An investigation of the characteristics of the onset and cessation of the rains in Nigeria   总被引：1，自引：0，他引：1  

N. J. Bello 《Theoretical and Applied Climatology》1996,54(3-4):161-173

Summary Rainfall and potential evapotranspiration (PE) data spanning 35 years (1959–1993) were analysed to determine the onset and cessation of the rains for 4 selected stations in each of the 4 major selected zones of Nigeria. The characteristics of onset and cessation of the rains have been categorised as normal, early and late. The pattern of occurrence of each category varies among the ecological zones. For instance, the occurrence of normal onset of the rains is highest at locations in the Forest and Guinea Savanna Zones. In the Sudan Savanna area, however, the occurrence of normal onset of the rains is equal with that of late occurrence. It was, however, found that the occurrence of normal cessation of the rains is higher than early or late cessation at locations in all the zones. Furthermore, the occurrence of each category of the cessation of the rains is more consistent than that of the onset. The influence of the Inter-Tropical Discontinuity (ITD) on the latter observation have been noted. Further analysis of the characteristics of the onset and cessation of the rains showed that occurrence of short-falls in the duration of the rainfalls for normal agricultural activaties is peculiar to all the zones. However, such shortfalls are lower in the Forest Zone than in the Savanna regions, indicating that the reliability of the duration of the rainfalls for normal agricultural activities decreases northwards from the forest to the Sudan Savanna region. The implications of the observations for farm operations have been stressed.With 10 Figures  相似文献   

Lacustrine stromatolites: Useful structures for environmental interpretation – an example from the Miocene Ebro Basin     

Leticia Martin‐Bello  Concha Arenas  Brian Jones 《Sedimentology》2019,66(6):2098-2133

The significance of stromatolites as depositional environmental indicators and the underlying causes of lamination in the lacustrine realm are poorly understood. Stromatolites in a ca 600 m thick Miocene succession in the Ebro Basin are good candidates to shed light on these issues because they are intimately related to other lacustrine carbonate and sulphate facies, grew under variable environmental conditions and show distinct lamination patterns. These stromatolites are associated with wave‐related, clastic‐carbonate laminated limestones. Both facies consist of calcite and variable amounts of dolomite. Thin planar stromatolites (up to 10 cm thick and less than 6 m long) occurred in very shallow water. These stromatolites represented first biological colonization after: (i) subaerial exposure in the palustrine environment (i.e. at the beginning of deepening cycles); or (ii) erosion due to surge action, then coating very irregular surfaces on laminated limestones (i.e. through shallowing or deepening cycles). Sometimes they are associated with evaporative pumping. Stratiform stromatolites (10 to 30 cm high and tens of metres long) and domed stromatolites (10 to 30 cm high and long) developed in deeper settings, between the surge periods that produced hummocky cross‐stratification and horizontal lamination offshore. Changes in stromatolite lamina shape, and thus in the growth forms through time, can be attributed to changes in water depth, whereas variations in lamina continuity are linked to water energy and sediment supply. Growth of the stromatolites resulted from in situ calcite precipitation and capture of minor amounts of fine‐grained carbonate particles. Based on texture, four types of simple laminae are distinguished. The simple micrite and microsparite laminae can be grouped into light and dark composite laminae, which represent, respectively, high and low Precipitation/Evaporation ratio periods. Different lamination patterns provide new ideas for the interpretation of microbial laminations as a function of variations in climate‐dependent parameters (primarily the Precipitation/Evaporation ratio) over variable timescales.  相似文献   

Spatial Distribution of Nitrous Oxide (N<Subscript>2</Subscript>O) in the Reloncaví Estuary–Sound and Adjacent Sea (41°–43° S), Chilean Patagonia     

Mariela A. Yevenes  Estrella Bello  Sandra Sanhueza-Guevara  Laura Farías 《Estuaries and Coasts》2017,40(3):807-821

