Sorry to jump into this thread so late, but someone was asking about
data on global tide observations....
It turns out that we *finally* have such a thing available. The
TOPEX/Poseidon satellite (a joint US-French mission) measures the
height of the world ocean to within a few centimeters. (Seems like
magic to me, but apparently it really works.) In order to get the
dynamically important component of ocean height (i.e. the lumps of
water that, combined with Coriolis, tell us where the strongest ocean
currents are), you first need to subtract out the tides. The satellite
was specifically designed with this in mind. This means that TOPEX/Poseidon
has given us, for the first time, a truly global observation of the
"bulges" of water that represent the tides. Of course, those bulges
do *not* travel as twin bulges pointing towards and away from the
moon. Rather, each ocean basin has a bulge travelling around and
around--the result of (1) astronomical forcing (sun, moon, etc.)
(2) topographically-determined resonance in each basin, and
(3) Coriolis forcing due to the Earth's spin.
One more point: As has been pointed out before, the phase speed
c=sqrt(gd), where d is total ocean depth, applies only to
*free* gravity-driven surface waves (when the wavelength is
comparable to the depth, as is the case for tides). Forced
waves, e.g. a ship's bow wave, travel at a speed determined by
the forcing. This means that the speed of the tidal wave (not
a tsunami---I mean the wave that makes up the tide) is not
constrained to be of order sqrt(gd).