by their corresponding transfer function and by pga amplifications are proposed the numerical results are compared with those previously obtained through microtremor measurements showing that predominant periods derived from nakamura s technique should be taken carefully

surface wave array tomography in se tibet from ambient seismic noise and two station analysis i phase velocity maps summary empirical green s functions egfs between pairs of seismographs can be estimated from the time derivative of the long time cross correlation of ambient seismic noise these egfs reveal velocity dispersion at relatively short periods which can be used to resolve structures in the crust and uppermost mantle better than with traditional surface wave tomography we combine rayleigh wave dispersion estimates from egfs and from traditional two station ts analysis into a new approach to surface wave array tomography with data from dense receiver arrays we illustrate the methodology with continuous broad band recordings from a temporary seismographic network on the southeastern part of the tibetan plateau in sichuan and yunnan provinces sw china the egfs are robust under temporal changes in regional seismicity and the use of either ambient noise approximated by records without signal from events with magnitude mb 5 or 4 or surface wave coda produces similar results the egfs do not strongly depend on the presence of large earthquakes but they are not reciprocal for stations aligned in the n s direction this directionality reflects the paucity of seismicity to the north of the array using a far field representation of the surface wave green s function and an image transformation technique we infer from the egfs the rayleigh wave phase velocity dispersion in the period band from 10 30 s a classical ts approach is used to determine rayleigh wave phase velocity dispersion between 20 120 s together they constrain phase velocity variations for t 10 120 s which can be used to study the structure from the crust to the upper mantle beneath se tibet short and intermediate period 10 80 s phase velocities are prominently low suggesting that the crust and upper mantle beneath se tibet is characterized by slow shear wave propagation

propagation of north pacific interdecadal subsurface temperature anomalies in an ocean gcm propagation of subsurface north pacic inter decadal variations is investigated with an ocean general cir culation model forced by observed sea surface temperature anomalies subsurface temperature anomalies subducted in the central subtropical north pacic take a more westward pathway than a passive temperature tracer and reach the western boundary to the north of the bifurcation latitude this prevents them from extending into the equator on the boundary between the subtropical and the subarctic gyres on the other hand the upper 500 m heat content anomaly is found to propagate eastward as high vertical modes of rossby waves advectedbythemean eastward cur rent this notion is supported by a sign reversal in temper ature anomaly underneath

preliminary map of soil s predominant periods in barcelona using microtremors in order to evaluate soil effects in the urban area of barcelona the nakamura s technique has been used to estimate the predominant periods of soils noise measurements for 195 sites were performed using a strong motion accelerograph and a velocimeter in this work the resulting preliminary map of predominant periods is presented the obtained predominant periods are coherent with the geological and geotechnical features of the area the analysis of the information has allowed the distinctions among several types of soil and underlying materials a predominant period of about 0 06 s is evaluated for sites located over outcrop paleozoic rock in the tibidabo collserola mountains for sites consisting of material named tricycle that is the most extensive and also the most heterogeneous zone predominant period range from 0 10 s up to 2 0 s depending on the thickness of the surface materials and the kind and thickness of the underlying materials in the besos river two zones are observed the riverside with periods between 0 50 s and 0 83 s and a second area with periods between 1 0 and 2 1 s in the llobregat river delta the obtained periods are quite homogeneous with values around 0 72 s other predominant periods are found in some tertiary rock outcrop

exploring the mesoscale activity in the solomon sea a complementary approach with a numerical model and altimetric data the solomon sea is an area of high level of eddy kinetic energy eke and represents a transit area for the low latitude western boundary currents llwbcs connecting the subtropics to the equatorial pacific and playing a major role in enso dynamics this study aims at documenting the surface mesoscale activity in the solomon sea for the first time our analysis is based on the joint analysis of altimetric data and outputs from a 1 12 model simulation the highest surface eke is observed in the northern part of the basin and extends southward to the central basin an eddy tracking algorithm is used to document the characteristics and trajectories of coherent mesoscale vortices cyclonic eddies generated in the south basin are advected to the north by the llwbcs before merging with stationary mesoscale structures present in the mean circulation anticyclonic eddies are less numerous they are generated in the southeastern basin propagate westward reach the llwbcs and dissipate the seasonal and interannual modulations of the mesoscale activity are well marked at seasonal time scale maximum minimum activity is in may june september at interannual time scale the mesoscale activity is particularly enhanced during la nina conditions if instabilities of the regional circulations seem to explain the generation of mesoscale features the modulation of the mesoscale activity seems to be rather related with the intrusion at solomon strait of the surface south equatorial current rather than to the llwbcs by modulating the horizontal and vertical shears suitable for instabilities

