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  • 1
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    Stochastic environmental research and risk assessment 11 (1997), S. 17-31 
    ISSN: 1436-3259
    Keywords: Bivariate density ; meta-Gaussian density ; normal quantile transform ; likelihood ratio dependence ; correlation coefficient
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Convenient bivariate densities found in the literature are often unsuitable for modeling hydrologic variates. They either constrain the range of association between variates, or fix the form of the marginal distributions. The bivariate meta-Gaussian density is constructed by embedding the normal quantile transform of each variate into the Gaussian law. The density can represent a full range of association between variates and admits arbitrarily specified marginal distributions. Modeling and estimation can be decomposed into i) independent analyses of the marginal distributions, and ii) investigation of the dependence structure. Both statistical and judgmental estimation procedures are possible. Some comparisons to recent applications of bivariate densities in the hydrologic literature motivate and illustrate the model.
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  • 2
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    Stochastic environmental research and risk assessment 11 (1997), S. 33-50 
    ISSN: 1436-3259
    Keywords: Unit hydrograph ; uncertainty analysis ; linearly constrained Monte-Carlo simulation ; reliability analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Unit hydrographs (UHs), along with design rainfalls, are frequently used to determine the discharge hydrograph for design and evaluation of hydraulic structures. Due to the presence of various uncertainties in its derivation, the resulting UH is inevitably subject to uncertainty. Consequently, the performance of hydraulic structures under the design storm condition is uncertain. This paper integrates the linearly constrained Monte-Carlo simulation with the UH theory and routing techniques to evaluate the reliability of hydraulic structures. The linear constraint is considered because the water volume of each generated design direct runoff hydrograph should be equal to that of the design effective rainfall hyetograph or the water volume of each generated UH must be equal to one inch (or cm) over the watershed. For illustration, the proposed methodology is applied to evaluate the overtopping risk of a hypothetical flood detention reservoir downstream of Tong-Tou watershed in Taiwan.
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  • 3
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    Stochastic environmental research and risk assessment 11 (1997), S. 1-16 
    ISSN: 1436-3259
    Keywords: Nash cascade reservoir model ; rainfall-runoff ; EM algorithm ; filtering ; maximum likelihood estimation ; martingale estimating function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Abstract: Linear continuous time stochastic Nash cascade conceptual models for runoff are developed. The runoff is modeled as a simple system of linear stochastic differential equations driven by white Gaussian and marked point process noises. In the case of d reservoirs, the outputs of these reservoirs form a d dimensional vector Markov process, of which only the dth coordinate process is observed, usually at a discrete sample of time points. The dth coordinate process is not Markovian. Thus runoff is a partially observed Markov process if it is modeled using the stochastic Nash cascade model. We consider how to estimate the parameters in such models. In principle, maximum likelihood estimation for the complete process parameters can be carried out directly or through some form of the EM (estimation and maximization) algorithm or variation thereof, applied to the observed process data. In this research we consider a direct approximate likelihood approach and a filtering approach to an algorithm of EM type, as developed in Thompson and Kaseke (1994). These two methods are applied to some real life runoff data from a catchment in Wales, England. We also consider a special case of the martingale estimating function approach on the runoff model in the presence of rainfall. Finally, some simulations of the runoff process are given based on the estimated parameters.
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  • 4
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    Stochastic environmental research and risk assessment 11 (1997), S. 173-192 
    ISSN: 1436-3259
    Keywords: Uncertainty analysis ; unit hydrograph ; regression analysis ; probabilistic point estimation methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Hydrologic model parameters obtained from regional regression equations are subject to uncertainty. Consequently, hydrologic model outputs based on the stochastic parameters are random. This paper presents a systematic analysis of uncertainty associated with the two parameters, N and K, in Nash's IUH model from different regional regression equations. The uncertainty features associated with N and K are further incorporated to assess the uncertainty of the resulting IUH. Numerical results indicate that uncertainty of N and K from the regional regression equations are too significant to be ignored.
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  • 5
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    Stochastic environmental research and risk assessment 11 (1997), S. 145-171 
    ISSN: 1436-3259
    Keywords: Hydrologic regionalization ; unit hydrograph ; regression analysis ; multivariate regression ; seemingly unrelated regression ; validation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Hydrologic regionalization is a useful tool that allows for the transfer of hydrological information from gaged sites to ungaged sites. This study developed regional regression equations that relate the two parameters in Nash's IUH model to the basin characteristics for 42 major watersheds in Taiwan. In the process of developing the regional equations, different regression procedures including the conventional univariate regression, multivariate regression, and seemingly unrelated regression were used. Multivariate regression and seeming unrelated regression were applied because there exists a rather strong correlation between the Nash's IUH parameters. Furthermore, a validation study was conducted to examine the predictability of regional equations derived by different regression procedures. The study indicates that hydrologic regionalization involving several dependent variables should consider their correlations in the process of establishing the regional equations. The consideration of such correlation will enhance the predictability of resulting regional equations as compared with the ones from the conventional univariate regression procedure.
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  • 6
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    Stochastic environmental research and risk assessment 11 (1997), S. 193-210 
    ISSN: 1436-3259
    Keywords: Turbulence ; sediment ; fluvial ; river ; bursting process ; statistics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Entrainment of sediment particles from channel beds into the channel flow is influenced by the characteristics of the flow turbulence which produces stochastic shear stress fluctuations at the bed. Recent studies of the structure of turbulent flow has recognized the importance of bursting processes as important mechanisms for the transfer of momentum into the laminar boundary layer. Of these processes, the sweep event has been recognized as the most important bursting event for entrainment of sediment particles as it imposes forces in the direction of the flow resulting in movement of particles by rolling, sliding and occasionally saltating. Similarly, the ejection event has been recognized as important for sediment transport since these events maintain the sediment particles in suspension. In this study, the characteristics of bursting processes and, in particular, the sweep event were investigated in a flume with a rough bed. The instantaneous velocity fluctuations of the flow were measured in two-dimensions using a small electromagnetic velocity meter and the turbulent shear stresses were determined from these velocity fluctuations. It was found that the shear stress applied to the sediment particles on the bed resulting from sweep events depends on the magnitude of the turbulent shear stress and its probability distribution. A statistical analysis of the experimental data was undertaken and it was found necessary to apply a Box-Cox transformation to transform the data into a normally distributed sample. This enabled determination of the mean shear stress, angle of action and standard error of estimate for sweep and ejection events. These instantaneous shear stresses were found to be greater than the mean flow shear stress and for the sweep event to be approximately 40 percent greater near the channel bed. Results from this analysis suggest that the critical shear stress determined from Shield's diagram is not sufficient to predict the initiation of motion due to its use of the temporal mean shear stress. It is suggested that initiation of particle motion, but not continuous motion, can occur earlier than suggested by Shield's diagram due to the higher shear stresses imposed on the particles by the stochastic shear stresses resulting from turbulence within the flow.
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  • 7
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    Stochastic environmental research and risk assessment 11 (1997), S. 211-227 
    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The principle of maximum entropy (POME) was employed to derive a new method of parameter estimation for the 2-parameter generalized Pareto (GP2) distribution. Monte Carlo simulated data were used to evaluate this method and compare it with the methods of moments (MOM), probability weighted moments (PWM), and maximum likelihood estimation (MLE). The parameter estimates yielded by POME were comparable or better within certain ranges of sample size and coefficient of variation.
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  • 8
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    Stochastic environmental research and risk assessment 11 (1997), S. 523-547 
    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Kernel density estimators are useful building blocks for empirical statistical modeling of precipitation and other hydroclimatic variables. Data driven estimates of the marginal probability density function of these variables (which may have discrete or continuous arguments) provide a useful basis for Monte Carlo resampling and are also useful for posing and testing hypotheses (e.g bimodality) as to the frequency distributions of the variable. In this paper, some issues related to the selection and design of univariate kernel density estimators are reviewed. Some strategies for bandwidth and kernel selection are discussed in an applied context and recommendations for parameter selection are offered. This paper complements the nonparametric wet/dry spell resampling methodology presented in Lall et al. (1996).
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  • 9
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    Stochastic environmental research and risk assessment 11 (1997), S. 459-482 
    ISSN: 1436-3259
    Keywords: Karhunen-Loéve expansion ; Empirical Orthogonal Functions ; stochastic simulation ; gaussian fields ; analytical covariance functions ; eigenfunctions ; kriging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Simulation of multigaussian stochastic fields can be made after a Karhunen-Loéve expansion of a given covariance function. This method is also called simulation by Empirical Orthogonal Functions. The simulations are made by drawing stochastic coefficients from a random generator. These numbers are multiplied with eigenfunctions and eigenvalues derived from the predefined covariance model. The number of eigenfunctions necessary to reproduce the stochastic process within a predefined variance error, turns out to be a cardinal question. Some ordinary analytical covariance functions are used to evaluate how quickly the series of eigenfunctions can be truncated. This analysis demonstrates extremely quick convergence to 99.5% of total variance for the 2nd order exponential (‘gaussian’) covariance function, while the opposite is true for the 1st order exponential covariance function. Due to these convergence characteristics, the Karhunen-Loéve method is most suitable for simulating smooth fields with ‘gaussian’ shaped covariance functions. Practical applications of Karhunen-Loéve simulations can be improved by spatial interpolation of the eigenfunctions. In this paper, we suggest interpolation by kriging and limits for reproduction of the predefined covariance functions are evaluated.
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  • 10
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    Stochastic environmental research and risk assessment 11 (1997), S. 51-63 
    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A basic problem in hydrology is computing confidence levels for the value of the T-year flood when it is obtained from a Log Pearson III distribution in terms of estimated mean, estimated standard deviation, and estimated skew. In an important paper Chowdhury and Stedinger [1991] suggest a possible formula for approximate confidence levels, involving two functions previously used by Stedinger [1983] and a third function, λ, for which asymptotic estimates are given. This formula is tested [Chowdhury and Stedinger, 1991] by means of simulations, but these simulations assume a distribution for the sample skew which is not, for a single site, the distribution which the sample skew is forced to have by the basic hypothesis which underlies all of the analysis, namely that the maximum discharges have a Log Pearson III distribution. Here we test these approximate formulas for the case of data from a single site by means of simulations in which the sample skew has the distribution which arises when sampling from a Log Pearson III distribution. The formulas are found to be accurate for zero skew but increasingly inaccurate for larger common values of skew. Work in progress indicates that a better choice of λ can improve the accuracy of the formula.
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  • 11
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    Stochastic environmental research and risk assessment 11 (1997), S. 94-94 
    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
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  • 12
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    Stochastic environmental research and risk assessment 11 (1997), S. 95-114 
    ISSN: 1436-3259
    Keywords: Soil moisture ; time scale ; non-Gaussian ; colored-noise
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Large-scale fields of soil moisture are forced by atmospheric precipitation and radiative forcing. When these forcing factors are themselves influenced by surface and soil moisture processes, the result is a nonlinear land-atmosphere system with inherent feedback mechanisms that may strongly modulate variability in climate. Given such feedbacks, simple randomness in the forcing factors may be manifested as a complex statistical signature in the surface hydrology. In this paper, we investigate the impacts of non-Gaussian and colored-noise on the probability distribution of soil moisture resulting from the statistical-dynamical land-atmosphere interaction model of Rodriguez-Iturbe et al. (1991). Persistence of hydroclimatologic anomalies as characterized by the correlation time scale of soil moisture is discussed.
