We performed the experiments with several different wave amplitudes and
frequencies. The parameters are shown in Figure 4. The Brünt-Väisärä frequency in
these experiment is 1.4(s-1).
When the amplitude of the wave is small, mean flow does not occur and the
wave only propagates downwards. Animation 1 shows a typical movement of fluid visualized
with floaters in the case of no mean flow. Since the floaters that are located far from
the wave source move with small amplitudes, it is obvious that the waves are weakened