Fjords and estuaries exchange large amounts of solutes, gases, and particulates between fluvial and marine systems. These exchanges and their relative distributions of compounds/particles are partially controlled by stratification and water circulation. The spatial and vertical distributions of N₂O, an important greenhouse gas, along with other oceanographic variables, are analyzed from the Reloncaví estuary (RE) (~41° 30′ S) to the gulf of Corcovado in the interior sea of Chiloé (43° 45′ S) during the austral winter. Freshwater runoff into the estuary regulated salinity and stratification of the water column, clearly demarking the surface (<5 m depth) and subsurface layer (>5 m depth) and also separating estuarine and marine influenced areas. N₂O levels varied between 8.3 and 21 nM (corresponding to 80 and 170 % saturation, respectively), being significantly lower (11.8 ± 1.70) at the surface than in subsurface waters in the Reloncaví estuary (14.5 ± 1.73). Low salinity and NO₃ ^?, NO₂ ^?, and PO₄ ^3? levels, as well as high Si(OH)₄ values were associated with low surface N₂O levels. Remarkably, an accumulation of N₂O was observed in the subsurface waters of the Reloncaví sound, associated with a relatively high consumption of O₂. The sound is exposed to increasing anthropogenic impacts from aquaculture and urban discharge, occurring simultaneously with an internal recirculation, which leads to potential signals of early eutrophication. In contrast, within the interior sea of Chiloé (ISC), most of water column was quasi homohaline and occupied by modified subantarctic water (MSAAW), which was relatively rich in N₂O (12.6 ± 2.36 nM) and NO₃ ^? (18.3 ± 1.63 μM). The relationship between salinity, nutrients, and N₂O revealed that water from the open ocean, entering into ISC (the Gulf of Corcovado) through the Guafo mouth, was the main source of N₂O (up to 21 nM), as it gradually mixed with estuarine water. In addition, significant relationships between N₂O excess vs. AOU and N₂O excess vs. NO₃ ^? suggest that part of N₂O is also produced by nitrification. Our results show that the estuarine and marine waters can act as light source or sink of N₂O to the atmosphere (air–sea N₂O fluxes ranged from ?1.57 to 5.75 μmol m^?2 day^?1), respectively; influxes seem to be associated to brackish water depleted in N₂O that also caused a strong stratification, creating a barrier to gas exchange.  相似文献   

Fault–valve action and vein development during strike–slip faulting: An example from the Ribeira Shear Zone, Southeastern Brazil     

Frederico Meira Faleiros  Ginaldo Ademar da Cruz Campanha  Rosa Maria da Silveira Bello  Kazuo Fuzikawa 《Tectonophysics》2007,438(1-4):1-32

Fluid inclusion microthermometry and structural data are presented for quartz vein systems of a major dextral transcurrent shear zone of Neoproterozoic–Cambrian age in the Ribeira River Valley area, southeastern Brazil. Geometric and microstructural constraints indicate that foliation–parallel and extensional veins were formed during dextral strike–slip faulting. Both vein systems are formed essentially by quartz and lesser contents of sulfides and carbonates, and were crystallized in the presence of CO₂–CH₄ and H₂O–CO₂–CH₄–NaCl immiscible fluids following unmixing from a homogeneous parental fluid. Contrasting fluid entrapment conditions indicate that the two vein systems were formed in different structural levels. Foliation–parallel veins were precipitated beneath the seismogenic zone under pressure fluctuating from moderately sublithostatic to moderately subhydrostatic values (319–397 °C and 47–215 MPa), which is compatible with predicted fluid pressure cycle curves derived from fault–valve action. Growth of extensional veins occurred in shallower structural levels, under pressure fluctuating from near hydrostatic to moderately subhydrostatic values (207–218 °C and 18–74 MPa), which indicate that precipitation occurred within the near surface hydrostatically pressured seismogenic zone. Fluid immiscibility and precipitation of quartz in foliation–parallel veins resulted from fluid pressure drop immediately after earthquake rupture. Fluid immiscibility following a local pressure drop during extensional veining occurred in pre-seismic stages in response to the development of fracture porosity in the dilatant zone. Late stages of fluid circulation within the fault zone are represented dominantly by low to high salinity (0.2 to 44 wt.% equivalent NaCl) H₂O–NaCl–CaCl₂ fluid inclusions trapped in healed fractures mainly in foliation–parallel veins, which also exhibit subordinate H₂O–NaCl–CaCl₂, CO₂–(CH₄) and H₂O–CO₂–(CH₄)–NaCl fluid inclusions trapped under subsolvus conditions in single healed microcracks. Recurrent circulation of aqueous–carbonic fluids and aqueous fluids of highly contrasting salinities during veining and post-veining stages suggests that fluids of different reservoirs were pumped to the ruptured fault zone during faulting episodes. A fluid evolution trending toward CH₄ depletion for CO₂–CH₄–bearing fluids and salinity depletion and dilution (approximation of the system H₂O–NaCl) for aqueous–saline fluids occurred concomitantly with decrease in temperature and pressure related to fluid entrapment in progressively shallower structural levels reflecting the shear zone exhumation history.  相似文献   