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  • 13
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    Stochastic environmental research and risk assessment 11 (1997), S. 115-127 
    ISSN: 1436-3259
    Keywords: Rainfall-runoff modeling ; transfer response ; dynamic non-linear models ; normal and gamma observational distribution ; predictive performance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The rainfall-runoff modeling is very useful for forecasting purposes. A good methodology for forecasting the future stream flow is a key requirement for designers and operators of water resources systems. A compromise between conceptual and classical time series modeling is applied to model the relationship between rainfall and runoff. The dynamic nonlinear model is composed of a probability distribution describing the observation, a link function relating its mean to the so called state parameters and a system of equations defining the evolution of these parameters. Its Bayesian nature permits to take into account subjective information, making forward intervention, defining monitoring schemes and introducing smoothing facilities. An application using the data of Fartura river's basin is reported. The assessment of the prior distribution is discussed and the predictive performance of the linear and the non-linear models is reported.
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  • 14
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    Stochastic environmental research and risk assessment 11 (1997), S. 129-143 
    ISSN: 1436-3259
    Keywords: Stochastic analysis ; perturbation methods ; unsaturated transport ; heterogeneous porous media
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Within the framework of stochastic theory and the spectral perturbation techniques, three-dimensional dispersion in partially saturated soils with a finite correlation scale of log-hydraulic conductivity is analyzed. The effects of spatial variability of the moisture distribution parameter on the asymptotic spreading behavior of a unsaturated solute plume are assessed. This is accomplished by comparing two asymptotic macrodispersivities and two variance of solute concentration, obtained for a constant moisture content and spatially varied moisture, respectively.
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  • 15
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    Stochastic environmental research and risk assessment 11 (1997), S. 65-93 
    ISSN: 1436-3259
    Keywords: Nonparametric ; Monte Carlo ; precipitation ; weather
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A nonparametric resampling technique for generating daily weather variables at a site is presented. The method samples the original data with replacement while smoothing the empirical conditional distribution function. The technique can be thought of as a smoothed conditional Bootstrap and is equivalent to simulation from a kernel density estimate of the multivariate conditional probability density function. This improves on the classical Bootstrap technique by generating values that have not occurred exactly in the original sample and by alleviating the reproduction of fine spurious details in the data. Precipitation is generated from the nonparametric wet/dry spell model as described in Lall et al. [1995]. A vector of other variables (solar radiation, maximum temperature, minimum temperature, average dew point temperature, and average wind speed) is then simulated by conditioning on the vector of these variables on the preceding day and the precipitation amount on the day of interest. An application of the resampling scheme with 30 years of daily weather data at Salt Lake City, Utah, USA, is provided.
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  • 16
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    Stochastic environmental research and risk assessment 11 (1997), S. 255-266 
    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract It has been observed that the field biodegradation rates for soluble hydrocarbon plumes are significantly smaller than the aerobic rates observed in the laboratory. It is believed that this difference is related to the fact that in the field oxygen and hydrocarbon must be mixed before the biodegradation reaction can occur, and that the effective degradation rate is controlled by the actual, not mean, concentrations of oxygen and hydrocarbon. In this work, we present a conceptual model of oxygen-mixing limited biodegradation, which indicates that the effective degradation rate should depend on the cross correlation between the oxygen and hydrocarbon concentration fluctuations. This is followed by a development of a rigorous, field-scale model.
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  • 17
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    Stochastic environmental research and risk assessment 11 (1997), S. 229-254 
    ISSN: 1436-3259
    Keywords: Model validation ; analysis of uncertainty ; model verification ; quality assurance ; system identification ; model calibration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The development and use of models for predicting exposures are increasingly common and are essential for many risk assessments of the United States Environmental Protection Agency (EPA). Exposure assessments conducted by the EPA to assist regulatory or policy decisions are often challenged to demonstrate their “scientific validity”. Model validation has thus inevitably become a major concern of both EPA officials and the regulated community, sufficiently so that the EPA's Risk Assessment Forum is considering guidance for model validation. The present paper seeks to codify the issues and extensive foregoing discussion of validation with special reference to the development and use of models for predicting the impact of novel chemicals on the environment. Its preparation has been part of the process in formulating a White Paper for the EPA's Risk Assessment Forum. Its subject matter has been drawn from a variety of fields, including ecosystem analysis, surface water quality management, the contamination of groundwaters from high-level nuclear waste, and the control of air quality. The philosophical and conceptual bases of model validation are reviewed, from which it is apparent that validation should be understood as a task of product (or tool) design, for which some form of protocol for quality assurance will ultimately be needed. The commonly used procedures and methods of model validation are also reviewed, including the analysis of uncertainty. Following a survey of past attempts at resolving the issue of model validation, we close by introducing the notion of a model having maximum relevance to the performance of a specific task, such as, for example, a predictive exposure assessment.
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  • 18
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    Stochastic environmental research and risk assessment 11 (1997), S. 303-321 
    ISSN: 1436-3259
    Keywords: Simulation ; hydrograph rise and recession ; rainfall process ; probability distribution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A model is developed for annual low flow hydrographs. Its two primary components reflect the fact that hydrologic processes during streamflow rise (function of water input) and recession (function of basin storage) are different. Durations of periods of rise (wet intervals) and recession (dry intervals) are modelled by discrete probability distributions — negative binomial for dry intervals and negative binomial or modified logarithmic series for wet intervals depending on goodness of fit. During wet intervals, the total inflow is modelled by the lognormal distribution and daily amounts are allocated according to a pattern-averaged model. During dry intervals, the flow recedes according to a deterministic-stochastic recession model. The model was applied to three Canadian basins with drainage area ranging from 2210 to 22000 km2 to generate 50 realizations of low flow hydrographs. The resulting two standard-error confidence band for the simulated probability distribution of annual minimum 7-day flows enclosed the probability distribution estimated from the observed record. A sensitivity analysis for the three basins revealed that in addition to the recession submodel, the most important submodel is that describing seasonality. The state of the basin at the beginning of the low flow period is of marginal importance and the daily distribution of input is unimportant.
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  • 19
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    Stochastic environmental research and risk assessment 11 (1997), S. 267-295 
    ISSN: 1436-3259
    Keywords: Space/time processes ; stochastic analysis ; regression model ; solute contents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A regression model is used to study spatiotemporal distributions of solute content ion concentration data (calcium, chloride and nitrate), which provide important water contamination indicators. The model consists of three random and one deterministic components. The random space/time component is assumed to be homogeneous/stationary and to have a separable covariance. The purely spatial and the purely temporal random components are assumed to have homogenous and stationary increments, respectively. The deterministic component represents the space/time mean function. Inferences of the random components involve maximum likelihood and semi-parametric methods under some restrictions on the data configuration. Computational advantages and modelling limitations of the assumptions underlying the regression model are discussed. The regression model leads to simplifications in the space/time kriging and cokriging systems used to obtain space/time estimates at unobservable locations/instants. The application of the regression model in the study of the solute content ions was done at a global scale that covers the entire region of interest. The variability analysis focuses on the calculation of the spatial direct and cross-variograms and the evaluation of correlations between the three solute content ions. The space/time kriging system is developed in terms of the space direct and cross-variograms, and allows the separate estimation of the regression model components. Maps of these components are then obtained for each one of the three ions. Using the estimates of the purely spatial component, spatial dependencies between the ions are studied. Physical causes and consequences of the space/time variability are discussed, and comparisons are made with previous analyses of the solute content dataset.
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  • 20
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    Stochastic environmental research and risk assessment 11 (1997), S. 323-330 
    ISSN: 1436-3259
    Keywords: Kolmogorov-Smirnov test ; identification of periodic component ; goodness-of-fit test for white noise ; periodogram ; residuals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A modified version of the widely used Kolmogorov-Smirnov (K-S) test of null hypothesis is constructed, that a given time series is Gaussian white noise, against the alternative hypothesis that the time series contains an added or multiplicative deterministic-periodic component of unspecified frequency. The usual KS test is treated as a special case. The proposed test is more powerful than the ordinary K-S test in detecting extreme (low or high) hidden periodicities. Computational procedure necessary for implementation are also given.
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  • 21
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    Stochastic environmental research and risk assessment 11 (1997), S. 297-302 
    ISSN: 1436-3259
    Keywords: Perturbation ; conservative chemical ; velocity variance ; eulerian
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A recursive perturbation solution to the eulerian transport problem for a conservative solute in a random conductivity field is reported. The stochastic concentration is given to arbitrary order inσ ν, the variance of fluctuating velocity. The result gives the stochastic concentration as a perturbation to the deterministic concentration for constant mean flow. The closed form solution is easy to implement numerically via FFT.
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  • 22
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    Stochastic environmental research and risk assessment 11 (1997), S. 331-348 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Under the assumption that local solute dispersion is negligible, a new general formula (in the form of a convolution integral) is found for the arbitrary k-point ensemble moment of the local concentration of a solute convected in arbitrary m spatial dimensions with general sure initial conditions. From this general formula new closed-form solutions in m=2 spatial dimensions are derived for 2-point ensemble moments of the local solute concentration for the impulse (Dirac delta) and Gaussian initial conditions. When integrated over an averaging window, these solutions lead to new closed-form expressions for the first two ensemble moments of thevolume-averaged solute concentration and to the corresponding concentration coefficients of variation (CV). Also, for the impulse (Dirac delta) solute concentration initial condition, the second ensemble moment of thesolute point concentration in two spatial dimensions and the corresponding CV are demonstrated to be unbound. For impulse initial conditions the CVs for volume-averaged concentrations axe compared with each other for a tracer from the Borden aquifer experiment. The point-concentration CV is unacceptably large in the whole domain, implying that the ensemble mean concentration is inappropriate for predicting the actual concentration values. The volume-averaged concentration CV decreases significantly with an increasing averaging volume. Since local dispersion is neglected, the new solutions should be interpreted as upper limits for the yet to be derived solutions that account for local dispersion; and so should the presented CVs for Borden tracers. The new analytical solutions may be used to test the accuracy of Monte Carlo simulations or other numerical algorithms that deal with the stochastic solute transport. They may also be used to determine the size of the averaging volume needed to make a quasi-sure statement about the solute mass contained in it.
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  • 23
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    Stochastic environmental research and risk assessment 11 (1997), S. 349-368 
    ISSN: 1436-3259
    Keywords: Data assimilation ; Kalman filter ; Square root filter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The Kalman filter algorithm can be used for many data assimilation problems. For large systems, that arise from discretizing partial differential equations, the standard algorithm has huge computational and storage requirements. This makes direct use infeasible for many applications. In addition numerical difficulties may arise if due to finite precision computations or approximations of the error covariance the requirement that the error covariance should be positive semi-definite is violated. In this paper an approximation to the Kalman filter algorithm is suggested that solves these problems for many applications. The algorithm is based on a reduced rank approximation of the error covariance using a square root factorization. The use of the factorization ensures that the error covariance matrix remains positive semi-definite at all times, while the smaller rank reduces the number of computations and storage requirements. The number of computations and storage required depend on the problem at hand, but will typically be orders of magnitude smaller than for the full Kalman filter without significant loss of accuracy. The algorithm is applied to a model based on a linearized version of the two-dimensional shallow water equations for the prediction of tides and storm surges. For non-linear models the reduced rank square root algorithm can be extended in a similar way as the extended Kalman filter approach. Moreover, by introducing a finite difference approximation to the Reduced Rank Square Root algorithm it is possible to prevent the use of a tangent linear model for the propagation of the error covariance, which poses a large implementational effort in case an extended kalman filter is used.
