Executive Summary

The mission of the Climate and Global Dynamics (CGD) Division is to: (1) obtain a comprehensive understanding of the Earth’s climate system components and the interactions among them; (2) to represent this understanding in models of the components and of the coupled system; and (3) to further our understanding by applying the models to scientific and societal questions and thereby provide a basis for prediction of weather and climate. The Division fulfills this mission through a strong record of achievement in scientific research, community modeling and data set development in collaboration with colleagues from the university, government and international research communities. The staff of CGD also fulfill the mission of NCAR through their community service, leadership of national and international research programs, and educational and outreach activities.

Development and Evaluation of Community Climate Models

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 continues to be a high priority of CGD research. This requires strong support of ongoing fundamental research on climate processes operating in the atmosphere, ocean, land and cryosphere. It also requires the continual development of software engineering methods to improve performance and portability, and extensive infrastructure and support for external collaborators and users.

1. Process-oriented research

Atmosphere

A major effort during FY04 was the development and release of the new Community Atmosphere Model (CAM3). CAM3 includes a large number of significant improvements and enhancements to the treatment of physical processes. These include: cloud and ice-phase processes; interactions among water vapor, solar radiation, and terrestrial thermal radiation; effects of aerosols, including prognostic sulfate, on the reflection and absorption of solar radiation; and dynamical frameworks suitable for modeling atmospheric chemistry. CAM3 also includes new standard capabilities such as a Slab Ocean Model (SOM) configuration, a single column modeling (SCM) feature, and improvements to the software engineering implementation of the model. The CAM3 consists of configurations at multiple resolutions, where the T85 spectral Eulerian configuration is the highest resolution atmospheric model configuration ever released by NCAR, and leads the way for other global modeling activities. CAM3 is incorporated as the atmospheric component of the Community Climate System Model (CCSM3). In strong collaboration with colleagues at the Geophysical Fluid Dynamics Laboratory (GFDL)of NOAA, CGD scientists continued to make progress toward understanding sensitivities and the sources of agreement or differences in climate sensitivity between CCSM and the GFDL coupled climate model.

Ocean and Cryosphere

Research in FY04 to improve our understanding of the large-scale ocean circulation and the dynamics of climate through studies of the important processes in the ocean and sea-ice, in air-sea-ice interactions, and in coupled systems continued. New treatments of physical processes in the ocean and sea-ice components of CCSM3 include improvements to the representation of the ocean mixed layer; inclusion of solar heating by chlorophyll; infrastructure for studying vertical mixing in the ocean; advanced sea ice rheology; explicit ice-thickness distribution physics; explicit treatment of brine pockets; and an improved scheme for horizontal advection of sea ice . In addition, CGD scientists are actively involved in two funded Climate Process Team (CPT) proposals. These are highly collaborative projects, bringing observationalists, process modelers, and modeling centers together to expedite the incorporation of new discoveries into climate models. The funded proposals concern the deep gravity currents and entrainment with particular emphasis on their role in water mass formation, and hence, the thermohaline circulation, and the interaction between mesoscale eddies and mixed layers. Among the objectives are to develop new or modified parameterizations that can be reliably used in ocean models and to assess their impacts on the climate model simulations. In addition, collaborative efforts in high resolution (0.1º) global ocean modeling continued to establish the role of mesoscale ocean processes in the mean climate and the response to climate forcing.

Land

Scientists in CGD continued their work in FY04 to implement biogeochemistry and its feedback on climate in the Community Land Model (CLM) and CCSM. This work resulted in a new version of the land model that includes detailed treatments of terrestrial carbon and nitrogen cycles, and interactions of the water and energy budgets with biogeochemical processes. The new model also includes a greatly improved scheme for representing the biophysical and biochemical characteristics of sunlit and shaded fractions of the canopy, as well as a simple algorithm for prognostic wildfire. Offline simulations demonstrate that the land biogeochemistry behaves reasonably under prescribed atmospheric forcing. Simulations coupling the new land model to the atmosphere in CCSM3 (with prescribed ocean and ice boundary conditions) suggest that both the improved canopy integration scheme and the prognostic carbon and nitrogen cycles have a significant impact on the coupled climate simulation. A major contributor to climate feedback in the new model is the prognostic canopy leaf area, which causes the seasonal, interannual, and long-term dynamics of the canopy to respond directly to the model climate, in contrast to the default land model which prescribes the seasonal cycle and spatial distribution of canopy leaf area from satellite observations. This effort involves strong collaborative work between CGD and the Atmospheric Chemistry Division (ACD).

