Processes That Influence The Damaging Potential of Bow Echo Mesovortices

This study examines the damaging potential of low-level, meso gamma-scale mesovortices formed within bow echoes. This was accomplished by analyzing quasi-idealized simulations of the 10 June, 2003 Saint Louis bow-echo event observed during the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX). This bow echo produced both damaging and non-damaging mesovortices.

A series of sensitivity simulations were performed to assess the impact of low and mid-level shear, cold-pool strength, and Coriolis forcing on mesovortex strength. By analyzing the amount of circulation, maximum vertical vorticity, and number of mesovortices produced at the lowest grid level, it was observed that more numerous and stronger mesovortices were formed when the low-level environmental shear nearly balanced the horizontal shear produced by the cold pool. As the magnitude of deeper layer shear increased, the number and strength of mesovortices increased. Larger Coriolis forcing and stronger cold pools also produced stronger mesovortices.

Variability of ground-relative wind speeds produced by mesovortices was noted in many of the experiments. It was observed that the strongest ground-relative wind speeds were produced by mesovortices that formed near the descending rear-inflow jet (RIJ). The strongest surface winds were located on the southern periphery of the mesovortex and were created by the superposition of the RIJ and mesovortex flows. Mesovortices formed prior to RIJ genesis or north and south of the RIJ core produced weaker ground-relative wind speeds. The detection and warning implications of these results will be discussed. The genesis of the mesovortices is discussed in a companion paper.