Linear and non-linear T–S models for the eastern North Atlantic from Argo data: Role of surface salinity observations     

Joaquim Ballabrera-Poy  Baptiste Mourre  Emilio Garcia-Ladona  Antonio Turiel  Jordi Font 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(10):1605-1614

Linear and non-linear empirical models for salinity (S) are estimated from the Argo temperature (T) and salinity (delayed) data. This study focuses on the reconstruction of salinity in the upper 1200 m of the eastern North Atlantic Ocean, a region characterized by the presence of many different water masses. While previous studies have found it necessary to split this region by boxes to fit different polynomial models in each box, a unique model valid for the entire region is fitted here. Argo profiles are randomly distributed on two sets: one for fitting the models and one for testing them. Non-linear regressions are built using neural networks with a single hidden layer and the fitting data set is further divided into two subsets: one for adjusting the coefficients (training data) and one for early stopping of the fitting (validation data). Our results indicate that linear regressions perform better than the climatologic T–S relationship, but that non-linear regressions perform better than the linear ones. Non-linear training using a three-data subsets strategy successfully prevents overfitting even when networks with 90 neurons in the hidden layer are being trained. While the presence of local minima may complicate the generalization of non-linear models to new data, network committees (created by training the same network from different random initial weights) are shown to better reproduce the test data. Several predictors are tested, and the results show that geographical, or surface, information does provide significant information. These results highlight the potential applications of future satellite missions measuring sea-surface salinity to reconstruct, when combined with temperature profiles, vertical salinity profiles.  相似文献   

Corrections to Watts' charts varying with libration     

G. Rosselló  C. Jordi  A. Salazar 《Astrophysics and Space Science》1991,177(1-2):331-338

About 169000 observations of lunar occultations of stars are analysed for systematic corrections to Watts' charts of the marginal zone of the Moon. Corrections to the radius and shape varying with libration are derived. These are in good agreement with previous results.  相似文献   

Constraining velocity and density contrasts across the crust–mantle boundary with receiver function amplitudes     

Jordi Julià 《Geophysical Journal International》2007,171(1):286-301

This paper investigates the ability of P -wave receiver functions to constrain both the velocity and density contrasts across the Moho. Expressions for receiver function amplitudes corresponding to a layer over a half-space are extended to media with depth-dependent properties by explicitly accounting for free-surface reflection coefficients. Forward numerical computations show that receiver function amplitudes become frequency-dependent for depth-dependent structures and that, for a given frequency, wavelengths associated to Ps converted phases are larger than wavelengths associated to multiply reverberated phases. When consistent measurements of the amplitudes of Ps phase and multiples can be obtained, the extended expressions suffice to account for the observed amplitudes. Receiver function amplitudes are sensitive to both velocity and density contrasts across the Moho, and a two-step grid-search procedure is proposed to recover the contrasts from their measurement. The near-surface velocity is recovered in the first step from the amplitude of the direct P wave and then used in the second step to work out the relative density and S -wave velocity contrast from the amplitude of the secondary phases. Examples from central Spain (PAB) and the Indian Shield (HYB) are discussed and demonstrate that receiver function amplitudes can constrain contrasts across the Moho accurately enough to be utilized in geological interpretation.  相似文献   

High dispersal capacity of a broad spectrum of aquatic invertebrates via waterbirds     

Dagmar Frisch  Andy J. Green  Jordi Figuerola 《Aquatic Sciences - Research Across Boundaries》2007,69(4):568-574

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Chrysophyte cysts from lake sediments reveal the submillennial winter/spring climate variability in the northwestern Mediterranean region throughout the Holocene     

Sergi Pla  Jordi Catalan 《Climate Dynamics》2005,24(2-3):263-278

In the last decade, much effort was dedicated to the reconstruction of past climate at high temporal resolution. Here, we show the suitability of chrysophyte cysts from lake sediments for revealing continental climate variability when used in sensitive sites, such as those in high mountains. We demonstrate that altitude is a main factor influencing the present distribution of chrysophytes and develop a transfer function to evaluate the local altitude anomaly on a lake site throughout time. Based on our knowledge of chrysophyte ecology, the altitude anomalies are interpreted as winter/spring climate signatures. The method was applied to a Holocene record from a lake in the Pyrenees showing submillennial climatic variability in this northwestern Mediterranean zone. A warming trend was present from the early Holocene to 4 kyear BP. Comparison with pollen-based reconstructions of summer temperatures denoted a contrasting decrease in continentality between the two parts of the Holocene. Oscillations of 1 cycle per ca. 2,000 years appeared throughout the record. The warmest Holocene winters were recorded during the Medieval Warm Period at ca. AD 900 and 450 and the Roman Warm Period (2.7–2.4 kyear BP). Winters in the period AD 1,050–1,175 were inferred to be as cold as in the Little Ice Age. The period between 3 and 7 kyear BP showed lower intensity in the fluctuations than in early and late Holocene. The cold event, 8,200 years ago, appeared embedded in a warm fluctuation. Another cold fluctuation was recorded around 9 kyear BP, which is in agreement with Irish and Greenland records.This revised version was published online in January 2005 with corrections to the background of figures 9 and 12.  相似文献   