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    Stochastic environmental research and risk assessment 11 (1997), S. 369-395 
    ISSN: 1436-3259
    Keywords: Random fields ; diagrams ; perturbation ; non-local ; effective conductivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract This work presents a stochastic diagrammatic theory for the calculation of the effective hydraulic conductivity of heterogeneous media. The theory is based on the mean-flux series expansion of a log-normal hydraulic conductivity medium in terms of diagrammatic representations and leads to certain general results for the effective hydraulic conductivity of three-dimensional media. A selective summation technique is used to improve low-order perturbation analysis by evaluating an infinite set of diagrammatic terms with a specific topological structure that dominates the perturbation series. For stochastically isotropic media the selective summation yeilds the anticipated exponential expression for the effective hydraulic conductivity. This expression is extended to stochastically anisotropic media. It is also shown that in the case of non homogeneous media the uniform effective hydraulic conductivity is replaced by a non-local tensor kernel, for which general diagrammatic expressions are obtained. The non-local kernel leads to the standard exponential behavior for the effective hydraulic conductivity at the homogeneous limit.
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    Stochastic environmental research and risk assessment 11 (1997), S. 483-510 
    ISSN: 1436-3259
    Keywords: Conceptual-stochastic models ; shot noise ; streamflow simulation ; time aggregation
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    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A conceptual-stochastic approach to short time runoff data modelling is proposed, according to the aim of reproducing the hydrological aspects of the streamflow process and of preserving as much as possible the dynamics of the process itself. This latter task implies preservation of streamflow characteristics at higher scales of aggregation and, within a conceptual framework, involves compatibility with models proposed for the runoff process at those scales. At a daily time scale the watershed response to the effective rainfall is considered as deriving from the response of three linear reservoirs, respectively representing contributions to streamflows of large deep aquifers, with over-year response lag, of aquifers which run dry by the end of the dry season and of subsurface runoff. The surface runoff component is regarded as an uncorrelated point process. Considering the occurrences of effective rainfall events as generated by an independent Poisson process, the output of the linear system represents a conceptually-based multiple shot noise process. Model identification and parameter estimation are supported by information related to the aggregated runoff process, in agreement to the conceptual framework proposed, and this allows parameter parsimony, efficient estimation and effectiveness of the streamflow reproduction. Good performances emerged from the model application and testing made with reference to some daily runoff series from Italian basins.
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    Stochastic environmental research and risk assessment 11 (1997), S. 511-521 
    ISSN: 1436-3259
    Keywords: Runoff events ; arrival times ; partial duration series ; arid areas ; Israel ; probabilistic modeling ; Pearson III distribution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Present descriptions of arrival times of runoff events are based upon modeling of interarrival intervals. Maintaining the traditional assumption that arrival times are independent random variables, these times can be directly described through a continuous distribution fitted to recorded data. A case study for the arid Negev region in Israel indicates that the Pearson type III distribution satisfactorily achieves this goal. The direct description can apply nonuniform functions, respond to multi-modal distributions, and be extended to regional modeling.
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    Stochastic environmental research and risk assessment 11 (1997), S. 397-422 
    ISSN: 1436-3259
    Keywords: Random flow field ; diffusion ; concentration ; fluctuations ; covariance ; variance
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    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The concentration c(x,t) of a nonreactive solute undergoing advection and diffusion in a spatially random divergence-free flow field is analyzed. A leading order formulation for the spatial covariance of the concentration field, $$\overline {c'\left( {x,t} \right)c'\left( {x,t} \right)} $$ , is made. That formulation includes the velocity variability induced macrodispersive flux of the covariance field, and the smoothing effects of diffusion. Previous formulations of the concentration covariance had dropped at least one of these effects. It is shown that both these effects need to be included to obtain a qualitatively correct description of the concentration fluctuations.
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    Stochastic environmental research and risk assessment 11 (1997), S. 423-431 
    ISSN: 1436-3259
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    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The value of Shannon entropy for a given set of data depends on the class interval chosen to compute the relative frequency of each class. For three data sets, expressed in dimensional as well as nondimensional form, the entropy value was computed for different class-interval sizes. Entropy was found to decrease with increasing class interval as well as with increasing sampling interval. It is suggested that these intervals should be selected with care.
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  • 29
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    Stochastic environmental research and risk assessment 11 (1997), S. 449-457 
    ISSN: 1436-3259
    Keywords: Settling tank ; diffusion in open sets ; elastic reflection ; boundary conditions ; efficiency ; exit time
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    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract When the diffusion term is supposed not to be zero at the boundary of a settling tank, we show that an alternate (and equivalent) description to the basic advection-diffusion equation for the concentration of micro pollutant consists in modelling the micro pollutant particles' trajectories as a diffusion stochastic process. Indeed, the density of this latter satisfies the same Pde as the advection-diffusion equation. Our emphasis here is on the computation of the so called tank efficiency and on the bottom boundary conditions. We claim that our interpretation in terms of a diffusion process helps to enlighten the choice of the appropriate mathematical boundary conditions. What is more, we introduce a scouring parameter and give its range as well as its physical interpretation.
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    Stochastic environmental research and risk assessment 11 (1997), S. 433-448 
    ISSN: 1436-3259
    Keywords: Risk ; uncertainty ; reservoir operation ; sedimentation ; computer application
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract An attempt of using stochastic hydrologic technique to assess the intrinsic risk of reservoir operation is made in this study. A stochastic simulation model for reservoir operation is developed. The model consists of three components: synthetic generation model for streamflow and sediment sequences, one-dimensional delta deposit model for sediment transport processes in reservoirs, and simulation model for reservoir operation. This kind of integrated simulation model can be used to simulate not only the inflow uncertainty of streamflow and sedimentation, but also the variation in operation rules of reservoirs. It is herein used for the risk assessment of a reservoir, and the simulation is performed for different operation scenarios. Simulation for the 100-year period of sediment transport and deposition in the river-reservoir system indicates that the navigation risk is much higher than that of hydropower generation or sediment deposition in the reservoir. The risk of sediment deposition at the river-section near the backwater profile is also high thereby the navigation at the river-segment near this profile takes high risk because of inadequate navigation depth.
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    The annals of regional science 31 (1997), S. 21-38 
    ISSN: 1432-0592
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    Topics: Architecture, Civil Engineering, Surveying , Geography , Economics
    Notes: Abstract. The development of High-Speed Rail has been one of the central features of recent European Union transport infrastructure policy. This paper reviews the developments which have taken place in a number of countries and assesses the outcome. It identifies the lack of genuine network development which has taken place, criticises the failure to provide a more integrated framework between modes and questions the assumptions of improved regional development and cohesion which are claimed for the policy. Instead there is evidence of increasing concentration into the main metropolitan centres served by the emerging network.
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    The annals of regional science 31 (1997), S. 57-76 
    ISSN: 1432-0592
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    Topics: Architecture, Civil Engineering, Surveying , Geography , Economics
    Notes: Abstract. Labor market issues are reviewed in terms of mobility and policy resulting from transportation improvements. Research on Meso level regional adjustment versus micro level search processes are reviewed. A spatial interaction approach to assessing changes in regional access and regional industrial mix is outlined. Hypotheses with respect to transportation and labor markets are discussed. Empirical evidence of the impact of high-speed rail on labor markets and their structure is reviewed. Conclusions are drawn and new research questions are identified.
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    The annals of regional science 31 (1997), S. 155-174 
    ISSN: 1432-0592
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    Topics: Architecture, Civil Engineering, Surveying , Geography , Economics
    Notes: Abstract. This article establishes a relationship between the net present value (NPV) of a High-Speed Rail (HSR) project and its social value, its transportation consumers‘ surplus (TCS) and its regional economic impact in terms of growth. First, it is shown that if the NPV is positive, it may generate growth even if no bottleneck exists. Second, when shadow-pricing and externalities are included in the calculations, and the HSR demand has been forecasted by a multinomial logit model, the NPV differs from its net economic impact. For instance, one variant of the project, though acceptable, reduces growth elsewhere in the economy. Decision-making is then in a quandary.
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    The annals of regional science 31 (1997), S. 259-271 
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    Notes: Abstract. This paper contrasts the implications, for cartel stability, of the non-spatial (‘Chamberlinian’) and the spatial (‘Hotelling’) models of product differentiation. Using the special case of a linear demand framework, we show that whereas the former approach suggests that cartel stability is non-monotonic but predictable in the degree of differentiation, the outcome is very much more ambiguous when the latter formulation is employed. We examine also the implications for stability when demand shocks occur, and show that even in the case of linear demand, when differentiation is modelled in spatial terms the results are consistent with non-linear non-spatial demand functions, as well as with those obtained in more complicated models of firm behaviour.
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    The annals of regional science 31 (1997), S. 285-298 
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    Topics: Architecture, Civil Engineering, Surveying , Geography , Economics
    Notes: Abstract. In interregional analysis, supply models are based typically on defined sets of ‘representative firms’ with given ‘averaged’ technological and cost coefficients, such that, when aggregated as identical units into both sectors and regions, they reproduce the total output of each sector in each region. Then, deterministic models obtain profit-maximising patterns of input demands and corresponding output, prior to aggregating these quantities as if the firms were truly identical and homogeneous. In this paper, the above optimisation models are replaced by a probabilistic framework, which nevertheless guarantees convergence to the above classical deterministic solutions in the limit. The models are estimated on ‘observed’ flows, technological coefficients and prices, and a CES function (optionally) handles substitution between primary factors. These new input-output models become explicitly price-responsive, allowing tâtonnement with spatial models of final demand.
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    The annals of regional science 31 (1997), S. 369-389 
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    Topics: Architecture, Civil Engineering, Surveying , Geography , Economics
    Notes: Abstract. In Europe traffic congestions make it impossible to estimate travel time. The increasing number of cars calls for a transportation policy towards an improved efficiency of the transportation system. However, extending road infrastructure to reduce the congestion externality implies another type of externality, air pollution. Designing a transportation policy in industrialized countries one has to consider this trade-off. Our objective is to investigate the role of transportation services and their pricces within an interindustry framework. The authority wishes to minimize total cost of production with respect to the provision of infrastructure subject to an emission standard. By omitting a financial constraint to finance infrastructure we determine the size of infrastructure where no congestion occurs. The productivity effect of infrastructure and the cost savings from a dissolved congestion determine the optimal stock of infrastructure. Our congestion index is unity in that case of no financial constraint. If the extension of infrastructure has to be paid for by taxation, we obtain a lower level of infrastructure. In view of the trade-off between the benefit of a productivity gain from a dissolved congestion and the deadweight loss from taxation this lower level of infrastructure will result in an index of congestion higher than unity, implying a negative externality to the economy.
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    The annals of regional science 31 (1997), S. 451-471 
    ISSN: 1432-0592
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    Topics: Architecture, Civil Engineering, Surveying , Geography , Economics
    Notes: Abstract. Tenure at jobs and houses, along with commuting patterns between home and work, were studied for residents of metropolitan Washington. Two alternative potential outcomes were considered: (1) because moving or switching jobs can be used as an opportunity to reduce commuting duration in an era of rising congestion, those who recently moved or changed jobs should have shorter than average commutes; and (2) because most new residential construction is at the urban fringe, an area of longer commutes, those who recently moved to new homes should have longer commutes. Evaluation of the effect of commuting duration on job and housing tenure suggests that those who move, on average, maintain commute duration rather than having a major increase or decrease. This corroborates the idea that there are offsetting factors, where increases in commute lengths due to suburbanizing residences are counteracted by the correlated process of suburbanizing jobs.
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  • 38
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    Topics: Geography , Physics
    Notes: Summary The motion of an idealized vortex near a large-scale mountain range is examined by numerically integrating the single-layer shallow-water equations on an equatorial beta plane. Modification of the asymmetric circulation by divergent vorticity generation as the air is forced across the ridge greatly affects the motion of the vortex. Attention is focused on the role of the vortex structure, the mountainrange width and orientation, and the stratification of the model atmosphere in influencing the motion of the vortex. A scale analysis is used to explain the sensitivity of the vortex track to changes in the model's external parameters. The sensitivity of the model vortex track to the slope and orientation of the mountain range is used to help explain some features of the observed tracks of hurricanes that make landfall on the east coast of Mexico.
