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51.
Pablo Sangrà Ananda Pascual Ángel Rodríguez-Santana Francisco Machín Evan Mason James C. McWilliams Josep L. Pelegrí Changming Dong Anna Rubio Javier Arístegui Ángeles Marrero-Díaz Alonso Hernández-Guerra Antonio Martínez-Marrero Maricel Auladell 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(12):2100-2114
We report, from remote sensing and in situ observations, a new type of permanent structure in the eastern subtropical Atlantic Ocean, that we call the “Canary Eddy Corridor”. The phenomenon, is a zonal long-lived (>3 months) mesoscale eddy corridor, whose source is the flow perturbation of the Canary Current and the Trade Winds at the Canary Islands. The latitudinal range of the corridor spans 22°N–29°N and extends from the Canaries to at least 32ºW, near the mid-Atlantic. This is the main region of long-lived westward-propagating eddies in the subtropical northeast Atlantic. From a age-distribution study we observe that at least 10% of mesoscale eddies in this region are long-lived, with a dominance of anticyclones over cyclones. Another four westward-propagating eddy corridors were also detected: two small corridors north and south of the Azores Front; a small zonal corridor located near 31ºN, south of the island of Madeira; and a small corridor located near the Cape Blanc giant filament. The existence of these corridors may change, at least for the northeastern subtropical Atlantic, the general idea that mesoscale eddies are disorganized, ubiquitous structures in the ocean. The Canary Eddy Corridor constitutes a direct zonal pathway that conveys water mass- and biogeochemical properties offshore from the Canary Island/Northwest Africa upwelling system, and may be seen as a recurrent offshore pump of organic matter and carbon to the oligotrophic ocean interior. Estimates of volume and mass transport indicate that Canary Eddy Corridor westward transport is more than one-fourth of the southward transport of the Canary Current. The westward transport of kinetic energy by the eddies of the Canary Corridor is as important as the southward transport by the Canary Current. The total primary production related to the Corridor may be as high as the total primary production of the northwest Africa upwelling system for the same latitude range. 相似文献
52.
Local events which occurred in the Timanfaya volcanic field are analysed and their spectral contents are interpreted as being due to the effect of a finely layered medium with large impedance contrast, the presence of which is well known from well-logging data. By considering the layered medium as a filter, its spectral response (amplitude and phase) is computed from different randomly generated values of its parameters (total thickness, mean thickness of the individual layers and impedance contrast), showing that this stratigraphic filter acts as a low-pass filter. This effect can be correctly modelled by means of an exponential correlation function. However, in some cases resonant peaks appear in the spectrum superimposed on the low-pass filter effect, which can only be attributed to resonant scattering. An analysis of the phase and group delay associated with the amplitudes is made and strongly suggests that it is necessary to incorporate the theory of resonant scattering for the retrieval of medium properties. From the point of view of the amplitudes, the superposition of both effects, low-pass filter and resonant peaks, allows us to reproduce the gross features that are usually attributed to source effects. The need for a careful analysis of the local site response previous to any interpretation of the spectral features in terms of source characteristics is thus emphasized. 相似文献
53.
Barry R. Bickmore Christopher J. Tadanier Will D. Monn 《Geochimica et cosmochimica acta》2004,68(9):2025-2042
Bond-valence methods for the prediction of (hydr)oxide solution monomer and surface functional group acidity constants are examined in light of molecular structures calculated using ab initio methods. A new method is presented that is based on these calculated structures, and it is shown that previously published methods have neglected one or more of four essential features of a generalized model. First, if the apparent pKa values of solution monomers are to be used to predict intrinsic pKa values of surface functional groups, similar electrostatic corrections must be applied in both cases. In surface complexation models, electrostatic corrections are applied by representing a charged surface as a uniform plane of charge density, and an analogous correction can be made to solution monomers by treating them as charged spheres. Second, it must be remembered that real surfaces and real monomers are not homogeneous planes or spheres. Rather, charge density is distributed rather unevenly, and a further electrostatic correction (which is often quite large) must be made to account for the proximity of electron density to the point of proton attachment. Third, the unsaturated valence of oxygen atoms in oxyacids, hexaquo cations, and oxide surfaces is strongly correlated with acidity after electrostatic corrections are made. However, calculation of unsaturated valence for oxyacids and oxide surfaces must be based on realistic MeO bond lengths (taking into account bond relaxation), which can be obtained from ab initio structure optimizations. Finally, unsaturated valence must be divided between possible bonds (four for oxygen atoms) to reflect the fact that O-H bonds are localized to particular regions of the O atoms.Empirical models that take all these factors into account are presented for oxyacids and hexaquo cations. These models are applied to the gibbsite (100), (010), (001), and cristobalite (100) surfaces, and it is demonstrated that the model for oxyacids predicts reasonable intrinsic pKa values for oxide surfaces. However, the prediction of surface pKa values is complex, because the protonation state of one functional group affects the pKa values of neighboring groups. Therefore, calculations of larger periodic systems, progressively protonated and reoptimized, are needed. 相似文献
54.
