CONFIDENTIAL
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3. METEOROLOGICAL CONSIDERATIONS
(a)
Wind
Between April 1949 and March 1950, winds were observed at the Ping
Shan police station. Wind speeds were measured by an anemometer mounted 10 feet
above ground while wind directions were measured by a wind-vane mounted 30 feet
above ground. Details of the data collection programme are described in Ref. 1.
Only the statistics of winds exceeding 13 knots are given by Ref. 1. Fig. 2
shows the frequency of winds exceeding 13 knots from the various wind directions
(10-degree sectors) during the 12-month period. Commenting on the results, Ref. 1
states that:
"It is obvious that more reliable results would have been obtained
from a longer series of observations, for a single spell of strong
winds lasting a day or two would materially affect the frequency
distribution shown in the wind rose [Fig. 2]. For what they are worth,
however, the results indicate that fresh or strong winds are
comparatively infrequent at Ping Shan, and that the most suitable
orientation for a runway in this area is probably ENE-WSW."
Adopting 13 knots cross-wind as a criterion, the usability factor of Ping Shan
as the site of an airport was computed to be 99.6%. However, a single typhoon
in September 1949 contributed 17 out of the 27 cases with cross-wind exceeding
13 knots. The computed usability factor should be treated as a rough estimate
only.
In January 1975, a used spare Dines pressure-tube anemometer was
installed at the Tsim Bei Tsui Police Post at a height of 17.5 m above ground
(43.7 m above mean sea level) in an attempt to obtain early indications of
arrival of cold surges from the north. The location of the anemometer and the
nearby terrain are shown in Fig. 3. The site is sheltered from winds from the
CONFIDENTIAL