9317599 Lewellen Tornadoes are among the most powerful of natural disasters. Over several years of research, general characteristics of the dynamics of tornado vortices have been described and many aspects of their parent storms have been defined. Nonetheless, some basic questions still remain as to the nature of the flow within tornadic vortices and what factors control their structure. The Principal Investigator proposes to further knowledge of tornadoes using an advanced numerical model and observational information. The type of numerical model to be used is called a large eddy simulation model (LES) and marks the first time this technology has been applied to the study of tornadic vortices. The major advantage of this model is that its high resolution allows the resolution of enough of large turbulent eddies to that sub-grid parameterizations of turbulent transport is not nearly as critical as it is in lower resolution simulations. Model boundary conditions will be determined from available field data and numerical simulations of thunderstorms. It is anticipated that the project will result in better definition of the distinctive features of the turbulent wind field associated with tornadoes. It should permit the answers to such questions as: (1) how is the probability of reaching a given extreme speed at a given height related to values of convergence and vorticity averaged over this tornado vortex domain; (2) what is the sensitivity of the tornado wind field to various boundary conditions; (3) what sub-grid parameterizations for this type flow provide the proper interactions for simulations over larger domains with lower resolution? ***
