East Asia and Western Pacific METEOROLOGY AND CLIMATE

451
Numerical Simulation of Mesoscale Meteorological
Phenomena in Hong Kong
K.K. Yeung, W.L. Chang, B. Wan
Royal Observatory, 134A, Nathan Road, Kbwloon, Hong Kong.
1. Introduction
Traditionally, methods for the objective forecast of
temperature are based mostly on empirical relationships between temperature,
wind speed and direction, sky condition, dew point and other
meteorological parameters. Such methods have been developed by Chin
(1974) for use in Hong Kong. Other examples include the probabilistic
methods of Murphy and Winkler (1974), Winkler and Murphy (1979) and
the regression formula given by Roodenburg (1983). For applications in
complex terrain, McCutchan (1979) has given a method based on Fourier
analysis. As for climatic applications, one can refer to Hansen and
Driscoll (1977) for the generation of hourly temperatures.
With the advent of high speed computers, numerical models
have been employed to give temperature forecasts. An example of this
is a primitive equation model, by Druyan (1974), which give short
range forecasts of global temperatures. Models simulating the evolution
of the atmospheric boundary layer have also been used such as the
one described by Stull (1984) which can be applied in relatively level
terrain far away from cold fronts.
For operational forecasting of temperature, the method
which, in recent years, seems to have gained the greatest popularity
is Model Output Statistics (MOS). This method seeks to establish
statistical relationships between the prognoses from the numerical
models and the weather elements to be forecast. For temperature
forecasts, trials using the MOS method have been reported by several
researchers, amongst whom are Klein et.al.(1975) for the United
States; Francis et.al. (1982) for the United Kingdom; Woodcock (1984)
for Australia and Lemcke et.al. (1988) for the Netherlands. The relationship
between subjective and these numerical-statistical methods
has been examined by Murphy et.al. (1988).
To provide forecasts of temperature (as well as other
weather elements) for Hong Kong's fast growing new towns presents
special difficulties and challenges. This is because of the rugged and
inhomogeneous nature of Hong Kong's terrain (Fig v 1). The lateral
dimension of the topography averages 20 km or less so that if the
influence of the local features is to be taken into consideration, the
mesh size of the model should be less than 10 km. This paper reports
on our numerical experiments using such a local circulation model