Category Archives: observation

Wave-watching

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Do you know the feeling when you, even on the most beautiful of days, want to get out of the pretty parks as quickly as possible so you can finally see the water?

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Especially when it’s foggy?

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And it is so worth it, there is always something to see. For example on that day: what a nice field of shallow water waves!

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And what an awesome criss-crossing of waves being reflected on the sea wall on which I was standing when taking that picture.

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And how sad that this lake was frozen over! :-)

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P.S.: Still looking for a christmas present for your nerdy friend, your niece, anyone who should spend more time looking at water? Check out my book :-)

Wavelength dependency of wave-object-interactions

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Wavelength dependency of wave-object-interactions. What a title! :-) But that is exactly what I observed over the enormous timespan of three full minutes (as shown by the time stamps of my camera) when I went strolling along Kiel Fjord one Saturday morning.

First, I saw this old, overgrown tyre in a wave field that was dominated by small wind waves. We clearly see how they are diffracted around the tyre and how there is a nice interference pattern downwind of the tyre (to the left in the picture below).

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Tyre in the Kiel Fjord and diffraction of small wind waves around it, leading to a beautiful interference pattern to the left of the tyre

Also I quite like how there are absolutely no waves inside the tire, where the wind is shaded off by the tyre and the stuff growing on it.

Then, a really short while later, the wave field was dominated by longer waves running in from the distance. Below, we still see remnants of the old interference pattern to the left of the tyre, but also how the longer waves run around it. In the picture below, the wave crest that was broken up by the tyre is about to rejoin.

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And then, only an instant later, this is what the wave field looked like. Hardly and ripples caused by local wind, but many short waves. No real interaction between tyre and waves visible any more.

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Isn’t that fascinating? And it all happened within three minutes! :-)

P.S.: Still looking for a christmas present for your nephew, your friends’ kid, your geeky friend? Check out my book! :-)

Reflections on reflections

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When we think about reflections in water, we usually think of calm lakes and trees on the shore opposite to us. Or clouds. Or at least that’s what I think of: Everything is so far away, that it seems to be reflected at an axis that is a horizontal line far away from us.

Then the other day I walked along Kiel Fjord and it hit me that I had never actually consciously observed reflection of things that are located close to my position, and especially things who are not pretty much equidistant to me, but where one end is a lot closer than another one. Consider the picture below: Do you notice something that looks kinda odd to you (while at the same time looking super familiar)?

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If you are wondering what I mean, I marked it in red in the picture below: The rope and its reflection! It’s embarrassing to say that (as someone who has been sailing A LOT since the age of 7) this was the first time I really noticed, but it struck me how the maximum of the parable of the reflected rope isn’t right below the minimum of the parable of the rope, but seems shifted to the left. Of course this is exactly how it should be if we think about the optics, but I was really shocked that I had never noticed before and never thought about it before! I bet if I had had to draw the reflection I would have done it wrong and probably not even noticed…

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Here is another picture to show you what I mean. This is what it looks like:

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Below I’ve drawn in the original objects in blue, the axis of reflection in red and then the reflection in green:

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So far, so good, everything looking the way it’s supposed to look. Right? Then look at the picture below:
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Sorry if this seems obvious to you, but I’m fascinated with this right now :-)

But it leads to another interesting thought: Asking people to draw stuff in order to both check their understanding and also make them reflect on their understanding. I recently had the opportunity to observe a class of master students draw the SST of the mean state of the Pacific Ocean (which was an exercise that I had suggested in connection with a class on El Nino. I thought it would be neat to have them draw the mean state and then later the anomalies of El Nino and La Nina to activate prior knowledge) and it was surprising how difficult that was even though I’m sure they would all have claimed to know what the mean state looks like. Having to draw stuff really confronts us with how sure we are of things we just assumed we knew…

And then I’m pretty sure that once we’ve drawn something that we have constructed ourselves from what we knew (rather than just copied a drawing from the blackboard or a book, although I think that also helps a lot), we are a lot less likely to forget it again.

Anyway, this is a type of exercise I will use — and recommend — a lot more in the future!

Surface films dampen waves

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On Tuesday I talked about sea weed accumulating close to the sea wall in Kiel fjord, and I showed you the picture below.

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One thing that I found really interesting about that is how the floating sea weed dampens out all the waves. You can see it in the image above, bit it might be easier to see in the picture below: Can you see how there are a lot of ripples near the top of the image and none close to the sea wall at the bottom of the image?

