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901.
902.
W. Boulila I.R. Farah K. Saheb Ettabaa B. Solaiman H. Ben Ghézala 《International Journal of Applied Earth Observation and Geoinformation》2011
The interpretation of remotely sensed images in a spatiotemporal context is becoming a valuable research topic. However, the constant growth of data volume in remote sensing imaging makes reaching conclusions based on collected data a challenging task. Recently, data mining appears to be a promising research field leading to several interesting discoveries in various areas such as marketing, surveillance, fraud detection and scientific discovery. By integrating data mining and image interpretation techniques, accurate and relevant information (i.e. functional relation between observed parcels and a set of informational contents) can be automatically elicited. 相似文献
903.
Caribbean Sea rainfall variability during the rainy season and relationship to the equatorial Pacific and tropical Atlantic SST 总被引:1,自引:1,他引:0
The present study investigates the Caribbean Sea rainfall variability during the early and late rainy seasons and its association with sea surface temperature (SST) and air?Csea interaction based on observational estimates, the NCEP Climate Forecast System (CFS) and Global Forecast System (GFS) simulations, and the CFS retrospective forecasts. Analysis of the observational estimates indicates that air?Csea interaction is important over the Caribbean Sea, whereas the atmospheric forcing of SST dominates over the Gulf of Mexico. The CFS simulation captures the basic elements of this observed air?Csea relationship. The GFS simulation produces spurious SST forcing of the atmosphere over the Gulf of Mexico largely due to prescribing SST. The CFS forecasts capture the air?Csea relationship in the late rainy season (August?COctober), but cannot reproduce the SST forcing of atmosphere over the Caribbean Sea in the early rainy season (May?CJuly). An empirical orthogonal function (EOF) analysis indicates that the leading modes of percent anomalies of the rainy season precipitation have the largest loading in the southern Caribbean Sea in observations. The model simulations and forecasts skillfully reproduce the spatial pattern, but not the temporal evolution. The Caribbean Sea rainfall variability in the early rainy season is mainly due to the tropical North Atlantic (TNA) SST anomalies in observations, is contributed by both the TNA and eastern equatorial Pacific (EEP) SST anomalies in the CFS simulation, and has an overly large impact from the EEP SST anomalies in the GFS simulation and the CFS forecasts. The observed Caribbean Sea rainfall variability in the late rainy season has a leading impact from the EEP SST anomalies, with a secondary contribution from the TNA SST anomalies. In comparison, the model simulations and forecasts overestimate the impacts of the EEP SST anomalies due to an earlier development and longer duration of the El Ni?o-Southern Oscillation in the CFS compared to observations. 相似文献
904.
Imen Hamdi Nasr Adnen Amiri Mohamed Hédi Inoubli Abdelhmid Ben Salem AbdelHak Chaqui Said Tlig 《Pure and Applied Geophysics》2011,168(10):1835-1849
Detailed gravity data in conjunction with available surface geology are analyzed to infer the organization of the underlying
structures in Jendouba area. Gravity data analysis benefits from the gravity Bouguer anomaly, upward continuations, residual
distribution, derivatives and Euler deconvolved maps. The main results display a positive amplitude gravity anomaly as the
response of Triassic evaporitic bodies and important NE trending features at the boundaries between the Triassic outcrops
and their enveloping strata. Integration of gravity, geological and structural maps let to the identification of major structural
directions and trends of the study area. It confirms some structural elements gathered from outcrops. It defines also new
ones. 相似文献
905.
