The use of an instrumented aircraft in studying the characteristics of terrain-disrupted airflow at the Hong Kong International Airport (HKIA)

In the development and verification of windshear alerting algorithms at HKIA, the pilot reports have been used as the sky truth. However, it is well known that such reports are prone to the subjective perception of the individual pilots, and there may not be consistency among the pilots in the reporting of low-level windshear. In order to build up an objective database of windshear data at HKIA, the meteorological measuring system (MMS) of a fixed-wing aircraft of the Government Flying Service was upgraded by the Hong Kong Observatory (HKO) in mid-2009 to collect wind data at a frequency up to 20 Hz. The paper describes the characteristics of the system, which consists of one air data probe, two GPS antennae and a number of data processing modules inside the cabin. The MMS is found to give horizontal wind data of good quality by comparing with the headwind data collected by the two LIDAR systems at HKIA.

Using the MMS wind data, some salient features of terrain-induced windshear at the airport are documented in this paper. The spatial distribution of the vertical velocity measured by the system would also be described in case studies. Since the opening of the airport, this is the first time that vertical velocity data of high temporal frequency (20 Hz) are collected directly using aircraft. Turbulence in the terrain-disrupted airflow is also analyzed by calculating the eddy dissipation rate (EDR) based on the horizontal wind. Further enhancements of MMS will also be described in the paper.