Radio Science, 43, RS3008. DOI: 10.1029/2007RS003728 -- Abstract. (BibTeX: camps.etal.2008)
This work describes the main effects that have to be taken into account to model the sea surface emission at L-band, and the existing approaches to perform the sea surface salinity retrieval from multiangular radiometric measurements. This manuscript reviews the activities carried out in these fields during the past years by the Universitat Polite`cnica de Catalunya (UPC) in collaboration with the Institut de Cie`ncies del Mar (ICM - CSIC). They cover the precise measurement of the dielectric permittivity of the seawater at L-band, the sea surface emissivity (including the effect of wind-driven waves, swell, currents, rain, and oil spills), the comparison of experimental data with numerical models, and the development of sea surface salinity retrieval algorithms for SMOS using multiangular radiometric data. The first salinity retrievals using 2D aperture synthesis radiometry are also presented.
Journal of Geophysical Research, 113, C10027. DOI: 10.1029/2007JC004480 -- Abstract. (BibTeX: aretxabaleta.etal.2008a)
Keywords: Bay of Fundy, model simulations, gyre climatology..
The characteristics of a persistent gyre in the mouth of the Bay of Fundy are studied using model simulations. A set of climatological runs are conducted to evaluate the relative importance of the different forcing mechanisms affecting the gyre. The main mechanisms are tidal rectification and density-driven circulation. Stronger circulation of the gyre occurs during the later part of the stratified season (July-August and September-October). The density-driven flow around the gyre is set up by weak tidal mixing in the deep basin in the central Bay of Fundy and strong tidal mixing on the shallow flanks around Grand Manan Island and western Nova Scotia. Spring river discharge has an important influence on near-surface circulation but only a small effect when averaged over the entire water column. Retention of particles in the gyre is controlled by the residual tidal circulation, increased frontal retention during stratified periods, wind stress, and interactions with the adjacent circulation of the Gulf of Maine. Residence times longer than 30 days are predicted for particles released in the proximity of the gyre.
Marine Ecology Progress Series, 364, 169-180. DOI: 10.3354/meps07461 -- Abstract. (BibTeX: sabates.etal.2008)
Keywords: Sardinella aurita · Engraulis encrasicolus · Larvae · Eggs · Microzooplankton · Vertical distribution · NW Mediterranean.
In recent years a northward expansion of Sardinella aurita has been reported in the western Mediterranean. Considering the coexistence of its larvae with those of the dominant species Engraulis encrasicolus, the present study was conducted to compare their vertical distributions in 2 areas off the Catalan coast with different vertical environmental conditions. During summer, the water column was stratified with a deep chlorophyll maximum (DCM) beneath the pycnocline. However, the southern area, under the influence of the Ebro River, was characterized by a secondary surface chlorophyll maximum. Vertical distribution of larval food, nauplii and copepodites showed good agreement with the high chlorophyll layers. In the earliest stages of development, larvae of both species remained in the upper levels. From 6 mm standard length on they developed a day/night migratory behaviour to search for food during the day (feeding period). Therefore, in the south, where the abundance of potential food in the upper layers was relatively high, larvae of both species remained in the upper levels during the day. However, in the north, where food was restricted to the DCM, only E. encrasicolus larvae were able to reach these deep levels. The low temperatures (~15°C) detected at the DCM may restrict the vertical migration of S. aurita in accordance with their thermophilic character. This limitation might might represent a restriction for the northward expansion of this species in the western Mediterranean.
Geo-Temas, 41, 1, 015501. DOI: 10.1088/1751-8113/41/1/015501 -- Abstract. (BibTeX: turiel.etal.2008b)
Multifractal formalism in the microcanonical framework has proved to be a valuable approach to understand and analyze complex signals, typically associated with natural phenomena in scale invariant systems. In this paper, we discuss the multifractal microcanonical formalism in a comprehensive, unified way, including new theoretical proofs and validation tests on real signals, so completing some known gaps in the foundations of this theory. We also review the latest advances and describe the present perspectives in this field. Some technical details on the implementation of involved algorithms and relevant open issues are also discussed
Remote Sensing of Environment, 112, 2246-2260. DOI: 10.1016/j.rse.2007.10.007 -- Abstract. (BibTeX: turiel.etal.2008a)
Keywords: Physical oceanography; Streamlines; Singularity analysis; Wavelet analysis; Multifractal; Pattern recognition.
In the recent years, the power of employing singularity analysis of scalar variables to perform pattern recognition in complex images has been evidenced. This approach is particularly useful when the image under study corresponds to a scalar variable submitted to a turbulent flow because, in that case, the arrangement of singularity manifolds corresponds to the multifractal hierarchy from the underlying turbulent flow. In this paper we will show how this intimate connection between Image Processing and Physics, when applied to Microwave Sea Surface Temperature images, allows to uncover global circulation patterns in the ocean at a daily basis with the resolution of 1/4 of degree. Using this technique, details not evidenced in the non-processed image are revealed. The emerging patterns provide a description of the global oceanic currents much richer than the usual global circulation scheme; in particular, instabilities, eddy generation and filamentation are distinctly identified. A pattern extraction of this kind is useful in order to measure and track mesoscale oceanic phenomena, opening the way to many operational and reanalysis applications.
