Category Archives: wave watching

#WaveWatchingWednesday

Haven’t posted a #WaveWatchingWednesday in a while — but I am very regularly posting over on my Instagram @fascinocean_kiel. Check it out if you fancy a more regular supply of pics!

Finally a sunny day again! Which means that I HAVE to get outside. And voila: awesome #WaveWatching! See the waves radiating as half circles from a point source from the lower right corner? That’s a dog drinking!

This morning, there was only a super thin layer of ice on the pond — enough to trap small air bubbles in some spaces, but still flexible — and on it, the fern-like structures in which the ice grew were still visible. So pretty!⁠

Do you see the large ring waves on the left, where a duck is riding on the edge of the wave? It was caused by the three ducks reaching the “ice edge” (well, the edge of super thin ice floes that weren’t even connected) and the first duck deciding to fly to the next spot of open water, where it landed with a splash in the center of that wave, and then flew another wing flap or two to where it is sitting now, while the wave spread. But the ice the duck was avoiding explains why the wave looks so much smaller on its right side than on the left where the duck is! The ice also explains why it’s really difficult to see the wakes of the other two ducks on the right — all the waves are dampened away by the ice.⠀

Ice looks differently depending on the conditions it formed in. Here, supercold & calm water recently froze in long needles. If there had been waves, needles wouldn’t have been able to grow so long, slush would have formed and then pancakes. If there had been salt in the water, it would look more milky and less clear. If the ice had started melting and then refrozen, the structures of the needles would have gotten destroyed. Fascinating how much ice can tell us about what conditions must have been prevalent!⁠⠀

Ice needles are a prominent feature of freshly formed ice on calm puddles or lakes when the water is supercooled. They form all over, growing longer and longer, until they meet another needle. Only then do the spaces between needles start to fill.

No waves? No problem! (Thanks to these amazing #GreatWave mittens by @kjersti.daae ) And what looks like melt ponds on the ice here is snow falling on a more-or-less intact ice sheet. The more intact, the more snow. The wetter, the better — for wave watching Good thing it’s the weekend now!

There is enough water in this pic — in frozen form in the snow, and as tiny droplets in the fog — to warrant an appearance here. What a beautiful day!

Wet snow is definitely better than no snow. And even better when work meetings can happen on the phone and we can at least do virtual walk & talk meetings :)

This picture shows a puddle, that froze and got snowed on, then someone broke that snowy ice sheet and bits of ice got pushed into the water while others were pushed out (see for example the grey thing on the right). The puddle then froze again (all the clear ice you see) and hoar frost grew on some of the old pieces of ice (those needles you see. The long ones are longer than a centimeter!). And all of this in just one puddle!

I am fascinated with phase transitions at the moment. Here, snow fell on this bush. It then partly melted in the sun the next day, and the next night the liquid water refroze, forming an icicle.

Hoarfrost grew on a puddle the froze, broke open again, froze again⠀

Very distracting to work under a skylight… Turns out it is pretty difficult to take pics because they melt so quickly and it’s super difficult to focus on the right depth in between all the melt water puddles that have a much higher contrast!

More snowflakes! Here the same ones with slightly different tilt of the camera — against the bright sky vs thr dark tree. Such different results!

Too much snow on the skylight above my desk to look outside, so I had to actually go outside to look at snow. And it was so fluffy that one could really see individual snow flakes! How cool is that???

Albedo effects: where there is snow, it’s easier for more snow to accumulate because the white surface reflects incoming sunlight and stays relatively cold. Darker surfaces warm up faster, snow melts, surfaces remain darker, snow still melts more easily than on white surfaces… In this pic we see this both on a larger scale and on the micro scale in some animal’s footprints! Where the animal compacted the snow, it melted less than around it, so new snow accumulated on the old footprints but not around them. Therefore they stay visible for days!

More pretty snowflakes spotted “in the wild” <3⠀

Using #WaveWatching and #KitchenOceanography to prepare students for a one-day research cruise

When students have only one day at sea, it’s important to prepare them well for what will happen there so they get the chance to make the most of the experience. For example, let’s consider a one day student cruises just outside of Bergen. Students are divided in teams that use different types of instrumentation and that investigate different questions. After the cruise, students use the data they acquired during the cruise to write a report on the data.

There are several different aspects that I would like to prepare the students for:

  1. Recognizing and understanding the relevant physical processes they are supposed to investigate
  2. Dealing with the data both onboard and once they get back home

Below, I’m expanding on my thoughts on how to do that.

