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Re: Bulges





On Tue, 4 Mar 1997, Jim Green wrote:

Donald, this info is really good, thanks.

Jim,

I pulled the article this afternoon, and it's ok. When (if?) I get the
Stenger posts edited, I think they will be more comprehensive.

But remember that there is a BIG difference between "tidal forces" and "the
ocean tides" per se. The forces are well understood and have been readily
calculated by several people (including NOAA) even though we are going on ad
nauseum on the method here.

Oh, agreed. I simply *was not interested* during that thread in the
complications of oceans and continents, but was interested in freshman
textbook explanations of why there ought to be *two* tidal bulges.

I pulled a couple of books from our library on a hurried trip
there between classes, including George Darwin's book. Now I think I see
why so many textbook accounts have, in my view, unsatisfactory and
misleading accounts of the relative importance of field gradient effects
(tidal 'forces') and the centripeteal effects. They are trying to copy
Darwin's explanation!

It is the RESULT of those tidal forces which is grossly missunderstood by
almost everyone --

The assumption is that because the tidal force potential gradient is some
sort of prolate spheroid, that the oceans are the same shape. They are NOT.

Agreed.

Another comment: as you suggest the first order force gradients of the
several planets is each much less than those of the Moon or Sun at the
surface of the Earth, BUT some the coefficients of the planetary tidal force
harmonic terms are *greater* than some of the coefficients of the Moon or
Sun harmonic terms.

Again, I was concerned *only* with the size of the force gradient, and the
resulting physical deformation of an elastic sphere, not on oceans. When I
think of tidal forces, I don't think of oceans, since I grew up in Iowa.

Are you refering here to the harmonic components due to varying distance
of the object from the earth?

The planets DO have an influence on the ocean tides
when their frequencies are a match for an ocean basin -- It is true that
NOAA and the like ignore this. Of course long before this question is
considered, they really ignore the whole issue and do a Fourier transform on
the real raw water height data for their predictions.

I don't disagree, having not looked at the numbers. But aren't they rather
small? Can we experimentally verify these planetary effects or separate
them from the rich mix of influences, including effects due to varying
ocean depth?

Our concerns were obviously focused on different aspects of this
phenomena.

-- Donald

......................................................................
Dr. Donald E. Simanek Office: 717-893-2079
Prof. of Physics Internet: dsimanek@eagle.lhup.edu
Lock Haven University, Lock Haven, PA. 17745 CIS: 73147,2166
Home page: http://www.lhup.edu/~dsimanek FAX: 717-893-2047
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