Re: More "Moon's synchronism"

[brian whatcott <inet@intellisys.net>]

At 09:40 4/1/98 -0500, you wrote:

> 	Jim's most excellent web site HAS this mid-ocean data!
> 			Check it OUT!
>
> Chuck Britton=20

This URL is as follows:

http://www.sisna.com/users/jmgreen

I did as Chuck suggested and reviewed Jim's web presentation - which is
nicely done in my view. But I have taken the liberty of extracting a little
of Jim's text for review here below. The world map to which he refers shows
lines of isochronal tides. The map projection is not particularly helpful
in one respect - if one would like to see where the ocean tide runs more or
less parallel to the meridians as in the North Pacific, it is necessary to
imagine their projected shape which is not a straight line of course.
 I direct you particularly to his second and third paragraph quoted below:

                    [Jim Green]
"The map shows that the speed of the tides is usually not at the speed of
the Moon -- about 15deg/hr. This angular velocity at the equator would be
about 1000mi/hr or about 1600km/hr and at 60 degrees north or south
latitude would be about 800km/hr. [ 8 ] However, in the region between
Japan and New Guinea, the map shows that the motion is westward at less
than 300 km/hr."

"In the previous example, the high water crest travels the 1000 miles from=
 Los
Angeles to Seattle in the same one hour interval as it takes to travel the
100 miles from San Diego to Los Angeles."=20

"Indeed the speed of the tides can not be as high as 1600 km/hr. For
shallow water waves -- waves with wavelength much greater than the depth of
the water basin like tidal crests -- the speed is given as sqrt(gd) with g
=3D 9.81 m/s=B2 and d =3D the basin depth. [ 9 ] The ocean depth is about 3-=
5km
so the maximum speed of an ocean wave is of the order of 600-800km/hr. So
any so called "tidal bulge" motion could not keep up with the Moon except
at a latitude greater than about 60 degrees. [ 9 ]
[Cf. Appendix B for details of these calculations.] "
--------------------------------------------------------------------------



On the face of it, Jim appears to argue that the oceanic tide cannot run at
1600 km/hr (his third para)   but that the tide DOES in fact run at 1000
miles/hr
between LA and Seattle (his second para). The world chart appears to show
quite a few places in the deep ocean where the tide in fact runs faster
than 1600 km/hr so I am at a loss to justify his position on this.

  But his graphic world model (the numbers are apparently synthesized) is a
vivid illustration of Jim's main thrust, I suggest - the tidal progression
is very, very untidy - very far from a stately progression of meridional
change round the globe.


Whatcott   Altus OK