Yesterday, I happened to be at Parsteiner See for work.
At first, the sea was completely calm and the only waves were the ones we made doing our photo shoots, like so:
Other than that, the lake was completely calm.
But then suddenly, I spotted a breeze going over the lake. It becomes visible in the dark areas with higher surface roughness, where capillary waves have formed.
As the wind keeps blowing over the capillary wave area, those waves grow and then at some point become “regular” gravity waves, that travel out of the region where they are directly forced by the wind. See below: In the background you still see the area with higher surface roughness, whereas in the foreground gravity waves are coming towards the shore.
As the wind keeps blowing over the surface, forming capillary waves over larger and larger areas, those areas all show up as darker and rougher.
And the cute little waves keep coming to the shore :-)
What I find really fascinating about watching waves in the atmosphere rather than on water is that all the waves that become visible are not surface waves like on water, but internal waves. Which we have to go to great lengths to make visible in water (for example by adding dyes in tank experiments) but which we can’t just visually observe in the sea in the same way as we can in a transparent atmosphere.
In the atmosphere, however, we also don’t see every internal wave going on, either, we need very specific conditions for them to become visible. So whenever I see one, I start pondering why we see exactly what we see, why there are clouds in some places and not in others. Below, for example, we see the troughs of an internal waves in cloud stripes, but the crests don’t form clouds. Fascinating how just displacing air by a little bit can cause clouds to form and to disappear!
And things become super cool when you combine atmospheric wave watching with “normal” wave watching like in the picture above. There you see the rough surface with tiny little wind waves in the background, waves coming around the break water, the calm water in the lee of the break water, sheltered from the wind, and then the reflection of the atmospheric waves on the water.
And you thought it couldn’t get any better? Well, you were wrong! Now there are also some waves on the water, plus soap bubbles! :-)
Now, for a thought experiment: What would soap do to the waves? Would destroying surface tension actually matter? I think not in this case, or t least not close to land in the picture above, since the waves are mainly gravity waves, not capillary waves. But what do you think?
On a bike tour with my friend Frauke in Greetsiel two or three weeks ago, she pointed out how well one could see that the waves on the puddles left in the Wadden Sea close to low tide were wind-generated. That was that for the bike tour — now I had to take pictures.
Below you nicely see the ripples that are created where there are longer stretches of puddle aligned with the wind direction, i.e. where there is enough fetch. And you see how the waves get diffracted behind topography, fanning out downwind of slits! The wind is coming from the right here, almost in the direction pointed out by the looks-like-an-arrow-but-is-plastic marine litter.
Here we are looking in the opposite direction, the wind now going left-to-right. Do you see the one slit in the lower half of the picture and how wave crests propagate almost perpendicularly to the wind direction, just because there are waves going through that slit? Pretty cool, me thinks!
The really shallow water with all the stones in it made it really easy to look at waves from different directions. Below, we are looking downwind, at the back of the waves.
And below we are looking upwind. See how different things look now? You still see the wind pushing the waves, the front slope of the wave is a lot steeper than the back slope.
I love the picture above, makes me want to put my hand in the water and play with the waves :-)
Wakes are always interesting to watch. But usually, I am showing wakes of ships going straight ahead. So today, I have something cool for you: The wake of a ship doing a 90 degree turn!
And what that does is that the feathery wake that is usually V-shaped now gets deformed!
And this deformation of the wake means that on one side of the wake, the feathery waves that are usually parallel now become fanned open, while on the other side they get bunched together. See?
After the ship had gone a lot further, there were still effects of its wake visible, both of the waves created as well as the turbulent wake that is still visible in a surface roughness that is different from the rest of Kiel fjord, and a little foam.
Fascinating how long such a wake stays visible!
And fascinating that such a small boat — even though it was going a lot faster — does create waves that are a lot higher than the much larger ColorLine does!
If you look at the large ColorLine, you see that there is a large turbulent wake, but (at this speed) hardly any waves created, so hardly a V-shaped wake!
