Analyses of the low-level winds in two tornadoes that crossed the Hong Kong International Airport

The low-level wind structure of two tornadoes (20 May 2002 and 6 September 2004) that occurred at the Hong Kong International Airport (HKIA) were studied using the HKIA Terminal Doppler Weather Radar (TDWR), a LIDAR, and a surface weather station, which was impacted by the core of one of the tornadoes (06 September 2004). TDWR data indicated that the first tornado was produced by a supercell storm, while the second tornado was anticyclonic and formed along the gust-front of a non-supercell storm. The axisymmetric structure of both tornadoes was derived by applying the GBVTD technique to the LIDAR data. GBVTD analyses indicated that both tornadoes underwent a similar structural evolution, transitioning from radial inflow at low levels, coupled with a central updraft, to low-level radial outflow and a central downdraft.

The center of the tornado that occurred on 6 September 2004 passed within 40 m of the surface weather station, permitting a time history of the low-level winds both outside and just inside the tornado core flow. Comparison of the winds to a Rankine vortex profile indicated that angular momentum was approximately conserved outside the core flow radius. Comparisons between the 10-m winds and the winds measured at 50 m AGL (the lowest LIDAR observation level) revealed little variation in wind speed with height.