Blog

Diffraction

I find it really fascinating to watch waves being bent by objects in their way. See how the wave is spreading out from the little slit?

Or here how waves are coming in with straight wave crests that get bend once they run into the lee of the pier?

Surfactants 

When I was talking about foam stripes the other day, you might have noticed that the foam stripe wasn’t a foam stripe all the way, but became “just a stripe”. And since I have been thinking about surfactants a lot recently, I think that’s actually what we are seeing in places where the stripe is just a stripe: Some kind of film on the water.

Inside “the stripe” the water looks a lot smoother and waves are dampened out.

At first I thought that it was maybe due to being sheltered from the wind, but clearly that wasn’t the case. If anything, the stripe was in a location where it was more windy (see where it comes out underneath the pier? That should be funneling wind around that corner, not sheltering from the wind!). But surfactants would make sense if they collected in the convergence zone of the stripe.

See how the reflections from the sun are different where there is stuff on the water and the waves are dampened out?

Waves reflecting on a sea wall

I really like it when waves reach a sea wall at an angle, because the resulting criss-cross looks so cool :-)

And especially cool when you see it gradually building up, like below where the sea wall is partly protected by the gravel (or whatever you call those heaps of stones running in parallel to the sea wall?). The energy of waves hitting the sea wall at that part is dissipated, hence no reflected wave is sent off. However waves that hit the sea wall directly are reflected. Can you see how the reflections spread?

See it more easily in the movie below:

Foam stripes

One sunny morning, I noticed The Stripe again:

Running all the way up and down the coast.

In places where there is a large fetch the stripe is clearly foamy:

But looking downwind from the pier the picture above was taken from, the foam stripe becomes just a stripe!

And looking in the same direction, but from further out on the pier, we see that there is in fact a lot of foam on the water, somewhat organised in rows.

Later the same day the wind had picked up and it became even clearer:

See?

Asymmetric propeller blades

On a recent flight to Copenhagen (actually, to Bergen, but that’s another story) I happened to sit with a great view of one of the plane’s propellers. And it struck me how asymmetrical the dark areas caused by the moving propeller above and below the axis looked!

I guessed the explanation would have to be that the propellers were asymmetric in some way, too. Kept me entertained until I saw this:

What could have happened there? Why would there be a seam between completely different patterns of clouds?

I guess there is no reason there shouldn’t be, especially since the cloud / no cloud border is often quite sharp, too. But still, pretty intriguing!

But then a pretty approach to Cph:

And finally: a good view of the propellers. Ha!

And now that I am writing this I am wondering. What’s the difference between asymmetric and asymmetrical? Googling has to wait, I have a plane to catch…

Standing waves in a current

The other day I found the perfect standing waves on a current:

This egg-carton-like pattern really stays pretty constant over time and I think the changes in the wave pattern are mostly due to changes in the sand bed below!

You see the sharp edge that is currently being eroded, and sometimes you catch bits and pieces breaking off.

I think this is super fascinating. Movie below!

Playing with a ROV

The KiFo owns a ROV that — until now — has never been fully operational. But since I like a challenge (and have a really skilled research assistant who really deserves all the credit) it’s working again!

We first went to test it in a tiny lake on campus.

This was exciting enough, since it seemed to have been leaking on previous attempts.

But this time round it did not, and the lake wasn’t deep enough to test whether it was actually water proof even at increasing pressure.

So off to the Kiel Fjord we went!

And after some careful preparations…

…and a careful launch…

…it worked! :-)

Well, at least until the laptop battery died. But it’s a start! Thanks again for the great work, Nico!!!

Expedition learning

In July I will be involved in teaching an “expedition learning” course for a week. It will be all about coastal protection in the Kiel region, so two colleagues and I went on a private expedition to scout out what can be explored where. This is a very picture-heavy post, be warned! It’s more a note-to-self to document the different beaches we looked at than something I expect anyone else to be interested in.

We started out in Friedrichsort, where there were nice breaking waves to be observed. My part of the course, you might have guessed it, will be on observing waves…

img_9010

In Friedrichsort there is a lighthouse on a small headland, and there are sand banks around it that make for very interesting wave fields, like for example below, where the sand bank almost seems to filter out some wavelengths.

img_9021

Looking seaward over the sandbank, we see breaking waves over the shallow part, and waves being bent around the sand bank.

img_9039

A similar thing could be seen on a tiny headland: Can you see how one and the same wave crest gets wrapped around the headland?

img_9049

See? So cool!

img_9052

Btw, you might have noticed the weather changing a lot over the last couple of pictures. It’s April, I guess… But a couple of raindrops here and there make nice tracers for the time since the last wave washing up over the beach ;-)

img_9060

Always fascinating: When you can see wave-less spots that are shielded from the wind, and then local wind waves and others that are travelling in from further away. And breaking on a sand bank…

img_9068

Also, did you see how nice the weather was for a couple of minutes every now and then? ;-)

img_9072

And here is a close-up of the waves breaking on the sand bank.