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    Meteorology and atmospheric physics 64 (1997), S. 51-59 
    ISSN: 1436-5065
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    Topics: Geography , Physics
    Notes: Summary During an expedition to the high Andes of Southern Peru in June–July 1977, measurements of direct solar radiation in four spectral bands (0.270–0.530–0.630–0.695–2.900 μ) were conducted at six sites in elevations ranging from sea level to 5645 m. These measurements were evaluated in Langley plots to determine total optical depths (τ) and irradiances at the top of the atmosphere. In addition, water vapor optical depths (τwv) were calculated from the mean radiosounding over Lima during the expedition, and Rayleigh (τray) and ozone (τoz) optical depths were obtained from published tabulations. Subtracting τray, τoz, and τwv from τ yielded estimates of aerosol optical depth τaer. The components τray and τoz decrease from the shorter towards the longer wavelength bands and from the lower towards the higher elevation sites; τaer also decreases towards the higher elevations. Particularly pronounced is the decrease of τaer and τ from the lowlands of the Pacific coast to the highlands of the interior, reflecting the effect of a persistent lower-tropospheric inversion and the contrast from the marine boundary layer to the clear atmosphere of the high Andes.
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    Meteorology and atmospheric physics 64 (1997), S. 21-50 
    ISSN: 1436-5065
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    Topics: Geography , Physics
    Notes: Summary A number of problems related to mesoscale numerical prediction of low stratus in the Alpine region are formulated, and addressed in a series of experiments for two wintertime cases. These problems include modelling aspects and issues of data assimilation which are relevant particularly in relation to the observation nudging technique. A focus is on the influence of orography. A comparison of operational optimum interpolation, and nudging of routine rawinsonde and surface-level data reveals that nudging often yields better analyses and forecasts of low stratus, and notably of the sharp vertical temperature and humidity gradients. However, the humidity advection scheme of the model and, near steep terrain, particularly the horizontal diffusion along the model's σ-levels are identified to contribute to spurious vertical smoothing which can result in erroneous cloud dissipation. On occasions, forecasts succeeding a nudging period are more sensitive to this process due to the sharper initial vertical gradients. Specific problems of representiveness arise when low-level rawinsonde information is spread laterally along the sloping σ-levels from low to high terrain. A new concept for σ-layer models is introduced by speading the observational information along isentropic surfaces, and this tends to improve the low stratus prediction over steep and even moderate orography. A partly successful attempt to take advantage of the steep Alpine orography is made by applying this concept to surface-level humidity data from a high-resolution network of Alpine surface stations which are distributed relatively uniformly in the vertical.
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    Notes: Summary In this paper, a procedure for the computation of the divergent part of wind from Outgoing Longwave Radiation (OLR) data is described. This divergent part is included in the global analysis scheme and its impact is studied by computing the vertical velocity, velocity potential etc., using the analysed fields with and without modifying the divergent part and also making 24 hr and 48 hr rainfall forecasts. Results show that magnitudes of vertical velocity were increased when the divergent part was modified in the wind analysis. There were also changes observed in the analysed wind field over convective regions and the changes over the oceanic regions were higher, suggesting that the impact of divergent part is more pronounced over data sparse regions. Marginal increase was observed in 24 hr and 48 hr rainfall forecast over the Indian region. The area averaged rainfall forecast at each time step in the first 6 hours of model integration was also higher in the case when the wind field contained the divergent part. To sum up, it can be stated that the inclusion of the divergent part from OLR data in the initial wind field has brought out positive impact on the wind analyses and rainfall forecast.
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    Meteorology and atmospheric physics 62 (1997), S. 71-78 
    ISSN: 1436-5065
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    Topics: Geography , Physics
    Notes: Summary Measurements of the surface heat budget were conducted on an ice cap in the Andes of Southern Peru at 5645 m during an expedition in July 1977. Because of the high surface albedo, net software radiative gain is nearly offset by the longwave loss in the average over the diurnal cycle. The diurnal temperature wave has at the surface an amplitude of about 5°C, and by 50 cm depth this is nearly dampened out. During the day, the shortwave radiative gain is in part used to balance the longwave loss, some heat is stored in the top snow layer and lost by sensible heat transfer to the overlying atmosphere, and the greater part fuels the sublimation. At night, the longwave radiative loss is not completely compensated by heat depletion and downward directed sensible heat transfer. This deficit is made up by the downward transfer of latent heat, resulting in heat release at the surface and deposition. Regarding the mass balance, the nighttime deposition approximately cancels the daytime sublimation. At lower elevations of the ice cap, albedo is much less, allowing larger absorption of solar radiation. As a consequence, more energy is available for ablation. Melting occurs during the day, so that re-freezing and concurrent latent heat release can help to compensate the longwave radiative loss at night.
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    Meteorology and atmospheric physics 62 (1997), S. 79-89 
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    Notes: Summary An inviscid form of the hydrodynamical equations is solved with enhanced horizontal shear, which is a synoptic feature consistent with stronger African Easterly Jet (AEJ) in Sahelian dry years, for unstable waves generated along the boundary between the two tropospheric air masses in tropical north Africa (i.e. the moist south-westerlies and the dry north-easterlies). Using a two-layer model of the atmosphere in order to correctly simulate the tropospheric synoptic situation in the sub-region, results show that the mode of the waves which is known to be fundamental to the development of West African squall lines is more unstable in dry years. This instability is found to be most-pronounced when the surface of discontinuity between the south-westerlies and the north-easterlies is at 700 mb level. Further, it is shown that in Sahelian dry years, the zone of these unstable waves shifts slightly southwards. This shift causes a deficit in rainfall in West African isohyet bands north of latitude 12°. The persistence of this deficit is linked with the continuous warming, in July, August and September of the 18-year period 1969–1986, of the three oceans (Indian, Pacific and South Atlantic) whose sea-surface temperature (SST) anomalies influence rainfall in tropical north Africa. It is shown that anytime these oceans warm up anomalously, the strength of the AEJ is enhanced leading to the climate-change process of: SST anomaly, increased AEJ strength, southward shift of the zone of squall-inducing waves and consequent reduction in total annual rainfall north of latitude 12° in tropical north Africa.
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    Notes: Summary Using the ECMWF and NMC analyses, this study documents the composite structures of the African and of the 6–9 day waves. In spite of the fact that the two types of disturbances develop over almost the same area, i.e. Central and West Africa and the tropical Atlantic, during the same season, i.e. summer, in spite of the fact that they have almost the same East-West velocity, i.e. 7–8 degree longitude per day, the structures of the two waves are very different. At 12.5°N, the African wave has an amplitude maximum in the meridional wind component whilst the zonal wind component is almost unperturbed. On the contrary, in the 6–9 day wave, at 12.5°N and also at 12.5°S, the zonal wind component has an amplitude maximum whilst the meridional wind component is very small and there is an amplitude maximum for the meridional wind component at the equator and 20°N.
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    Meteorology and atmospheric physics 62 (1997), S. 141-160 
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    Notes: Summary Extended integrations of semi-Lagrangian and Eulerian shallow water primitive equation models are performed. The semi-Lagrangian model used the semi-implicit two-time-level scheme. The Eulerian model used a conserving nonlinear advection scheme. For low resolution and longer integrations, difficulties were encountered with the semi-Lagrangian model which were absent in the Eulerian model. These difficulties are discussed.
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    Meteorology and atmospheric physics 62 (1997), S. 129-140 
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    Notes: Summary This is a sequel to Bennett, Chua and Leslie (1996), concerning weak-constraint, four-dimensional variational assimilation of reprocessed cloud-track wind observations (Velden, 1992) into a global, primitive-equation numerical weather prediction model. The assimilation is performed by solving the Euler-Lagrange equations associated with the variational principle. Bennett et al. (1996) assimilate 2436 scalar wind components into their model over a 24-hour interval, yielding a substantially improved estimate of the state of the atmosphere at the end of the interval. This improvement is still in evidence in forecasts for the next 48 hours. The model and variational equations are nonlinear, but are solved as sequence of linear equations. It is shown here that each linear solution is precisely equivalent to optimal or statistical interpolation using a background error covariance derived from the linearized dynamics, from the forcing error covariance, and from the initial error covariance. Bennett et al. (1996) control small-scale flow divergence using divergence dissipation (Talagrand, 1972). It is shown here that this approach is virtually equivalent to including a penalty, for the gradient of divergence, in the variational principle. The linearized variational equations are solved in terms of the representer functions for the wind observations. Diagonalizing the representer matrix yields rotation vectors. The rotated representers are the “array modes” of the entire system of the model, prior covariances and observations. The modes are the “observable” degrees of freedom of the atmosphere. Several leading array modes are presented here. Finally, appendices discuss a number of technical implementation issues: time convolutions, convergence in the presence of planetary shear instability, and preconditioning the essential inverse problem.
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    Meteorology and atmospheric physics 62 (1997), S. 161-177 
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    Notes: Summary By using a coupled ocean-atmosphere model with an oceanic surface boundary layer, including linear atmospheric and oceanic dynamics and linearized SST prognostic equation with respect to spatially varying climatological background states, we have investigated the eigenvalue problem of the linearized coupled system in the tropical Pacific, including the characteristic periods, horizontal structures, temporal-spatial evolution and instability of the unstable interannual oscillation characteristic modes and their associations with ENSO. The main results show that the quasi-biennial (QB) oscillation was found to act as the most unstable mode in the tropical Pacific coupled air-sea system. Only the most unstable QB mode displays the ENSO-like structure and temporalspatial evolution, and its existence seems likely to have no essential dependence on the climatological annual cycle (AC). Unfortunately, from the linearized coupled system we have not derived a most unstable mode relevant to the observed principle mode with the preferred 3–4 year lower-frequency (LF) oscillation period in the real world ENSO variability. Therefore, we infer that the LF mode would likely result from certain nonlinear interaction, in which the QB mode that acts as the shortest ENSO cycle could be fundamentally important. Also, we believe that the results in present work could be helpful to fully understand the multiple time scales and the associated mechanism responsible for the real world ENSO variability.
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    Meteorology and atmospheric physics 62 (1997), S. 101-128 
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    Notes: Summary This work deals with idealized modelling experiments designed to understand the dynamical evolution of low frequency intraseasonal monsoonal oscillations that result from interactions between the large scale monsoon Reverse Hadley Cell (RHC) and moist convective processes. The monsoon differential heating, which primarily determines the low-level convergence of the large-scale monsoon flow, is found to play a decisive role in affecting the northward progression of the monsoonal modes. A strong north-south differential heating leads to a robust generation and steady maintenance of northward propagating monsoonal oscillations. A weaker land-ocean thermal contrast leads to feeble low frequency monsoonal modes that have relatively longer periods in the 30–50 day band. This increase in the period of the monsoonal oscillations due to weak north-south thermal contrast is in good agreement with the observational findings of Yasunari (1980) and Kasture and Keshavamurty (1987). It is speculated that such an increase in the oscillatory period may be an outcome from an elongation in the meridional scale of the transient Hadley type cells which act as resonating cavities for the monsoonal modes. A Mobile Wave CISK (MWC) form of interaction between the large scale monsoon and the transient circulations associated with the Madden Julian Oscillation (MJO) is projected as a viable physical mechanism for the northward movement of low frequency modes. It is demonstrated that the effective low level convergence, following such an interaction, tends to shift northward relative to the site of interaction. This enables the heating perturbations to be displaced northward which in turn causes the secondary circulations and wind perturbations to follow. The essential criterion for the occurrence of a prolonged northward propagation of the low frequency modes is that the heating perturbations should phase lead the wind perturbations at all times. An examination of the ψ-χ interactions on the 30–50 day time scale reveals that the conversion from the transient divergent motions to rotational motions is quite intense (feeble) in the strong (weak) monsoon differential heating experiments. Because of the closer proximity to the monsoon heat source and also due to the latitudinal variation of earth's rotational effects, the ψ-χ interactions tend to be more pronounced to the north of 15°N while they are less robust in the near equatorial latitudes. The regularity of the monsoonal modes is found to depend on the strength of the monsoon differential heating and also on the periodic behaviour of the equatorial intraseasonal oscillations. The monsoonal modes are quite steady and exhibit extreme regularity in the presence of a weak north-south differential heating provided the equatorial forcing due to the MJO varies in a periodic manner. This result supports the findings of Mehta and Krishnamurti (1988) who found greater regularity of the 30–50 day modes during bad monsoon years. The low frequency monsoonal modes are found to be quite sensitive to the moisture availability factor (m) and the vertical profile of heating used in the MWC parameterization. A small increase in the value of (m) is found to significantly intensify the amplitude of the monsoonal oscillations while there is no considerable shift in the spectral frequency within the 30–50 day band as such. The 30–50 day motions show significant enhancement, with a relatively sharp spectral peak around 45 days, when the vertical profile of MWC heating has a maximum in the lower troposphere. However an upward displacement of the heating maximum tends to weaken the low frequency oscillations.
