Kiel to Bergen, the mini series. Part 11, in which our wake meets another small island

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And here we are again, driving past the next interesting structure. Above, you see our feathery wake (telling you that we are driving left-to-right past that bay).

And below, I am turning backwards to still see the bay, therefore you now get a glimpse of our turbulent wake, too. Also you see where the waves of the feathery wake are crushing against the coast, the waves are breaking and splashing quite a bit.

Still looking back towards that bay — and isn’t this a beautiful view of our own wake? As you see the ship is turning, and this smooth water surface in the wake looks so cool against the normal, wavy, water surface outside of the area that was ironed flat by the ship.

Kiel to Bergen, the mini series. Part 10, in which our wake meets a tiny island

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In the picture above, you see the waves that constitute our feathery wake *almost* reaching the little island (we are driving towards the lower right corner of the picture).

And now, they are here! See how they lap against the rocks?

Below you also see parts of the wake as they are reflected by the little island, and you see our turbulent wake in the lower left corner of the picture.

Also: How cute is that house? I would totally not mind not having a garden if that was where I got to live!

Kiel to Bergen, the mini series. Part 9, in which we look at what the other ships do when they meet our wake

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After all this wake watching, you probably noticed that the ferry I am on has a large wake. So it was fun to see how other boats changed their course as soon as we were close: Heading straight into the wake! I would rather head straight into it than being hit by it from the side, too…

Don’t know if you see it in the picture below, but even larger boats were bobbing about quite a bit when they were hit by our wake.

Kiel to Bergen, the mini series. Part 8, in which we do a lot of very cool #wakewatching

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Now we have reached Oslofjorden. Look at our beautiful wake!

Since the water is calm inside the fjord, we now also see another interesting feature of the wake: The waves that connect the “feathers” of the V. Looks a bit as if we had been going over speed bumps for as far as we can see :-D

And looking down to the side, we quite clearly see the different parts of the wake. The feathers, the turbulence. Did I mention I love watching turbulence in water?

Also very interesting: The wake behind that little light house. Do you see how the surface reflects the sunlight differently in a streak going to the right and slightly up? That’s where the water is more turbulent in the wake of the light house (since the lighthouse is stationary, the current must currently be going out of the fjord).

My phone isn’t really good at capturing pictures in this light (or, well, maybe I am just not supposed to point the camera at the sun?) but it makes me really happy to see the reflection on the one slope of the feathers of the wake :-)

Planetary Rossby waves filmed with co-rotating camera

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And here is my new favourite experiment again: Planetary Rossby waves! This time filmed with a co-rotating camera.

We have a square tank with a sloping bottom at solid body rotation (except this annoying slogging because the rotating table wasn’t levelled out [meaning: I didn’t level it before starting the experiment…]). We then release a blue ice cube in the eastern corner of the shallow end of the tank and watch as the melt water column stretches down to the bottom, and is driven back up the slope to conserve vorticity. A planetary Rossby wave develops and propagates westward!

Above, we are looking at the tank east-to-west. Note the sloping bottom with the deep side on the left. And just look at all these beautiful eddies!

This is what it looks like in motion:

Watch the full experiment here if you are still curious after seeing the 1.5 minutes above :-)

Topographic Rossby wave

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Finally trying the topographic Rossby wave experiment I wrote about theoretically here!

And it is working — ok-ish. If you know what you are looking for, you can kind of see it. So check out the picture above so you know what you expect to see below ;-) We are rotating the tank fairly rapidly (and there are a lot of inertial oscillations in the water even after a long spinup, don’t know why) and then slow it down just a little bit to create a current relative to the topography.

So it turns out that following instructions better might actually have been a good idea. We will do that some other day on a different rotating table.

Here is what we did today:

Setup of the topographic Rossby wave experiment

For a demonstration of topographic Rossby waves, we want the Coriolis parameter f to stay constant but have the depth H change. We use the instructions by geosci.uchicago.edu as inspiration for our experiment and

  • build a shallow ridge into the tank. My solution: Take a 2.3 cm (outer) diameter hose, tape it to the bottom of a tank to achieve a ridge with smooth edges
  • important difference to the geosci.uchicago.edu setup: We are just using our cylindrical tank without a solid cylinder in the middle. Therefore our ridge goes all the way across the tank. Main reason is that our rotating tank’s camera sits on six rods, so at fast rotations it is very difficult to insert dye and I thought this way might be easier. But that might not actually be true…
  • 10 cm water depth
  • spin up the tank to approximately 26 rpm (23 seconds for 10 rotations == 36.5 on the display of GFI’s large rotating table)
  • wait for it to reach solid body rotation (ca 10 min)
  • introduce dye upstream of the ridge,
  • reduce rotation slightly, to approximately 23 rpm (26 seconds for 10 rotations == 33 on the display of GFI’s large rotating table) so the water inside the tank moves relative to the tank itself, and thus has to cross the ridge which is fixed to the tank
  • watch it change from laminar flow to eddies downstream of the ridge. Hopefully ;-)

Kiel to Bergen, the mini series. Part 7, in which I find evidence for a rough night at sea

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Remember how the morning was beautiful but windy? As I got up and saw how the sea spray was flying, I remembered having woken up during the night, noticing the ship move. Since it’s quite a large ship I remember being a little surprised, but falling asleep quickly again since I really love sleeping on a moving ship.

Anyway, check out that stack of chairs in the far corner of the Sun Deck. You would think that if it got wet, that would be only from rain, right?

Nope. Judging from the brine visible on the arm rests, the air must have been full of sea spray during the night (And it has to have been during the night and not some other time, because the previous day I had gotten a chair from that pile and there wasn’t anything like that on them for sure). Again I was super happy about my rain gear so I could just sit down in the brine, knowing full well that I would have salt all over me later…

The sun lights objects on Earth from the exact same direction as it lights the moon, and some wave watching

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The sun lights objects on Earth from the exact same direction as it lights the moon (see a thought experiment on that here). So far so not surprising, at least in theory. In practice, I still find it kinda amazing every time I notice.

Like this weekend, when I was “fishing” with two kids, 3 and 6 years old, who happened to be very keen observers. The 3-year old pointed out that the moon was visible in broad day light as she’d sometimes seen before. The 6-year old said that only the part of the moon that was lit by the sun was actually visible. And when I pointed towards the moon, I noticed that my ring actually nicely showed parts of the spheres illuminated from the sun, and other parts in the shadows. Just like the moon! Thus the two pictures, one focussed on my hand above, the other one focussed on the moon below. This phenomenon can very nicely demonstrated with any kind of sphere!

The 3-year old also pointed out that the clouds were very pretty, but looked as if it was very windy up there.

And — much to my delight — that the mountains seemed to be moving! At least when not looking at the mountains directly, but rather at their reflection on the water. And the 6-year old added that the houses seemed to grow and shrink with every wave on the water that went through their image.

Luckily for us, there were all kinds of different waves — from a completely calm lake in earlier pictures, to longer wavelengths from the wake of a boat above, to also very short wavelengths from people dangling their feet in the water. So much fun to do wave watching with kids!