Chemical composition of eclipsing binaries: a new approach to the helium-to-metal enrichment ratio     

Ignasi Ribas  Carme Jordi  Jordi Torra  Álvaro Giménez 《Monthly notices of the Royal Astronomical Society》2000,313(1):99-111

The chemical enrichment law Y ( Z ) is studied by using detached double-lined eclipsing binaries with accurate absolute dimensions and effective temperatures. A sample of 50 suitable systems was collected from the literature, and their effective temperatures were carefully re-determined. The chemical composition of each of the systems was obtained by comparison with stellar evolutionary models, under the assumption that they should fit an isochrone to the observed properties of the components. Evolutionary models covering a wide grid in Z and Y were adopted for our study. An algorithm was developed for searching the best-fitting chemical composition (and the age) for the systems, based on the minimization of a χ ² function. The errors (and biases) of these parameters were estimated by means of Monte Carlo simulations, with special care put on the correlations existing between the errors of both components. In order to check the physical consistency of the results, we compared our metallicity values with empirical determinations, obtaining excellent coherence. The independently derived Z and Y values yielded a determination of the chemical enrichment law via weighted linear least-squares fit. Our value of the slope, Δ Y /Δ Z =2.2±0.8, is in good agreement with recent results, but it has a smaller formal error and it is free of systematic effects. Linear extrapolation of the enrichment law to zero metals leads to an estimation of the primordial helium abundance of Y _p=0.225±0.013, possibly affected by systematics in the effective temperature determination.  相似文献   

Delineating coastal groundwater discharge processes in a wetland area by means of electrical resistivity imaging, 224Ra and 222Rn          下载免费PDF全文

Mario Zarroca  Rogelio Linares  Valentí Rodellas  Jordi Garcia‐Orellana  Carles Roqué  Joan Bach  Pere Masqué 《水文研究》2014,28(4):2382-2395

Coastal groundwater discharge (CGD) plays an important role in coastal hydrogeological systems as they are a water resource that needs to be managed, particularly in wetland areas. Despite its importance, identifying and monitoring CGD often presents physical and logistical constraints, restraining the application of more traditional submarine groundwater discharge surveying techniques. Here we investigate the capability of electrical resistivity imaging (ERI) in the Peníscola wetland (Mediterranean coast, Spain). ERI surveying made it possible to identify and delineate an ascending regional groundwater flow of thermal and Ra‐enriched groundwater converging with local flows and seawater intrusion. The continuous inputs of Ra‐rich groundwater have induced high activities of Ra isotopes and ²²²Rn into the marsh area, becoming among the highest previously reported in wetlands and coastal lagoons. Geoelectrical imaging enabled inferring focused upward discharging areas, leaking from the aquifer roof through a confining unit and culminating as spring pools nourishing the wetland system. Forward modelling over idealized subsurface configurations, borehole datasets, potentiometric records from standpipe piezometers, petrophysical analysis, and four natural and independent tracers (²²⁴Ra, ²²²Rn, temperature and salinity) permitted assessing the geoelectrical model and a derived hydrogeological pattern. The research highlights the potential of ERI to improve hydrogeological characterization of subsurface processes in complex contexts, with different converging flows. Additionally, a hydrogeological conceptual model for a groundwater‐fed coastal wetland was proposed, based on the integration of surveying datasets. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Performance Evaluation of the Boundary-Layer Height from Lidar and the Weather Research and Forecasting Model at an Urban Coastal Site in the North-East Iberian Peninsula   总被引：1，自引：0，他引：1  

Robert F. Banks  Jordi Tiana-Alsina  Francesc Rocadenbosch  José M. Baldasano 《Boundary-Layer Meteorology》2015,157(2):265-292

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The “Castilian bend” of Rudolf Staub (1926): historical perspective of a forgotten orocline in Central Iberia     

José R. Martínez Catalán  Domingo G. A. M. Aerden  Jordi Carreras 《Swiss Journal of Geoscience》2015,108(2-3):289-303

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Dynamics of water vapor flux and water separation processes during evaporation from a salty dry soil     

Meritxell Gran  Jesús Carrera  Jordi Massana  Maarten W. Saaltink  Sebastia Olivella  Carlos Ayora  Antonio Lloret 《Journal of Hydrology》2011,396(3-4):215-220

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