Scientia Marina, 70, 1, 147-152. -- Abstract. (BibTeX: lombarte.etal.2006d)
Keywords: otolith, shape analysis, Curvature Scale Space, Wavelets, Fourier..
We present an automatic system for describing and identifying fish otolith shapes combining information technologies with modern advances in signal analysis. As a major novelty with respect to past studies the system includes wavelets (WT) and curvature space scale (CSS) analyses that have been shown to provide local morphologic information and characteristics (landmarks) of the sagitta otolith outline for non-specialists. By applying this electronic catalogue directly the system is very helpful for determining teleostean fish size, population and species. Both the electronic catalogue and the shape analysis are implemented through the AFORO database, which at present contains more than 1250 high resolution images of the left sagitta from 292 species and 94 families of teleostan fishes sampled mainly in Mediterranean and Antarctic waters.
Scientia Marina, 70, 2, 167-175. -- Abstract. (BibTeX: marrerodiaz.etal.2006)
Keywords: S-T relationship, eastern North Atlantic Subtropical Gyre (NASG), climatology, XBT probe, geostrophic transport.
We study the dependence of salinity on temperature in two by two degrees latitude-longitude boxes, for surface and upper-thermocline waters of the eastern North Atlantic subtropical gyre. The initial data set, from historical databases as well as from recent hydrographic cruises in the region, is carefully scrutinized to reject dubious measurements. We search for polynomial relations of variable degree between salinity and temperature, the optimal fit is selected as the polynomial with the lowest degree that satisfies several statistical criteria. An independent hydrographic cruise is used to confirm that the method performs substantially better than estimates from climatological data, and leads to relatively low deviations in geopotential anomaly and other derived quantities. An error propagation analysis using the Monte Carlo method shows equally good results.
Continental Shelf Research, 26, 429-457. DOI: 10.1016/j.csr.2005.11.012 -- Abstract. (BibTeX: martins.pelegri.2006a)
Keywords: Ocean colour; Phytoplankton variability; Continental shelf; South Atlantic Bight; Gulf Stream.
We examine all available high-resolution Coastal Zone Colour Scanner (CZCS) data for the South Atlantic Bight (SAB), and adjacent Gulf Stream, during low vertical stratification months (October-May, from 1978 to 1986) to investigate the seasonal/long-time variations and the dominant spatial scales and patterns of near surface pigment concentrations. Each CZCS image is divided into four regions and 21 areas, as well as into 24 across-and 21 along-shelf transects. A distinct seasonal cycle is observed everywhere, superimposed to a linear time decay that reached almost 50% by the end of the mission. Mean winter SAB pigment concentrations (1.3 mgm-3) are about 50% greater than spring values (0.8 mgm-3), confirming that winter chlorophyll production represents a significant fraction of the total year’s production. Mean pigment concentration (and absolute variability) generally decreases seaward, in winter from 2.2 mgm-3 (1.3 mgm-3) over the inner shelf to about 0.3 mgm-3 (0.3 mgm-3) over the Gulf Stream. Local maxima take place in the inner and middle shelves off all capes, in the northern region separated by some 150 km. High relative pigment variability is observed both along and across-shelf in narrow bands (order 10 km) on the middle and outer shelves (except across-shelf off Charleston). Along-shelf dominant scales of pigment variability increase offshore, from some 50 km in the inner and middle shelves, possibly related to squirt type fingers, to some 90 km in the outer shelf, related to Leander-streamer patterns, and up to 170 km in the Gulf Stream, associated to the meanders themselves. High pigmento concentrations in the inner shelf appear to be overestimated due to high turbidity water, permanently off the capes and on a seasonal basis (fall/winter maxima) within the inner and middle shelves. There are instances of squirts that emanate from all along the coast, although the dominant feature in the northern inner and middle shelves are along-shelf filaments stretching from the capes. Cold air outbreaks are responsible for the frequent vertical redistribution of chlorophyll and nutrients, which may originally be associated to Gulf Stream intrusions, and cause that winter productivity is not nutrient-limited
Journal of Computational Physics, 216, 362-390. DOI: 10.1016/j.jcp.2005.12.004 -- Abstract. (BibTeX: turiel.etal.2006c)
Keywords: Fractals; Multifractals; Wavelets; Singularity analysis; Numerical methods; WTMM.
Physical variables in scale invariant systems often show chaotic, turbulent-like behavior, commonly associated to the existence of an underlying fractal or multifractal structure. However, the assessment of multifractality over experimental, discretized data requires of appropriate methods and to establish criteria to measure the confidence degree on the estimates. In this paper we have evaluated the quality of different techniques used for multifractal analysis. We have tested four different techniques: the moment (M) method, the wavelet transform modulus maxima (WTMM) method, the gradient modulus wavelet projection (GMWP) method and the gradient histogram (GH) method, which are used to estimate the singularity spectra of multifractal signals. The test consists in analyzing synthetic multifractal 1D signals with given multifractal spectrum. We have compared the results, studying the sensibility of each method to the length of the series, size of the ensemble and type of spectrum. Our results show that GMWP method is the one attaining the best performance, providing reliable estimates which can be improved when the statistics is increased. All the other methods are affected by problems such as the linearization of the right tail of the spectrum, and some of them are very demanding in data.
Revista de Teledetección, SP, 25, 134-138. -- Abstract. (BibTeX: turiel.etal.2006a)
Keywords: singularity analysis, pattern recognition, motion estimation, multifractality.
One of the greatest challenges in the remote sensing of the ocean is the obtention of relevant dynamical quantities from satellite images of different tracers (e.g., SST, chlorophyll concentration, etc). In this paper we will discuss how the use of new techniques on singularity analysis allow to retrieve the main instantaneous stream lines, and how these can be used, in the context of the geostrophic approximation, to deduce the associated stream function, with better spatial and temporal resolution than other methods. Besides, we will discuss some of the potential applications of this method.