Journal of Physical Oceanography, 38, 1, 243-256. DOI: 10.1175/2006JPO3692.1 -- Abstract. (BibTeX: viudez.2008)
Three-dimensional numerical simulations of rotating, statically and inertially stable, mesoscale flows show that wave packets, with vertical velocity comparable to that of the balanced flow, can be spontaneously generated and amplified in the frontal part of translating vortical structures. These frontal wave packets remain stationary relative to the vortical structure (e.g., in the baroclinic dipole, tripole, and quadrupole) and are due to inertia–gravity oscillations, near the inertial frequency, experienced by the fluid particles as they decelerate when leaving the large speed regions. The ratio between the horizontal and vertical wavenumbers depends on the ratio between the horizontal and vertical shears of the background velocity. Theoretical solutions of plane waves with varying wavenumbers in background flow confirm these results. Using the material description of the fields it is shown that, among the particles simultaneously located in the vertical column in the dipole’s center, the first ones to experience the inertia–gravity oscillations are those in the upper layer, in the region of the maximum vertical shear. The wave packet propagates afterward to the fluid particles located below.
Journal of Fluid Mechanics, 614, 145-172. DOI: 10.1017/S0022112008003364 -- Abstract. (BibTeX: viudez.2008a)
The concept of piecewise constant symmetric vortex in the context of threedimensional baroclinic balanced geophysical flows is explored. The pressure gradients generated by horizontal cylinders and spherical balls of uniform potential vorticity (PV), or uniform material invariants, are obtained either analytically or numerically, in the general case of Boussinesq and f -plane dynamics as well as under the quasigeostrophic and semigeostrophic dynamical approximations. Based on the order of magnitude of the different terms in the PV inversion equation, approximated PV equations are deduced. In some of these cases, radial solutions are possible and the interior and exterior solutions are found analytically. In the case of non-radial dependence, exterior solutions can be found numerically. Linear, and upper and lower bound approximations to the full PV inversion equations, and their respective solutions, are also included. However, the general solution for the pressure gradient in the vortex exterior does not have spherical symmetry and remains as an important theoretical challenge. It is suggested that, in order to maintain everywhere the inertial and static stability of the balanced geophysical flows, small balls of finite radius, rather than PV singularities, could become, specially in numerical applications, useful mathematical objects.
Geophysical Research Letters, 35, L11609, DOI: 10.1029/2008GL033971 -- Abstract. (BibTeX: biescas.etal.2008b)
This work illustrates the great potential of multichannel seismic reflection data to extract information from the finestructure of meddies with exceptional lateral resolution (10–15 m). We present seismic images of three meddies acquired in the Gulf of Cadiz (SW Iberian Peninsula), which consist of concentric reflectors forming oval shapes that sharply contrast with the background oceanic structure.The seismic images reveal the presence of different regions within the meddies that are consistent with those observed in historical temperature (T) and salinity (S) data. The core region, characterized by smooth T and S variations, is weakly reflective. The double-diffusive upper and lower boundaries and the lateral-interleaving outer edges, characterized by stronger T and S contrasts, display strong reflectivity bands. These new observations clearly show differences between layers developed at the upper and lower boundaries that can contribute to the knowledge of mixing processes and layering formation in oceans.
Ocean Modelling, 23, 21-32. DOI: 10.1016/j.ocemod.2008.03.002 -- Abstract. (BibTeX: mourre.etal.2008a)
Keywords: Sea surface salinity Sensitivity experiments Regional ocean model Atmospheric forcing Eastern subtropical North-Atlantic.
The surface salinity response to changes of various external forcings and model parameters is investigated in a regional 1/3º configuration of the NEMO-OPA model implemented over the eastern North-Atlantic subtropical Ocean. Fourteen realistic climatological simulations are run. By default, neither relaxation to climatological surface salinity nor temperature is included. Forcing fields and parameters expected to impact the surface salinity are modified. These include: the wind stress, the surface temperature, wind speed and relative humidity entering the bulk calculation for sensible and latent heat fluxes,the precipitation, the data specified at open boundaries, the lateral viscosity operator, the salt lateral diffusivity, the vertical mixing scheme, the on/off switch of the double diffusion parameterization, the river runoffs and the SSS/SST restoring terms. The SSS standard deviation over this ensemble of model simulations is of the order of 0.1 psu, which is also the order of the annual cycle of the surface salinity field in this area. In this experimental framework, the wind stress is found to have the largest impact on the model SSS, both in terms of mean field and annual variability. The sensitivity to the precipitation, atmospheric temperature, open boundary external data, and to the relaxation to climatological SSS and SST, is also significant. Of all the model parameterizations, the lateral salt diffusivity is the one associated to the strongest surface salinity model response. This work allows the identification of the main sources of error for model surface salinity. It paves the way for a more comprehensive investigation of SSS model error statistics, which is needed for future data assimilation experiments motivated by the close launch of the new SSS-observing SMOS and Aquarius satellite missions
Scientia Marina, 72, 2, 329-336. -- Abstract. (BibTeX: gabarro.etal.2008)
Keywords: remote sensing, radiometry, SMOS, salinity measurements, oceanographic campaigns.
In preparation for the European Space Agency SMOS (Soil Moisture and Ocean Salinity) satellite mission, radiometric and oceanographic measurements were performed in December 2000 and January 2001 and in November 2001 from a fixed platform in the NW Mediterranean to improve the modelling of the sea surface emissivity at L-band and new semi-empirical models were derived. Now one of these models has been used to retrieve sea surface salinity from L-band radiometric data acquired with a different instrument and different location. These data were acquired in August 2003 over the continental shelf within the influence of the Rio de la Plata, from Argentina to Brazil, southern Atlantic ocean with the STARRS airborne radiometer. Results show that the radiometer is capable of realistically detecting natural variations in surface salinity even though the model was derived in very different oceanographic conditions and from data collected by a different instrument.