Recognizing and understanding the relevant physical processes

Let’s look at two typical teams on those student cruises: the “drifter” team that deploys surface drifters and interprets the trajectories later on, and the “CTD” team that takes profiles of temperature, salinity and other properties of the water column and then interprets those afterwards.

Interpreting surface drifter data

In the area investigated during the student cruise, there are several processes that influence which way a passive surface drifter will take, e.g. tidal currents, wind-driven currents, the circulation induced by fresh land run-off, wave-induced drift. Also there might be effects of wind on the drifter (although when designing the drifters, care was taken to minimize the effect) or of other processes. The relative importance of those processes is not necessarily clear beforehand (or even when looking at the data), and it is most likely neither constant in time nor in space. So even though it seems like it should be simple enough, it’s not an easy task!

Additionally, even though students are theoretically familiar with some of the processes, their familiarity is mostly restricted to theoretical considerations of ideal cases, not with messy mixtures and real-life cases. So my suggestion would be to help them familiarize themselves with these processes, for example like this:

First: help them realize that there are many many many processes happening simultaneously

One way to do this is to provide a picture that shows many different things at once and ask students to annotate it with a certain number of processes they can spot. Knowing that there are at least four (or however many) processes to discover in the one picture they are given gives them confidence to name at least that many, or to keep looking until they’ve found that numer.

I usually use a different example, but since tomorrow is #CTDappreciationday and I’ve been looking at old CTD pics, I thought I’d give you a new one:

In this picture of a submerged CTD, we see any different processes, for example looking at waves: a wake-like wave where the CTD wire has been cutting through the water as the ship moves relative to the water, the splashes that happen when drops from the crane fall into the water and the little crowns they form, how the waves spread as rings from the points of impact, how different waves are supperposed and the interference pattern they form. Or ALL the optics of light going in and out of water: how shapes appear deformed, how colors change, … And many more!

Obviously it would be advisable to chose a picture that shows processes related to what the students are supposed to investigate.

Second: ask them to observe a given location and observe and describe as many different (or three, or five) situations as possible

This task is similar to the first one, but not having the reassurance that there are so-and-so many processes visible at the same time makes it a little more difficult. But it’s a great exercise to try and find as many different things going on in a system, because it will later help them to think of processes that might influence their observations.

For location ideas, check out the #BergenWaveWatching series over on Elin’s blog!

Third: ask them to go & discover a process “in real life”

Now that students have seen that life is messy and processes aren’t usually occuring in isolation, but are superimposed on or interacting with others, they are ready to go find a process in real life. To prepare students of the drifter group, useful tasks could be to find (and document) instances of

  • a tidal current (and how do you know it’s a tidal current and not just a regular gravity-driven current like in a river? You might have to come back at a different time, or relate the current to tide tables)
  • wave propagation and current direction not being aligned (since surface waves are a lot easier to observe than current direction, it’s easy to assume they are always in the same direction. They are not!)
  • land run-off forming a buoyant (and possibly differently colored) plume in saltwater (or any other water forming a plume in a larger body of water, e.g. a storm drain going into a lake)

Even if students might not find the exact process you were hoping for, that’s ok! They will probably have an explanation for why their replacement is a good one, and that means that they put some thought into it, too.

Four: ask them to observe (some of) the relevant processes in real life and collect data

I find it a very useful exercise to try and collect data on a phenomenon without any proper equipment. For example, a tidal current can be related to the position of buoys within it, or the tidal elevations can be estimated by repeatedly taking pictures of the same pylon of a bridge. And then, of course, plot the data and discuss it!

It might seem like busywork, but I would argue that it really helps practicing observational skills. And they are going to appreciate instrumentation so much more once they get to work with it later on! :-)

Five: relate it to what to expect at sea

This is the really difficult part. From their short cruise, students will come back with a data file full of numbers, i.e. the positions at the drifter at a given time. How does that relate to what they’ve been observing until now?

Well, the idea is for them to come back with so much more than just the one data file with drifter positions. Ideally, since they know how messy the system is they are about to interpret, they’ll come back with data on the wind field (either from what the atmosphere group measured, or from the regional weather forecast), with data on the tides (from tidal gauges in the area, or models), with observations of wave height to calculate Stokes drift, with observations of anything unusual (like once when one of our drifters got caught by a ship and displaced). Ideally, all the practices we did beforehand prepared them to realize that they will want to have all this data, even if only to exclude the influence of one or several of those factors.

Ok, so much for our drifter group. Now on to the CTD group!

