Ensemble Simulation Data Research Articles

Analyzing uncertainty in probable maximum precipitation estimation with large ensemble climate simulation data

AbstractThis study aimed to evaluate probable maximum precipitation (PMP) estimated using surface dew points (SDP) or actual precipitable water obtained from upper‐air data (UAD) in the moisture‐maximization method with the help of sufficient extreme precipitation events using large‐scale climate ensemble simulation data (d4PDF). The deviations between the PMP variables estimated by the SDP and UAD approaches were analyzed for southern and northern areas of Japan to consider the regional characteristics of the deviations. We found that the deviations were high in northern areas where the SDPs are relatively low during precipitation events. The PMPs estimated using each approach were also compared to the extreme‐scale reference precipitation proposed in this study. The SDP approach overestimated the PMPs by over 20% compared to the reference precipitation in the northern region. However, the UAD approach showed very low average errors in all southern and northern areas. This tendency of the SDP approach was significantly related to the regional climatic characteristics of the SDP, which indicated that the SDP approach may estimate an uncertain PMP value depending on each regional climatic characteristic compared to the UAD approach. Regional climatic characteristics should be considered when using the SDP approach to estimate the PMP.

Application of Large-scale Climate Simulation Data to Evaluate the Scale of Extreme Rainfall Events: A Case of the 2018 Hiroshima Extreme-scale Rainfall Event

This study aims to apply large-scale climate ensemble simulation data to evaluate the magnitude of extreme rainfall events. It was conducted on the basis of extreme rainfall that occurred in the Hiroshima region in 2018. This event recorded an extreme rainfall magnitude corresponding to a return period of 1,000 years at a 24-h rainfall duration; it is difficult to evaluate this magnitude with the concept of probability rainfall based on frequency analysis due to the short observation period. To overcome this limitation, the data for policy decision making for future (d4PDF) climate change database based on a large-scale climate ensemble simulation was used. These data provided 3,000 annual maximum daily rainfall values, which were used to empirically estimate the probability rainfall with a return period of 10-1,000 years based on a non-parametric approach without statistical methods. The estimated probability rainfall of the d4PDF was compared with the estimated probability obtained from the observed rainfall and frequency analysis. The difference between the two probability rainfall values was 3.53% for the return period of 50 years. However, as the return period increases, the error increases to more than 10%. This indicates that the estimation of the probability rainfall with a long-term return period using the observed data of a relatively short period may present uncertainties. Regarding the probability rainfall using d4PDF under present climate conditions, the Hiroshima event represented a return period of nearly 300 years. Meanwhile, for the probability rainfall using the d4PDF under future climate conditions, the Hiroshima event had a return period of nearly 100 years. Consequently, the magnitude of the probability rainfall increased in future climate conditions, and the probability of the occurrence of extreme rainfall corresponding to the Hiroshima event increased from 0.33% to 1%. Therefore, d4PDF can be used to quantitatively evaluate the magnitude of extreme rainfall events under present and future climate conditions.

EFESTA: Ensemble Feature Exploration with Surface Density Estimates.

We propose surface density estimate (SDE) to model the spatial distribution of surface features-isosurfaces, ridge surfaces, and streamsurfaces-in 3D ensemble simulation data. The inputs of SDE computation are surface features represented as polygon meshes, and no field datasets are required (e.g., scalar fields or vector fields). The SDE is defined as the kernel density estimate of the infinite set of points on the input surfaces and is approximated by accumulating the surface densities of triangular patches. We also propose an algorithm to guide the selection of a proper kernel bandwidth for SDE computation. An ensemble Feature Exploration method based on Surface densiTy EstimAtes (eFESTA) is then proposed to extract and visualize the major trends of ensemble surface features. For an ensemble of surface features, each surface is first transformed into a density field based on its contribution to the SDE, and the resulting density fields are organized into a hierarchical representation based on the pairwise distances between them. The hierarchical representation is then used to guide visual exploration of the density fields as well as the underlying surface features. We demonstrate the application of our method using isosurface in ensemble scalar fields, Lagrangian coherent structures in uncertain unsteady flows, and streamsurfaces in ensemble fluid flows.

