Observation and numerical simulation of vortex/wave shedding for terrain-disrupted airflow at Hong Kong International Airport during Typhoon Nesat in 2011



A case of vortex/wave shedding at a mountain near Hong Kong International Airport (HKIA) in a tropical cyclone situation is studied in this paper. Compared with similar studies at HKIA in the past, this paper contains novel results by considering both actual observations and numerical simulation of the event, and by studying the shedding in a neutral boundary layer instead of a stably stratified atmosphere in the spring time. The vortex/wave shedding is clearly observed from the radial velocity imagery of Terminal Doppler Weather Radar (TDWR). The shedding period is about 7 min, which is consistent with previous results in the literature. The vortex/wave adjacent to the background strong southeasterly flow also leads to significant wind shear over the arrival runway corridor to the west of the north runway of HKIA. It may also be associated with the significant headwind changes encountered by an arriving aircraft that had to conduct missed approach due to the rapidly fluctuating winds. The shedding event is simulated by using the Regional Atmospheric Modelling System (RAMS) version 4.4 with a horizontal resolution down to 50 m. The model is found to capture the vortex/wave shedding successfully. The simulated shedding period is similar to actual observations, though the associated area of reverse flow is much smaller. As such, with faster computers, it may be possible to forecast the occurrence of significant wind shear associated with vortex/wave shedding in an area of complex terrain and provide earlier alert to the aviation weather forecasters. Copyright © 2012 Royal Meteorological Society