Characteristics of supercells simulated with tornadic and non-tornadic RUC-2 proximity soundings. Part I: Sensitivity to convective initiation mechanisms

Soundings that were extracted from the RUC-2 within the near-storm environment of radar-observed mature (≥ 2 h after development) supercell storms by Thompson et al. (2003; 2007) have been simulated in a numerical cloud model at 1 km horizontal resolution (250 m vertical). The soundings were originally obtained near supercells that were non-tornadic (454 cases), weakly tornadic (F0-F1; 309 cases), and significantly tornadic (F2-F5; 134 cases).

In Part I, we show that storm type and longevity are strongly influenced by the initiation mechanism. This has important implications for storm scale forecasting and other idealized modeling studies. Simulations were carried out using 1 km horizontal resolution for 2 h cloud time, with three different types of initiation mechanisms: A) using the traditional thermal bubble method; B) using a localized mesoscale convergence method by Loftus et al. (2008); and C) using a local updraft forcing technique (by Straka). Success in producing a supercell was defined objectively using an automatic supercell identification method (based upon correlation between vertical vorticity and updraft) as well as subjectively analyzing each case for the presence of an precipitation-free vault, rightward propagation, hook appendage, and so forth. The “bubble method” is least successful in producing sustained storms due to the capping inversions represented in most of the RUC-2 soundings. We also investigate the sensitivity of storm sustenance to the length of time that the forcing is applied in initiation methods B and C. investigate the sensitivity of storm sustenance to the length of time that the forcing is applied in initiation methods B and C.

This study is funded in part by the National Science Foundation (AGS-0843269). Simulations were conducted on NCSA's Tungsten (Dell PowerEdge Linux Clusters).