Mariner-9 based simulation of radiative convective temperature changes in the Martian dust-laden atmosphere-soil system

A numerical simulation of radiative, conductive, and convective heat transfer of the Martian dust-laden atmosphere-soil system is presented with particular emphasis given to heating/cooling in regions of sharp variation in temperature or absorption and its resultant impact on outgoing planetary spectral radiance, as measured by the Mariner 9 IRIS. Thermal coupling between the ground and atmospheric subsystems is modeled by the total heat flux balance at the interface. In the simulation procedure, local thermodynamic equilibrium (LTE) is assumed, and a combined strong-weak line transmission function permits short- and long-range exchanges of energy from the surface toward space. Direct absorption of insolation in the near-IR bands by both silicate dust and CO2 is incorporated

Is Climate Change Predictable? Really?

This project is the first application of a completely different approach to climate modeling, in which new prognostic equations are used to directly compute the evolution of two-point correlations. This project addresses three questions that are critical for the credibility of the science base for climate prediction: (1) What is the variability spectrum at equilibrium? (2) What is the rate of relaxation when subjected to external perturbations? (3) Can variations due to natural processes be distinguished from those due to transient external forces? The technical approach starts with the evolution equation for the probability distribution function and arrives at a prognostic equation for ensemble-mean two-point correlations, bypassing the detailed weather calculation. This work will expand our basic understanding of the theoretical limits of climate prediction and stimulate new experiments to perform with conventional climate models. It will furnish statistical estimates that are inaccessible with conventional climate simulations and likely will raise important new questions about the very nature of climate change and about how (and whether) climate change can be predicted. Solid progress on such issues is vital to the credibility of the science base for climate change research and will provide policymakers evaluating tradeoffs among energy technology options and their attendant environmental and economic consequences

Climate system modeling on massively parallel systems: LDRD Project 95-ERP-47 final report

Global warming, acid rain, ozone depletion, and biodiversity loss are some of the major climate-related issues presently being addressed by climate and environmental scientists. Because unexpected changes in the climate could have significant effect on our economy, it is vitally important to improve the scientific basis for understanding and predicting the earth`s climate. The impracticality of modeling the earth experimentally in the laboratory together with the fact that the model equations are highly nonlinear has created a unique and vital role for computer-based climate experiments. However, today`s computer models, when run at desired spatial and temporal resolution and physical complexity, severely overtax the capabilities of our most powerful computers. Parallel processing offers significant potential for attaining increased performance and making tractable simulations that cannot be performed today. The principal goals of this project have been to develop and demonstrate the capability to perform large-scale climate simulations on high-performance computing systems (using methodology that scales to the systems of tomorrow), and to carry out leading-edge scientific calculations using parallelized models. The demonstration platform for these studies has been the 256-processor Cray-T3D located at Lawrence Livermore National Laboratory. Our plan was to undertake an ambitious program in optimization, proof-of-principle and scientific study. These goals have been met. We are now regularly using massively parallel processors for scientific study of the ocean and atmosphere, and preliminary parallel coupled ocean/atmosphere calculations are being carried out as well. Furthermore, our work suggests that it should be possible to develop an advanced comprehensive climate system model with performance scalable to the teraflops range. 9 refs., 3 figs

Large eddy simulation of two-dimensional isotropic turbulence

Large eddy simulation (LES) of forced, homogeneous, isotropic, two-dimensional (2D) turbulence in the energy transfer subrange is the subject of this paper. A difficulty specific to this LES and its subgrid scale (SGS) representation is in that the energy source resides in high wave number modes excluded in simulations. Therefore, the SGS scheme in this case should assume the function of the energy source. In addition, the controversial requirements to ensure direct enstrophy transfer and inverse energy transfer make the conventional scheme of positive and dissipative eddy viscosity inapplicable to 2D turbulence. It is shown that these requirements can be reconciled by utilizing a two-parametric viscosity introduced by Kraichnan (1976) that accounts for the energy and enstrophy exchange between the resolved and subgrid scale modes in a way consistent with the dynamics of 2D turbulence; it is negative on large scales, positive on small scales and complies with the basic conservation laws for energy and enstrophy. Different implementations of the two-parametric viscosity for LES of 2D turbulence were considered. It was found that if kept constant, this viscosity results in unstable numerical scheme. Therefore, another scheme was advanced in which the two-parametric viscosity depends on the flow field. In addition, to extend simulations beyond the limits imposed by the finiteness of computational domain, a large scale drag was introduced. The resulting LES exhibited remarkable and fast convergence to the solution obtained in the preceding direct numerical simulations (DNS) by Chekhlov et al. (1994) while the flow parameters were in good agreement with their DNS counterparts. Also, good agreement with the Kolmogorov theory was found. This LES could be continued virtually indefinitely. Then, a simplifiedComment: 34 pages plain tex + 18 postscript figures separately, uses auxilary djnlx.tex fil

