Tag Archives: fetch

More wave-spotting in “urban environments”

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I recently started looking at waves in “urban environments” (in contrast to “on the sea”) with a new found fascination. The reason why will be revealed soon, but for now just know that there are more waves coming up on this blog!

Today, let’s start by looking at more waves on Store Lungegårdsvannet, like we did before.

Here, you look downwind and see the flat water right in front of you, shaded from the wind by the walls around the lake. And then the further away you look, the larger the waves grow.

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Another very funny picture of a similar situation below: See how parts of the lake’s surface reflect the buildings and mountains and clouds really well (since that part of the surface is really flat), whereas other parts are way too choppy and appear a lot greyer on the picture?

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Yes, I admit, the purpose of this blog post was not so much to talk about waves as to show you how beautiful Bergen is in May. I miss this city… And my AMAZING Bergen friends!!! <3

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Walking around a lake to look at waves from all sides

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The most awesome thing about being on vacation is that I have the time to stare at water as much as I like.

For example the other day, I walked around Lille Lungegårdsvannet on a windy day.

Looking downwind, one sees a very smooth surface right in front of us, and then waves start developing further away. Looking at the fountain, you see that it is actually pretty windy.

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Lille Lungegårdsvannet in Bergen

Walking a quarter of the way around the lake, we now look at the fountain at a 90 degree angle to the wind: it is blown over to the right. We now see wave crests traveling and see the shape of the waves much more clearly.

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Lille Lungegårdsvannet in Bergen

Walking further, we see the waves coming directly towards us; the fountain is also blown in our direction. All of a sudden the water looks a lot more rough. And of course it feels a lot more windy, too, when the wind is coming right towards us and not in our back.

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Lille Lungegårdsvannet in Bergen

And bonus picture: A rainbow in the fountain when we’ve gone 3/4 of the way around the lake. Beautiful day in a beautiful city!

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Lille Lungegårdsvannet in Bergen

 

 

Foam stripes on the water.

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Sometimes you need to look at the bigger picture to understand what is going on, especially when looking at phenomena on the water.

My dad recently sent me the images below from Schleswig: Weird foamy stripes on the water.

They don’t really make a lot of sense until you look at it from a different angle:

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Now you see how the foam is forming in the waves all over, but that only some of that foam makes it through the gaps in that floating pier, forming a stripe behind every single gap. Cool, isn’t it?

What I found also really interesting in one of the pictures was this:

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The different wave fields upwind and downwind from the pontoons. On the upwind side (right side of the picture above), you see really choppy water. On the downwind side, though, close to the pontoons, the water is pretty calm, and only with increasing distance from the pontoons waves start to build again. And we can see that the waves at the far left of that picture are still a lot smaller than those coming in on the right side, just right of the pontoons!

Waves on Aasee in Münster. By Mirjam S. Glessmer

More wave phenomena on a lake, and a bit about wind

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Last week I showed you the results of my “wave hunt expedition” on Aasee in Münster. Today, I am following up with the same lake on the day after and the day after that. Even more wave phenomena to observe!

First, on my second day in Münster on my way to the conference:

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Clearly it had been windy for a while with more or less constant winds: You see Langmuir circulation cells.

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So imagine my surprise when, on day 3, I wake up to this view:

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Absolutely no waves at all, and no wind! Reason enough for a pre-breakfast stroll.

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As I was walking the wind picked up, as you can see in the increased surface roughness in the middle of the lake.

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But many parts of the lake were still completely calm. For example that weird building, which I sat at for the next half hour or so.

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Sitting there, I watched the “sea state” turn to slightly more wavy (see above — aren’t those pretty reflection patterns? :-))

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And I love how you have those tiny wave trains. So pretty!

At some point it got too windy for my liking, and I wandered on. And noticed a spot that I had missed on my last walk: A drain going into the lake, making more pretty patterns!

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Eventually I had walked all the way around the lake again into the lee of the land, which would have been really boring if it had not been for some duckies:

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Oh, and of course more pretty reflections.

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Hope you have a great day, too! :-)

Waves on Aasee in Münster. By Mirjam S. Glessmer

Wave hunt expedition. You don’t need to live close to the coast to observe all kinds of wave phenomena!

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A 1.5 hour walk around a lake — and 242 photos of said lake — later I can tell you one thing: You definitely don’t need to live close to the coast in order to observe wave phenomena!

