How reliable are finite-size Lyapunov exponents for the assessment of ocean dynamics?     

Ismael Hernández-Carrasco  Cristóbal López  Emilio Hernández-García  Antonio Turiel 《Ocean Modelling》2011,36(3-4):208-218

Much of atmospheric and oceanic transport is associated with coherent structures. Lagrangian methods are emerging as optimal tools for their identification and analysis. An important Lagrangian technique which is starting to be widely used in oceanography is that of finite-size Lyapunov exponents (FSLEs). Despite this growing relevance there are still many open questions concerning the reliability of the FSLEs in order to analyse the ocean dynamics. In particular, it is still unclear how robust they are when confronted with real data. In this paper we analyze the effect on this Lagrangian technique of the two most important effects when facing real data, namely noise and dynamics of unsolved scales. Our results, using as a benchmark data from a primitive numerical model of the Mediterranean Sea, show that even when some dynamics is missed the FSLEs results still give an accurate picture of the oceanic transport properties.  相似文献   

Sources of Salinity Variation in a Coastal Lagoon in a Karst Landscape     

Israel Medina-Gómez  Björn Kjerfve  Ismael Mariño  Jorge Herrera-Silveira 《Estuaries and Coasts》2014,37(6):1329-1342

Bahia de la Ascension (BA) is a shallow, mangrove-fringed coastal bay connected to the Caribbean through two inlets, outlined by the Mesoamerican Barrier Reef System. This work represents an initial investigation of the relative contribution of hydrometeorological and hydrodynamic forcing on salinity variation in this lagoon. Our objective is to assess the sensitivity of the salinity in BA to fluctuations in freshwater inflow and coastal oceanography. Two field trips were undertaken during rainy and dry seasons in 2007. Surface salinity was mapped across the system and CTD deployments carried out within BA and in the sea end-member to characterize temperature, conductivity, and water level. Also, cross-sectional CTD profiles were implemented to examine vertical stratification. The water balance indicated that 16 % of rainfall over the drainage basin (DB) becomes groundwater discharge plus surface runoff into BA during dry season, while 68 % of the precipitation input to the DB is supplied through groundwater–surface runoff to the bay during rainfalls. This combined inflow showed larger fluctuations than direct rainfall and, thus, has a greater potential to alter the seasonal salinity variations within BA. The tidal signal is selectively attenuated within BA, as diurnal frequencies are more readily filtered out than semidiurnal frequencies. Mesohaline conditions in the southwest bay are associated with freshwater sources, while saline water masses in the inlet are influenced by prevalent SE winds in the region and tidal phase, establishing a strong horizontal SW-NE estuarine salinity gradient.  相似文献   

Microstructure and geochemistry studies on Messinian gypsum deposits from the Northern Coast of Egypt     

Ahmed Melegy  Ismael S. Ismael 《Arabian Journal of Geosciences》2014,7(4):1313-1322

Messinian gypsum deposits from Dir El-Baraqan area, Northern Coast of Egypt, were investigated by stable sulfur isotope method, X-ray diffraction, infrared spectroscopy, optical microscopy, and scanning electron microscopy to differentiate features formed under substantial microbial influences as indicator of paleoenvironments. Petrographically, gypsum deposits were classified into three types: biolaminated gypsum, disordered selenite, and swallow-tail selenitic crystals. Biolaminated gypsum is characterized by regular alternating dark and light laminae, which were formed due to the seasonal environmental changes in Dir El-Baraqan area. Stable sulfur isotope data show that the gypsum deposits are characterized by δ³⁴S values ranging from +18.1 to +28.1 ‰. In swallow-tail gypsum, the δ³⁴S values are characterized by a narrow range (from +20.0 to +20.2 ‰) which is considered as the primary phase. In biolaminated gypsum, the δ³⁴S values ranged from +22.8 to +28.1 ‰ which is considered as the secondary phase. However, the white laminae are characterized by δ³⁴S values ranging from +22.8 to +24.1 ‰, while dark laminae are characterized by δ³⁴S values ranging from +27.2 to +28.1 ‰. The high δ³⁴S values of dark laminae revealed the increasing activity of sulfate-reducing bacteria.  相似文献   

The warm molecular gas in the Galactic Center     

N.J. Rodríguez-Fernández  J. MartÍn-Pintado  P. de Vicente  A. Fuente 《Astrophysics and Space Science》2002,281(1-2):331-332

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Geometric characterization of the Arjuna orbital domain     

C. de la Fuente Marcos  R. de la Fuente Marcos 《Astronomische Nachrichten》2015,336(1):5-22

Arjuna‐type orbits are characterized by being Earth‐like, having both low‐eccentricity and low‐inclination. Objects following these trajectories experience repeated trappings in the 1:1 commensurability with the Earth and can become temporary Trojans, horseshoe librators, quasi‐satellites, and even transient natural satellites. Here, we review what we know about this peculiar dynamical group and use a Monte Carlo simulation to characterize geometrically the Arjuna orbital domain, studying its visibility both from the ground and with the European Space Agency Gaia spacecraft. The visibility analysis from the ground together with the discovery circumstances of known objects are used as proxies to estimate the current size of this population. The impact cross‐section of the Earth for minor bodies in this resonant group is also investigated. We find that, for ground‐based observations, the solar elongation at perigee of nearly half of these objects is less than 90°. They are best observed by space‐borne telescopes, but Gaia is not going to improve significantly the current discovery rate for members of this class. Our results suggest that the size of this population may have been underestimated by current models. On the other hand, their intrinsically low encounter velocities with the Earth induce a 10–1000‐fold increase in the impact cross‐section with respect to what is typical for objects in the Apollo or Aten asteroid populations. We estimate that their probability of capture as transient natural satellites of our planet is about 8 %. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

PSR B1849+00 Probes the Tiny-Scale Molecular Gas?     

