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31.
Non-stationary extreme value analysis in a changing climate 总被引:1,自引:0,他引:1
This paper introduces a framework for estimating stationary and non-stationary return levels, return periods, and risks of climatic extremes using Bayesian inference. This framework is implemented in the Non-stationary Extreme Value Analysis (NEVA) software package, explicitly designed to facilitate analysis of extremes in the geosciences. In a Bayesian approach, NEVA estimates the extreme value parameters with a Differential Evolution Markov Chain (DE-MC) approach for global optimization over the parameter space. NEVA includes posterior probability intervals (uncertainty bounds) of estimated return levels through Bayesian inference, with its inherent advantages in uncertainty quantification. The software presents the results of non-stationary extreme value analysis using various exceedance probability methods. We evaluate both stationary and non-stationary components of the package for a case study consisting of annual temperature maxima for a gridded global temperature dataset. The results show that NEVA can reliably describe extremes and their return levels. 相似文献
32.
Barry Jay Katz 《Journal of Paleolimnology》2001,26(2):161-179
Although much of the world's petroleum resource-base is associated with marine systems, regionally lacustrine petroleum systems are important. Individual accumulations may exceed several billion barrels. In each of these cases the oil is derived from a lacustrine source rock and may be produced from either nonmarine or marine reservoir rocks. The purpose of this paper is to describe the factors that control lacustrine source rock development and the nature of lacustrine reservoirs. Lacustrine oils display different physical and chemical characteristics than their marine counterparts. These differences can be related to the nature of their precursor material. Although the nature of the products are different, the geochemical threshold criteria for defining source rocks in both settings are the same because of common expulsion requirements. Commercially significant lacustrine systems require the presence of large, long-lived lakes. Such lake settings are tectonic in origin and restricted to climatic settings where precipitation exceeds evaporation. Within these large lake systems three primary factors determine source rock potential and quality. These factors are primary productivity level, organic preservation potential, and matrix sedimentation rate, which controls the dilution of preserved organic matter. Source rock potential is maximized where both productivity and preservation potential are maximized and sedimentation rate is minimized. To some degree these factors can compensate for each other. Hydrocarbon reservoir potential within lacustrine basins is partially impacted by overall tectonic setting. Within extensional settings, transport distances tend to be limited, with much of the sediment being transported away from the basin. The sediments delivered to the lake are poorly sorted and sedimentologically immature, commonly resulting in poor reservoirs due to both primary properties and their susceptibility to diagenesis. Within rifts better reservoirs tend to develop along platform or flexural margins. Stacking of reservoirs is important in lacustrine systems but baffles and barriers are often present between individual sand units. These barriers form as a result of lake level fluctuations. In compressional settings transport distances tend to be longer, resulting in more mature, better sorted sediments leading to higher quality reservoirs. These reservoirs typically develop in fluvial-deltaic and wave-dominated shoreline settings. Lacustrine carbonate reservoirs are locally important. These carbonates tend to develop during lake level lowstands and are dependent on diagenesis (dissolution and karstification) for porosity and permeability development. Lacustrine reservoirs are often stratigraphically and areally limited and display low individual well production rates. Within pure lacustrine systems exploration opportunities appear to be often restricted by either reservoir presence or quality (i.e., production rates). The best exploration opportunities in lacustrine basins appear to be associated with hybrid systems where a lacustrine source and marine reservoir exist. 相似文献
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35.