Ovis: A Framework for Visual Analysis of Ocean Forecast Ensembles.

We present a novel integrated visualization system that enables interactive visual analysis of ensemble simulations of the sea surface height that is used in ocean forecasting. The position of eddies can be derived directly from the sea surface height and our visualization approach enables their interactive exploration and analysis.The behavior of eddies is important in different application settings of which we present two in this paper. First, we show an application for interactive planning of placement as well as operation of off-shore structures using real-world ensemble simulation data of the Gulf of Mexico. Off-shore structures, such as those used for oil exploration, are vulnerable to hazards caused by eddies, and the oil and gas industry relies on ocean forecasts for efficient operations. We enable analysis of the spatial domain, as well as the temporal evolution, for planning the placement and operation of structures.Eddies are also important for marine life. They transport water over large distances and with it also heat and other physical properties as well as biological organisms. In the second application we present the usefulness of our tool, which could be used for planning the paths of autonomous underwater vehicles, so called gliders, for marine scientists to study simulation data of the largely unexplored Red Sea.

Saturation properties of 1-alkyl-3-methylimidazolium based ionic liquids.

We study the liquid-vapor saturation properties of room temperature ionic liquids (RTILs) belonging to the homologous series 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Cnmim][NTf2]) using Monte Carlo simulation. We examine the effect of temperature and cation alkyl chain length n on the saturated densities, vapor pressures, and enthalpies of vaporization. These properties are explicitly calculated for temperatures spanning from 280 to 1000 K for RTILs with n = 2, 4, 6, 8, 10, and 12. We also explore how the identity of the anion influences saturation properties. Specifically, we compare results for [C(4)mim][NTf2] with those for 1-butyl-3-methylimidazolium tetrafluoroborate ([C(4)mim][BF4]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([C(4)mim][PF6]). Simulations are completed with a recently developed realistic united-atom force field. A combination of direct grand canonical and isothermal-isobaric temperature expanded ensemble simulations are used to construct phase diagrams. Our results are compared with experimental data and Gibbs ensemble simulation data. Overall, we find good agreement between our results and those measured experimentally. We find that the vapor pressures and enthalpies of vaporization show a strong dependence on the size of the alkyl chain at low temperatures, whereas no particular trend is observed at high temperatures. Finally, we also discuss the effect of temperature on liquid phase nanodomains observed in RTILs with large hydrophobic groups. We do not observe a drastic change in liquid phase structure upon variation of the temperature, which suggests there is not a sharp phase transition between a nanostructured and homogeneous liquid, as has been suggested in earlier studies.

Statistical thermodynamics of fluids with both dipole and quadrupole moments

New Gibbs ensemble simulation data for a polar fluid modeled by a square-well potential plus dipole-dipole, dipole-quadrupole, and quadrupole-quadrupole interactions are presented. This simulation data is used in order to assess the applicability of the multipolar square-well perturbation theory [A. L. Benavides, Y. Guevara, and F. del Río, Physica A 202, 420 (1994)] to systems where more than one term in the multipole expansion is relevant. It is found that this theory is able to reproduce qualitatively well the vapor-liquid phase diagram for different multipolar moment strengths, corresponding to typical values of real molecules, except in the critical region. Hence, this theory is used to model the behavior of substances with multiple chemical bonds such as carbon monoxide and nitrous oxide and we found that with a suitable choice of the values of the intermolecular parameters, the vapor-liquid equilibrium of these species is adequately estimated.

