Self Study Example – EXTREME WIND STATISTICAL ANALYSIS
The Excel file “Extreme wind data” contains the maximum gust wind
speed (m/s) recorded from synoptic winds at East Sale, Australia, for
each year between 1952 and 1998. The data were obtained at the
standard meteorological height of 10m above the ground and the
measuring device (anemometer) has been in the same place for the
entire period. Most of the extreme values recorded at the site are from
gales associated with large synoptic depressions (lows). However, the
few gusts that were produced from short-term, thunderstorm
downbursts have been removed from the list in order to achieve a
statistically consistent data set.
(a) Carry out an extreme value analysis of these data using the two
different equations for the reduced variate (y):
(1) Gumbel [Answers: Fitted constants; a = 0.376, U = 27.81 m/s]
(2) Gringorten [Answers: Fitted constants; a = 0.398, U = 27.84 m/s]
(b) Based on these analyses what are the predicted extreme (gust)
speeds that would be expected from each method with return periods
of:
(1) 10 years [Answers: Gumbel = 33.8 m/s, Gringorten = 33.5 m/s]
(2) 50 years [Answers: Gumbel = 38.2 m/s, Gringorten = 37.7 m/s]
(3) 1,000 years [Answers: Gumbel = 46.2 m/s, Gringorten = 45.2 m/s]
(c) Re-analyze the data set for the years 1952 to 1997, in other words
ignoring the unusually high value measured in 1998. What effect does
this have on the prediction of the 50 year and 1,000 year return period
extreme wind values?