Researchers simulate tornadoes to high resolution

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In the US, tornadoes incur billions of dollars in damages, dozens of deaths, and thousands of injuries annually. Yet, despite their power, many mysteries remain regarding how tornadoes form. 'Various theories exist that try to explain the cause of rotation in tornadoes,' says Ming Xue, professor of meteorology at the University of Oklahoma, and director of the Center of Analysis and Prediction of Storms (CAPS), 'but the true causes are still not well understood.'

Xue is on the forefront of tornado simulation and prediction research. Using the Ranger supercomputer at the Texas Advanced Computing Center (TACC), Xue has been able to simulate various historic tornados with unprecedented fidelity, obtaining simulations that match well with the observed storm in its characteristics, path and timing. Xue's detailed analysis of the model output is providing insights into how and why tornadoes form, and how microphysical processes within the cloud affect tornado formation.

The use of the Doppler radar data is important for prediction of all weather phenomena that involve precipitation. These forecasts 'require sophisticated methods and software to effectively incorporate the data into numerical prediction models, a processing called data assimilation. Only a few groups in the world do this kind of work,' Xue said, 'and our centre, CAPS, pioneered this area of research.'

On Ranger, Xue and Dawson have produced 3D simulations of a particularly destructive storm to a resolution of 12.5 metres throughout the entire thunderstorm, comprising 500 million grid points. This is a higher resolution than any previous investigation. The simulations, which used more than one million computing hours in 2008, showed the formation of a condensation funnel that looks very much like an actual tornado and illustrated tornado paths only a few kilometres from the observed paths.

Xue's group at CAPS has been able to simulate tornadoes with unprecedented realism, especially using their new methods for assimilating high-resolution Doppler radar data and for synthesising this information into 3D visualisations of evolving storms. However, to turn these methods into a predictive tool that can say where, when and how a twister will hit in real-time is still a distant dream. 'The full simulations can take up to a week to complete, but the actual tornado forecast has to be done in a matter of minutes,' Xue clarified. 'To actually use the tools for real-time prediction, computers need to be much faster.'