Decadal variation of surface solar radiation in the Tibetan Plateau from observations, reanalysis and model simulations     

Qinglong You  Arturo Sanchez-Lorenzo  Martin Wild  Doris Folini  Klaus Fraedrich  Guoyu Ren  Shichang Kang 《Climate Dynamics》2013,40(7-8):2073-2086

In this study, the annual and seasonal variations of all-sky and clear-sky surface solar radiation (SSR) in the eastern and central Tibetan Plateau (TP) during the period 1960–2009 are investigated, based on surface observational data, reanalyses and ensemble simulations with the global climate model ECHAM5-HAM. The mean annual all-sky SSR series shows a decreasing trend with a rate of ?1.00 Wm^?2 decade^?1, which is mainly seen in autumn and secondly in summer and winter. A stronger decrease of ?2.80 Wm^?2 decade^?1 is found in the mean annual clear-sky SSR series, especially during winter and autumn. Overall, these results confirm a tendency towards a decrease of SSR in the TP during the last five decades. The comparisons with reanalysis show that both NCEP/NCAR and ERA-40 reanalyses do not capture the decadal variations of the all-sky and clear-sky SSR. This is probably due to a missing consideration of aerosols in the reanalysis assimilation model. The SSR simulated with the ECHAM5-HAM global climate model under both all-sky and clear-sky conditions reproduce the decrease seen in the surface observations, especially after 1980. The steadily increasing aerosol optical depth (AOD) at 550 nm over the TP in the ECHAM5-HAM results suggests transient aerosol emissions as a plausible cause.  相似文献   

Seismic reflection-based evidence of a transfer zone between the Wagner and Consag basins: implications for defining the structural geometry of the northern Gulf of California     

Mario González-Escobar  Francisco Suárez-Vidal  José Antonio Hernández-Pérez  Arturo Martín-Barajas 《Geo-Marine Letters》2010,30(6):575-584

This study examines the structural characteristics of the northern Gulf of California by processing and interpreting ca. 415 km of two-dimensional multi-channel seismic reflection lines (data property of Petróleos Mexicanos PEMEX) collected in the vicinity of the border between the Wagner and Consag basins. The two basins appear to be a link between the Delfín Superior Basin to the south, and the Cerro Prieto Basin to the north in the Mexicali-Imperial Valley along the Pacific–North America plate boundary. The seismic data are consistent with existing knowledge of four main structures (master faults) in the region, i.e., the Percebo, Santa María, Consag Sur, and Wagner Sur faults. The Wagner and Consag basins are delimited to the east by the Wagner Sur Fault, and to the west by the Consag Sur Fault. The Percebo Fault borders the western margin of the modern Wagner Basin depocenter, and is oriented N10°W, dipping (on average) ～40° to the northeast. The trace of the Santa María Fault located in the Wagner Basin strikes N19°W, dipping ～40° to the west. The Consag Sur Fault is oriented N14°W, and dips ～42° to the east over a distance of 21 km. To the east of the study area, the Wagner Sur Fault almost parallels the Consag Sur Fault over a distance of ～86 km, and is oriented N10°W with an average dip of 59° to the east. Moreover, the data provide new evidence that the Wagner Fault is discontinuous between the two basins, and that its structure is more complex than previously reported. A structural high separates the northern Consag Basin from the southern Wagner Basin, comprising several secondary faults oriented NE oblique to the main faults of N–S direction. These could represent a zone of accommodation, or transfer zone, where extension could be transferred from the Wagner to the Consag Basin, or vice versa. This area shows no acoustic basement and/or intrusive body, which is consistent with existing gravimetric and magnetic data for the region.  相似文献   

Lithologic controls on mineralization at the Lagunas Norte high-sulfidation epithermal gold deposit, northern Peru   总被引：1，自引：0，他引：1  

Luis M. Cerpa  Thomas Bissig  Kurt Kyser  Craig McEwan  Arturo Macassi  Hugo W. Rios 《Mineralium Deposita》2013,48(5):653-673

