Tag Archives: foam stripes

Foam stripes and sand ripples

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So you might have seen my novel on the formation of sand ripples last week, and the tl;dr: I have a vague idea of how sand ripples form, but it’s not as clear to me as I would like.

But imagine my delight when, after two days of foam stripes like this one…

…there was a distinctly different ripple pattern directly underneath the foam stripe!!!

In some places, there was even a tiny little bit of foam left. Where? Right on top the anomalous stripe in the ripple pattern!!!

So now I still don’t understand what’s going on in the sand, but at least it’s lining up exactly with a phenomenon in the waves that I don’t understand, either! :-D

Weekend wave-watching

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Of course I did not only take pictures of lighthouses and instructional activities during the teacher training at Lotseninsel last week. I also took TONS of pictures of water! Some of which I’ll share with you now.

For example below you see where the Schlei flows into the Baltic Sea. This is actually a fairly narrow outlet, and you can see the strong current and the eddies that are formed where it flows into the Baltic Sea! It had been raining a lot previously, so there was a lot of water trying to get out of the Schlei!

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A similar pattern can be spotted at the outlet of the marina, but in this it’s mainly wind-driven.

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And very nice here: Long swell and short wind waves on top of it.

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Of course I also looked at wakes. This is a particularly nice one:

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Oh, and reflections. Isn’t it super pretty how the mast gets reflected with all these little twists and turns?

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And then we had some shielding from the wind, and waves only appearing after a certain fetch.

Btw, that’s the house we all — and all the teachers — stayed in.

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Here we see waves being dampened by some algae stuff, and being deflected downwind of those patches.

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Here is another view of the strong current going out of the Schlei and the distinct separation between the two water masses.

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And now the same thing in combination with the sailboat’s wake. So pretty!

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When we were on our way home, the wind had picked up substantially and we saw lots of foam stripes! Langmuir circulation, nowhere near the coast line.

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Here we get a last glimpse of the house we had stayed in… And more foam stripes!

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And some more ;-)

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And then in Maasholm, we see the waves arriving upwind of the pier and then the tiny ones in the sheltered area. You can see a gust of wind somewhere in the foreground to the right, where there are all those small ripples in a darker patch.

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It was a pretty windy day!

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And more foam stripes…

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And a wake!

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And another wake!

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And just a couple of pictures of water, because I love water.

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Foam stripes

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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?

More foam stripes

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As you might have noticed, I am getting a little obsessed with those foam stripes. Another day, a little more wind, looking up the coast:

And down the coast…

Do you notice the irregularities in the foam stripe in the pictures above? Those are the places where, in much calmer weather, you see the funny waves. I.e. there are steps that disturb the wave pattern and hence the foam stripe.

But remember we saw a foam stripe connecting one going in parallel with the pier to one going parallel to the sea wall? It’s here again:

Its taking a very similar path like it did last time, but this time it joins the one parallel to the sea wall, rather than forming a second stripe parallel to the first one.

And if we continue further down the coast, we see a similar phenomenon (we are now walking towards that edge in the background of the picture below).

Looking back, we see another foam stripe coming from the other edge of the pier, joining the one parallel to the sea wall.

See, this is how they meet at the sea wall?

And, funnily enough, a similar stripe can be seen going through the sailing harbour: Entering it through an opening in the pier and then going across the harbour and out the other end, until it finally joins the stripe at the sea wall.

This stripe finally convinced me: There don’t need to be convergences for the stripes to exist, at least not for those that aren’t running in parallel to the coast. Because I cannot imagine a convergence zone running in such a way through the harbour that is partly sheltered from the wind, has pylons in it, and just has completely different conditions than the open fjord. Or at least the mechanisms forming that convergence zone would have to be very different from those forming the other stripes. So now I am thinking those stripes are just advecting foam from places where it accumulated (in front of the pier) to new places where it accumulates some more.

And finally it just gets stranded on land:

See how nicely the foam stripe is going around the obstacle? :-)

Foam stripes mystery — closer to figuring out what’s going on?

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I think I might be getting closer to understanding the foam stripe mystery. Remember how we’ve always observed them going in parallel to the coast?

Yesterday I saw this again, looking up the coast in one direction…

…and down the other direction. I’ve had the hypothesis that they might be somehow related to Langmuir circulation, but in any case there must be some kind of convergence zone there.

But let’s move closer to that pier we see in the background of the picture above. Here we see a foam stripe parallel to the pier, but at a 90 degree angle to the see wall that I am standing on and that has a foam stripe running in parallel, too! And even more curious: at the edge of the pier, the foam strip detaches and runs toward the coast! See?

Looking down the coast again, we see that foam stripe coming in at an angle, and running in parallel to the coastal stripe in the far back.

Looking up the coast from the pier right where it meets the sea wall, we see both foam stripes running in parallel (as we saw in the picture above):

I think what is happening here is that the foam of the foam stripes doesn’t form locally (which was an implicit assumption I had whenever I was staring at the water, trying to observe more wave breaking there than in other places). Instead, foam forms somewhere else (probably pretty much all over the place) and just accumulates in those stripes. That’s actually pretty likely if we think back to the eel grass or leaf stripes: the eel grass and leaves were clearly advected from somewhere else, too. And actually that’s the same with Langmuir circulation, too: stuff just accumulates in convergence zones but isn’t formed there.

So for some reason there is a convergence parallel to the sea wall as well as the pier, and foam just accumulates there. And as for the part of the stripe that detaches from the pier and runs to the coast? It is going more or less downwind. So it’s probably just part of the stripe parallel to the pier that gets advected around the corner and blown toward the coast.

Why does that stripe end up in parallel to the one at the coast rather than joining it? I don’t know yet. But at least now I only need to figure out why there are convergences in some places and I can let go of the obsession with foam formation in the stripe itself :-)

Do you have any idea that might explain those foam stripes? I’d love to hear from you!

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… :-)