Comparative evaluation of EDTA, pyridine and acetic acid for the assessment of available heavy metals from domestic and industrial sludges     

A. A. Olajire  M. O. Bello  M. Abdul-Hammed  O. M. Olabemiwo 《International Journal of Environmental Science and Technology》2006,3(4):341-349

Various sludge samples from different domestic and industrial wastewater treatment plants were analyzed by Flame Atomic Absorption Spectrometry (FAAS) to evaluate their total and available contents of heavy metals (Pb, Hg, Cd and Zn). The EDTA, pyridine and acetic acid single extraction techniques were applied to these samples with the objective of studying the leaching behavior of the metals in different sludges and also to predict their possible mobility when these wastes are disposed on the environment and landfills. In EDTA, higher extraction efficiency was observed for major part of the elements studied in the industrial sludges except for Hg and Cd, which were also considerably released from domestic sludges. Acetic acid and pyridine gave a better extraction efficiency for Zn in industrial sludge than EDTA. Moreover, the results of total digestions were compared, for total metal contents, with those obtained using pseudototal digestion procedure and a good correlation (r² = 0.95) was found between the two methods of digestion.  相似文献   

The GREGOR Fabry‐Pérot Interferometer     

K.G. Puschmann  C. Denker  F. Kneer  N. Al Erdogan  H. Balthasar  S.M. Bauer  C. Beck  N. Bello Gonzlez  M. Collados  T. Hahn  J. Hirzberger  A. Hofmann  R.E. Louis  H. Nicklas  O. Okunev  V. Martínez Pillet  E. Popow  T. Seelemann  R. Volkmer  A.D. Wittmann  M. Woche 《Astronomische Nachrichten》2012,333(9):880-893

The GREGOR Fabry‐Pérot Interferometer (GFPI) is one of three first‐light instruments of the German 1.5‐meter GREGOR solar telescope at the Observatorio del Teide, Tenerife, Spain. The GFPI uses two tunable etalons in collimated mounting. Thanks to its large‐format, high‐cadence CCD detectors with sophisticated computer hard‐ and software it is capable of scanning spectral lines with a cadence that is sufficient to capture the dynamic evolution of the solar atmosphere. The field‐of‐view (FOV) of 50″×38″is well suited for quiet Sun and sunspot observations. However, in the vector spectropolarimetric mode the FOV reduces to 25″×38″. The spectral coverage in the spectroscopic mode extends from 530–860 nm with a theoretical spectral resolution of R ≈250 000, whereas in the vector spectropolarimetric mode the wavelength range is at present limited to 580–660 nm. The combination of fast narrow‐band imaging and post‐factum image restoration has the potential for discovery science concerning the dynamic Sun and its magnetic field at spatial scales down to ∼50 km on the solar surface (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

