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1.
Quasi-periodic fluctuations in the Greenland–Iceland–Norwegian Seas region in a coupled climate model 总被引:1,自引:1,他引:0
We report an analysis of the mechanisms responsible for interannual variability in the Greenland–Iceland–Norwegian (GIN) Seas
in a control integration of the HadCM3 coupled climate model. Interannual variability in sea surface temperature (SST) and
sea surface salinity (SSS) is dominated by a quasi-periodic ∼7-year signal. Analyses show that the mechanism involves a competition
between convection and advection. Advection carries cold, fresh, Arctic water over warm, salty, Atlantic water, while convection
periodically mixes these two water masses vertically, raising SST. Convection is able to raise SST because of the presence
of a subsurface temperature maximum. The GIN Seas convection in HadCM3 is forced by wind stress anomalies related to the North
Atlantic Oscillation (NAO). The consequent SST anomalies feedback positively to force the atmosphere, resulting in a weak
spectral peak (at ∼7 years) in GIN Seas sea level pressure. Although there is no evidence of a similar oscillation in reality,
key aspects of the simulated mechanism may be relevant to understanding variability in the real GIN Seas. In particular, the
potential for increases in convection to raise SST offers a possible new explanation for increases in SST that occurred between
the 1960s and the late 1980s/early 1990s. These SST increases may have contributed to the observed sea-ice retreat. In addition,
a positive feedback between GIN Seas SST and the atmosphere could contribute to the persistence of the NAO, potentially helping
to explain its red spectrum or recent northeastward shift.
相似文献
Sonia R. Gamiz-FortisEmail: |
2.
Pierre Kestener Alain Arneodo 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(3):421-435
Extreme atmospheric events are intimately related to the statistics of atmospheric turbulent velocities. These, in turn, exhibit
multifractal scaling, which is determining the nature of the asymptotic behavior of velocities, and whose parameter evaluation
is therefore of great interest currently. We combine singular value decomposition techniques and wavelet transform analysis
to generalize the multifractal formalism to vector-valued random fields. The so-called Tensorial Wavelet Transform Modulus
Maxima (TWTMM) method is calibrated on synthetic self-similar 2D vector-valued multifractal measures and monofractal 3D vector-valued
fractional Brownian fields. We report the results of some application of the TWTMM method to turbulent velocity and vorticity
fields generated by direct numerical simulations of the incompressible Navier–Stokes equations. This study reveals the existence
of an intimate relationship between the singularity spectra of these two vector fields which are found significantly more intermittent than previously
estimated from longitudinal and transverse velocity increment statistics.
相似文献
Alain ArneodoEmail: |
3.
Davide D’Alimonte Dan Cornford 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(5):613-620
This paper, addresses the problem of novelty detection in the case that the observed data is a mixture of a known ‘background’ process contaminated with an unknown other process, which generates the outliers, or novel observations. The framework we
describe here is quite general, employing univariate classification with incomplete information, based on knowledge of the
distribution (the probability density function, pdf) of the data generated by the ‘background’ process. The relative proportion of this ‘background’ component (the prior ‘background’ probability), the pdf and the prior probabilities of all other components are all assumed unknown. The main contribution is a new classification scheme that
identifies the maximum proportion of observed data following the known ‘background’ distribution. The method exploits the Kolmogorov–Smirnov test to estimate the proportions, and afterwards data are Bayes
optimally separated. Results, demonstrated with synthetic data, show that this approach can produce more reliable results
than a standard novelty detection scheme. The classification algorithm is then applied to the problem of identifying outliers in the SIC2004 data set, in order
to detect the radioactive release simulated in the ‘joker’ data set. We propose this method as a reliable means of novelty
detection in the emergency situation which can also be used to identify outliers prior to the application of a more general
automatic mapping algorithm.
相似文献
Davide D’AlimonteEmail: |
Dan Cornford (Corresponding author)Email: |
4.
Amitrajeet A. Batabyal 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(3):253-257
Recently, Batabyal and Nijkamp (Environ Econ Policy Stud 7:39–51, 2005) have used a theoretical model of antibiotic use to study the relative merits of interventionist (antibiotics) and non-interventionist
(no antibiotics) treatment options. A key assumption in their paper is that the default treatment option is the interventionist
option. Because there are several instances in which this assumption is invalid, in this paper, we suppose that the default
treatment option is the non-interventionist option. Specifically, we first derive the long run average cost of treating a
common infection such as acute otitis media (AOM). Next, we show that there is a particular tolerance level and that when
a physician uses this tolerance level to determine when to administer the non-antibiotic medicine, the long run average cost
of treating the common infection under study is minimized.
