Internal Ocean Tides (2021)

svs.gsfc.nasa.gov

32 points·raattgift··3 comments

This is very cool. I did my PhD in tidal interactions, but in the context of stars and giant planets - bodies that can typically be treated as having spheroidal symmetry. (In fact, one thing I was looking at was the corrections as you moved away from as assumption of spherical symmetry to include the equatorial bulge.)

The Earth's tides are far more complex because of the shape of the ocean basins, and it has quite a high dissipation rate. I'm not sure how much the internal tide contributes to that, but I suspect a lot given that the amplitude (tens of meters) is much greater than the surface displacement.

Anyway, gorgeous visualisation!

> Within the water column the vertical displacement of water in these waves is large, often tens of meters, and even larger in a few places.

> Their characteristic wavelength - about 50 to 100 km from peak to trough

Do we see floating underwater objects, such as fish or other organisms (many of which mostly float and don't propel themselves) or even submarines, being propelled by this current? How much power does it have? Or maybe the effects are too subtle locally due to such long wavelengths?

My gut reaction was that the horizontal motion (away from narrow inlets) is very small.

I tried a calculation. On the US East Coast, St. John's Bay to Cape Cod is about 500km. So, take a 500km long trough that's 1km deep. If the water sloshes so that one end rises by 10m and the other falls by 10m, with a smooth slope between, the midpoint of the body of water would shift by 1.25km, which is more than I expected. But remember that that's over six hours, so, the peak water velocity would be on the order of 2cm/second. It would be pretty hard to capture power from that slow a current.

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