Geoscience Reference
In-Depth Information
southwest orientation moved southeastwards from inland areas across the coast. At HKIA,
the TDWR issued microburst alerts of 30 knots headwind loss for the aircraft between 09:20
and 09:27 UTC.
Figure 6(a) shows the moment when a microburst associated with the thunderstorms
affected the runway corridors to the east of HKIA. Divergent flow feature was found at 0.6-
degree conical scan of TDWR. For an aircraft arriving at the north runway of HKIA
(location in Figure 1) from the east, the windshear associated with the microburst is
performance decreasing (due to decreasing headwind). Using the formulae above, the F-
factor for the microburst is determined to be about 0.14, which exceeds the must alert
threshold and the windshear associated with the microburst is considered to be hazardous
to the aircraft. Flight data are obtained for an aircraft arriving at the north runway from the
east at that time. They are processed by the algorithm in Haverdings (2000) and the
variation of F-factor along the glide path is shown in Figure 6(b). At about the location of
the microburst (near the eastern threshold of the north runway), the F-factor is found to be
about 0.13, which is generally consistent with the value determined from TDWR data. Thus
for microburst associated with the thunderstorm, the F-factor determined from TDWR
measurements and that from QAR data of the aircraft are comparable with each other. The
other peaks/troughs of F-factor from the QAR data (Figure 6(b)) are not revealed in the
TDWR measurements. They may not be properly handled by the microburst model for F-
factor calculation.
Fig. 6. (a) Divergence features (highlighted in lighter colours) associated with microburst on
18 May 2007, overlaid on the radial velocity from the TDWR (colour scale on the right). F-
factor of each feature is given as a number next to the box indicating the location of the
feature. (b) F-factor as recorded on an aircraft flying at about the same time as in (a) along
the glide path shown as a red arrow in (a). The red arrow in (b) is the approximate location
of the windshear feature encountered by the aircraft.
To study the change in the F-factor following the evolution of the microburst, the intense
convective event on 8 June 2007 is considered. Severe gusts associated with thunderstorms
and microburst with a recorded maximum of 35.9 m/s affected HKIA in the morning of that
day. A helicopter parked on the apron toppled in strong winds during the passage of the
intense storm cells. We just focus on the windshear hazard associated with the microburst.
The divergence features determined from the radial velocity of the TDWR at 0.6-degree
conical scans are shown in Figure 7. Stronger winds associated with the microburst got
Search WWH ::




Custom Search