Re: gravity waves

[John Mallinckrodt <ajmallinckro@CSUPomona.Edu>]

On Thu, 23 Oct 1997, John DaCorte wrote:

> Could someone describe the difference between gravity waves and
> gravitational waves.  I recently saw a picture and caption from a magazine
> on a bulletien board that said gravity waves were responsible for the
> formation of noctilucent clouds (clouds with ripples).  The caption also
> differentiated between gravity waves and gravitational waves.  I thought I
> had a vague idea about one of these concepts but now think I have been to
> one too many rock concerts.  Thanks in advance for any help.

Gravity waves are what you see when you look out over Frenchman Bay.
Gravitational waves are what you feel when you visit a pair of orbiting
black holes.

To be a little less coy: "Gravity waves" are waves on the surface of a
fluid that result when the restoring force of a constant "gravitational
field" ("real" or "artificial," whatever that means!) acts on a
disturbance of the fluid surface from equilibrium.  In the case of the
atmosphere, the "surface" is less well defined but there is, nevertheless,
an equilibrium density profile that decreases with altitude and can be
disturbed.  Clouds can make the disturbance visible. 

"Gravitational waves" are waves in the gravitational field itself and are
the result of accelerating masses. The mechanism is similar to that by
which accelerating charges produce electromagnetic waves. Both can be
considered to be the result of the finite velocity with which local
alterations in the field source density are communicated to more distant
regions.

John
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