Application of the K?ppen classification for climatic zoning in the state of Minas Gerais, Brazil     

Arionaldo de Sá Júnior  Luiz Gonsaga de Carvalho  Fábio Fernandes da Silva  Marcelo de Carvalho Alves 《Theoretical and Applied Climatology》2012,108(1-2):1-7

The knowledge of the climatic conditions of a region is crucial for its agricultural development. It is also extremely important for understanding the fact that certain cultures have to develop under prevailing temperature and humidity conditions and assist in the adoption of a suitable irrigation technique, as well as its management and operationalization. The K?ppen system of climate classification is widely used for the identification of homogeneous climate zones as it considers only rainfall and temperature as the meteorological elements for classification. For this study, we used climatic databases of rainfall and temperature in a raster format, with a spatial resolution of 30″ of arc (an approximate area of 0.86?km²?pixel^?1), from 1961 to 1990. Through geoprocessing techniques, we obtained a map of climatic classification for the state of Minas Gerais. We found that the state has the following three major climatic groups: A, B and C, which correspond to tropical rainy, dry and warm temperate climates, respectively. The climate classes obtained were Aw, Am, BSh, Cwa and Cwb, with Aw, Cwa and Cwb classes occupying 99.89% of the territorial area of the state. The validation of the results showed a satisfactory agreement, with 93.75% reliability.  相似文献   

Cloud condensation nuclei from biomass burning during the Amazonian dry-to-wet transition season   总被引：1，自引：0，他引：1  

Jorge Alberto Martins  Fábio Luiz T. Gonçalves  Carlos A. Morales  Gilberto F. Fisch  Francisco Geraldo M. Pinheiro  João Bosco V. Leal Júnior  Carlos J. Oliveira  Emerson M. Silva  José Carlos P. Oliveira  Alexandre A. Costa  Maria Assunção F. Silva Dias 《Meteorology and Atmospheric Physics》2009,104(1-2):83-93

Aircraft measurements of cloud condensation nuclei (CCN) during the Large-Scale Biosphere–Atmosphere Experiment in Amazonia (LBA) were conducted over the Southwestern Amazon region in September–October 2002, to emphasize the dry-to-wet transition season. The CCN concentrations were measured for values within the range 0.1–1.0% of supersaturation. The CCN concentration inside the boundary layer revealed a general decreasing trend during the transition from the end of the dry season to the onset of the wet season. Clean and polluted areas showed large differences. The differences were not so strong at high levels in the troposphere and there was evidence supporting the semi-direct aerosol effect in suppressing convection through the evaporation of clouds by aerosol absorption. The measurements also showed a diurnal cycle following biomass burning activity. Although biomass burning was the most important source of CCN, it was seen as a source of relatively efficient CCN, since the increase was significant only at high supersaturations.  相似文献   

Probing the relationship between surface waters and aquifers by <Superscript>18</Superscript>O measurements on the top of the Araripe Plateau/NE Brazil     

Luiz?Alberto?Ribeiro?Mendon?a  Horst?FrischkornEmail author  Maria?Marlúcia?Freitas?Santiago  Josué?Mendes Filho 《Environmental Geology》2004,46(2):295-302

The Araripe Plateau in northeastern Brazil has an area of about 8,000 km², confined by 39°05E and 40°55E, and 7°10S and 7°50S. Due to high permeability of soils, a surface drainage system is practically inexistent. Water is stored in excavations with clayey soil, the barreiros. Monthly samples were taken for ¹⁸O measurements, from September 1999 to August 2000, from four barreiros, three dug wells and five drilled wells. Results show that (1) groundwaters in the eastern part of the plateau are derived from present-day rainfall (¹⁸O–3.2), whereas groundwaters in the western portion are isotopically different (¹⁸O–5.0); (2) barreiros are strongly marked seasonally by elevated ¹⁸O during the dry period due to elevated evaporation; (3) a dug well at a distance of 30 m from a barreiro exhibits ¹⁸O similar to that of the reservoir, indicating a strong interaction between groundwater and surface water; and (4) a tubular well of 242-m depth, located in a fault, exhibits strong seasonal changes in ¹⁸O and electrical conductivity, revealing downward leakage between aquifers.  相似文献   

Shrimp U–Pb zircon dating and palynology of bentonitic layers from the Permian Irati Formation, Paraná Basin, Brazil     

Roberto Ventura Santos  Paulo A. Souza  Carlos Jos Souza de Alvarenga  Elton Luiz Dantas  Marcio Martins Pimentel  Claudinei Gouveia de Oliveira  Laury Medeiros de Araújo 《Gondwana Research》2006,9(4):456-463

