Category Archives: wave watching

Watching the tides cause an hydraulic jump in the Irish Sea!

Looking at the picture above, taken in the South Walney Island Nature Reserve on our walk yesterday, what is the first thing you notice?

For me, it is not the cute little hide which is a perfect spot for seal and bird watching, for me it is — obviously! — what is going on with the waves! So much so that I spent the better part of an hour looking at the opposite direction of where all the seals were frolicking in the waves (except for one that came and played in the most fun part of the sea — more about that later).

Looking at the picture below, do you notice how different the different areas of water surface look? To the left of the wave breaker and going offshore from there, the surface is quite rough, with many waves of different wavelengths. But then going directly offshore from the wave breaker, the surface is smooth(er)! Followed by a rougher stripe, before it becomes smooth again, and a couple of well-defined wave crests reach the shore.

Zooming in on that area right off the wave breaker, you see that there are actually waves breaking towards the smoother area, away from the beach. Any idea what’s going on here, what might be causing those waves? (Hint: Even though there is a boat in the background, it is not some ship’s wake!)

What we can observe here is actually a pretty cool phenomenon, called a hydraulic jump. Due to the tide going out, there is a current developing around the tip of Walney Island, going from left to right in the picture above. This current goes over the still-submerged part of the wave breaker. Since the cross section through which the water has to squeeze is all of a sudden a lot smaller than before and after, the water has to accelerate. And it accelerates so much that waves traveling on it are just flushed downstream and the surface looks smooth(er). Only when the cross section is wider and the water has slowed down, waves become visible again.

The spot where waves are exactly as fast as the current, but running against it, is called “hydraulic jump”. You can spot it right where the waves are breaking: They are trying to go back upstream but don’t manage to, so they stay locked in one place (see here for an analogy of people running up and down escalators to explain this phenomenon). You do see hydraulic jumps “in the wild” quite often, for example in rapids in rivers (and even more so in regulated rivers, very nice example here!). In case of the hydraulic jump right here, there was a seal playing in the current, clearly enjoying the wave action (and quite possibly also feeding on poor fish that suddenly get swept away with the current).

And indeed, 20 minutes later, the same spot looks like this: the surface roughness is a lot higher towards the right of the wave breaker, but all in all there are much fewer, and much smaller waves.

And another 20 minutes later, the formerly submerged wave breaker is revealed!

I find it always so cool when you see a wave field and just from what that wave field looks like, you can deduce what the ground underneath has to be like! In this case from seeing the hydraulic jump, you know that the wave breaker has to continue on offshore.

Wanna see the whole thing in action? Then here is a movie for you!

And the coolest thing is that this spectacle will repeat with every outgoing tide, so pretty much twice a day! And I am fairly confident that it will also happen halfway between, again, when the tide comes in and the current goes in the opposite direction. I would love to go back and check!

Astrid sent me a #friendlywaves from Whitstable for remote #wavewatching

Astrid, #wavewatching supporter from Day 1, sent me these pictures for a #friendlywaves post. Today, I want to start with a spoiler picture (or, rather, I did start with a spoiler picture already — see above) that shows you the setting at low tide to help us explain the wave pattern that we then observe at high(er) tide.

Note the headland in the picture above? Below shows what it looks like when it is covered in water:

Astrid, as a real #wavewatching pro, also sent me a video, so I can show you the super cool interference happening here.

Wave crests from far offshore (probably caused by a storm somewhere far away) arrive in shallower water and get broken up into parts on either side of the (now submerged) headland. But on either side, the wave crests also change their shape, being refracted towards the headland. And some of the wave crests make it over the headland, now at an angle to each other, meeting waves from the other side. And where they meet, they steepen up and even break occasionally. Doesn’t it look super cool to watch waves run towards each other in such a way, creating these interference pattern?

This wave pattern always reminds me of one that I saw years ago — coincidentally with Astrid! — when we were in Iceland in 2013, the day after my dad’s heart surgery. And while watching those waves then was beautiful and calming, seeing this pattern still always reminds me of a pretty traumatic time. So I am happy that this new wave pattern will now at least partially overwrite some of those memories with a very happy day: Herzlichen Glückwunsch und alles alles Gute, liebe Simone* & family!

