Observation of Terrain-Induced Windshear around Hong Kong International Airport under stably stratified conditions

To facilitate the warning of wind shear associated with convective storms, a Terminal Doppler Weather Radar (TDWR) was installed roughly 12 km to the northeast of the Hong Kong International Airport (HKIA) at Chek Lap Kok. Since its commissioning in 1997, apart from microbursts, significant wind shear due to terrain to the south of the HKIA has been observed by the TDWR.

The HKIA lies on the lee side of Lantau Island when winds come from the east through southwest. Lantau has a northeast-southwest oriented ridge, with a width of about 5 km, length of about 20 km, and several peaks rising to between 700 and 950 m above mean sea level. The TDWR Doppler radial velocities were studied to characterize the wind shear at HKIA caused by Lantau. Under stable conditions when cooler surface easterlies were capped by warmer southeasterlies, areas of radial velocity towards the TDWR could be identified in a flow that were generally away from the TDWR suggesting the formation of vortices induced by the cross-mountain flow.

Previous study had observed counter-rotating quasi-steady eddies in the wake of the island of Hawaii in stable stratification based on aerial observations. This paper discusses the terrain-induced wind shear at HKIA under stable stratification, based on the observations including TDWR and flight deck data from commercial aircraft. Typical cases, including one involving terrain-induced wind shear observed on 8 March 1999, are presented.