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!

Tilting frontal surface under rotation / cylinder collapse

Torge and I are planning to run the “tilting of a frontal surface under rotation / cylinder collapse” experiment as “remote kitchen oceanography” in his class on Thursday, so I’ve been practicing it today. It didn’t work out quite as well as it did when Pierre and I were running it in Bergen years ago, so if you are looking for my best movie of that experiment, you should go read the old blog post.

The idea is that a density front is set up by spinning up a tank in which a bottom-less cylinder contains a denser fluid, set up into a less dense fluid. Once the tank is spun up, the cylinder is removed, releasing the denser fluid into the less dense one. In contrast to the non-rotating case, where the dense water would sink to the bottom of the tank and form a layer underneath the less dense water, here the cylinder changes its shape to form a cone that retains its shape. The slope of the front is determined by both the rotation rate and the density contrast.

What I can show you today is what it looks like on my DIYnamics rotating table in my kitchen (and it’s pretty cool that all these different experiments can be run on such a simple setup, isn’t it?!). This is from two weeks ago:

And a second attempt done today (I’m not showing you all the failed ones in between, and since I’m a little sick, I’m also not showing you what I look like, and spare you the sound of my incoherend explanations ;-)). But: Now everything is set up so I can use my right hand to pull out the cylinder to introduce fewer disturbances (spoiler alert: didn’t work out — see all the waves on the tank after I remove the cylinder?)

Check out the flower “floats” — the ones on the remains of the cylinder are rotating in the same direction as the tank, only faster! That’s something we didn’t show in Bergen and that I think is really neat.

What I learned about how to set up the experiment: I filled the cylinder with ice cubes and then filled water into the donut outside of the cylinder. That way, water pressure would push water through the petroleum jelly seal at the bottom of the cylinder inside, but the dye of the melting ice cubes would not seep out (very much). Also, the cold melt water would make the water inside the cylinder denser (make sure to stir!). The whole fancy “get water out and refill using a syringe” stuff sounds nice but just isn’t feasible in my setup…

In this case, having a larger tank would be really helpful, because the disturbances introduced in either case are probably more or less the same, but the smaller the tank, the larger the relative effect of a disturbance… Also, my tripod was making it really difficult for me to reach into the tank without hitting it, both for filling the tank and for removing the cylinder. I guess if we didn’t need a top view, things would be a lot easier… ;-)

Rotating vs non-rotating turbulence

Last Thursday, Torge & I invited his “atmosphere & ocean dynamics class” to a virtual excursion into my kitchen — to do some cool experiments. As you know, I have the DIYnamics rotating table setup at home, so this is what it looked like:

We did two experiments, the very boring (but very important) solid body rotation, and then the much more exciting (and quite pretty, see pic at the very top or movie below!) comparison of turbulence in a non-rotating and a rotating system.

We didn’t manage to record the class as we had planned, so I redid & recorded the experiments. Here are 8 minutes of me talking you through it. Enjoy!

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! :-)

A common misconception in rotating tank experiments, and one way of maybe not reinforcing it

A very common misconception when looking at atmosphere & ocean dynamics in a rotating tank is that the center of the tank represents one of the poles and the edge of the tank the equator. And there is one experiment that — I fear — might reinforce that misconception, and that is the one we love to show for rotation vs thermal forcing, baroclinic instabilities (fast
rotation), Hadley cell circulation (slow rotation).

When we do this experiment, the tank looks like a polar stereographic view of the Earth, with the pole (represented by the blue ice in the picture below) in the center and the equator at the edge of the tank. And when we then talk about the eddies we see as representing weather pattern, it’s all too easy to assume that the Coriolis parameter also varies throughout the tank similarly as it would on Earth, only projected down into the tank. Which is not the case!

But the good news is that it’s super easy to drive this experiment by heating rather than cooling in the center of the tank. The physics are exactly the same, only the heat transport is now happening radially outward rather than radially inward. And that it’s now not the easiest assumption any more that we are looking down at the pole.

Also: Heating in the middle is a lot easier to do spontaneously than cooling using ice — no overnight stay in the fridge required, just a kettle! :-)

What are other misconceptions related to rotating tanks that you commonly come across? And do you have any advice on how to prevent these misconceptions or elicit, confront, resolve them?