Journal of Fluid Mechanics, 562, 73-82. DOI: 10.1017/S0022112006001182 -- Abstract. (BibTeX: viudez.2006b)
High-resolution three-dimensional numerical experiments show that initially balanced (void of waves) geophysical flows, static and inertially stable, generate spiral patterns of small-amplitude inertia-gravity waves (IGWs). The spiral wave patterns are due to the spontaneous generation of IGW packets emitted from fluid volumes (the IGW sources) experiencing large local changes of potential vorticity. The IGW packets spread away from the vortical flow and cause spiral wave patterns of the same sense of spiralling, cyclonic or anticyclonic, as the moving IGW sources. The spiral patterns are noticeable in the vertical velocity in deep layers, away from the large amplitude balanced vertical velocity. The generation of the spiral wave patterns is illustrated through several examples, namely, the single ellipsoidal vortex (cyclone and anticyclone), the merging of two spherical vortices, the dipole, and the anticyclonic shear instability.
Journal of Fluid Mechanics, 553, 107-117. DOI: 10.1017/S0022112005008311 -- Abstract. (BibTeX: viudez.dritschel.2006a)
The generation and propagation of a packet of small-amplitude inertia-gravity waves (IGWs) in a rotating stratified balanced flow is described. The initially balanced geophysical flow is an unstable baroclinic jet which breaks up into a street of cyclonic and anticyclonic vortices. The small-amplitude unbalanced component of the flow is extracted from the large-amplitude mesoscale balanced flow using the optimal potential vorticity balance approach. This analysis reveals that during the instability the balanced flow spontaneously emits bursts of IGWs. The emission occurs along two directions, into and out of the anticyclonic vortices. The inward-waves remain trapped inside the vortices while the outward-waves propagate away from them as a packet of small-amplitude IGWs with a three-dimensional helical structure. The wave packet emission is confirmed for different spatial resolutions (128 3, 160 3, 192 3 and 256 3 grid points). The ratio between the balanced vertical and horizontal velocity components is of the order of 10-3, as is typical of mesoscale geophysical flows. The ratio between the unbalanced vertical and horizontal components is about 0.1. Since the unbalanced horizontal and the balanced vertical velocity components are of similar magnitude, the vertical velocity of the IGWs is about 10-4 times the balanced horizontal velocity. The IGWs are dominated by frequencies close to the inertial frequency and have a clockwise-rotating horizontal velocity, similar to plane wave solutions
Philosophical Transactions of the Royal Society A-Mathematical Physical and Engineering Sciences, 364, 867-884. DOI: 10.1098/rsta.2006.1743 -- Abstract. (BibTeX: mourre.etal.2006b)
Keywords: tide-gauge; sea-level; operational oceanography; model validation; North Atlantic; storm surge modelling.
The contribution of tide-gauge data, which provide a unique monitoring of sea-level variability along the coasts of the world ocean, to operational oceanography is discussed in this paper. Two distinct applications that both demonstrate tide-gauge data utility when delivered in real-time are illustrated. The first case details basin-scale operational model validation of the French Mercator operational system applied to the North Atlantic. The accuracy of model outputs in the South Atlantic Bight both at coastal and offshore locations is evaluated using tide-gauge observations. These data enable one to assess the model's nowcasts and forecasts reliability which is needed in order for the model boundary conditions to be delivered to other coastal prediction systems. Such realtime validation is possible as long as data are delivered within a delay of a week. In the second application, tide-gauge data are assimilated in a storm surge model of the North Sea and used to control model trajectories in real-time. Using an advanced assimilation scheme that takes into account the swift evolution of model error statistics, these observations are shown to be very efficient to control model error, provided that they can be assimilated very frequently (i.e. available within a few hours).
Ocean Dynamics, 56, 5-6, 473-486. DOI: 10.1007/s10236-006-0081-2 -- Abstract. (BibTeX: mourre.etal.2006)
Keywords: North Sea . Barotropic dynamic . Wide swath ocean altimeter . Altimeter constellations . Tide gauges . Ensemble Kalman Filter.
We evaluate in this paper the ability of several altimeter systems, considered separately as well as together with tide gauges, to control the time evolution of a barotropic model of the North Sea shelf. This evaluation is performed in the framework of the particular model errors due to uncertainties in bathymetry. An Ensemble Kalman Filter (EnKF) data assimilation approach is adopted, and observing-systems simulation experiments (OSSEs) are carried out using ensemble spread statistics. The skill criterion for the comparison of observing networks is, therefore, not based on the misfit between two simulations, as done in classic twin experiments, but on the reduction of ensemble variance occurring as a consequence of the assimilation. Future altimeter systems, such as the Wide Swath Ocean Altimeter (WSOA) and satellite constellations, are considered in this work. A single WSOA exhibits, for instance, similar performance as two-nadir satellites in terms of sea-level correction, and is better than three satellites in terms of model velocity control. Generally speaking, the temporal resolution of observations is shown to be of major importance for controlling the model error in these experiments. This result is clearly related to the focus adopted in this study on the specific high-frequency response of the ocean to meteorological forcing. Altimeter systems lack adequate temporal sampling for properly correcting the major part of model error in this context, whereas tide gauges, which provide a much finer time resolution, lead to better global statistical performance. When looking into further detail, tide gauges and altimetry are demonstrated to exhibit an interesting complementary character over the whole shelf, as tide gauge networks make it possible to properly control model error in a ∼100-km coastal band, while high-resolution altimeter systems are more efficient farther from the coast.
Progress in Oceanography, 70, 2-4, 416-447. DOI: 10.1016/j.pocean.2006.03.019 -- Abstract. (BibTeX: machin.etal.2006f)
Keywords: Canary Basin; Water masses; Mass flux; Nutrient flux; Canary current; Coastal upwelling; Inverse model; (18–9W/27–33N).
