Understanding the development and evolution of violent tornadoes in supercell thunderstorms

Leigh G. Orf, University of Wisconsin-Madison

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Leigh G. Orf, Jason Keeler, Catherine Finley, Peter Lindstrom, Austin Dixon, Kelton Halbert, Michelle Elmore, Vitaly Galinsky, Lawrence Frank, Thomas Lesperance

Each year, tornadoes cause millions to billions of dollars of property damage in the United States. Since 1990, an average of 78 U.S. citizens were killed annually by tornadoes. In 2011, 553 lost their lives from 59 tornadoes out of 1,690 that occurred that year in 48 states.

Despite advances in observational and modeling/computing technology, the behavior of tornadoes remains a mystery. We are currently unable to predict whether a given thunderstorm will produce a tornado, much less whether it will be short-lived and weak, or long-lived and powerful. The proposed work will use Blue Waters to simulate many different violent tornadoes at resolutions in which the tornado is resolved from its genesis through its dissipation. By simulating many storms in different environments, the project hopes to identify the factors involved in the formation and maintenance of the most devastating tornadoes, as well as learn more about its structure and evolution. This work has the potential to improve the forecasting of the most devastating storms, ultimately saving lives. Once specific features related to the genesis and maintenance of long-lived violent tornadoes are identified in simulations on Blue Waters, field researchers can search for such features in observed storms. Such features identified on operational weather radar could help forecasters issue specific, targeted warnings for unusually violent tornadoes. Furthermore, modifications to the code used in the study, CM1, will be shared with the weather modeling community. In a prior work, the project conducted a breakthrough ultra-high resolution simulation (30 meter grid spacing) on Blue Waters of a long-lived violent tornado spawned from a supercell that was based upon the observed 24 May 2011 EF5 tornadic supercell in central Oklahoma. The project proposes to build upon this previous work to explore the sensitivity of tornado morphology in the 24 May 2011 storm to parameters such as cloud microphysics, turbulence parameterization and low-level environmental wind shear. In addition, the project will enable the use of arbitrarily stretched vertical grids in CM1 in order to focus resolution at key vertical levels, such as near the ground. Moreover, the project will apply surface friction in a physically realistic manner, add functionality to CM1 that enables the centrifuging of rain and hail in regions of intense rotation, and explore other storm environments in which violent tornadoes occurred. Finally, the project will add the ability for CM1 to interpolate restart files from a coarser mesh to a finer mesh, allowing the model to simulate periods of the storm's life cycle where extreme resolution is focused on the core of storm.