East Asia and Western Pacific METEOROLOGY AND CLIMATE

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the rugged coastline terrain. A model study can be performed using the
observed sea breeze characteristics.
Mathematical model using equations of fluid motion had been
developed to model sea breeze fronts, Clarke( 2 ).
Three dimensional model is
needed for the complex terrains in Hong Kong. Three dimensional
calculations
for flow past non-rectangular bodies are notoriously difficult
and time consuming on the computer.
The other alternative is the use of
scale modelling. A wind tunnel with the capability for cooling a
significant portion of the test section floor is required for simulating sea
breeze, Meroney et al( 5 ). This type of meteorological wind tunnel is
expensive to build and run. There are only a few existing in this world. A
cheaper alternative has to be found for modelling sea breeze intrusion.
Fortunately
SimpsonW noticed the internal structure of sea breeze front
was similar to the gravity current formed when a lock-gate separating two
fluids of different density was opened suddenly.
This experiment can be
performed very inexpensively in the laboratory with a long water
channel.
To see whether the laboratory experiment can really model the
nature, a particularly complex situation of the crossing of two fronts was
simulated in the water tank. Sometimes, the interaction between a
thunderstorm outflow and a sea/lake breeze may occur. Observations of
such interactions were reported by Boyd(^), Moraz and Hewson(^). For
large islands or peninsulas, collision of sea breeze fronts had been also
observed. A well documented case near Stansted was reported by Rider and
S imp son (7). The movement of the fronts were followed by the radar echos
of swifts. Some qualitative and quantitative results were published in that
paper. Clarke(^) also performed a numerical computation on a two
dimensional double sea breeze collision.
In this paper the experimental procedure on the collision between
two gravity currents is described. Suggestions for performing a sea breeze
intrusion into complex terrain in a water tank is put forward.