相似文献
Amitrajeet A. BatabyalEmail: |
5.
Ram Ranjan Ruben N. Lubowski 《Stochastic Environmental Research and Risk Assessment (SERRA)》2005,19(5):315-325
We examine the management of livestock diseases from the producers‘ perspective, incorporating information and incentive asymmetries
between producers and regulators. Using a stochastic dynamic model, we examine responses to different policy options including
indemnity payments, subsidies to report at-risk animals, monitoring, and regulatory approaches to decreasing infection risks
when perverse incentives and multiple policies interact. This conceptual analysis illustrates the importance of designing
efficient combinations of regulatory and incentive-based policies.
相似文献
Ram RanjanEmail: |
6.
Storm-related sea level variations 1958–2002 along the North Sea coast from a high-resolution numerical hindcast are investigated and compared to the results of earlier studies. Considerable variations were found from year to year and over the entire period. The large-scale pattern of these variations is consistent with that derived from previous studies, while the magnitudes of the long-term trends differ. The latter is attributed to different analysis periods, improvements in the atmospheric forcing, and the enhanced spatial resolution of the numerical simulation. It is shown that the different analysis periods, in particular, represent an issue as the increase in storm-related sea levels was found to be weaker over the last few years that have not been included in earlier studies. These changes are consistent with observed changes of the storm climate over the North Sea. It is also shown that observed and hindcast trends may differ significantly. While the latter are in agreement with observed changes in the storm climate, it may be concluded that observed sea level changes along the North Sea coast comprise a considerable fraction that cannot be attributed to changes in the large-scale atmospheric circulation.
相似文献
Ralf WeisseEmail: |
7.
Ocean/ice interaction at the base of deep-drafted Antarctic ice shelves modifies the physical properties of inflowing shelf
waters to become Ice Shelf Water (ISW). In contrast to the conditions at the atmosphere/ocean interface, the increased hydrostatic
pressure at the glacial base causes gases embedded in the ice to dissolve completely after being released by melting. Helium
and neon, with an extremely low solubility, are saturated in glacial meltwater by more than 1000%. At the continental slope
in front of the large Antarctic caverns, ISW mixes with ambient waters to form different precursors of Antarctic Bottom Water.
A regional ocean circulation model, which uses an explicit formulation of the ocean/ice shelf interaction to describe for
the first time the input of noble gases to the Southern Ocean, is presented. The results reveal a long-term variability of
the basal mass loss solely controlled by the interaction between waters of the continental shelf and the ice shelf cavern.
Modeled helium and neon supersaturations from the Filchner–Ronne Ice Shelf front show a “low-pass” filtering of the inflowing
signal due to cavern processes. On circumpolar scales, the simulated helium and neon distributions allow us to quantify the
ISW contribution to bottom water, which spreads with the coastal current connecting the major formation sites in Ross and
Weddell Seas.
相似文献
Christian B. RodehackeEmail: |
8.
Initial ensemble generation and validation for ocean data assimilation using HYCOM in the Pacific 总被引:2,自引:0,他引:2
A method to initialize an ensemble, introduced by Evensen (Physica, D 77:108–129, 1994a; J Geophys Res 99(C5):10143–10162, 1994b; Ocean Dynamics 53:343–367, 2003), was applied to the Ocean General Circulation Model (OGCM) HYbrid Coordinate Ocean Model (HYCOM) for the Pacific Ocean.
Taking advantage of the hybrid coordinates, an initial ensemble is created by first perturbing the layer interfaces and then
running the model for a spin-up period of 1 month forced by randomly perturbed atmospheric forcing fields. In addition to
the perturbations of layer interfaces, we implemented perturbations of the mixed layer temperatures. In this paper, we investigate
the quality of the initial ensemble generated by this scheme and the influence of the horizontal decorrelation scale and vertical
correlation on the statistics of the resulting ensemble. We performed six ensemble generation experiments with different combinations
of horizontal decorrelation scales and with/without perturbations in the mixed layer. The resulting six sets of initial ensembles
are then analyzed in terms of sustainability of the ensemble spread and realism of the correlation patterns. The ensemble
spreads are validated against the difference between model and observations after 20 years of free run. The correlation patterns
of six sets of ensemble are compared to each other. This study shows that the ensemble generation scheme can effectively generate
an initial ensemble whose spread is consistent with the observed errors. The correlation pattern of the ensemble also exhibits
realistic features. The addition of mixed layer perturbations improves both the spread and correlation. Some limitations of
the ensemble generation scheme are also discussed. We found that the vertical shift of isopycnal coordinates provokes unrealistically
large deviations in shallow layers near the islands of the West Pacific. A simple correction circumvents the problem.
