Let's take a look at the experiment results. The
white dots on the screen are the neutrally floating
beads. Looking at this, a current is flowing
horizontally around the water tank in addition to the
short-cycle waves. Further, you can see that the
current is reversing periodically from the bottom of
the tank (i.e. the top of the stratosphere).
This happens because the wave does
not simply oscillate back and forth but
the waves have momentum
in the direction of the phase velocity. The wave
which passes through the current carries reverse
momentum opposite to the current far away. This
momentum reverses the current.
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