Approach your career as if you were growing a tree, not building a house

Today marks the 10-year anniversary of being awarded my doctorate. Time flies! And as good a time as any to reflect on my career so far. I recently read the advice to approach something as if you were “growing a tree, not building a house”. It was in a slightly different context than career development, but it resonated with me so much that I wanted to share it here, applied to career development.

Ever since I was a teenager, I have had long-term plans for what I wanted my career to look like, and my life with that career. Yes, long-term planS, plural. In contrast to many of my friends (hi, Joke!), I have always had several vastly different plans that I found interesting simultaneously. Sometimes several that I could see myself being equally happy with. For a long time I struggled with what path to take, what career to pick. All these decisions that seemed huge and final, and also urgent to take: because I was thinking of building a career similarly to how one would build a house. In oder to build a house, you usually have all the plans and blueprints and buiding permits and everything in place first. Then you start building. You might have ordered your built-in kitchen or started sewing the window drapes before the walls of the house are even up.

If you grow a tree, however, you can’t plan in a similar way. You can influence a tree’s growth for the better by providing good conditions and guidance, but it will develop organically. Maybe not exactly the way you envisioned initially, but beautiful nonetheless. And I really like this approach to career building — it takes off so much pressure!!! –, and it’s how I approach my own career these days, which works well for me. Like so:

Preparing the soil: First steps in your career

Before you plant a tree or grow it from a seed, you need to figure out what to grow it on. Same with your career: What you learn in school and university is the foundation for what you can do later on. But similar to seedlings that can easily be put in different pots if you so choose as long as they are healthy, it’s not so much about what study courses you take rather than actually learning things there. Facts, of course, but mainly skills of how to learn, how to work hard, how to organize yourself, how to find information. I’ve recently been involved in several events with pupils and they all wanted to know how to figure out what to study in order to be in the best position for your future career. And my advice is always to study what you are most interested in, and be good at it. All the rest will fall into place.

In my case, the last years in high school I took neither Physics nor English classes (because there were other topics I was much more interested in at the time). And guess what I am doing now? Writing about physic(al oceanography) in English. Would my studies have been easier had I been able to build on the same previous knowledge as most of my peers? Definitely. Would that have made me miserable in highschool? You bet. Would it have been worth doing topics I wasn’t interested in in highschool just because I would need to learn that stuff later on for what I wanted to do? ABSOLUTEY NO WAY. (Also, at that time I didn’t knew that oceanography even existed, so I had no idea I would ever need physics or English. In fact, I was looking to study chemistry & informatics in France, among other things)

You have to water & fertilize your tree: Looking after your tree

No matter what approach you take to career building, it is going to take sustained effort. Your tree might need water and the occasional sprinkle of fertilizer, your career certainly needs many many hours of dedicated work to become an expert in whatever you do.

But the way you look after your career development itself, you need to look after yourself, too. Make sure you take breaks, go on vacations, really enjoy the process. If it’s fun, it will grow. For example if you check out my wave watching posts — those happened organically, because once I started, taking pictures of waves took on a life of its own; it’s just fun to do and I enjoy “collecting” all the different wave field pictures. Now it’s quite an impressive collection, but it didn’t feel like any effort. It’s just getting into the habit of thinking about the physics I see and of taking pictures.

Tying a tree to a trellis: Shaping your career

Sometimes there are boundary conditions that we do not want to challenge, or very specific goals we definitely want to achieve, then it might make sense to shape career growth similarly to tying our tree to a trellis to force it into the shape we want. This might mean making it through classes that we aren’t really interested in because they are a required part of a degree we want (for example I was really not interested in experimental physics in university, but obviously needed to take quite a lot of that in order to become a physical oceanographer). It might also mean learning the language of a country that you are looking to work in, or a programming language that everybody is using.

It might also mean taking jobs that get you in the direction of what you want to be doing: For a couple of years, I worked as “coordinator of teaching innovation” in the faculty of mechanical engineering, ship building and marine technology. The job itself was fun: I like figuring out how to improve teaching, I like mentoring people, I think university politics are fun if you are an active player without too much emotional investment. The topic I was working on, though, was close enough to oceanography that I felt confident that I would find it interesting and could apply my knowledge, but mainly learn things that would be relevant for a similar job working with geoscientists in the future. Turns out I was right; that’s what I am currently doing: A similar kind of job, but on my topic. Similarly, in the next job, I wanted to learn about science education and communication research. Did that, then left, now know what I wanted to know (plus whom to ask & where to learn more should I desire to).

