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Subsurface Ocean Waves Can Be More Than 500 Meters High
An anonymous reader writes: New field studies out of MIT found that "internal waves" — massive waves below the surface of the ocean — can reach enormous sizes. The most powerful internal waves known to science are in the South China Sea, and they can be over 500 meters high. These waves mix disparate layers of ocean water, and contribute to evening temperatures between various bodies of water (abstract). The waves grow larger as they propagate, and carry on all year. These waves have enough mass to affect the earth-moon system: "To cut a long story short, it's not unreasonable to say internal waves play a role in the moon moving away or receding from the Earth. They are big enough that they affect large-scale celestial motions."
I can tell you that undersurface waves are freaking awesome for those with a good sense of adventure :-) Best rides I have ever had.
There is water at the bottom of the ocean!
There is no God, and Dirac is his prophet.
I think you mean that their amplitude can be as much as 500m. For a start these are not surface waves so they do not raise the water surface. Additionally, although the article does not really specify it, I would expect that they are actually far more longitudinal than transverse in nature and so the displacement will be almost entirely in the same direction of the wave motion i.e. horizontal. Fluids generally tend to be very poor transmitters of transverse waves because they cannot support a shear stress.
No, I don't think so.
This actually sounds like now that we look closer, the waves are propagating in 3 dimensions, are much larger than we've previously thought, and much more of a big deal.
But for a very long time we've probably though "waves, on top of the water, got it" ... and now they're saying "waves, propagating in 3D and getting bigger and far more powerful".
I don't think we're re-defining wave, so much as understanding what all that entails.
So, maybe we need to look at your dictionary.com definition as being "woefully inadequete to explain what is really happening".
If you've ever seen a high speed picture of an explosion and see the bubble of the shock wave, it's propagating in a sphere, and not just along the surface.
This isn't some new and inconsistent definition of wave. But it is something which says they're realizing how much more complex it actually is.
Lost at C:>. Found at C.
"Internal waves" are no different than (i.e. obey the same scientific principles as) surface waves. They are both "interfacial waves". The difference is that the air/water density difference is much greater than the water/water density difference.
It has an impact on land-based life as it can drive upwelling, which both causes cooler temperatures near the shore and provides nutrients for sea life.
Generally when talking about water, the definition of a wave specifies it is on the surface:
http://dictionary.reference.com/browse/wave"a disturbance on the surface of a liquid body, as the sea or a lake, in the form of a moving ridge or swell."
If you are using another definition of the word wave (such as that used by physics to refer to light, sound, etc.) when talking about water, you really should specify what you mean.
Given that their paper was published in Nature, they used the correct term for the phenomena.
Internal gravity waves, the subsurface analogue of the familiar surface gravity waves that break on beaches, are ubiquitous in the ocean. Because of their strong vertical and horizontal currents, and the turbulent mixing caused by their breaking....
Generally when talking about water, the definition of a wave specifies it is on the surface:
When oceanographers (the people involved in this report) talk about waves, they can be referring to any interfacial wave. The equations are the same, but the density difference between air and water for surface waves means the density components of the equations can be omitted for simplicity without loss of accuracy.
Internal waves are a long-known phenomenon. And no, they aren't talking about currents. Currents are something else which can be driven by waves, but are inherently due to pressure differences from any source, not just waves. E.g., a rip current can be driven by a non-uniform wave field creating different levels of setup on a beach, or by uniform waves on a non-uniform beach doing the same.
They are not currents because the water isn't flowing, it is moving in place, albeit a 500m range.
Waves in all definitions are movements within a fluid where the particles move back and forward around a fixed point. The dictionary definition is inaccurate by stating that the disturbance is at the surface, the movement happens through the body of water. It is visible at the surface, but it takes place in the body.
Trying to become famous by taking photos. Visit my homepage please.
The definition above is a visual description of what are generally caused by wind. You want definition 11 in your link.
No, definition 1 is correct. The "body" is not the ocean as a whole, it is the body of denser water within the ocean, and the "surface" is not that of the ocean, but the surface of the higher density water.
The full wave equations are the same, but at the surface there is a simplifying assumption that density of water is much greater than density of air and the density terms can be ignored. The density term is something like (d2-d1)/(d2+d1). If d1 (density of upper layer) is very small compared to d2 (density of lower layer) then that term is essentially d2/d2, or 1. That's not true for an internal wave at the boundary between water layers of different salinity or temperature.
This is an example of internal waves, although it is intended to evoke the calming effect of ocean surface waves. If you had just water and air in that box, the waves would be too small and fast, but by using two liquids of similar density the celerity and amplitude of the waves will be slower and larger, simulating the large scale behavior of ocean surface waves.
The turbulence as internal waves move is also not completely unknown. It is possible to see surface effects of internal waves created by ship wakes, for example.