# Blog

## Wakes of ducks

I really like observing the wakes of ducks. Much easier to watch than those of ships because the scale is much more person-standing-on-the-sea-wall friendly. Also much less turbulence messing up the pattern. And you can get closer than you usually could.

All three pictures from the same morning, taken within a minute of each other!

Another awesome way to make my point about how waves look really differently depending on the angle one looks at them. Below for example my “other” way to observe waves: See how the wake leaves a shadow on the sea floor?

And some more ducks from a different day, because I like them :-)

## Burning foam

One weekend, my godson’s family took me to the Explorado Duisburg, Germany’s largest museum for kids. And one thing we learned there was to make foam that you can ignite in your palm! (Although, to be fair, they didn’t tell the kids what they put in, I had to walk up on the stage and ask ;-))

Watch the movie to see how much fun my godson’s mom and I had once the kids were asleep!

Of course we repeated the experiment with the kids the next day, too. So much fun :-)

## Group velocity and phase velocity

When I recently wrote about observing waves in a different way, I talked about light being focussed by the waves on the sea floor.

In the other post, I focussed on how looking at the light and dark pattern on the sea floor makes waves visible that are otherwise hard to see when just looking at the surface of the water:

But it also makes something else easier to notice, and that is how phase velocity and group velocity are really different. We know they should be, but on a choppy water surface it is really difficult to keep track of individual waves as they wobble through each other. But looking at the light and dark pattern on the sea floor, it actually becomes easier to observe. See those brighter areas and darker areas? Wave groups!

And in the movie below, you’ll see how they eat up waves that run into them, and how other wave crests come out in the front as they are overtaking the group. Cool! :-)

## Observing waves differently

When we speak about “observing waves”, we usually mean looking at the water’s surface as an opaque surface that reflects the sky and where we see waves mainly due to being lit differently on different sides. But there are other ways to observe waves!

For example by how they focus light on the ground below. In the picture below you clearly see several groups of waves formed of smaller ripples.

Of course what we see when we look at the lighter and darker spots on the sea floor is not only an image of the waves above, but it is also influenced by the structure of the seafloor itself. You see that below: The ripples in the sand distort the image of the waves a little. Nevertheless, it isn’t too difficult to see which general shapes are due to the waves and which due to irregularities in the surface below.

Sometimes the lighting is such that you can see both into the water in some places and then see the sky reflected in others. The places that reflect the sky are showing waves the way we would usually observe them. In the picture below, we see wind ripples in the background, and in the foreground two main wave fields: one coming towards the viewer with crests parallel to the shore line on which I am standing, and a second field, whose crests are perpendicular to those of the first field.

But in the region where we can look into the water, only the second wave field shows up clearly in the lighter and darker regions on the sea floor!

Still, those regions give us a lot of information about the wave field that we don’t usually observe. For example all the small structures below don’t show up as clearly when we look at the sky-reflecting regions, do they?

I find it quite fascinating how all those structures that show up on the ground are a lot more difficult to observe when just looking at the sea surface.

Would you have guessed that there are so many tiny ripples on the surface?

And also here, the wave crests perpendicular to the shore I am standing on show up a lot more clearly in the light and dark on the sea floor than on the surface, don’t they?

Even easier to spot in a movie:

Beautiful day to be watching the water! :-)

## Using real time data of ship positions in teaching?

This morning I was looking for the current position of a research vessel on MarineTraffic.com and noticed something that should maybe not have been surprising, but that I had never really thought about: How all the fishing vessels (orange) are sitting right on the shelf break! I guess that’s where they should be when we think about currents and nutrients and primary production and fish, but how cool is it to actually see it?

And see that area west of Lofoten where there are a lot of fishing boats in a circle? An unnamed inside source told me that that’s where cod is spawning right now, so everybody is going there to fish. Tomorrow, the cluster might be in a completely different place. And even now, some 10 hours later, it seems to have migrated a little northward? Will definitely check again tomorrow!

I obviously had to look whether fishing on the shelf break was just a thing in Northern Norway and turns out that it’s the same on the Greenland Shelf.

Now that I got into playing, I found it also really interesting to see that there is a lot of fishing in the equatorial Pacific going on. And how clearly you can see major traffic routes even in just the distribution of ships.

And then, ShipTracker even offers a density map of ship traffic:

Which I had to screen-shoot in two parts because of reasons:

This site would be such a great tool for all kinds of teaching purposes. Realtime data on shipping is just a click away, even with the free version! There are so many things that students could do estimates on using this site, on transport, fishing, pollution, just pick your topic! And using authentic data makes the whole thing a lot more interesting than looking at maps or numbers a teacher would provide. Pity I’m not teaching right now!

## Playing with a thermal imaging camera

I recently borrowed a thermal imaging camera from work. So much fun!

Below you see a cold sky, warmer trees and two really warm people walking through the park.

One thing that really surprised me was to see reflections of the warmer trees on the little lake below. Although thinking about it, I am not sure why I should be surprised: If it was a “normal” image and not a thermal image, reflections wouldn’t surprise me at all. So why should thermal radiation behave any different?

But it messed up my plans quite a bit. I had hoped to maybe be able to see heat being transferred when waves crashed against the sea wall. But a) there were no waves, and b) what did the waves do? Correct: reflect the sky.  Just like they always do…

So this is what we see:

And this is what the thermal imaging camera sees:

On a different day you clearly see the warmer clouds:

As well as the apparently much warmer ships.

And looking down from the sea wall:

And what the camera sees:

## Wind field

Another boundary layer experience last week: On my way from work I stopped to take pictures of flags that were outside my university’s main building and that very nicely visualised the wind field (as flags tend to do).

If you just look at the flags, they look weird — they wind field was clearly not changing over time, yet the flags were at a weird angle to each other.

