Some observations of low level wind shear at the Hong Kong International Airport in association with tropical cyclones

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Abstract
In summer, Hong Kong is affected by tropical cyclones moving northwestwards over the northern part of the South China Sea. They may bring strong southeasterly airflow to the territory. The wind is disturbed by complex terrain to the south of the Hong Kong International Airport, resulting in turbulent airflow in the airport area and leading to the occurrence of low level wind shear and turbulence. This study documents the observations of wind shear at the airport in some recent cases of tropical cyclones in Hong Kong. The alerts from three operational wind shear algorithms are described, based on anemometers, the light detection and ranging system and microwave radar. The situations at the maximum wind shear magnitudes are presented. This is followed by a statistical analysis of the occurrences of wind shear against the wind shear magnitude and sign. A logarithmic relation between the two is found, and it is applicable for all tropical cyclone cases under study and different wind shear algorithms. However, there is no uniform equation for the logarithmic distribution, apart from the case of laser radar wind shear alerts for headwind loss. Finally, the accuracy of wind shear alerts of one tropical cyclone case is presented by comparison with pilot wind shear reports. It is hoped that the documentation in this study could serve as a useful reference to aviation weather forecasters at other airports with similar wind shear situations, as well as contributing to an improved understanding of the statistical behaviour of the wind shear phenomenon.

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