Spatiotemporal analysis of precipitation trends in the Yangtze River catchment   总被引：2，自引：2，他引：2  

Stefan Becker  Marco Gemmer  Tong Jiang 《Stochastic Environmental Research and Risk Assessment (SERRA)》2006,20(6):435-444

Precipitation trends in the Yangtze River catchment (PR China) have been analyzed for the past 50 years by applying the Mann-Kendall trend test and geospatial analyses. Monthly precipitation trends of 36 stations have been calculated. Significant positive trends at many stations can be observed for the summer months, which naturally show precipitation maxima. They were preceded and/or followed by negative trends. This observation points towards a concentration of summer precipitation within a shorter period of time. The analysis of a second data set on a gridded basis with 0.5° resolution reveals trends with distinct spatial patterns. The combination of classic trend tests and spatially interpolated precipitation data sets allows the spatiotemporal visualization of detected trends. Months with positive trends emphasize the aggravation of severe situation in a region, which is particularly prone to flood disasters during summer. Reasons for the observed trends were found in variations in the meridional wind pattern at the 850 hPa level, which account for an increased transport of warm moist air to the Yangtze River catchment during the summer months.  相似文献   

Influence of hydraulic conductivity on communities of microorganisms and invertebrates in porous media: a case study in drinking water slow sand filters   总被引：3，自引：0，他引：3  

Laurie Mauclaire  Andreas Schürmann  Florian Mermillod-Blondin 《Aquatic Sciences - Research Across Boundaries》2006,68(1):100-108

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Stress Sensitivity of Seismic and Electric Rock Properties of the Upper Continental Crust at the KTB     

Axel Kaselow  Katharina Becker  Serge A. Shapiro 《Pure and Applied Geophysics》2006,163(5-6):1021-1029

We test the hypothesis that the general trend of P-wave and S-wave sonic log velocities and resistivity with depth in the pilot hole of the KTB site Germany, can be explained by the progressive closure of the compliant porosity with increasingly effective pressure. We introduce a quantity θ_c characterizing the stress sensitivity of the mentioned properties. An analysis of the downhole measurements showed that estimates of the quantitiy θ_c for seismic velocities and electrical formation factor of the in situ formation coincide. Moreover, this quantity is 3.5 to 4.5 times larger than the averaged stress sensitivity obtained from core samples. We conclude that the hypothesis mentioned above is consistent with both data sets. Moreover, since θ_c corresponds approximately to the inverse of the effective crack aspect ratio, larger in situ estimates of θ_c might reflect the influence of fractures and faults on the stress sensitivity of the crystalline formation in contrast to the stress sensitivity of the nearly intact core samples. Finally, because the stress sensitivity is directly related to the elastic nonlinearity we conclude that the elastic nonlinearity (i.e., deviation from linear stress-strain relationship i.e., Hooke's law) of the KTB rocks is significantly larger in situ than in the laboratory.  相似文献   

The effect of mountainous topography on moisture exchange between the “surface” and the free atmosphere   总被引：1，自引：0，他引：1  

Andreas P. Weigel  Fotini K. Chow  Mathias W. Rotach 《Boundary-Layer Meteorology》2007,125(2):227-244

Typical numerical weather and climate prediction models apply parameterizations to describe the subgrid-scale exchange of moisture, heat and momentum between the surface and the free atmosphere. To a large degree, the underlying assumptions are based on empirical knowledge obtained from measurements in the atmospheric boundary layer over flat and homogeneous topography. It is, however, still unclear what happens if the topography is complex and steep. Not only is the applicability of classical turbulence schemes questionable in principle over such terrain, but mountains additionally induce vertical fluxes on the meso-γ scale. Examples are thermally or mechanically driven valley winds, which are neither resolved nor parameterized by climate models but nevertheless contribute to vertical exchange. Attempts to quantify these processes and to evaluate their impact on climate simulations have so far been scarce. Here, results from a case study in the Riviera Valley in southern Switzerland are presented. In previous work, measurements from the MAP-Riviera field campaign have been used to evaluate and configure a high-resolution large-eddy simulation code (ARPS). This model is here applied with a horizontal grid spacing of 350 m to detect and quantify the relevant exchange processes between the valley atmosphere (i.e. the ground “surface” in a coarse model) and the free atmosphere aloft. As an example, vertical export of moisture is evaluated for three fair-weather summer days. The simulations show that moisture exchange with the free atmosphere is indeed no longer governed by turbulent motions alone. Other mechanisms become important, such as mass export due to topographic narrowing or the interaction of thermally driven cross-valley circulations. Under certain atmospheric conditions, these topographical-related mechanisms exceed the “classical” turbulent contributions a coarse model would see by several times. The study shows that conventional subgrid-scale parameterizations can indeed be far off from reality if applied over complex topography, and that large-eddy simulations could provide a helpful tool for their improvement.  相似文献   