equilibrium structure and dynamics of the california current system this paper addresses the structure and dynamical mechanisms of regional and mesoscale physical variability in the subtropical northeast pacific ocean using the regional oceanic modeling system roms the model is configured with a u s west coast domain that spans the california current system ccs with a mesoscale horizontal resolution up to as fine as 3 5 km its mean seasonal forcing is by momentum heat and water fluxes at the surface and adaptive nudging to gyre scale fields at the open water boundaries its equilibrium solutions show realistic mean and seasonal states and vigorous mesoscale eddies fronts and filaments the level of eddy kinetic energy eke in the model is comparable to drifter and altimeter estimates in the solutions with sufficiently fine resolution because the model lacks nonseasonal transient forcing the authors conclude that the dominant mesoscale variability in the ccs is intrinsic rather than transiently forced the primary eddy generation mechanism is the baroclinic instability of upwelling alongshore currents there is progressive movement of meanseasonal currents and eddy energy offshore and downward into the oceanic interior in an annually recurrent cycle the associated offshore eddy heat fluxes provide the principal balance against nearshore cooling by mean ekman transport and upwelling the currents are highly nonuniform along the coast with important influences by capes and ridges in both maintaining mean standing eddies and launching transient filaments and fronts

mesoscale to submesoscale transition in the california current system part ii frontal processes this is the second of three papers investigating the regime transition that occurs in numerical simulations for an idealized equilibrium subtropical eastern boundary upwelling current system similar to the california current the emergent upper ocean submesoscale fronts are analyzed from phenomenological and dynamical perspectives using a combination of composite averaging and separation of distinctive subregions of the flow the initiating dynamical process for the transition is near surface frontogenesis the frontal behavior is similar to both observed meteorological surface fronts and solutions of the approximate dynamical model called surface dynamics i e uniform interior potential vorticity q and diagnostic force balance in the intensification of surface density gradients and secondary circulations in response to a mesoscale strain field however there are significant behavioral differences compared to the surface dynamics model wind stress acts on fronts through nonlinear ekman transport and creation and destruction of potential vorticity the strain induced frontogenesis is disrupted by vigorous submesoscale frontal instabilities that in turn lead to secondary frontogenesis events submesoscale vortices and excitation of even smaller scale flows intermittent submesoscale breakdown of geostrophic and gradient wind force balance occurs during the intense frontogenesis and frontal instability events

on the limitation of the h v spectral ratio using seismic noise as an exploration tool application to the grenoble valley france a small apex ratio basin the h v spectral ratio method based on seismic noise hvsrn was used in the grenoble basin france an alpine valley characterized by a small apex ratio the resonance frequencies obtained in the experiments were compared to the thickness of the sediments deduced from a microgravimetric survey and to the 1 d theoretical assessment of site responses given the abundance of data on the sediments and depth of the basin the values of the theoretical resonance frequency fo can be determined quite accurately however it has been observed that the effects of basin geometry can disturb fo measurements using the hvsr method in particular for a case like the grenoble basin which has a small apex ratio w h and strong suspected 2 d and or 3 d effects interpretation of fo values in terms of bedrock depth gives rise to estimation errors of about 10 in certain cases with the most significant errors 50 occurring on the edges of the basin where subsurface layers are characterised by larger heterogeneities and where the basin topography is accentuated this study suggests that great care must be taken when using the hvsrn method as an exploration tool at least in valleys with a small apex ratio

an eddy permitting model of the atlantic circulation evaluating open boundary conditions as part of the french clipper project an eddy permitting model of the atlantic circulation has been run for 22 years the domain has open boundaries at drake passage and at 30 e from africa to antarctica the simulated mean circulation as well as the eddy activity is satisfactory for a 1 3 model resolution and the meridional heat transport at 30 s is within the range estimated from observations we use the mixed open boundary algorithm of barnier et al 1998 which has both a radiation condition and a relaxation to climatology the climatological boundary forcing strongly constrains the solution in the whole domain the model heat balance adjusts through the surface heat flux retroaction term more than the open boundaries the radiation phase velocities calculated within the algorithm are analyzed this shows quite surprisingly that both the eastern and western boundaries have a similar behavior regardless of the preferred directions for advection mainly eastward and wave propagation mainly westward our results confirm that open boundary algorithms behave differently according to the dynamics of the region considered the passive boundary condition that penduff et al 2000 applied successfully in the north eastern atlantic does not work in the present south atlantic model we emphasize the need for a careful prescription of the climatology at the open boundary for which a new approach based on synoptic sections is implemented

