Understanding the generation of high winds associated with bow echoes: The Omaha bow echo during BAMEX

The entire evolution of a quasi-linear convective system into a bow-shaped echo near Omaha, Nebraska is shown based on data collected by an airborne Doppler radar. This is believed to be the first time that a detailed kinematic study of a bow echo has been performed during the time it was producing damaging winds at the surface. A comprehensive post-storm aerial and ground survey revealed a damage swath that was approximately 50 km wide and 200 km long with the peak intensity exceeding F1 on the Fujita scale. Recent numerical simulations have suggested that mesovortices that develop at the leading edge of the storm outflow determine where the intense swaths of “straight-line” wind damage develop. Fortunately, the life cycle of a cyclonic mesovortex that developed near the apex of the Omaha bow echo was captured in the data set. Comparison with the damage survey revealed that the strongest wind speeds developed on the side of the mesovortex where translation and rotation were in the same direction. Accordingly, the wind field can best be described as the superposition of a vortex and the flow in which it is embedded. The tangential gradient of perturbation pressure plays a secondary role in generating these strong winds. The descending rear-inflow jet appears to be responsible for weaker damage (rated F0 or less) spread over a larger region.