Geoscience Reference
In-Depth Information
3
Aviation Applications of Doppler Radars in the
Alerting of Windshear and Turbulence
P.W. Chan
1
and Pengfei Zhang
2
1
Hong Kong Observatory, Hong Kong,
2
University of Oklahoma, Norman, OK,
1
China
2
USA
1. Introduction
Doppler radars are indispensable nowadays in the assurance of aviation safety. In particular,
many airports in the world are equipped with Terminal Doppler Weather Radar (TDWR) in
the alerting of low-level windshear and turbulence. The microburst alerts from certain TDWR
are taken as “sky truth” and the aircraft may not fly when microburst alerts are in force.
This chapter summarizes some recent developments on the aviation applications of TDWR
in Hong Kong (Figure 1). It first starts with a case study of a typical event of microburst
alert associated with severe thunderstorms. The applications of TDWR in the alerting of
windshear and turbulence are then described, namely, in the calculation of windshear
hazard factor using the radial velocity data from the radar, and the calculation of eddy
dissipation rate based on the spectrum width data of the radar. It is hoped that this chapter
could serve as an introduction to the aviation applications of TDWR, for the reference of the
weather services of other airports.
2. A typical microburst event leading to missed approaches of aircraft
The missed approaches at the Hong Kong International Airport (HKIA) took place during
the overnight period of 8 to 9 September 2010 when intense thunderstorm activity brought
heavy rain and frequent lightning to the whole Hong Kong. During the period, an intense
rain band with north-south orientation swept from east to west across Hong Kong. More
than 50 millimeters of rainfall in an hour were generally recorded over the territory and a
record-breaking number of 13,102 cloud-to-ground lightning strokes were registered during
the hour just after midnight. When the thunderstorms edged close to the HKIA which is
situated at the western part of the territory, gusty strong easterlies from the downdraft of
the thunderstorm first affected the flight paths east of the airport resulting in an abrupt
change in the prevailing winds from southwesterlies to easterlies.
Two flights, which tried to land as the thunderstorms approached HKIA, aborted landing and
diverted to Macao eventually. Both flights approached the HKIA from the east under the
prevailing southwesterly winds (Figure 2). The first aircraft went around twice. The first