Three-dimensional high-resolution simulations of Rayleigh-Taylor instability and turbulent mixing

Preliminary results of three-dimensional simulations of compressible Rayleigh-Taylor instability and turbulent mixing in an ideal gas using the piecewise-parabolic method (PPM) (with and without molecular dissipation terms) are presented. Simulations with spatial resolutions up to 512{sup 3} were performed. Two types of convergence studies are presented. Statistical analyses of the data are discussed, include: 1: spectra, and; 2) horizontally-averaged terms in the kinetic energy and onstrophy density evolution equations. The application of this statistical data to the development and testing of subgrid-scale models appropriate for compressible Rayleigh-Taylor instability-induced turbulent mixing is discussed

Three-dimensional high-resolution simulations of compressible rayleigh-taylor instability and turbuelnt mixing

Preliminary results of three-dimensional simulations of compressible Rayleigh-Taylor instabilities and turbulent mixing in an ideal gas using the piecewise-parabolic method (PPM) with and without molecular dissipation terms are presented. Simulations with spatial resolutions up to 512 were performed. Two types of convergence studies are presented. The first investigates the Reynolds numbers for which the simulations with molecular dissipation are converged with respect to spatial resolution, and the second investigates whether PPM simulations at different spatial resolutions reproduce fully-resolved PPM simulations with molecular dissipation. Finally, statistical analyses of the data are discussed, including spectra and horizontally-averaged terms in the kinetic energy and enstrophy density evolution equations. The application of this statistical data to the development and testing of subgrid-scale models appropriate for compressible Rayleigh-Taylor instability-induced turbulent mixing is discussed

Three Dimensional High-Resolution Simulations of Richtmyer-Meshkov Mixing and Shock-Turbulence Interaction

Three-dimensional high-resolution simulations are performed of the Richtmyer-Meshkov (RM) instability for a Mach 6 shock, and of the passage of a second shock from the same side through a developed RM instability. The second shock is found to rapidly smear fine structure and strongly enhance mixing. Studies of the interaction of moderately strong shocks with a pre-existing turbulent field indicate amplification of transverse vorticity and reduction of stream-wise vorticity, as well as the mechanisms for these changes

Three-Dimensional Simulations of Compressible Turbulence on High-Performance Computing Systems

A three-dimensional hydrodynamics code based on the Piecewise Parabolic Method (PPM) is used to examine compressible fluid turbulence in three dimensions. The code runs on a number of parallel architectures, including MPP s and SMP clusters. We consider problems of current interest, such as Rayleigh-Taylor and RichtmyerMeshkov instability and turbulent mixing, and interactions of a shock with pre-existing turbulence. We present performance results on leading-edge platforms, including those supported under the DOE Accelerated Strategic Computing Initiative (ASCI). 1 Introduction In many hydrodynamics applications, the relevant length scales range over several orders of magnitude, so that finite-difference direct numerical simulations (DNS) are computationally not feasible for the driving parameters of interest. To simulate the dynamically important range of scales, large-eddy simulations (LES) are performed instead, in which the dynamical effects of the unresolved scales are modeled by..

Very High Resolution Simulation of Compressible Turbulence on the IBM-SP System

Understanding turbulence and mix in compressible flows is of fundamental importance to real-world applications such as chemical combustion and supernova evolution. The ability to run in three dimensions and at very high resolution is required for the simulation to accurately represent the interaction of the various length scales, and consequently, the reactivity of the intermixing species. Toward this end, we have carried out a very high resolution (over 8 billion zones) 3-D simulation of the Richtmyer-Meshkov instability and turbulent mixing on the IBM Sustained Stewardship TeraOp (SST) system, developed under the auspices of the Department of Energy (DOE) Accelerated Strategic Computing Initiative (ASCI) and located at Lawrence Livermore National Laboratory. We have also undertaken an even higher resolution proof-of-principle calculation (over 24 billion zones) on 5832 processors of the IBM, which executed for over an hour at a sustained rate of 1.05 Top/s, as well as a sh..