Ocean studies in the 1970s provided an improved knowledge of the coastal upwelling region off NW Africa while in the 1980s and 1990s they led to a good description of the open ocean flow patterns in the Canary Basin. It was not until the late 1990s that major research addressed the open-coastal ocean coupled response. Here we examine the mean and seasonal circulation patterns in the Canary Basin with data from four hydrographic cruises carried out in the region between Cape Ghir, Madeira Island, and the Canary Islands. We apply an inverse box model to an ocean divided into 14 layers, with several layers representing each water mass or stratum, to obtain mass fluxes consistent with the thermal wind equation. An optimum flow description is obtained using conservation of mass, salt and heat anomaly, biologically corrected oxygen, and silicate, and allowing for Ekman transport in the surface layer and dianeutral mixing between adjacent layers. The deep waters show no predominant flow direction while the intermediate waters display localized southward flowing Mediterranean Water far from shore, and northward flowing Antarctic Intermediate Water near the continental slope, specially in the passage between the eastern Canary Islands and the African slope. The mean upper-thermocline Canary Current, composed of North Atlantic Central Water, flows south with an open-ocean branch transporting about 3 ± 1 Sv (1 Sv = 10 6 m3 s-1 = 10 9 kg s-1), and an upwelling-related branch near the continental slope carrying 1 ± 0.3 Sv. The seasonal transport by the open-ocean branch intensifies and moves offshore from spring to fall (2.8 ± 1.2 Sv in spring, 2.9 ± 1.1 Sv in summer, and 4.5 ± 1.2 Sv in fall), while it carries its lowest southward mass flux in winter (1.7 ± 1.0 Sv), possibly as a result of a migration offshore the sampled region. Upwelling-related southward flow is present in spring and summer (1.9 ± 0.1 Sv and 2.4 ± 0.1 Sv, respectively) while in fall and winter it merges with the offshore southward branch. This westward migration allows a northward mass flux between the Canary Islands and the African coast (1.8 ± 0.1 Sv), that by winter reaches Cape Ghir (0.5 ± 0.2 Sv). Seasonal air–sea heat fluxes fit well with the climatological values. The net phosphate transport in the surface layer indicates that primary production was negligible in this region during January 1997 and April 1998, though in this last month production was probably starting as a result of significant nutrient supply.
Geophysical Research Letters, 33, L04605. DOI: 10.1029/2005GL02548 -- Abstract. (BibTeX: machin.pelegri.2006a)
We apply an inverse model to a hydrographic cruise that completely closes the Canary Islands to investigate their effect on the water masses transports. Most central waters are transported south between the eastern islands and the African coast, with 2.5 Sv out of a total of 3.5 Sv. Intermediate waters are effectively blocked by the islands passages, with Mediterranean/Antarctic waters predominantly found north/south of the islands, and most deep waters loop around the archipelago plateau. A process model upholds the existence of intense two-way exchange between central and intermediate waters along the eastern passage, with vertical velocities of order 10-5 m s-1.
Deep-Sea Research Part II: Topical Studies in Oceanography, 53, 1161-1181. DOI: 10.1016/j.dsr2.2006.04001 -- Abstract. (BibTeX: machin.etal.2006)
Keywords: Salinity-temperature algorithms; Mass exchange; Quasigeostrophic model; North Atlantic Central Water; Strait of Gibraltar; Gulf of Cádiz (10.5-5.5W/33.5-37:.5N).
We have used several data sets (expandable bathythermograph sections, buoy trajectories, current-meter moorings, and surface wind stress) to investigate the temporal variation of the upper-thermocline (North Atlantic Central Waters) circulation patterns in the southern Gulf of Cádiz. The main data set consists of eight expandable bathythermograph sections (two per season) running between the Strait of Gibraltar and Cape Beddouza, just offshore the continental slope and approximately parallel to the Morocco coastline. A salinity-temperature polynomial, obtained from historical conductivity-temperaturedepth data, is used to infer dynamic properties (salinity, density, dynamic height, geostrophic velocity and transport). Dynamic heights are calculated referred to the 1027,25 kgm-3 neutral density surface, which we justify is a good reference level for this section. These observations are then combined with a process-oriented, one-layer, quasigeostrophic model for the northeastern corner of the North Atlantic subtropical gyre with modified eastern boundary conditions. The results indicate the existence of about 1 Sv onshore transport all year long into a 300 km long coastal transition zone off Morocco, which must follow south as a narrow current. During winter the flow is zonal towards the slope and recirculates south as a very narrow jet of less than 100 km width. During summer the flow probably becomes more intense but is deflected southeastward before reaching the slope, such that the onshore geostrophic transport into the coastal transition zone decreases and the recirculating band widens.
Fisheries Oceanography, 15, 5, 390-401. DOI: 10.1111/j.1365-2419.2005.00398.x -- Abstract. (BibTeX: maynou.etal.2006b)
Keywords: early life histories, European hake, ichthyoplankton, negative binomial, patchiness.
We estimated patchiness for different life stages (egg, larvae and juveniles) of European hake (Merluccius merluccius) from two ichthyoplankton surveys (September and November 1999) and four bottom-trawl surveys (November 1998, February, June and September 1999). Lloyd's patchiness P = 1 + 1/k, where k is the dispersion parameter of the negative binomial distribution, was calculated. Juveniles showed lower indices of patchiness than early ontogenetic stages. In juveniles, patchiness was highest for smaller size classes (3.5-5 cm TL) settling to their near-bottom habitat and was very low for those larger than 5 cm up to the 30-35 cm size class (approximately 3 yr of age, 50% mature individuals). Patchiness of settling juveniles was especially high in the June and September surveys, coinciding with peak recruitment to the bottom. Both eggs and yolk sac larvae showed patchiness values <10, increasing in flexion stage larvae from 12 to 20. This pattern is different to that observed in other studies for pelagic species, where patchiness of early-stage eggs is very high, but coincides with results obtained for other demersal species with pelagic eggs. Factors that may explain these patterns are discussed in light of oceanographic conditions, adult distribution and larval ontogenesis.
Revista de Teledetección, SP, 25, 158-162. -- Abstract. (BibTeX: font.camps.2006a)
Keywords: salinity, global ocean circulation, interferometric radiometry, microwaves, ESA..
