Mesovortex Production in Simulated Interactions Between Quasi-linear Convective Systems and Supercell Thunderstorms

Meso-gamma (horizontal scale on the order of 10 km) vortices associated with quasi-linear convective systems, commonly referred to as mesovortices, have been shown to be responsible for producing damaging winds and tornadoes.  However, owing to the small spatial scale, shallow depth, and sometimes short lifespan these types of vortices, they present a challenging scenario for severe weather forecasters trying to issue warnings for the associated high-impact weather.  To this end, the present study is using cloud model simulations to evaluate the effect that the presence of a discrete supercell thunderstorm ahead of a squall line may have on mesovortex production along the line.

To address this research goal, a series of simulations were run using the CM1 cloud model to simulate a squall line approaching an isolated supercell. In one set of simulations, the supercell’s along-line position is held constant, as its initial distance ahead of the line is varied.  In the second set, its initial distance ahead of the line is held constant at 100 km, while the location along the line is varied.  The simulations are run until the line merges with the supercell.

Results indicate limited effects on mesovortex development prior to the two storms merging together.  In select cases, dependent on the initial supercell position, interactions between the supercell’s outflow and squall line serve to enhance pre-existing vortices.  In other cases, new, weak mesovortices form at intersections between the supercell and squall line gust front boundaries.  Mesovortex production is most widespread, and the resultant vortices strongest, however, after the two storms merge. This is particularly evident when a strong bow echo results from the merger, as discussed in previous studies.  In these cases, mesovortex development appears to be more strongly linked to processes related to the bow echo rather than remnant supercell circulations.