Multiple chemical constituents (nutrients; N, O, H, C stable isotopes; 64 organic wastewater compounds, 16 pharmaceutical
compounds) and microbiological indicators were used to assess the impact on groundwater quality from the land application
of approximately 9.5 million liters per day of treated municipal sewage effluent to a sprayfield in the 960-km2 Ichetucknee Springs basin, northern Florida. Enriched stable isotope signatures (δ18O and δ2H) were found in water from the effluent reservoir and a sprayfield monitoring well (MW-7) due to evaporation; however, groundwater
samples downgradient from the sprayfield have δ18O and δ2H concentrations that represented recharge of meteoric water. Boron and chloride concentrations also were elevated in water
from the sprayfield effluent reservoir and MW-7, but concentrations in groundwater decreased substantially with distance downgradient
to background levels in the springs (about 12 km) and indicated at least a tenfold dilution factor. Nitrate-nitrogen isotope
(δ15N–NO3) values above 10 ‰ in most water samples were indicative of organic nitrogen sources except Blue Hole Spring (δ15N–NO3 = 4.6–4.9 ‰), which indicated an inorganic source of nitrogen (fertilizers). The detection of low concentrations the insect
repellent N,N-diethyl-metatoluamide (DEET), and other organic compounds associated with domestic wastewater in Devil’s Eye Spring indicated
that leakage from a nearby septic tank drainfield likely has occurred. Elevated levels of fecal coliforms and enterococci
were found in Blue Hole Spring during higher flow conditions, which likely resulted from hydraulic connections to upgradient
sinkholes and are consistent with previoius dye-trace studies. Enteroviruses were not detected in the sprayfield effluent
reservoir, but were found in low concentrations in water samples from a downgradient well and Blue Hole Spring during high-flow
conditions indicating a human wastewater source. The Upper Floridan aquifer in the Ichetucknee Springs basin is highly vulnerable
to contamination from multiple anthropogenic sources throughout the springs basin. 相似文献
36.
The absence of a trench and the existence of a separate, western chain of islands in the central New Hebrides island arc are
a consequence of earlier tectonic evolution, and not the result of subduction of the d'Entrecasteux Zone as was previously
suggested. Because of tectonic consolidation in the western islands prior to present subduction, a resistant block was created
opposing subduction, and a trench never did form, here. The d'Entrecasteux Zone is responsible only locally for additional
deformation of the subducting plate, in a way that can be regarded as an initial stage of obduction. 相似文献
37.
Cosmic-ray (CR) fluctuations in both the drift and diffusion approximations are investigated and the results compared with experimental data. Kinetic equation is used to obtain equations for the second moment of the CR distribution function (the correlation function of the distribution function fluctuations) in both approximations. An application of these approximations to the correlation function equation gives the relations between the CR power spectra and random magnetic fields in interplanetary space. Different magneto-turbulence models are taken in consideration and the relations between the spectral indices are obtained in various frequency intervals.The theoretical results are compared with experimental data obtained by the network of neutron monitors. The CR power spectra observed at the ground level during the years 1978–1981 has been calculated. The investigated frequency range of 3×10–8 to 10–4 Hz consists of two parts, with a transient region of 10–6 to 10–5 Hz. Together with the background CR fluctuations the contribution of both the periodic and aperiodic phenomena is observed. 相似文献
38.
In order to study the turbulence structure behind a multiscale tree-like element in a boundary layer, detailed particle image
velocimetry measurements are carried out in the near-wake of a fractal-like tree. The tree is a pre-fractal with five generations,
each consisting of three branches and a scale-reduction factor of 1/2 between consecutive generations. Detailed mean velocity
and turbulence stress profiles are documented, as well as their downstream development. Scatter plots of mean velocity gradient
(transverse shear in the wake) and Reynolds shear stress exhibit a good linear relation at all locations in the flow. Therefore,
in the transverse direction of the wake evolution, the data support the Boussinesq eddy-viscosity concept. The measured mixing
length increases with streamwise distance, in agreement with classic wake expansion rates. Conversely, the measured eddy viscosity
and mixing length in the transverse direction decrease with increasing elevation, which differs from the behaviours measured
in the vertical direction in traditional boundary layers or in canopy flows studied before. In order to find an appropriate
single length scale to describe the wake evolution behind a multiscale object, two models are proposed, based on the notion
of superposition of scales. One approach is based on the radial spectrum of the object while the second is based on its length-scale
distribution evaluated using fractal geometry tools. Both proposed models agree well with the measured mixing length. The
results suggest that information about multiscale clustering of branches must be incorporated into models of the mixing length
for flows through single or sparse canopies of multiscale trees. 相似文献
39.
Accretion, feedback and galaxy bimodality: a comparison of the GalICS semi-analytic model and cosmological SPH simulations 总被引:1,自引:0,他引:1
40.