Interpreting temperature & salinity profiles

Temperature and salinity profiles have arguably been the most important type of oceanic data in the history of oceanography. They are also not something that is easy to come by, because you typically need a ship and some instrumentation to measure them. But there are still ways to help students familiarize themselves with the idea of temperature and salinity profiles in a practical way before their cruise.

First: help them realize that there are many many many processes happening simultaneously

Temperature and salinity profiles are really difficult to interprete because there are SO MANY things influencing them! A really good way to realize that is by asking students to do a simple overturning experiment and draw profiles over time in fixed location.

In the very simple overurning experiment, T and S profiles could look something like what’s sketched in above. The red dye is heated (in order to make it buoyant enough to stay on top and mark the surface flow). I’m writing “S” in quotation marks, because I’m lumping both red and blue dye together as “something dissolved in water”, which I abbreviate as “salinity” for this purpose… And of course, all the overshoots in S don’t make sense, as I realized when I couldn’t be bothered any more to draw it again… But a good point to discuss, maybe? :-D

Here we see that it’s not just the cooling driving a circulation, we also see salt fingering occurring as the red dye cools and thus becomes denser than the clear water at the same temperature. So even in such a simple experiment there are different processes happening at the same time!

Second: ask them to observe a given location and observe and describe as many different (or three, or five) situations as possible

Same as I suggested for the “drifter” group, possibly with a focus on processes that influence temperature and salinity (river runoff, rain, evaporation, mixing by surface waves, parts of the body of water that are in the sun vs shade). The point is not necessarily to find the most relevant process, but to recognize which processes might potentially have an influence (even if minuscule) and thus make interpretation of observations more difficult later on.

Three to five

The temperature and salinity profiles are influenced by similar processes as I described for the drifter group, because they are shaped by advection of water with different properties and from different directions. So trying to observe the processes described above makes a lot of sense here, too! As do the other steps I described above.

But now how do we prepare students to cope with the data once they are back from their cruise?

Dealing with the data

Students are provided with finished programs that read in and plot the data, that they only need to modify if they want to show things in a different way. Yet it’s surprisingly difficult for them to manage that when they come back from the cruise.

There are several aspects to dealing with data that we can help students prepare for:

  • getting data into the program you want to work with, and making plots
  • interpreting plots
  • interpreting data

Of course, all of this could be done just by using last year’s data (and actually maybe it’s not such a bad idea to ask students to re-run someone else’s analysis, because then they KNOW it worked a year ago, so unless they changed something, it should be working again now). After reproducing last year’s figures, students could read last year’s interpretations of those figures and discuss whether they agree with them or what they would do differently (obviously this works best if last year’s interpretations are somewhat helpful).

BUT it could also be done using new data that the students generate themselves as part of their observations earlier. For example for the temperature and salinity profiles in the easy overturning experiment, they could use some depth axis and assign numbers to the profiles that qualitatively represent the shape they drew earlier (or, if you wanted to get fancy, you could probably use temperature probes in the tank and get actual numbers). The idea here is not to get data that is as complex as they would get on the cruise, but to get a data file that is similarly structured to the ones they are expecting to get, to read it in, to plot it, and maybe practice to modify axes etc..

What do you think? Any suggestions, comments, feedback?

Published in Oceanography: How to Teach Motivating and Hands-On Laboratory and Field Courses in a Virtual Setting

One of the few “behind the scenes” shots of me taking #WaveWatching pictures! See the super awesome current right at my feet? :-D⁠⠀
⁠⠀
Similar to kitchen oceanography, I believe that wave watching is a great tool in education and outreach, especially during times where activites have to be socially distant. My article “How to Teach Motivating and Hands-On Laboratory and Field Courses in a Virtual Setting”, where I am elaborating on both, just came out in Oceanography, the official magazine of The Oceanography Society. Check it out at https://tos.org/oceanography/article/how-to-teach-motivating-and-hands-onlaboratory-and-field-courses-in-a-virtual-setting⁠!

Glessmer, M.S. 2020. How to teach motivating and hands-on laboratory and field courses in a virtual setting. Oceanography 33(4):130–132, https://doi.org/10.5670/oceanog.2020.417.

DIY #WaveWatching “fortune teller” on #WaveWatchingWednesday

How about a little wave watching game to celebrate #WaveWatchingWednesday?

The minute I saw Andrea Lopez Lang’s tweet, where she made a “fortune teller” (no idea that’s what they were called) as going-away and please-remember-what-you-learned gift for her class, I HAD to make something like that!

