Severe Turbulence during the Passage of Typhoon Imbudo
During the passage of Typhoon Imbudo on 24 July 2003, a total of 31 aircraft reported encounters with turbulence at the Hong Kong International Airport (HKIA). Of these, 15 were moderate to severe turbulence reports. It was a single day with the largest number of severe turbulence reports since airport opening in 1998. Just like windshear, turbulence can affect flight safety as the pilot may experience a momentary loss of control of the aircraft in severe turbulence.
The figure below shows the wind pattern revealed by the Doppler LIght Detection And Ranging (LIDAR) System that morning when an aircraft on approach from the west reported severe turbulence. As shown in the figure, there were small-scale, irregularly-arranged wind disturbances with a length scale of several hundred metres affecting the airport and its surrounding areas to the north of Lantau, indicating the presence of severe turbulence.
Apart from the turbulence reports, the Observatory also received 66 reports of significant windshear from pilots on the same day. With timely alerts issued by the Observatory, the pilots landing and taking off were all prepared. Throughout the day, more than 30 flights conducted go-arounds on first approach owing to the windshear and turbulence. All aircraft landed and took off safely that day.
Small-scale wind disturbances (marked in red circles) revealed by the LIDAR during the passage of Typhoon Imbudo on 24 July 2003. The white arrow indicates the background wind direction.