This paper presents the first SHRIMP zircon age data from bentonitic ash fall layers intercalated with the Irati sedimentary rocks, as well as palynofossils retrieved from the PETROBRAS-Six mine, Paraná State, southern Brazil. The Permian Irati Formation is one the most important oil source horizons within the Paraná Basin, and consists mainly of siltstones, gray claystones, as well as organic-rich claystones intercalated with limestones. Zircon morphology based on cathodoluminescence images includes two different populations: a dominant population of euhedral, prismatic, elongate to acicular grains which are most likely related to an ash fall volcanism; and a population of rounded to large prismatic grains, that were interpreted as detrital grains. SHRIMP analysis performed on the euhedral and prismatic grains revealed an age of ca. 278.4 ± 2.2 Ma (7 points with 95% confidence) interpreted as the crystallization age of the volcanic eruption. Based on this new dating, the Irati Formation should be placed on the Lower Permian (Cisuralian), Artinskian in age, modifying substantially the traditional ages previously attributed to this unit. The palynofossils from this level include key species of the Lueckisporites virkkiae Zone (such as L. virkkiae, L. densicorpus, L. stenotaeniatus, Weylandites lucifer, Alisporites splendens). Typical species of this zone also occur in African and other South American (Argentina) Permian strata, allowing stratigraphical correlations. The origin of the ash falls is not clearly defined. It may be related either to calc-alkaline arc magmatism associated to the Sanrafaelica Orogeny (275 and 250 Ma) or to bimodal volcanic events associated to an early intracontinental rift developed within southwestern Gondwana at ca. 278 My. The dating of this unit is significative to calibrate biostratigraphic schemes along the Paraná Basin, as well as equivalent zones in Gondwana areas, mainly in its Occidental portion.  相似文献   

Interactions of river discharge and tidal modulation in a tropical estuary, NE Brazil     

Luiz Bruner de Miranda  Alessandro Luvizon Bérgamo  Belmiro Mendes de Castro 《Ocean Dynamics》2005,55(5-6):430-440

Observations of thermohaline properties and currents were undertaken in the Curimataú River estuary (6°18′S), Rio Grande do Norte state (RN), Brazil, during consecutive neap–spring tidal cycles in the austral autumn rainy season. Highly asymmetric neap tide along channel velocities (−0.4 to 0.9 m s⁻¹) and highly stratified conditions were generated by an increase of the buoyancy energy from the freshwater input (R _iE≈5.6). During the spring-tidal cycle the river discharge decreased and the longitudinal velocity components were higher, less asymmetrical (−0.8 to 1.1 m s⁻¹) and semidiurnal, associated with moderately stratified conditions (R _iE≈0.1) due to the increase of the kinetic tidal energy forcing mechanism. The overall salinity variation from surface to bottom during two tidal cycles was from 20.5 to 36.3 and 29 to 36.7 in the neap and spring tide experiments, respectively; in the last experiment, the tropical water (TW) mass intrusion was enhanced. The net salt transport reversed from down to up estuary during the neap and spring tide experiments, respectively, varied from 6.0 to –2.0 kg m⁻¹ s⁻¹, an indication of changes in the main forcing of the estuary dynamics. Evaluation of a classical steady analytical model, in comparison with nearly steady experimental vertical profiles of velocity, shows an agreement classifiable as reasonably fair.  相似文献   

U–Pb and Sm–Nd geochronology of amphibolites from the Curaçá Belt, São Francisco Craton, Brazil: Tectonic implications     

Luiz Jos Homem D'el-Rey Silva  Elton Luiz Dantas  Joo Batista Guimares Teixeira  Jorge Henrique Laux  Maria da Glria da Silva 《Gondwana Research》2007,12(4):454-467

The Curaçá terrane is part of the Itabuna–Salvador–Curaçá (I–S–C) Paleoproterozoic orogen in the São Francisco craton, northeastern Brazil, and comprises supracrustal rocks, gneisses of their probable basement, amphibolites, and mafic-ultramafic Cu-bearing bodies (including the Caraíba Cu-Mine), all affected by D₁-D₃ deformation events associated to M₁-M₃ metamorphism under high-T granulite and amphibolite facies, and assisted by G₁-G₃ tonalitic-granodioritic-granitic intrusions. U–Pb and Sm–Nd Thermal Ionization Mass Spectrometry (TIMS) isotopic data from amphibolite, tonalite, and granite, sampled in a well-known outcrop, indicate partial reset and heterogeneous modification of the original isotopic systems, attributable to deformation and metamorphism. The ages obtained from these systems agree with each other, and also with other previously published U–Pb data, and imply that 2.6 Ga is the crystallization age of the protolith of the amphibolite. Together with key structural relationships, they also indicate a 2.08–2.05 Ga interval for M₃ metamorphism, and make even a less precise age (2.2–2.3 Ga) acceptable, as it suggests contamination in the amphibolite with material in a syn-D₂ tonalite crystallized 2248 ± 36 Ma ago. The new data demonstrate the existence of Neoarchean fragments of both oceanic and continental crusts and constrain the Archean-Paleoproterozoic development of the Curaçá belt, the I–S–C orogen, and the São Francisco craton.  相似文献   

The Archean BIF-hosted Cuiabá Gold deposit, Quadrilátero Ferrífero, Minas Gerais, Brazil     