S. Stanimirović  J.M. Weisberg  J.M. Dickey  A. de la Fuente  K. Devine  A. Hedden  S.B. Anderson 《Astrophysics and Space Science》2004,292(1-4):167-172

In this paper we present and discuss the great difference in OH absorption spectra against PSR B1849+00 and SNR G33.6+0.1 along the same line-of-sight. This finding is important as it clearly demonstrates that statistics of absorbing molecular gas depends on the size of the background source.  相似文献   

Sources of contamination to weak lensing tomography: redshift-dependent shear measurement bias     

Elisabetta Semboloni  Ismael Tereno  Ludovic van Waerbeke  Catherine Heymans 《Monthly notices of the Royal Astronomical Society》2009,397(2):608-622

The current methods available to estimate gravitational shear from astronomical images of galaxies introduce systematic errors which can affect the accuracy of weak lensing cosmological constraints. We study the impact of KSB shape measurement bias on the cosmological interpretation of tomographic two-point weak lensing shear statistics.
We use a set of realistic image simulations produced by the Shear Testing Programme (STEP) collaboration to derive shape measurement bias as a function of redshift. We define biased two-point weak lensing statistics and perform a likelihood analysis for two fiducial surveys. We present a derivation of the covariance matrix for tomography in real space and a fitting formula to calibrate it for non-Gaussianity.
We find the biased aperture mass dispersion is reduced by  ∼20 per cent  at redshift ∼1, and has a shallower scaling with redshift. This effect, if ignored in data analyses, biases σ₈ and w ₀ estimates by a few per cent. The power of tomography is significantly reduced when marginalizing over a range of realistic shape measurement biases. For a Canada-France-Hawaii Telescope Legacy Survey (CFHTLS)-Wide-like survey,  [Ω_m, σ₈]  confidence regions are degraded by a factor of 2, whereas for a Kilo-Degree Survey (KIDS)-like survey the factor is 3.5. Our results are strictly valid only for KSB methods, but they demonstrate the need to marginalize over a redshift-dependent shape measurement bias in all future cosmological analyses.  相似文献   

Rare Earth Elements in Egyptian Phosphorites     

I.S.ISMAEL 《中国地球化学学报》2002,21(1):19-28

Egyptian phosphorites from Abu Tartur(Western Desert),El Mahamide mine(Nile Valley) and Rabah mne(Eastern Desert)show variable degrees of relative REE enrichment.Black plateau phosphorites of Abu Tartur are substantially enriched in REE as compared to the Red Sea and Nile Valley phosphorites.P-rich organic matter from the Abu Tartur and Rabah mines recorded negative Ce and positive Eu anomalies.Positive Eu anomaly reveals an anoxic event prior to the phase of Late Cretaceous phosphate formation.Ce is a redox indicator.Mixing of sea water and upwelling during the Late Cretaceous was responsible for the recording of positive Eu and negative Ce anomalies in the Egyptian phosphorites.  相似文献   

Internal consistency of a water analysis and uncertainty of the calculated distribution of aqueous species at 25°C     

Enrique Merino 《Geochimica et cosmochimica acta》1979,43(9):1533-1542

Many water analyses contain more than the minimum number of analytical determinations needed to calculate the distribution of species at ~ 25°C. The speciation of a water that contains $\text{n}$ cations and ligands other than H⁺ and OH^? can be calculated if just $\text{n}$ analytical determinations are available. In the frequent case where $\text{n + 1}$ (or more) determinations are available, one can calculate from the speciation a value for the ($\text{n + 1}$)th variable. The comparison between this computed value and its analytical counterpart (not used in calculating the speciation) constitutes a test for internal consistency among the $\text{n + 1}$ determinations that make up the whole analysis.Application of this test requires knowing the uncertainties of the calculated speciation and of the value computed for the ($\text{n + 1}$)th variable from the speciation. Such uncertainties have been ignored in previous algorithms, but have been determined herein by a Monte Carlo method of error propagation which is very well suited to systems of nonlinear algebraic equations.By comparing the titration alkalinity against the alkalinity calculated from the speciation, several published analyses for which the cation/anion balance is < 3% can be shown to be internally inconsistent. Such analyses may be unsuitable for geochemical calculations (water/rock interaction, estimation of reservoir temperatures, etc.).Several existing speciation algorithms disregard the possibility that the analytical data used as input are internally inconsistent.  相似文献   

Generation of evenly-spaced pressure-solution seams during (late) diagenesis: A kinetic theory     

Enrique Merino  Peter Ortoleva  Peter Strickholm 《Contributions to Mineralogy and Petrology》1983,82(4):360-370

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