Category Archives: wave watching


Ooops, long time no see! But even though I haven’t posted a #WaveWatchingWednesday on my blog in a while, I’ve still been active over on Instagram.

These are the last pictures I took on a beach walk before going to visit my family (sadly far away from the sea ;-))

After being away from Kiel and mostly offline for a week, I saw this beautiful swan family one morning, leaving wakes in the wind waves that in some spots reflect the sky, in others let us look into the water (never thought back in physics class that partial reflection would be something that actually had any real world relevance). So much beauty in nature, and such cool physics!

And some cool wave watching the next day: Are they coming? Are they going? The answer is both — or neither. The waves reflected at the seawall run directly into uncoming waves (both of the exact same wavelength) such that a standing wave develops. Where two wave crests or troughs meet, the crest is twice as high (or the trough twice as low) as for only one wave. But where a crest and a trough meet, they cancel out exactly in destructive interference. And that leads to this weird wave field!

Wakes, but only one of them has a bird at the tip of the V? What’s going on? Carps, apparently! :D

Next, there was another trip to the beach.

Nice to see how waves get bent around that groyne!


Why is the surface roughness changing in the shallow water where all of a sudden the surface gets smoother while the waves get higher?
Waves get higher as they run into shallow water & start interacting with the bottom. And it’s full of stuff growing in the water there, taking energy out of the wave field such that only longer waves remain visible.

…And by the time I had whipped my phone out of my pocket, the bird was gone. But what was left — even if only for a really short time, before they disappeared, too — was even more fascinating to me. Those waves! You see them mainly in the pattern of light and dark on the seafloor. Only looking out further into the water do we start seeing a reflection of the sky, too… Dreamy!

Ha! All this mud in the water at the very top of the pic? That’s where the water is shallow enough for waves to stirr up the ground! See how it gets so much clearer if you only look a little bit further away from the coast where the water is slightly deeper?

Not even the seagull is enjoying the fog…

Even though it might not look like it, I am very happy I decided to use the 20 min between calls to bring my coffee & run to the water!

It’s funny how even a tiny little peak of the sea makes me instantly happy :)

#wavewatchingmakes me happy :)

What a beautiful pattern in the waves & light again :) Wave field reflected at the sea wall and interference forming a checkerboard-like pattern in the waves. Beautiful! :)

125 years of Kiel canal today! One of my favourite wave watching spots. Even without ships it’s interesting — see how windy it is? Looks like there is Langmuir circulation developing which you see by those rows of foam in downwind direction.

A ship being tugged around in a narrow canal before all that wake action in the next pictures can happen. Quite interesting to watch!

Interesting ship watching today: first a nice wake, then a lot of mud being stirred up in the turbulent wake! I’ve never noticed that as clearly before.

One last wake. Because it’s so beautiful. And because I find the structure absolutely fascinating. A V, consisting of individual wavelets, with a boat at its tip. And the waves filling the space in between the wavelets. Then the turbulent wake right in the middle, showing the ship’s trajectory. So simple, yet so complex. Totally and utterly fascinated!

And another beautiful wake. The wavelets of one side of the V are about to reach the shore, the turbulent wake still shows where the pilot boat came out of its berth and sailed towards the locks.

Interestingly, of all the wave pics I send to my sisters & a couple of friends every day, this picture got the most positive reactions in weeks. Which I find hilarious. The one day where there is nothing to see on the water in terms of wave watching and physics, and I have to fall back on taking pictures of other people’s boating houses, people get excited? Really?

And btw, it’s not that I don’t think this boat house thingy is pretty. But don’t you agree that it’s so much more interesting with a little wave action going on (as compared to yesterday’s pic)?

Oh look, that seagull made such pretty waves. Just love the sunshine that they focus on the ground, and the reflection of the bird. What would I do without water?

