Validation of a homogeneous 41-year (1961–2001) winter precipitation hindcasted dataset over the Iberian Peninsula: assessment of the regional improvement of global reanalysis     

M. G. Sotillo  M. L. Martín  F. Valero  M. Y. Luna 《Climate Dynamics》2006,27(6):627-645

A 44-year (1958–2001) homogeneous, Mediterranean, high-resolution atmospheric database was generated through dynamical downscaling within the HIPOCAS (Hindcast of Dynamic Processes of the Ocean and Coastal Areas of Europe) Project framework. This work attempts to provide a validation of the monthly winter HIPOCAS precipitation over the Iberian Peninsula and the Balearic Islands and to evaluate the potential improvement of these new hindcasted data versus global reanalysis datasets. The validation was performed through the comparative analysis with a precipitation database derived from 4,617 in situ stations located over Iberia and the Balearics. The statistical comparative analysis between the observed and the HIPOCAS fields highlights their very good agreement not only in terms of spatial and time distribution, but also in terms of total amount of precipitation. A principal component analysis is carried out, showing that the patterns derived from the HIPOCAS data largely capture the main characteristics of the observed field. Moreover, it is worth to note that the HIPOCAS patterns reproduce accurately the observed regional characteristics linked to the main orographic features of the study domain. The existence of high correlations between the hindcasted and observed principal component time series gives a measure of the model performance ability. An additional comparative study of the HIPOCAS winter precipitation with global reanalysis data (NCEP and ERA) is performed. This study reveals the important regional improvement in the characterization of the observed precipitation introduced by the HIPOCAS hindcast relative to the above global reanalyses. Such improvement is effective not only in terms of total amount values, but also in the spatial distribution, the observed field being much more realistically reproduced by HIPOCAS than by the global reanalysis data.  相似文献   

Velocity Oscillations in Active Sunspot Groups     

Balthasar  H.  MartÍnez Pillet  V.  Schleicher  H.  Wöhl  H. 《Solar physics》1998,182(1):65-72

Time series of two-dimensional spectra were taken with the Göttingen 2D spectrometer at the VTT on Tenerife in 1996. They were investigated for Doppler velocities and velocity oscillations in small spots and pores of rapidly evolving sunspot groups. For the present measurements the magnetically insensitive lines Fe i 557.6 nm and Fe i 709.0 nm were selected. Spots with penumbrae exhibit the Evershed effect. Some pores seem to be connected with downflows, but the centres of the downflows are somewhat displaced from their associated pores. The surroundings of the pores show red shifts relative to the whole field of view. The power in the 5-min range is reduced inside the spots and pores as well as in their immediate vicinity. This reduction inside the spots is in agreement with former results. Outside the area of the spot group the 5-min power has a patchy structure with a typical size of 5 arc sec. For periods below 3.3 min, the behaviour of individual spots and pores is different. Some spots show clearly enhanced power for these periods, and it remains high down to the Nyquist period at 1.5 min. The small pores do not show enhanced three-minute oscillations compared with their vicinity. Inside one spot we find a ring of enhanced power in the period range between 8 and 20 min corresponding to the time scales of granular variations. This result could be an indication of a relation between spots and convection, but magneto-accoustic waves are also possible. The same ring exhibits also enhanced power for short periods.  相似文献   

Relationship between waterfowl and the seagrassRuppia maritima in a Southwestern Atlantic coastal lagoon     

Alejandro Bortolus  Oscar O. Iribarne  Mariano M. Martínez 《Estuaries and Coasts》1998,21(4):710-717