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  • 49
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    Notes: Summary The numerical simulation of a long-lived, stationary mesoscale convective system (MCS) already described in a previous paper (Fernández et al., 1995) is analyzed in greater detail. The influence of various external forcings, such as sea surface temperature, local orography or terrain roughness, upon the characteristics of the system is studied. This analysis makes it possible not only to identify the most important factors, but also to deduce the importance of some other internal forcings and to propose explanations for some dynamic features of the system that were difficult to understand. Hence, the sensitivity test methodology applied seems to be a useful tool to clarify the complex dynamics of some moist convective events. In the modelled MCS, sea surface temperature and orography are identified as key factors. The results also indicate that the upstream triggering of convection provoked by an orographic blocking effect is the main cause of the development of the system, while upslope triggering plays a secondary role.
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  • 50
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    Notes: Summary In this paper, multilayered feedforward neural networks trained with the error-back-propagation (EBP) algorithm have been employed for predicting the seasonal monsoon rainfall over India. Three network models that use, respectively, 2, 3 and 10 input parameters which are known to significantly influence the Indian summer monsoon rainfall (ISMR) have been constructed and optimized. The results obtained thereby are rigorously compared with those from the statistical models. The predictions of network models indicate that they can serve as a potent tool for ISMR prediction.
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    Meteorology and atmospheric physics 62 (1997), S. 1-8 
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    Notes: Summary A hydrostatic model is applied to a case study from the Pyrenean field experiment PYREX. The results from this simulation are compared with measurements, with the aim to evaluate the model behaviour in the case of a flow past a steep orography. The initial and boundary data, which were used for the simulation, were produced with the T213 reassimilation system at Reading by the European Center for Medium-Range Weather Forecasts (ECMWF). The comparison of the results with observations show that the local wind systems are captured reasonably well by the model. In particular the evolution of two counter rotating eddies in the lee of the Pyrenean mountain range are simulated correctly in space and time. Also the calculated orographic drag and vertical wave momentum flux agreed well with the measurements.
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    Meteorology and atmospheric physics 62 (1997), S. 9-22 
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    Notes: Summary A mesoscale convective system that affected Northeastern Spain on October 10, 1994, with rainfall amounts up to 400 mm, is simulated reasonably well by a nested 3-dimensional hydrostatic mesoscale model. Previous studies carried out in this region had already portrayed the main synoptic patterns that give rise to these devastating episodes. The present contribution takes a further step since it goes down to the mesoscale by means of a numerical model providing a more detailed representation not otherwise achieved by earlier analysis methods. Although the model was unable to forecast accurately the precipitation fields, it captured satisfactorily the framework in which the convective system originated and evolved.
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    Meteorology and atmospheric physics 62 (1997), S. 23-31 
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    Notes: Summary The correlation between the normal component of theQ-vector(Q n ) and the pixel values in IR satellite images has been investigated on a six-months data set. The average linear correlation coefficients are negative in all three selected isobaric levels, but not of significant magnitude (the correlation is best for the 850 hPa level, with a correlation coefficient of about 0.3), indicating an only slight tendency for negative values ofQ n to be associated with high IR grey shade values or, in other words, with cold cloud tops. It is explained why a better correlation should be expected for frontal cases, followed by an evaluation of 14 IR images containing cloudiness of cold fronts that occurred in February 1995. The correspondence betweenQ n at the 850 hPa level and IR pixel values in those cases is compared to the statistics for the whole month of February 1995, including also nonfrontal cases. The more pronounced connection is found for frontal cases, as expected. Finally, examples of frontogenesis and frontolysis demonstrate the possibility of using the prognostic quantityQ n in combination with IR satellite imagery as a tool for operational nowcasting and/or forecasting of the development or decay of frontal cloudiness.
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  • 54
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    Meteorology and atmospheric physics 62 (1997), S. 49-70 
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    Notes: Summary Mesoscale flow characteristics in the Alpine region are deduced from a set of daily large-scale analyses (1981–1990) by means of statistical-dynamical downscaling. This method utilizes the results of a large number of mesoscale numerical simulations in combination with known statistics of the forcing large-scale conditions. The investigation is restricted to cross-Alpine large-scale flow from 165 to 265 degrees at 500 hPa. Such types of flow are favourable to south foehn. The results provide model-based climatological estimates of surface wind direction and upper-level gravity-wave formation at a horizontal resolution of 20 and 10 km. Simulated surface wind roses agree well with observations and show a dominance of low-level flow around the Alps with bimodal frequency distributions of wind direction north and south of the mountains. The areas where splitted flows preferably merge are identified. Gravity waves are most likely to occur above the western parts of the Alps. A secondary maximum of likelihood was found above Tyrol and Trentino. Surface wind roses and gravity-wave formation are both checked with respect to their sensitivity to season (spring vs. autumn) and large-scale flow direction (south to southwest vs. southwest to west).
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    Meteorology and atmospheric physics 62 (1997), S. 33-48 
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    Notes: Summary With the increasingly widespread adoption of massively parallel processing (MPP) computers for applications in computational fluid dynamics it becomes appropriate to reconsider the geometrical configuration of the computational grid that best suits the problem. In the case of global numerical weather prediction we have recently advocated a conformal spherical-cubic geometry. Among its merits, this grid lends itself naturally to simple domain-decomposition and obviates the need for polar filtering. Here we extend the same principles, but with an emphasis on the problem of regional forecasting. In this case we observe that it is possible to cover the global domain with a conformal grid geometry based on the mapping to the sphere of a back-to-back pair of octagonal regions. In the most symmetrical case, each octagon maps to a hemisphere. By compounding this mapping with a nonhomogeneous conformal mapping of the sphere to itself, one can also arrange to have quasi-uniform enhanced resolution of the resulting grid inside any chosen circle on the sphere, at the expense of relatively coarse resolution degrading gradually with distance outside the circle of interest. With appropriate grid dimensions, the new ‘conformal octagon’ decomposes naturally into several identical square subdomains for efficient distribution over the nodes of an MPP computer.
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    Meteorology and atmospheric physics 64 (1997), S. 187-201 
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    Notes: Summary The Gulf of Mexico (GOM) circulation is simulated using the DieCAST ocean model, with a horizontal resolution of 1/12° and 20 vertical layers. The results compare well with observations of both large and small scale features, including Loop Current frontal occlusions associated with frontal eddies. The simulation is carried out without any data assimilation. The frontal eddies tend to be spaced at about 90° intervals around the Loop Current, leading to a Loop Current head shaped like a square with rounded corners. The pattern rotates as the eddies circle the Loop, and frontal eddies elongate as they squeeze through the Florida Strait. Major warm core eddies separate regularly from the Loop Current and propagate to the western GOM. Old warm core eddies in the western Gulf dissipate through bottom drag effects, which also generate cyclonic parasitic eddies. Newly arrived warm core eddies merge with old ones in the western GOM. Recently separated elongated Loop Current eddies can rotate and reattach temporarily to the Loop Current. The barotropic flow component develops eddies between the main separated warm core eddy and the Loop Current due to eastward dispersion, as the main eddy itself propagates westward into the Gulf.
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    Meteorology and atmospheric physics 64 (1997), S. 203-213 
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    Notes: Summary Daily 200-hPa relative vorticity data have been used to study the dominant patterns related to the cyclonic vortices over the South Atlantic Ocean in the vicinities of northeast Brazil, during the 1980–1989 period. Reference modes were obtained through empirical orthogonal function (EOF) analysis of the 200-hPa filtered vorticity anomalies over northeast Brazil, considering all the southern hemisphere (SH) summers within the study period. The amplitude time series of the first reference mode, separately for each SH summer, was correlated with the corresponding filtered vorticity anomalies in a larger area extending from 20°N to 40°S and between 120°W and 20°W. The correlation patterns feature a wave-like structure along eastern South America, with three main centers: the first one, over the South Atlantic off the northeast Brazil coast, is associated with the cyclonic vortices; the second one, over eastern Brazil, represents the corresponding anomalously amplified ridges; and the third one, over southern Brazil/Uruguay, is related to the equatorward incursions of midlatitude upper level troughs. This wave-like pattern is consistent with the vortex formation mechanism suggested in previous works. Another wave-like pattern southwest-northeast oriented is evident over the tropical southeastern Pacific, for some years. The internannual variability of these patterns is discussed in this paper.
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    Meteorology and atmospheric physics 64 (1997), S. 255-256 
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  • 59
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    Notes: Summary Lower tropospheric (1000–500) hPa kinetic energy (KE), temporal variations of KE and nonlinear KE transfer of rotational and divergent flows and energy conversion between them, partitioning further into stationary and transient components in the Fourier spectral domain and the mechanism for the evolution of significant transient waves for the month July 1979 in the latitudinal belt 10° S–30° N are studied. Divergent zonal and eddy KE show their maxima at the lowest level 1000 hPa. Lower tropospheric monsoon motion provides a non-divergent level close to 850 hPa. The daily flow patterns bear little resemblence to the climatology over tropics at 500 hPa. Although the transient mode of synoptic scale waves is stronger than that of planetary scale waves they are comparable. Analysis of energetics over global tropics can get signature of transient activities embedded in the large scale system. Summer momentum flux in the lower troposphere is essentially associated with stationary planetary and transient synoptic scale waves. Waves 1, 3 and 6 are the most preferred transient waves. Divergent to rotational KE conversion is the most dominating mechanism for the maintenance of planetary and synoptic scale waves. All categories of waves contribute towards the maintenance of zonal flows. The primary source of energy for transient synoptic scale waves is the transient divergent rotational KE transfer whereas the interaction between zonal stationary and transient wave is likely to be secondary source. Transient KE and all transient interactions, stationary KE and all stationary interactions are found to be strongest at 500 hPa and 850 hPa respectively. Growth and decay of transient waves 1 and 3 are mainly controlled by divergent-rotational KE conversions whereas those of transient wave 6 are controlled by KE transfer due to zonal-wave interaction.
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    Meteorology and atmospheric physics 64 (1997), S. 243-254 
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    Notes: Summary The meteorological structure of flood-producing weather systems affecting northern Madagascar is examined using ECMWF data. Daily rainfall in the austral summer is used to select 16 cases for a composite analysis of flood events in the period 1987–1992. Anomaly maps demonstrate a pair of convective vortices over SE Africa and the SW Indian Ocean which converge over northern Madagascar. Thermodynamic variables indicate an eastward shift of unstable moist conditions from SE Africa. A surge of monsoon northwesterlies and upper tropical easterlies are key features of flood producing systems over NW Madagascar.