Remote Sensing of Environment, 112, 12, 4242-4260. DOI: 10.1016/j.rse.2008.07.010 -- Abstract. (BibTeX: pottier.etal.2008a)
Keywords: Oceanic phytoplankton Satellite ocean color images Missing data Turbulence cascading Wavelet representation.
Oceanic turbulent flows develop complicated patterns, with eddies, filaments and shear currents. Although usually referred as chaotic, their inner organization is strongly hierarchical: turbulent flows develop cascades, which transfer properties such as energy or scalar density from larger to smaller scales. In this work, we present a novel algorithm based on the cascade and able to fill data gaps in satellite images (particularly, chlorophyll concentration maps). The first step is to show that cascade processes for chlorophyll-a concentration images take a simple, explicit form when an appropriate wavelet (here Battle-Lemarié of order 3) representation is used. A reconstruction algorithm exploiting the cascade structure is then given with a detailed description. We discuss the validity and quality of this algorithm when applied to SeaWiFS and MODIS-Aqua ocean color images. An application to merging data from multiple satellite missions is presented together with a demonstration of the benefit of this algorithm over two other merging methods
IEEE Transactions on Geoscience and Remote Sensing, 56, 11, 5709-5713. (BibTeX: simon.etal.2008b)
Journal of Physical Oceanography, 38, 1, 213-234. DOI: 10.1175/2007JPO3716.1 -- Abstract. (BibTeX: pallassanz.viudez.2008)
The spontaneous generation and propagation of short-scale inertia–gravity waves (IGWs) during the merging of two initially balanced (void of IGWs) baroclinic anticyclones is numerically investigated. The IGW generation is analyzed in flows with different potential vorticity (PV) anomaly, numerical diffusion, numerical resolution, vortex aspect ratio, and background rotation. The vertical velocity and its vertical derivative are used to identify the IGWs in the total flow, while the unbalanced flow (the waves) is diagnosed using the optimal PV balance approach. Spontaneous generation of IGWs occurs in all the cases, primarily as emissions of discrete wave packets. The increase of both the vortex strength and vortex extent isotropy enhances the IGW emission. Three possible indicators, or theories, of spontaneous IGW generation are considered, namely, the advection of PV, the material rate of change of the horizontal divergence, and the three-dimensional baroclinic IGW generation analogy of Lighthill sound radiation theory. It is suggested that different mechanisms for spontaneous IGW generation may be at work. One mechanism is related to the advection of PV, with the IGWs in this case having wave fronts similar to the PV isosurfaces in the upper layers, and helical patterns in the deep layers. Trapped IGWs are ubiquitous in the vortex interior and have annular wave front patterns. Another mechanism is related to the spatially coherent motion of preexisting IGWs, which eventually cooperate to produce mean flow, in particular larger-scale horizontal divergence, and therefore larger-scale vertical motion, which in turns triggers the emission of new IGWs.
Scientia Marina, 72, 4, 779-799. DOI: 10.3989/scimar.2008.72n4779 -- Abstract. (BibTeX: machin.etal.2008)
Keywords: XBT probes, operational oceanography, inverse method.
A methodology for recovering salinity from expendable bathythermograph (XBT) data is presented. The procedure exploits climatological relationships between temperature, salinity and depth to build regional characteristic curves by fitting a polynomial function that minimises both the variance of residuals and unknowns. Hence, salinity is computed and recovered as a function of temperature and depth. Empirical formula are provided to recover the salinity field from temperature-depth measurements for the Cantabrian Sea and Galician Area. The method is validated and applied in the context of two marine rescue exercises carried out in the Bay of Biscay close to the north coast of Spain and in the Finisterre region, where a series of XBT and conductivity-temperature-depth (CTD) profiles were acquired during fast samplings. The results agree reasonably well with independent data in terms of the spatial structure, with the largest errors in the upper 100 m of the ocean and at intermediate levels. The first diagnoses of the surface geostrophic velocity fields obtained through the salinity reconstruction are coherent and may help in rescue and safety operations during marine emergencies. Hence, we recommend that a technical unit should consider this kind of expandable sampling strategy with both XBT and XCTD data during marine emergencies, since it provides useful and comprehensive information rapidly with minimal interference by means of formal operations on board search and rescue ships.
Journal of Plankton Research, 30, 8, 873-883. DOI: 10.1093/plankt/fbn048 -- Abstract. (BibTeX: maynou.etal.2008a)
We analyse the spatial structure of early developmental stages of three ecologically important small pelagic schooling fish species in the northwestern Mediterranean Sea: the anchovy Engraulis encrasicolus, the round sardinella Sardinella aurita, and the sardine Sardina pilchardus. We used data on egg and larval abundance (arranged by development stage), hydrographic data and potential prey biomass collected during two cruises in summer and autumn 2005. Our analysis is based on the computation of Lloyd's patchiness index during the ontogeny of early developmental stages, as well as the computation of spatial auto-correlograms and cross-correlograms with environmental variables. The combined analysis allowed determination of the relative role of behavioural traits and the influence of hydrographic conditions in shaping the spatial structure of the three clupeiforms. We show that the spawning and developmental strategies of the two summer-spawning species (E. encrasicolus and S. aurita) are different. Engraulis encrasicolus has relatively low patchiness for all early developmental stages, while the importance of trophic variables in determining spatial structure increases during development. Sardinella aurita spawns in a trophically favourable environment and the patchiness of its early developmental stages increases for older larvae, becoming decoupled from environmental variables. The autumn spawned S. pilchardus eggs and larvae showed a development strategy similar to S. aurita, with limited importance of environmental variables in determining their patchiness.