We evaluated the distribution of waterfowl in relation to a seagrass (Ruppia maritima) patch, to infauna, and on its relationship with substrate characteristics. An experiment performed in the Mar Chiquita coastal lagoon (37°46′S, 57°27′W; Argentina) was used to evaluate the effect of herbivory on widgeon grass,R. maritima. Control plots of equal size, located between bird exclosures, were exposed to herbivory. The experiment ran for 31 d, starting on December 1, 1994. Censuses showed that black-necked swan ( $\bar x = 50$ birds ha^?1, SD = 37, n = 10) and coots ( $\bar x = 42$ birds ha^?1, SD = 28, n = 10) were the most important (always present) of the waterfowl seen feeding onR. maritima. The results of the experiment showed greater leaf lengths, lower belowground (rhizomes and roots) biomass, greater aboveground (leaves and shoots) biomass, and greater abundance of the polychaeteHeteromastus similis in exclosure plots. There were no exclosure effects on total biomass (belowground plus aboveground), reproductive parts (fruits and pre- and postpollination flowers), or abundance of most benthic infauna. Topographic surveys showed that sediment surface was higher within theR. maritima patches, but there were no significant differences in granulometric composition. Surveys also showed that bird distribution was strongly associated with the presence ofR. maritima.  相似文献   

From subduction to transform motion: a seabeam survey of the Hellenic trench system     

Xavier Le Pichon  Jacques Angelier  Jean Aubouin  Nicolas Lyberis  Serge Monti  Vincent Renard  Henri Got  Ken Hsu¨  Yossi Mart  Jean Mascle  Drummond Matthews  Dimitri Mitropoulos  Pandelis Tsoflias  Georges Chronis 《Earth and Planetary Science Letters》1979,44(3):441-450

Preliminary results of a multi-narrow beam survey of the Hellenic trench system, in the Eastern Mediterranean, are presented. The southwestern Ionian branch is divided in small basins, partly filled with Pleistocene sediments. The morphology suggests that the basins are deformed by a compressional stress acting roughly perpendicularly to the trench along N50°E. This direction is the direction of the regional slip vector of the shallow thrust-type earthquakes. The structure of the southeastern Pliny-Strabo branch is quite different. Narrow en-e´chelon slots, oriented N40°E, have been mapped within the main troughs oriented N60°E. The regional earthquake slip vector is also oriented along N40°E. We conclude that the Hellenic trench system is an active subduction system, dominated by thrust along the Ionian branch and by transform motion along the Pliny-Strabo branch.  相似文献   

Cretaceous and Paleogene geologic history of coastal Ecuador     

Dr. Tomas Feininger  Dr. C. Roger Bristow 《International Journal of Earth Sciences》1980,69(3):849-874

Following a general review of the Cretaceous and Paleogene geology of Ecuador, we propose a geologic history from early Cretaceous through Oligocene time with emphasis on the coastal part of the country that is based on the interpretive interaction of three oceanic plates (the Bolívar, proto-Nazca, and Nazca) and the continental South American plate. The proposed history invokes large lateral displacements, the intervention of the previously unrecognized Bolívar plate, the development of three successive subduction zones, the formation of a distant oceanic island arc and its subsequent collision with the South American plate, the emplacement of a major olistostrome complex, and an intricate record of displacement on a currently inactive transform fault. The proposed history offers a viable solution to four major problems of the geology of coastal Ecuador.

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Zusammenfassung Aus der Kreide- und Paläogen-Geschichte Ecuadors läßt sich die Entwicklung der Küstenregion ableiten. Sie wird vom Zusammenwirken von drei ozeanischen Platten (Bolivar, Proto-Nazca und Nazca) und der kontinentalen Platte Südamerikas bestimmt. Die Entwicklung umfaßt ausgedehnte Seitenverschiebungen, das Auftreten einer bisher nicht erkannten Bolivar-Platte, die Anlage von drei aufeinanderfolgenden Subduktionszonen, die Bildung eines Inselbogens und die folgende Kollision mit der Südamerikanischen Platte, die Ablagerung eines großen Olisthostrom-Komplexes und die Verschiebungen entlang einer heute inaktiven Transform-Verwerfung. Damit sind eine Reihe von Problemen der Geologie des Küstenabschnittes Ecuadors gelöst.