Cell ensemble modeling of metabolic oscillations in continuous yeast cultures

Continuous cultures of the yeast Saccharomyces cerevisiae exhibit autonomous oscillations under certain environmental conditions. Three distinct type of oscillations have been experimentally observed and characterized: glycolytic oscillations, respiratory oscillations and cell cycle related oscillations. Because they are metabolically driven and independent of cell cycle progression, glycolytic and respiratory oscillations are well suited for the study of intracellular metabolism and regulatory dynamics. The incorporation of metabolic structure within the cell population balance equation (PBE) framework leads to computational infeasibility due to the high dimensionality of the cell distribution function. An alternative approach based on large ensembles of metabolically structured cell models is shown to be effective for modeling the synchronization of glycolytic and respiratory oscillations. A simple method for computing transient number distribution functions from ensemble simulation data is presented. The paper concludes with a brief overview of our future work on ensemble modeling of respiratory and cell cycle related oscillations.

Combined Metabolic and Cell Population Modeling for Yeast Bioreactor Control

Abstract Several investigators recently have explored the use of cell population balance equation (PBE) models for the design of biochemical reactor control strategies. A major disadvantage of the PBE modeling approach is that the incorporation of intracellular reactions needed to accurately describe cellular processes leads to substantial computational difficulties. We investigate an alternative modeling technique in which the cell population is constructed from an ensemble of individual cell models. The average value or the number distribution of any intracellular property captured by the cell model can be computed from ensemble simulation data. To illustrate the basic procedure, a single cell model of yeast glycolytic oscillations is used to construct large cell ensembles for the investigation of cell population synchronization. The potential use of cell ensemble models for bioreactor controller design are discussed.

The thermodynamics of mixtures and the corresponding mixing rules in the SAFT-VR approach for potentials of variable range

The statistical associating fluid theory (SAFT) has been extended recently to describe the thermodynamic properties of chain molecules formed from monomeric segments interacting with attractive potentials of variable range (VR) (Gil-Villegas, A., Galindo, A., Whitehead, P. J., Mills, S. J., Jackson, G., and Burgess, A. N., 1997, J. chem. Phys., 106, 4168). The SAFTVR approach is based on an accurate and compact representation of the free energy of chain molecules in terms of the contact value of the radial distribution function of the monomer reference system. This paper takes advantage of the SAFT-VR approach to focus on the nature of the expressions for mixtures of non-conformal molecules. A number of mixing rules are proposed, from the usual van der Waals one-fluid prescription to a complete description in terms of the pair distribution functions of the pair interactions that goes beyond the one-fluid level. As a first test of the adequacy of the theory for mixtures the SAFT-VR prediction is compared with Gibbs ensemble simulation data for the vapour-liquid and liquid-liquid equilibria of two prototype mixtures containing square-well molecules.

Deviation from corresponding-states behaviour for polar fluids

The influence of the strength of the reduced dipole moment μ* of a Stockmayer fluid on thermodynamic phase behaviour is systematically investigated by means of computer simulations. Gibbs ensemble simulation data are presented for Stockmayer fluids with μ*2=5 and μ*2=6 in the reduced temperature range of 0·78–0·98 (respectively 0·99). Critical properties are estimated from Gibbs ensemble Monte Carlo data. The critical temperature increases strongly with increasing dipole moment, and the critical density shows a decrease for higher dipole moment values. The critical pressure increases only slightly, with the resulting reduced compressibility factor showing a clear decreasing trend. These trends are correlated with the reduced dipole moment. The Pade approximation of perturbation theory, compared with four other theories, follows the ‘exact’ critical-property correlations closest. The simulation results show that dipolar forces alone are sufficient to induce a deviation from corresponding-states behaviour: ...

