Collaborative Research: Damage Analysis and Numerical Simulation of Convectively Driven Wind Events Observed during the Bow Echo and Mesoscale Vortex Experiment (BAMEX)

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The bow echo is known as a prolific producer of severe, though primarily non-tornadic, wind damage at the ground. The generally accepted explanation for the damaging wind involves a strong surface cold pool and associated rear-inflow jet (RIJ) that descends to the ground behind the apex of the bow. Recent idealized numerical simulations and limited observations are suggesting a different model, in which damaging surface winds are also induced tens of kilometers north of the apex by low-level, meso-gamma scale (order 10 km diameter) vertical vortices. Simulations suggest that, under certain conditions, mesovortex winds can be stronger, have longer durations, and produce a larger area of significant damage than can the RIJ winds at the apex. Adequate observations to validate this new explanation have yet to be collected. Further, the generality of this damaging-wind producing mechanism has yet to be established in instances when the mesoscale environment of the bow echo is significantly inhomogeneous. Underscoring the importance of this are recent observational studies that indicate a relation between reports of damaging straight-line (and/or tornadic) winds and the interaction of a bow echo and mutually perpendicular "external" outflow boundary.The primary objectives of this research are to: (i) conduct detailed aerial and ground surveys of wind damage following bow echo events, relating the severity and scale of damage to radar-observed convective system location and structural characteristics; and (ii) perform analyses and mesoscale model simulations of bow echo events in order to investigate dependencies of damaging winds, meso-vortexgenesis, and convective system structure on the inhomogeneous mesoscale environment. The bow echo and mesoscale convective vortices (MCV) experiment (BAMEX) will provide the framework for the proposed work. BAMEX seeks to understand and improve prediction of: the meso- and cellular-scale processes, within bow-shaped mesoscale convective systems, that lead to damaging winds at the ground; and MCVs and the deep cumulus convection they often trigger. BAMEX will be conducted over a large experimental domain centered on St. Louis, Missouri, and will involve unprecedented data collection via specialized airborne and ground-based observing platforms. Post-event damage surveys, a critical component of the BAMEX dataset, will be conducted under this award and used to meet numerous BAMEX objectives beyond those to be addressed under this award.The results of this research will significantly clarify the understanding of damaging wind production in bow echoes and will illuminate where the most damaging winds are most likely to occur, with what radar-observable attributes, and under what mesoscale environmental conditions. Ultimately, results may be applied by operational forecasters to issue more timely and accurate forecasts and warnings of damaging nontornadic surface winds.