The 13.1-Moz high-sulfidation epithermal gold deposit of Lagunas Norte, Alto Chicama District, northern Peru, is hosted in weakly metamorphosed quartzites of the Upper Jurassic to Lower Cretaceous Chimú Formation and in overlying Miocene volcanic rocks of dacitic to rhyolitic composition. The Dafne and Josefa diatremes crosscut the quartzites and are interpreted to be sources of the pyroclastic volcanic rocks. Hydrothermal activity was centered on the diatremes and four hydrothermal stages have been defined, three of which introduced Au ± Ag mineralization. The first hydrothermal stage is restricted to the quartzites of the Chimú Formation and is characterized by silice parda, a tan-colored aggregate of quartz-auriferous pyrite–rutile ± digenite infilling fractures and faults, partially replacing silty beds and forming cement of small hydraulic breccia bodies. The δ³⁴S values for pyrite (1.7–2.2?‰) and digenite (2.1?‰) indicate a magmatic source for the sulfur. The second hydrothermal stage resulted in the emplacement of diatremes and the related volcanic rocks. The Dafne diatreme features a relatively impermeable core dominated by milled slate from the Chicama Formation, whereas the Josefa diatreme only contains Chimú Formation quartzite clasts. The third hydrothermal stage introduced the bulk of the mineralization and affected the volcanic rocks, the diatremes, and the Chimú Formation. In the volcanic rocks, classic high-sulfidation epithermal alteration zonation exhibiting vuggy quartz surrounded by a quartz–alunite and a quartz–alunite–kaolinite zone is observed. Company data suggest that gold is present in solid solution or micro inclusions in pyrite. In the quartzite, the alteration is subtle and is manifested by the presence of pyrophyllite or kaolinite in the silty beds, the former resulting from relatively high silica activities in the fluid. In the quartzite, gold mineralization is hosted in a fracture network filled with coarse alunite, auriferous pyrite, and enargite. Alteration and mineralization in the breccias were controlled by permeability, which depends on the type and composition of the matrix, cement, and clast abundance. Coarse alunite from the main mineralization stage in textural equilibrium with pyrite and enargite has δ³⁴S values of 24.8–29.4?‰ and $ {\delta^{18 }}{{\mathrm{O}}_{{\mathrm{S}{{\mathrm{O}}_4}}}} $ values of 6.8–13.9?‰, consistent with H₂S as the dominant sulfur species in the mostly magmatic fluid and constraining the fluid composition to low pH (0–2) and logfO₂ of ?28 to ?30. Alunite–pyrite sulfur isotope thermometry records temperatures of 190–260 °C; the highest temperatures corresponding to samples from near the diatremes. Alunite of the third hydrothermal stage has been dated by ⁴⁰Ar/³⁹Ar at 17.0?±?0.22 Ma. The fourth hydrothermal stage introduced only modest amounts of gold and is characterized by the presence of massive alunite–pyrite in fractures, whereas barite, drusy quartz, and native sulfur were deposited in the volcanic rocks. The $ {\delta^{18 }}{{\mathrm{O}}_{{\mathrm{S}{{\mathrm{O}}_4}}}} $ values of stage IV alunite vary between 11.5 and 11.7?‰ and indicate that the fluid was magmatic, an interpretation also supported by the isotopic composition of barite (δ³⁴S?=?27.1 to 33.8?‰ and $ {\delta^{18 }}{{\mathrm{O}}_{{\mathrm{S}{{\mathrm{O}}_4}}}} $ ?=?8.1 to 12.7?‰). The Δ³⁴S_py–alu isotope thermometry records temperatures of 210 to 280 °C with the highest values concentrated around the Josefa diatreme. The Lagunas Norte deposit was oxidized to a depth of about 80 m below the current surface making exploitation by heap leach methods viable.  相似文献   

Geostatistical simulation of spatial variability of convective storms in Mexico City Valley     

