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Comment by pavel_lishin | Hacker News Reader

> The study, in the July 27 issue of the journal Nature, concludes that the storm in the Great Red Spot produces two kinds of turbulent energy waves that collide and heat the upper atmosphere. Gravity waves are much like how a guitar string moves when plucked, while acoustic waves are compressions of the air (sound waves). Heating in the upper atmosphere 500 miles (800 kilometers) above the Great Red Spot is thought to be caused by a combination of these two wave types “crashing,” like ocean waves on a beach.

I'm surprised that gravity waves from something that small can have an affect on the atmosphere.

(Yes, I know that Jupiter is big, and so is the Spot, but gravity is incredibly weak.)

EDIT: apparently there is a very big difference between "gravity waves" and "gravitational waves"; I withdraw my comment, but leave it for posterity so that others can be enlightened!

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Gravity waves are the waves forming on top of atmospheric layers, like ripples in a pond.

Gravitational waves are the spacetime waves generated by black hole mergers and the like.

Very different phenomena.

Google search seems complicit in this misconception. A search for gravity waves (without quotes) yields only results for gravitational waves. Searching "gravity waves" is only slightly better, yielding the actual meaning as the second definition (and result).

http://www.planetary.org/blogs/guest-blogs/2016/atmospheric-...

> It’s important to clarify that atmospheric or oceanic gravity waves are not to be confused with gravitational waves, the outward propagating perturbations in spacetime that are associated with cool physics graphics and, apparently, any and all Google searches on either subject.

Well, it's two different phenomena wth unfortunately similar names. Of course it's going to trip up search engines.

So "gravity waves" are what we commonly call "waves"?

To be fair, both are 'waves' of some sort.

But, yeah, gravity waves are closer to the common understanding of the word 'waves'.

The current understanding of waves on a liquid surface is attributed to a clear boundary between two fluids with a density difference and a velocity gradient. Gravity plays no role in this.

Kelvin-Helmholtz instability: https://en.wikipedia.org/wiki/Kelvin%E2%80%93Helmholtz_insta...

Two fluids with a density difference and a velocity gradient usually have a common force acting upon them, e.g. gravity, which enforces so-said interface. Perturbations to the average interface are restored via this force, and these perturbations are called gravity waves.

KH Instabilities give rise to gravity waves.

Big water waves are gravity waves, but ripples are capillary waves, I think.

But likening them to ripples in a guitar string is still silly.

Why choose this somewhat distant similie when ordinary water waves are real gravity waves, and are even more familiar to people than are guitars (let alone the excitations of their strings)?

Perhaps the gravity waves in question are standing waves?

See https://en.wikipedia.org/wiki/Gravity_wave

Thanks.

So gravity waves are just what laypeople call waves...

what crappy naming! the essential mechanism is fluid-dynamics not gravity...how confusing

Name seems fine to me.

From the first paragraph of the wiki-page:

In fluid dynamics, gravity waves are waves generated in a fluid medium or at the interface between two media when the force of gravity or buoyancy tries to restore equilibrium. An example of such an interface is that between the atmosphere and the ocean, which gives rise to wind waves.

but the same waves could be reproduced without gravity in an appropriate accelerating frame (e.g. in a rotating body at a Lagrange point) so gravity isn't _essential_, whereas it is for gravitational waves

Gravity is the result of an appropriately accelerating frame (i.e. the curvature of spacetime).

In many scientific disciplines, gravity waves are called "g waves" to prevent confusion with actual gravity. Alas, that doesn't help when Googling.

BTW, gravity is not incredibly weak. It's what makes Jupiter warm, and powers brown dwarf stars.

When people say gravity is weak, they usually mean "relative to other forces of nature"

Put a small magnet above a paperclip. When the magnet is close enough, the paperclip will jump up and stick to it.

At that moment, the magnetic force of the magnet pulling the paperclip upwards is larger than the gravitational force of THE ENTIRE EARTH pulling it downwards.

Is gravity as a force weak, or are we just used to materials where the electrical charge is disproportionate to its mass?

Maybe the kilogram is just a tiny unit compared to the coulomb, and if that relationship was normalised the forces would appear abouh equal.

All tongue in cheek, of course. They're just different ways of saying the same thing. In our collective experience with our regular materials, magnetic forces, when present, tend to be stronger at short distances than gravitational forces.

The coupling constants of the various fields are unitless and the gravity coupling constant is order of magnitude smaller than the others.

That is cool information. Where can I read more about that?

I suppose it's a scale thing. At a small scale, including human scale, gravity is weak and the other forces are strong. At a large scale, the other forces don't really exist at all, and so it is gravity that is strong.

Oh, I totally get the usual reason. But as an astronomer, when I look up at the night sky, I think about how all that glowing stuff was assembled by gravity, with magnetism playing a supporting role by driving the Balbus-Hawley instability in accretion disks[1].

1: https://en.wikipedia.org/wiki/Magnetorotational_instability

I agree, gravity does create its most beautiful artwork at the cosmic scale.

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