17 research outputs found
The Impacts of Dry Dynamic Cores on Asymmetric Hurricane Intensification
The article of record as published may be found at http://dx.doi.org/10.1175/JAS-D-16-0055.1The fundamental pathways for tropical cyclone (TC) intensification are explored by considering axisym- metric and asymmetric impulsive thermal perturbations to balanced, TC-like vortices using the dynamic cores of three different nonlinear numerical models. Attempts at reproducing the results of previous work, which used the community WRF Model, revealed a discrepancy with the impacts of purely asymmetric thermal forcing. The current study finds that thermal asymmetries can have an important, largely positive role on the vortex intensification, whereas other studies find that asymmetric impacts are negligible.
Analysis of the spectral energetics of each numerical model indicates that the vortex response to asym- metric thermal perturbations is significantly damped in WRF relative to the other models. Spectral kinetic energy budgets show that this anomalous damping is primarily due to the increased removal of kinetic energy from the vertical divergence of the vertical pressure flux, which is related to the flux of inertia–gravity wave energy. The increased kinetic energy in the other two models is shown to originate around the scales of the heating and propagate upscale with time from nonlinear effects. For very large thermal amplitudes (50 K), the anomalous removal of kinetic energy due to inertia–gravity wave activity is much smaller, resulting in good agreement between models.
The results of this paper indicate that the numerical treatment of small-scale processes that project strongly onto inertia–gravity wave energy can lead to significant differences in asymmetric TC intensification. Sensitivity tests with different time integration schemes suggest that diffusion entering into the implicit solution procedure is partly responsible for the anomalous damping of energy.Institute of Geophysics, Planetary Physics and Signatures (IGPPS) at Los Alamos National LaboratoryOffice of Naval Research through program element PE-0602435Institute of Geophysics, Planetary Physics and Signatures (IGPPS) at Los Alamos National LaboratoryOffice of Naval Research through program element PE-060243
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Numerical Investigation Into Effects of Complex Terrain on Spatial and Temporal Variability of Precipitation
This study is part of an ongoing research effort at Los Alamos to understand the hydrologic cycle at regional scales by coupling atmospheric, land surface, river channel, and groundwater models. In this study the authors examine how local variation of heights of the two mountain ranges representative of those that surround the Rio Grande Valley affects precipitation. The lack of observational data to adequately assess precipitation variability in complex terrain, and the lack of previous work has prompted this modeling study. Thus, it becomes imperative to understand how the local terrain affects snow accumulations and rainfall during winter and summer seasons respectively so as to manage this valuable resource in this semi-arid region. While terrain is three dimensional, simplifying the problem to two dimensions can provide some valuable insight into topographic effects that may exist at various transects across the Rio Grande Valley. The authors induce these topographic effects by introducing variations in heights of the mountains and the width of the valley using an analytical function for the topography. The Regional Atmospheric Modeling System (RAMS) is used to examine these effects
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Validation of Coupled Atmosphere-Fire Behavior Models
Recent advances in numerical modeling and computer power have made it feasible to simulate the dynamical interaction and feedback between the heat and turbulence induced by wildfires and the local atmospheric wind and temperature fields. At Los Alamos National Laboratory, the authors have developed a modeling system that includes this interaction by coupling a high resolution atmospheric dynamics model, HIGRAD, with a fire behavior model, BEHAVE, to predict the spread of wildfires. The HIGRAD/BEHAVE model is run at very high resolution to properly resolve the fire/atmosphere interaction. At present, these coupled wildfire model simulations are computationally intensive. The additional complexity of these models require sophisticated methods for assuring their reliability in real world applications. With this in mind, a substantial part of the research effort is directed at model validation. Several instrumented prescribed fires have been conducted with multi-agency support and participation from chaparral, marsh, and scrub environments in coastal areas of Florida and inland California. In this paper, the authors first describe the data required to initialize the components of the wildfire modeling system. Then they present results from one of the Florida fires, and discuss a strategy for further testing and improvement of coupled weather/wildfire models
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Coupled Weather and Wildfire Behavior Modeling at Los Alamos: An Overview
Over the past two years, researchers at Los Alamos National Laboratory (LANL) have been engaged in coupled weather/wildfire modeling as part of a broader initiative to predict the unfolding of crisis events. Wildfire prediction was chosen for the following reasons: (1) few physics-based wild-fire prediction models presently exist; (2) LANL has expertise in the fields required to develop such a capability; and (3) the development of this predictive capability would be enhanced by LANL`s strength in high performance computing. Wildfire behavior models have historically been used to predict fire spread and heat release for a prescribed set of fuel, slope, and wind conditions (Andrews 1986). In the vicinity of a fire, however, atmospheric conditions are constantly changing due to non-local weather influences and the intense heat of the fire itself. This non- linear process underscores the need for physics-based models that treat the atmosphere-fire feedback. Actual wildfire prediction with full-physics models is both time-critical and computationally demanding, since it must include regional- to local-scale weather forecasting together with the capability to accurately simulate both intense gradients across a fireline, and atmosphere/fire/fuel interactions. Los Alamos has recently (January 1997) acquired a number of SGI/Cray Origin 2000 machines, each presently having 32 to 64 processors. These high performance computing systems are part of the Department of Energy`s Accelerated Strategic Computing Initiative (ASCI). While offering impressive performance now, upgrades to the system promise to deliver over 1 Teraflop (10(12) floating point operations per second) at peak performance before the turn of the century