mixing structures in the mediterranean sea from finite size lyapunov exponents 1 we characterize horizontal mixing and transport structures in the surface circulation of the mediterranean sea as obtained from a primitive equation circulation model we calculate the finite size lyapunov exponents fsles of the velocity data set which give a direct measure of the local stirring by proper election of the fsle parameters we focus on the mesoscale structures locating a number of vortices embedded in an intricate network of high stretching lines these lines control transport in the system at the edge of the vortices a dense tangle of line intersections appears identifying strong mixing the spatial distribution of fsles averaged over one year allows to classify areas in the mediterranean basin according by their mixing activity the space average of fsles on selected geographical regions gives a measure for quantifying and comparing the mixing seasonal variability

mesoscale to submesoscale transition in the california current system part i flow structure eddy flux and observational tests in computational simulations of an idealized subtropical eastern boundary upwelling current system similar to the california current a submesoscale transition occurs in the eddy variability as the horizontal grid scale is reduced to o 1 km this first paper in a series of three describes the transition in terms of the emergent flow structure and the associated time averaged eddy fluxes in addition to the mesoscale eddies that arise from a primary instability of the alongshore wind driven currents significant energy is transferred into submesoscale fronts and vortices in the upper ocean the submesoscale arises through surface frontogenesis growing off upwelled cold filaments that are pulled offshore and strained in between the mesoscale eddy centers in turn some submesoscale fronts become unstable and develop submesoscale meanders and fragment into roll up vortices associated with this phenomenon are a large vertical vorticity and rossby number a large vertical velocity relatively flat horizontal spectra contrary to the prevailing view of mesoscale dynamics a large vertical buoyancy flux acting to restratify the upper ocean a submesoscale energy conversion from potential to kinetic a significant spatial and temporal intermittency in the upper ocean and material exchanges between the surface boundary layer and pycnocline comparison with available observations indicates that submesoscale fronts and instabilities occur widely in the upper ocean with characteristics similar to the simulations

ssh wavenumber spectra in the north pacific from a high resolution realistic simulation abstractfollowing recent studies based on altimetric data this paper analyses the spectral characteristics of the sea surface height ssh using a new realistic simulation of the north pacific ocean with high resolution in the horizontal and 100 vertical levels this simulation resolves smaller scales down to 10 km than altimetric data limited to 70 km because of the noise level in high eddy kinetic energy eke regions as in the western part ssh spectral slope almost follows a k 4 with k the wavenumber or slightly steeper law in agreement with altimeter studies the new result is that unlike altimeter studies such a k 4 slope is also observed in low eke regions as in the eastern part in these regions this slope mostly concerns scales not well resolved by altimetric data such k 4 ssh spectral slopes are weaker from what is expected from quasigeostrophic turbulence theory but closer to surface quasigeostrophic sqg turbulence theory the consequence is that the small scales concerned

late winter generation of spiciness on subducted isopycnals the origins of density compensating anomalies of temperature and salinity spice are investigated using a model forced with the most realistic surface products available over the 40 years 1958 97 in this hindcast the largest interannual spiciness anomalies are found in the pacific ocean near the isopycnal s 0 5 25 5 where deviations as great as 1 28c and 0 6 psu are generated equatorward of winter outcropping in the eastern subtropics in both hemispheres these source regions are characterized by very unstable salinity gradients and low mean density stratification in winter two related signatures of winter mixing in the southeast pacific sep are density that is well mixed deeper than either temperature or salinity and subsurface density ratios that approach 1 all ocean basins in the model are shown to have regions with these characteristics and signatures however the resultant spiciness signals are focused on different isopycnals ranging from s 0 5 25 0 in the northeast pacific to s 0 5 26 5 in the south indian ocean a detailed examination of the sep finds that large positive anomalies are generated by diapycnal mixing across subducted isopycnals e g s 0 5 25 5 whereas negative anomalies are the result of a steady isopycnal advection moderated by vertical advection and heave there is considerable interannual variability in the strength of anomalies and in the density on which they occur historical observations are consistent with the model results but are insufficient to verify all aspects of the hindcast including the processes of anomaly generation in the sep it was not possible to relate isopycnal anomaly genesis to local surface forcing of any kind a complex scenario involving basinwide circulation of both the ocean and atmosphere especially of surface water through the subtropical evaporation zones is put forward to explain the decadal time scale evident in sep salinity anomalies on s 0 5 25 5 pacific anomalies generated on s 0 5 25 5 can be traced along mean geostrophic streamlines to the western boundary where decadal salinity variations at 78s are about 2 times as large order 60 1 psu as at 128n although there may be more variance on shallower isopycnals in the north at least portions of the s 0 5 25 5 signals appear to continue along the boundary to a convergence at the equator suggesting that the most robust sources of pacific spiciness variance coincide with equatorial exchange pathways