*That is Astrid’s friend Simone, not my own sister Simone, although of course alles Gute to her, too :-)

A #friendlywaves from Tampa, Florida

Anyone who might be new to my blog because of yesterday’s presentation at #SiPManc — please don’t be scared and run away, this is the most complicated #friendlywaves I have ever gotten, usually things are A LOT easier! :-)

I love #friendlywaves! Victor sent me the picture above. He took it in 2017 in Tampa, Florida, and I think it’s so fascinating! There is so much going on, let’s try to make sense of it!

First, the most obvious thing making waves here: The two boats. Clearly they are making waves, and they might explain a lot of what we see here. But on the other hand, they might not.

Below, you see the part of the wave field that is 100% due to these two ships: Their V-shaped wakes (in red) and the turbulent wake behind one of the ships (in yellow).

The very prominent wave pattern (marked in red in the image below) might be due to these two ships as was suggested to me, but if it is, then those ships changed course quite drastically before they created the waves I marked in the previous picture (and I can see no evidence of such a change of course, usually a turn would leave a trace similar to this one).

If the boats, as I assume they did, came out from underneath the bridge and sailed in a more or less straight line (and that seems to be the case judging from their wakes as indicated in the picture above), there is no way they could have made waves that travel in front of their V-shaped wake. Similarly to how you can’t hear the supersonic aircraft before the supersonic boom (because the sound can’t travel faster than the speed of sound and the pressure signal thus gets formed into the Mach cone), waves can’t outrun their wake (which is like their 2D Mach cone). So I don’t believe that those waves were made by those two ships. Rather, I believe that they were made by a ship that is no longer visible in the area we are able to see.

So remember, this is the wave pattern we are trying to explain (Marked is only one wave crest, but you see that there are several parallel to the marked one):

We do nicely see how the wave is reflected by the straight sea walls. But what direction is it traveling in? And what caused it? Let’s speculate!

First: let’s consider the very weird shape of the body of water shown in the picture. Quick search for Tampa on Google Maps lets me believe is that the picture was taken more or less from the position of the white star and the view is the area between the two red lines. Looking at that map, we see that the water we see opens up into four different water ways: One to the north, one to the east, one to the south east, and one to the south west. The two to the south eventually open up into Tampa Bay.

The wave field that we are trying to explain would look somewhat similar to what I drew in below (green):

My best explanation of that green wave field above is this: A boat that went on the course that I drew in in yellow:

So far, so good. Wanna know why I believe this is what happened? Then this is the picture for you!

Assuming the boat followed along the yellow track, the other lines are the wake it would have produced:

  • green: Those are two parts of the wave field that I marked above that I am fairly confident of: The wake propagated across the body of water, got reflected and came then over towards the photographer. Note how not all waves reach the shoreline close to the photographer yet? That’s because they are the “newer” waves that haven’t traveled for long enough to reach that spot
  • light blue: The “newest” waves that aren’t very long yet and are traveling in an area where we can’t clearly make out the presence or absence, let alone direction, of waves. They are fanning away from the “green waves” because the ship is turning (similar to here).
  • dark blue: Those is a part from the wake that originated on the other side of the ship, got reflected, and now traveled across the body of water to reach the point where the picture was taken from. They do so at an angle that looks like they might be reflections of the incoming green waves (which is another possibility which I can’t rule out with 100% certainty). Newer wakes from that side, once they’ve been reflected on the shore, will lead to waves almost parallel to the green part of the wake and would be indistinguishable from those in the picture.
  • orange: Those are “old” wakes that must have happened when the ship came out of that inlet, but that would not interfere with our picture because their reflection stays caught within the inlet itself.

This is the best explanation of what must have happened that I can come up with, and I have thought about this quite some time (more on that at the end of this post) :-)

But then there are tons of shorter wave length waves that we have to explain, too: See those marked in red, yellow and green below.

I am confident that the ones I marked in red are wind-driven waves coming across the open area. Their direction also agrees quite well with the wind directions the flags indicate (marked with a white arrow above). I believe that the ones I marked in yellow and in green are two separate wave fields at a slight angle, but that might be an optical illusion, I am not quite sure.

