Community models

Developing numerical models and making them available to the scientific community is at the heart of ESSL’s research and service to the community. Leading the way are the Community Climate System Model (CCSM) and the Weather Research and Forecasting Model (WRF). CCSM is a coupled model combining representations of the atmosphere, ocean, land, and sea ice. WRF is a next-generation mesoscale numerical weather prediction system designed to serve both operational forecasting and atmospheric research needs. There is strong community participation both in developing the models and in using them. Additionally, ESSL continues to develop and use together with the community to a lesser extent a variety of other models within ESSL. This combined model development will contribute to the creation of a comprehensive Earth System Model, a top priority for ESSL and a task that will likely be undertaken in collaboration with CISL. This system will be developed around the interactions of the Earth’s physical, chemical and biogeophysical systems with future inclusion of human and societal elements. Described below are ESSL’s accomplishments and projects related to community models, research models and the creation of an Earth system model, with NCAR highlights on CCSM and the NCAR participation to the IPCC campaign, and on the CGD-MMM collaboration on Nested Regional Climate modeling which, for relatively short timescales, will allow for a direct input to societal and economical matters.

CCSM and IPCC [NAR Highlight w/Detail] - CGD
WRF - MMM

CCSM AND IPCC

	Figure 1. The annual mean Arctic sea ice thickness averaged over years 401 – 410 from the new run using the FV atmospheric core (b30.081) and the CCSM3 T85 version (b30.009). The figure shows comparable sea ice distributions in the Labrador Sea. The difference plot shows that the new FV run has a thicker, more realistic sea ice thickness over much of the Arctic Ocean, and especially north of Canada and Greenland. High resolution figure
	Figure 2. The mean precipitation distribution during December-February (left) and June-August (right) from observations (top) and the CCSM3 (bottom). The observed fields are satellite-based estimates over 1979-2000; the simulated fields are from 100 years of CCSM3 data. The CCSM3 simulation captures many of the observed features in the global precipitation distribution, although it is not perfect. The reduction of systematic differences from the observations is a high priority of ESSL research. High resolution figure

Historical context and rationale

The development and continuous improvement of a comprehensive climate modeling system that is at the forefront of international efforts to understand and predict the behavior of the Earth’s climate is a high priority of NCAR research. This includes the Community Climate System Model (CCSM) as well as its component models. The CCSM, run on some of the world’s most powerful supercomputers, simulates the many interconnected events that drive Earth’s climate. These include changes in the atmosphere and oceans, the ebb and flow of sea ice, and the subtle impacts of forests and rivers.

CCSM is unique among powerful models. Primarily supported by the National Science Foundation (NSF) and the Department of Energy (DOE), with additional support from the National Aeronautics and Space Administration (NASA) and the National Oceanic and Atmospheric Administration (NOAA), it belongs to the entire community of climate scientists, rather than to a single institution. Hundreds of specialists from across the United States and overseas collaborate on improvements to CCSM. The model’s underlying computer code is freely available on the Web. As a result, scientists throughout the world can use CCSM for their climate experiments.

The CCSM project was started in 1994, although climate modeling at NCAR has a much longer history than this stretching back to about 1980. The first version of CCSM was unveiled in 1998, and the most recent version, CCSM-3, was released in 2004. CCSM-3 represents a major advance over earlier versions of the model because it contains far more information about Earth’s physical processes. For example, it tracks the flow of major rivers that empty into the oceans and influence currents such as the Gulf Stream, and it now resolves five different thickness categries of sea ice within each grid cell, such as the thickness and the melt rate. Moreover, the finer scale of its resolution allows scientists to capture significantly greater detail about ocean currents and the mixing of salt and fresh water.

CCSM is constantly being updated and improved, CCSM4 is most likely to be released in 2009. In addition to remaining at the forefront of international modeling efforts, the scientific goals of the CCSM project are as follows:

• to use the modeling system to investigate and understand the mechanisms that lead to interdecadal, interannual, and seasonal variability in Earth’s climate;
• to explore the history of Earth’s climate through the application of versions of the CCSM suitable for paleoclimate simulations; and
• to apply this modeling system to estimate the likely future of Earth's environment in order to provide information required by governments in support of local, state, national, and international policy determination.

