Assessment of gust factors and wind speed decomposition methods for thunderstorms

Abstract

This paper examines wind decomposition methods for nonstationary thunderstorms based on the frequency responses. A wide range of methods have been used for this task, including weighted-average methods, Savitzky-Golay filters, and multi-resolution techniques. Two problems arise in the evaluation: (1) how to decide which methods are good, and (2) how to compare the wind properties from one decomposition to another. To determine the most suitable method, the overshoot and sharpness of their frequency responses are evaluated and compared. The half-power cutoff frequency is proposed to connect different methods, so that the wind properties, e.g., gust factor, can be compared. The choice of the cutoff frequency for thunderstorms is also examined with artificially generated nonstationary winds. Records from four thunderstorms are decomposed with the different methods and cutoff frequencies. The gust factors with different gust averaging times are calculated and compared with those for stationary winds. Underlying differences between the gust factor curves are also examined. Finally, the paper provides recommendations for the selection of decomposition method and cutoff frequency for nonstationary winds like those in thunderstorms.