While much has been learned over the last decade on the formation of tornadoes, it is still unknown why some supercell storms produce tornadoes and others do not. The objective of this renewal project is to provide a better understanding of the near surface dynamics of a tornado vortex evolving within a mesocyclone. The Principal Investigators expect to expand upon the results of their prior grant involving a sensitivity study of the flow in the tornadic corner flow region where the turbulent interaction of the central vortex with the surface produces maximum wind speeds in a very unique environment. This renewal study will include looking at the effects of unsteadiness and asymmetry in the boundary conditions on the tornado domain; increasing the size of the domain of interest; and attempting to incorporate some of the small-scale results obtained into subgrid parameterizations appropriate for use with larger domain simulations. The project will rely heavily on the use of the authors' existing high-resolution, three-dimensional, numerical model for simulations of tornado like vortices. A key objective is to discover more about the special conditions which allow a mesocyclone to spawn a dangerous tornado.
Results from the authors' prior grant demonstrated that the interaction between a tornado like vortex and the surface can lead to a strong intensification of the winds with the degree of intensification depending critically on the angular momentum within the surface layer inflow. This suggests that the essential difference between similar mesocyclones, some of which generate strong tornadoes and some of which fail to do so, may largely depend upon the boundary layer flow. By exploring the impact of different boundary conditions which the tornado vortex domain inherits from the mesocyclone, the authors hope to extend idealized results from their prior grant in order to have a significant impact on the problem of tornadogenesis.
It is expected that this study will determine which dynamical features of the mesocyclone (ideally ones which may be determined from observational radar data) are most closely related to the near surface intensity of the tornado evolving within it. This potentially may lead to an improved ability to forecast these severe events.