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    Meteorology and atmospheric physics 64 (1997), S. 231-241 
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    Notes: Summary This study presents an analytical investigation of the local behaviour of the solution to a mesoscale model with Newtonian nudging when observed winds are time varying. The analysis examines each Fourier component of the time series of observed winds. Unlike the case with a constant observed wind, the nudged wind vector does not asymptotically approach the observed wind. In response to sinusoidal oscillation of the observed wind, the nudged wind vector is always on a half circle connecting the vector ends of the observed and un-nudged modelled winds. When nudging parameter α→0, the nudged wind vector approaches the un-nudged wind; when α→∞, the nudged wind vector approaches the observed wind. For commonly used values of nudging parameter α, the modelled wind field always carries errors. A target nudging scheme is devised in this study in order to ensure the model result is identical to observed winds with sinusoidal oscillation. Investigation shows that such a target wind exists for a finite value of α, and the magnitude of the target-nudging term is about the same as that of a normal nudging term if α∼f∼ω, wheref is the Coriolis parameter and ω is the frequency of the wind oscillation.
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    Meteorology and atmospheric physics 62 (1997), S. 201-214 
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    Notes: Summary The influence of turbulent friction on the propagation of cold fronts is investigated by numerical simulations using a two-dimensional mesoscale model. We compare the frictional effect with the effects of large-scale shear forcing and energy conversion at the earth's surface and discuss the synergic effect of all three mentioned processes. There is no pure superposition of these effects indicating that nonlinear interaction plays a role. In addition it is possible to show that—depending on the along-front jet—friction does not necessarily slow down the front but can also accelerate it. The direction of the along-front jet within the planetary boundary layer (PBL) is crucial for that question.
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    Meteorology and atmospheric physics 62 (1997), S. 215-224 
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    Notes: Summary The rate of oceanic heat storage of the upper 200m of the Arabian Sea is explained in terms of net air-sea heat flux (Q F), heat change due to horizontal divergence and vertical motion (Q V) and heat change due to lateral advection (Q A). The analysis revealed that the heat storage of the Arabian Sea is mainly controlled byQ V while the effect ofQ A is much larger than expected. Parameterisation of summer cooling revealed that the depletion of energy from the mixed layer is mainly due to upwelling and horizontal advection though large amount of heat is accumulated due to net air-sea heat flux. The annual heat balance of the upper 200m of the Arabian Sea suggested large heat gain by air-sea exchange processes. About two third of this heat gain is compensated by horizontal advection and one third by vertical advection.
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    Meteorology and atmospheric physics 63 (1997), S. 119-129 
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    Notes: Summary A new regional atmospheric model was set up in a joint effort by DKRZ (Deutsches Klimarechenzentrum), DWD (Deutscher Wetterdienst), GKSS (Forschungszentrum Geesthacht) at the MPI (Max-Planck-Institut fuer Meteorologie). This model, called REMO (REgional MOdel) can be used in the weather forecast mode as well as in the climate mode. It is based on the Europa-Model (EM), the main weather forecast model of the new numerical weather prediction system of the Deutscher Wetterdienst. In addition to the physical parameterizations implemented in the EM, REMO has the possibility of using the same physics as the global climate model (MPI) into which it is nested to assess the scale dependence of physical parameterizations within the same dynamical framework. This paper gives an overview over different case studies investigating the dependence of model results on simulation domain size, horizontal resolution, initial conditions and lateral boundaries especially for long term calculations. A sample of one month long integrations for an arbitrary July month, a four year long run for the Baltic Sea and its drainage basin and two summer seasons of the Indian Monsoon will be used to demonstrate the sensitivity of regional climate model results to different environments. The sensitivity studies show that it is very important to use realistic large scale driving fields at the lateral boundaries. The regional model results are strongly influenced by the driving fields. The domain size and the simulation length are also influencing the results.
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    Meteorology and atmospheric physics 63 (1997), S. 131-148 
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    Notes: Summary The paper concerns the sensitivity of the regional mesoscale model (MM4) to a moisture transport algorithm with different accuracies, and the effective improvement of the capability to simulate meso-scale synoptical event by using the revised version of the algorithm. The two advective schemes of second-order moment conservational Prather scheme (PRS hereinafter) and the polynomial-fitted fourth-order Bott scheme and the upstream scheme (UPS) are introduced into the MM4 to calculate moisture transport in order to provide other types of the algorithm with different accuracies for choice in addition to the original B grid second-order central scheme. Of the three schemes, the first two ensure the positive definite character with high accuracy (almost no numerical disspation and computational dispersion); and the last one also keeps the positive definite feature, but possesses stronger capability of numerical dissipation. Case studies have been undertaken of several rainstorm and typhoon events by virtue of the different-accuracy moisture transport algorithm, other things being the same. Results reveal great differences between them. An significant improvement is found in determining meso-scale synoptic system structure, rain cluster activity, rainstorm belt and its center, severity and its persistence, and the false alarm of or failure to report subrainstorm center when the PRS scheme is employed. Obviously, these differences and improvement are only due to moisture re-distribution for different schemes of moisture transport and the related variation of latent heat. The paper investigates the influences of different numerical schemes. The high accuracy and positive solution PRS application which produces a significant improvement in the model result, demonstrating the sensitivity of the model to moisture distribution in the model represents an important measure to improve the simulation by means of revising the numerically calculating method.
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    Meteorology and atmospheric physics 63 (1997), S. 149-158 
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    Notes: Summary Numerical investigation of the nature of one of the most typical Eastern Mediterranean atmospheric circulation phenomena — the Red Sea Trough is undertaken. The role of interaction of typical atmospheric flow systems with the local topography of the North African region is analyzed with the help of idealized numerical simulations employing the Penn State and the National Center for Atmospheric Research (NCAR) MM4 modeling system. The simulations are designed, based on results of a climatological evaluation of the 250 hPa wind field. Idealized initial data sets corresponding to typical transient and winter period positions of the upper tropospheric westerly jet stream are constructed. The data for the analysis are from the National Center for Environmental Prediction (NCEP) 25 y (1965–1989) objective analysis archive. It was found that the primary factor in the Red Sea trough generation is the interaction of the mid-tropospheric westerlies with the terrain in the area of the Red Sea.
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    Meteorology and atmospheric physics 63 (1997), S. 171-178 
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    Notes: Summary Wavelet transform (WT) has been employed to study the behavior of the 10–20-day and 25–50-day modes during Indian monsoon onset. Daily time-series of the zonal and meridional components of surface wind over off the Somali coast and onset dates over south Kerala during 23 years (1954–1976) have been used. In 63% of cases the results of this analysis indicate a link between summer monsoon onset and the 10–20-day and 25–50-day bands expressed by the simultaneously occurrence of fluctuations in these two bands. This suggests the presence of undulatory behavior within the Somali jet whose periods are situated in the 10–20-day and 25–50-day bands during summer monsoon onset.
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    Meteorology and atmospheric physics 63 (1997), S. 217-226 
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    Notes: Summary The back radiation has been measured with an Eppley pyrgeometer on board the R/V Vickers in the tropical Pacific Ocean during the field campaigns COARE (Coupled Ocean Atmosphere Response Experiment) and CEPEX (Central Equatorial Pacific Experiment) in February and March 1993, respectively. As part of these compaigns radiosondes have been launched from the Vickers several times per day and cloud cover was observed frequently. The radiosonde and cloud observations are used together with a radiative transfer model to calculate the back radiation for a subsequent intercomparison with the pyrgeometer measurements. Another means of comparison is derived from space-borne SSM/I (Special Sensor Microwave/Imager) measurements. The mean difference between pyrgeometer measurements and simulated downwelling irradiance at the sea surface is less than 2 W/m2, at a mean of 425 W/m2 in the warm pool, with a standard deviation of 8 W/m2. The comparison of satellite measurements with pyrgeometer readings shows a mean difference of-3 W/m2 and a standard deviation of 14 W/m2. The mean difference between satellite-derived back radiation and simulated one is 3 W/m2 with a standard deviation of 14 W/m2. Comparisons with results obtained from bulk formulae applied to surface meteorological observations show a good performance of the bulk parameterisations in the cloud-free case but a general overestimation of the back radiation in cloudy situations.
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    Meteorology and atmospheric physics 63 (1997), S. 243-244 
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    Meteorology and atmospheric physics 63 (1997), S. 195-215 
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    Notes: Summary This paper describes an attempt to model soil moisture over the Australian continent with an integrated system of dynamic models and a Geographic Information System (GIS) data base. A land surface scheme with improved treatment of soil hydrological processes is described. The non-linear relationships between soil hydraulic conductivity, matric potential and soil moisture are derived from the Broadbridge and White soil model. For a single location, the prediction of the scheme is in good agreement with the measurements of the Hydrological and Atmospheric Pilot Experiment (HAPEX). High resolution atmospheric and geographic data are used in soil moisture prediction over the Australian continent. The importance of reliable land surface parameters is emphasized and details are given for deriving the parameters from a GIS. Predicted soil moisture patterns over the Australian continent in summer, with a 50 km spatial resolution, are found to be closely related to the distribution of soil types, apart from isolated areas and times under the influence of precipitation. This is consistent with the notion that the Australian continent in summer is generally under water stress. In contrast, predicted soil temperatures are more closely related to radiation patterns and changes in atmospheric circulation. The simulation can provide details of soil moisture evolution both in space and time, that are very useful for studies of land use sustainability, such as plant growth modelling and soil erosion prediction.
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    Meteorology and atmospheric physics 63 (1997), S. 235-241 
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    Notes: Summary In the present study, the daily, annual and seasonal variations of the electric field in Athens-Greece, for all weather as well as for fair weather conditions, for the 16-years period 1965–1980 were examined. The daily variation of the electric field follows a double oscillation. A Fourier analysis was also used for the study of its diurnal variation. The results of the Man-Kendall test showed that the electric field at National Observatory of Athens (NOA), during the 16-years period, is essentially constant. In addition, the influence of the air pollution due to smoke and of wind speed on electric field was examined. It was deduced that an increase of air pollution results in an increase of electric field, while the electric field decreases as the wind speed increases.
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    Meteorology and atmospheric physics 64 (1997), S. 83-105 
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    Notes: Summary The effect of mountains on the occurrence of precipitation systems on Taiwan island is very significant, especially as mountain areas occupy about two-thirds of the land-mass. The mountains are, on average, about 3 km high. To investigate the formation of precipitation systems influenced by Pacific high pressure systems, we selected five cases (May 24, 25 and 26, June 19 and 20 in 1987) during a field program, TAMEX (Taiwan Area Mesoscale Experiment, Kuo and Chen, 1990). In all cases most of the rainfall took place in the afternoon when the level of free convection (LFC) was at about the 1 km height. If the average wind (below 3 km in height) was from the south (May 25 and 26), higher amounts of precipitation would be found along the sloped areas of western and eastern Taiwan. Rainfall also occurred in southern and northern Taiwan. If the average wind was from the southwest (May 24), the precipitation pattern was similar to that on May 25, except over the plains area in southwest and northeast Taiwan, where the amount was less. However, if the prevailing wind direction changed little with height and the average wind was from the south-southeast (June 19), higher rainfall amounts occurred from northwestern to central Taiwan. If the average wind was from the south and wind direction changed little with height (June 20), higher rainfall amounts took place in northern and central Taiwan. A nonhydrostatic model was used to simulate the formation of precipitation systems in all five cases. Simulation results indicated that the mixing ratio of rainwater could occur on the upstream side of a mountain slope and in the central mountain areas, where topographic lifting from the environmental wind and an upslope flow due to surface heating were evident. On the downstream side of the mountain, upward motion due to lee-side convergence and upslope motion from surface heating would also help rain form.