Biomediation of calcrete at the gold anomaly of the Barns prospect,Gawler Craton,South Australia     

Andreas Schmidt Mumm  Frank Reith 《Journal of Geochemical Exploration》2007

Anomalously high Au concentrations (2.5 to 50 ppb) in regolith carbonate accumulations, such as calcrete and calcareous sands in aeolian sand dunes overlying Au mineralisation of the Gawler Craton, South Australia, show a marked covariance of Au with K, Mg and most notably Ca. This relationship appears to be linked to the authigenic formation of smectites and carbonates within the aeolian dunes in the region. However, little is known about the processes involved in the formation of carbonates under semi-arid and arid conditions. In this study the geochemical properties of aeolian dunes along several depth profiles of 2 to 4 m are investigated in order to assess the relationship between Au mobility and calcrete formation. In the profiles a strongly systematic relationship between Au and the increasing Ca–Mg contents at depth highlights the close association between the enrichment of Au in the calcrete and the underlying hydrothermal mineralisation. Intense calcrete formation and concurrent Au enrichment also occurs in the vicinity of roots penetrating the dune. Thin section petrography and cathodoluminescence show that most of the calcrete in the regolith profiles is micritic; some sparic crystallites have also been identified. To demonstrate the presence of microbial processes that may mediate the formation of calcrete, samples from a depth profile in the dune were taken under sterile conditions. After amendment with urea and incubation of up to 24 h, up to 18 mg/l of NH₄⁺ were detected in near surface samples. At depth of 2.3 m 1 mg/l NH₄⁺ were detected compared to a control that contained below 0.05 mg/l NH₄⁺. These results suggest that the genesis of calcrete and pedogenic carbonate in the area may be partly biologically mediated via processes such as the metabolic breakdown of urea by resident microbiota which generates a pH and pCO₂ environment conducive to the precipitation of carbonate. In the process of urea breakdown organic Au complexes such as Au-amino acid complexes may become destabilised in solution and Au may be co-precipitated, resulting in the fine, non-particulate distribution of Au throughout the micritic calcrete carbonate. In conclusion, this study suggests a coupled mechanism of biologically mediated and inorganic mechanisms that lead to the formation of Au-in-calcrete anomalies.  相似文献   

On the robustness of ENSO teleconnections     

Andreas Sterl  Geert Jan van Oldenborgh  Wilco Hazeleger  Gerrit Burgers 《Climate Dynamics》2007,29(5):469-485

Using observations covering the last 128 years we show that apparent changes in El Niño-Southern Oscillation (ENSO) teleconnections can be explained by chance and stem from sampling variability. This result is backed by experiments in which an atmosphere model is driven by 123 years of observed sea surface temperature. The possibility of ENSO teleconnection changes in a warming climate is further investigated using coupled GCMs driven by past and projected future greenhouse gas concentrations. These runs do not exclude physical changes in the teleconnection strength but do not agree on their magnitude and location. If existing at all, changes in the strength of ENSO teleconnection, other than obtained by chance, are small and will only be detectable on centennial time scales.  相似文献   

Earthquake recurrence-time variations with and without fault-zone interactions   总被引：1，自引：0，他引：1  

Thorsten W. Becker  & Harro Schmeling 《Geophysical Journal International》1998,135(1):165-176

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Solar and meteoritic abundance of silicon     

U. Becker  P. Zimmermann  H. Holweger 《Geochimica et cosmochimica acta》1980,44(12):2145-2149

Recent lifetime measurements on excited electronic states of neutral silicon (Beckeret al., Phys. Lett. In press, 1980) lead to a reassessment of widely used experimental transition probabilities Garz, Astron. Astrophys., 26, 471–477, 1973 of Si I lines. This translates into a 25% downward revision of the Si abundance determined from the solar spectrum.A solar atomic ratio, Si/Ca = 15.5 is inferred. This value coincides with that found in carbonaceous chondrites, but contrasts with ordinary and enstatite chondrites.  相似文献   

Deformation microstructures in experimentally deformed Maryland diabase     

Andreas K Kronenberg  Glenmore L Shelton 《Journal of Structural Geology》1980,2(3):341-353