Vapour-liquid equilibria of stockmayer fluids

By M. E. VAN LEEUWEN, B. SMIT and E. M. HENDRIKS Koninklijke/Shell-Laboratorium, Amsterdam, P.O. Box 3003, 1003 AA Amsterdam, The Netherlands (Received 16 April 1992; accepted 1 July 1992) Gibbs ensemble simulation data for Stockmayer fluids with #.2 = 3.0 and #.2 = 4.0 in the reduced temperature range of 0-77 (resp. 0.80)-098 and pre- sented and compared with predictions based on the perturbation theories of Stell, G., Rasaiah, J. C., and Narang, H., 1972, Molec. Phys., 23, 393; 1974, 27, 1393. The description of the reference fluid is improved by applying the mod- ified Benedict-Webb-Rubin equation of state instead of the Verlet-Weis imple- mentation of the Weeks-Chandler-Andersen perturbation scheme. Second virial coefficients predicted by perturbation theory to order #4 agree for Stock- mayer fluids with #,2 < 4 very well with exact values. Perturbation theory is capable of describing the low-density region of Stockmayer fluids with rather strong dipole moments. For these high values of the dipole moment, the Pad6 approximation of perturbation theory deviates significantly from the simulated coexistence curves in density and pressure. Compared with perturbation theory to order #4, however, it is a far better approximation of the Stockmayer fluid coexistence curve. The behaviour of the Pad6 approximation in the critical region is not satisfactory. 1. Introduction Electrostatic interactions affect thermodynamic behaviour. For relatively simple polar model fluids several theories have been developed [1-3]. A convenient model for a polar fluid is a 'soft-core' dipolar molecule, represented by the Stockmayer potential (Lennard-Jones potential with an embedded point dipole). The two most important molecular theories for model polar fluids are integral equation theories and (Pople-Stell) perturbation theories. If the Ornstein-Zernike equation is supplemented with an approximate closure relation, an integral equation is obtained for the direct correlation function and the radial distribution function [2]. For polar fluids this involves expansions of angular- dependent functions. Starting from the well known hypernetted-chain equation Patey and others [4-6] considered linear expressions (LHNC) and quadratic expressions (QHNC), and obtained a numerically tractable scheme. Fries and Patey [7] devel- oped a general method for fluids with anisotropic interactions, the reference hypernetted-chain (RHNC) theory. Lee et al. [8] applied this approximation to Stockmayer fluids, and found that the dielectric constant predicted with the full RHNC theory agrees better with computer simulation results than those predicted with the LHNC and QHNC theories. Another approach to describe the behaviour of simple polar model fluids is the use of perturbation theories, as pioneered by Pople and further developed by Stell et al. [9-13]. In these theories, the free Helmholtz energy is expressed as the sum of a

Solvation thermodynamics: An approach from analytic temperature derivatives

A method is presented that uses integral equation theory to determine analytic temperature derivatives of the radial distribution functions. It is illustrated by studying the solvation thermodynamics of monatomic solutes in aqueous solution. The results agree well with the density derivative method developed previously [Yu and Karplus, J. Chem. Phys. 89, 2366 (1988)]. An expression for the solvation enthalpy is derived which allows direct comparison with experimental and isobaric–isothermal (NPT) ensemble simulation data. Satisfactory agreement with experiment is found for pure water and for the aqueous solvation of monovalent ions. Simple equations that exploit the site–site HNC closures are given for the decomposition of the potential of mean force into its enthalpic (or energetic) and entropic components. Since the extended RISM (HNC-RISM) theory yields an incorrect (trivial) value of the dielectric constant, two different ways to correct for the asymptotic behavior of the solute–solute potential of mean force are compared. They lead to similar results but the method in which the solvent dielectric constant is modified from the outset can be applied more generally. The interactions between nonpolar and between polar solutes in water are decomposed into enthalpic and entropic contributions. This is difficult to do by computer simulations because of the lack of precision in such calculations. The association of nonpolar solutes in water is found to have comparable enthalpic and entropic contributions; this result disagrees with the usual description of an entropy-dominated hydrophobic interaction. For ions, the somewhat surprising result is that the association of like-charged species is enthalpy driven while for oppositely charged ions entropic effects are dominant. The process of bringing two like-charged ions together leads to higher local charge density; the more favorable solvation enthalpy arising from this increase in charge density (q2 dependence) more than compensates for the Coulombic repulsion. For oppositely charged ions, association leads to a partial charge neutralization in which the favorable Coulombic attraction is overwhelmed by the loss of stabilizing solvation enthalpy. The entropic increase is due to the greater freedom of the surrounding water molecules resulting from the partial charge neutralization.