Accidental #WaveWatching in my coffee. You are welcome! :D
(This was actually part of an experiment that I was hoping would show something completely different… ;))

Always cool to see how waves become both taller and steeper as they run into shallow water, until they tuble and eventually break on the beach

Have you ever wondered about the physics of splashing waves? A wave travelling towards the beach, hitting a rock, and then water and foam going flying everywhere? I am pretty fascinated by the conversion of energy going on in these cases, would you have thought there was so much energy in a simple wave?

Time for another “seriously. How can water be flying this high up just because a small wave hit a small rock???” moment. Isn’t physics amazingly counterintuitive?

Next, I went and posted my first IGTV video! It’s the “turbulence in rotating and non-rotating fluids ones” that you probably know already… ;-) But curious to see how it’s being taken up!

And that’s it for now. Happy wave watching, everybody!

A #WaveWatching memory game for #SciCommChall

So I don’t know if this is a good idea that anyone would actually want to play with. But when I was visiting my sister last week, she was working on designing a memory game for kids, and it looked so much fun that I made one of my own, and then also made it June’s #SciCommChall.

Making a memory game — finding a concept that you think is important, and a depiction of that concept, and doing that over and over again — is definitely something that makes you think about a field in a different way! It actually reminded me of preparing for examinations during my university studies — I used to always make these little fact sheets with sketches and minimal descriptions and I remember how much I enjoyed those back then, too. And I find trying to be creative around topics you are studying (even only by drawing the little pictures and coloring them in) helps remembering them better and just organize them more neatly in my brain.

So maybe this is something to suggest to students for a fun activity? And if anyone decides to actually play with such memory games they’ll definitely think long and hard about waves! :-D

For a download of my memory game, click on the image below (or here).

Click on the image to get a b/w print version of this memory

Is this something you would suggest to your students? If not why not? I think it’s fun! :-)

Walk along the cliffline & beach in Stohl

About a week ago, I went on a lovely walk with my parents, and here are the pictures.

How I love the beach!

As I am looking more at ripples in the sand, I am seeing them everywhere now. Below, we are looking at a little area on the beach (the water would be just outside the top of the picture) and we have two different grains sizes of sand, and remnants of wave ripples. And a pothole forming aroud the stone. Fascinating!

This part of the coast is super interesting anyway, there are so many fossils to be found!

And it really shows the force of the sea, nibbling away at these cliffs.

Even though it looks so calm and peaceful!

I also find it fascinating how there are these different lines on the beach with pebbles of different sizes. Probably left there by storms, or other events with higher water levels. But it looks different every time!

Also fascinating: a ship and lighthouse that seem to be hovering in the air above the horizon. Optics are so much fun!

Kiel is really a great place to live! :-)

Irregular wave ripples, and some left on the beach when the water is gone

I’m getting more and more fascinated with wave ripples. I kinda understand how they form, but not enough to be able to explain as much about them as I would like to.

For example below: Why is the pattern so different where sand has been washed on top of the shallow stones? Yes, the water depth is different there, which will have an influence on the wave field, which will, in turn, have an influence on sediment transport. But HOW?

Here is another example. The wave ripples look choppy everywhere (and kinda cool!), but on that shallow, flat surface of the stone the wave length is completely different as is the orientation. And this is still all submerged, you can kinda estimate the water depth from the tips of the kelp stuff just reaching the surface.

Same day, slightly different area. Isn’t it cool to see how in the upper left there are no wave ripples but those streaks of larger pebbles?

And look at this. Utter chaos in the middle, little more orderly ripples to the sides! Why???

Or here. Steep wave ripple crests, long and shallow troughs in which larger stuff has been deposited (or is it the finer grain that has been transported away from the troughts into the crests and the coarser stuff got washed free and just stayed?). Estimates of water depth with help of kelp tips just breaking the water surface again…

Different day, more orderly wave ripples. But wavelength changes with distance from the sea wall. And weird things happen on the shallow stones…

On a low water day, parts of the sea floor got exposed. Now. I know for sure there were ripples all the way to the seawall. But at some point, the water retreated. When did they get smoothed out? The problem is that I can only really observe the seafloor when the water is calm, yet ripple marks form when there are waves. What happens during the transitional period? Or here, when the water level sinks?