International Journal of Remote Sensing, 29, 14, 4189-4205. DOI: 10.1080/01431160701840174 -- Abstract. (BibTeX: yahia.etal.2008)
In this article it is shown that the multifractal microcanonical formalism (herein referred to as MMF) has strong potential for bringing new solutions to a known problem in the analysis of some remotely sensed datasets: the determination of fire plumes in NOAA–AVHRR data. It has been proven that NOAA–AVHRR data can be used to detect plumes caused by fire accidents of different kinds. This work builds on previous studies and uses the MMF to introduce novel methods for the determination of plumes. The MMF can be used to derive geometrical superstructures (like certain multifractal topological manifolds and most importantly the so-called reduced signals) that are able to deal with the multiscale properties of turbulent geophysical fluid flows. These multiscale properties make use of the spatial distribution of grey-level values in the datasets and they are used in conjunction with previous pixel-based descriptors to enhance the determination of plume pixels.
Polar Biology, 31, 6, 691-707. DOI: 10.1007/s00300-008-0408-1 -- Abstract. (BibTeX: a.catalan.etal.2008a)
Keywords: Antarctica, Fish larvae and juveniles, Salps, Krill , Distribution, Abundance, Size structure, Hydrography, Density front, Segregation.
The spatial distribution, biomass and size structure of key mesozooplankton species and micronekton in the Bransfield Strait (Antarctica) are described in relation to environmental variables during the austral summer 2001. Stratified (BIONESS) biological sampling at five depth-ranges and CTD casts were performed at 40 stations, including a cross-Strait transect. Six families, 11 genera and 16 species composed the total catch of larval and juvenile fish, which were more abundant in the upper 75 m. Trematomus scotti was the most abundant fish and large individuals dominated at depths >75 m. The fish distribution patterns were associated with the main water masses in the area and with bottom depth. Spatial segregation in density and biomass of krill (Euphausia superba) and salps (Salpa thompsoni) was observed at a relatively small scale, in relation to the main water masses. Also, size-related spatial segregation was found in krill. The present study suggests that the spatial distribution of krill, salps and early life stages of fish, are influenced by the main water masses in the Strait, and that species may adapt their reproductive strategies not only to seasonal production peaks, but to transport processes within water bodies that maximise their fitness through optimum temperature and/or trophic.
Computers & Geosciences, 34, 5, 456-463. DOI: 10.1016/j.cageo.2007.04.011 -- Abstract. (BibTeX: rodriguez.etal.2008a)
Keywords: Wide-angle seismics; Software; Signal processing; Plug-in; Object oriented programming.
WASPAR (Wide-Angle reflection–refraction Seismic data Processing And Representation) is a new free multi-platform software tool to process and display wide-angle seismic data. It has been designed to read different raw data formats, construct record sections, process them using existing and newly developed algorithms, pick seismic phases and generate graphic files using a single, user-friendly interface. The main characteristics of WASPAR are its flexibility and expandability. It has been designed in a modular way using a plug-in architecture to manage raw data access and processing functionalities. We thus obtain a stable base easily maintainable and expandable. We have chosen the C++ programming language in combination with an object oriented methodology to facilitate the development of a multi-platform software tool, which is already available on Linux and MS Windows. In order to allow its expansion and upgrade, the program will be freely distributed under the terms of GPL license. The philosophy of this software tool is to leave it open to external contributions.
CIESM Workshop Monographs, 34, 5-17. (BibTeX: font.etal.2008e)
Journal of Coastal Research, 24, 6, 1612-1619. DOI: 10.2112/07-0886.1 -- Abstract. (BibTeX: guillen.etal.2008a)
Keywords: Urban beaches, beach occupation, tourist season.
Images from an Argus beach monitoring station were analyzed to count the number of people on two city beaches in Barcelona (NW Mediterranean) every hour for 4 years. Daily, weekly, seasonal, and interannual user distribution patterns were clearly established. Two different fit models were applied to the data based on a Fourier polynomial and nonlinear criteria, including external factors such as temperature and wind conditions, as well as predisposition factors. Finally, the evolution of beach users was compared with morphological beach changes caused by natural processes and human action. The results demonstrated that video observations provide a suitable method for counting people on the beach that could be useful for a number of coastal management applications.
Scientia Marina, 72, 1, 185-202. -- Abstract. (BibTeX: pelegri.2008)
Keywords: deep-water formation, thermocline circulation, ocean physiology, Milankovitch cycles.
One possible path for exploring the Earth’s far-from-equilibrium homeostasis is to assume that it results from the organisation of optimal pulsating systems, analogous to that in complex living beings. Under this premise it becomes natural to examine the Earth’s organisation using physiological-like variables. Here we identify some of these main variables for the ocean’s circulatory system: pump rate, stroke volume, carbon and nutrient arterial-venous differences, inorganic nutrients and carbon supply, and metabolic rate. The stroke volume is proportional to the water transported into the thermocline and deep oceans, and the arterial-venous differences occur between recently-upwelled deep waters and very productive high-latitudes waters, with atmospheric CO2 being an indicator of the arterial-venous inorganic carbon difference. The metabolic rate is the internal-energy flux (here expressed as flux of inorganic carbon in the upper ocean) required by the system’s machinery, i.e. community respiration. We propose that the pump rate is set externally by the annual cycle, at one beat per year per hemisphere, and that the autotrophic ocean adjusts its stroke volume and arterial-venous differences to modify the internal-energy demand, triggered by long-period astronomical insolation cycles (external-energy supply). With this perspective we may conceive that the Earth’s interglacial-glacial cycle responds to an internal organisation analogous to that occurring in living beings during an exercise-recovery cycle. We use an idealised double-state metabolic model of the upper ocean (with the inorganic carbon/nutrients supply specified through the overturning rate and the steady-state inorganic carbon/nutrients concentrations) to obtain the temporal evolution of its inorganic carbon concentration, which mimics the glacial-interglacial atmospheric CO2 pattern.