相似文献
Liying WanEmail: |
9.
Majid Mathlouthi Fethi Lebdi 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(4):513-528
The paper focuses on the development of reservoir operating rules for dry and rainfall events, and their implementation in
the case of the Ghézala dam located in northern Tunisia (characterized by Mediterranean climate). Rainfall events are defined
in terms of depth and duration that are correlated to each other. A depth analysis per event is performed, conditioned on
the event duration. The gamma distribution provides a good fit to depth per event, especially for events lasting at least
6 days. The event duration fits a geometric distribution, whereas the dry events during the rainy season fit a negative binomial
distribution. The climatic cycle length is fitted to a gamma distribution. On this basis, many 50-year synthetic event series
were generated. Every synthetic streamflow sequence obtained from synthetic rainfall sequences as well as the one derived
from the historic rainfall events time series were optimized and optimal decisions were formulated. These decisions were assessed
by means of multiple regression analysis to estimate the relation between the optimal decision to every stage (dry or rainfall
event) and other system variables. Optimal rules, which have a linear form, were derived by predetermined useful storage interval
and depend on storage, inflows and downstream demand at dry or rainfall event t. The range of t is 1–13 days (rainfall event) and 1–57 days (dry event). The rules were satisfactory for every predetermined useful storage
interval. The simulated dam performance generated by the operation rules was compared with the deterministic optimum operation
and the historical operation. Also included is the comparison of the implicit stochastic optimization-based operation policy
per event during the water years 1985–2002.
相似文献
Fethi LebdiEmail: |
10.
Robert Haining Jane Law Ravi Maheswaran Tim Pearson Paul Brindley 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(5):501-509
Bayesian modelling of health risks in relation to environmental exposures offers advantages over conventional (non-Bayesian)
modelling approaches. We report an example using research into whether, after controlling for different confounders, air pollution
(NOx) has a significant effect on coronary heart disease mortality, estimating the relative risk associated with different levels
of exposure. We use small area data from Sheffield, England and describe how the data were assembled. We compare the results
obtained using a generalized (Poisson) log-linear model with adjustment for overdispersion, with the results obtained using
a hierarchical (Poisson) log-linear model with spatial random effects. Both classes of models were fitted using a Bayesian
approach. Including spatial random effects models both overdispersion and spatial autocorrelation effects arising as a result
of analysing data from small contiguous areas. The first modelling framework has been widely used, while the second provides
a more rigorous model for hypothesis testing and risk estimation when data refer to small areas. When the models are fitted
controlling only for the age and sex of the populations, the generalized log-linear model shows NOx effects are significant at all levels, whereas the hierarchical log-linear model with spatial random effects shows significant
effects only at higher levels. We then adjust for deprivation and smoking prevalence. Uncertainty in the estimates of smoking
prevalence, arising because the data are based on samples, was accounted for through errors-in-variables modelling. NOx effects apparently are significant at the two highest levels according to both modelling frameworks.
相似文献
Paul BrindleyEmail: |
11.
Jamesina J. Simpson 《Surveys in Geophysics》2009,30(2):105-130
Advances in computing technologies in recent decades have provided a means of generating and performing highly sophisticated
computational simulations of electromagnetic phenomena. In particular, just after the turn of the twenty-first century, improvements
to computing infrastructures provided for the first time the opportunity to conduct advanced, high-resolution three-dimensional
full-vector Maxwell’s equations investigations of electromagnetic propagation throughout the global Earth-ionosphere spherical
volume. These models, based on the finite-difference time-domain (FDTD) method, are capable of including such details as
the Earth’s topography and bathymetry, as well as arbitrary horizontal/vertical geometrical and electrical inhomogeneities
and anisotropies of the ionosphere, lithosphere, and oceans. Studies at this level of detail simply are not achievable using
analytical methods. The goal of this paper is to provide an historical overview and future prospectus of global FDTD computational
research for both natural and man-made electromagnetic phenomena around the world. Current and future applications of global
FDTD models relating to lightning sources and radiation, Schumann resonances, hypothesized earthquake precursors, remote sensing,
and space weather are discussed.
相似文献
Jamesina J. SimpsonEmail: |
12.
