排序方式: 共有263条查询结果,搜索用时 265 毫秒
31.
Young-Kwon Lim Lydia B. Stefanova Steven C. Chan Siegfried D. Schubert James J. O��Brien 《Climate Dynamics》2011,37(5-6):1061-1080
This study assesses the regional-scale summer precipitation produced by the dynamical downscaling of analyzed large-scale fields. The main goal of this study is to investigate how much the regional model adds smaller scale precipitation information that the large-scale fields do not resolve. The modeling region for this study covers the southeastern United States (Florida, Georgia, Alabama, South Carolina, and North Carolina) where the summer climate is subtropical in nature, with a heavy influence of regional-scale convection. The coarse resolution (2.5° latitude/longitude) large-scale atmospheric variables from the National Center for Environmental Prediction (NCEP)/DOE reanalysis (R2) are downscaled using the NCEP/Environmental Climate Prediction Center regional spectral model (RSM) to produce precipitation at 20?km resolution for 16 summer seasons (1990?C2005). The RSM produces realistic details in the regional summer precipitation at 20?km resolution. Compared to R2, the RSM-produced monthly precipitation shows better agreement with observations. There is a reduced wet bias and a more realistic spatial pattern of the precipitation climatology compared with the interpolated R2 values. The root mean square errors of the monthly R2 precipitation are reduced over 93% (1,697) of all the grid points in the five states (1,821). The temporal correlation also improves over 92% (1,675) of all grid points such that the domain-averaged correlation increases from 0.38 (R2) to 0.55 (RSM). The RSM accurately reproduces the first two observed eigenmodes, compared with the R2 product for which the second mode is not properly reproduced. The spatial patterns for wet versus dry summer years are also successfully simulated in RSM. For shorter time scales, the RSM resolves heavy rainfall events and their frequency better than R2. Correlation and categorical classification (above/near/below average) for the monthly frequency of heavy precipitation days is also significantly improved by the RSM. 相似文献
32.
William L. Bandy Yuri Taran Carlos Mortera Guti��rrez Vladimir Kostoglodov 《Pure and Applied Geophysics》2011,168(8-9):1251-1253
33.
E. Bertrand A.-M. Duval J. R��gnier R. M. Azzara F. Bergamashi P. Bordoni F. Cara G. Cultrera G. Di Giulio G. Milana J. Salichon 《Bulletin of Earthquake Engineering》2011,9(3):809-823
During the microzonation studies of the April 6th, 2009 L??Aquila earthquake, we observed local seismic amplifications in the Roio area??a plane separated from L??Aquila city center by mount Luco. Six portable, digital instruments were deployed across the plain from 15 April to mid-May 2009. This array recorded 152 aftershocks. We analyzed the ground motion from these events to determine relative site amplification within the plain and on surrounding ridges. Horizontal over vertical spectral ratio on noise data (HVSRN), aftershock recordings (HVEQ) and standard spectral ratio (SSR) showed amplifications at 1.3 and 4.0?Hz on quaternary deposits. Seismic amplifications in the frequency range of 4 and 6?Hz were also observed on a carbonate ridge of Colle di Roio, on the northwestern border of the plateau. A small amplification was noticed near the top of mount Luco, another rocky site. Large discrepancies in the amplification levels between methods have been observed for these sites, but the HVSRN, HVEQ and SSR gave similar results at the stations located in the Roio plain. On the rocky sites, the SSR was more reliable than the HVSRN at estimating the transfer function of the site, even if the resonance frequency seemed to be well detected by the latter method. 相似文献
34.
Compositional Bayesian indicator estimation 总被引:1,自引:1,他引:0
Carolina Guardiola-Albert Eulogio Pardo-Ig��zquiza 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(6):835-849
Indicator kriging is widely used for mapping spatial binary variables and for estimating the global and local spatial distributions
of variables in geosciences. For continuous random variables, indicator kriging gives an estimate of the cumulative distribution
function, for a given threshold, which is then the estimate of a probability. Like any other kriging procedure, indicator
kriging provides an estimation variance that, although not often used in applications, should be taken into account as it
assesses the uncertainty of the estimate. An alternative approach to indicator estimation is proposed in this paper. In this
alternative approach the complete probability density function of the indicator estimate is evaluated. The procedure is described
in a Bayesian framework, using a multivariate Gaussian likelihood and an a priori distribution which are both combined according
to Bayes theorem in order to obtain a posterior distribution for the indicator estimate. From this posterior distribution,
point estimates, interval estimates and uncertainty measures can be obtained. Among the point estimates, the median of the
posterior distribution is the maximum entropy estimate because there is a fifty-fifty chance of the unknown value of the estimate
being larger or smaller than the median; that is, there is maximum uncertainty in the choice between two alternatives. Thus
in some sense, the latter is an indicator estimator, alternative to the kriging estimator, that includes its own uncertainty.