And in the next picture you see why: Because the air had to flow around an obstacle, so stream lines were bunching up.

The next morning, I went past there again and stopped to take more pictures, when a colleague of mine stopped next to me, looking a little puzzled that I was taking pictures of our not especially nice main building.

I explained what I was doing, and we got talking about how you see the world with completely new eyes once you have noticed, or have been shown, something tiny. Isn’t that exciting? :-)

## On the impact of blogging — or how far does my message mix?

What is the impact of this blog? And who am I writing it for?

Those are not questions I regularly ask myself. The main reason I started blogging was to organise all the interesting stuff I was collecting for my introduction to oceanography lecture at the University of Bergen in one place, so I would be able to find it when I needed it again. And I wanted to share it with friends who were interested in teaching oceanography or teaching themselves.

Another of the reasons why I blog is that I notice a lot of exciting features in everyday life that relate to oceanography and/or physics, that other people would just walk past and not notice, and that I would like to share the wonder of all those things with others. And noticing all this stuff is so much FUN! The blog “gives me permission” to play, to regularly do weekend trips to weirs or ship lifts or other weird landmarks that I would probably not seek out as often otherwise.

But the other day I was browsing the literature on science blogging in order to come up with recommendations for the design of what is to become the Kiel Science Outreach Campus’ (KiSOC) blog. I came across a paper that resonated with me on so many levels: “Science blogs as boundary layers: Creating and understanding new writer and reader interactions through science blogging” by M-C Shanahan (2011). First, I really liked to see the term “boundary layer” in the title, since it brings to mind exciting fluid mechanics. Then second, I read that the boundary phenomena I was thinking of were really where the term “boundary layer” came from even in this context. And then I realised that I have had “boundary layer” experiences with this blog, too!

So what are those boundary layers about? Well, in fluid mechanics, they are the regions within fluids that interact with “something else” — the boundary of a flow, e.g. a pipe, or a second fluid of different properties.  They are a measure for the region over which temperature or salinity or momentum or any other property is influenced by the boundary. But the same construct can be used for social groups, i.e. in my case oceanographers and non-oceanographers. (You should, btw, totally check out the original article! Her example is even more awesome than mine)

But here is my own boundary layer experience: My sister sent me an email with the subject “double-diffusive mixing” and a picture she had taken! My sister is not an oceanographer, and I wasn’t even aware that she associated the term “double-diffusive mixing” with anything in particular other than me writing my Diplom thesis about it and probably talking about a lot. But that she would recognise it? Blew my mind!

Turns out what she saw is actually convection, but it doesn’t look that dissimilar from salt fingers, and how awesome is it that she notices this stuff and thinks of oceanography?

Obviously I asked for follow-up pictures:

And I had another boundary layer experience recently: A sailor on the Norwegian research vessel Håkon Mosby with many many years experience at sea had seen my book and told me that he now looks at waves in a new way. How awesome is that? That’s the biggest compliment my book could get, to teach something new about visual observations of the ocean to someone who looks at the ocean every single day!

Anyway. Reading this article made me think about how happy both those boundary layer experiences made me, and that maybe I should actually start aiming at creating more of those. Maybe not with this blog, that I kinda want to keep as my personal brain dump, but there are so many different ways to interact more with people who would potentially be super interested in oceanography if only they knew about it… I guess there is a reason why I am working the job I am :-)

Shanahan, M. (2011). Science blogs as boundary layers: Creating and understanding new writer and reader interactions through science blogging Journalism, 12 (7), 903-919 DOI: 10.1177/1464884911412844

## More funny waves

I think I might need to find a new route to walk along the Kiel fjord. When I was walking — in the most beautiful sunshine! — with my friend over the weekend, she pointed out that there are funny waves and it looked like there was water dripping in, and I went without looking “no, there is a step right there that’s causing those“.

You see it in the picture below: Every wave crest washes over the step, and then when it retreats it sends off its own little waves.

It’s a funny thing with professionalized perception. What I notice walking along the Kiel fjord is really highly trained and specialised, I guess. But still a lot of fun! And it makes me really look forward to the excursion that I’ll do later this summer with a couple of high school students where they’ll learn to observe waves my way :-)

## Nonlinear effects in shallow water waves

I recently googled for something related to the shape of waves and came across a photo of a wave that caught my eye, and it took me to a journey that lead to the article “nonlinear shallow ocean wave soliton interactions on flat beaches” by Ablowitz and Baldwin (2012).

What’s discussed in that article is that while many wave interactions can be seen as (more or less) linear, sometimes there are nonlinear effects that can be replicated in a model. So far so not surprising. But I got fascinated because the phenomenon they look at I have seen over and over again and never really paid any attention to it: Wave crests forming X or Y shapes. But looking through my archives, I even had dozens of pictures of this exact phenomenon! (Actually, I didn’t have to look further back than to a beautiful day last November, when I also observed the wavelength dependency of wave-object interactions)

Take for example the picture below: Do you see the H shape in the waves closest to shore? (In the article they would probably call it a more-complex shape, since it’s a double Y shape…)

Below I’ve drawn into the picture what I mean by H-shape in green, and the typical kind of linear wave interaction in red (all crests just move on without influencing each other except in the spot where they occur at the same time, there they just add to each other):

Or below, I spot an X-shape:

And here are several X- and Y-shapes

And the picture below just to give you an orientation of where you are: Yep, it’s the same spot where we usually observe foam stripes, funny waves, or ice

Mark J. Ablowitz, & Douglas E. Baldwin (2012). Nonlinear shallow ocean wave soliton interactions on flat beaches Physical Review E, vol. 86(3), pp. 036305 (2012) arXiv: 1208.2904v1