img_9073

Oh, and looking back to where we came from: That’s the lighthouse on it’s headland right there! And my two colleagues figuring out what’s wrong with the GPS they brought. Their part of the course will focus on more geological things than mine…

img_9077

But I really like this view!

img_9081

See how nice and regular the waves are that reach the beach even though the local wind field is really messy (as you see a little further offshore) and the waves have gone over the sandbank?

img_9090

Oh, and always one of my favourites: When nice and regular waves hit a stone and it sends off wave rings. Love it!

img_9094

One more, because it’s so nice!

img_9098

And here waves bending around a wave breaker thingy.

img_9101

And this is a picture that really nicely shows how if you don’t have wind, you don’t have waves. The lagoon there is sheltered so well that you can actually see the reflection of the bird sitting on the edge!

img_9107

And here we have a very nice superposition of waves coming from different directions and with different wavelengths.

img_9111

And waves coming through the “slit” between sandbanks and spreading as segments of a circle. Nice!

img_9113

Oh, and more waves breaking on the sand bank.

img_9119

After a while, we reached Falckenstein:

img_9120

Not so far away from where we started out at that lighthouse over there:

img_9129

Another interesting superposition of wave fields.

img_9131

Oh, did I mention we did a lot of walking in the sand? About 20k steps. Well, I guess that isn’t even too bad…

img_9146

Below I really liked the criss-crossing of waves. It’s actually one wave crest crossing itself after being bend by the shallowing water.

img_9151

And those waves get deformed a lot, too!

img_9168

And here we knew that it was a matter of minutes until those rain showers would be where we were…

img_9183

Luckily, this shower went over quickly, too.

img_9204

And this is the kind of stuff the other courses will be dealing with: Awesome formations in the coast!

img_9208

Ha, another weather front:

img_9214

And this is my favourite geological feature: there are interesting features in the sand/soil/stone (however you call it?) and then erosion marks, clearly made by water, right below!

img_9223

A little bit further along the coast, there are weird wave breakers and if the wind hadn’t died down, we would probably have been able to see more interesting waves than these…

img_9224

But the waves below were really cool: There were the ones that you clearly see on the picture at an angle to the coast, and then there were waves that came in perpendicular to the coast (so the wave crests were parallel to the coast) and they washed the other waves on the beach and back into the sea. I should really upload the movie…

img_9227

So those waves above caused ripples in the sand which are parallel to the water line, even though in the pictures the other wave field is a lot more visible!

img_9233

See?

img_9235

We ended up in Schilksee and had a look around the marina. Apart from the typical wind / no wind resulting in waves / no waves, we saw……

img_9241

…this! Pretty cool, huh?

img_9242

And again:

img_9243

One last look at the coast near Bülk.

img_9249

At this point, only one of us still felt like exploring every nook and cranny…

img_9252

Even though there were some pretty nice wave fields, but we could see them from our vantage point without doing an extra step ;-)

img_9253

Actually, there were a couple of cool features on the beach still. What’s up with those little bays?!

img_9255

img_9256

We ended the day with trying this very cool contraption to measure the coast with. It was actually a lot of fun!

img_9262

And you wouldn’t believe how much work it was to hold that ruler thingy in the wind!

img_9267

So yeah, that’s what we did. And how was your day in the office? :-)

Air-sea gas exchange inhibited by oil layer on water? Yes, but not always

I have been brainstorming hands-on experiment ideas for a project dealing with the influence of oil films on air-sea gas exchanges, and one idea that I really liked was this one: Use sparkling water, pour oil on top, observe how outgassing stops.

Now. I should probably have realised that this was a stupid idea before trying it, but in my defence: I have a really really busy week at work and I just wanted a quick and dirty experiment.

As you probably know, sparkling water bottles are under a lot of pressure. Especially when you have been carrying them home right before opening them. As you will see from all the drops on my backsplash shown in the movie below, mine exploded all over my kitchen when I opened it…

But even that wasn’t enough of a clue for me to realise that the process that drives CO2 out of sparkling water probably isn’t just a gradient in concentrations between the water and the atmosphere, but that the CO2 can only be kept in solution under high pressures. So yeah, my oil film doesn’t inhibit gas exchange at all, my sparkling water with oil on top is outgassing just as happily as the one without. I suspect the oil film will only have an impact once outgassing doesn’t happen via bubbles any more, and hence isn’t visible any more. Fail!

But the movie is pretty, anyway.

I guess we would actually have to measure gasses in the atmosphere and water in order to run such an experiment… Which makes it a lot less appealing. I would really have liked to be able to stop sparkling water from sparkling just by pouring oil on top. Bummer! :-)