24 Days of #KitchenOceanography — Wind-driven mixing
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Tag Archives: wind
Strong gusts of wind -> lots of energy transferred to the water -> wind waves with large amplitudes
We are still in the “interesting weather” period here in Kiel. Feels more like April than like September, but I am not complaining. I love the rapid change between dark clouds and blue skies and sunshine! Also I like how much more interesting wave pattern get if the wind comes in gusts rather than blowing just consistently the same.
Below, you see strong gusts of wind in the dark areas with the high surface roughness, but you also see that the small waves in the foreground have higher amplitudes and more pointy peaks than we usually see. Additionally, there are longer wave length waves coming in with crests more or less parallel to the images lower edge. And on top of all of this, there is the seagull’s wake. Can you still spot it even though it’s superposed on all the other waves?
Below, you clearly see the different wind strength in different areas. The shiny, flat surface with lower wind speeds, the rougher areas, and the comparatively short waves with large amplitudes in the foreground that show that there really is a lot of energy input over a relatively short fetch.
Below, in some regions we can also see hints of a checkerboard interference pattern of longer waves that were reflected at the sea wall, with the small, short wavelength waves superimposed.
Here is another look at these waves. I find them so fascinating!
And below is another strong gust of wind visible. And do you see the wave crests parallel to the edge of the floating part of the pier, created by that part of the pier moving in the waves?
And, just in case you didn’t know: At the end of the rainbow, you will find a … research ship!
Wave watching in Kleinwaabs — and my first real Insta story!
So today (and tomorrow and the day after) is the big event that I have been working towards all year in my not-so-new-anymore job: The GEO-Tag der Natur! If you are curious about what’s going on there, check out our Instagram account @geo.tag.der.natur that Kati is doing an amazing job with!
As you can imagine, the weeks running up to this weekend were quite busy and a little stressful, too. So last Sunday I went to the beach to hang out with friends and do some wave watching! Because nothing has a more calming effect on me than watching water…
For example below we see nicely the effect of the wave (and wind) breakers on the wave field. In the lee of the wave breaker, the water is completely calm, whereas towards the right of the bay waves form and grow larger and larger.
And below we see a pretty cool “diffraction at slit” example: Straight wave fronts reach the slit between two wave breakers, and as they propagate through the slit, they become half circles.
But to relax and get my thoughts away from my job, I tried something new: I created and posted my first ever Instagram story! I’m not quite sure it’s my format, but I definitely had fun! What do you think? Would you like to see more of those? (I only just realized the story is in german and my blog in English. Posting anyway… Would anyone like to see this kind of stuff in English? Then please let me know and I’ll see what I can do…)
https://vimeo.com/341862851
(P.S.: Since I made this for Instagram, the format of the video was optimized for viewing on a mobile phone. Therefore it looks crap embedded in a blog. But some you win, some you loose…)
What do you do to relax and get your mind off of work? Wave watching and posting about it on social media? Have you ever tried that? Or what else would you recommend?
Wave watching from a train
You know how they say that the journey is the destination? That was certainly the case for my spontaneous mini-vacation yesterday (and how awesome is it that my #BestTravelBuddy is up for a cross country trip on a day’s notice?). We went all the way from the east coast to the west coast — which in Germany admittedly isn’t that terribly far — to visit the island Sylt in the North Sea for a day.
Even the train ride itself is spectacular, though, at least if you are as easily excited as we are. Wave watching from the bridge across the Kiel canal in Rendsburg (below): A super neat wake of the ship, showing the turbulent wake as well as the feathery V-shaped wake. And as you can see from the rows of foam on the water that are a sign of Langmuir circulation (more about that here): It was pretty windy, too!
But it got even better when we reached the west coast. This is my kind of train ride!
Below is a view of the dam that connects the island Sylt with the main land, and here again you see how windy it is, and this is in the lee of the island. In the lee of those shallow dams you see that it really doesn’t take long for the surface roughness to increase again.
So are you excited to see the wind-ward side of the island now? I’ll post some wave watching from that side soon, but I first have to wade through literally thousands of pictures to cut it down to a handful. I’m already down to about the 100 best, but now I can’t decide which ones to post, because I like them all…
But here is a picture of the train ride back. Do you notice how there are regions with really low surface roughness on either side of the dam, suggesting that this dam is sheltering the water surface from the wind in two directions? Of course it isn’t — it’s just ebb tide and the smooth surface areas towards the right of the dam are wet sand that look similar to a smooth water surface.
So that’s my wave watching from the train! Excited to go back soon! :-)
A #scicommbookforkids for #scicommchall
I hope by now you have heard about my pet project of the moment: #scicommchall! For #scicommchall, I give myself (and quite a few other people by now) monthly challenges related to trying out new science communication formats. And this month, we are doing science communication books for kids! (For more instructions, see #scicommchall’s post. And everybody is welcome to join!).
My book deals with learning to observe where the wind is coming from (English version at the end of this post, too).
I think it turned out quite nicely!
I did struggle a little with the very short format — only six pages inside the book, plus a cover — but quite liked the challenge of having to come to the point.
The flag on the cover, in case you were wondering, is that of my hometown Hamburg.
I hope this book is actually useful and fun for kids (I did include some kids’ humor, or at least I tried ;-))
And I know what I would include if I wasn’t too lazy to re-draw the images: A question about on which side of some kind of structure one would sit down if one wanted shelter from the wind. Bummer I forgot to include that!
