A wind engineering perspective on wind speed estimation in tornadoes

Gregory A. Kopp

Professor, Department of Civil and Environmental Engineering, and Associate Dean, Graduate and Postdoctoral Studies, University of Western Ontario

Wind speed estimation based on damage observations from tornadoes is a significant challenge because of the variability of all of the parameters involved. In particular, a detailed lack of knowledge of building aerodynamics and the wind field close to the ground are significant issues that are far from being resolved. The paper focuses on the issues related to building aerodynamics and discusses wind tunnel procedures that may be used to increase our understanding and ability to calculate such wind loads. A conditional-averaging approach is recommended, which requires that temporally and, in certain circumstances, spatially-resolved wind field measurements be made simultaneously with the aerodynamic loads. Such an approach also enables comparisons with “traditional” atmospheric boundary layers, which are important given the large body of knowledge of building aerodynamics in these wind fields. This approach implies that tornadoes can be viewed as gusts with particular structure (i.e., vorticity and velocity fields, swirl, shape, size, etc.). As a result, this approach may also enable determination of wind loads for tornadoes by using straight-line wind tunnels in the future. It is further suggested that we focus on two limiting cases: (i) large tornadoes with relatively small buildings, and (ii) small tornadoes with relatively large buildings. Results for the former case are presented and discussed.