15 Matching Results

Search Results

Advanced search parameters have been applied.

A High-Resolution Global Climate Simulation

Description: A major factor limiting the quality and usefulness of global climate models is the coarse spatial resolution of these models. Global climate models today are typically run at resolutions of {approx}300 km (or even coarser) meaning that the smallest features represented are 300 km across. As Figure 1 shows, this resolution does not allow adequate representation of small or even large topographic features (e.g. the Sierra Nevada mountains). As a result of this and other problems, coarse-resolution global models do not come close to accurately simulating climate on regional spatial scales (e.g. within California). Results on continental and larger sales are much more realistic. An important consequence of this inability to simulate regional climate is that global climate model results cannot be used as the basis of assessments of potential societal impacts of climate change (e.g. effects on agriculture in the Central Valley, on management of water resources, etc.).
Date: January 23, 2001
Creator: Duffy, P B
Partner: UNT Libraries Government Documents Department

Global warming and changes in ocean circulation

Description: This final report provides an overview of the goals and accomplishments of this project. Modeling and observational work has raised the possibility that global warming may cause changes in the circulation of the ocean. If such changes would occur they could have important climatic consequences. The first technical goal of this project was to investigate some of these possible changes in ocean circulation in a quantitative way, using a state-of -the-art numerical model of the ocean. Another goal was to develop our ocean model, a detailed three-dimensional numerical model of the ocean circulation and ocean carbon cycles. A major non-technical goal was to establish LLNL as a center of excellence in modelling the ocean circulation and carbon cycle.
Date: February 1998
Creator: Duffy, P. B. & Caldeira, K. C.
Partner: UNT Libraries Government Documents Department

Interpretation of Recent Temperature Trends in California

Description: Regional-scale climate change and associated societal impacts result from large-scale (e.g. well-mixed greenhouse gases) and more local (e.g. land-use change) 'forcing' (perturbing) agents. It is essential to understand these forcings and climate responses to them, in order to predict future climate and societal impacts. California is a fine example of the complex effects of multiple climate forcings. The State's natural climate is diverse, highly variable, and strongly influenced by ENSO. Humans are perturbing this complex system through urbanization, irrigation, and emission of multiple types of aerosols and greenhouse gases. Despite better-than-average observational coverage, we are only beginning to understand the manifestations of these forcings in California's temperature record.
Date: September 21, 2007
Creator: Duffy, P B; Bonfils, C & Lobell, D
Partner: UNT Libraries Government Documents Department

Advanced integrated modeling and measurement: The global carbon cycle

Description: Most of the carbon dioxide added to the atmosphere by human activities comes from burning fossil fuels Only about half the CO2 we release into the atmosphere remains there, however, and the fate of the CO2 that does not remain in the atmosphere is uncertain As carbon dioxidecomes in contact with the sea surface it may be absorbed into the ocean, and as it comes in contact with the leaves of plants it may be absorbed and transformed into plant tissue, but the rates at which the sea or land plants can absorb CO2 are poorly characterized Hence, there is a great deal of uncertainty as to how much of the CO2 we release today will be found in the ocean, or in land plants, or in the atmosphere 10, 20 or 100 years from now The nanowing of these uncertainties is essential to making reliable predictions of the climate consequences of fossil fuel burning and deforestation
Date: June 1, 1998
Creator: Duffy, P. B.
Partner: UNT Libraries Government Documents Department

Detection of anthropogenic climate change: a modeling study

Description: This project involved two related areas of research: (1) simulating natural climate variability using a global climate model, and (2) using the computer resources of the Accelerated Strategic Computing Initiative (ASCI) Blue computer for specific problems in atmospheric science and climate. Although originally scheduled to last two years, this ER project ended after one year; the work is begin continued under a larger (Strategic Initiative) project which started in FY99.
Date: February 17, 1998
Creator: Duffy, P B & Eltgroth, P G
Partner: UNT Libraries Government Documents Department

Climate Modeling using High-Performance Computing

Description: The Center for Applied Scientific Computing (CASC) and the LLNL Atmospheric Science Division (ASD) are working together to improve predictions of future climate by applying the best available computational methods and computer resources to this problem. Over the last decade, researchers at the Lawrence Livermore National Laboratory (LLNL) have developed a number of climate models that provide state-of-the-art simulations on a wide variety of massively parallel computers. We are now developing and applying a second generation of high-performance climate models. As part of LLNL's participation in DOE's Scientific Discovery through Advanced Computing (SciDAC) program, members of CASC and ASD are collaborating with other DOE labs and NCAR in the development of a comprehensive, next-generation global climate model. This model incorporates the most current physics and numerics and capably exploits the latest massively parallel computers. One of LLNL's roles in this collaboration is the scalable parallelization of NASA's finite-volume atmospheric dynamical core. We have implemented multiple two-dimensional domain decompositions, where the different decompositions are connected by high-speed transposes. Additional performance is obtained through shared memory parallelization constructs and one-sided interprocess communication. The finite-volume dynamical core is particularly important to atmospheric chemistry simulations, where LLNL has a leading role.
Date: March 3, 2005
Creator: Mirin, A A; Wickett, M E; Duffy, P B & Rotman, D A
Partner: UNT Libraries Government Documents Department