Javier Méndez-Venegas  Graciela S. Herrera  Martín A. Díaz-Viera  Arturo Valdés-Manzanilla 《Geofísica Internacional》2013,52(2):111-120

Precipitation is one of the main components of the hydrological cycle and knowledge of its spatial distribution is fundamental for the prediction of other closely related environmental variables, for example, runoff, flooding and aquifer recharge. Most of the precipitation in Mexico City is due to convective storms characterized by a high spatial variability, implying that modeling its behavior is very complex. In this work stochastic simulation techniques with a geostatistical approach were applied to model the spatial variability of the rainfall of three convective storms. The analysis of the results shows that using the proposed methodology spatial distributions of rain are obtained that reproduce the statistical characteristics present in the available information.  相似文献   

The Mesolithic–Neolithic transition in southern Iberia     

Miguel Cortés Sánchez  Francisco J. Jiménez Espejo  María D. Simón Vallejo  Juan F. Gibaja Bao  António Faustino Carvalho  Francisca Martinez-Ruiz  Marta Rodrigo Gamiz  José-Abel Flores  Adina Paytan  José A. López Sáez  Leonor Peña-Chocarro  José S. Carrión  Arturo Morales Muñiz  Eufrasia Roselló Izquierdo  José A. Riquelme Cantal  Rebecca M. Dean  Emília Salgueiro  Rafael M. Martínez Sánchez  Nuno F. Bicho 《Quaternary Research》2012,77(2):221-234

New data and a review of historiographic information from Neolithic sites of the Malaga and Algarve coasts (southern Iberian Peninsula) and from the Maghreb (North Africa) reveal the existence of a Neolithic settlement at least from 7.5 cal ka BP. The agricultural and pastoralist food producing economy of that population rapidly replaced the coastal economies of the Mesolithic populations. The timing of this population and economic turnover coincided with major changes in the continental and marine ecosystems, including upwelling intensity, sea-level changes and increased aridity in the Sahara and along the Iberian coast. These changes likely impacted the subsistence strategies of the Mesolithic populations along the Iberian seascapes and resulted in abandonments manifested as sedimentary hiatuses in some areas during the Mesolithic–Neolithic transition. The rapid expansion and area of dispersal of the early Neolithic traits suggest the use of marine technology. Different evidences for a Maghrebian origin for the first colonists have been summarized. The recognition of an early North-African Neolithic influence in Southern Iberia and the Maghreb is vital for understanding the appearance and development of the Neolithic in Western Europe. Our review suggests links between climate change, resource allocation, and population turnover.  相似文献   

Leaf retention in streams of the Agüera basin (northern Spain)     

Santiago Larrañaga  José Ramón Díez  Arturo Elosegi  Jesús Pozo 《Aquatic Sciences - Research Across Boundaries》2003,65(2):158-166

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An improved approach for assigning pumping rates to heterogeneous aquifer models     

Pinales A  Chavez A  Llerar G  Manzanares L  Keer A 《Ground water》2005,43(2):274-279

A common assumption of ground water models formulated using a block-centered finite-difference method is that a well is located at the center of a cell regardless of its actual location. Due to this assumption, errors are introduced in the spatial distribution of simulated heads. This paper presents an alternative approach for assigning the pumping rates of wells that are located off cell centers. This approach consists of assigning the pumping rate not only to the cell in which the well is located but also to adjacent cells, taking into account the length of the well screen, the hydraulic conductivity, and the distance from the well to the center of its cell. The advantage of this alternative approach over the conventional one is illustrated with a test problem of a synthetic aquifer. Statistical measures of error indicate a much better model fit when pumping rates of wells are distributed over several cells.  相似文献   

The climatology of tornadoes and waterspouts in Italy   总被引：1，自引：0，他引：1  

Dario B. Giaiotti  Mauro Giovannoni  Arturo Pucillo  Fulvio Stel   《Atmospheric Research》2007,83(2-4):534-541