Pollinating your tree: Seeking specific input to your career development

There are two approaches to pollinating trees that I am aware of: Pollinating by hand, or putting a beehive close by. Both have analogues in career development:

If you are “pollinating by hand”, you are carefully selecting the input that shapes your career. You are taking specific courses, developing specific skills that open up new pathways. This might be based on advice you got, or on job ads that asked for skills you don’t yet posess.

If you are “putting a beehive close by”, you are open to everything, look for inspiration, take random classes that strike your fancy. That’s more my approach, because it’s more interesting, but of course both are perfectly valid approaches!

You might want to prune your tree: Focussing your career

If you want to grow a few really large fruits rather than a lot of small ones or too many leaves, you prune your tree. If you want to make sustantial progress in one domain, maybe it’s time to let other projects go (or at least not to try working on too many simultaneously).

Or you decide on not making progress as quickly in one domain, but making slower progress in several domains at the same time. I have always had many different things happening simultaneously: Studying for a Masters of Higher Education while doing a PhD in oceanography. Doing higher education consulting while leading a citizen science project. In fact, I purposefully chose a 50% position for my current “day job” in order to have time to pursue all my other interests and freelance work! So pruning really isn’t my strongest side, I admit. But there are people for whom it works, or so I have heard ;-)

Cut down branches from your tree: Letting go of certain aspects of your career

Sometimes branches are sick, too heavy for the tree, or shading your favourite garden bench, then it’s time to cut them off. Similarly in your career: Maybe certain aspects feel too heavy, are not fun any more, or stand in the way of more important aspects of your life. Maybe for a while you really enjoyed the travel that came with your job and now you are sick and tired of trains and hotels (I know I was at that point right before Corona and then it magically all went away ;-)), then it’s maybe time to transition into a role that doesn’t need to travel as much. Or maybe you’ve been very active in both research and teaching, and then decide to focus on one or the other. Or, in my case, you decide that you only want to work 50% in order to be free for other things on the side.

For me, changing jobs is such a way of cutting off branches — once I am done learning what I want to learn in a position, I leave for a new one with new challenges. And so far, this has led to a pretty healthy tree!

Repotting your tree: Starting a new career

Ok, maybe this is where the analogy breaks down. Or maybe not: While your tree is small, it’s a healthy thing to repot it every now and then (similarly how it’s good for your career to work in different environments, see different work cultures and different fields). It maybe gets more difficult to try out completely new things the more your career has grown, and might need more planning and larger equipment to repot that large tree, but it’s not impossible!

If you look at my career, I studied something that usually builds on topics that I didn’t take. Then I changed topics radically between my PhD and first postdoc, between my first postdoc and the job I had afterwards (which was that higher education consulting job), between that job and my second postdoc (which was on science communication and education research), between that second postdoc and my current day job (which is leading a large scicomm project).

This morning (what a fitting celebration of my 10 year anniversary of my doctorate!) I joined a video call from my kitchen and shared some kitchen oceanography with my friend’s Atmosphere and Ocean Dynamics class. I had two devices logged on to give a side view and top view on my rotating table, and students told me what parameters to modify in the experiments. So much fun! And this is something that organically grew on my career tree: At some point, I started playing with kitchen oceanography to complement my own teaching. At another point, I started doing higher education consulting and teaching innovation projects. Those two came together, and have been blooming and come to fruition over the last couple of years. And now part of my job is to play with water and food dye in my kitchen while on a video call (see below)! How awesome is that?

I am probably not done with getting interested in new things and changing jobs in order to have time (and be paid) to pursue those. But right now, I am pretty much exactly where I want to be career-wise in terms of what I want to be doing, the environment & teams I want to do it in, and last not least the work-life-balance. So any future oportunities had better be amazing, or my tree won’t be growing in that direction! :-)

What is your approach? Are you growing a tree or building a house? What thoughts did come up for you while reading this blogpost?

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! :-)

Solid body rotation

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 the spinup of a tank until it reaches solid body rotation. 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. Watching a tank until it reaches olid body rotation is probably the most boding tank experiment ever done, but understanding the concept of solid body rotation and why we need it in tank experiments is the foundation of everything we do on a rotating tank. So here we go!

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?