Ram Ranjan 《Stochastic Environmental Research and Risk Assessment (SERRA)》2006,20(5):353-362
This paper estimates the expected annual impacts of the Pink Hibiscus Mealybug infestation on the economies of Florida and the rest of the United States. The approach involves a Markov chain analysis wherein both short run and long run expected damages from infestation are calculated. Use is made of the CLIMEX model that predicts the potential pest-establishment regions in the US. While predictions based upon the CLIMEX model extend the scope of damages beyond Florida, the damages are significantly dependent upon the rate of arrival and detection of species in those regions. Damages are significantly higher when a longer time horizon is considered. When nursery owners bear the full cost of quarantines in the form of loss of sales and treatment costs of infected plants, the cost-effectiveness of quarantines as a regulatory tool is diminished. The long run propensity of the system, in terms of the fraction of time spent in the possible ‘states’ of infestation and control, determines the extent of damages, and not the annual value of crops that could be potential hosts to the pest.
相似文献
Ram RanjanEmail: Phone: +1-352-3921881Fax: +1-352-3929898 |
13.
Derivation of Photosynthetically Available Radiation from METEOSAT data in the German Bight with Neural Nets 总被引:1,自引:0,他引:1
Kathrin Schiller 《Ocean Dynamics》2006,56(2):79-85
Two different models, a Physical Model and a Neural Net (NN), are used for the derivation of the Photosynthetically Available
Radiation (PAR) from METEOSAT data in the German Bight; advantages and disadvantages of both models are discussed. The use
of a NN for derivation of PAR should be preferred to the Physical Model because by construction, a NN can take the various
processes determining PAR on a surface much better into account than a non-statistical model relying on averaged relations.
相似文献
Kathrin SchillerEmail: |
14.
Christoph Clauser 《Surveys in Geophysics》2009,30(3):163-191
The heat of the Earth derives from internal and external sources. A heat balance shows that most of the heat provided by external
sources is re-emitted by long-wavelength heat radiation and that the dominant internal sources are original heat and heat
generated by decay of unstable radioactive isotopes. Understanding of the thermal regime of the Earth requires appreciation
of properties and mechanisms for heat generation, storage, and transport. Both experimental and indirect methods are available
for inferring the corresponding rock properties. Heat conduction is the dominant transport process in the Earth’s crust, except
for settings where appreciable fluid flow provides a mechanism for heat advection. For most crustal and mantle rocks, heat
radiation becomes significant only at temperatures above 1200°C.
相似文献
Christoph ClauserEmail: |
15.
Beatriz Vaz de Melo Mendes Luis Raúl Pericchi 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(3):399-410
We model multivariate hydrological risks in the case that at least one of the variables is extreme. Recently, Heffernan JE,
Tawn JA (2004) A conditional approach for multivariate extremes. J R Stat Soc B 66(3):497–546 (thereafter called HT04) proposed a conditional multivariate extreme value model which applies to regions where
not all variables are extreme and simultaneously identifies the type of extremal dependence, including negative dependence.
In this paper we apply this modeling strategy and provide an application to multivariate observations of five rivers in two
clearly distinct regions of Puerto Rico Island and for two different seasons each. This effective dimensionality of ten-dimensions
cannot be handled by the traditional models of multivariate extremes. The resulting fitted model, following HT04 model and
strategies of estimation, is able to make long term estimation of extremes, conditional than other rivers are extreme or not.
The model shows considerable flexibility to address the natural questions that arise in multivariate extreme value assessments.
In the Puerto Rico 5 rivers application, the model clearly puts together two regions one of two rivers and another of three
rivers, which show strong relationships in the rainy season. This corresponds with the geographical distribution of the rivers.
相似文献
Beatriz Vaz de Melo MendesEmail: |
16.
Solomon Tesfamariam Rehan Sadiq 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(1):1-15
The concepts of system load and capacity are pivotal in risk analysis. The complexity in risk analysis increases when the
input parameters are either stochastic (aleatory uncertainty) and/or missing (epistemic uncertainty). The aleatory and epistemic
uncertainties related to input parameters are handled through simulation-based parametric and non-parametric probabilistic
techniques. The complexities increase further when the empirical relationships are not strong enough to derive physical-based
models. In this paper, ordered weighted averaging (OWA) operators are proposed to estimate the system load. The risk of failure
is estimated by assuming normally distributed reliability index. The proposed methodology for risk analysis is illustrated
using an example of nine-input parameters. Sensitivity analyses identified that the risk of failure is dominated by the attitude
of a decision-maker to generate OWA weights, missing input parameters and system capacity.
相似文献
Rehan Sadiq (Corresponding author)Email: |
17.
