Occasionally working from home is awesome for many reasons, but mainly because I can use the time usually spent on commuting on … wait for it … wave watching. With my cup of coffee so I can warm up my fingers in between taking tons of pictures.
But I just love it. See below how the seagull is making waves where it is swimming, but is surrounded by a much larger circle, too, that it started when it landed on the water?
And especially gorgeous in the morning light: The reflections of sunlit structures on the water. The pier you see above gets distorted into something like this:
And if you look closely, you see the ring waves radiating from where the pylons disturb the water surface as waves go by.
I absolutely love to watch how the much longer waves can cause these ring waves with such a short wave length, and how they are deformed again by the waves that caused them. I can look at this for a long time without getting bored, it is so calming to me! Especially in the early morning light.
But anyway, time to start working. Have a great day everybody!
Berlin is full of interesting history to discover … for example that of ships that have gone past on the Spree! :-D
Let’s start with some easy wave watching. In the picture above, you see a ship and its wake (both parts: the turbulent one where the ship has gone, and the feathery wake that forms the V with the ship at its tip). And you can make out the wake of a ship that has already gone round that bend of the Spree: the turbulent part showing a different surface roughness, and reflected remains of the feathery V on the right shore of the Spree. So far, so good!
Below, you see two turbulent wakes: The one of the ship you still see, and then the one of a ship that went the other way, but already went out of the area captured in the picture.
Berlin Cathedral Church seen from across the Spree
And here is a series where you see the feathery wake reach the side of the Spree…
Bode museum and television tower Berlin
…get reflected there…
…and then meet the reflection of the other side of the V to form a checkerboard pattern! Would you have known what’s going on here if you hadn’t spotted the ship just about to leave the picture, or seen the previous images?
Below is another nice one. What happened here? A ship sat there, waiting, and then started moving again right before I took the picture! This is the beginning of a turbulent wake right here.
Reichstag, home of parlament
And below another nice wake plus reflection.
And here you see another feathery wake, plus the turbulent wake of the same ship on the other side of the Spree.
Reichstag, home of parlament
Similar picture as above, except in a different spot…
German Chanellery in Berlin seen across the Spree
Yes, that’s a pretty good representation of what sightseeing trips with me are like ;-)
On a recent evening stroll with a friend, the seal basin looked like this:
“Do you think there are any seals in there today?” she asked. “Why yes, of course, don’t you see the waves?” I replied. Because obviously in a basin sheltered by the wind and with no moving parts in it except possibly a seal or three, there is no other mechanism that I could imagine that would create such a wave field. Sometimes I wonder what everybody else is thinking about all the time that I am thinking about waves while they aren’t… Who’s missing out on the cooler thoughts, me or them?
Anyway, we got to do some proper seal watching and wave watching, respectively:
Pretty, isn’t it? the wake of a seal. Pay close attention, I might be testing you on this some time soon ;-)
I just love this picture: The two boats in the front are going at the same speed (the trainer is driving right next to the person in the row boat over a long distance), yet look at how different the two ships’ wakes look!
The motor boat has this huge, breaking, turbulent wake. Even though it rides so high up in the water, it displaces a lot of water and creates a wake with a large amplitude (how large the amplitude is is visible in the picture below, where some poor people were sitting in row boats when a motor boat sped past. But also here: Look at how cool these feathery waves that constitute the wake look together!).
But then, going back to the original picture (which I am showing again below) — look in contrast at the row boat’s wake. You see the paired eddies where the oars were in the water, and you see a tiny little trail where the body of the ship went. But that’s all. Yet both boats are going at exactly the same speed! Pretty cool, isn’t it? (Also pretty scary how much energy the motor boat is spending on moving water and moving a larger hull and a heavy engine rather than just propulsion when the payload of both boats is more or less the same — one person)
Looking at Kiel fjord in the picture below, it is quite obvious from the shape of the waves that those waves are some ship’s wake.
