Abstract:

ESDU 87034 explains the various mechanisms producing high winds, such as depressions, thunderstorms, tropical storms and tornadoes, and describes their characteristics and geographical occurrence. Detailed procedures are given for analysing annual and storm maxima records and for analysis by direction. The Lieblein method of fitting the maxima with a Fisher-Tippett Type 1 distribution is detailed and an alternative method of predicting extreme values from the parent probability distribution function (of Weibull form) is provided and allows good estimates of extreme speeds to be obtained from relatively short records. Methods of analysing and synthesising data when more than one storm mechanism contributes to the extremes are included. Methods are recommended for extrapolating extreme values for depressions, thunderstorms or tropical storms to heights and terrain roughnesses different from those at the measurement site. To assist in the analysis of historical wind speed records, types of anemometers used and their possible inaccuracies are discussed. Methods for estimating response and effective averaging time in relation to gusts are also provided.