| One of the
first program tasks was to perform a meteorological review and analysis of
historical Hong Kong data. An initial report included a review of scientific theory on
airflow around complex terrain, analysis and identification of the conditions which could
cause terrain-induced windshear and turbulence near Chek lap Kok, numerical experiments
aimed at gaining additional insight into conditions that produce windshear caused by
terrain, and an estimate of the timing and location of significant windshear at the new
airport. That review indicated
that the primary parameters for determining the nature of the airflow include wind
direction and speed, stability, and the presence of critical levels. These parameters were
further studied by performing small-scale modeling simulations using the Clark model of a
wide range of atmospheric phenomena such as downslope winds, gravity waves and wave
amplification, which are often associated with terrain-induced wind flow perturbations.
Preliminary results indicated that both mechanical and gravity-wave processes contribute
to windshear and turbulence and confirmed that the intensity and location of the
turbulence are sensitive, among other things, to wind direction, speed and stability.
|
A study of
test flight results indicated that terrain-induced windshear and turbulence was not
related to a single weather phenomenon and should be expected at any time of year. The
atmosphere during the turbulence events was variable, although wind speed appeared to have
a dominant role in determining intensity. Using 10 years of data, it was found that
significant episodes of terrain-induced windshear and turbulence could last from a period
of several hours up to a number of days since they were governed by long-term atmospheric
motions. Principal phenomena likely to affect aircraft operations at Chek Lap Kok include
crosswinds, longitudinal windshear, large wind changes, turbulence, updrafts and
downdrafts. It was unclear which condition, if any, would dominate. Using the knowledge gained from preparing
the first meteorological report and from other sources, WITI designed a field experiment
to understand fine-scale wind flow in the vicinity of Chek Lap Kok. The basic objectives
of the experiment, which was conducted between March 1994 and September 1995, were to
quantify the frequency and severity of turbulence and windshear; define more clearly the
meteorological conditions under which significant terrain-induced windshear and turbulence
occur; validate airflow predictions made by the small-scale model; determine the elements
necessary to develop the windshear warning system; and collect verification data. |