Marine Pollution Bulletin, 56, 4, 686-703. DOI: 10.1016/j.marpolbul.2007.12.021 -- Abstract. (BibTeX: g.sotillo.etal.2008b)
Keywords: Oil-spill; Operational oceanography; Real-time; Forecast; Spanish waters.
The ESEOO Project, launched after the Prestige crisis, has boosted operational oceanography capacities in Spain, creating new operational oceanographic services and increasing synergies between these new operational tools and already existing systems. In consequence, the present preparedness to face an oil-spill crisis is enhanced, significantly improving the operational response regarding ocean, meteorological and oil-spill monitoring and forecasting. A key aspect of this progress has been the agreement between the scientific community and the Spanish Search and Rescue Institution (SASEMAR), significantly favoured within the ESEOO framework. Important achievements of this collaboration are: (1) the design of protocols that at the crisis time provide operational state-of-theart information, derived from both forecasting and observing systems; (2) the establishment, in case of oil-spill crisis, of a new specialized unit, named USyP, to monitor and forecast the marine oceanographic situation, providing the required met-ocean and oil-spill information for the crisis managers. The oil-spill crisis scenario simulated during the international search and rescue Exercise 'Gijón-2006', organized by SASEMAR, represented an excellent opportunity to test the capabilities and the effectiveness of this USyP unit, as well as the protocols established to analyze and transfer information. The results presented in this work illustrate the effectiveness of the operational approach, and constitute an encouraging and improved base to face oil-spill crisis.
Geophysical Research Letters, 35, L01601. DOI: 10.1029/2007GL031862 -- Abstract. (BibTeX: hanshaw.etal.2008)
Past studies have shown that surface chlorophyll-a concentrations increase in the wake of hurricanes. Given the reported increase in the intensity of North Atlantic hurricanes in recent years, increasing chlorophyll-a concentrations, perhaps an indication of increasing biological productivity, would be an expected consequence. However, in order to understand the impact of variable hurricane activity on ocean biology, the magnitude of the hurricane-induced chlorophyll increase relative to other events that stir or mix the upper ocean must be assessed. This study investigates the upper ocean biological response to tropical cyclones in the North Atlantic from 1997–2005. Specifically, we quantitatively compare the anomalous chlorophyll-a concentrations created by cyclone activity to the total distribution of anomalies in the subtropical waters. We show that the cyclone-induced chlorophyll-a increase has minimal impact on the integrated biomass budget, a result that holds even when taking into consideration the lagged and asymmetrical response of ocean color.
Journal of Atmospheric and Oceanic Technology, 25, 11, 2133-2144. -- Abstract. (BibTeX: lehenaff.etal.2008)
Keywords: Satellite observations, Data assimilation, Remote sensing.
The authors investigate the potential qualitative improvement brought by wide-swath, interferometry-based ocean altimetry measurements with respect to classical nadir altimeters in a coastal/shelf data assimilation system. In addition, particular attention is paid to roll errors, which could significantly reduce the expected benefits of wide-swath altimetry. A barotropic, nonlinear free-surface model is set up over the European shelf as part of an ensemble Kalman filter. Experiments assimilating simulated data are performed over the North Sea to test the ability of altimeter configurations to reduce model errors due to the action of meteorological forcing in the presence of bathymetric uncertainties. A simplified wide-swath observation scheme is used, composed of nadir altimeter height plus a nadir-centered cross-track sea level slope measurement. The simplified wide-swath measurements are found to be able to constrain events unsampled by a single nadir altimeter owing to a wider domain of influence in the cross-track direction and the ability to detect cross-track gradients. Since the satellite-borne interferometer is highly sensitive to the platform behavior, especially satellite roll, experiments taking roll errors into account are then carried out. Whereas observational errors are considered independent in most data assimilation studies, the roll of the platform correlates those errors along the path of the satellite. Despite the large amplitude of the roll errors, the contribution of the wide-swath altimeter in coastal zones remains valuable as long as the roll frequency is known (within Gaussian error) and the assimilation scheme is designed to take observational error correlations into account.
IEEE Transactions on Geoscience and Remote Sensing, 1-4. DOI: 10.1109/MICRAD.2008.4579463 . ISBN: 978-1-4244-1987-9 -- Abstract. (BibTeX: talone.etal.2008i)
The SMOS (Soil Moisture and Ocean Salinity) Mission is the second of the ESApsilas Living Planet Programme Earth Explorer Opportunity Missions and it is scheduled for launch on November 2008. Its objective is to provide global and frequent Soil Moisture (SM) and Sea Surface Salinity (SSS) maps. SMOSpsila single payload is the Microwave Imaging Radiometer by Aperture Synthesis (MIRAS) sensor, an L-band two-dimensional aperture synthesis interferometric radiometer. To help in the retrieval process, auxiliary data must be used in combination with the brightness temperatures measured by MIRAS. The output products of SMOS at Level 3 will be SSS remote measurements with global coverage and an accuracy of 0.1-0.4 psu (practical salinity units) over 100 x 100 - 200 times 200 km2 in 30 - 10 days. In this study pseudo SMOS Level 3 Products have been obtained in order to test the impact at Level 3 of introducing ARGO salinity measurements in the SMOS data processing chain. To do so: 1) The Ocean Parallelise (OPA) Model has been run to provide geophysical parameters; 2) The SMOS End-to-end Processor Simulator (SEPS) has been used to compute the brightness temperatures as measured by the MIRAS; 3) The SMOS Level 2 Processor Simulator (SMOS-L2PS) has been applied to retrieve SSS values for each point and overpass. To asses also the possible impact of the coastal vicinity effect, two different zones have been simulated; the first one in open ocean and the second one in a coastal region, near the Canary islands (Spain) where SMOS and Aquarius CAL/VAL activities are foreseen. The results for both simulation scenarios are presented and discussed.
