Supercell-Cell Mergers and Mesocyclone Evolution in Different Environments

Cell mergers with supercells are relatively common, but much remains unknown about how they may influence subsequent supercell hazards. Furthermore, many outstanding questions regarding mesocyclone evolution exist despite numerous studies linking supercell hazards with the background environments in which they occur. In this study, we analyze the Multi-Year Reanalysis of Remotely Sensed Storms (MYRORSS) dataset along with hundreds of supercell tracks from 2003–2011 to begin addressing these ideas. In line with recent studies, the outcome of a supercell-cell merger (in terms of the low-level supercell mesocyclone intensity) is not strongly related to the background environment. Of the parameters that we tested, mixed-layer (ML) LCL exhibited the largest correlation, with higher MLLCLs tending to yield a stronger post-merger mesocyclone. This relationship is significant at the 90% confidence level, but the coefficient of determination is quite small, suggesting limited operational use.

Incorporating Rapid Update Cycle (RUC) analysis yields novel quantification of observed mesocyclone strengths in different environments. Of the environmental characteristics tested, kinematic parameters like 0–3-km SRH and 0–3-km shear are more correlated with peak mesocyclone intensity than thermodynamic variables like CAPE and CIN. 0–3-km SRH exhibits the largest correlation and explains roughly one-third of the variance of peak azimuthal shear. MLLCL exhibited the largest correlation of the thermodynamic variables. We show trends in peak mesocyclone intensity across the 0-3-km SRH/MLLCL parameter space, as well as the broadly referenced 0–6-km shear/MLCAPE parameter space. These analyses may be useful for predicting short-term mesocyclone intensity changes in real time.