This is the blogpost I wanted to write today before I got distracted by all the adventures on MS Stadt Kiel with sightseeing and swing dancing and all the good stuff that wasn’t wave watching. I had even uploaded all the pictures of this morning’s wave watching walk on my blog already, but then things just got too exciting… But here we go now!
Here we see a really nice example of shallow water waves: The wavelength is a lot longer than the water depth and the shape of the waves looks very different from the almost sinusoidal waves in deep water: The troughs are very long and the crests short and steep.
And here they show the influence of water depth on phase velocity: Where the water gets shallower and eventually the land falls dry, the waves get slowed down. This means the part of the wave crest that is still in deeper water is faster, overtaking the shallower part, and thus the waves get bent around, towards the shallower areas in the water.
For comparison here the shape of waves in deeper water. Do you see how they are much more sinus-shaped?
Above we also see fairly well how gusts of wind change the water’s surface roughness: where the water surface looks darker, it is covered in small capillary waves caused by gusts of wind.
Btw, if you were wondering where the longer wave length waves came from: They are the wake of a boat accompanying the training session of some race kayakers.
When those waves hit the sea wall, we see nice reflections and a checkerboard pattern!
Btw, I find it super eye opening how the structures that, to me, absolutely dominate the picture above are not picked up as dominant in my comic app (see below). Of course the structures of the power plant or sea wall are more prominent, but the criss cross of the reflected waves is hardly visible. Maybe that’s how little it is visible to most people even in the photos? On my Instagram poll on whether comic-y-fying pictures helps to show what I am talking about, 60% of the responses were that yes, comics make it easier to see what I mean. Not quite sure yet what I will do with that information moving forward…
Something else really curious today, btw: The way the sea floor looked! Usually there are lots of ripples here, mostly parallel to the sea wall. And today these weird patterns of darker (finer?) sediment. I think I need to observe the sea floor more consciously to figure out what’s going on there!
And now the race kayak and accompanying boat are coming back. I love how you see their wake and then that bird’s wake in the picture below!
And then, finally, some larger waves, again the wake of some ship that I didn’t pay attention to.
And sometimes, the reflections are just suuuuuper difficult to see when you don’t know what you are looking for. Do you see them in the picture below?
Yesterday, I took some pretty pictures of a red balloon floating on Kiel fjord, some seagulls swimming close to it, and — of course, most importantly — the seagull’s waves. You see some that they just made where you can still see how they relate to where they are swimming now. But then there are also these large circles from previous movement, and the origin of those we can only guess. As we see from the seagulls’ wakes, they haven’t been swimming in that direction long, and they started out from a resting position. Maybe the large circles are from when they landed? We can only speculate.
I’m showing you the pictures of the seagulls and the ballon because I think they are pretty, but also to have a reference for what “normal” waves look like. “Normal” meaning that they are waves whose restoring force is gravity.
There is, of course, other kinds of waves.
Check out the picture below. It’s super choppy, but do you see parts that look different? It’s an overall choppy day, so it might be a little difficult to see what I am talking about.
Let’s zoom in to see some capillary wave action! Capillary waves are the ones that are restored by surface tension rather than gravity. They are a lot shorter than “normal” waves, wavelengths are only up to less than 2 cm long! And they often appear as several wave crests right behind each other, like below. Short wavelengths travel faster than longer ones, which is why from a main crest, more and more capillary waves emerge which seem to be bunched up moving right in front of the main crest. Pretty cool, I think!
Edit, a couple of minutes after initial publishing this blog post:
I saw a friend use a comic app on Instagram and, of course, went down that rabbit hole. So here is a recap of the pictures as the app sees them below. Do you feel like the waves are easier to see in the comics than in the pictures?
Below, you see the seagulls as they have just started paddling forward, and the large circles are still fairly close to where the seagulls are.