Unfortunately I’m not teaching a class right now where I could easily see how this could be done, but luckily there is always wave watching!

Grafic with instructions to build a wave-watching-themed "fortune teller"

Click to get the pdf!

And Kjersti had a great idea for how this could be used right away: To send students out with these toys and ask them to discover one example for each of the waves shown on the toy. Plus then of course document it, and share on social media… ;-)

Waves are traditionally taught in a theoretical and very dry manner, and the transfer to the real world is hardly happening at all (especially since the large tank in the basement at GFI has been demolished, which still breaks my heart), so this is a fun way to get students outside and try & find contents from their lecture in real life.

P.S.: It’s not as difficult as it might seem at first once you start observing and get a little creative. Nobody said that the rock that makes the ring waves had to have been there when you got there, and wakes can be created by ships or bird or even if you pull a stick through the water…

[annotated photo] Photo of water flowing over a weir, annotated with arrows showing particle velocities

Testing the new particle tracking app “Flow on the Go”

The new particle tracking app “Flow on the Go” became available for testing on iOS yesterday. And it is SO AWESOME!!!

The idea is that particle that are advected in a flow can be used to visualize a flow field (similar to what we did when we were at the 13-m-diameter rotating swimming pool in Grenoble, where we added particles with neutral density to the tank in order to track currents). So the app latches on to something that it recognized as “particle” and then displays arrows as it follows that feature from frame to frame. Pretty amazing, isn’t it?

(If you are impatient, scroll to the second-to-last video of this post for my best example, otherwise stay with me as I walk you through different scenarios…)

First, I tested with movies I already had on my phone, for example storm waves in Kiel. Which might not be the nicest test case as wave crests break and thus new “particles” appear, but then vanish in a trough behind another wave etc.. So even though the app tracks them, it all seems a bit messy. The movies always start with a short glimpse of the original movie and then the tracking begins…

 

Then, I tried the “soap protects you from Corona” demo that my adorable nieces are presenting for you. There is water on the plate sprinkled with pepper (or something), and they dip their fingers in with a little bit of dish soap, break the surface tension, and the particles all get pushed to the edge of the plate. (Spoiler alert: Kids’ hands — no matter how cute — will be recognized as particles…. :-D)

 

At this point I decided that it was definitely time for my parents and me to go for a walk to film some flows.

Below: Laminar flow towards the edge, then turbulent flow at the bottom. Interesting observations here (beside the super cool flow field that is captured surprisingly well): Where there is a lot of foam and everything appears white, it’s not easy for the app to find “particles” to trace. And when reflections on the water move (like the handrail when there are waves) that looks like “particles” to the app.

 

Here is one example where there are plenty of bubbles passing by on the other side of the river (which are tracked very nicely) and my dad threw in some leaves on our side so there were particles that showed the recirculation. Nice! (No idea what the app sees in the top left corner, though)

 

Then I had the brilliant idea to film the large scale flow field with lots of bubbles in it. But, as you, dear reader, will probably have guessed already, the reflected trees are the much more dominant signal. That’s what happens when you film tons of things and only process them afterwards…

 

But here is a very nice example for you: Fast, laminar flow upstream of the weir, then a waterfall, a submerged hydraulic jump and turbulence at the bottom. Nice!

 

Back home, I decided I wanted to test some tank experiments. Below I’m first showing a couple of seconds of the original “thermal overturning circulation” movie (because I knew my hands would mess up the particle tracking when I’m dripping dye into the tank) and then cut to the processed one.

I thought that this was one of my better movies with few reflections on the tank, a nice background, etc.. Turns out: Still waaaay too much going on! Reflections on the glass, shadows on the wall behind it as we are watching… I’m sure there are settings in the app that would lead to much better results (if I knew how to use it) but for now I know that using the app is a little more difficult than I thought.

 

In any case, I think it’s a brilliant app, and I am looking forward to playing with it some more and figuring out how to use it best! There are so many settings that I haven’t figured out yet, so I know what I’ll be doing over the next couple of days… ;-) And I can’t wait to use it on our DIYnamics rotating tank experiments!

#WaveWatchingWednesday

Even though I haven’t done a #WaveWatchingWednesday in a looong time, there has of course been a lot of wave watching going on. But the longer I wait with copying all the Instagram posts into a blog post, the more work it gets, the longer I put it off. Vicious circle! But here we go today. Plenty of interesting and plenty of beautiful pics! Enjoy!

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