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    Meteorology and atmospheric physics 64 (1997), S. 107-121 
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    Notes: Summary An ozone mini-hole is a region of strongly depleted column total ozone amounts, associated with the growth of synoptic-scale wave disturbances. Their formation is illustrated here using a sequence of idealised model experiments. Simplified barotropic dynamics are used to drive an ozone tracer advection model on an f-plane representing a hemisphere. Firstly, the Contour Dynamics method is used to integrate the barotropic vorticity equation. Vorticity contours are initialised to simulate typical planetary wave structures and the developing wind field advects components of the ozone model. The vertical profiles of ozone mixing ratio are represented by simple linear functions, separated by a tropopause height field and capped by an upper model boundary. Integrating these profiles thus yields a total column ozone field which is closely dependent on tropopause height. In addition to horizontal advection, a vertical motion parametrisation is included, based on a quasi-geostrophic theory for tropopause displacement. The model is also used to simulate the formation of an actual mini-hole which occurred over northern Europe. Here, observed fields of vorticity, ozone and tropopause height are employed and the system integrated using a pseudo-spectral method. The mini-hole is successfully simulated, despite the simple model dynamics. The results demonstrate the correlation between column total ozone and the tropopause height and confirm the crucial role played by vertical air motions and by the meridional gradients of mid-stratospheric ozone mixing ratios for the formation of ozone mini-holes.
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    Meteorology and atmospheric physics 64 (1997), S. 123-150 
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    Notes: Summary This study entails a reanalysis of the TOGA-COARE, CEPEX period covering the months December 1992 through March 1993. Four times daily data sets were reanalyzed for the period. The unique aspect of this reanalysis is that (i) it incorporates physical initialization i.e. assimilation of rainfall from raingauge and satellite (OLR and microwave radiometric data), (ii) this reanalysis is carried out at a very high resolution, T170, global spectral model (space resolution of roughly 70 km at equator) and (iii) ECMWF reanalysis is used as a first guess field for this study. This analysis is global and is carried out at 15 vertical levels using the FSU global spectral model. In this study we have analyzed a large number of meterological variables such as wind, temperature, humidity, surface pressure, vertical velocity, cloud, rainfall, surface fluxes and diabatic heating. In this part of the paper we present the monthly mean and samples of daily fields of the reanalysis. Some of the major results of the reanalysis include the relationships among the flow fields and the ITCZ convection; the shallow northeast monsoon current and its rapid turning towards westerlies with height; an overabundance of middle clouds over the region of the ITCZ; and the distribution of heat sources and sinks. A motivation for this reanalysis is the forthcoming Indian Ocean Experiment (INDOEX), which is an international field experiment to be conducted during the winter monsoon time frame in 1999.
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    Notes: Summary In this part II of the reanalysis of the global data, we present an interpretation of the transient motion of the winter monsoon over Asia and the India Ocean. This includes an analysis of the surface layer meridional flow channels that are important for the transport of pollutants for the land mass of Asia towards the ITCZ, which is located near 10° S. We have also examined the scales of the space-time variability of the near surface flows of the winter monsoon of the 1992–1993 season. Sample forecasts of these inflow features, using a very high resolution model, are illustrated to show that the field phase of the proposed Indian Ocean Experiment (INDOEX) can receive guidance from real time numerical experimentation. The final part of this paper addresses four dimensional trajectories and passive tracer addresses four dimensional trajectories and passive tracer transports with integration over a winter monsoon domain covering several samples of 10 day periods.
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    Meteorology and atmospheric physics 64 (1997), S. 173-186 
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    Notes: Summary The MST (Mesosphere-Stratosphere-Tropospher) Radar Facility at Gadanki (13.47° N, 79.18° E), near Tirupati, Andhra Pradesh, India has been operated over seven diurnal cycles—three in November 1994, one in September 1995 and three in January–February 1996 with an objective to study the wind and stability characteristics in the troposphere and lower-stratosphere. The radar-measured height profiles of both zonal (EW) and meridional (NS) wind components and near-simultaneous radiosonde measurements from Madras (13.04° N, 80.7° E) and Bangalore (12.85° N, 77.58° E), the two stations close to either side of the radar site, have been compared and they are found to be in gross agreement within the limitations of the sensing techniques. The results of the study also indicated multiple stable and turbulent structures/stratification throughout the height region from about 4 to 30 km. It is noticed that the stable layers are well marked around the altitudes 4 km, 12 km and the tropopause while the turbulent layers exist a few kilometers below the tropopause. These stable and turbulent layer structures showed good correspondence with the radar-measured wind gradients and also with the radiosonde-derived temperature and wind distributions over Madras. The maximum positive gradient in the signal-tonoise ratio (SNR) which corresponds to ‘radar tropopause’ is found to coincide with the greater potential temperature gradient and smaller wind gradient. The time evolution of atmospheric stability structure, derived from the SNR, spectral width and vertical wind revealed a ‘diffused tropopause’ or ‘tropopause weakening’ which is found to be associated with broader spectral width and larger gradients of winds. This feature is considered to be due either to the instability associated with large vertical gradients in horizontal winds (dynamical instability) or to the instability generated by the convection (convective instability).
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    Meteorology and atmospheric physics 62 (1997), S. 241-248 
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    Notes: Summary The atmospheric concentrations of several primary species: NO, NO2, NOx, CO, SO2, reactive hydrocarbons (ROG) and other 15 atmospheric and meteorological variables have been measured at several locations in Córdoba city, Argentina since June 1995. The measurements are carried out using two mobile stations to cover several important areas of Córdoba. The objective of this work is to estimate the effects of meteorology and urban structure on the air quality levels for this city using simple statistics. We analyze the correlation between primary pollutants (CO and NOx) and site locations of the air quality monitoring stations (AQMS) during the whole 1995 field campaign. In this study we take the measured data for primary pollutants and group them by location and time of the year. The results of this work may be useful to forecast air pollution episodes. Also we can get indirect information about emissions and maybe identify source characteristics. Once the influences of topography, meteorology, and land use will be fully characterized, the existing monitoring data will be used to do air quality modeling analysis and to select monitoring locations. The use of mobile stations instead of stationary ones at this stage is justified because of limited funding. Therefore, it is a valid option to decide in the future the additional instrumentation required to characterize completely the atmospheric urban area.
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    Meteorology and atmospheric physics 63 (1997), S. 1-1 
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    Meteorology and atmospheric physics 62 (1997), S. 249-256 
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    Notes: Summary Serious events of radiative frost were reported in an important agricultural area of central Macedonia, the valley of Lagadas, at the end of March 1994. Since the phenomenon has a strong local character and no surface observations are available, a simulation is performed using a three dimensional numerical model in order to investigate the horizontal and vertical thermal structure of the lower troposphere during the frost event. The synoptic analysis reveals that the background flow was weak, associated with anticyclonic circulation and insignificant pressure gradient in the lower troposphere. Under these synoptic conditions, it was demonstrated that the meteorological model represents successfully the temperature and wind fields over the valley of Lagadas during the frost event. It appears that the model can serve as an alternative method to analyse the characteristics of the radiative frost that occurs very frequently over the examined area associated with substantial economic repercussion.
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    Meteorology and atmospheric physics 63 (1997), S. 3-14 
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    Notes: Summary Following a few historical remarks, approximations used in formulating the “dynamics” of limited-area and variable resolution atmospheric forecasting models are reviewed. Particular attention is given to current efforts to relax or remove the hydrostatic approximation. Turning to numerical methods used in discretizing the equations, an attempt is made to record recent work and to clarify the motivation for the various approaches being followed by different modeling centers. Topics commented upon include: semi-Lagrangian methods, numerical formulation of nonhydrostatic models, resolution, the eta (step-mountain) vs sigma or isentropic/sigma vertical coordinate, choice of the vertical grid, numerics of the propagation of gravity waves, and the box-average vs pointsample treatment of predicted variables. It is finally pointed out that the extraordinary diversity of roads being taken shows that a lot remains to be discovered as to what possible rewards may be found in exploring one or the other of the principles underlying the methods being developed.
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    Meteorology and atmospheric physics 63 (1997), S. 31-38 
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    Notes: Summary This paper presents a brief overview of a few variable resolution techniques in the context of the horizontal discretization of the meteorological equations. These are the grid refinement method, the static and dynamic coordinate transformation methods and the variable resolution in physical space method. The latter is illustrated by a variable resolution reformulation of the popular C-grid discretization suitable for use in a limited area model.
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    Meteorology and atmospheric physics 63 (1997), S. 15-29 
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    Notes: Summary The goal of regional modeling is to make a detailed forecast for a given limited area of interst by focusing resolution over it and the immediate vicinity. As a consequence, the period of validity is necessarily more restricted than would otherwise be the case, and this is the price that must be paid for locally-enhanced resolution. The principal attributes of the non-interactive and interactive strategies for regional modeling are described. For the non0interactive strategy, particular emphasis is placed on the importance, difficulty, and impact, of well-posedness for open-domain problems. A methodology is given for estimating the size of numerical buffer zones required to obtain a forecast uncontaminated by the inward propagation of inaccurately-specified lateral boundary conditions. The interactive strategy addresses the well-posedness issue of (non-interactive) limited-area models. A computational overhead is incurred but this can be reduced through the use of variable resolution. It is argued that regardless of the preferred regional modeling strategy, experiments should be undertaken to today's regional models under carefully-controlled conditions, to reflect the significant reduction over the past two decades of other sources of error.
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    Meteorology and atmospheric physics 63 (1997), S. 39-51 
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    Notes: Summary Quantitatively comparative experiments of moist convection using hydrostatic and non-hydrostatic models are reviewed and a further study is made of the suitability of the hydrostatic approximation for a high-resolution model when the grid size falls below 20 km. Idealized moist convection is treated, and then the torrential rain that occurred on 6 August 1993 in Kagoshima, southern Kyushu, Japan is simulated by each model. An explicit warm-rain process predicting cloud water and rainwater and the scheme of moist convective adjustment are individually or conjunctively employed in the model. The effect of hydrostatic water loading is also examined in detall. For the simulation of idealized convection, the hydrostatic simulation tends to overestimate and overexpand precipitation in comparison with the non-hydrostatic counterpart, and the drag effect of hydrostatic water loading is more significant for convective development than the non-hydrostatic effect. In the 20-km simulations, however, the hydrostatic simulation with hydrostatic water loading produces results that are comparable to the nonhydrostatic counterpart. For the simulation with real data, the comparative results well correspond to those of idealized convection. Furthermore, the 5 km hydrostatic simulation overestimates total precipitation more than that of dealized convection. On the basis of these results, when developing 10∼20 km numerical weather prediction (NWP) models, hydrostatic water loading should be evaluated in preference to adopting non-hydrostatic models, and a non-hydrostatic model with hydrostatic water loading is thought to be recommendable for a high-resolution NWP model.
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    Meteorology and atmospheric physics 63 (1997), S. 89-104 
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    Notes: Summary Regional operational prediction requires the development, implementation and steady improvement of a modelling system which comprises different components like the data assimilation scheme, numerical forecast model, postprocessing and application modules as well as packages for monitoring, diagnostics and verification. The text highlights the impact of some of those components like lateral boundary conditions, data assimilation and statistical postprocessing on the quality of operational regional prediction systems and proposes some important research directions for an improvement of the systems from the operational point of view.
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    Meteorology and atmospheric physics 63 (1997), S. 71-88 
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    Notes: Summary The current opportunities of progress for short term numerical weather prediction in the domain of physical parametrizations are reviewed. Attention is paid to the fact that many models now resolve very short space and time scales, and the consequences of this situation in terms of physical parametrizations are outlined. It is argued that the most profitable areas of work are currently surface processes and cloud microphysics. The parametrization of deep cumulus convection will probably remain necessary for the next few years, but present operational schemes should be modified to take into account the breakdown of the quasi-equilibrium assumption as space and time resolutions of the models increase.