If we go back to the map, I believe the wave fields I marked above would look pretty similar to the ones I drew in below (I changed the red waves above to magenta waves below, because red was already taken. Note the wind direction marked with a white arrow: it looks pretty much perpendicular to the now-magenta wave crests):

And looking at the angles in that depiction of the waves, I could imagine that the green wave field is a reflection of the magenta wave field where that one hits the shore on the side where the picture was taken from (see light blue wave crests). As for the yellow one: I still have no idea what caused that. But maybe there need to be some mysteries left to life? ;-)

To end on something that I am confident in: The half circles near the bottom of the picture are the result of something (two buoys? two small boats?) moored on that pier, bobbing up and down in the waves, thus radiating wave rings with shorter wavelengths and higher frequency than the wave that is exciting the movement.

But after all this hard work (more on that at the bottom of this post) — let’s take a minute and look at those beautiful interference pattern again where the wave fields cross each other and create a checkerboard pattern. How amazing is this?

Phew! I love #friendlywaves, but this was quite a challenge! How did I do, Victor? :-)

If you or anyone else have any comments or suggestions — I would love to chat about alternative explanations!

P.S.: Just to give you an idea of what my process was like: It involved late night scribbles on a tea bag (because that was the best “paper” I had available on my bedside table in the hotel in Manchester) and I needed to play scenarios through in my head…

…and some sketches on my phone while I was on a train…

This is how much I love wave watching! :-)

What #wavewatching means to me. My presentation at #sipmanc

Did you miss my talk at the Science in Public conference in Manchester? Well, you are in luck — here it is!

Three years ago, I visited my sister and her then four month old daughter. We spent an evening on the shores of the german river “Schlei”, close to their home. It was a beautiful day — sunny but with some clouds that brought visual interest to the sky — and we were looking at the water and taking pictures. We stood for quite some time in silence, each of us lost in thought, looking out over the river.

My sister and my goddaughter that fateful evening in May 2016

Later that evening, I wrote a blog post about what I had seen [link to that original blogpost!].

The next morning, my sister came into my room, her phone with my blogpost still open in her hand, and asked in a very surprised voice “This is what you saw last night, when I was standing right next to you??? I just watched the sun sparkle on the water!”

I really enjoy watching the sun sparkle on water, too, but nevertheless: That was when I decided that my four-month old niece — or any other child, for that matter — should not grow up deprived of seeing what I saw that evening, in addition, obviously, to what my sister saw. Therefore, I wrote a book as a gift to my niece to her baptism one months after that day, and just like that, #wavewatching was born.

Wave watching, to me, is so much more than just “watching waves”. Wave watching is how I want to live my life, and how I want everybody to approach theirs. Wave watching means a certain way of looking at the world around us.

Here is a picture I took that evening. When you look at that picture, what is it that you notice? The colorful clouds, their reflection on the water?

What I notice, and what I want people to notice, is that the waves look very different in different areas of the water.

On the right side, wave crests are more or less straight. That’s where the wind has had a wide and long area over which it has been blowing over the water, a long fetch, creating these waves and driving them down the river. At least until they can’t continue on because there suddenly is a wave breaker in their way.

But if you look here in the foreground, there are waves downwind of the wave breaker, in it’s lee, filling the space behind it. But the waves are not straight any more, they are now curvy.

If we look at a spot on the water slightly to the left of the picture above, what will we see? Keep in mind what the waves, propagating to the left, look like where they hit the shore:

This is what the water looks like just slightly to the left of the picture I showed before.

Here we have the same wave crests that were propagating out of the previous frame:

But what we also see is a second set of wave crests at an angle to the first one:

And those are the kinds of things I want you to notice.

I want you to look around, to observe pattern and where pattern break down. And I want you to think about whether you can explain those pattern, and what could help you find explanations.

Quick side note for those of you who have been wondering what exactly is going on here, just to give you some piece of mind: What you saw in the first picture you are probably familiar with from physics classes: It’s a wave showing diffraction at a slit.

Except that in this case, we have a very wide slit and therefore the situation is a little more complicated than in your physics text book.

And in the second picture, we saw very simple reflection, which you are probably again very familiar with.

Only that here we have multiple waves being reflected simultaneously.

But I did not show you this to talk to you about physics today. I am showing you this because this is where I see my place in science communication — in showing people the world the way I see it, but way beyond that: in helping them see the world with different eyes, and in challenging them to do so. And it’s not important whether people observe waves or anything else specific, it’s the general approach to the world that I find so important.

