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Gust distributions at Sydney Airport, particularly when sufficiently large populations are considered, have zero means and small skewnesses. Consideration of true-direction gusts at Sydney Airport established some properties of the gust distributions on strong wind days but also identified the need for a gust classification method from which conclusions of relevance to aviation safety could be drawn. The simple techinque of considering operations-relevant gusts can be used to calculate the risks of alternative operations directions. This technique is suggested for any airport where an analysis of risk factors for operations in the terminal zone is required. All that is needed is a network of low-level anemometers and provision for continuous logging of the data, preferably at a sampling rate of 2 seconds or faster.
Analyses were made of operations-relevant gusts at Sydney Airport on days on which there were strong synoptically-generated winds and on days on which there were thunderstorms. These show that aircraft operations in direction 07 face the greatest risk from gusts, particularly from along-track gusts. Direction 25 seems to pose the next highest risk, with operations on the long runway (16/34) the safest.
Nevertheless, the conditional probabilities of gusts over 5 
are
still low, the maximum such probability being less than 4 in 1000. Absolute
probabilities will be lower still because the choice of a particular operations
direction is subject to a further probabilistic factor, reflecting the
advantage of runways aligned in more than one direction.
The variances are larger for the days of strong synoptically-generated winds than for thunderstorm days. Although thunderstorms can make unpredictable winds over periods of some minutes, they do not create sustained gusty winds over long enough times to make an impact on the statistics considered here. However, predictions of operations directions that pose the least risk are less certain on thunderstorm days, because the strong gusts from thunderstorms are spread more widely over the operations directions.
Along-track gusts are generally more severe than cross-track gusts, particularly on the days of strong synoptically-generated winds. This is probably due to the nature of the turbulence structure in the boundary layer over land.
Further work on wind gusts should address two topics easily researched using the existing Sydney Airport dataset, to which data is continually being added. Firstly, probability distributions similar to the ones presented here should be calculated exclusively during those hours when thunderstorms are present; secondly, probability distributions of horizontal wind shear should be investigated.
ACKNOWLEDGEMENTS
We are grateful to the Australian Civil Aviation Authority for the provision of data from their anemometers and to Greg Nippard, who implemented the data pre-processing scheme. This research was supported by the Australian Research Council (grant A89030563).
R. Manasseh Papers
R. Manasseh Home