Experimentally deformed Maryland diabase has been examined using the transmission electron microscope in order to determine the mechanisms of deformation operative over a range of temperatures and pressures and thereby aid in the interpretation of polyphase flow data. Deformation mechanisms within the plagioclase and clinopyroxene of the diabase have been compared to those within monomineralic aggregates of these phases deformed at the same conditions. Both phases deform by microfracturing, mechanical twinning, and intracrystalline slip.Data for the monomineralic aggregates show that plagioclase is stronger than clinopyroxene at <800°C, but weaker at ≥ 800°C, for a pressure of 15 kbar and strain rate of 10^?6/sec. Observations of the diabase are consistent with this result: at < 800°C, the plagioclase and pyroxene grains are about equally strained, whereas at ≥ 800°C, almost all of the sample strain is accommodated by the plagioclase, the more continuous phase.  相似文献   

Altersbeziehungen zwischen Metamorphosen,mechanischen Deformationen und Intrusionen am Südrand des Rhodope-Massivs (Makedonien,Griechenland)     

Dr. Andreas Kokkinakis 《International Journal of Earth Sciences》1980,69(3):726-744

Zusammenfassung Ausgedehnte Granodiorit- und Granitmagmen intrudierten am Südrand des Rhodope-Massivs (Symvolongebirge und Kavala-Gebiet, Nordgriechenland) syntektonisch in bezug auf eine Formung, die durch überwiegend flach nach NE bis ENE tauchende Faltungs- und Scherungsachsen gekennzeichnet ist (B₂-Tektonik). Die metamorphen Hüllgesteine wurden von der B₂-Tektonik ebenfalls kräftig erfaßt. Ihr älteres Gefüge, das durch mittelsteil nach NNW tauchende B₁-Achsen bestimmt war, kommt daher nur noch reliktisch vor. Der Mineralbestand sowohl der Magmatite als auch ihres metamorphen Rahmens wurde im Zuge der B₂-Tektonik retrograd metamorph umgewandelt.Radiometrische Altersbestimmungen lassen erkennen, daß die magmatischen Gesteine spätestens im Oberkarbon kristallisierten, anschließend jedoch wiederholt aufgewärmt wurden. Das Alter der prämagmatischen Metamorphose der Hüllgesteine und der mit dieser in Zusammenhang stehenden B₁-Tektonik kann demnach nicht jünger als kaledonisch sein.

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Extensive granodioritic and granitic magmas were intruded in the southern margin of the Rhodope-Massif (Symvolon mountains and Kavala region, northern Greece). The intrusions took place syntectonically to a deformation which is characterized by predominantly gently NE to ENE plunging fold- and shear-axes (B₂-folding). The mantling rocks, which have been metamorphosed long before this B₂-folding have an older structure which is characterized by mediumly NNW plunging B₁-axes, visible only in relicts. During the B₂-folding the mineral contents of the igneous rocks and their metamorphic mantling rocks have been metamorphosed retrogressively.Radiometric dating indicates that the crystallization of the magmatic rocks have a minimum age of Upper-Carboniferous, but subsequently these rocks were reheated repeatedly. The age of the premagmatic metamorphism of the mantling rocks and that of the related B₁-foldnig, therefore, cannot be younger than Caledonic.

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Résumé Dans la partie sud du massif du Rhodope (montagnes du Symvolon et région de Kavala, Grèce du Nord) existent de grandes intrusions de magmas granodioritiques et granitiques. Les intrusions eurent lieu syntectoniquement au cours d'une phase de déformation caractérisée par des axes de plis et de cisaillement, généralement à plongement faible vers le NE à ENE (tectonique B₂). Les roches encaissantes, qui furent métamorphisées longtemps avant cette phase de tectonique B₂, ont une structure plus ancienne, caractérisée par des axes B₁ plongeant moyennement vers le NNW. Cette structure est reconnaissable seulement dans des parties réiduelles. Durant la tectonique B₂ les roches éruptives et les roches encaissantes métamorphisées subirent un métamorphisme rétrograde.Des datations radiométriques indiquent, pour la cristallisation des roches magmatiques, au minimum un âge Carbonifère supérieur. Dans la suite ces roches furent réchauffées â plusieures reprises. Le métamorphisme plus ancien des roches encaissantes et la tectonique B₁ associée à ce métamorphisme ne peuvent donc pas Être plus récents que l'époque calédonienne.

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Rhodope ( Symrolon Kavala, ) - . , , , , NE ENE (B₂- ). ₂. , B₁ NNW, . , , . , , , , . , - B₁ .

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