Post‐fire hydrological response and suspended sediment transport of a terraced Mediterranean catchment
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Julián García‐Comendador Josep Fortesa Aleix Calsamiglia Adolfo Calvo‐Cases Joan Estrany 《地球表面变化过程与地形》2017,42(14):2254-2265
In July 2013, a wildfire severely affected the western part of the island of Mallorca (Spain). During the first three post‐fire hydrological years, when the window of disturbance tends to be more open, the hydrological and sediment delivery processes and dynamics were assessed in a representative catchment intensively shaped by terracing that covered 37% of its surface area. A nested approach was applied with two gauging stations (covering 1.2 km2 and 4.8 km2) built in September 2013 that took continuous measurements of rainfall, water and sediment yield. Average suspended sediment concentration (1503 mg L?1) and the maximum peak (33 618 mg L?1) were two orders of magnitude higher than those obtained in non‐burned terraced catchments of Mallorca. This factor may be related to changes in soils and the massive incorporation of ash into the suspended sediment flux during the most extreme post‐fire event; 50 mm of rainfall in 15 min, reaching an erosivity of 2886 MJ mm ha?1 h?1. Moreover, hysteretic counter‐clockwise loops were predominant (60%), probably related to the increased sensitivity of the landscape after wildfire perturbation. Though the study period was average in terms of total annual precipitation (even higher in intensities), minimal runoff (2%) and low sediment yield (6.3 t km?2 y?1) illustrated how the intrinsic characteristics of the catchment, i.e. calcareous soils, terraces and the application of post‐fire measures, limited the hydrosedimentary response despite the wildfire impact. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
55.
Josep M. Paredes J. Martí D. F. Torres G. E. Romero J. A. Combi V. Bosch-Ramon J. García-Sáanchez 《Astrophysics and Space Science》2005,297(1-4):223-233
We present preliminary results of a campaign undertaken with different radio interferometers to observe a sample of the most
variable unidentified EGRET sources. We expect to detect which of the possible counterparts of the γ-ray sources (any of the
radio emitters in the field) varies in time with similar timescales as the γ-ray variation. If the γ-rays are produced in
a jet-like source, as we have modelled theoretically, synchrotron emission is also expected at radio wavelengths. Such radio
emission should appear variable in time and correlated with the γ-ray variability. 相似文献
56.
57.
A strategy to predict strain across geological structures, based on previous techniques, is modified and evaluated, and a practical application is shown. The technique, which employs cross-section restoration combined with kinematic forward modelling, consists of restoring a section, placing circular strain markers on different domains of the restoration, and forward modelling the restored section with strain markers until the present-day stage is reached. The restoration algorithm employed must be also used to forward model the structure. The ellipses in the forward modelled section allow determining the strain state of the structure and may indirectly predict orientation and distribution of minor structures such as small-scale fractures. The forward model may be frozen at different time steps (different growth stages) allowing prediction of both spatial and temporal variation of strain. The method is evaluated through its application to two stages of a clay experiment, that includes strain markers, and its geometry and deformation history are well documented, providing a strong control on the results. To demonstrate the method's potential, it is successfully applied to a depth-converted seismic profile in the Central Sumatra Basin, Indonesia. This allowed us to gain insight into the deformation undergone by rollover anticlines over listric normal faults. 相似文献
58.
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60.
Stéphane Reboulet Peter F. Rawson Josep A. Moreno-Bedmar Maria B. Aguirre-Urreta Ricardo Barragán Yuri Bogomolov Miguel Company Celestina González-Arreola Vyara Idakieva Stoyanova Alexander Lukeneder Bertrand Matrion Vasily Mitta Hasina Randrianaly Zdenek Vaši?ek Evgenij J. Baraboshkin Didier Bert Stéphane Bersac Tamara N. Bogdanova Luc G. Bulot Jean-Louis Latil Irina A. Mikhailova Pierre Ropolo Ottilia Szives 《Cretaceous Research》2011,32(6):786-793
The 4th Kilian Group meeting (Dijon, France, 30th August 2010) focused on the Aptian and Albian Stages. For the Aptian, a two-fold division of the stage was adopted for the Mediterranean area with a boundary between the Dufrenoyia furcata and Epicheloniceras martini Zones. The main changes to the zonal scheme concern the Lower Aptian with: the introduction of a Deshayesites luppovi Subzone in the upper part of the Deshayesites oglanlensis Zone; the replacement of Deshayesites weissi by Deshayesites forbesi as new index-species of the second interval zone; the introduction of a Roloboceras hambrovi Subzone in the upper part of the D. forbesi Zone; and the subdivision of the D. furcata Zone into the D. furcata and Dufrenoyia dufrenoyi Subzones. For the Albian, the upper part of the Douvilleiceras mammillatum Zone (Lower Albian) is now characterized by a Lyelliceras pseudolyelli Subzone. The main amendments concern the Upper Albian. The base of this substage is defined by the base of the Dipoloceras cristatum Zone. Above it, the Upper Albian zonal scheme comprises in stratigraphic order the Mortoniceras pricei, Mortoniceras inflatum, Mortoniceras fallax, Mortoniceras rostratum, Mortoniceras perinflatum and Arrhaphoceras briacensis Zones. 相似文献