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Résumé Passant en revue la géologie de l'Equateur au Crétacique et Paléogène, les auteurs proposent une histoire géologique allant depuis le Crétacique inférieur à l'Oligocène en mettant l'accent sur la région cÔtière, et en se basant sur l'interaction de trois plaques océaniques (bolivienne, proto-Nasca et Nasca) et de la plaque continentale de l'Amérique du Sud. L'histoire proposée fait appel à de grands déplacements, à l'intervention de la plaque bolivienne non reconnue antérieurement, au développement de trois zones de subduction successives, à la formation d'une guirlande d'Îles océaniques distante et sa collision subséquente avec la plaque de l'Amérique du Sud, à la mise en place d'un grand complexe olistostromique et à un déplacement sur une faille transformante inactive. L'histoire proposée apporte une solution viable à quatre problèmes de la géologie de la Région cÔtière de l'Equateur.

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. (, protoNazca Nazca) . : , , , , , Olistostrome . .

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Contribution No. 6 A, Departamento de Geología, Escuela Politécnica Nacional, Quito, Ecuador.  相似文献   

The impact of land use change and check‐dams on catchment sediment yield     

Carolina Boix‐Fayos  Joris de Vente  María Martínez‐Mena  Gonzalo G. Barberá  Víctor Castillo 《水文研究》2008,22(25):4922-4935

Extensive land use changes have occurred in many areas of SE Spain as a result of reforestation and the abandonment of agricultural activities. Parallel to this the Spanish Administration spends large funds on hydrological control works to reduce erosion and sediment transport. However, it remains untested how these large land use changes affect the erosion processes at the catchment scale and if the hydrological control works efficiently reduce sediment export. A combination of field work, mapping and modelling was used to test the influence of land use scenarios with and without sediment control structures (check‐dams) on sediment yield at the catchment scale. The study catchment is located in SE Spain and suffered important land use changes, increasing the forest cover 3‐fold and decreasing the agricultural land 2·5‐fold from 1956 to 1997. In addition 58 check‐dams were constructed in the catchment in the 1970s accompanying reforestation works. The erosion model WATEM‐SEDEM was applied using six land use scenarios: land use in 1956, 1981 and 1997, each with and without check‐dams. Calibration of the model provided a model efficiency of 0·84 for absolute sediment yield. Model application showed that in a scenario without check dams, the land use changes between 1956 and 1997 caused a progressive decrease in sediment yield of 54%. In a scenario without land use changes but with check‐dams, about 77% of the sediment yield was retained behind the dams. Check‐dams can be efficient sediment control measures, but with a short‐lived effect. They have important side‐effects, such as inducing channel erosion downstream. While also having side‐effects, land use changes can have important long‐term effects on sediment yield. The application of either land use changes (i.e. reforestation) or check‐dams to control sediment yield depends on the objective of the management and the specific environmental conditions of each area. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Evaluating infiltration losses in a Mediterranean wetland: Las Tablas de Daimiel National Park,Spain     

S. Castaño‐Castaño  P. Martínez‐Santos  P. E. Martínez‐Alfaro 《水文研究》2008,22(26):5048-5053

Las Tablas de Daimiel National Park is a series of wetlands which naturally originated from groundwater discharges from the Mancha Occidental aquifer, Spain. Despite the relatively large size of this aquifer, 30 years of intensive groundwater pumping have significantly depleted the water table. As a result, wetlands only remain functional due to artificial inflows. Infiltration loss is therefore a key parameter to evaluate how much water is needed to maintain ecosystem functionality. Although yearly infiltration estimates existed prior to this work, these did not take into account key parameters such as the temporal evolution of the flooded area. This paper presents a more concrete estimate of the average infiltration losses. Infiltration is calculated as the closure term of daily water balances during a period of time where all other elements were known to an acceptable accuracy. A validation mechanism is provided to check the potential utility of the calculated infiltration in wetland management practices. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Numerical modelling of the potential effects of a dam on a coastal aquifer in S. Spain     

M. L. Calvache  S. Ibáñez  C. Duque  W. Martín‐Rosales  M. López‐Chicano  J. C. Rubio  A. González  C. Viseras 《水文研究》2009,23(9):1268-1281