Why is that obvious? Because the waves a) have a very short wavelength for their height, and b) are also all of the same wavelength. What I mean by that is a) on Kiel fjord, if we see waves that high that are driven by the wind, their wavelength is a lot longer since the waves have been building up over a long distance. For short waves to display such an amplitude, the waves would have to run up a fairly steep slope which I know is not the case in this location (and which would also lead to two or three high crests in the shallowest part of the water, not to as many as far out as we see here). B) we don’t see a spectrum of wavelengths as we would expect in a wind-driven wave field. In fact, the water surface doesn’t display any ripples or other evidence of wind at all.
And what do you see when you look at water at night? :)
But before I get to that, this is the setting on Sylt. A sandy beach opening up to the North Sea, that is separated from the land by sand dunes which are overgrown with some kind of beach grass.
Yesterday was a windy day as you see from the waves, but neither was the water level very high, nor was the wind anywhere near as strong as it gets here during winter storms, so the erosion happening yesterday is not very strong compared to what it is like during more extreme weather conditions (and the process I am focussing on here is probably one of the least important ones).
In order to prevent erosion of the dunes which protect the inland from storm surges etc, it is crucial that the beach grass growing on the dunes isn’t stepped on by the hundreds of tourists visiting this beach every day (probably thousands during summer). Therefore there are these wooden staircases installed in regular, short intervals to bring people across the dunes without them doing any damage to the vegetation.
Therefore, in most places, the dunes look like this.
In some places, though, there is little or no grass growing on the dunes, so imagine what kind of damage strong winds can do here, let alone a storm surge!
And in one of these open sand areas I observed what I think are roll waves. Do you see what looks like a drag mark a little right of the center in the picture below?
Check it out in the movie below (it zooms in after 5 seconds to show it more clearly) — there is sand surging down this track! To me this looks very similar to roll waves, and I know roll waves have been observed in sediment flows and lots of other places, so why not in the sand of these dunes? What do you think?
You know how they say that the journey is the destination? That was certainly the case for my spontaneous mini-vacation yesterday (and how awesome is it that my #BestTravelBuddy is up for a cross country trip on a day’s notice?). We went all the way from the east coast to the west coast — which in Germany admittedly isn’t that terribly far — to visit the island Sylt in the North Sea for a day.
But it got even better when we reached the west coast. This is my kind of train ride!
Below is a view of the dam that connects the island Sylt with the main land, and here again you see how windy it is, and this is in the lee of the island. In the lee of those shallow dams you see that it really doesn’t take long for the surface roughness to increase again.
So are you excited to see the wind-ward side of the island now? I’ll post some wave watching from that side soon, but I first have to wade through literally thousands of pictures to cut it down to a handful. I’m already down to about the 100 best, but now I can’t decide which ones to post, because I like them all…
But here is a picture of the train ride back. Do you notice how there are regions with really low surface roughness on either side of the dam, suggesting that this dam is sheltering the water surface from the wind in two directions? Of course it isn’t — it’s just ebb tide and the smooth surface areas towards the right of the dam are wet sand that look similar to a smooth water surface.
So that’s my wave watching from the train! Excited to go back soon! :-)
Below, I really liked how the wave rings have such different sizes and amplitudes depending on whether they were made by rain drops or ducks (you might have to click the image to enlarge to see what I am talking about).
And below, I love so much about this picture. The long waves with the very small amplitude that are coming into Kiel fjord from some far-away storm. The short waves and small scale turbulence that is created where wave crests just manage to flood a step on the staircase, but the water then flows off it again during the next wave trough. The small speckles made by rain drops. The fact that it seems to almost be summer again because the beach chairs are back! And, of course, that I caught the splash and the flying drops of the wave.
I read this poem by E.E. Cummings on Saturday that really speaks to me. It ends in
“For whatever we lose (like a you or a me)
it’s always ourselves that we find in the sea”
In the gif below, I have drawn in several things. First, in red, the “weird” tracks that we are trying to explain. Then, in green, the crests of two different wave fields that are at a slight angle to each other. I’m first showing one, then the other, then both together. Lastly, I am overlaying the red “tracks”.