The idea to go on a “wave hunt expedition” is actually not mine (although it definitely sounds like something I could have come up with!), it’s Robinson’s idea. Robinson had students go on wave hunt expeditions as part of their examination, and present their results in a poster. I was so impressed with that, that I had to do it myself. Obviously. So the second best thing about work travel (right after the best thing, again, obviously!) is that I find myself in a strange place with time on my hand to wander around and explore. Not that Münster might not have been a nice city to explore, but the lake…

Anyway. I only want to show you 53 out of the 242 pictures. I was going to annotate all of them so you actually see what I mean. And I started annotating. But since I am giving a workshop tomorrow (which is all prepared and ready, but I do need my beauty sleep!) I only drew the key features in the pictures, and you will have to come up with the correct keywords all by yourself (have your pick: refraction! diffraction! fetch! interference! :-)) So click through the gallery below and see first the original photo and then one that I drew in. Do you spot the same stuff that I saw, or what else do you see? Let me know!

Waves on Aasee in Münster. By Mirjam S. Glessmer

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If you think it would be useful to see all those pictures with proper annotations and descriptions at some point please let me know. I might still be excited enough to actually do it, who knows…

P.S.: I actually really enjoy work travel for the work parts, too. For example, I went to a great workshop in Dortmund earlier this year to learn about a quality framework for quantitative research, and that workshop was amazing. And a week ago, I went to Stuttgart for a meeting with all the fellows of the Stifterverband für die Deutsche Wissenschaft, which was also great. And now I am giving this workshop in Münster, that I am actually really excited about because I managed to condense pretty much all I know about “active learning in large groups” into a 2.5 hour workshop. Just so you don’t get the wrong idea about my priorities. Obviously water comes first, but then work is a very close second ;-)

Fetch and wind waves

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Summer holidays in beautiful Cornwall – what more can you ask for? If only these pictures weren’t from last year… Anyway, one can dream.

And one can find awesome oceanography everywhere. Take for example the picture below. Do you see how the bow lines of the ships have enough slack to hang in the water?

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Mevagissey harbour

If you look closely, this is what you see: Wind waves being dampened out by the swimming ropes, and then gradually building up again on the other side of the rope.

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Wind waves

Oceanography is everywhere! :-)

Wind waves meet current

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Wind waves on one side of the current – no waves on the other.

Recently in Bergen, I was walking to meet up with a friend at the kayak club, and I had to cross a bridge that has always fascinated me. Underneath the bridge, there is only a very narrow opening connecting basically the ocean on one side and a small bay on the other side. On this part of the Norwegian coast, the tidal range is easily of the order of a meter, so this narrow opening under the bridge makes for some pretty strong currents. In fact, when paddling through that opening, when the tide is right you can really see how the surface elevation changes from one side of the bridge to the other.

So when I was walking there recently, this is what I saw:

Strong current from the lower left to the upper right of the picture, wind blowing from the right, hence waves on the right side of the current and no waves on the left side.

This might be difficult to see on this picture, but there is a strong current going from the lower left corner of the picture towards the upper right. And on the right side of that current there are a lot of wind waves. But on the left side there are hardly any, even though there is nothing blocking the wind, just the current blocking the propagation of waves. Wind is coming from the right here.

I found it really fascinating how this current acted as a barrier to the waves and stood a couple of minutes watching. A couple of people stopped and looked, too, but didn’t find anything interesting to see and were slightly puzzled. But what I see is fetch (or that there isn’t enough of it on the left side of the current) and hydraulic jumps (or that the current is clearly going faster than the waves are). Which means that I start wondering how fast that current would have to be in order to stop waves from propagating across. Which then means I start estimating the wave lengths in oder to estimate the waves’ velocities to answer the previous question. So that’s reason enough to stand there for quite some time, just watching, right?

A fetching title for a fetching photo post

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Using a photo from one of my research cruises to explain the formation of wind waves.

Wind waves are (surprise coming up!) waves generated by wind that blows over the ocean’s surface. The size of those waves depends on several factors: The strength of the wind, the length of time the wind has been blowing over the ocean, and  the fetch (hence the “fetching” title of this post).

The bow of the RRS James Clark Ross and wind-generated waves in front of it. Note how the wind direction is indicated by the wind vane, and how parts of the ocean are sheltered by the ice floes.

The image above is really useful to talk about this concept. We see the wind direction indicated by the wind vane at the bow of the RRS James Clark Ross. In the lee of the ice floes, the water surface is smooth because it is sheltered from the wind. As the distance from the ice flow, and hence the fetch, increases, waves start forming again. In addition to the formation of waves, you can see how waves are refracted around the ice floe.

I like teaching using photos that I took myself. Not only do they show exactly what I want to talk about, but they also give me the opportunity to share stories, like in this case of how I took that photo when we were first approaching the ice edge in the Greenland Sea and then the next day there was ice everywhere and we saw polar bears. Not only are students entertained and fascinated hearing personal stories of experiences at sea, I think that those stories are also important for helping students form their self-image as an oceanographer, and for motivating them to stick it out through the tougher spots of their studies. Stories also help students remember content, and story telling is a very useful method in the classroom (but more about that in another post).