Global and Planetary Change, 63, 2-3, 177-184. DOI: 10.1016/j.gloplacha.2007.09.001 -- Abstract. (BibTeX: vargasyanez.etal.2008a)
Keywords: Western Mediterranean; continental shelf; warming trends; sea level; NAO index.
We analyse hydrographic, meteorological and sea level time series in the continental shelves of Málaga Bay and L'Estartit, in the South and North Western Mediterranean. We have detected an important reduction of the warming rates reported for the 90s decade, showing that the warming process of the Mediterranean is superimposed on several years lasting oscillations. These accelerations or interruptions, typically account for a fraction of the total trend, and therefore they are not able to obscure the warming detection if the time series are long enough. On the other hand, they can produce artificial results if the time series are short when compared with the length of these cycles. The warming of the shelf waters, its acceleration during the 90s and the reversal during the beginning of the XXI century, are also observed in air temperature time series along the Spanish Mediterranean. We have also checked the influence of the warming acceleration/disruption on the sea level rise. Mean sea level trends are around 1 mm/yr when long time series are analysed, but shorter time series can result in rising trends as large as 13 mm/yr, for accelerated warming periods, or even no sea level change for reversals of the warming trends. Another factor to study is the influence of the NAO on these warming/cooling periods as well as on the strength of upwelling favourable winds, which could have a great importance on shelf ecosystems.
Continental Shelf Research, 28, 7, 915-936. DOI: 10.1016/j.csr.2008.01.011 -- Abstract. (BibTeX: pastor.etal.2008)
Keywords: Coastal upwelling; Central waters; Frontal features; Double diffusion; Transport processes; Interleaving; Cape Verde; Geographic bounding coordinates (17–26°N) (22–14°W).
A historical data set is used to describe the coastal transition zone off Northwest Africa during spring 1973 and fall 1975, from 17° to 26°N, with special emphasis on the interaction between subtropical (North Atlantic Central Waters) and tropical (South Atlantic Central Waters) gyres. The near-surface geostrophic circulation, relative to 300 m, is quite complex. Major features are a large cyclonic pattern north of Cape Blanc (21°N) and offshore flow at the Cape Verde front. The large cyclone occurs in the region of most intense winds, and resembles a large meander of the baroclinic southward upwelling jet. The Cape Verde frontal system displays substantial interleaving that may partly originate as mesoscale features at the coastal upwelling front. Property–property diagrams show that the front is an effective barrier to all properties except temperature. The analysis of the Turner angle suggests that the frontal system is characterized by large heat horizontal diffusion as a result of intense double diffusion, which results in the smoothing of the temperature horizontal gradients. Nine cross-shore sections are used to calculate along-shore geostrophic water-mass and nutrient transports and to infer exchanges between the coastal transition zone and the deep ocean (import: deep ocean to transition zone; export: transition zone to deep ocean). These exchanges compare well with mean wind-induced transports and actual geostrophic cross-shore transport estimates. The region is divided into three areas: southern (18–21°N), central (21–23.5°N), and northern (23.5–26°N). In the northern area geostrophic import is roughly compensated with wind-induced export during both seasons. In the central area geostrophic import is greater than wind-induced export during spring, resulting in net import of both water (0.8 Sv) and nitrate (14 kmol s−1), but during fall both factors again roughly cancel. In the southern area geostrophy and wind join to export water and nutrients during both seasons, they increase from 0.6 Sv and 3 kmol s−1 during fall to 2.9 Sv and 53 kmol s−1 during spring.
CIESM Workshop Monographs, 34, 81-86. -- Abstract. (BibTeX: puig.etal.2008a)
Cascading of dense shelf water from continental shelves is a global phenomenon whose effects have been largely underestimated. The north-western Mediterranean is one of the regions of the world where massive dense water formation occurs because of cooling and evaporation of surface waters during winter-time. Concurrent with the well known open-sea convection process over the MEDOC region, coastal surface waters over the wide shelf of the Gulf of Lions also become denser than the underlying waters and cascade downslope until reaching their equilibrium depth. Through this climate-driven phenomenon, dense shelf waters carrying large quantities of particles in suspension are rapidly advected hundreds of meters deep, mainly through submarine canyons. Recent observations within the frame of several research initiatives conducted in the north-western Mediterranean found that major dense shelf water cascades from the Gulf of Lions have a direct effect on the deep water (i.e. WMDW) thermohaline properties and on the long-term fluctuations of deep-sea fisheries, notably the shrimp Aristeus antennatus. Because of the flushing and recurrent behaviour of such cascading events, a continuous monitoring of this phenomenon under a system of Integrated Mediterranean Marine Observatories initiative could be conducted by means of establishing permanent real-time deep-sea observatories at specific key sites in the Mediterranean, in places where this process has been clearly identified (i.e. Gulf of Lions, southern Adriatic and Aegean shelves). Such infrastructures will allow studying this phenomenon using a transdisciplinary approach to assess in detail its effects and implications in the Mediterranean deep-sea ecosystem and living resources
IEEE Transactions on Signal Processing, 56, 7, 2771-2780. DOI: 10.1109/TSP.2008.917029 -- Abstract. (BibTeX: ventosa.etal.2008b)
Keywords: adaptive filters, signal reconstruction, signal sampling, time-frequency analysis, wavelet transforms.