Evaluation of DC, FDEM and IP resistivity methods for imaging perched saltwater and a shallow channel within coastal tidal flat sediments 总被引:1,自引:0,他引:1
Mohamed Attwa Thomas GüntherMichael Grinat Franz Binot 《Journal of Applied Geophysics》2011,75(4):656-670
Presently, electrical resistivity methods are applied in a wide variety of geological and environmental site investigations. Geologically, the coastal tidal flat sediments formed shallow channel-like features at the northern part of Germany. Three geoelectrical methods are applied to image the near surface sediments including a shallow conductive zone within the tidal deposits at the North Sea coast. These methods, direct current (DC) resistivity, frequency domain electromagnetic (FDEM) and spectral induced polarization (SIP), are evaluated to show which one can provide the required spatial resolution under study area conditions. This evaluation also includes a synthetic modeling to assess the DC resistivity imaging technique.The results constitute an encouraging example using these geophysical methods in characterizing the coastal aquifers. The inversion results show that the subsurface resistivity distribution of tidal sediments can change rapidly within a short distance. A thin high conductive layer is observed above the peat and clay layers reflecting a perched saltwater. The 2D IP section shows that the perched saltwater is restricted to patched forms above an impermeable layer of clay. According to the IP images the boundaries of the clay layer are recognized with a good resolution due to the high membrane polarization of the clays. The EM and DC profiles show a shallow channel-like feature within tidal deposits. In this paper, the best FDEM field parameters and the role of EM in lithologic studies are emphasized. Two main limitations can be observed from DC synthetic modeling: (a) A smearing in the lower boundary of the perched saltwater; (b) an amplification of the lateral effect of the highly conductive layer. These limitations decrease the resolution of DC imaging for accurate defining our targets. Because the IP response depends on microgeometry, fluid chemistry and saturation, the 2D IP results demonstrate the suitability of this method to characterize the tidal deposits in the coastal area with a good resolution. In this study, the success of SIP method supports further investigations into studying the hydraulic parameters of tidal deposits in this area. The obtained results during this investigation provide an overview of the coastal aquifer and they can serve as a basis for refining the conceptual model of morphological elements and sedimentary sequences of the coastal tidal flat. 相似文献
906.
Ruth S. Hindshaw Ben C. Reynolds Ruben Kretzschmar 《Geochimica et cosmochimica acta》2011,75(1):106-7046
The biogeochemical cycling and isotopic fractionation of calcium during the initial stages of weathering were investigated in an alpine soil chronosequence (Damma glacier, Switzerland). This site has a homogeneous silicate lithology and minimal biological impacts due to sparse vegetation cover. Calcium isotopic compositions, obtained by TIMS using a 43Ca-46Ca double spike, were measured in the main Ca pools. During this very early stage of weathering, the young soils which have formed (δ44/42Ca=+0.44‰) were indistinguishable to the rocks from which they were derived (δ44/42Ca=+0.44‰) and stream water (δ44/42Ca=+0.48‰) was also within error of the average rock. This lack of variation indicates that the dissolution of the bulk silicate rock does not strongly fractionate Ca isotopes. The only Ca pool which was strongly fractionated from bulk rock was vegetation, which exhibited an enrichment of light Ca isotopes. Significant Ca isotope fractionation between bulk rock and the dissolved flux of Ca is likely to only occur where the Ca biogeochemical cycle is dominated by secondary processes such as biological cycling, adsorption and secondary mineral precipitation. 相似文献
907.
Florence Bocquet Ben Balsley Michael Tjernström Gunilla Svensson 《Boundary-Layer Meteorology》2011,138(1):43-60
Tethered Lifting System (TLS) estimates of the dissipation rate of turbulent kinetic energy (e){(\varepsilon)} are reasonably well correlated with concurrent measurements of vertical velocity variance (sw2){(\sigma_{w}^{2})} obtained from sonic anemometers located on a nearby 60-m tower during the CASES-99 field experiment. Additional results in
the first 100 m of the nocturnal stable boundary layer confirm our earlier claim that the presence of weak but persistent
background turbulence exists even during the most stable atmospheric conditions, where e{\varepsilon} can exhibit values as low as 10−7 m2 s−3. We also present a set of empirical equations that incorporates TLS measurements of temperature, horizontal wind speed, and
e{\varepsilon} to provide a proxy measurement for sw2{\sigma_{w}^{2}} at altitudes higher than tower heights. 相似文献
908.