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    Meteorology and atmospheric physics 63 (1997), S. 53-69 
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    Notes: Summary Selected small domain LAM forecasts modulated by highly corrugated underlying topography, and driven by different state-of-science outer models suggest that uncertain outer model guidance for LAMs produces large, domain averaged sensitivity. A further literature survey indicates that many LAM forecasts are relatively insensitive to details of the local initial state, and that mesoscales show slight error growth, in contradiction to classical predictability theory. A series of global predictability experiments is presented in order to reconcile the contradiction. The experiments imply that, even in baroclinically unstable atmospheres, the most common sources of local error growth are associated with small uncertainties of the larger spatial scales rather than small uncertainties of the smaller spatial scales. Variable resolution, real-data experiments of barotropic versions of the global model display substantial mesoscale error growth, due principally to the effect of larger scales. The uncertainties possessing largest spatial scale appear as boundary uncertainties in LAMs, and explain the strong boundary sensitivity and weak local initial data sensitivity observed in many LAMs. We infer that accurate depiction of the largest spatial scales is a first order priority for accurate local prediction, and that for the advective portion of the dynamics, errors of the outer model that provides lateral boundary conditions may impose the largest current practical limitation for many LAM predictions.
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    Meteorology and atmospheric physics 63 (1997), S. 105-117 
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    Notes: Summary Regional climate modelling is becoming increasingly popular. The most common technique employs high resolution limited-area models to economically produce detaited climatologies for selected regions. A short review is presented of the underlying principles, recent simulations limitations of the method and future prospects.
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    Meteorology and atmospheric physics 63 (1997), S. 159-169 
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    Notes: Summary A case of development of a meridionally oriented Red Sea Trough (RST) system and its intensification over the Eastern Mediterranean (EM) region during the ALPEX1982 3–5 March period, is investigated. The MM4 mesoscale model of Penn State University/National Center for Atmospheric Research was first applied for a large scale investigation of the processes. The relative roles of the different acting factors, i.e., terrain, latent heat release and the surface fluxes were calculated employing the factor separation method. Topography and sensible heat flux were found to be the dominant ones. The high resolution non-hydrostatic RAMS 3a model of Colorado State University with nested grids of 100 and 20 km illustrated the finer details of the cyclogenetic processes in the mountainous area of the Abyssinean Highlands, Ethiopia, and the Arabian peninsula, where initiation of the trough took place. Results of the factor separation showed that the topography blocking acted as a cyclolytic factor, preventing the process of the northward trough propagation. The situation changed only after about 30 h of the simulation, when the trough already propagated into the EM area after intensification of the mid-tropospheric westerlies over the central part of the Red Sea area. Starting from this time, terrain was acting as one of two major cyclogenetic factors. The second local effect also working as a cyclogenetic one was the sensible heat flux. Its role was especially important after 36 h of the simulations when strong winds over the sea area caused more active heat transfer from the sea surface to the atmosphere.
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    Meteorology and atmospheric physics 63 (1997), S. 179-193 
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    Notes: Summary An investigation of the relationships between New South Wales (NSW) seasonal rainfalls and fluctuations of geopotential height at four Australian radiosonde stations is presented. The connection between the Southern Oscillation Index (SOI) and the geopotential height was explored up to the mid-troposphere. The study determined that the 800 and 600 hPa heights at Woomera show stronger and more consistent correlations with winter and spring rainfalls respectively, than occur between SOI and rainfall. The 900 hPa height at Brisbane is also strongly correlated with autumn rainfall for much of coastal NSW. These correlations are found to be stable during high and low phases of the SO cycle. It was found that the effects of the considered geopotential data on rainfall are independent of the influence of the SO phenomenon. The study also found that the fluctuations of geopotential heights at Woomera are related to rainfall variability over a wide region of southern Australia. At Darwin the 800 hPa surface appears to be the highest altitude at which there is any influence from the Southern Oscillation during winter. Furthermore, airmass movement over inland NSW is quite strongly related to SOI but coastal airmass movement is only weakly related to SOI. A mechanism for the influence of the Southern Oscillation on NSW rainfall is suggested.
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    Meteorology and atmospheric physics 63 (1997), S. 227-233 
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    Notes: Summary Daily integration of optical air mass should be of interest by its own merit as a synoptic factor, yet available solutions have been limited as numerical (and probably in error). This paper reports on a generic solution to daytime mean air mass by first defining instantaneous air mass in an integrable function. Daily air mass is then shown to be a key forcing factor in a numerically-derived formula solution to daily solar irradiance.
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    The annals of regional science 31 (1997), S. 39-56 
    ISSN: 1432-0592
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    Topics: Architecture, Civil Engineering, Surveying , Geography , Economics
    Notes: Abstract. This paper proposes a dynamic multi-regional growth model with free mobility of capital and population. The economic system consists of multiple cities interconnected by high-speed railway systems with each city consisting of one production sector as well as residential land use. The railway systems provide production sectors of different cities with the opportunity of face-to-face communication for knowledge production. The model describes the dynamic interdependence between capital and knowledge accumulation, wage and land rent structures, urban patterns with endogenous city size and inter-city interactability. It is emphasized how differences in geographic and qualitative factors of high-speed railway systems may affect regional economic development. The model simulates the dynamic processes of economic development of city systems.
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    Notes: Abstract. We show that enriching logit mode choice model specification by mode attributes, socio economic variables and trip purpose characteristics significantly improves model quality, and that Box-Cox transformations applied to model attributes imply an asymmetry of the reaction curve, as well as more reasonable properties (diminishing marginal values of time savings, elasticities and values of time that differ among the modes) than those of the linear logit model. Moreover, the model yielded very different high speed rail market shares for Germany than results obtained with the usual linear utility functions.
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    The annals of regional science 31 (1997), S. 273-284 
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    Notes: Abstract. This paper examines the impact of demand on the location decision of a monopsonistic firm in the Weber-Moses triangle with one output and two inputs. When the distance of the plant location from the product market is held constant and the expansion path is linear through the origin, the analysis shows that as demand for output increases, the monopsonist has an incentive to move the plant away from the monopsonized input market and towards other markets. When the distance of the plant location from the product market is a choice variable, the linearly homogeneous production function is not sufficient to ensure that the location decision of the monopsonistic firm is independent of the demand function. These results differ significantly from the well-established results in location theory where the firm is a price taker in all the input markets.
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    The annals of regional science 31 (1997), S. 353-367 
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    Notes: Abstract. In this paper we derive endogenous tariff rates for a tariff revenue maximizing policy and a welfare maximizing policy (optimal tariff) in a spatial framework. The underlying model is that of a spatial oligopolistic market with domestic and foreign firms. We assess the outcomes of the model for different tariff rates and the free trade situation, the stress being on welfare considerations. Compared to the traditional theory of international trade and tariffs, this approach affords useful insights into the role of firms‘ locations and transportation costs for profits and consumers‘ surplus in the case of alternative trade policies.
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    The annals of regional science 31 (1997), S. 77-98 
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    Notes: Abstract. This paper intends to evaluate impacts of high-speed rail transit, i.e., Shinkansen network in Japan on spatial dispersion of economic activities and population. For doing so, a simple supply-oriented regional econometric model is constructed, and simulation analyses are carried out for alternative hypothetical scenarios of the Shinkansen network. The results show that denser Shinkansen network will not necessarily contribute to regional dispersion.
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    The annals of regional science 31 (1997), S. 121-153 
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    Notes: Abstract. High-speed rail (HSR) lines are usually planned to serve corridors with existing conventional rail (CR) lines, since these corridors typically have large markets concentrated around major cities. This paper formulates a new analytical model to estimate market shares of HSR and CR in a fundamental way, and from an individual behavior point of view. Passengers are divided into those who can take an HSR train directly to their destination stations and those who cannot. Optimal route choices are assumed by minimizing the „generalized total travel time”. The relationship among demand-supply attributes such as value of time, train departure time, speed, trip length and fares is explored to identify market boundaries by comparing different routing strategies for each type of passenger. Individual route choices are aggregated by accumulating a transformation probability density function of value of time to estimate the spatial distribution of markets for two types of rail lines. The result estimates detail market distributions for passengers alighting at stations along the corridor. HSRs are shown to best serve medium- to long-trip markets, while CRs are shown to serve best for commuter travel and as feeders for the HSRs.
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    The annals of regional science 31 (1997), S. 235-258 
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    Notes: Abstract. The continuos inflow of new products is a fundamental condition for a well-functioning market economy. It has been argued that new products are the outcome of a process which is based upon the principle “novelty by combination”. This characterization applies well to the type of product development analyzed in this paper, which comprises the development of new products and the renewal of old products in the Swedish engineering industry through the adoption of a specific type of innovation, namely the incorporation of information technology based components and their pertinent software, i.e. microelectronics. According to the theoretical perspective presented in the paper, a new or a renewed product may result from “random collisions” or from a cautious matching between technical opportunities and customer needs. A necessary condition for such “collisions” or matching to occur is communication and, hence, communication in innovation networks is one key factor in product development. The empirical part of the paper contains an empirical test of the role of establishment characteristics, innovation networks, infrastructure endowment and agglomeration economies for the first use of micro-electronics in product development at the plant level. The empirical results seem to confirm the importance of innovation networks as well as of infrastructure endowment and agglomeration economies for an early use of micro-electronics in product development.
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    The annals of regional science 31 (1997), S. 325-351 
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    Notes: Abstract. In this paper we outline an I-O modeling approach tailored to the needs of rural area analysis. We cover four essential features. First, the rural area I-O model must convey an individual community focus. Second, the household sector must be defined in a manner that specifically captures the great openness of rural community economies. Third, the model should offer a degree of closure that provides an assessment of the community economic base. And finally, the rural community I-O model must be defined to include estimates of intercommunity trade, and intercommunity multiplier effects. Having laid the theoretical foundations, we identify subcounty data sources, and describe a collection of nonsurvey and hybrid approaches for estimating model components. The community I-O approach is illustrated next, with an empirical example from central Idaho. The paper closes with a discussion that considers the implications of community I-O in other contexts, including I-O analysis in less developed countries, and in addressing modeling issues in larger nonrural regions.
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    Electronic Resource
    Springer
    The annals of regional science 31 (1997), S. 431-449 
    ISSN: 1432-0592
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography , Economics
    Notes: Abstract. This study shows that there has been a statistically significant shift in the quality of life (QOL) in central cities of the 25 largest metro areas relative to their suburbs since 1980. This follows actual improvement of central cities in the ‘50s, followed by steady degradation in the ‘60s and ‘70s. These conclusions are based on a statistical analysis of key variables derived from a revealed preference conception of QOL. This is an important methodological advance, since relevant variables for directly constructing hedonic measures of QOL normally are unavailable for central cities. The basic Census data used in the analysis also indicate that the observed “turnaround” is evident without respect to size of metro area within the set of 25 largest and without respect to region of the country.
    Type of Medium: Electronic Resource
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    ISSN: 1432-0592
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography , Economics
    Notes: Abstract. In this paper we estimate value of time savings specifically applied to the case of the Rion-Antirion suspension bridge which will connect the Western part of Greece through the Rion-Antirion sea strait with the region of Patras and consequently with Athens providing a faster and more efficient service for the passage of the sea strait than the existing obsolete ferry system. Value of time savings are important in determining that the correct level of tolls are based not only on market-oriented values but that they also ensure revenue maximization and user acceptance. Estimation of a multinomial logit model is done for the value of time savings for business and non-business categories of travellers who can only choose between private cars and buses. Our results show that for the case of non-business the value of time is about 60% of the wage rate, for the case of business, it is 85% of the wage rate.
    Type of Medium: Electronic Resource
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