Accomplishments in FY 2006

A major project that has involved ESSL staff has been development of the Fourth Assessment Report (AR4) by Working Group One (WG I) of the Intergovernmental Panel on Climate Change (IPCC). ESSL scientists have served as convening lead authors, lead authors, and many as contributing authors. ESSL scientists have also reviewed chapters for WG I as well as WG II, and they have contributed to the Technical summary and Summary for Policy Makers. The research of ESSL is prominently featured in the IPCC AR4.

In addition, the CCSM project played a major role in the IPCC AR4 through the completion and analysis of an extensive series of emission scenario experiments. The suite of CCSM-3 experiments is the most extensive and highest-resolution multimember ensemble of any of the international global coupled models run for the IPCC AR4. The resulting large data sets are freely available to the climate research and education community via the Earth System Grid (ESG), and a subset of the data is archived at the DOE Program for Climate Model Diagnosis and Intercomparison (PCMDI). The CCSM data are part of the Climate Model Evaluation Project (CMEP), which includes over 200 researchers from around the world who analyzed the multi-model data set for the IPCC AR4.

A major accomplishment in FY06 was that ESSL scientists, with external collaborators, played a role not only in CMEP, but in describing, documenting and analyzing the CCSM-3 for the broader climate research community. In particular, results from the CCSM-3 have been documented in two special issues of leading journals. The software engineering aspects of CCSM3, including its performance and portability, were documented in a special issue of the Journal for High Performance Computing Applications. In addition, 26 original research papers from nearly 100 authors, nearly half of whom come from outside of NCAR, appeared in a special issue of the Journal of Climate. The papers include an overview of CCSM-3; descriptions of the climate state for each component model; documentation of the responses of the model to past, present, and future forcing states; an evaluation of the major coupled modes of variability; and a documentation of the climate sensitivity of the model. In general, the climate for present-day conditions produced by CCSM-3 has greater fidelity to the observed climate than do simulations from previous generations of CCSM.

Another accomplishment of the past year was the production of a coupled integration that is as good as that from the CCSM-3, but using the Finite Volume (FV) dynamical core in the atmosphere component. Previous attempts using the FV core had produced a too cold Arctic climate and too much sea ice, especially in the Labrador Sea. This was corrected by changing the horizontal viscosity parameterization in the ocean component, which produced a much more realistic, warmer climate in the central Labrador Sea. The sea ice distributions from the new FV version and the released CCSM-3 version are very comparable (Figure 1). The new coupled run using the FV core was run out for 410 years, and this version of the CCSM will now form the basis for future model development. Using the FV core is very important when chemistry is added to the model, for example, because of its conservation properties.

A third accomplishment has been made by the CCSM Software Engineering Group (CSEG). A single executable version of the multiple-executable (MPMD), concurrent CCSM has been produced and validated. The single executable implementation is easier to port and debug than the MPMD version, and it will also be able to run on machines that do not currently support MPMD implementations, such as the NCAR IBM BlueGene/L.

CSEG has ported CCSM to the Oak Ridge National Laboratory (ORNL) Cray X1 and Cray XT3 and the NCAR IBM Linux Cluster. Current work is underway to port CCSM to the NCAR IBM Bluegene/L. CSEG has also put in place numerous infrastructure improvements. A new testing framework has been implemented to ensure system robustness as new science is incorporated across model components. A new model run database is being created that will permit CCSM runs to be easily reproduced, searched and documented. And a user-friendly performance utility has been created that provides users with the capability of easily determining the optimal load-balanced configuration for their production runs.

In FY06, the CCSM data models were completely rewritten to ensure uniform functionality and code re-use across all data model components. In addition, new slab-ocean functionality was added to the data ocean model. The new data models have been an integral part of the land component inter-comparison and the biogeochemistry spin-up experiments. Significant progress has also been made in the creation of a sequential, single-executable CCSM. The goal is to create a sequential system that contains backwards compatibility with the current concurrent system, provides "plug and play" capability of data and active components and produces the same climate as the current concurrent system.

Plans for FY 2007

One of the higher-priority short-term activities of the CCSM program is a concerted effort to address systematic model biases in the tropics on seasonal and longer time scales, such as the appearance of a double Inter-Tropical Convergence Zone (Figure 2) and warm sea surface temperatures (SST) under the stratocumulus regions off the west coasts of North America, South America and Africa. Several hypothesis-driven activities are under way in collaboration with colleagues outside of NCAR to address such biases, which are common in other global models as well. In addition, new collaborative efforts have started within ESSL to examine, in climate simulations with embedded regional models, the importance of explicitly resolving mesoscale and microscale processes that govern weather and local climate but that may also have significant impacts on the large-scale circulation.

