Comparison between Tornadic and Nontornadic Mesocyclones Using the Vorticity (Pseudovorticity) Line Technique

Abstract

Comparisons between tornadic and nontornadic mesocyclones using the concept of fractal geometry are presented. Both the maximum vertical vorticity (?max) and pseudovorticity (?pv) associated with a mesocyclone at low levels are found to be scaling with the horizontal grid spacing (ε) according to a power-law relationship. The linear least square best fitting of ln (?max) or ln (?pv) versus ln (ε) for different scales can be obtained for each mesocyclone at a certain time, and it is named the vorticity (pseudovorticity) line of a mesocyclone. Different mesocyclones have different vorticity (pseudovorticity) line slopes that are closely related to the fractal dimension of vorticity (pseudovorticity) of a mesocyclone as a possible fractal structure. Various factors that may affect the accurate estimate of the vorticity (pseudovorticity) line of a mesocyclone are also discussed in detail. Differences between tornadic and nontornadic mesocyclones are found in terms of the slope of vorticity (pseudovorticity) lines based on three tornadic and two nontornadic mesocyclones. A possible reason why previous studies were not able to identify the difference(s) between tornadic and nontornadic mesocyclones is discussed. Self-similarity (scale invariance), which is a basic characteristic of a fractal structure, seems to be valid between tornado and mesocyclone scales based on the analysis of the vorticity (pseudovorticity) line of the tornadic Kellerville, Texas, mesocyclone. It is hypothesized that a steeper slope of the vorticity (pseudovorticity) line may be indicative of a tornadic mesocyclone.