“It is our goal to produce quantitative, transparent and accessible scientific knowledge to address climate change consequences, mitigation actions, and the needs for future societal adaptation,” said Thomas Zacharia, Deputy Director for Science and Technology at the Oak Ridge National Laboratory and a professor and PI of the NICS project at UT Knoxville. “We established the Oak Ridge Climate Change Science Institute (ORCCSI) as a multi-agency, multi-disciplinary climate change research partnerships at ORNL that integrates scientific projects in modeling, observations, and experimentation with the powerful computational and informatics capabilities to answer some of the most pressing global change science questions.”

Athena, the 166-teraflop Cray XT4 system which is four times as powerful as the Earth Simulator, is being utilized in a dedicated mode in an attempt to resolve the role of clouds in climate variability and change.

The effort is the result of a partnership of climate research organizations from the United States [NICS, ORCCSI, Center for Ocean-Land-Atmosphere Studies (COLA)], Europe [European Centre for Medium-Range Weather Forecasts (ECMWF)], and Japan [the University of Tokyo and the Japan Agency for Marine-Earth Science and Technology (JAMSTEC)] and funded by the National Science Foundation.

“The ultimate goal of these simulations is to explore the possibility of revolutionizing climate and weather prediction, taking advantage of a large computing resource,” said Principal Investigator and COLA Director Jim Kinter. The project has been allocated the entire Athena system for at least three months, beginning its work on October 1.

“Using Athena’s computational might to more fully understand the interaction between the earth’s weather, its land and its oceans, is a step in the right direction to addressing the vexing issues associated with climate change,”  said Tim Killeen, NSF’s assistant director for Geosciences.  “We applaud the University of Tennessee for leveraging these resources and taking leadership in this international collaboration.”

According to Kinter, clouds were too complex to accurately include as a part of the global climate system in past climate models. They were treated in bulk and their behavior was largely estimated using fairly crude approximations. These approximations are the primary restraint preventing climate models from evolving from good to great, said Kinter.

Two suites of simulations, one using the ECMWF’s operational weather prediction code and the other using the University of Tokyo’s NICAM, a code that represents global atmosphere (which contains clouds) and a thin layer of upper ocean at “cloud system resolving scales,” will be run to test one hypothesis: Approximate clouds in a climate model negatively influence the accuracy of the model—explicit clouds will enhance the accuracy. This is the first time the NICAM code has been run in production outside of the Earth Simulator.

However, resolving cloud systems means refining models to unprecedented resolutions, in this case as small as 7 kilometers. For comparison, the current model used by the United States’ National Weather Service uses a grid spacing of 35 kilometers. If these scales are successfully resolved, these simulations could lead to more realistic precipitation forecasting, enhancing seasonal-scale numerical weather forecasts and more accurately simulating changes in the distribution and intensity of extremes of precipitation and tropical cyclones associated with climate projection.

In order to achieve such fine resolution, however, researchers need a big machine. “Athena makes this possible,” said Kinter, adding that a dedicated, leading-edge system enables the testing of such a computationally intensive hypothesis.

“The dedicated use of Athena by a single group solving a time critical problem of societal significance is an important direction for high performance computing, and we are pleased to work with Jim Kinter and his group on this. Athena certainly represents the extraordinary strength and success of the partnership between UT and ORNL to advance scientific discovery at unprecedented scale,” said Phil Andrews, NICS Project Director.