2. CCSM

The CCSM3 was released on June 23, 2004 to climate scientists worldwide. CCSM3 includes major improvements in its physics and software that expand the range of scientific investigations that can be undertaken. The release was one of the highlights of the Ninth Annual CCSM Workshop held in Santa Fe, New Mexico during July 2004. Using CCSM3, the CCSM Climate Change Working Group and the Kyosei Consortium are completing an extensive suite of climate simulationsfor the upcoming Fourth Assessment Report (AR4) by Working Group One of the Intergovernmental Panel on Climate Change (IPCC). This production effort has also strongly involved scientists and software engineers at the Oak Ridge National Laboratory (ORNL), National Energy Research Supercomputing Center (NERSC) and the Lawrence Berkeley National Laboratory (LBNL).

The CCSM3 release includes the model code, comprehensive documentation, and the largest set of model results ever provided to the community. It includes four NCAR technical notes on the new atmosphere, land, dynamic vegetation, and sea ice models. The range of computer hardware suitable for CCSM applications has been expanded and should enable investigators to run CCSM on Linux systems popular in university departments. As of October 2004 nearly 170 groups had downloaded CCSM code. For the first time, the model produces realistic simulations over a wide range of spatial resolutions, enabling inexpensive simulations lasting several millennia or detailed studies of continental-scale climate change.

The project is distributing simulations for the present climate and recent past using the new Earth System Grid (ESG) developed with support from the Department of Energy. The ESG will also serve as the main pathway for distribution of the multi-model ensemble of climate-change simulations for the IPCC AR4.

Because of major enhancements to the component models, the climate produced by CCSM3 has greater fidelity to the observed climate than simulations from previous generations of CCSM. The improvements include better simulations of surface temperatures, snow and sea-ice distributions, ocean currents, and teleconnections between ENSO and the northern Pacific. These and other scientific features of the new model will be discussed in a special two-volume issue of the Journal of Climate. The software engineering underlying CCSM3 will be presented in a special issue of the International Journal of High Performance Computing Applications.

3. WACCM

CGD scientists have worked closely with ACD and High Altitude Observatory (HAO) colleagues toward the implementation of interactive chemistry and a solar module in the Whole Atmosphere Community Climate Model (WACCM). Implementation of interactive chemistry is completed, and a large number of scientific studies using WACCM are underway. Once the solar cycle module has been incorporated the effects of the solar cycle on the middle atmosphere and improvements to tropical wave variability will be explored. Plans are to release to the community WACCM version 3 in early 2005. Using CCSM as a common numerical framework, interdivisional development of WACCM continues the evolution toward complete Earth system models at NCAR.

Climate Analysis: Diagnostic, Theoretical and Modeling Studies

A goal of this high priority CGD research is to increase our understanding of atmospheric and climate variability and climate change through parallel development and analysis of observational, assimilated, model-generated and model-forcing datasets; and, by using these datasets for empirical studies, diagnostic analyses, and model experimentation to document comprehensively climate variability, its causes and the processes involved. Further, systematic numerical experimentation using models provides insights and assesses predictability that may allow attribution of observed variability to processes and causes. A crucial question is how well do we simulate the full spectrum of natural variability in models such as CCSM, and thereby provide a sound basis for future projections? The answer depends on a strong and balanced program in data analysis, theoretical and model application studies.

1. Empirical and diagnostic analyses of models and observations

Atmosphere

During FY04 CGD scientists published studies contributing to significant advances in the understanding of a wide variety of phenomena. A small sampling includes studies of: the diurnal cycle of precipitation, the total mass of the atmosphere and its variations globally, the flow of energy through the climate system, the global water cycle, droughts and their historical variability, the prospects for increasing extremeswith climate change, the role of tropical oceans in observed regional climate change, multi-decadal variations in surface pressure and rainfall throughout the Pacific, analyses of upper ocean and sea ice variations and the sensitivity of the atmosphere to those variations, and studies of tropical Atlantic variabilityand the role of air-sea interaction. Going beyond the physical system, several aspects of how climate variability affects terrestrial and marine ecosystems were also published.

Ocean

An emphasis of ocean research during FY04 was the analysis of the CCSM integrations in support of the IPCC AR4. Among other studies, CGD scientists have investigated: the attribution and impact of upper ocean biases, including the mean and seasonal cycle of equatorial temperature, salinity, and velocity; the ventilation rate of the thermocline and deep ocean in simulations of the 20 th Century; the response of the thermohaline circulation (THC) to transient climate forcing, primarily focusing on the dominant physical processes affecting the THC; the heat uptake in the ocean component of CCSM; the variability in the North Pacific using chlorofluorocarbon (CFC) ages and ideal age in a CCSM Parallel Ocean Program (POP) experiment with realistic forcing data; the dominant modes of sea ice variability in the Southern Hemisphere; and the consequences of a seasonally ice-free Arctic Ocean.