In this work 10 years of reports collected by weather amateurs are used to define a preliminary climatology of tornadoes and waterspouts in Italy. The results show behaviors different from those observed in other countries. Generally, tornadoes and waterspouts are more frequent in late summer and autumn than in the other seasons. The seasonality of tornadoes and waterspouts appears different for different Italian zones, in particular in the Po Valley and Friulian plain and coast (south to the Alps) tornadoes and waterspouts are more frequent in spring and early summer while in the Tirrenian and Ionian coasts (western and southern Italy), tornadoes and waterspouts are more frequent in late summer and autumn. As observed in other studies (Brooks, H., E. and Doswell, C. A. III, 2001. Some aspects of the international climatology of tornadoes by damage classification. Atmos. Res., 56, 191–201.) Italian tornadoes and waterspouts are statistically weaker than in other countries but this difference cannot be completely ascribed to the presence of waterspouts. The “CAPE Storm-Relative-Helicity diagrams” and “Shear Magnitude diagrams” obtained for Italian tornadoes and waterspouts show different characteristics than those obtained for US. The cause of these differences is still unknown, it can rely in the sample selection (problems with the concept of proximity sounding) or in a real climatic effect.  相似文献   

Structure of the rift basins in the central Gulf of California: Kinematic implications for oblique rifting     

Manuel Aragn-Arreola  María Morandi  Arturo Martín-Barajas  Luis Delgado-Argote  Antonio Gonzlez-Fernndez 《Tectonophysics》2005,409(1-4):19-38

We use structural and seismostratigraphic interpretation of multichannel seismic reflection data to understand the structure and kinematic history of the central Gulf of California. Our analysis reveals that oblique strain in the central Gulf formed two tectono–sedimentary domains during distinct deformation stages. The eastern domain, offshore Sonora, is bounded by the East and West Pedro Nolasco faults that may constitute the southernmost segments of the Tiburón Fault System. Within this domain, the dip-slip Yaqui Fault controlled deposition of 3.9 km of sediments in the half-graben Yaqui Basin. The western domain, offshore Baja California, is bounded by the Guaymas Transform Fault, which controlled the accumulation of 1.45 km of sediments within a half-graben that formed the early Guaymas Basin. The tectono–sedimentary activity offshore Sonoran likely ranges from Late Miocene–Pliocene to Late Pliocene time, while activity in the Guaymas Basin commenced in Late Pliocene time. Extinction of the main faults offshore Sonora was nearly coeval to the initiation of the Guaymas Transform Fault. Our results suggest that oblique strain has been accommodated by strain partition since the onset of rifting in the central Gulf. The Guaymas Basin is now a nascent spreading center, but prior to this, it evolved as a half-graben controlled by the Guaymas Transform Fault; such drastic transition is not constrained, but likely occurred during the Pleistocene time and must be localized < 30 km north of the axial troughs. The faults within the central Gulf transpose the Miocene N–S oriented grabens of Basin and Range style preserved onshore in the conjugate rifted margins.  相似文献   

Changes in the Wetlands of Andalusia (Doñana Natural Park, SW Spain) at the End of the Little Ice Age     

Arturo Sousa  Pablo García-Murillo 《Climatic change》2003,58(1-2):193-217

The Little Ice Age is a climatic period still insufficiently known. This ignorance is more marked in the case of Andalusia (southern Spain), where only recent works throw any light on the topic. Our studies, primarily from the perspective of botany and changes in the plant landscape, reveal the effects that this period had in these latitudes, and in particular on the Doñana Natural Park (SW Spain). This work shows an aridization in climatic conditions coinciding with the end of the Little Ice Age. The results corroborate the most recent theses on this period in Spain. Furthermore, the effects on the marsh areas studied lead us to conclude that the interpretation of the Little Ice Age in these southern latitudes should be different to that normally given for more northerly latitudes – much better known and more studied than the Mediterranean regions.  相似文献