Characteristics of supercells simulated with tornadic and non-tornadic RUC-2 proximity soundings. Part III: Comparisons at tornado-resolving gridspacing

In Part I of this series, an investigation of convective initiation and forcing methods required to obtain long-lived supercell storms using RUC proximity soundings from Thompson et al. was performed. In Part II, the relationship between simulated supercell low-level rotation strength and longevity and the original non-tornadic, weakly-tornadic and strongly tornadic RUC input sounding parameters was elucidated using statistical means testing. Now, in Part 3, we investigate simulated supercell tornadogenesis and tornadogenesis failure using two soundings from the RUC sounding group associated with “strongly tornadic” (F2-F5) supercells in nature. In particular, we seek to understand reasons why one significantly tornadic RUC sounding produces a tornado in the model (peak vorticity greater than 0.4 s–1 over a depth of the lowest 3 km at dx=100m resolution) while another significantly tornadic RUC sounding fails to do so.

The storms in both simulations exhibit characteristics of supercells such as rightward propagation, a hook-like appendage in the precipitation mixing ratio field, and the presence of a midlevel mesocyclone. The goal of this study is to examine these two simulations and identify key storm-scale processes that promote tornadogenesis and tornadogenesis failure. Analysis of the simulations will focus on rear-flank downdraft (RFD) thermodynamics, low-level storm relative inflow, and the transport of midlevel angular momentum to the surface. In addition, a trajectory analysis is being performed to determine the origins of air parcels entering the low-level mesocyclone.

This study is funded in part by the National Science Foundation (AGS-0843269). Simulations are being conducted on NICS' Cray XT5.