Special Climatea

Speaker: Alex Schenkman from Berkshire Hathaway

Dr. Schenkman is going to present his work on "Examining supercell tornadogenesis using high-resolution simulations initialized with real data". 

Following is the abstract of his talk:

"It is widely known that supercell thunderstorms are responsible for most tornadoes. However, the processes responsible for tornadogenesis are still somewhat uncertain. In this talk, I will first review supercell thunderstorm dynamics and with a focus on the origin of low-level rotation that gives rise to tornadoes. Following this review, a very high resolution (50-m grid spacing) simulation of a supercell that occurred on 8 May 2003 in Oklahoma City will be discussed. This simulation was produced via 3DVAR data assimilation of radar and other conventional observations. The simulated supercell produced a long-track tornado that occurred near one of the actual tornadoes observed on this date. Analysis of vorticity generation along backward air parcel trajectories into the incipient tornado, shows that surface drag plays a key role in the origin of low-level rotation responsible for tornadogenesis. This is contrary to most other theories regarding tornadogenesis which emphasize the role of buoyancy gradients in the generation of low-level rotation. The simulation also produces numerous internal momentum surges that appear to play a key role in tornado formation. These surges and their relation to tornado formation have been noted in numerous other observation and simulation-based supercell studies. The origin of these surges in the 8 May 2003 simulation is complex but appears to be related to pressure gradients associated with convergence between the environmental flow and the storm generated low-level mesocyclone. I will close with comments on possible future experiments to build upon the simulation presented herein."