Engineering Analysis of a Full-Scale High-Resolution Tornado Wind Speed Record

Abstract

A three-dimensional (3D) sonic anemometer at a height of 2.5 m serendipitously recorded a tornado event in Arizona on October 6, 21. The anemometer, which was in place for carbon flux experiments and sampling at 2 Hz, recorded a peak instantaneous wind speed of 83 m/s. Over a 45-s period, which included the peak wind speed, the wind speed and direction time history showed evidence of seven distinct periods of behavior. These periods corresponded to rapid changes in wind speed (i.e., acceleration) and wind direction. This period also included significant positive and negative vertical wind speeds. Although 9 s of recorded data in this period was missing due to issues with data recording, these data could be an invaluable starting point for the future of tornado-based structural design. Analyzing the record in the context of wind engineering, variables and statistics typically used in wind engineering showed marked differences from those assumed in wind load codes and standards, including large gust factors for very short averaging times and significant changes in pressure coefficients for a roof corner. These differences should be further researched and quantified.