This study presents the results of a three‐dimensional variable‐density numerical modelling of the Motril‐Salobreña coastal aquifer and the possible effects of the entry into service in May 2005 of the Rules Dam, located just 17 km from the coast. Present parameters of the Motril‐Salobreña aquifer show that the system's conditions are very similar to a natural regime. The dam will substantially alter aquifer recharge, as the entry flow through the alluvial sediments of the Guadalfeo River will be entirely cut off or drastically reduced. Different scenarios reproducing the possible evolution of the aquifer under operation of the Rules Dam have been modelled. In most cases, results indicate that the conditions of the aquifer would worsen, with a general advance of the freshwater–saltwater interface. The area with most risk of saltwater intrusion is the old mouth of the Guadalfeo River, where the mixing zone could advance 1200 m inland. It is proposed that maintaining a 5–6 Mm³ year^?1 ‘ecological flow’ in the Guadalfeo River could prevent this saline advance. This application demonstrates that variable‐density models are potentially useful tools for estimating the effects of dams on the hydrodynamic and hydrochemical conditions of a coastal aquifer. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

The search for hot spots associated with the Cygnus X-3 relativistic jet     

J. Martí  D. Pérez-Ramírez  P. Luque-Escamilla  J. L. Garrido  J. M. Paredes  A. Muñoz-Arjonilla  J. R. Sánchez-Sutil 《Astrophysics and Space Science》2007,309(1-4):309-313

We report and shortly discuss here the observational work carried out in order to test the possibility that two previously detected radio sources, in the vicinity of the well known microquasar Cygnus X-3, could be hot spot tracers of interaction between its relativistic jet and the interstellar medium (ISM). The motivation behind this search is in part justified considering recent theoretical models of high energy γ-ray emission which strongly rely on the interaction sites of galactic relativistic jets with nearby ISM clouds. The results presented in this paper include an improved radio exploration of the several arc-minute field around Cygnus X-3 using the Very Large Array (VLA), as well as deep near infrared (NIR) imaging with the Calar Alto 3.5 m telescope. We anticipate here that our observations do not appear to support the initial hot spot hypothesis. Instead, the resulting images suggest that the two radio sources, originally believed to be hot spot candidates, are most likely background or foreground objects.  相似文献   

Geochemical study of products associated with spontaneous oxidation of coal in the Cerro Pelado Formation,Venezuela     

M. Martínez  G. Márquez  F.J. Alejandre  J.J. Del Río  A. Hurtado 《Journal of South American Earth Sciences》2009,27(2-3):211-218

The aim of this research work is a geochemical, mineralogical, and textural characterization of spontaneously smouldered coal-derived products in northwestern Venezuela (Cerro Pelado Formation, some 10 km from Pedregal city). Several solid samples were collected from this formation, six of unweathering coal, an other six of resulting unmelted rocks forming on a surface coal bed, and the last four of mineralizations found accumulating around gas vents. The fresh coal and the unmelted material were analysed by scanning electron microscopy, X-ray diffraction, and proximate techniques. Products such as magnetite and chabazite-K were identified in the alteration rocks. Likewise, both materials were also studied in order to determine the mobilization of 17 elements into the environment; such elements were analysed through inductively coupled plasma atomic emission spectroscopy on extracts obtained by a sequential extraction method: each sample was firstly extracted with MilliQ water and then the resultant residue was washed. This and the subsequently resulting residues are extracted according to the mentioned procedure by using, respectively, ammonium acetate, chlorhydric acid, peroxide and chlorhydric acid, nitric acid and fluorhydric acid, and nitric acid. The studied elements are classified as highly mobile (Na, Ni, ...), nearly immobile (Ti, P) and partially mobile (Mg, Fe, K, ...). In regards to mineralizations around fumaroles associated with smoldering coal seams, Fourier-transform infrared spectroscopy and X-ray diffraction analyses have revealed the presence of salammoniac, mascagnite and other solid combustion compounds formed by reaction of gas emitted from coal oxidation, in addition to previously non-reported sulfur-rich by-products associated with gas fissures, particularly ammonium thiosulfate, a phase first obtained only synthetically in the laboratory. Another objective of the research was to collect and analyse gases escaping from surficial vents. Relatively high concentrations of several aromatic compounds were detected in the gas collected at the studied coal outcrop, as well as aliphatic hydrocarbons including ethane, propane, butanes, among others. High contents of carbon monoxide, methane and carbon dioxide were also measured for gas samples.  相似文献