When I decided that I was going to stop under a tree for a while to let the shower of rain pass before heading home, the weather looked like this.
Not even half a minute later, I was very happy I had stopped! Because the wave watching got a lot better as the wind drove larger wave over the lake, and also because the rain got a lot heavier and I was semi-dry under the tree. But that makes for some fun drop photography!
All those little wave rings look so cool!
And it’s impressive how a little wind quickly changes the wave field on the lake, too.
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!
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”
When we watch rain falling on a water surface, we observe that each raindrop causes several concentric waves with different radii. In my post on Tuesday I just stated that that was what we observe, but today I want to look into the explanation.
This is what it looks like when it rains on a water surface. Not much surprise here!
But when I was visiting my parents last weekend, it started to rain with nice and heavy drops that were few and far between. So I saw my chance, grabbed my camera and ran outside to try and capture exactly what happens when a rain drop hits the water surface. Not an easy task, since everything happens very fast and it’s impossible to anticipate where the next drop will fall, so I had to rely on my camera’s auto focus and just press the trigger as often as possible. And guess what? It stopped raining within a minute! How annoying is that?
But I still managed to capture enough pictures to show you what I wanted to show (see image below):
First, a raindrop just causes a dent in the surface, starting the first circular wave. But if the raindrop was sufficiently large and fast, the surface will bounce back, throwing a secondary (and sometimes tertiary) droplet up into the air. Those droplets will fall in the same spot as the first one, causing the smaller waves.
Isn’t this amazing? I’ll definitely work on better pictures in the future, but I am not sure it can be done with my camera.
[Edit 20.4.2016, 12:24. We don’t actually need the secondary and/or tertiary droplets, as Martin pointed out. It is sufficient that the surface gets deformed by the first rain drop, then bounces back and overshoots. When the water that overshot falls back down, this has the same effect as a secondary droplet: to cause a new circular wave just inside of the first one. And of course, the overshooting and triggering of new waves can happen several times, depending on the impact of the initial drop. In a way, my secondary / tertiary drops are just the extreme case of this more moderate version of wave formation.]
To wrap up this post — a bonus picture: Four stages of wave development all captured in one (lucky) shot!
Are you looking forward to the next rainy day now because then you can go outside and observe all this cool stuff?