Kevin J. Johnson Christian P. Minor Verner N. Guthrie Susan L. Rose-Pehrsson 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(2):237-252
The remediation of sites contaminated with unexploded ordnance (UXO) remains an area of intense focus for the Department of
Defense. Under the sponsorship of SERDP, data fusion techniques are being developed for use in enhancing wide-area assessment
UXO remediation efforts and a data fusion framework is being created to provide a cohesive data management and decision-making
utility to allow for more efficient expenditure of time, labor and resources. An important first step in this work is the
development of feature extraction utilities and feature probability density maps for eventual input to data fusion algorithms,
making data fusion of estimates of data quality, UXO-related features, non-UXO backgrounds, and correlations among independent
data streams possible. Utilizing data acquired during ESTCP’s Wide-Area Assessment Pilot Program, the results presented here
successfully demonstrate the feasibility of automated feature extraction from light detection and ranging, orthophotography,
and helicopter magnetometry wide-area assessment survey data acquired at the Pueblo Precision Bombing Range #2. These data
were imported and registered to a common survey map grid and UXO-related features were extracted and utilized to construct
survey site-wide probability density maps that are well-suited for input to higher level data fusion algorithms. Preliminary
combination of feature maps from the various data sources yielded maps for the Pueblo site that offered a more accurate UXO
assessment than any one data source alone.
相似文献
Susan L. Rose-PehrssonEmail: |
18.
F. G. Bastante J. Taboada L. Alejano E. Alonso 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(6):727-735
Some of the major advances in the field of mining in the last three decades have referred to the development of new design
and planning techniques for optimizing open-pit mining and the inclusion of a stochastic perspective in economic models that
is more revealing than a purely deterministic perspective. These advances include the use of parametric techniques in the
design and planning process, the formulation of criteria for establishing an optimum cut-off grade policy when the economic
goal is to optimize net present value (NPV), and the introduction of economic risk analysis. This paper examines some of the
difficulties involved in applying these techniques—arising largely as a result of a lack of knowledge of the spatial location
and distribution of the deposit grades—and analyses how these difficulties can be tackled with the help of geostatistical
simulation techniques that take probabilistic criteria into consideration during the optimization process. These techniques
enable equally likely representations of the deposit to be obtained that reproduce the main dispersion features for the starting
experimental data (covariance or variogram, as well as the histogram). Consequently, the uncertainty in regard to the deposit
as well as its influence on the economic assessment of the deposit in risk terms can be evaluated. This paper also describes
a simple method for introducing price and cost increases into the risk analysis via the Monte Carlo method and shows how geological,
technical and economic uncertainty can be integrated in risk analyses. Although it is true that the relationship between prices
and costs is maintained constant in mining planning based on using parametric techniques, it is no less true that the risk
analysis requires the use of models in which the main parameters with a bearing on deposit economics are considered as stochastic
variables. The proposed methodology simplifies the calculations and easily integrates the different sources of uncertainty.
相似文献
F. G. BastanteEmail: |
19.
Topography and morphodynamics in the German Bight using SAR and optical remote sensing data 总被引:3,自引:0,他引:3
Morphological changes in coastal areas, especially in river estuaries, are of high interest in many parts of the world. Satellite
data from both optical and radar sensors can help to monitor and investigate these changes. Data from both kinds of sensors
being available for up to 30 years now, allow examinations over large timescales, while high resolution sensors developed
within the last decade allow increased accuracy. So the creation of digital elevation models (DEMs) of, for example, the wadden
sea from a series of satellite images is already possible. ENVISAT, successfully launched on March 1, 2002, continues the
line of higher resolution synthetic aperture radar (SAR) imaging sensors with its ASAR instrument and now also allows several
polarization modes for better separation of land and water areas. This article gives an overview of sensors and algorithms
for waterline determination as well as several applications. Both optical and SAR images are considered. Applications include
morphodynamic monitoring studies and DEM generation.
相似文献
Andreas NiedermeierEmail: |
20.
A Survey of Techniques for Predicting Earthquake Ground Motions for Engineering Purposes 总被引:2,自引:0,他引:2
Over the past four or five decades many advances have been made in earthquake ground-motion prediction and a variety of procedures
have been proposed. Some of these procedures are based on explicit physical models of the earthquake source, travel-path and
recording site while others lack a strong physical basis and seek only to replicate observations. In addition, there are a
number of hybrid methods that seek to combine benefits of different approaches. The various techniques proposed have their
adherents and some of them are extensively used to estimate ground motions for engineering design purposes and in seismic
hazard research. These methods all have their own advantages and limitations that are not often discussed by their proponents.
The purposes of this article are to: summarise existing methods and the most important references, provide a family tree showing
the connections between different methods and, most importantly, to discuss the advantages and disadvantages of each method.
相似文献
John DouglasEmail: |