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It’s not quite a surface film, yet its impact is the same.

Foam stripes parallel to the coast, take 2

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I recently got a new comment on my blog post on foam stripes parallel to the coast, and since you guys hardly ever comment on my blog (I like getting your emails! Really! But why not comment on here? ;-)) it spiked my interest enough to look out for more foam stripes. So about a month ago, I saw this in Kiel: Yes! A foam stripe parallel to the coast!

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I’m actually pretty sure that they are there most of the time, at least when there is some wave action going on, but I just never noticed since they are so close to the sea wall and it’s easy to just look out over the fjord and never look down.

But again, as much as I tried, I could not see how the position of the stripe related to the wave field.

But now that I was intrigued, I went back the next morning to take a look. A lot less wind than the night before, and shorter waves. And what do we see?

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At first glance, there is no foam stripe, but instead there is a stripe where floating sea weed accumulated (indication of a convergence zone? Can you see it? Sorry about the bad picture).

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But then in other spots, there is a little bit of foam, too, where the sea weed accumulated. And this time I could actually see where it came from: That is the area where most of the wave breaking happens when reflected waves meet incoming waves. Mind, though, I could not observe that on previous occasions!

Plus, waves break when they meet the sea wall, and that creates more foam that sits between the foam stripe and the sea wall.

Since at that point I was really intrigued, I went back around lunch time the same day. And what do we see?

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Foam stripes are gone, but there is a lot more sea weed now! And all confined to a narrow stripe along the coast.

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Actually,  if we look really carefully, we can see that there still is a foam stripe parallel to the coast, but very very close to the sea wall now.

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And looking down the other direction, there are even two stripes with sea weed, and only the one closer to the coast also has foam on it. It gets weirder and weirder :-)

Anyway. I guess what we need for foam stripes is enough choppy wave action that waves break (waves alone are not enough as you can see in this post on standing waves which happens to talk about the exact same spot), because if waves weren’t breaking, where would the foam come from? Although sea weed could still accumulate, I guess?

I will investigate further. In the meanwhile, does anyone have any more ideas of what is going on? Do you now see those foam stripes everywhere, too? :-)

P.S.: Kiel peeps, btw, you probably know exactly when I took those pictures, since there is the Sweden ferry coming in on one and then the Norway ferry going out on the other… :-)

Estimating volumes

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Good thing laboratory equipment is always labeled with the volume!

Even though I have played plenty with Legos as a child and am fairly good at 3D stuff, my mind just can’t estimate these volumes correctly. To me, the 500 ml cylinder looks a lot larger than 1 l volumetric flask and it blows my mind that if I fill the complete content of the cylinder into the volumetric flask, it is only half full.

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Anyone else or is it just me?

Swell and wind waves

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Sometimes waves are very regular and mostly of the same length. Those are the ones that I usually talk about when I talk about interference of waves. But of course, other times, there are different kinds of waves with different histories and different lengths, and those do interfere, too. For example in the picture below, there are long swell waves caused by a distant storm, and then small wind waves on top of those, caused by a local breeze.

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The really long swell you can’t even see in the picture, because waves with a couple hundred meters wavelength and just a dozen or so centimeters height are just really hard to photograph… But you get the idea!

Wavelets on bow wave

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The other day (well, the other day when I was still at sea and wrote that blog post. Been quite a while since…), when sailing in calm waters, I noticed the wavelets of a bow wave.

And I cannot not see them these days! No matter how much the other waves try to disguise any trace the boat might be trying to leave to prove its existence, the bow wave wavelets put up a fight to be noticed.

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Below, you see the direction the ship is sailing in (yellow), the wash from the broken bow waves (green) and the wavelets that form the bow wave (red).

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And they look extremely pretty in the setting sun, too!

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If you like pictures like this, you’ll love my book! Stay tuned!

Moving sandbanks

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A while ago I wrote a blog post on how the sand banks in this little creek form. Below you see the picture I showed then:

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Then, about two weeks ago, I passed that spot again when it was raining, and this is what it looked like:

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Now we can actually see the flow field, and we can see that the sand bank in the far back has moved quite a bit. We also see that during the night it must have rained more at some point, since the leaves on the sandbank on the left that got stranded there, must have been carried there by a higher water level.

I went back later that day when it had stopped raining, and then it looked like this:

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Now that the water level has sunk again, you can clearly see that the sand banks have shifted compared to where they were in the first picture a couple of weeks ago.

Funny how much you can discover if you actually look at the world around you :-)