Alerting of terrain-induced windshear using wind data measured over the mountains

Though the Doppler LIDARs and weather radars are the primary weather sensors for the alerting of low-level windshear at the Hong Kong International Airport (HKIA) in all weather conditions, the use of ground-based anemometer stations is still crucial in the provision of the alerting services, such as automatic detection of low-level shear lines, as well as assisting the aviation weather forecasters in issuing windshear warnings for the Automatic Terminal Information Service (ATIS). Since the opening of HKIA, a cross-wind rule based on the mountain weather station at Nei Lak Shan (NLS) near HKIA is used operationally for windshear alerting. Apart from NLS station, a large number of anemometers have also been set up inside and around HKIA, such as adjacent to the runways, over the waters under the flight paths, at the valleys and the mountain gap exits of the complex terrain nearby the airport.

This study is the first effort to comprehensively review the use of all these anemometer stations in the alerting of low-level windshear. The most commonly used arrival runway corridor in the peak windshear season in the spring-time is considered over a period of 4 years. Application of the wind data collected at the anemometer stations in the alerting of windshear over this runway is studied by considering a number of metrics, such as cross-wind strength, gust factor and standard deviation of the wind speed. Performance of the various anemometer-based windshear rules is examined by looking at the balance between hit rate of pilot windshear reports and the total alerting duration.

It is found that, by considering the standard deviation of wind speeds measured at certain strategically situated anemometer stations, it is possible to achieve the alerting of low-level windshear with performance on par with or even better than the existing NLS cross-wind rule. The additional windshear rules found in the present study could bring new insight to the weather forecasters in issuing the windshear warnings for ATIS.