I am sure that next time you look at water — be it when walking around puddles on the side walk, or when looking at water going down the drain when washing your hands — you will look at water differently, and you will notice waves in a way you have not done before. And you will think about why there are these waves, why they look that way, and you will — whether you want it or not — be thinking about physics. And I hope that you will be wave watching with as much awe and wonder, curiosity and joy as me, my goddaughter and her younger sister do!

Me, my goddaughter and her younger sister in June 2019

If you are curious about the other two hashtags I had in the original title of my talk, just check out the hashtags on twitter; I put up posts on my blog (on #kitchenoceanography and #dropphotography). Or come and talk to me, or shoot me a message!

AND WHAT I FORGOT? TO PLUG #FRIENDLYWAVES! #friendlywaves is the hashtag people can use to send me pictures of waves that they took, and I will try to explain what’s going on on their pictures. So send me all your wave pictures and I will do my best! :-)

Edit on July 13th: Thank you everybody for you amazing comments about my presentation on Twitter and in person, it feels truly heart-warming to look through all of this! I arrived knowing only one person but left with many new friends. Thank you! (Collected tweets here)

Some #wavewatching in Manchester

I’m in Manchester for Science in Public 2019 and I couldn’t help myself, I had to do some wave watching.

To be fair, though: These pictures really don’t do Manchester justice as a city. It is such an amazing city! Last time I was here, I spent a whole day exploring four historical libraries that were breathtakingly beautiful, and I would totally recommend you do the same if you are here, even before wave watching. And that is saying something! And I love all the architecture here, and the Science and Industry Museum! But my blog is about Adventures in Oceanography and Teaching, so I am not showing you that side of the city here, only the river Irwell and some reflections of buildings in it.

First: A storm drain run-off into the river. Do you see the waves radiating away from where the water drips into the river?

And here is a “before” picture of the river…

…so you appreciate the “after” picture with all the cute little waves made by raindrops. (No irony here — I really enjoyed watching this!)

And it does look pretty, doesn’t it? I especially like the wave rings on the boundary between the dark reflections of the buildings and trees, and the brighter reflection of the sky, blurring the line, bringing the sky and the city together…

Oh, and one of my favourite wave pattern: The V-shaped wake of a row boat and the pairs of eddies, rotating in opposite directions, where the oars pushed through the water!

Some #friendlywaves from Berlin

My friend Alice is currently in Berlin, and as one does when visiting Germany’s capital city: She’s wave watching!

I can only say: I approve! That’s what I always do there, too (exhibit 1, exhibit 2).

And knowing that I always like the challenge, she sent me a #friendlywaves picture. Meaning a picture of waves that she would like me to explain.

We aim to please… So here we go! (gif of the original Insta story above, individual pictures for easier viewing below)

Clearly this was done as an Instagram story and not designed to be posted on my blog, and I am not quite sure if it works. Please let me now what you think!

#DayOfTheSeafarer — #WakeWatching on Kiel fjord

I’ve been on my fair share of ships over the years, but even though I enjoy my month or two at sea every year, I cannot even begin to express the respect I have for seafarers who spend all their working life at sea. Being away from home for at least half the year, living in a small, confined space with people they did not get to choose themselves, not even having the autonomy to choose what meals to cook while at sea, all while doing hard physical work.

The seafarers I know personally do this out of their free will — their love of the ocean compensates for the sacrifices they make to be at sea. But let’s not forget that there are also many people who don’t have the luxury to choose what job they work in.

Anyway, seafarers’ work influences us all: It provides us with wave watching opportunities: The ferry you saw in the picture above left the wake you now see below.

Jokes aside: Shipping gives us access to goods that we otherwise wouldn’t have access to. It provides us with jobs, with food, with transportation. With knowledge about the world and the ocean — without the amazing work the crews on research ships do, there wouldn’t be any oceanography!

Our lives would be very different without the work that seafarers do every day, the sacrifices they make and the risks they take. On the Day of the Seafarer, maybe stop and think for a minute about what your life would look like if it wasn’t for all these men and women, doing the work they do. I, for one, am full of respect for what they are doing! And I’ll be sure to let the seafarers that I personally know know about this today! Thank you to all the crews on the research ships that I’ve sailed on, you guys and girls are amazing!

