East Asia and Western Pacific METEOROLOGY AND CLIMATE

422
EXPERIMENT:
Only simple and easily available equipments were needed, namely,
a large water tank, common salt, acrylic or wooden lock-gates, self-winding
camera, clock with fractional seconds showing, translucent paper and a
high wattage lamp. Briefly, the experimental set-up is described in Figure
1. The water tank used for the experiment on the collision of two sea breeze
fronts was of size 20 x 52 x 348 cm (width x depth x length). Two locks were
fitted 30 cm from each end. A saline solution of varying specific gravity
was prepared. The saline solution was introduced to the bottom of the tank
between the ends and the locks. The water tank was already filled with
fresh water to about 40 cm depth. The saline solution was introduced very
carefully and slowly so as not to enhance mixing. The specific gravity of
the saline solution was measured by a reflectometer. The salt solution was
filled up to 10 cm height so that the free surface of the fresh water was
sufficiently far away, to minimize its effect on the gravity currents.
To observe the movement of the gravity currents, a shadowgraph
was rigged up. A bright lamp was placed at the back of the tank and the
tank was illuminated through a translucent paper. The translucent paper
was marked by a grid and attached to the back side of the tank. As the
fluids were of different specific gravity, the interfaces could easily been
seen using the shadowgraph method. A digital stop watch showing
fractions of seconds was attached to the front of the tank. The locks were
raised one after another. The advancement and collision of the gravity
currents was recorded by a camera taking photographs at the rate of about
one second a frame. Quantitative parameters such as the velocity of the
fronts and the depths of the gravity currents were measured from the
photographs. Dye could be added for better identification of fluids of
different specific gravities.