Luiz Cludio Ribeiro-Rodrigues  Claudinei Gouveia de Oliveira  Gunther Friedrich 《Ore Geology Reviews》2007,32(3-4):543

The Cuiabá Gold Deposit is located in the northern part of the Quadrilátero Ferrífero, Minas Gerais State, Brazil. The region constitutes an Archean granite–greenstone terrane composed of a basement complex (ca. 3.2 Ga), the Rio das Velhas Supergroup greenstone sequence, and related granitoids (3.0–2.7 Ga), which are overlain by the Proterozoic supracrustal sequences of the Minas (< 2.6–2.1  Ga) and Espinhaço (1.7 Ga) supergroups.The stratigraphy of the Cuiabá area is part of the Nova Lima Group, which forms the lower part of the Rio das Velhas Supergroup. The lithological succession of the mine area comprises, from bottom to top, lower mafic metavolcanics intercalated with carbonaceous metasedimentary rocks, the gold-bearing Cuiabá-Banded Iron Formation (BIF), upper mafic metavolcanics and volcanoclastics and metasedimentary rocks. The metamorphism reached the greenschist facies. Tectonic structures of the deposit area are genetically related to deformation phases D₁, D₂, D₃, which took place under crustal compression representing one progressive deformational event (E_n).The bulk of the economic-grade gold mineralization is related to six main ore shoots, contained within the Cuiabá BIF horizon, which range in thickness between 1 and 6 m. The BIF-hosted gold orebodies (> 4 ppm Au) represent sulfide-rich segments of the Cuiabá BIF, which grade laterally into non-economic mineralized or barren iron formation. Transitions from sulfide-rich to sulfide-poor BIF are indicated by decreasing gold grades from over 60 ppm to values below the fire assay detection limit in sulfide-poor portions. The deposit is “gold-only”, and shows a characteristic association of Au with Ag, As, Sb and low base-metal contents. The gold is fine grained (up to 60 μm), and is generally associated with sulfide layers, occurring as inclusions, in fractures or along grain boundaries of pyrite, the predominant sulfide mineral (> 90 vol.%). Gold is characterized by an average fineness of 0.840 and a large range of fineness (0.759 to 0.941).The country rocks to the mineralized BIF show strong sericite, carbonate and chlorite alteration, typical of greenschist facies metamorphic conditions. Textures observed on microscopic to mine scales indicate that the mineralized Cuiabá BIF is the result of sulfidation involving pervasive replacement of Fe-carbonates (siderite–ankerite) by Fe-sulfides. Gold mineralization at Cuiabá shows various features reported for Archean gold–lode deposits including the: (1) association of gold mineralization with Fe-rich host rocks; (2) strong structural control of the gold orebodies, showing remarkable down-plunge continuity (> 3 km) relative to strike length and width (up to 20 m); (3) epigenetic nature of the mineralization, with sulfidation as the major wall–rock alteration and directly associated with gold deposition; (4) geochemical signature, with mineralization showing consistent metal associations (Au–Ag–As–Sb and low base metal), which is compatible with metamorphic fluids.  相似文献   

Thermal re-emission effects on GPS satellites     

Jânia Duha  Germano Bruno Afonso  Luiz Danilo Damasceno Ferreira 《Journal of Geodesy》2006,80(12):665-674

Highly precise satellite-derived coordinates depend on accurate orbit predictions, which cannot be achieved with purely empirical models. Global positioning system (GPS) satellites undergo several periodic perturbing forces that have to be modeled and understood. In this scenario, small non-gravitational forces can no longer be neglected when the purpose of the orbital analysis is to obtain accurate results (Vilhena de Moraes 1994). Together with solar radiation pressure, thermal re-emission effects due to solar heating and Earth albedo are the two most important non-gravitational effects. While solar radiation pressure is widely understood, our knowledge about thermal re-emission effects on GPS satellites is in its infancy. Few models have been proposed in recent years and despite the interest of the scientific community, there is a lack of detailed results concerning the magnitude and the behavior of such forces. The aim of this work is to provide a thermal re-emission force model for GPS satellites, simple enough to minimize the problem of modeling a satellite of complex shape with several components on its surface, but accurate enough to provide an estimate of the magnitude and the behavior of these forces, as well as to provide some input to the present knowledge about photon thrust on GPS satellites. Some results of this work point to the fact that thermal re-emission effects are good candidates to partially explain the Y-bias for GPS satellites.  相似文献   

A comment on the insolation at Mercury     

Robert Landau 《Icarus》1982,52(1):202-204

E. Van Hemelrijck and J. Vercheval [Icarus48, 167–179 (1981)] presented calculations of the insolation at Mercury and Venus which neglect the finite angular size of the Sun. To determine the temperature structure in the subsurface a more accurate calculation is needed, especially at longitudes ±90° on Mercury, where the Sun takes 18 days to rise or set. These calculations are presented here.  相似文献   

Updating global Hg emissions from small-scale gold mining and assessing its environmental impacts     

Luiz de Lacerda 《Environmental Geology》2003,43(3):308-314

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