On the other hand, the mode of the posterior distribution estimator, assuming a uniform prior, is coincidental with the simple
kriging estimator. Additionally, because the indicator estimate can be considered as a two-part composition which domain of
definition is the simplex, the method is extended to compositional Bayesian indicator estimation. Bayesian indicator estimation
and compositional Bayesian indicator estimation are illustrated with an environmental case study in which the probability
of the content of a geochemical element in soil being over a particular threshold is of interest. The computer codes and its
user guides are public domain and freely available. 相似文献
35.
Adapting a texture synthesis algorithm for conditional multiple point geostatistical simulation 总被引:2,自引:1,他引:1
��lvaro Parra Juli��n M. Ortiz 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(8):1101-1111
Computer vision provides several tools for analyzing and simulating textures. The principles of these techniques are similar
to those in multiple-point geostatistics, namely, the reproduction of patterns and consistency in the results from a perceptual
point of view, thus, ensuring the reproduction of long range connectivity. The only difference between these techniques and
geostatistical simulation accounting for multiple-point statistics is that conditioning is not an issue in computer vision.
We present a solution to the problem of conditioning simulated fields while simultaneously honoring multiple-point (pattern)
statistics. The proposal is based on a texture synthesis algorithm where a fixed search (causal) pattern is used. Conditioning
is achieved by adding a non-causal search neighborhood that modifies the conditional distribution from which the simulated
category is drawn, depending on the conditioning information. Results show an excellent reproduction of the features from
the training image, while respecting the conditioning information. Some issues related to the data structure and to the computer
efficiency are discussed. 相似文献
36.
Evidence for Century-Timescale Acceleration in Mean Sea Levels and for Recent Changes in Extreme Sea Levels 总被引:2,自引:0,他引:2
Two of the most important topics in Sea Level Science are addressed in this paper. One is concerned with the evidence for the apparent acceleration in the rate of global sea level change between the nineteenth and twentieth centuries and, thereby, with the question of whether the twentieth century sea level rise was a consequence of an accelerated climate change of anthropogenic origin. An acceleration is indeed observed in both tide gauge and saltmarsh data at different locations around the world, yielding quadratic coefficients ??c?? of order 0.005 mm/year2, and with the most rapid changes of rate of sea level rise occurring around the end of the nineteenth century. The second topic refers to whether there is evidence that extreme sea levels have increased in recent decades at rates significantly different from those in mean levels. Recent results, which suggest that at most locations rates of change of extreme and mean sea levels are comparable, are presented. In addition, a short review is given of recent work on extreme sea levels by other authors. This body of work, which is focused primarily on Europe and the Mediterranean, also tends to support mean and extreme sea levels changing at similar rates at most locations. 相似文献
37.
Patrick Mercier-Langevin Mark D. Hannington Beno?t Dub�� Val��rie B��cu 《Mineralium Deposita》2011,46(5-6):509-539
Volcanogenic massive sulfide deposits contain variable amounts of gold, both in terms of average grade and total gold content, with some VMS deposits hosting world-class gold mines with more than 100?t Au. Previous studies have identified gold-rich VMS as having an average gold grade, expressed in g/t, exceeding the total abundance of base metals, expressed in wt.%. However, statistically meaningful criteria for the identification of truly anomalous deposits have not been established. This paper presents a more extensive analysis of gold grades and tonnages of 513 VMS deposits worldwide, revealing a number of important features in the distribution of the data. A large proportion of deposits are characterized by a relatively low gold grade (<2?g/t), with a gradual decrease in frequency towards maximum gold grades, defining a log-normal distribution. In the analysis presented in this paper, the geometric mean and geometric standard deviation appear to be the simplest metric for identifying subclasses of VMS deposits based on gold grade, especially when comparing deposits within individual belts and districts. The geometric mean gold grade of 513 VMS deposits worldwide is 0.76?g/t; the geometric standard deviation is +2.70?g/t Au. In this analysis, deposits with more than 3.46?g/t Au (geometric mean plus one geometric standard deviation) are considered auriferous. The geometric mean gold content is 4.7?t Au, with a geometric standard deviation of +26.3?t Au. Deposits containing 31?t Au or more (geometric mean plus one geometric standard deviation) are also considered to be anomalous in terms of gold content, irrespective of the gold grade. Deposits with more than 3.46?g/t Au and 31?t Au are considered gold-rich VMS. A large proportion of the total gold hosted in VMS worldwide is found in a relatively small number of such deposits. The identification of these truly anomalous systems helps shed light on the geological parameters that control unusual enrichment of gold in VMS. At the district scale, the gold-rich deposits occupy a stratigraphic position and volcanic setting that commonly differs from other deposits of the district possibly due to a step change in the geodynamic and magmatic evolution of local volcanic complexes. The gold-rich VMS are commonly associated with transitional to calc-alkaline intermediate to felsic volcanic rocks, which may reflect a particularly fertile geodynamic setting and/or timing (e.g., early arc rifting or rifting front). At the deposit scale, uncommon alteration assemblages (e.g., advanced argillic, aluminous, strongly siliceous, or potassium feldspar alteration) and trace element signatures may be recognized (e.g., Au?CAg?CAs?CSb ± Bi?CHg?CTe), suggesting a direct magmatic input in some systems. 相似文献
38.
