Category Archives: observation

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

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:

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

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

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

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

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.

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

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!

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:

Oh, and of course more pretty reflections.

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

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!

[Best_Wordpress_Gallery id=”2″ gal_title=”Münster Aasee”]

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 ;-)

One of the most exciting things about work travel?

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One of the most exciting things about work travel? Staying in tons of different hotels, which all have different opportunities to play with water.

For example at a recent team event, there was this tap with a really efficient aerator, that made the hydraulic jump look even more exciting than usual:

And then at a conference last week, this happened:

Can you see what happened? Obviously, I turned the water on, and the right side of the armature fogged up because of all the cold water going through! (Even though I can assure you: My shower was nice and warm!)

And I am not even going to apologise for how excited I get by observing these kinds of things. Remember the kind of tap I have at home?

Still the coolest tap I have ever seen! :-)

Observing hydrodynamics on a very large scale

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You know I like to point out where you can spot hydrodynamics concepts in your everyday lives (at least if your everyday lives include strolls along rivers and generally a lot of water)

A while back we went to Geesthacht. We were hoping for more ice on the Elbe river, but sadly there was none. But! In Geesthacht they have a weir, combined with locks. They keep water back to bring the level of the Elbe upstream of Geesthacht up to 4 m above sea level for shipping purposes. But then they obviously need a lock to get ships up and down this sill. But the coolest thing is the weir:

Weir on Elbe river near Geesthacht

200 m of pure hydrodynamics! You know I love a good hydraulic jump…

Weir on Elbe river near Geesthacht

Do you see the three different states the fluid in the picture above is in?
Looking from right to left (i.e. with the direction of the flow), we first see normal flowing water. You can see that there are waves and ripples going in all directions. Then, the middle part of the picture, all disturbances on the water surface are clearly oriented right-to-left. That is because here the water is shooting (meaning flowing faster than waves can propagate), and all disturbances get deformed by the flow rather than spread by themselves. And then on the very left, we have a submerged hydraulic jump (which we cannot see, because, as the name says, it is submerged) and above massively turbulent water.

Weir on Elbe river near Geesthacht

I just love the look of it!

Watch the video below to see the whole thing in motion.

Observing hydrodynamic phenomena on a creek

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Looking at a creek on a Sunday stroll, and seeing lots and lots of concepts from hydrodynamics class.

For example below, you see waves radiating from each of the ducks. And you see interference of waves from all those ducks.

What happens if the ducks bring their waves closer?

At some point, all those waves from the ducks are going to hit the weir in the picture below.

And there, they are going to somehow react to the flow field caused by the changes in topography.

And you can spot so many different phenomena: Standing waves, hydraulic jumps, and lots more!

Watch the movie below to see the whole thing even better!

Btw, you might remember this spot, I have talked about standing waves from right there before. Interestingly, the wave pattern in the other post looks really different, probably due to different water levels or changes in topography (maybe someone threw in rocks or they did some construction work on the weir?). But it is still just as fascinating as last time :-)

And for those of you who like to see a “making of”:

Frost flowers – when water vapour freezes to ice without going through the liquid phase. Examples “at sea”

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Frost flowers! I learned about those in the context of Arctic and Antarctic ice formation. I kinda assumed that ice flowers only formed in salt water, because I remember hearing about how the ice needles that form wick up brine and that, due to their large surface (which you will remember noticing in the last post where we looked at them forming on trees), they are super important in the air-sea exchange of all kinds of stuff, like for example bromine. So imagine my excitement when I saw them growing the other day!

Frozen Schlei river in Schleswig

Frost flowers are really pretty by themselves, but they also tell us a lot about recent weather conditions. For example, they only form when the air is A LOT colder than the water/ice surface. Do you know the snowy ice crystals you sometimes find on the inside of ice cream containers when you’ve opened and refrozen them? Yep – same thing! I even suspect that the ice crystals I was talking about in this post are also frost flowers.

Frost flowers

I find it really fascinating how they are distributed over the larger surface of the Schlei river.

Schlei river in Schleswig coated in frost flowers

Here, for example, you see them forming on the edges of ice that has been broken up by some mechanical process. Judging from their placement, I would suspect that they only formed after the ice was broken and some of the pieces tilted up.

Cracked ice and frost flowers

Here, they were probably everywhere, but then the ice got broken up and some parts submerged. When the water there refroze, no snow flowers formed, just “normal” ice. However, the existing snow flowers seem to have continued growing!

Ice with frost flowers. Partially submerged and then refrozen into “normal” ice

The really interesting thing is that frost flowers don’t actually form from the water that is freezing below, but from water vapour in the air. Which, btw, explains why they can form on benches, ice cream lids or trees (all of which would be really difficult if they could only form on open water surfaces).