Ben D. Stanley Marc M. Hirschmann Anthony C. Withers 《Geochimica et cosmochimica acta》2011,75(20):5987-6003
To understand possible volcanogenic fluxes of CO2 to the Martian atmosphere, we investigated experimentally carbonate solubility in a synthetic melt based on the Adirondack-class Humphrey basalt at 1-2.5 GPa and 1400-1625 °C. Starting materials included both oxidized and reduced compositions, allowing a test of the effect of iron oxidation state on CO2 solubility. CO2 contents in experimental glasses were determined using Fourier transform infrared spectroscopy (FTIR) and Fe3+/FeT was measured by Mössbauer spectroscopy. The CO2 contents of glasses show no dependence on Fe3+/FeT and range from 0.34 to 2.12 wt.%. For Humphrey basalt, analysis of glasses with gravimetrically-determined CO2 contents allowed calibration of an integrated molar absorptivity of 81,500 ± 1500 L mol−1 cm−2 for the integrated area under the carbonate doublet at 1430 and 1520 cm−1. The experimentally determined CO2 solubilities allow calibration of the thermodynamic parameters governing dissolution of CO2 vapor as carbonate in silicate melt, KII, (Stolper and Holloway, 1988) as follows: , ΔV0 = 20.85 ± 0.91 cm3 mol−1, and ΔH0 = −17.96 ± 10.2 kJ mol−1. This relation, combined with the known thermodynamics of graphite oxidation, facilitates calculation of the CO2 dissolved in magmas derived from graphite-saturated Martian basalt source regions as a function of P, T, and fO2. For the source region for Humphrey, constrained by phase equilibria to be near 1350 °C and 1.2 GPa, the resulting CO2 contents are 51 ppm at the iron-wüstite buffer (IW), and 510 ppm at one order of magnitude above IW (IW + 1). However, solubilities are expected to be greater for depolymerized partial melts similar to primitive shergottite Yamato 980459 (Y 980459). This, combined with hotter source temperatures (1540 °C and 1.2 GPa) could allow hot plume-like magmas similar to Y 980459 to dissolve 240 ppm CO2 at IW and 0.24 wt.% of CO2 at IW + 1. For expected magmatic fluxes over the last 4.5 Ga of Martian history, magmas similar to Humphrey would only produce 0.03 and 0.26 bars from sources at IW and IW + 1, respectively. On the other hand, more primitive magmas like Y 980459 could plausibly produce 0.12 and 1.2 bars at IW and IW + 1, respectively. Thus, if typical Martian volcanic activity was reduced and the melting conditions cool, then degassing of CO2 to the atmosphere may not be sufficient to create greenhouse conditions required by observations of liquid surface water. However, if a significant fraction of Martian magmas derive from hot and primitive sources, as may have been true during the formation of Tharsis in the late Noachian, that are also slightly oxidized (IW + 1.2), then significant contribution of volcanogenic CO2 to an early Martian greenhouse is plausible. 相似文献
909.
Orbital timing of the Indian,East Asian and African boreal monsoons and the concept of a ‘global monsoon’ 总被引:1,自引:0,他引:1
Thibaut Caley Bruno Malaizé Marie Revel Emmanuelle Ducassou Karine Wainer Mohamed Ibrahim Dina Shoeaib Sébastien Migeon Vincent Marieu 《Quaternary Science Reviews》2011,30(25-26):3705-3715
Our understanding of monsoon circulation timing’s at the orbital scale is currently a matter of debate. Here, we compare previous and recently published results of Indian, East Asian, West African and East African monsoon variability. We note different timings between the East African, West African, Indian and East-Asian monsoon systems for the most recent 45 ka, where the age models are constrained by AMS dating. On this basis, we construct different orbital forcing “reference curves” and apply them to the 200 ka time period for the different monsoon systems. Our results indicate that the ‘global monsoon’ concept at the orbital scale is a misnomer. We find real regional differences in the timing of the monsoon response to orbital forcing and differences in the weight of precession and obliquity in the monsoon records. This work highlights the necessity of studies aimed at understanding the underlying physics of these regional response patterns. This is crucial to a better understanding of monsoon dynamics and improved climate model simulations and comparisons with proxy data. 相似文献
910.
N. Santillán Soto O.R. García Cueto S. Ojeda Benítez N. Velázquez Limón M. Quintero Núñez M. Schorr 《Atmósfera》2013,26(4):499-507
Solar radiation is one of the most important energy resources of our planet. The interest in its use as a renewable and clean energy to mitigate the greenhouse gases (GHG) effects has increased significantly. This paper evaluates the measurements of global solar radiation and its energy potential and presents a comparison between both of them, as an example of the effort to reduce GHG emissions. The measurements were made with pyranometers installed in the city of Mexicali, Baja California, located in northwestern Mexico, and the city of Yuma, Arizona, located in the southwestern United States. Separated by a distance of 96 km, both cities have a sustained development and are climatically similar, since they present numerous sunny days, extreme hot temperatures and little precipitation. The results presented show differences in their behavior and in the solar radiation measurement values, especially for the critical spring and summer seasons, with values 15.73% (0.042 kW/m2) higher in Mexicali with respect to Yuma. Energy power is estimated, and it is discussed with some variables as global solar radiation, rainfall, air temperature, relative humidity and climatology of clear, partly cloudy, and cloudy days. With this estimation, the solar energy used and GHG avoided is projected for Mexicali. It is assessed that 291 tons of GHG are prevented. The Mexicali values of potential energy are higher than those of Yuma; therefore, this solar and energy comparative study provides reasons to develop these technologies in Mexico, but solar technologies should be deployed also in Yuma. The measured data at the regional level demonstrate their importance, and the relevance of the proposed mitigation strategy for climate change. 相似文献