The European Space Agency SMOS (Soil Moisture and Ocean Salinity) mission aims at obtaining global maps of both variables from space for large scale and climatic studies. It uses an L-band microwave interferometric radiometer with aperture synthesis (MIRAS) to measure the brightness temperature (Tb) emitted by the Earth’s surface and then computes from it the two geophysical parameters. The retrieval of salinity is a complex process that requires the knowledge of other environmental information, as sea surface temperature and roughness, and an accurate processing of the radiometer measurements
Journal of Physical Oceanography, 36, 1, 87-103. -- Abstract. (BibTeX: isernfontanet.etal.2006c)
The presence of coherent vortices makes observed mesoscale fields of the ocean resemble twodimensional turbulence. Using this analogy, a common definition of a coherent structure has been used to study the statistical properties of Mediterranean Sea vortices observed by satellite altimeters over a 7-yr period. A vortex has been defined as the simply connected region with values of the Okubo-Weiss parameter W < -0.2 sigmaW, where sigmaW is the spatial standard deviation of W, and the same sign of vorticity. This definition is shown to be appropriate to detect and characterize, statistically, properties such as size, mean kinetic energy, and amplitude of vortices in the Mediterranean basin from sea level anomaly maps corresponding to the period from October 1992 to October 1999. The distribution of such properties for the Mediterranean vortices suggests a heuristic criterion to extract and select very coherent and long-lived vortices from the whole set of structures identified in altimetric maps. Such coherent vortices appear to be selected for amplitudes greater than 2 sigmaW, where the amplitude has been defined in terms of the Okubo-Weiss parameter rather than vorticity, and strongly correspond to those reported from observations with independent data. Systematic locating and tracking of such vortices provide, for the first time, a general picture of their preferential paths in the Mediterranean basin, which are characterized by complex but rather well defined patterns.
Journal of Physical Oceanography, 36, 11, 2153-2164. -- Abstract. (BibTeX: isernfontanet.etal.2006d)
Velocity probability density functions (PDFs) are a key tool to study complex flows and are of great importance to model particle dispersion. The PDFs of geostrophic velocities derived from sea level anomalies maps for the Mediterranean Sea have been computed and analyzed, guided by recent results found in studies of two-dimensional and geostrophic turbulence. At the basin scale results show that the geostrophic velocity PDF derived from SLA maps is non-Gaussian. To understand the origin of this non-Gaussianity, a topological partition of the flow based on the Okubo-Weiss parameter is applied to separate the contribution of coherent vortices from the background field. After such separation the non-Gaussian part of the PDF appears mostly associated with the presence of such structures. Only about 20% of the vortices identified in the dataset are mainly responsible for this deviation. These vortices, called intense vortices in previous works, are those vortices with values of the amplitude larger than or equal to two standard deviations of the Okubo-Weiss parameter and correspond to vortices with a radius on the order of 40 km.
Progress in Oceanography, 70, 366-406. DOI: 10.1016/j.pocean.2006.03.018 -- Abstract. (BibTeX: pelegri.etal.2006b)
Keywords: Nutrient cycles; Subtropical zone; Isopycnals; North Atlantic; Gulf stream; Upwelling.
The North Atlantic, as all major oceans, has a remarkable duality in primary production, manifested by the existence of well-defined high and low mean primary production regions. The largest region is the North Atlantic Subtropical Gyre (NASTG), an anticyclone characterized by bowl shaped isopycnals and low production. The NASTG is surrounded at its margins by smaller cyclonic high-production regions, where these isopycnals approach the sea surface. The most extensive cyclonic regions are those at the latitudinal extremes, i.e. the subpolar and tropical oceans, though smaller ones do occur at the zonal boundaries. In this article we review historical data and present new analyses of climatological data and a selected number of hydrographic cruises in the western/northwestern and eastern/southeastern boundaries of the NASTG, with the objective of investigating the importance of upward epipycnal advection of nutrient-rich subsurface layers (irrigation) in maintaining high primary production in the euphotic layers. In the North Atlantic Subpolar Gyre (NASPG) irrigation implies intergyre exchange caused by the outcropping extension of the Gulf Stream (GS), following the formation of the deep winter mixed-layer. In the eastern boundary of the NASTG irrigation is attained through a permanente upwelling cell, which feeds the Canary Upwelling Current (CUC). In the southeastern corner irrigation occurs in fall, when the Guinea Dome (GD) is reinforced, and in winter, when the CUC reaches its southernmost extension. Other characteristics of the north/south extension of the GS/CUC are the seasonal nutrient replenishing of subsurface layers (spring restratification of NASPG and winter relaxation of the GD) and the maintenance of high levels of diapycnal mixing during the last phase of nutrient transfer to the euphotic layers. Off the Mid-Atlantic Bight the GS transports a total of about 700 kmol s-1 of nitrate, with almost 100 kmol s-1 carried in the surface (sigma theta< 26.8) layers and some 350 kmol s-1 in the intermediate (26.8 sigma theta < 27.5) layers. A box model suggests that north of Cape Hatteras most surface and upper-thermocline nitrates are used to sustain the high levels of primary production in the NASPG. Off Cape Blanc there is winter along-shore convergence of order 10 kmol s-1 of nitrate in the near-surface layers (possibly larger in summer), with only a small fraction used to sustain local primary production in the coastal upwelling band and the remainder carried to the interior ocean. Nutrients and biomass exported from these cyclonic regions may account for the concentration levels observed within the NASTG.
Progress in Oceanography, 70, 91-112. DOI: 10.1016/j.pocean.2006.07.002 -- Abstract. (BibTeX: pelegri.etal.2006c)
Keywords: Csanady; Oceanographer; Biography; Ocean circulation; Turbulent diffusion; Air-sea interaction.
Gabriel T. Csanady turned 80 in December 2005 and we celebrate it with this special Progress in Oceanography issue. It comprises 20 papers covering some of the many areas that Gabe contributed significantly throughout his professional career. In this introductory paper we briefly review Gabe’s career as an engineer, meteorologist and oceanographer, and highlight some of his major contributions to oceanography, both as a scientist as well as an educator. But we also use this opportunity to remember and thank Gabe, and his wife Joyce, for being such good friends and mentors to several generations of oceanographers. The authors of the collection of papers in this volume deserve special thanks for their efforts. We also are pleased to acknowledge the support of Progress in Oceanography's editor, Detlef Quadfasel, and the many anonymous reviewers who generously contributed their time and expertise.
Neurocomputing, 69, 1224-1227. DOI: 10.1016/j.neucom.2005.12.081 -- Abstract. (BibTeX: delgado.etal.2006)
Keywords: Sensory coding; Learning; Feature detectors; Natural images.