Anyway, here is the download (German & English). Please let me know what you think, I’d love to get some feedback!
Click to download
When not the fetch but a funnel shapes the wave field
As you know we are currently preparing for future wave riddles. So this afternoon I went out for a wave hunt again and found something beautiful for you!
The ship coming out of the Kiel-Holtenau locks into the Kiel Canal is making waves, but although those are pretty exciting, too, there are more things going on in the picture above…
Many processes can create waves
In addition to waves made by ships, seagulls, the locks opening and closing, and those waves being shaped by reflection, refraction, and all those other processes, most waves look actually pretty similar, and they are all formed by the same process.
Most waves are wind waves
In almost all situations it’s a safe guess that most of the waves you see are caused by the wind. Either locally, or by storms far away. Of course, the waves might look very different from day to day and location to location. But as a rule of thumb, the stronger the wind, and the longer it has been blowing, and the longer its way over water without any obstacles in its way, the higher the waves.
Usually the length of the fetch shapes the wave field
This uninterrupted stretch that the wind can blow over the water is called the “fetch”. And it explains why you don’t have really large waves on small ponds: if the fetch isn’t long enough, waves just don’t have enough time to build up from when they are generated at the upwind side of the pond until they have reached the downwind side.
Sometimes obstacles shape the wind field
Sometimes though, there are obstacles in the wind field that cause interesting wave phenomena. Below you see that the wind that has been coming across Kiel Canal is interrupted by those pylons. Upwind of the pylons the waves are fairly regular and pretty boring.
But remember your Bernoulli? If the area across a flow decreases, for continuity reasons the flow speed has to increase.
Since air is “flowing” in that sense, too, it’s accelerated where it goes in between and around those pylons since it has to squeeze through a smaller cross section than it had to its deposal further upwind.
The wind field is mirrored in the wave field — well, kind of
Do you see how the faster wind causes all these nice little ripples? Maybe “mirroring” the wind field isn’t quite the right way to express it, but you can definitely see where the wind speeds are different from the rest of the Kiel Canal just by looking at the waves! From there the waves then propagate as sectors of circles outwards and leave the areas of the high wind speed, but they quickly dissipate and vanish again.
Wave watching is awesome. Can you think of anything better to do on a Saturday afternoon? :-)
Candles in the wind. Or: The things that keep a nerd entertained during speeches at a conference dinner.
What keeps you entertained at conference dinners is probably different for different people, but we quite enjoyed watching how the candles placed closer to the door to the balcony burned a lot faster (and a lot more messy) than those on other tables…
Tiny islands, shelter from the storm and the wings of the morning
If I take the wings of the morning, and dwell in the uttermost parts of the sea…
Expedition learning
Last week, we ran an “expedition learning” course for 17-year olds. They were separated into several groups, working on different topics, and mine (unsurprisingly) worked on waves. You can see here what kind of stuff we observed when first testing the stretch of coastline we wanted to do our expedition to. And now you’ll get a picture dump of the actual expedition.
We started out in not-so-ideal-but-really-not-too-bad-either kind of weather, as you can read off the tracks below: It had been raining a little, but not very hard, and it had stopped by the time we got there.
The drift lines looked quite promising.
My group dove right into it (only figuratively, luckily, not literally). However I wasn’t quite sure if this guy knew what he was getting into?
At this point we were still very close to the car, so I thought that it might be quite smart strategically to let them figure out here how high the waders go and what happens if the waves are higher than the waders… And the wakes of two ships meeting up at a headland are a very good place to learn about that kind of things!
This headland is a very good place to start observing waves in any case. Especially at the typical wind direction found here. Because then, looking back from the light house to the land, you see a large area that is sheltered where waves only build up gradually. Which is a very nice contrast to the waves arriving upwind and makes it very easy to observe differences.
And then if you look downwind from the headland, you see waves sneaking around the headland from both sides. Those coming from the right are from the fully developed wave field that has been growing all the way down Kiel fjord, and then those coming in from the left are the ones that only started growing downwind of the little barrier shown in the picture above.
Can you see it? Maybe easier on a panorama kind of picture?
Of course we always like to look at the ring waves that appear when other waves hit stones…
I didn’t foresee that wave watching would happen mostly from within the water, but the guys in my group made a good case for walking on the sand bank to actually measure the wave hight depending on the water depth (rather than just observing and estimating from dry land, as I would have done), but why not?
Luckily, they found the shallowest part of the sand bank in exactly the same spot I would have told them to look for it based on the wave field ;-)
Btw, a nice example of coastal dynamics right below. We had a coastal dynamics group, too, but I don’t even know if they looked at this kind of stuff, I mainly saw them taking soil samples.
And I know I made the same observation in the same spot last time, too, but I think it’s fascinating how the different directions of the ripples and drift lines and waves all come together.
In any case, a nice day at the beach!
Well, most of the time anyway.
Luckily, we found shelter!
Those, btw, are Annika and Jeannine, who were working with a different group on coastal vegetation.
But: New and interesting pattern on the beach once the rain was done!
The kids spent the next two days putting all their observations on maps and preparing a presentation, and I am really happy with how it turned out. Of course there is some room for improvement still, but how boring would it be if there wasn’t? ;-) All in all I think it was a pretty successful course!
Traces in the sand
Yes, I am really that fascinated by sand that this is the second post in a week about it.
And I still think the picture below looks like the place in Qumran where the Dead Sea Scrolls were found!