A retrospective of the GREGOR solar telescope in scientific literature     

C. Denker  O. von der Lühe  A. Feller  K. Arlt  H. Balthasar  S.‐M. Bauer  N. Bello Gonzlez  Th. Berkefeld  P. Caligari  M. Collados  A. Fischer  T. Granzer  T. Hahn  C. Halbgewachs  F. Heidecke  A. Hofmann  T. Kentischer  M. Klva&#x;a  F. Kneer  A. Lagg  H. Nicklas  E. Popow  K.G. Puschmann  J. Rendtel  D. Schmidt  W. Schmidt  M. Sobotka  S.K. Solanki  D. Soltau  J. Staude  K.G. Strassmeier  R. Volkmer  T. Waldmann  E. Wiehr  A.D. Wittmann  M. Woche 《Astronomische Nachrichten》2012,333(9):810-815

In this review, we look back upon the literature, which had the GREGOR solar telescope project as its subject including science cases, telescope subsystems, and post‐focus instruments. The articles date back to the year 2000, when the initial concepts for a new solar telescope on Tenerife were first presented at scientific meetings. This comprehensive bibliography contains literature until the year 2012, i.e., the final stages of commissioning and science verification. Taking stock of the various publications in peer‐reviewed journals and conference proceedings also provides the “historical” context for the reference articles in this special issue of Astronomische Nachrichten/Astronomical Notes (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Devonian F-rich peraluminous A-type magmatism in the proto-Andean foreland (Sierras Pampeanas,Argentina): geochemical constraints and petrogenesis from the western-central region of the Achala batholith     

Juan A. Dahlquist  Pablo H. Alasino  Carina Bello 《Mineralogy and Petrology》2014,108(3):391-417

A new LA-ICP-MS crystallization age of 370?±?8 Ma is presented for monzogranite from the Achala batholith, the largest Devonian igneous body in the Sierras Pampeanas, confirming previous U-Pb zircon ages and indicating emplacement within a relatively short episode. Granitic rocks from the central area of the batholith display restricted high SiO₂ contents (69.8–74.5 wt.%). Major element plots show ferroan and alkaline-calcic to calc-alkaline compositions with an A-type signature. High concentrations of the high field-strength elements such as Y, Nb, Ga, Ta, U, Th, and flat REE patterns with significant negative Eu anomalies, are also typical of A-type granites. The aluminium saturation index (1.10–1.37) indicates aluminous parent magmas which are further characterised by high FeO/MgO ratios (2.6–3.3) and F contents of igneous biotites (0.9–1.5 wt%), as well as relatively high Al^IV (2.39–2.58 a.p.f.u.) in biotites and the occurrence of primary muscovite. Petrogenetic modelling supports a source enriched in plagioclase and progressive fractional crystallization of feldspar. The central area of the batholith displays small-scale bodies composed predominantly of biotite (80 %), muscovite (10 %) and apatite (10 %), yielding rock compositions with 2.3–5.4 wt. % P₂O₅, and 6–7 wt.% F, together with anomalous contents of U (88–1,866 ppm), Zr (1081–2,581 ppm), Nb (257–1,395 ppm) and ΣREE (1,443–4,492 ppm). Previous studies rule out an origin of these bodies as metasedimentary xenoliths and they have been interpreted as cumulates from the granitic magma. An alternative flow segregation process is discussed here.  相似文献   

Distribution and geochemical significance of dibenzofurans,phenyldibenzofurans and benzo[b]naphthofurans in source rock extracts from Niger Delta basin,Nigeria     

Ogbesejana  Abiodun B.  Bello  Oluwasesan M. 《中国地球化学学报》2020,39(6):973-987

Acta Geochimica - The distribution and geochemical significance of dibenzofurans, phenyldibenzofurans and benzo[b]napthofurans in source rocks from Niger Delta basin, Nigeria, were investigated by...  相似文献