Aircraft Meteorological Observation for Tropical Cyclones
The Observatory has been in close collaboration with the aviation community to collect meteorological observations for enhancing our weather services, for instance the investigation flights were conducted to study the low-level windshear and turbulence effects around the Airport. In 2009, the Observatory commenced the regular flight data collection with the Government Flying Service(GFS). A fixed-wing aircraft Jetstream-41 of GFS was equipped with a dedicated meteorological measuring system to provide horizontal and vertical winds, temperature, pressure and humidity at a high frequency of 20 times per second. These high quality data are used to verify the windshear and turbulence alerts provided by the ground-based meteorological systems and to enhance the turbulence alerting algorithms of the Windshear and Turbulence Warning System (WTWS).
In 2011, our cooperation with GFS extended to reconnaissance flights to capture weather data for tropical cyclones (TCs) over the South China Sea (Figure 1). This greatly enhances our capacity in monitoring the location and intensity of TC that have been based on limited observations or satellite pictures.
Figure 1 The flight path of the fixed-wing aircraft on 22 July 2012 (red lines shown in the figure), overlaid on the visible satellite imagery at 2 p.m. on that day. It could be seen that the aircraft had once flown very close to the centre of the tropical cyclone Vicente. The winds near sea surface estimated from the flight data from point A to point B are shown on the right panel.
To further enhance meteorological data collection in TC situation, HKO and GFS have planned to implement a launcher on the replacement GFS aircraft to release a measuring instrument called dropsonde. Similardropsonde measurement missions have been in real-time experimental running. A dropsonde consists of a set of weather sensors hanged under a mini-parachute. As the dropsonde descends, it measures weather data for transmission to the Observatory via the aircraft. This would provide the vertical meteorological profile of TCs, and more importantly the near sea surface wind information for better determination of the storm intensity. It would be safer to do the measurements as the aircraft can release the dropsondes on a higher altitudes and leave immediately without confronting the severe convection associated with the tropical cyclones.