Another interesting pics with some ripple marks that are still there, and then these little, smooth spots that recently fell dry (within maybe 15 minutes or so — I took pictures that same morning when there was still water on top and you could only see that there was a bump under the surface by “reading the wave field”. And then when I came back, the water level had fallen and this piece of mud had been exposed). Did the ripples there get smoothed out when there was still water on top, or at what point did it happen?

Or here where we have these interesting rip-current like structures right at the bottom of the sea wall:

Here is another thing I find fascinating: Ripples towards the sea wall, and then these streaks of larger stuff probably aligned with the main direction of the waves (I think the larger stuff is less dense than the sand, though, maybe pieces of broken shells?). What has to happen in order to transition between these two regimes?

Also note how there is no sand on the large flat stones today!

And same spot, different day: More ripples gone, and even less sand on the large flat stones!

So how do I figure out what is really going on here? I guess I would need to capture both the wave field and the sea floor over time. Web cams above & below water level, plus measure water depth? Any suggestions?

Birthday on the beach

After, at that point, more than two week of self-isolation in my flat with only my early morning walks away from the flat, and only runs with my friend J. in human company that wasn’t virtual, my parents came to see me the day after my Birthday (which was already a while ago, I’ve been so busy posting all the rotating experiments from my kitchen and Teaching Tuesdays!). But it was a lovely day and I want to share the pictures.

Here, for example, I find it so fascinating how the same wave crest is breaking in one spot, then fairly pointy a little further away, then very flat and round a little further still, and then one can’t even make out the wave any more. Just because it’s shallower in some spots than in others!

And I always think that it’s super cool how vegetation takes energy out of a wave field. Look at the mirror-like water surface in the puddles in the foreground!

Same here. This little bay is sheltered by the wave breaker groyne, but what little is propagating around them and into the bay gets dampened out by the floating seaweed stuff.

And this picture shows very nicely how the groyne is sheltering the water right behind it both from wind and waves.

And one more of those…

And another study of wave breaking, and the broken turbulent wash running up on the beach.

Maybe it’s just me, but I can’t get enough of these.


Oh, now we have a bird’s wake in the sheltered water! Also the sky is blue (well, in some spots anyway ;-))

In the picture below, I was really fascinated how relatively long waves got reflected into groups of three short waves by some weirdly shaped beach.

The whole beach was full of dried out starfish. They looked so beautiful!

And smelled horribly. But I brought some home for Christmas decorations anyway. And I’m sure they’ll be done stinking eventually. Hopefully before Christmas…

At some point, there were a few drops of rain despite it clearly still being sunny (see reflection below!)

Did I mention I love these roses?

And here are my parents, looking for fossils.

Like this fossilised sea urchin I found :-)

And I was looking at pattern in the sand. Like below where we see exactly how high the last couple of waves went, and where the few raindrops fell that day.

No raindrops here, but pretty intricate pattern of “high waters” in the waves!

And a bird’s foot prints.

That was a beautiful day! :-)

Foam stripes and sand ripples

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


Several of my friends were planning on teaching with DIYnamics rotating tables right now. Unfortunately, that’s currently impossible. Fortunately, though, I have one at home and enjoy playing with it enough that I’m

  1. Playing with it
  2. Making videos of me playing with it
  3. Putting the videos on the internet
  4. Going to do video calls with my friends’ classes, so that the students can at least “remote control” the hands-on experiments they were supposed to be doing themselves.

Here is me introducing the setup:

Today, I want to share a video I filmed on planetary Rossby waves. To be clear: This is not a polished, stand-alone teaching video. It’s me rambling while playing. It’s supposed to give students an initial idea of an experiment we’ll be doing together during a video call, and that they’ll be discussing in much more depth in class. It’s also meant to prepare them for more “polished” videos, which are sometimes so polished that it’s hard to actually see what’s going on. If everything looks too perfect it almost looks artificial, know what I mean? Anyway, this is as authentic as it gets, me playing in my kitchen. Welcome! :-)

In the video, I am using an ice cube, melting on a sloping bottom in a rotating tank, to create planetary Rossby waves. Follow along with the whole process:

Also check out the video below that shows both a top- and side view of a planetary Rossby wave, both filmed with co-rotating cameras.