Much effort has been carried out to propose models of the early visual pathway based on the statistical analysis of natural images. These conventional frameworks lead to predictions on the RFs of simple cells which do not fit well their observed properties [D.L. Ringach, Spatial structure and symmetry of simple-cell receptive fields in macaque primary visual cortex, J. Neurophysiol. 2002 (2002) 455-463] In order to overcome these difficulties, we have been carrying a research program to derive robust coding principles from the statistics of natural images [A. Turiel, G. Mato, N. Parga, J.P. Nadal, Self-similarity properties of natural images, in: Proceedings of NIPS’97, vol. 10, MIT Press, 1997, pp. 836-842; A. Turiel, J.M. Delgado, N. Parga, Learning efficient internal representations from natural image collections, Neurocomputing 58-60 (2004) 915-921]. Two principles emerging from our study of image statistics are: first, there exists scale redundancy and this can be eliminated from the code; second, images are constructed by a combination (partly linear and partly non-linear) of some simple patterns of contrast (edges, bars, and composites of these two). These two principles can be used to derive filters which explain observed properties of the RFs of simple cells and which compare quite well with the results reported by Ringach [Spatial structure and symmetry of simple-cell receptive fields in macaque primary visual cortex, J. Neurophysiol. 2002 (2002) 455-463] and previous experimental work.
Drassana, 14, 41-51. (BibTeX: salat.2006d)
Journal of Marine Systems, 62, 46-54. DOI: 10.1016/jmarsys.2006.04.002 -- Abstract. (BibTeX: sole.etal.2006b)
Keywords: Harmful algal blooms; Feeding avoidance; Toxicity; Plankton; Predation.
A feature of marine plankton communities is the occurrence of rapid population explosions.When the blooming species are directly or indirectly noxious for humans, these proliferations are denoted as harmful algal blooms (HAB). The importance of biological interactions for the appearance ofHABs, in particular when the proliferatingmicroalgae produce toxins that affect other organisms in the food web, remains still poorly understood.Herewe analyse the role of toxins produced by a microalgal species and affecting its predators, in determining the success of that species as a bloom former. A three-species predator-prey model is used to define a criterion that determines whether a toxic microalga will be able to initiate a bloom in competition against a non-toxic one with higher growth rate. Dominance of the toxic species depends on a critical parameter that defines the degree of feeding selectivity by grazers. The criterion is applied to a particular simplified model and to numerical simulations of a full marine ecosystem model. The results suggest that the release of toxic compounds affecting predators may be a plausible biological factor in allowing the development of HABs.
Journal of Marine Systems, 61, 165-179. DOI: 10.1016/j.jmarsys.2005.06.004 -- Abstract. (BibTeX: sole.etal.2006a)
Keywords: Marine algae; Algal blooms; Toxicity; Allelopathy; Feeding avoidance; Model studies.
A multispecies dynamic simulation model (ERSEM) was used to examine the influence of allelopathic and trophic interactions causing feeding avoidance by predators, on the formation of harmful algal blooms, under environmental scenarios typical of a Mediterranean harbour (Barcelona). The biological state variables of the model included four functional groups of phytoplankton (diatoms, toxic and non-toxic flagellates and picophytoplankton), heterotrophic flagellates, micro- and mesozooplankton and bacteria. The physical-chemical forcing (irradiance, temperature and major nutrient concentrations) was based on an actual series of measurements taken along a year cycle in the Barcelona harbour. In order to evaluate potential effects of advection, some runs were repeated after introducing a biomass loss term. Numerical simulations showed that allelopathic effects of a toxic alga on a non-toxic but otherwise similar competitor did not have appreciable influence on the dynamics of the system. However, induction of avoidance of the toxic alga by predators, which resulted on increased predation pressure on other algal groups had a significant effect on the development of algal and predator populations. The presence of advection overrided the effect of these interactions and only allowed organisms with sufficiently high potential growth rates to thrive.
Journal of Non-Newtonian Fluid Mechanics, 133, 121-131. DOI: 10.1016/j.jnnfm.2005.12.002 (BibTeX: v.aleman.etal.2006)
Ocean Science, 2, 281-290. -- Abstract. (BibTeX: emelianov.etal.2006a)
A clustering methodology is applied to investigate the thermohaline structure of Levantine Intermediate Water (LIW) in the western Mediterranean basin. Sixteen free-drifting hydrographic profilers were deployed in the framework of the MFSTEP project (MEDARGO component) from September 2003. A total of 925 CTD profiles collected up to the beginning of February 2006 have been used in the analysis. The results are in good agreement with the general circulation scheme for intermediate waters in the basin and confirm the hypothesis about a "discrete-continuous" thermohaline structure of LIW.
Nano Letters, 6, 1, 110-115. DOI: 10.1021/nl0516862 -- Abstract. (BibTeX: kogan.etal.2006b)
The local heat delivered by metallic nanoparticles selectively attached to their target can be used as a molecular surgery to safely remove toxic and clogging aggregates. We apply this principle to protein aggregates, in particular to the amyloid beta protein (A beta) involved in Alzheimer's disease (AD), a neurodegenerative disease where unnaturally folded A beta proteins self-assemble and deposit forming amyloid fibrils and plaques. We show the possibility to remotely redissolve these deposits and to interfere with their growth, using the local heat dissipated by gold nanoparticles (AuNP) selectively attached to the aggregates and irradiated with low gigahertz electromagnetic fields. Simultaneous tagging and manipulation by AuNP of A beta at different stages of aggregation allow both, noninvasive exploration and dissolution of molecular aggregates.
Revista de Teledetección, SP, 25, 105-108. -- Abstract. (BibTeX: chic.etal.2006)
Keywords: sea surface temperature, AVHRR, QuikSCAT, SeaWiFS, near real-time.
Last 2 years a system to distribute temperature maps of West Mediterranean in near real-time from data acquired by an antenna builded-in CMIMA (Barcelona) was developed. Recently, it was complemented with a software application called SAIDIN (Satellite Image Database Interface) that allows to visualize, manipulate and distribute temperature data (AVHRR/NOAA), wind SeaWinds/QuikSCAT) and chlorophyll (SeaWiFS/OrbView2). Quicklooks could also be analyzed giving a good complementary information. Another quality control application allows to delete bad images or mark images as not good for averages. In the near future new average products will be included.