The S-transform is becoming popular for time-frequency analysis and data-adaptive filtering thanks to its simplicity. While this transform works well in the continuous domain, its discrete version may fail to achieve accurate results. This paper compares and contrasts this transform with the better known continuous wavelet transform, and defines a relation between both. This connection allows a better understanding of the S-transform, and makes it possible to employ the wavelet reconstruction formula as a new inverse S-transform and to propose several methods to solve some of the main limitations of the discrete S-transform, such as its restriction to linear frequency sampling.
IEEE Transactions on Geoscience and Remote Sensing, 46, 3, 621-645. DOI: 10.1109/TGRS.2008.915543 -- Abstract. (BibTeX: zine.etal.2008a)
Keywords: Microwave radiometry, oceanography, salinity.
The L-band interferometric radiometer onboard the Soil Moisture and Ocean Salinity mission will measure polarized brightness temperatures (Tb). The measurements are affected by strong radiometric noise. However, during a satellite overpass, numerous measurements are acquired at various incidence angles at the same location on the Earth's surface. The sea surface salinity (SSS) retrieval algorithm implemented in the Level 2 Salinity Prototype Processor (L2SPP) is based on an iterative inversion method that minimizes the differences between Tb measured at different incidence angles and Tb simulated by a full forward model. The iterative method is initialized with a first-guess surface salinity that is iteratively modified until an optimal fit between the forward model and the measurements is obtained. The forward model takes into account atmospheric emission and absorption, ionospheric effects (Faraday rotation), scattering of celestial radiation by the rough ocean surface, and rough sea surface emission as approximated by one of three models. Potential degradation of the retrieval results is indicated through a flagging strategy. We present results of tests of the L2SPP involving horizontally uniform scenes with no disturbing factors (such as sun glint or land proximity) other than wind-induced surface roughness. Regardless of the roughness model used, the error on the retrieved SSS depends on the location within the swath and ranges from 0.5 psu at the center of the swath to 1.7 psu at the edge, at 35 psu and 15degC. Dual-polarization (DP) mode provides a better correction for wind-speed (WS) biases than pseudofirst Stokes mode (ST1). For a WS bias of -1 mmiddots-1, the corresponding SSS bias at the center of the swath is equal to -0.3 psu in DP mode and to -0.5 psu in ST1 mode. The inversion methodology implicitly assumes that WS errors follow a Gaussian distribution, even though these errors should follow more closely a Rayleigh distribution. For this - reason, the use of wind components, which typically exhibit Gaussian error distributions, may be preferred in the retrieval. However, the use of noisy wind components creates WS and SSS biases at low WSs (0.1 psu at 3 mmiddots-1). At a sea surface temperature (SST) of 15degC, the retrieved SSS is weakly sensitive to the SST biases, with the SSS bias always lower than 0.3 psu for SST biases ranging from -0.5degC to -2degC. In DP mode, biases in the vertical total electron content (TEC) of the atmosphere result in SSS biases smaller than 0.2 psu. The pseudofirst Stokes mode is insensitive to TEC. Failure to fully account for sea surface roughness scattering effects in the computation of sky radiation contribution leads to a maximum SSS bias of 0.2 psu in the selected configuration, i.e., a descending orbit over the Northern Pacific in February. To achieve SSS biases that are smaller than 0.2 psu, special care must be taken to correct for biases at low WS and to ensure that the bias on the mean WS (averaged over 200 km times 200 km and ten days) remains smaller than 0.5 mmiddots-1.
Geophysical Research Letters, 35, L07603. DOI: 10.1029/2008GL033329 -- Abstract. (BibTeX: benitezbarrios.etal.2008)
Based on hydrographic sections carried out during the last decade in the Canary region at 29° 10′N, we show that there has been a statistically significant rise in temperature and salinity on isobars between 1500 and 2300 db. The maximum increase, found at 1600 db, is occurring at a rate of 0.29°C and 0.047 per decade. Isobaric change decomposition into changes on neutral surfaces and changes due to the vertical displacement of the isoneutrals was performed. Results reveal that the lower part of North Atlantic Central Water (NACW) cooled and freshened on neutral surfaces, suggesting changes in the freshwater fluxes at the outcropping region. However, the signal in deep waters (1500–2300 db) was principally due to a downward displacement of the isoneutrals, although water mass modification is observed in the range of Mediterranean Water (MW) influence.
In: Encyclopedia of Global Warming and Climate Change, Ed. S.G. Philander. Sage Publications. ISBN: 9781412958783 -- Abstract. (BibTeX: ballabrerapoy.etal.2008b)
The Encyclopedia of Global Warming and Climate Change is a collection of approximately 750 articles in a three-volume set, presented in an A to Z alphabetical format, exploring major topics related to global warming and climate change—ranging geographically from the North Pole to the South Pole, and thematically from social effects to scientific causes. Coverage includes the science and history of climate change, the polarizing controversies over climate-change theories, the role of societies, the industrial and economic factors, and the sociological aspects of climate change. The scope of the encyclopedia is focused on providing a primarily nonscientific resource to understanding the complexities of climate change for academic and public libraries, written by scholars and institutional experts in the geosciences.
