Wind data collected by a fixed-wing aircraft in the vicinity of a typhoon over the south China coastal waters

The fixed-wing aircraft of Government Flying Service of the Hong Kong Government has recently equipped with an upgraded meteorological measuring system. This system provides horizontal wind velocity components up to 90 m/s at an accuracy of 0.5 m/s for straight and level flight. Besides search and rescue (SAR) missions, this aircraft is also used for windshear and turbulence investigation flights at the Hong Kong International Airport. In a SAR operation in July 2009, the aircraft flew close to the eye of Typhoon Molave, when it was located at about 200 km to the east of Hong Kong over the south China coastal waters. The aircraft provided valuable information about the winds in association with Molave because aircraft reconnaissance for tropical cyclones is not carried out for South China Sea.

Based on the aircraft measurements, the 1-second mean wind reached the maximum value of about 127.5 knots at a height of 231 m above mean sea level. Assuming a power law with altitude with an exponent of 0.11 over open waters, the corresponding mean wind at a height of 10 m would be about 90 knots. The maximum 10-minute mean wind was measured at about the same time, reaching 92 knots with an average height of 220 m above mean sea level. The corresponding mean at 10 m would be about 65 knots, which provides further evidence that Molave was a typhoon at the time of the measurement.

Nowadays, the determination of the intensity of tropical cyclones over the South China Sea is normally based on remote sensing data only (e.g. radar and satellite observations). To the knowledge of the author, the results presented in the paper are the first time that direct measurements of the winds near the centre of a tropical cyclone over the northern part of the South China Sea are made with an aircraft.

Apart from the mean wind and gust, other properties of the wind field of Molave would be studied, e.g. frequency spectrum of the horizontal wind data, and thus the turbulence associated with this tropical cyclone.