G��nther J. Redhammer Anatoliy Senyshyn Martin Meven Georg Roth Sebastian Prinz Astrid Pachler Gerold Tippelt Clemens Pietzonka Werner Treutmann Markus Hoelzel Bj?rn Pedersen Georg Amthauer 《Physics and Chemistry of Minerals》2011,38(2):139-157
The compound NaFeGe2O6 was grown synthetically as polycrystalline powder and as large single crystals suitable for X-ray and neutron-diffraction experiments to clarify the low temperature evolution of secondary structural parameters and to determine the low temperature magnetic spins structure. NaFeGe2O6 is isotypic to the clinopyroxene-type compound aegirine and adopts the typical HT-C2/c clinopyroxene structure down to 2.5?K. The Na-bearing M2 polyhedra were identified to show the largest volume expansion between 2.5?K and room temperature, while the GeO4 tetrahedra behave as stiff units. Magnetic susceptibility measurements show a broad maximum around 33?K, which marks the onset of low-dimensional magnetic ordering. Below 12?K NaFeGe2O6 transforms to an incommensurately modulated magnetic spin state, with k?=?[0.323, 1.0, 0.080] and a helical order of spins within the M1-chains of FeO6 octahedra. This is determined by neutron-diffraction experiments on a single crystal. Comparison of NaFeGe2O6 with NaFeSi2O6 is given and it is shown that the magnetic ordering in the latter compound, aegirine, also is complex and is best described by two different spin states, a commensurate one with C2??/c?? symmetry and an incommensurate one, best being described by a spin density wave, oriented within the (1 0 1) plane. 相似文献
39.
Since 1940s, Mount Uludağ (Bithynian Olympus) has been considered famous with winter sports center in Turkey. In addition, it is one of the rare places because of its
plant diversity and is also one of the important plant areas of Turkey. The ski run constructions are rapidly increased in
the past decades in the alpine and subalpine belts of the mountain. Rate of nitrogen mineralization and some properties of
soil were investigated in the soils of the three ski runs and undisturbed neighborhood forest sites. These ski runs are at
the upper part of the forest belt in the mountain. Abies bornmuelleriana forest community is the postclimax and very sensitive to destruction. The rates of the nitrogen mineralization in the soils
were determined in controlled conditions (60% water-holding capacity, 20°C). Nitrification and nitrogen mineralization were
in the ski run inside where the natural recovery started, increased compared with the outside of the ski runs. Waterholding
capacity, organic carbon, and total nitrogen were decreased in the massive damaged ski run, and due to these changes, the
rates of mineralization and nitrification were also decreased. 相似文献
40.
Lourdes L��pez-Merino Ana Moreno Manel Leira Javier Sigr�� Pen��lope Gonz��lez-Samp��riz Blas L. Valero-Garc��s Jos�� Antonio L��pez-S��ez Manola Brunet Enric Aguilar 《Journal of Paleolimnology》2011,46(3):453-467
We present a study of two short sediment cores recovered from Lago Enol, in the Picos de Europa National Park, Cantabrian Mountains, northern Iberia. We inferred past climate conditions and anthropogenic impacts using geochemical and biological (pollen and diatoms) variables in the dated sequences, in conjunction with temperature and precipitation data collected since 1871 at meteorological stations in the region. The record provides evidence of environmental changes during the last 200 years. At the end of the Little Ice Age (~1800?C1875 AD) the region was characterized by an open landscape. Long-term use of the area for mixed livestock grazing in the mountains, and cultivation of rye during the nineteenth century, contributed to the expansion of grassland at the expense of forest. Warmer temperatures since the end of the nineteenth century are inferred from a change in diatom assemblages and development of the local forest. Socioeconomic transformation during the twentieth century, such as livestock changes related to dairy specialization, planting of non-native trees, mining activities, and management of the national park since its creation in 1918, caused profound changes in the catchment and in the lake ecology. The last several decades (~1970?C2007 AD) of the Lago Enol sediment record are strikingly different from previous periods, indicating lower runoff and increasing lake productivity, particularly since AD 2000. Today, the large number of tourists who visit the area cause substantial impacts on this ecosystem. 相似文献