Collaborative Research: Improved Understanding/Prediction of Severe Convective Storms and Attendant Phenomena through Advanced Numerical Simulation

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The objective of this research is to improve understanding of severe convective storms and attendant phenomena through the use of advanced numerical simulation. Areas of focus include1) environmental and model parameters influencing tornado genesis, intensity, and longevity;2) tornado representation using improved model physics;3) multiple storm interactions influencing the intensity and longevity of low-level rotation;4) analysis and simulation of the 30 May 2003 back-building supercell line;5) tornadogenesis owing to rapid environmental changes;6) advances in storm scale assimilation: ENKF using polarimetric radar data.There are several themes that connect these areas. One theme centers on low-level storm rotation and its relationship to tornado genesis, evolution, and decay, particularly within supercells. Not only are the above foci aimed at improved understanding through high resolution numerical simulations but also at explaining the structure and behavior of storms that produce long track tornadoes. Coupled with these investigations will be a focus on improving the microphysical representation within severe storms. Advanced microphysics is needed for more accurate depiction of storm and tornado evolution, associated surface weather, and proper assimilation of polarimetric radar data. The simple single moment microphysics parameterizations commonly used today do not properly represent squall lines and supercells simultaneously, cannot forecast supercell precipitation reliably, and incompletely represent the microphysics within simulated supercells as observed by polarimetric radar.Another theme centers on the interaction of existing storms with themselves or with the presence of a boundary. Motivated by severe storm behavior on 19 April 1996, one focus extends initial work aimed at understanding mergers of storms in multicell and supercell environments that result in increased storm strength, storm rotation, and increased tornadic potential. This investigation will benefit from new technologies being developed at the National Center for Supercomputing Applications and with the NSF funded LEAD ITR project for managing, mining, and visualizing large sets of simulations. Another focus is aimed at understanding the back-building nature of some lines such as the one that occurred on 30 May 2003. Observational analysis of this event will be followed by numerical simulations to study the hypothesis that this occurs through enhanced convergence located where the prevailing cold front interacts with a southward moving outflow boundary of the southernmost supercell.The implementation and testing of expanded microphysics will provide input to others storm modelers on the important microphysical processes. It will also provide an indication to short-term forecasters of the impact that sophisticated physics can have on storm-scale model forecasts. Furthermore, given that the National Weather Service may soon upgrade the WSR-88D radar network to include polarimetric measurements, preliminary work is needed to understand how to best assimilate such measurements into storm-scale forecast models and which microphysics schemes can best incorporate these new measurements.