Actually, there is no need to guess. If you tilt your head 45 degrees to the left, you are looking at Hamburg the way it would be shown on a map, North up. The Elbe river, which you see in the foreground, flows east-to-west into the North Sea. And now there are at least two spots in the image below where you can see fronts in the water, more turbid water in the main river bed, clearer water in side arms and bays. Those fronts always start at upstream headlands and go downstream from there, therefore it must be ebb tide, with the water going out into the North Sea. Easy peasy :-)
Funny how “upstream” and “downstream” make so little sense in a tidal river, yet everybody knows what I mean…
Would be interesting to see if you can see fronts when the tide is coming in, too, when the muddy river water is pushed into the more stagnant side arms and bays. I expect so but don’t actually know. Maybe I will be able to observe it on some future flight?
It’s bugging me that I don’t really understand what’s going on here or why… But look at how these eddies form on the beach right outside my window and for how long they persist!!
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…
Whale watching on Terceira was A-MAH-ZING. We saw three different kinds of dolphins: Bottle-nose, common and spotted. But what you should really be doing once you are done swooning over all the pictures below: go over to Elin Darelius & team’s blog and read about what is going on with the 13-m-diameter rotating tank! :-)
And here is a video. Be careful you don’t get sea sick — it was impossible to hold the camera steady on a moving boat, plus I was too excited to care much about it ;-)
This is what the way to and from the 13-meter-diameter rotating tank in Grenoble looks like (and you should really visit Elin & team’s blog to learn about all the exciting stuff we are doing there!!!)
And the best part is the Isère right next to the bike path:
And one thing that I find really impressive with this river (coming from a much flatter part of the world than Grenoble, where rivers aren’t typically as fast-flowing as the Isère) is how all these return flow pools form everywhere.
Watch the movie below to spot them yourself, or my annotated picture below:
It seems really counterintuitive that a strong current would make water on it’s side flow upstream instead of flushing everything downstream or even just going downstream through stagnant water, doesn’t it? But when I thought about why that is, it reminded me of the way a water jet pump works: You flush water from a tap down through a hose, and that hose is connected with another hose through which you want to suck something (usually some gas out of some container). So there it’s the same: The fast-flowing water pulls things in from the side and takes them with it. Now for continuity reasons, the water that is entrained in the jet needs to come from somewhere, so water has to be brought upstream in order to get sucked into the jet. That’s also similar to playing with Venturi tubes where the thinner the tube, the faster the flow, the lower the pressure… Anyway, riddle solved and I can think about other stuff again ;-)
But it is a really beautiful place to be:
I like water so much better than mountains, but mountains still have their charms, can’t deny that…
Today I went on a wave-hunt expedition to take pictures for posts on the Froude and Reynolds number over at Elin & team’s blog (which you should totally check out if you haven’t done that yet! I am actually proof-reading my posts there and that is saying something ;-))
Anyway. Let’s look at the picture below. Do you see how there are two qualitatively different flow regimes in the Isère? Closer to the banks, you see waves that look like normal waves, happily propagating wherever they want to. And towards the middle of the river, you see that there is a lot of turbulence, but disturbances don’t propagate wherever they want, they are being flushed downstream.
For comparison below a picture of a part of the Isère where it is turbulent all the way to the sides:
And below a nice example of how phase velocity of waves depends on wave length. See all the small, choppy stuff being flushed downstream and then standing waves caused by some obstacle in the middle of the river? That’s because the longer the wavelength, the faster the wave propagates (assuming that we are in deep water, which I think is a safe assumption in this case). So the river is so fast that the slower waves get flushed away and only waves of the length of those created by the obstacle (or longer) can stay in one place (or even propagate against the current). I think that’s pretty cool.
Below is one of my favourite wave-watching sights: A half slit.
And in the picture below, we can kinda see vortices detaching behind the obstacle (or is that just me)?
And what I really liked: see the spot below where there are all of a sudden standing waves appearing in the middle of the river? Clearly there is a sill below, but I like that you cannot see the obstacle, just deduce that it must be there from how the waves look :-)
It’s not a hardship to be here, I can tell you ;-)
It is quite a beautiful place! And, by the way, this is my 600th blog post on this blog. Can you believe this?
Today we have foam patterns again, but of a very different kind than usually:
I don’t know if I have just never noticed before (I can’t really imagine I would have missed that?), if it never happened when I have boiled eggs because I always boil my eggs with more bubbles and hence more turbulence, or if French eggs are just different from german eggs?
But living in this shared flat in Grenoble is proving to be quite educational. Not only have we learned that you should never wash eggs because that destroys some protective layer of “hen juice” (technical term coined by Nadine), we also learned that a peanut and a salted peanut have different names in French (l’arachide vs la cacahouètte), and that there are cheeses with a layer of ash in them.
But anyway, I don’t think it’s foam that comes off the eggs, I think it’s coming off the bottom of the pot. Because if those bubbles are raising up from the bottom, that would explain why there are more bubbles around the edges of the eggs (when they had to move around the eggs to get to the surface) than in between, and that there is hardly any foam above the eggs? Or what do you think?
And then, of course, we are learning all the cool oceanography stuff, too, and you can read all about it over on Elin’s blog!
Do you know the phenomenon that once you start noticing something, you see it everywhere? That’s been the case with me and total internal reflection. Not quite as impressive as last time, but still there:
And what I found really interesting this time: a swarm of tiny fishies making wave rings! I only noticed them because of those tiny waves. And if you look closely you can see so many of them just below the surface right where the wave rings are!
So funny to see the water almost boiling with fish on such a calm morning.
And another thing that fascinated me: how it’s so much easier to see into the water in places that are shaded (or dark) from the reflection of that pier. Not quite sure yet why it’s so much easier to see here, maybe just because there isn’t any glare? Any ideas?
Have you ever wondered why at some angles the sea looks blue (or whatever the color of the sky that day) and at others you can actually look into the water? That’s the phenomenon of total internal reflection. There is a critical angle at which you switch from “being able to look into water” to “total internal reflection”, i.e. the sky being reflected off the water’s surface and reaching your eye. Below you see a nice example of this: The more perpendicular you look at the water surface (i.e. those sides of the wave facing you), the better you can look into the water. Whereas all those parts of the sea surface that face away from you look blue and you can’t look into the water there.
I think this is totally fascinating! Don’t those pictures look almost fake?
And, btw, this doesn’t only happen if you look in parallel to the direction of wave propagation. Although it looks even weirder at an angle:
Can you see how all those tiny ripples on the wave each show the same phenomenon of either reflecting the sky or being transparent and showing the sea floor underneath? How cool is that? :-)
And something more from the teacher training at Lotseninsel: A mussel that sucks in water dyed with food coloring and then pumps it out on the other side again. Very fascinating for a physical oceanographer who has never dealt with anything living in the water before :-)