A preliminary study of non-merger interactions between squall lines and isolated supercell thunderstorms

A number of past studies of severe convective storms have noted isolated storms appearing to intensify as they approach a nearby squall line, prior to the two modes merging into a single system. In particular, recent work examining storm mergers noted an increase in low-level storm rotation and a relative increase in tornado reports as an isolated supercell draws close to a nearby squall line. These observed behaviors imply some type of interaction is occurring between these two organizational modes while they are still separated, at least insofar as the storms can be observed on radar. To date there has been little study of the details of such an interaction, including quantifying the evolution of the isolated supercell, and the processes responsible.

This study will present preliminary work using idealized numerical simulations to demonstrate that, for the same initial background environment, an isolated storm evolves differently in the presence of a squall line than when it remains completely isolated. Of particular note is that the low-level mesocyclone evolves in a cyclic fashion in the isolated case, but remains quasi-steady when the squall line is included. Hypotheses related to the influence of squall line-induced perturbations to the local environment will be explored as a possible mechanism for these changes in storm organization and intensity.