Present and Future Surface Climate in the Western U.S. as Simulated by 15 Global Climate Models

Description: We analyze results of 15 global climate simulations contributed to the Coupled Model Intercomparison Project (CMIP). Focusing on the western U.S., we consider both present climate simulations and predicted responses to increasing atmospheric CO{sub 2}. The models vary in their ability to predict the present climate. Over the western U.S., a few models produce a seasonal cycle for spatially-averaged temperature and/or precipitation in good agreement with observational data. Other models tend to overpredict precipitation in the winter or exaggerate the amplitude of the seasonal cycle of temperature. The models also differ in their ability to reproduce the spatial patterns of temperature and precipitation in the U.S. Considering the monthly mean precipitation responses to doubled atmospheric CO{sub 2}, averaged over the western U.S., we find some models predict increases while others predict decreases. The predicted temperature response, on the other hand, is invariably positive over this region; however, for each month, the range of values given by the different models is large compared to the mean model response. We look for possible relationships between the models' temperature and precipitation responses to doubled CO{sub 2} concentration and their ability to simulate some aspects of the present climate. We find that these relationships are weak, at best. The precipitation response over the western U.S. in DJF and the precipitation response over the mid- and tropical latitudes seem to be correlated with the RMS error in simulated present-day precipitation, also calculated over the mid- and tropical latitudes. However, considering only the responses of the models with the smallest RMS errors does not provide a different estimate of the precipitation response to a doubled CO{sub 2} concentration, because even among the most accurate models, the range of model responses is so large. For temperature, we find that models that have smaller RMS errors in present-climate ...
Date: August 9, 2004
Creator: Coquard, J; Duffy, P B; Taylor, K E & Iorio, J P
Partner: UNT Libraries Government Documents Department

Effects of Model Resolution and Subgrid-Scale Physics on the Simulation of Daily Precipitation in the Continental United States

Description: We analyze simulations of the global climate performed at a range of spatial resolutions to assess the effects of horizontal spatial resolution on the ability to simulate precipitation in the continental United States. The model investigated is the CCM3 general circulation model. We also preliminarily assess the effect of replacing cloud and convective parameterizations in a coarse-resolution (T42) model with an embedded cloud-system resolving model (CSRM). We examine both spatial patterns of seasonal-mean precipitation and daily-timescale temporal variability of precipitation in the continental United States. For DJF and SON, high-resolution simulations produce spatial patterns of seasonal-mean precipitation that agree more closely with observed precipitation patterns than do results from the same model (CCM3) at coarse resolution. However, in JJA and MAM, there is little improvement in spatial patterns of seasonal-mean precipitation with increasing resolution, particularly in the Southeast. This is owed to the dominance of convective (i.e., parameterized) precipitation in these two seasons. We further find that higher-resolution simulations have more realistic daily precipitation statistics. In particular, the well-known tendency at coarse resolution to have too many days with weak precipitation and not enough intense precipitation is partially eliminated in higher-resolution simulations. However, even at the highest resolution examined here (T239), the simulated intensity of the mean and of high-percentile daily precipitation amounts is too low. This is especially true in the Southeast, where the most extreme events occur. A new GCM, in which a cloud-resolving model (CSRM) is embedded in each grid cell and replaces convective and stratiform cloud parameterizations, solves this problem, and actually produces too much precipitation in the form of extreme events. However, in contrast to high-resolution versions of CCM3, this model produces little improvement in spatial patterns of seasonal-mean precipitation compared to models at the same resolution using traditional parameterizations. Thus, our results suggest that ...
Date: July 28, 2004
Creator: Duffy, P B; Iorio, J P; Govindasamy, B; Thompson, S L; Khairoutdinov, M & Randall, D
Partner: UNT Libraries Government Documents Department

A parallel coupled oceanic-atmospheric general circulation model

Description: The Climate Systems Modeling group at LLNL has developed a portable coupled oceanic-atmospheric general circulation model suitable for use on a variety of massively parallel (MPP) computers of the multiple instruction, multiple data (MIMD) class. The model is composed of parallel versions of the UCLA atmospheric general circulation model, the GFDL modular ocean model (MOM) and a dynamic sea ice model based on the Hiber formulation extracted from the OPYC ocean model. The strategy to achieve parallelism is twofold. One level of parallelism is accomplished by applying two dimensional domain decomposition techniques to each of the three constituent submodels. A second level of parallelism is attained by a concurrent execution of AGCM and OGCM/sea ice components on separate sets of processors. For this functional decomposition scheme, a flux coupling module has been written to calculate the heat, moisture and momentum fluxes independent of either the AGCM or the OGCM modules. The flux coupler`s other roles are to facilitate the transfer of data between subsystem components and processors via message passing techniques and to interpolate and aggregate between the possibly incommensurate meshes.
Date: December 1, 1994
Creator: Wehner, M. F.; Bourgeois, A. J.; Eltgroth, P. G.; Duffy, P. B. & Dannevik, W. P.
Partner: UNT Libraries Government Documents Department