Land

Considerable efforts continued in FY04 to increase scientific understanding of land-atmosphere interactions, and in particular surface forcing of climate. One example was climate model simulations performed to examine the sensitivity of simulated climate to different specifications of present-day land cover and natural potential vegetation. Uncertainty in the classification of present-day vegetation can produce large differences in the simulated climate. Present-day vegetation has generally cooled surface climate, especially in the middle latitudes due to the higher albedo of croplands compared to natural vegetation. Simulations using land cover for the year 2100 showed that the land cover forcing of climate can be large, especially in tropical South America and in the U.S., where agricultural land is projected to become more extensive. Other work within the division demonstrated that the degree of land-atmosphere interaction varies widely between current state-of-the-art atmospheric general circulation models.

2. Climate observations

CGD scientists played leadership roles in FY04 in designing and advocating the global climate observing system, institutionalizing reanalysis, and articulating the need for and benefits of a climate information system. In addition, CGD maintained a leadership position in the development of data assimilation techniques, including work as part of the NCAR Data Assimilation Initiative (DAI). CGD scientists are also involved in assimilation techniques for biogeochemistry and carbon cycle studies. As part of these efforts, CGD researchers played a lead role in the Airborne Carbon in the Mountains Experiment (ACME) that focused on quantifying carbon fluxes in mountain and mountain-valley complex landscapes using airborne and ground-based flux measurement techniques.

3. Community Data Set and Software Development

An ongoing CGD activity in FY04 continued to be the acquisition, evaluation, improvement, and restructuring of datasets, the production of high-level derived products, and improved community access to data and documentation through data catalogues. Software tools to increase access to and display of data continue to be developed, and a substantial service activity within CGD has been devoted to outreach and teaching of data processing software, in particular the NCAR Command Language (NCL) developed in collaboration with Scientific Computing Division (SCD).

4. Climate predictability

A goal of the CGD program is to define and extend the spatio-temporal domain over which scientifically and societally useful forecasts can be made. Efforts in FY04 included research to: model the initial uncertainty in atmospheric ensemble prediction through the development of a statistical model of analysis error; understand the sources of predictability in the tropical Atlantic region; and apply concepts and methodologies developed by the climate dynamics community to diagnose and interpret climate change scenarios. An example of the latter involved the analysis of a 62-member ensemble of CCSM simulations for the years 1940-2080 to study the interplay between the natural modes of variability of the atmosphere and long-term trends in the mean atmospheric circulation resulting from the secular forcing trends. The large sample size made it possible to detect and diagnose the two-way interaction between modes and trends.

5. Paleoclimate

Paleoclimate research within CGD during FY04 was conducted on studies of deep time, the past 150,000 years, and the past millennium. The boundary between the Late Permian and Triassic periods at 251 Ma marks the largest extinction recorded in Earth’s history, and CGD researchers are carrying out the first fully coupled climate simulation for this period using CCSM. Considerable effort was also placed on simulating and constructing high-resolution paleoclimate records of climate variability and abrupt climate change over the last deglacial and the Holocene. Abrupt changes at these times occurred over decades to centuries and were associated with the transition from the Holocene climatic optimum to the Neoglacial, during which temperature decreased in the middle to high latitudes and precipitation decreased in the tropics. CCSM simulations of the last millennium are key to understanding the roles of natural and anthropogenic forcings in the observed climate record. A clear solar influence has been found on the century time scale that is stronger than previously assumed. However, the same simulations also show that the late 20 th century warming cannot be attributed to solar irradiance changes.

6. Climate Change

Through both climate change simulations and analysis efforts, CGD scientists continued in FY04 to play a national leadership role in climate change research. CGD scientists remain heavily involved in IPCC AR4 as convening lead authors, lead authors and contributing authors, consistent with the mission statement of NCAR. The centuries long simulations and ensembles have allowed CGD scientists to conduct studies addressing all five of the key global change issues identified by the Climate Change Science Program (CCSP) and the U.S. Global Change Research Program (USGCRP): (1) seasonal to interannual climate variability; (2) climate change over decades to centuries; (3) changes in ozone, ultraviolet radiation, and atmospheric chemistry; (4) changes in land cover and in terrestrial and aquatic ecosystems; and (5) the role of aerosols.

Education and Outreach

CGD scientists in FY04 continued a strong tradition of participation in education and outreach activities. This included mentoring of Advanced Study Program (ASP) and Significant Opportunities in Atmospheric Research and Science (SOARS) students, leading tours of NCAR and giving public talks, visiting K-12 classrooms, participating in educational workshops and colloquia, providing scientific content for educational videos and websites, and handling many requests from the media. In addition, several CGD scientists contributed directly to the new Climate Discovery Exhibit at the NCAR Mesa Laboratory.