The reduction of such biases becomes even more important as the complexity of CCSM increases. Several of the most pressing scientific questions regarding the climate system and its response to natural and anthropogenic forcing require that physical models be extended to include the interactions of climate with biogeochemistry, atmospheric chemistry, ecosystems, glaciers and ice sheets, and anthropogenic environmental change. While the ultimate goal is a comprehensive Earth System Model (ESM), practical considerations suggest that there will be a multitude of versions with different capabilities. The CCSM project will work towards developing a first-generation coupled chemistry-climate model in the next two to three years. A project of this scope will necessarily involve scientific partnerships across ESSL, NCAR, and the external CCSM community. This model could be used to study the complex interactions among biota, chemical processes, and physical climate for paleoclimate studies or scenarios for future climate change. It could also be used to study variations of the chemistry of the present-day atmosphere driven by external forcing from solar variability and major internal natural modes of variability, such as the El Niño–Southern Oscillation.

The current long term plan of the CCSM project is to develop and freeze the next version of the model, CCSM-4, by the end of 2008. In addition to several other improvements, this version will most likely have new components for the carbon cycle and interactive atmospheric chemistry. This will enable a whole new range of scientific questions to be asked of, and answered by, the CCSM. In addition, the CCSM-4 will be the model used to contribute to the next IPCC report.

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WRF

Community participants in one of the three WRF tutorials held in 2006. In addition to the 7th Annual WRF users Workshop held in 2006, MMM also convened international workshops in Korea, Taiwan, and China. The growing user base for the WRF system, together with the strong community particpation in the users workshop and tuturials, relect the value of MMM community support for the WRF system. High resolution figure

The Weather Research Forecasting (WRF) model is being developed as a collaborative effort among the NCAR/ESSL MMM Division, NOAA's National Centers for Environmental Prediction (NCEP) and Earth System Research Laboratory (ESRL), the Department of Defense's Air Force Weather Agency (AFWA) and Naval Research Laboratory (NRL), the Center for the Analysis and Prediction of Storms (CAPS) at the University of Oklahoma, and the Federal Aviation Administration (FAA), along with the participation of numerous university scientists. The WRF model is intended to improve the forecast accuracy of significant weather features across scales ranging from cloud to synoptic, with priority emphasis on horizontal grids of 1 10 kilometers. MMM maintains and supports WRF for widespread community use. This greatly leverages resources by allowing researchers access to a sophisticated modeling system without a large resource investment, and provides the community the opportunity to contribute to and benefit from the advancement of a common modeling system.

NCAR continues to develop new capabilities for the Advanced Research WRF (ARW) model and to support its widespread use as a community resource. During the past year, 1,000 new users registered to download the model code, bringing the total number of registered users to over 4,200. Over half of these users are distributed over some 82 foreign countries. MMM organized and conducted the 7th Annual WRF Users Workshop in June 2006 for 203 participants from 101 different institutions, and conducted three user tutorials (one in India) to instruct new users in the use of the ARW model and WRF-VAR data assimilation system. MMM also convened international WRF workshops in Korea, Taiwan, and China to assist these groups in both research and operational applications with WRF. MMM manages the common repository for WRF code, assists community researchers in code development, coordinates the addition of new code to the repository, and oversees the integration and testing for new releases of the WRF code to the community. Last year, MMM released updated versions of WRF, V2.2.1 in November 2005 and V2.1.2 in January 2006, which contained a number of new physics packages and enhancements to existing physics, improved treatment of 2-way interacting nested grids, and modifications for nested regional climate applications.

In the coming year, MMM will continue to assist both domestic and international users of the WRF/ARW system, and will organize WRF workshops and tutorials to accommodate the expanding use of WRF for both research and operations. Current plans are to convene the 8th WRF Users Workshop in June 2007 and to conduct tutorials in January and July of next year. A major new code release (V2.2) is planned that will allow community access to all of the newly developed model features. The growing user base for the WRF system supported by MMM, together with the strong community participation in the users workshop and tutorials, reflect the value of MMM community support for the WRF system. In addition, MMM is negotiating to establish an external advisory board in cooperation with the DTC to provide community input on MMM code management and community-support activities. MMM’s community support of WRF effort is primarily funded by NSF.

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