Ice with frost flowers. Partially submerged and then refrozen into “normal” ice

Above you see a larger part of the Schlei’s surface: Seems like there used to be frost flowers everywhere, but when the ice broke up, some of it got pushed out of the water, and as such preserving the frost flowers and letting them continue to grow. Meanwhile, other parts got flooded and only normal ice formed there. Maybe because the temperature gradient at that point wasn’t large enough any more?

Isn’t this just beautiful??? I could watch this all day, every day.

Frozen Schlei river in Schleswig with frost flowers

But let’s look at some more details. No idea why that patch of frost flowers formed there! But they seem to always start in small patches, which eventually grow together if the conditions are stable enough over long enough periods of time.

Frost flowers on ice

Here, we see the opposite situation to the one a couple of pictures up: “Normal” ice had formed, and then was broken up. And then, when the crack froze over, frost flowers formed!

Frost flowers growing in a crack in the ice

Very cool stuff!

Frost flowers

Yep, I would still just sit there and watch!

Frozen Schlei river in Schleswig

Frost flowers – when water vapour freezes to ice without going through the liquid phase. Examples on land

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What happens when water vapour freezes to ice without going through the liquid phase? Frost flowers!!!

That’s when trees suddenly look like this:

Frosted tree.

Btw – the stem of that tree is painted white! That’s just to confuse you a little but…

But let’s take a closer look. This is what the branches look like: Tiny ice needles growing on the individual pine needles! And the orientation of the image below is correct. They are growing to the side!

Frosted tree.

You can clearly see them all growing to one direction, to one side!

Frosted tree.

When you take off a bit of frost, this is what it looks like. Needles, but with a fractal 3D structure! Since what happened here (water vapour freezing without becoming liquid in between) is basically snow forming on the surfaces down here instead of in the clouds up above, it isn’t too surprising that snow is exactly what the frost bits feel like.

A piece of frosting. This picture isn’t blurry – the ice needles have a fractal 3D structure!

Look below, you can clearly see the frost only growing to one side (and this picture is the right way up, too!):

Frosting on tree branches

Doesn’t it make you want to sit there and just watch?

What a nice picknick spot!

Although every time the slightest of breezes comes, this is what happens:

Tree being de-frosted by wind

Also really cool: These plants growing on a balcony behind a glass railing. Only the tips have been frosted!

Plants on balcony with frosted tips

And if you were wondering what this post has to do with oceanography, check out the image below. Can you spot it?

Frozen Schlei river in Schleswig

Can you spot it now? No, not my niece (although she is pretty cool, too!), the frost flowers!

Schlei river in Schleswig with frost flowers

We’ll talk about those next time :-)

Using the period of a swinging lamp to calculate the height of the ceiling

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Using the period of a swinging lamp to calculate the height of the ceiling.

When, on December 31st of last year, I was sitting in church on the gallery, listening to a friend of mine play music, I had a lamp right in front of my nose that swung ever so lightly because of warm air raising from a vent below. I’ve actually written about the same observation a year ago when I sat in pretty much the exact same spot, listening to the same friend play, but since you liked my recent post on a different church (actually built by the same team of architects!) I thought we’d go back to churches again today.

This is what the church looks like on the outside when it’s dark:

Johanneskirche in Hamm, Germany

And here is the inside.

Inside of the Johanniskirche, Hamm, Germany

The picture above was taken from a more or less central position on the gallery when we walked in. I ended up sitting a lot further to the left (as you can see in the video below).

Now. For small displacements from the equilibrium position, we can use the period of the lamp’s movements to calculate the height of the ceiling, since the period of a swing only depends on the acceleration due to gravity and the length of the cable.

Btw, in old pendulum clocks, the pendulum is often shaped as a disk. I always implicitly assumed that was to make sure it didn’t break the glass closing off the case in which the pendulum swings or to have a better surface to decorate, but according to Wikipedia it is to reduce air resistance. Which makes a lot more sense, obviously. Why I thought the pendulum might start swinging perpendicularly to its original path beats me. But then you never really think about why you assume stuff, do you?

Anyway. Since in this year’s video the lamp’s movement is a lot easier to spot than in last year’s, and it is therefore much easier to actually measure the period, here we go:

Taking the time for six swings, I measure something like 27 seconds, which would mean 4.5 seconds per swing.