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 74, 6, 061110-1/13. DOI: 10.1103/PhysRevE.74.061110 -- Abstract. (BibTeX: pont.etal.2006)
The design of appropriate multifractal analysis algorithms, able to correctly characterize the scaling properties of multifractal systems from experimental, discretized data, is a major challenge in the study of such scale invariant systems. In the recent years, a growing interest for the application of the microcanonical formalism has taken place, as it allows a precise localization of the fractal components as well as a statistical characterization of the system. In this paper, we deal with the specific problems arising when systems that are strictly monofractal are analyzed using some standard microcanonical multifractal methods. We discuss the adaptations of these methods needed to give an appropriate treatment of monofractal systems
Proceedings 5ª Asamblea Hispano-Portuguesa de Geodesia y Geofísica, . Universidad de Sevilla. CD, Sevilla, Spain. ISBN: 84-8320-373-1 -- Abstract. (BibTeX: auladell.etal.2006a)
Vortices have been widely studied because they are important on the transport of physical properties as heat, salt, momentum, as well as biological and chemical properties. An idealized model for vortices is developed using angular velocity as a conservative property. We have considered the diffusion equation in radial coordinates, with small radial advection as observed in real data. The radial velocity, associated with the existence of diapycnal transport within the vortex, has been calculated from the mass conservation equation for axisymmetric vortices. To estimate the diffusion coefficient we have used the inertial stability condition. The model has been validated using data from several buoys tracking in anticyclonic and cyclonic eddies in the Canary Basin and in the Mediterranean Sea. Moreover we have velocity data for an anticyclonic eddy from the Colorado University Princeton Ocean Model in the Gulf of Mexico. Our model gives a reasonable approximation for the temporal evolution of angular velocity especially for barotropic eddies although it needs to be improved
Proceedings IEEE Symposium IGARSS2006, . IEEE. IEEE. CD, 1697-1701. Piscataway NJ (USA). ISBN: 0-7803-9510-7 -- Abstract. (BibTeX: camps.etal.2006b)
This work summarizes the main findings of the activities carried out in the past years by the Microwave Radiometry Team at the Technical University of Catalonia (UPC) in the field of sea surface salinity retrieval within the frame of the SMOS mission in collaboration with the Institute of Marine Sciences (ICM/CMIMA-CSIC). They cover the measurement of the dielectric permittivity of the sea water at Lband, the impact on the sea emissivity of the surface roughness (waves, swell, currents, rain ...) and oil spills, and its comparison with numerical models, as well as the development of sea surface salinity retrieval algorithms for SMOS.
Proceedings The 4th EuroGOOS 2005 Conference: European operational oceanography: Present and future, . 576-584. ISBN: 92-894-9788-2 -- Abstract. (BibTeX: drago.etal.2006g)
Keywords: Metadatabase, operational oceanography, directory, web interface.
The Mediterranean network to Assess and upgrade the Monitoring and forecasting Activity (MAMA), a 3-year thematic network project shared by leading marine research institutions from all the Mediterranean countries, has contributed to strengthening the institutional and scientific platform for the establishment of operational oceanography in the region. A key task in the MAMA project consisted in the stocktaking of activities and identification of current capabilities in operational oceanography on a country basis with a focus on availability of technological infrastructures, human resources and funding, applications and product needs. The information was collected by: 1. Country Profiles on the operations of institutes/agencies/organisations dealing with marine monitoring; national structures supporting such activities and marine affairs in general; relevance of marine sectors in the economic activities of each country. 2. a structured questionnaire targeting a comprehensive inventory on the routine marine monitoring activities in the Mediterranean. The Mediterranean Directory on Operational Oceanography (MeDir-OP) presents this information through the use of a user-friendly internet-based graphical interface allowing easy viewing of the metadata according to a number of categories. Specific information sets are collated into searchable mini-databases. MeDir-OP provides the basis for assessing the needs and potentials for operational oceanography in the region. It serves as an essential step to identifying gaps in infrastructures, to underpin further research and technological developments specific to the region, and to designing an observing system that meets the needs of end-users.
Proceedings IEEE Inter. Geoscience and Remote Sensing Simposium IGARSS 2006, . CD, 1689-1692. DOI: 10.1109/IGARSS2006.437 . ISBN: 0-7803-9510-7 -- Abstract. (BibTeX: font.etal.2006m)
The European Space Agency SMOS (Soil Moisture and Ocean Salinity) mission aims at obtaining global maps of soil moisture and sea surface salinity from space for large scale and climatic studies. It uses an L-band (1400-1427 MHz) Microwave Interferometric Radiometer by Aperture Synthesis (MIRAS) to measure brightness temperature at the Earth surface at horizontal and vertical polarizations (Th and Tv). These two parameters will be used together to retrieve the geophysical variables. The retrieval of salinity is a complex process that requires the knowledge of other environmental information and an accurate processing of the radiometer measurements, due to the narrow range of ocean brightness temperatures and the strong impact in the measured values of different geophysical parameters (as sea state) other than salinity. Here we present the baseline approach chosen by ESA to retrieve sea surface salinity from MIRAS data, as it has been developed and implemented by the joint team of scientists and engineers responsible for the SMOS Ocean Salinity Level 2 Prototype Processor.
