About Project Athena

Responding to the call for a revolution in seamless weather and climate modeling made at the World Modeling Summit, held in May 2008 in Reading, UK (Shukla et al., 2009), Project Athena brought together an international team of over 30 people from six institutions on three continents (see the Acknowlegements for a complete list), including climate and weather scientists and modelers, and experts in high-end computing (HEC) to determine the feasibility of using dedicated HEC resources to rapidly accelerate progress in addressing one of the most critical problems facing the global community, namely, simulating climate variability and global climate change.

Computationally-intensive experiments with two different models of the global atmosphere made use of the entire 18,048-core Athena Cray XT-4 supercomputer at the University of Tennessee's National Institute for Computational Sciences, based at the Oak Ridge National Laboratory, with support from the U.S. National Science Foundation. The numerical experiments were designed to determine whether increasing weather and climate model resolution to accurately resolve cloud systems and mesoscale phenomena in the atmosphere can improve the fidelity of the models' climate simulations.

The Athena supercomputer was placed in dedicated mode for the period from 1 October 2009 to 1 April 2010, for experiments with the European Centre for Medium-range Weather Forecasts (ECMWF) Integrated Forecast System (IFS), and the Non-hydrostatic ICosahedral Atmospheric Model (NICAM) global atmospheric model from the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and the University of Tokyo. It was the first time that either model was run in such long simulations at the highest possible resolution. It was also the first time that either model was run in the U.S.

Multiple IFS simulations at multiple resolutions (T159 or 128-km grid; T511 or 40-km grid; T1279 or 16-km grid; and T2047 or 10-km grid) for multiple simulated decades were carried out, including experiments with boundary conditions representing end of the 21st century conditions under climate change conditions (so-called "time-slice" experiments). The effect of increasing greenhouse gas concentrations, associated with global warming, on the regional aspects of extreme temperature and precipitation, storminess, floods and droughts in key regions of the world was evaluated in the time-slice experiments. The T1279 version of IFS used in these long runs was the same as that used for operational 10-day numerical weather prediction on a daily basis by ECMWF.

The impact on climate simulation of explicitly resolving cloud processes in the atmosphere was tested in the NICAM simulations. The simulations were eight boreal summers (2001, 2002, 2004, 2005, 2006, 2007, and 2009) with 7-km icosahedral grid spacing.

Preliminary analysis of the Athena integrations indicates the major positive impact of high-resolution (16km, 10-km or 7-km grid spacing) on the representation of mean features of climate and its variability. In particular, the simulations have a better representation of blocking in the extratropics and trade winds in the tropics, better spatial and temporal distribution of snow, and better seasonal forecast skill, at high resolution. Several interesting features of climate change, such as annual mean warming over western Europe, as well as fine-scale features such as changes in alpine snowpack, were also substantially different at high resolution compared to lower resolution.

The project team maintained an exceptional level of utilization of the resource (>90%) for the six months of the project, as well as developing substantial experience with managing work flows on a large computing resource. The project generated nearly 900 TB of model output data stretching the limits of CPU, disk, I/O, metadata management and tape archive resources. The data generated by this project will be made available to the community of climate scientists in 2011.