High-Yield Expression of Heterologous [FeFe] Hydrogenases in Escherichia coli
BACKGROUND: The realization of hydrogenase-based technologies for renewable H(2) production is presently limited by the need for scalable and high-yielding methods to supply active hydrogenases and their required maturases. PRINCIPAL FINDINGS: In this report, we describe an improved Escherichia coli-based expression system capable of producing 8-30 mg of purified, active [FeFe] hydrogenase per liter of culture, volumetric yields at least 10-fold greater than previously reported. Specifically, we overcame two problems associated with other in vivo production methods: low protein yields and ineffective hydrogenase maturation. The addition of glucose to the growth medium enhances anaerobic metabolism and growth during hydrogenase expression, which substantially increases total yields. Also, we combine iron and cysteine supplementation with the use of an E. coli strain upregulated for iron-sulfur cluster protein accumulation. These measures dramatically improve in vivo hydrogenase activation. Two hydrogenases, HydA1 from Chlamydomonas reinhardtii and HydA (CpI) from Clostridium pasteurianum, were produced with this improved system and subsequently purified. Biophysical characterization and FTIR spectroscopic analysis of these enzymes indicate that they harbor the H-cluster and catalyze H(2) evolution with rates comparable to those of enzymes isolated from their respective native organisms. SIGNIFICANCE: The production system we describe will facilitate basic hydrogenase investigations as well as the development of new technologies that utilize these prolific H(2)-producing enzymes. These methods can also be extended for producing and studying a variety of oxygen-sensitive iron-sulfur proteins as well as other proteins requiring anoxic environments
The Impacts of Dry Dynamic Cores on Asymmetric Hurricane Intensification
The fundamental pathways for tropical cyclone (TC) intensification are explored by considering axisymmetric and asymmetric impulsive thermal perturbations to balanced, TC-like vortices using the dynamic cores of three different nonlinear numerical models. Attempts at reproducing the results of previous work, which used the community WRF Model, revealed a discrepancy with the impacts of purely asymmetric thermal forcing. The current study finds that thermal asymmetries can have an important, largely positive role on the vortex intensification, whereas other studies find that asymmetric impacts are negligible. Analysis of the spectral energetics of each numerical model indicates that the vortex response to asymmetric thermal perturbations is significantly damped in WRF relative to the other models. Spectral kinetic energy budgets show that this anomalous damping is primarily due to the increased removal of kinetic energy from the vertical divergence of the vertical pressure flux, which is related to the flux of inertia-gravity wave energy. The increased kinetic energy in the other two models is shown to originate around the scales of the heating and propagate upscale with time from nonlinear effects. For very large thermal amplitudes (50 K), the anomalous removal of kinetic energy due to inertia-gravity wave activity is much smaller, resulting in good agreement between models. The results of this paper indicate that the numerical treatment of small-scale processes that project strongly onto inertia-gravity wave energy can lead to significant differences in asymmetric TC intensification. Sensitivity tests with different time integration schemes suggest that diffusion entering into the implicit solution procedure is partly responsible for the anomalous damping of energy
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Tracer Modeling in an Urban Environment
The accurate simulation of the transport of a tracer released into an urban area requires sufficiently high model resolution to resolve buildings and urban street canyons. Within the authors' group a modeling effort has been underway to develop a model -- termed HIGRAD -- capable of simulating flow at the high spatial resolution required within the urban environment. HIGRAD uses state-of-the-art numerical techniques to accurately simulate the regions of strong shear found near edges of buildings. HIGRAD also employs a newly developed radiation package which in addition to standard shortwave and longwave heating/cooling effects can account for the shadowing effects of building complexes on the urban flow field. Idealized simulations have been conducted which clearly illustrate the role radiation plays in transport and dispersion in an urban setting. The authors have also modeled the flow of an inert tracer in a realistic, complex urban environment. Complex flow/building interactions were produced during the simulation and these interactions had a significant impact on the transport of the tracer
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Development of the First Nonhydrostatic Nested-Grid Grid-Point Global Atmospheric Modeling System on Parallel Machines
This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Evaluating the importance of global and regional climate response to increasing atmospheric concentrations of greenhouse gases requires a comprehensive global atmospheric modeling system (GAMS) capable of simulations over a wide range of atmospheric circulations, from complex terrain to continental scales, on high-performance computers. Unfortunately, all of the existing global circulation models (GCMs) do not meet this requirements, because they suffer from one or more of the following three shortcomings: (1) use of the hydrostatic approximation, which makes the models potentially ill-posed; (2) lack of a nested-grid (or multi-grid) capability, which makes it difficult to consistently evaluate the regional climate response to the global warming, and (3) spherical spectral (opposed to grid-point finite-difference) representation of model variables, which hinders model performance for parallel machine applications. The end product of the research is a highly modularized, multi-gridded, self-calibratable (for further parameterization development) global modeling system with state-of-the-science physics and chemistry. This system will be suitable for a suite of atmospheric problems: from local circulations to climate, from thunderstorms to global cloud radiative forcing, from urban pollution to global greenhouse trace gases, and from the guiding of field experiments to coupling with ocean models. It will also provide a unique testbed for high-performance computing architecture