Using T = 2π sqrt(L/g) with T the period and L the length of the cable, it follows that the cable is something like 5 meters long. Which seems realistic when you look at the size of the people in the benches. Now I should really go back to last year’s video and do the comparison, or at least take the time from this video a second time, to estimate the error. But I can’t take all the fun away from you, so please go ahead and let me know what you find! :-)

Reading ice on a river as tracer for flow fields

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For most of my readers it might be pretty obvious what the movement of floating ice says about the flow field “below”, but most “normal” people would probably not even notice that there is something to see. So I want to present a couple of pictures and observations today to help you talk to the people around you and maybe get them interested in observing the world around them more closely (or at least the water-covered parts of the world around them ;-)).

For example, we see exactly where the pillars of the bridge I was standing on are located in the river, just by looking at the ice:

What exactly is happening at those pillars can be seen even more clearly when looking at a different one below. You see the ice piling up on the upstream side of the pillar, and the wake in the lee. Some smaller ice floes get caught in the return flow just behind the pillar. Now imagine the same thing for a larger pillar – that’s exactly what we saw above!

And then we can also see that we are dealing with a tidal river. Looking at the direction of the current only helps half of the time only, and only if we know something about the geography to know which way the river is supposed to be going.

But look at the picture below: There we see sheets of ice propped up the rails where the rails meet the ice, and more sheets of ice all over the shore line. As the water level drops due to tides, newly formed ice falls dry and that’s all the sheets of ice you see on land.

The bigger ice floes in the picture have likely come in from the main arm of the Elbe river.

Small port on a tiny bay on the Elbe river in Hamburg. Look at the sheets of ice on shore!

It is actually pretty cool to watch the recirculation that goes on in all those small bays (movie below picture). Wouldn’t you assume that they are pretty sheltered from the general flow?

Using a shadow to estimate the date a photo was taken

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This post might be a bit nerdy, but at least it runs in the family: My dad was recently trying to find out when this photo inside a church had been taken.

Photo of the inside of the “Maria Magdalena” church in Hamburg Klein-Borstel, taken some time before its official opening in 1938. (Picture used with permission; HAA_ORh_028.9_(0567) of the Hamburgisches Architekturarchiv)

Since some parts of the altar aren’t finished yet, we knew it had been taken some time before the church was opened on December 11th, 1938. We also know that the church runs east-west, so in the picture above, we are facing east, south is to the right.

Zooming in on the shadows the benches make on the floor, we see that they are close to parallel to the joints in the floor, hence the sun must be pretty much south.

Detail of the photo above. (Picture used with permission; HAA_ORh_028.9_(0567) of the Hamburgisches Architekturarchiv)

Now we can estimate the height of the benches and the length of the shadows. Actually, we only need the ratio.

Detail of the photo above. (Picture used with permission; HAA_ORh_028.9_(0567) of the Hamburgisches Architekturarchiv)

Using all the random bits of trigonometry we can remember, we can calculate the angle of the sun in the sky.

Then, we can use that angle to go to a page like http://www.sonnenverlauf.de to find the date on which the sun is at that angle when also standing directly in the south.

Ignoring details like summer/winter times and the small angle we see between the shadow and the joints, it turns out that the picture was taken in early October.

Or at least that’s what I first thought, assuming that the church will not have been ready in early March if it only officially opened in December. Then my dad pointed out that you can see numbers of the songs up on the wall: Number 213, 391, 392, and 394.

HAA_ORh_028.9_(0567)_Ausschnitt_wie_KG_MM_1963_S_11

Photo of the inside of the “Maria Magdalena” church in Hamburg Klein Borstel, taken some time before its official opening in 1938. (Picture used with permission; HAA_ORh_028.9_(0567) of the Hamburgisches Architekturarchiv)

In 1938, that church most likely used the “Hamburgisches Gesangbuch, Einheitsgesangbuch der Evang.-luth. Landeskirche in Schleswig-Holstein-Lauenburg, Hamburg, Mecklenburg-Schwerin, Lübeck, Mecklenburg-Strelitz, Eutin” from 1930. Now if we had that song book, we could probably see whether the picture was taken in spring or fall.

But since I did all the heavy lifting with the trigonometry, it is now my dad’s turn to hunt down the song book and find out. I will report back! :-)

Adventures in Oceanography and Teaching

Dr. Mirjam S. Glessmer

Category Archives: observation

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

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

One of the most exciting things about work travel?

Observing hydrodynamics on a very large scale

Observing hydrodynamic phenomena on a creek

Frost flowers – when water vapour freezes to ice without going through the liquid phase. Examples “at sea”

Frost flowers – when water vapour freezes to ice without going through the liquid phase. Examples on land

Using the period of a swinging lamp to calculate the height of the ceiling

Reading ice on a river as tracer for flow fields

Using a shadow to estimate the date a photo was taken