PhD thesis. Director/es: A. Turiel (ICM-CSIC). Barcelona. -- Abstract. (BibTeX: u.nievescalatrava.2008b)
Turbulent ows are of major interest for scientists and engineers, playing an essential role in uid dynamics. Even though a precise denition of turbulence does not exist,it is generally assumed that turbulence is a ow regime characterized by instabilities at large Reynolds numbers. The Reynolds number is a measure of the ratio of inertial forces to viscous forces. In the ocean, Reynolds number are of the order of 106, and so ocean dynamics is strongly nonlinear involving a large spectra of processes across all space and time scales. However, the ocean seems to be very active at around 30-300 Km, which is known as mesoscale. A schematic diagram of the spatial and temporal scales of various oceanic phenomena is shown in Figure 1.1. Instabilities in the ocean explain the meandering nature of oceanic currents, which can isolate and shed eddies when the meanders reach large amplitudes . Examples of such ows are high- and low-pressure systems that are formed in the Gulf Stream area (see Figure 1.2). These systems have been related to coherent structures, which are a combination of the geometrical and dynamical properties of the ow, i.e., regions containing most of the surviving vorticity [56, 47]. As it occurs in the ocean, a turbulent ow self-organizes into a collection of coherent structures [91, 141]. The smaller eddies are exposed to the strain-rate eld of these coherent structures . In recent studies, coherent structures not only have been identied with vortices, but also their presence has been connected with non-Gaussian Probability Density Functions (PDFs) of velocity elds from the ocean [17, 40, 54, 51, 140]. In addition to this characteristic, a near Gaussian component is expected for the background ow. These statistical distributions of ocean velocity elds have similar characteristics to the ones of numerical simulations of bidimensional turbulence.
10th MicroRad (Specialist Meeting on Microwave Radiometry and Remote Sensing of the Environment, . Ed. IEEE. CD, Firenze, Italia. ISBN: 978-1-4244-1987-6 (BibTeX: camps.etal.2008d)
In: Remote sensing of the european seas, Vol. 22. Ed. V. Barale, M. Gade. Springer. 223-238. ISBN: 978-1-4020-6771-6 -- Abstract. (BibTeX: font.etal.2008d)
This chapter summarizes the main objectives and characteristics of the ESAs SMOS mission and its remote sensing applications. The SMOS payload is MIRAS, a new type of instrument in Earth observation: the first two-dimensional aperture synthesis interferometric radiometer. It operates at L-band, has multi-angular and multi-look imaging capabilities, and can be operated in dual-polarization or full-polarimetric modes. Due to its novelty, the principles of operation, imaging characteristics and its main performance parameters (spatial resolution and radiometric sensitivity and accuracy) are described, as well as the approach selected in the retrieval algorithms of sea surface salinity.
10th MicroRad (Specialist Meeting on Microwave Radiometry and Remote Sensing of the Environment, . Ed. IEEE. CD, Fireze, Italia. ISBN: 978-1-4244-1987-6 (BibTeX: font.etal.2008h)
Proceedings IEEE Inten. Geosciece and Remote Sensing Symposium IGARSS 2008, Boston, . IEEE. 4, 938-941. DOI: 10.1109/IGASS.2008.47798778 (BibTeX: talone.etal.2008d)
In: Ocean Remote Sensing : Recent Techniques and Applications, Ed. Raquel Niclòs. Research Signpost. Chap. 3. 55-71. ISBN: 978-81-308-0268-8 (BibTeX: turiel.garcialadona.2008c)
Ed. Inst. Español de Oceanografía, Minist. de Educación y Ciencia. IEO. 1, In: Temas de Oceanografía. 1-170. ISBN: 84-95877-39 -2 -- Abstract. (BibTeX: vargasyanez.etal.2008i)
Semi-enclosed and bounded by three continents, the Mediterranean sea is a region highly vulnerable to human activities, i.e.: the population surge along the coasts, the tourism pressure, the maritime traffic, the agriculture and the fishery exploitation, all have a potential impact on the Mediterranean environment. In addition, effective initiatives against the Global Climate Change need to be attempted in order to preserve our marine environment and to achieve a sustainable development of its resources. Prevention and adaptation to this new threat must be based on the rigorous and scientific knowledge accomplished through the systematic and continuous observation of the sea, and through the collection of multidisciplinary time-series and the subsequent analysis. This report responds to this necessity. The main goals of the Instituto Español de Oceanografía (IEO) are to generate scientific knowledge, as well as to assess and to inform the public about the state of the sea. The IEO is primary focussed on the study of the variety of phenomena influencing spanish coasts, including the process of Climate Change. To meet these objectives, a large set of actions have been planned. Some of them are already being implemented, such as a multidisciplinary observation system in the shelf and continental slope waters, or periodic scientific reports dealing with the detection and quantification of Climate Change effects and of other possible environmental impacts. The present report is the first of a series of future contributions. Besides the IEO, other Spanish institutions such as the ICM (CSIC), Puertos del Estado (PE), the IMEDEA (CSIC), the UMA, the UIB and the INM, involved in the monitoring, analysis and modelling of the Mediterranean sea, have also participated in it. The results show clear evidences of the effect of Climate Change in the physical properties of the mediterranean waters since 1948; in particular, the temperature and salinity increase of the deep waters, the accelerated rise of sea level since the early 1990s, and the air and sea surface temperature increase during the second half of the XX century.