2nd Recent Advances in Quantitative Remote Sensing 2006, . 854-859. ISBN: 84-370-6533-X -- Abstract. (BibTeX: font.etal.2006j)
The European Space Agency Soil Moisture and Ocean Salinity (SMOS) mission, the second of the ESA's Living Planet Program Earth Explorer Opportunity Missions, aims at obtaining global maps of soil moisture and sea surface salinity from space for large scale and climatic studies. This mission, with launch scheduled for early 2008, uses an L-band (1400-1427 MHz protected to human emissions) Microwave Interferometric Radiometer by Aperture Synthesis (MIRAS) to measure brightness temperature at the Earth surface at horizontal Th and vertical Tv polarizations (a fully polarized mode is also implemented and will be tested during the commissioning phase). These radiometric parameters will be used together to retrieve the two geophysical variables, following specifically designed algorithms that will be applied when the satellite field-ofview is covering land or ocean surfaces. The retrieval of salinity is a complex process that requires the knowledge of other environmental information and an accurate processing of the radiometer measurements, due to the narrow range of ocean brightness temperatures and the strong impact in the measured values of different geophysical parameters (as sea state) other than salinity. Here we present the baseline approach chosen by ESA to retrieve sea surface salinity from MIRAS data, as it has been developed and implemented by the joint team of scientists and engineers responsible for the SMOS Ocean Salinity Level 2 Prototype Processor
, 197 pp. (BibTeX: font.etal.2006c)
In: Complexus Mundi. Emergent patterns in nature, Vol. 9. Ed. Miroslav M. Novak. World Scientific. 247-256. ISBN: 981-256-666X -- Abstract. (BibTeX: grazzini.etal.2006c)
The ability of fractals to mimic Nature has led to the widespread acceptance of fractal, and, beyond, multifractal models. Such models are in the roots of new approaches in environmental sciences for processing images displaying turbulent-like systems. This paper addresses the problem of detecting critical areas associated with convection in satellite meteorological images. The technique we propose takes information about the spatial domain and relies on general statistical concepts. Due to the turbulent character of the observed atmospheric systems, the multifractal approach is naturaly adopted herein to describe not only the geometrical properties of images but also the underlying physical phenomena involved. The multifractal formalism leads first to the classification of different chaotic parts of systems according to their dynamical significance. It is further exploited to extract information about the places at which convection takes place in the flow. It is shown that it finally allows the determination of information that would be otherwise hidden. Without any temporal information, this remote sensing technique has potential application to infer the convective-scale processes occurring in individual convective systems. More generally, it leads to new insights into the analysis of natural phenomena from still images
Proceedings The 4th EuroGOOS 2005 Conference: European operational oceanography: Present and future, . 576-584. ISBN: 92-894-9788-2 -- Abstract. (BibTeX: isernfontanet.etal.2006e)
Keywords: singularity analysis, surface velocities, sea surface temperature.
This paper presents a new method for the estimation of surface currents from satellite images. This method is based on the multifractal singularity extraction technique, the Maximum Singular Stream-function Method (NSSM), which provides an approximation to the stream-function from experimental data in 2D turbulent systems. The essence of MSSM relies on statistical and geometrical properties associated with the energy cascade in flows; due to that association, the method provides an instantaneous velocity field and thus it does not require a sequence of images to evaluate velocities. The technique can be applied to images of different tracers; as an application, we show the results on AVHRR SST images
ULPGC-ICM (CSIC), (BibTeX: machin.etal.2006c)
Proceedings 5ª Asamblea Hispano-Portuguesa de Geodesia y Geofísica, . Universidad de Sevilla. CD, Sevilla, Spain. ISBN: 84-8320-373-1 -- Abstract. (BibTeX: machin.etal.2006g)
This work describes the circulation over Sedlo Seamount using hydrographic data acquired on November 2003, during Meteor's M60/1 cruise in the framework of project OASIS funded by the European Union. We use an inverse model, that assumes geostrophy and uses mass and salt anomaly conservation within a closed water volume around the seamount, to obtain a consistent circulation pattern. The results show flow patterns coherent with direct ship-borne ADCP measurements. The spreading of upper-thermocline and intermediate waters is conditioned by the presence of the seamount. In particular, westward spreading of Mediterranean Water is blocked by the seamount resulting in a patchy distribution. Finally, an independent hydrographic section with nutrient data is used to infer the nitrate, phosphate and silicate relationships with neutral density in the vicinity of Sedlo, from which we may estimate the fluxes of these properties over the seamount
Proceedings 5ª Asamblea Hispano-Portuguesa de Geodesia y Geofísica, . Universidad de Sevilla. CD, Sevilla, Spain. ISBN: 84-8320-373-1 -- Abstract. (BibTeX: v.pastor.etal.2006a)
Historical data have been used to study the seasonal variability of the water column and nutrients in the Cape Verde region. The area of study includes the coastal upwelling system off Northwest Africa and the Guinea Dome south of Cape Verde Islands. Data from four oceanographic cruises carried out between 1973 and 1975 are used to draw q-S diagrams and vertical distributions of properties; these distributions illustrate a North-to-South transition from North Atlantic Central Water to South Atlantic Central Water and the interleaving between these two water masses in the frontal zone off Cape Blanc. Seasonal horizontal distributions of temperature and nutrients from the World Ocean Atlas 2001 dataset describe the meridional migration of the upwelling front and the intensification of the Guinea Dome during summer. Nutrient availability in the water column through the year is explored in the Guinea Dome area.