So this is what those tracks are: They are the regions where one of the wave fields has a crest and the second one has a trough (i.e. where we are right in the middle between two consecutive crests). What’s happening is destructive interference: The wave crest from one field is canceled out exactly by the wave trough of the other field, so the sea level is in its neutral position. And the wave fields move in such a way that the sea level stays in a neutral position along these lines over time, which looks really cool:
And even though these weird neutral sea level stripes are parallel to the bright stripes on the sea floor, I don’t think that the latter one is caused by the first. Or are they? Wave lengths seem very different to me, but on the other hand what are those stripes on the sea floor if they aren’t related to the neutral stripes in the surface??? Help me out here! :-)
What is it that we actually look at when we go wave watching? Water is pretty much clear (or at least it is in the spots where I like to go wave watching), so how come we are able to see waves?
What we are looking at are not actually the waves themselves, but at how surfaces oriented in different directions reflect light from different directions towards us, and usually the light isn’t uniformly distributed, so we see lighter and darker areas on the waves that are associated with certain orientations of the surface, i.e. the slopes going up and down to and from the crests.
But this only happens if we look at water at a small angle — then the water surface acts to reflect most of the light from above. However if we look at water at a steep angle, we are actually able to look inside. See this in the picture above? This is due to a phenomenon called total internal reflection.
Now that light easily gets in and out of the water, the water surface does something weird: It acts as a lens and focusses light on the sea floor so we see bright areas and not so bright areas. And looking at how the brightness is distributed on the sea floor, we can figure out what the waves must be to have focussed the light in exactly that way, even though we can’t see the water surface.
Let’s start with an easy example. Below, you see the half circles of concentric waves radiating away from some obstacle at the bottom of the sea wall. The further away from the center you look, the more other waves you notice as the concentric circles become more and more difficult to see.
Moving on to a slightly more difficult case below.
You see the waves radiating away from the seagulls. Behind them, at a shallow angle, you mainly see the ambient light of the sky reflected on the waters surface to let you see the waves. Towards us, though, at a steeper angle, it gets more and more difficult to see the water surface and the waves, but we start seeing the light focussed on the sea floor, mirroring the circles of the waves above.
Here is another example of waves , except this time we see because of reflection of light on the surface further out, vs focussing of light on the sea floor closer to us, except that this time we are not looking at the same waves any more. The waves further out are wind waves and waves the birds made, the waves further in are similar to the ones in the second picture — created by an obstacle at the base of the sea wall.
But then sometimes it gets really difficult to reconcile the waves we see through these two different phenomena. Below, the wave field we see by looking at the light reflected at the surface seems to be dominated by wave crests coming towards us, with the crests being more or less parallel to the sea wall at the bottom of the picture. There is some small stuff going on on top of that, but it doesn’t seem very important.
But now looking at the pattern of light on the sea floor, we pick out something very different: The dominant wave crests are now perpendicular to the sea wall when you look at the middle of the picture below (towards the bottom we see those half circles again that we saw above, too)! Where do those wave crests come from that are perpendicular to the sea wall?
There are actually two things I can think of.
First: they are actually an important part of the wave field, we just don’t pick them up very well because — in contrast to the waves coming towards us with the side going up towards the crest reflecting the dark land behind us and the side going down towards the trough reflecting the bright sky — waves going perpendicularly to that field would mainly reflect the sky, so it would be hard to make out their crests and troughs since they appear to be the same color.
Second: I’m not actually sure this makes sense any more. I was going to say that the surface shape of wave crests moving away from the sun might be more suited to focus light than wave crests moving in a perpendicular direction. But looking at all the examples of circular waves that I posted above and that show up as circles, not just in areas where the wave crest was in specific directions, this probably doesn’t make sense. If anyone is reading this, what do you think??
Below is another example: Here we see a crisscross of waves, a checkerboard pattern of an incoming wave field and its reflection — as long as we look far out onto Kiel fjord. If we look into the water at a steep angle, we see again wave crests that don’t seem to match what we saw on the surface! (btw, don’t let yourself be distracted by the ripples in the sand that might look like they are also caused by light being focussed by the water surface. They are just ripples in the sand…)
Clearly I need to think about this some more to figure out what’s going on here. I’m grateful for any input anyone might have!