Now the seagulls have swum a little further, but you still see where they initially started out. And you see that the time lag between the two pictures really isn’t that large — the large wave ring hasn’t propagated a lot compared to the balloon (which is also freely drifting, so maybe that’s not the smartest comparison).
But my capillary waves become a little clearer now, I feel: The bunches of parallel wave crests on the right half of the picture that are now drawn in black (while all the choppy stuff is just shared, but not contoured).
What do you think? Are these pictures helping to show what exactly I am talking about, or is it just as confusing as before, only in a different way?
My friend Alice (of the awesome Instagram @scied_alice and the equally awesome blog, which you should totally follow) sent me a #friendlywaves from her trip to Cyprus. She said that this was a simple one, so I am looking forward to what else she has up her sleeve once I pass this test ;-)
So here we go with the pictures she send.
Clearly, she is on a boat trip, and she’s looking back at the wake of the ship. You see the one side of the feathery V of the wake, pretty much in the middle of the picture. On the “feather” closest to us, you can still make out the turbulent part of the breaking bow wave, where the water surface looks all crumpled up and not as smooth as it does further away from the ship. Actually, this is a really nice example to show that the waves are traveling away in the wake, but the water is not: All the other “feathers” further away have smooth surfaces as they have run away from the ship’s trajectory, while the turbulent wake traces out the exact path where the ship went (as long as there aren’t any currents moving around the water, which we’ll assume for now).
Picture by Alice Langhans, used with permission
The waves in the V-shaped wake are fairly steep, you can see them very slightly tipping over on occasion.
And Alice sent a second picture: Similar situation, except now it’s a little more windy. The turbulent wake is a little more foam-y than in the previous picture. This could be because the ship is sailing faster, or because it’s more windy. I would guess the first.
And when I say “sailing”, I am using this as the technical term for a ship driving. I am assuming that the boat Alice is on is not a sailboat. I’m thinking this because the wake looks fairly turbulent and sail boats usually don’t cause this much turbulence; also the little bit of the boat that I can see doesn’t really scream sailboat to me. We’ll have to wait to hear what she tells us, though!
Picture by Alice Langhans, used with permission
On both pictures, there is hardly any swell visible. Waves are usually not as visible when the water is deep as when they run up on a beach, and so far off shore we can assume that the water is fairly deep. But that also means that it isn’t very windy, hasn’t been very windy recently, and hasn’t been very windy anywhere near recently, either, so no large waves have traveled into the region.
So much for these #friendlywaves. How did I do, Alice? :-)
What I love about my job (in addition to the awesome job itself, obviously)? That my office is located in pretty much the coolest spot in Hamburg when it comes to touristy views of the city. So much great wave watching (and ship watching) to be done here!
For example below, see the small ferry on the right, and how well you see the bow waves in this kind of light?
And below, it has turned and is heading out into the main Elbe arm and you can spot the turbulent wake that reflects the sun very differently from the rest of the water on either side.
And then just casually strolling past dry docks, container terminals, huuuge ships…
I really enjoy this every day! Hamburg, the gateway to the world.
A beautiful picture: the pink sky, purple clouds, a peaceful channel flowing in between lush greens that the calm water surface mirrors back, a bridge somewhere in the background, connecting the shores, both in reality and in the image on the water. Early morning harmony. Hygge?
And what jumps at me?
Which I think are really beautiful: Featured in the dark images of the trees on the water, a duck’s wake reflects the light sky back to us, thus becoming visible. And once we spot the V in the waves, with the almost invisible duck at its tip, we can see how the space between the feathery sides of the V is filled with half circles, connecting the feathers. They get more and more difficult to see the further away from the duck we look. The contrast becomes less clear where they aren’t set against the dark backdrop, and the more the waves dissipate with time.
This kind of waves is so common all around us, all the time. Did you ever really stop and look? It’s so worthwhile to really observe these things, to me that is happiness :-)
The Teltow channel and the bridge connecting Lankwitz and Steglitz, by Henning Krause. Picture used with permission