Proceedings 5ª Asamblea Hispano-Portuguesa de Geodesia y Geofísica, . Universidad de Sevilla. CD, Sevilla, Spain. ISBN: 84-8320-373-1 -- Abstract. (BibTeX: pelegri.garciaolivares.2006a)
We examine the potential vorticity balance in an isopycnic layer within a boundary current flowing along a continental slope. We select a control volume that goes from the bottom boundary layer into a generic coordinate within the boundary current. The behaviour of the boundary current depends on the exchange of mass and vorticity between the bottom mixed layer and the interior ocean. The exchange at the top of the bottom mixed layer depends on how the bottom stress is transferred from the mixed layer into the interior ocean, so it depends on both the character of the boundary current and the dynamics of the mixed layer. The exchange at the outer end of the control volume, located within the boundary current, depends of the shear stress within the current. After several realistic idealizations we obtain an equation that allows us to determine the spatial structure of the current from the knowledge of the velocity normal to the slope, at the outer edge of the boundary current. The equation is numerically solved to simulate observations in the Gulf Stream, and the results compare satisfatorily with observations of the spatial distribution of this boundary current
Proceedings 5ª Asamblea Hispano-Portuguesa de Geodesia y Geofísica, . Universidad de Sevilla. CD, Sevilla, Spain. ISBN: 84-8320-373-1 -- Abstract. (BibTeX: salat.etal.2006a)
The meteorological conditions in winter 2005, with anomalously low precipitation and unusual persistency of northerlies over the NW Mediterranean, caused an unusual surface temperature and salinity distribution over the region. This situation particularly affected the convection process that produces the Deep Water of the Western Mediterranean (WMDW), which covered a region larger than usual. The information from satellite images and data obtained during EFLUBIO Cruise (March 2005) showed the presence of deep convection cells from the traditional \"MEDOC\" area near the Gulf of Lions extending up to the east of Menorca. Thus it is expected that a much higher volume of new WMDW than usual should be produced during that winter. A new WMDW, slightly denser (+0,01 kg m-3), warmer (+0.05°C) and saltier (+0.03) than usual has also been observed. It should be originated by the same convection process that typically produces the Western Intermediate Water (WIW), but due to the higher surface salinity and persistent winds, the resulting water became denser. The higher surface salinity may be related to both the low precipitation and the increase of deep convection in open sea that forced a higher extension of the Levantine Intermediate Water (LIW) compensatory upwelling. Moreover, at stations near the continental slope, a colder and even denser water was found (-0.1°C and +0.025 kg·m-3). This water should penetrate deeper than the deep waters formed in open sea and should be originated by cascading
Clima, Sociedad y Medio Ambiente (V Congreso AEC), . Ed. J.M. Cuadrat Prats, M.A. Saz Sánchez, S.M. Vicente Serrano, S. Lanjeri, M. de Luis Arrillaga, J.C. González-Hidalgo. Asociación Española de Climatología (AEC). Publicaciones de la Asociación Española de Climatología. Serie A, 283-290. Zaragoza. -- Abstract. (BibTeX: salat.pascual.2006)
Keywords: Tendencias climatológicas, Temperatura del agua de mar, nivel del mar, Ciclo estacional, Mediterráneo Occidental.
This text presents the air and sea temperature trends observed along the last 32 years in a coastal station located in the Western Mediterranean, over 90 m depth. The evolution of the interannual variability of the sea level during the last 15 years is also presented. The main results show an increase of temperature, especially during the spring period which implies an advance of the summer conditions at sea. The increasing trend observed in sea level can be related with the general trend of increasing heat content in the whole Western Mediterranean water mass.
PhD thesis. Director/es: A. Viudez (ICM-CSIC). Barcelona. -- Abstract. (BibTeX: pallassanz.2006d)
Aquesta tesi es una investigació de la generació espontània i propagació d’ones inercials-gravitatòries (OIGs) de petita escala en fluxos geofísics inicialment en balanç. La investigació inclou les fonts d’ones (flux en balanç) i les OIGs (flux que no està en balanç). La velocitat vertical de mesoescala w s’obté a partir de dades experimentals en el ‘Western Alboran Gyre’ (WAG) resolent una aproximació de l’equació ω generalitzada (equació ω), i la circulació ageostròfica tridimensional (3D) es simula numèricament en un dipol baroclí ‘quasi en balanç’ a partir d’un model de Bousinessq no-hidrostàtic. Aquests fluxos són inercialment estables amb nombres de Rossby màxims de Rmax≈0.9 i 0.7, respectivament. La velocitat vertical es relaciona, en ambdós fluxos, amb l’advecció de la component vertical de la vorticitat per la cisalla vertical. Les diferències entre w i la velocitat vertical quasigeostròfica en el WAG es deuen a la inclusió de la part ageostròfica del vector Q en l’equació ω. La trajectòria del dipol es relaciona amb el màxim de l’anomalia de vorticitat potencial (VP) i la grandària dels remolins. El flux ageostròfic del dipol depèn de la distància entre els remolins d0. Per a petites d0, la w té una distribució 3D octupolar i el dipol és compacte. Si augmentem d0, la velocitat del dipol i el màxim de |w| disminueixen, i les oscil·lacions internes o ‘heading’ trenquen ocasionalment l’estructura octupolar de w. La velocitat horitzontal ageostròfica s’explica per l’acceleració advectiva, concretament per l’acceleració centrípeta. Les OIGs es detecten en el flux total a partir de sèries temporals i distribucions horitzontals de w i de la seva derivada vertical. La generació espontània d'OIGs es mostra en diferents fluxos geofísics: un anticicló, un corrent de doll, un dipol, un tripol, i una col·isió entre dipols. Les OIGs són extretes, durant la interacció de dos anticiclons baroclins, amb el mètode ‘Optimal potential vorticity balance.’ Els paquets d’OIGs que es propaguen lliurement en el camp llunyà tenen fronts d’ones en forma d’espiral mentre que els quals es propaguen en l’interior del flux vortical poden ser atrapats i els fronts d’ona formar distribucions “frontals” o anulars. L’augment de la VP i de la isotropía del remolí incrementa l’emissió espontània d'OIGs. Es consideren tres indicadors possibles de la generació espontània d’OIGs: (i) la advecció de la VP, (ii) el residu de l’equació del balanç no lineal, i (iii) l’extensió 3D de l’analogia de la generació d'OIGs, en aigües succintes, de la teoria de radiació del so de Lighthill. L’anàlisi numèrica de les OIGs extretes suggereix la coexistència de dos mecanismes de generació. El primer es relaciona amb l’advecció de la VP, i el segon amb la interacció coherent d’OIGs preexistents que, ocasionalment, cooperen per a produir divergència horitzontal de major escala, l’ascens de les isopicnes, i amb això l’emissió d’un nou paquet d'OIGs de major amplitud.
In: Complexus Mundi. Emergent patterns in nature, Vol. 9. Ed. Miroslav M. Novak. World Scientific. 73-82. ISBN: 981-256-666X -- Abstract. (BibTeX: turiel.perezvicente.2006c)
The application of the multifractal formalism to the study of some time series with scale invariant evolution has given rise to a rich framework of models and processing tools for the analysis of these signals. The formalism has been successfully exploited in different ways and with different goals: to obtain the effective variables governing the evolution of the series, to predict its future evolution, to estimate in which regime the series are, etc. In this paper, we discuss on the capabilities of a new, powerful processing tool, namely the computation of dynamical sources. With the aid of the source field, we will separate the fast, chaotic dynamics defined by the multifractal structure from a new, so-far unknown slow dynamics which concerns long cycles in the series. We discuss the results on the perspective of detection of sharp dynamic changes and forecasting.