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

Description: 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.
Date: December 1, 1996
Creator: Mirin, A.A.; Dannevik, W.P.; Chan, B.; Duffy, P.B.; Eltgroth, P.G. & Wehner, M.F.
Partner: UNT Libraries Government Documents Department

Coupled ocean/atmosphere modeling on high-performance computing systems

Description: We investigate performance of a coupled ocean/atmosphere general circulation model on high-performance computing systems. Our programming paradigm has been domain decomposition with message- passing for distributed memory. With the emergence of SMP clusters we are investigating how to best support shaped memory as well. We consider how to assign processes to the major model components so as to obtain optimal load balance. We examine throughput on contemporary parallel architectures, such as the Cray-I3D, I3B, and the IBM-SP family.
Date: December 1, 1996
Creator: Eltgroth, P.G.; Bolstad, J.H.; Duffy, P.B.; Mirin, A.A.; Wang, H. & Wehner, M.F.
Partner: UNT Libraries Government Documents Department

Coupled ocean/atmosphere modeling on high-performance computing systems

Description: We investigate performance of a coupled ocean/atmosphere general circulation model on high-performance computing systems. Our programming paradigm has been domain decomposition with message- passing for distributed memory. With the emergence of SMP clusters we are investigating how to best support shared memory as well. We consider how to assign processors to the major model components so as to obtain optimal load balance. We examine throughput on contemporary parallel architectures, such as the Cray-T3D/T3E and the IBM-SP family.
Date: March 1, 1997
Creator: Eltgroth, P.G.; Bolstad, J.H.; Duffy, P.B.; Mirin, A.A.; Wang, H. & Wehner, M.F.
Partner: UNT Libraries Government Documents Department

Simulations of present and future climates in the western U.S. with four nested regional climate models

Description: We analyze simulations of present and future climates in the western U.S. performed with four regional climate models (RCMs) nested within two global ocean-atmosphere climate models. Our primary goal is to assess the range of regional climate responses to increased greenhouse gases in available RCM simulations. The four RCMs used different geographical domains, different increased greenhouse gas scenarios for future-climate simulations, and (in some cases) different lateral boundary conditions. For simulations of the present climate, we compare RCM results to observations and to results of the GCM that provided lateral boundary conditions to the RCM. For future-climate (increased greenhouse gas) simulations, we compare RCM results to each other and to results of the driving GCMs. When results are spatially averaged over the western U.S., we find that the results of each RCM closely follow those of the driving GCM in the same region, in both present and future climates. In present-climate simulations, the RCMs have biases in spatially-averaged simulated precipitation and near-surface temperature that seem to be very close to those of the driving GCMs. In future-climate simulations, the spatially-averaged RCM-projected responses in precipitation and near-surface temperature are also very close to those of the respective driving GCMs. Precipitation responses predicted by the RCMs are in many regions not statistically significant compared to interannual variability. Where the predicted precipitation responses are statistically significant, they are positive. The models agree that near-surface temperatures will increase, but do not agree on the spatial pattern of this increase. The four RCMs produce very different estimates of water content of snow in the present climate, and of the change in this water content in response to increased greenhouse gases.
Date: June 15, 2004
Creator: Duffy, P B; Arritt, R W; Coquard, J; Gutowski, W; Han, J; Iorio, J et al.
Partner: UNT Libraries Government Documents Department

Comprehensive climate system modeling on massively parallel computers

Description: A better understanding of both natural and human induced changes to the Earth`s climate is necessary for policy makers to make informed decisions regarding energy usage and other greenhouse gas producing activities. To achieve this, substantial increases in the sophistication of climate models are required. Coupling between the climate subsystems of the atmosphere, oceans, cryosphere and biosphere is only now beginning to be explored in global models. the enormous computational expenses of such models is one significant factor limiting progress. A comprehensive climate system model targeted to distributed memory massively parallel processing (MPP) computers is under development at Lawrence Livermore National Laboratory. This class of computers promises the computational power to permit the timely execution of climate models of substantially more sophistication than current generation models. Our strategy for achieving high performance on large numbers of processors is to exploit the multiple layers of parallelism naturally contained within highly coupled global climate models. The centerpiece of this strategy is the concurrent execution of multiple independently parallelized components of the climate system model. This methodology allows the assignment of an arbitrary number of processors to each of the major climate subsystems. Hence, a higher total number of processors may be efficiently used. Furthermore, load imbalances arising from the coupling of submodels may be minimized by adjusting the distribution of processors among the submodels.
Date: October 1, 1996
Creator: Wehner, M.F.; Eltgroth, P.G.; Mirin, A.A.; Duffy, P.B.; Caldeira, K.G.; Bolstad, J.H. et al.
Partner: UNT Libraries Government Documents Department