A pilot ship making waves, and what happens to the waves over time

This is the story of a pilot ship, merrily sailing along on a beautiful day, making waves.

Since it’s windy and Kiel fjord is a little choppy, the waves break and both side of the V-shaped wake with the pilot ship at its tip are visible. See the foam of the breaking waves? And in the middle of both sides of the V, visible as a lighter-colored stripe, there is the turbulent wake where the ship’s propeller has set the water into chaotic motion.

Both constituents of the wake — the V-shaped feathery waves and the turbulent wake — stay visible for quite some time after the ship has passed!

Can you spot the one side of the V approaching the shore?

A little while later, the pilot ship returns. nice bow wave (where its bow is breaking the water apart) and all. Also note the wave field inshore of the floating wave breaker — it is a lot calmer than on the outside!

But not for long. The pilot ship is making waves!

The V-shaped wave keeps spreading, one of its sides coming closer and closer to the wave breaker.

Wow, now it’s there! Can you imagine what it will do to the floating wave breaker, and what that in turn will do to the wave field inshore?

Below, you see that the V-shaped wake is now so wide that one end is reaching the edge of the wave breaker, which is already moving almost violently in the waves.

And the moving wave breaker now produces waves of its own, radiating away from the wave breaker, towards the shore.

See how those waves propagate further and further towards the shore and form a crisscross pattern with the waves that come in through the gap between wave breakers?

That was a nice wave watching break! :-)

Wave watching on Schwentine river

Surprise! I did some wave watching yesterday!

Ok, let’s start with something simple to warm you up: A duck’s wake.

And wind waves (coming in from the top right) hitting a patch of moss on the side of this little pier, and then radiating away as half circles.

Here is a movie of that because it’t pretty cool, actually.

Are you ready for the cool stuff? A water strider making waves in the movie below! It hops happily on the water, and every time it lands, capillary waves radiate outward from its point of impact.

And in the movie below, there is another water popping up after a couple of seconds. But what I find fascinating about the movie below: In the beginning, there are these smooth waves running through that were created by a breeze further upwind on the lake. But over the course of the movie, the texture of the surface changes: It gets rougher and ripples appear as the breeze moves in where I am filming. So within half a minute the lake looks substantially different!

And below a movie clip that should be used in physics classes because it illustrates so nicely that waves transport energy, not matter. How do we see that?

Can you spot the long waves going through right to left, and the small ripples that seem to, if anything, move from left to right? (Not true, that’s an optical illusion! They are moving right to left, too, only so much slower than the longer ones)

But if water was moving with the longer waves, the small waves would have to be transported with it, just riding on the other wave field. Clearly that is not the case! And that’s because only energy and the shape of the waves is transported, not the actual water the waves consist of.

And below is the picture that I would use to open my hypothetical wave photography exhibition with. Or maybe have it printed in a size to fill a whole wall if I ever had to furnish a large house.

Wave watching on Brodowinsee

What do you do the night before the most important three days of your whole work year? Yep — some wave watching with friends!

On Thursday night, we went to cool down and relax after preparing for GEO-Tag der Natur all day long. Don’t these images make you feel much more calm instantly?

And look at the waves in the atmosphere that only become visible because, as air is moved up and down by the waves, conditions change such that clouds form in the troughs but disappear at the peaks of the waves. Contemplating these things is so relaxing to me! Especially when looking at them both in the sky and in their reflection on the water.

And if you look carefully at the picture above, you see tiny little wave rings in the lower right corner. That’s small fish touching the lake’s surface from below, creating disturbances that propagate away from where the surface was deformed.

Other things make similar pattern, albeit on a larger scale. My colleagues K and K, for example, are creating wave rings, too. Theirs are much larger and propagate all the way across the lake!

And thanks to K&K’s waves, the reflections of the atmospheric waves on the water becomes even more interesting as they are deformed by surface waves on the lake.

Is there any better way to calm down any worries you might have?

And, btw, the GEO-Tag der Natur turned out a blast. I’ll update you on that once I’ve had A LOT OF SLEEP! Until then — go and do some wave watching! :-)