The tank is a doughnut-like cylindrical tank with
an inner diameter of 180 mm and an outer diameter of 295 mm. It is filled with stable stratified water to about 500-mm depth to represent the
tropical stratosphere. The wave in the real atmosphere occurs at the tropopause and
propagates upwards. But, in this experiment, considering the symmetry of the internal
gravity wave, the wave is generated in the upper part to facilitate the procedure.
The doughnut-like cover partitioned into 16 rooms is
placed on the tank. Figure 1 is a side view of the apparatus. A thin rubber membrane is on
the bottom of the cover. By pumping air in and out of the cover, the membrane moves upward
and downward, generating waves. Air is pumped with a piston
controlled by a stepping motor. The piston is moved sinusoidal to prevent the induction of
high harmonic waves.