Previous blog posts with more movies for example here.

Now. What are you curious about? What would you like to try? What would you do differently? Any questions for me? :-)

Such a pretty #friendlywaves!

My long time Twitter friend Anne shared these beautiful pictures and I absolutely had to do a #friendlywaves post where I explain other people’s wave pictures.

Take a moment to admire the beautiful picture below. Wouldn’t you love to be there? I certainly would!

What can we learn from this picture? First — it’s a windy day! Not stormy, but definitely not calm, either. See how the water outside of the surf zone is dark blue and looks a little choppy? That’s the local wind doing that.

And then there are the waves that we see breaking in the foreground. Without knowing where the picture was taken, I would think that they traveled in from a large water body where there was a long fetch so they could built up over quite some distance. And then they meet the coast!

You see breaking waves of two kinds: the one marked with red ovals below, where there is hardly any buildup of the wave before it meets a rock and breaks into white, foamy turbulence. The other type of breaking waves, the ones where I marked the crests with green lines, build up over a short distance before they break because there is a more gradual decrease in water depth. The stope is still quite steep so the waves change from deep water (where they can’t feel the sea floor and have a fairly low amplitude, so we can’t distinguish wave crests further offshore than the two I marked in green) to shallow water waves that feel the sea floor and build up to break.

In contrast, let’s look at the lovely picture below.

Here, we have a sandy beach on which the waves can run out. There slope right at the water’s edge is not very steep, but seeing that we can only really spot two wave crests there has to be a change in gradient. About where the offshore wave crest is in the picture below, or possibly a little further offshore, the water depth must suddenly increase, otherwise there would be more wave crest visible further offshore. Since there aren’t any, water must be a lot deeper there.

But what I found really cool about the picture above are the trains of standing waves in the little stream that flows into the sea here. I find it so fascinating to see standing waves break in the upstream direction — so completely unintuitive, isn’t it? So much so that I dug out some pics from January for you and posted them last Friday in preparation for today’s post. Sometimes I actually plan my posts, believe it or not!

Standing waves don’t move in space because the flow of the current they are sitting on is exactly as fast as they are moving, only in the opposite direction. What is happening in the picture is that in those standing waves sit on ripples in the sand. The waves become so steep that they are constantly falling back down onto the current, get carried up the ripples again, in an endless loop. So fascinating!

Birds make for super interesting wave watching!

My perfect Saturdays start like this: Early morning walk along the water, followed by coffee while blogging about waves. Today’s focus: The cool waves that birds make!

First, let’s look at the weird way in which seagulls take off from water. They make a big splash which develops into ring-shaped waves. So far, so good. But…

…that’s usually not all that happens: They usually hit the water a couple more times before they fully take flight, thus leaving a trail of circular waves radiating from each of the points where they hit the water.

This morning, there was a seagull sitting very close to the sea wall (which you see in the lower right corner of the picture), probably eating or washing its feathers; in any case radiating off waves. When I looked down, it flew up, hit the water once, landed again, and then began to swim away.

And you can see all of this in the waves!

The green cross below marks the spot where the seagull sat before I interrupted it. It must have been sitting there for a bit judging from the radius of the circular waves marked in green that radiate from that exact spot.

But then when the seagull saw me, it took off, dipped once into the water (green cross and corresponding wave circle), and then landed again (red cross) and swam away from there (following the red arrow on which the centers of the red circles fall).

How cool is this?

Once it was just swimming and not dipping in and out of the water, it begand to develop a regular, v-shaped wake (red V) that consists of individual “feathers” or wakelets (yellow).

It continued swimming away, albeit taking a little turn…

You still see the green waves from where it was sitting originally, and then the red waves from where it landed and swam away on the path marked by the red arrow.

This kind of stuff makes me so happy! :-)

From the waves in the picture below, can you tell me what that seagull did before the picture was taken?