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?
The morning I went to Heligoland I spent some time in the port of Hamburg, trying to film a phenomenon I had recently chatted about with the author of this inspiring guest post: How waves seem to propagate super slowly into smooth patches of water. It turned out to be really difficult to film (because ships didn’t go where I expected them to go [you see me walk a couple of steps half way through the video below, because I needed to get away where a boat was docking], other ships cross the water you are filming, and because filming water is pretty difficult in general).
Here is my best attempt:
So why does it seem to take waves so surprisingly long to propagate into smooth patches of water? Well, because what we see and notice is the phase speed of waves, with which the crests propagate. But the wave field itself only propagates with group speed, which is half the phase speed. So from the movement we notice, waves should be invading the smooth patches twice as fast as they actually do!
Now I need to go and find a good way to film this phenomenon…
Last week I had the chance to join students and alumni of the interdisciplinary bachelor project at Hamburg University of Technology for a flight above the port of Hamburg.
The students were flying for the very first time, so it got quite exciting at times, especially during turns.
But luckily they were quick learners and brought us home safely. Always nice to arrive at Hamburg Airport!
For all of you getting nervous now, let me take a step back and show you another picture:
We had the amazing opportunity to visit the German Aerospace Centre (DLR) in Braunschweig. And a couple of the students actually got the opportunity to fly the flight simulator! Even though I didn’t get to (sniff!) – it was absolutely fascinating. Even though the simulator opens up into a well-lit room, as you see in the picture above, it was so easy to forget we were staring at simulated landscapes in a simulated plane. It was really exciting! Some people even started feeling sick from all the turning. And we all kept staring out of the “windows” to see which part of the town we were flying over and whether we could spot our campus. Also the technology is pretty cool: the three projectors you see in the image above project onto concave mirrors, which makes the image be far away enough so the eye doesn’t focus on the screen, which makes the whole experience feel completely realistic.
We also got to see other parts of DLR which were pretty exciting, too, like the 3D view of Mars’s surface. Did you know that the highest mountain in our solar system is on Mars, and that it’s 22 km high? I bet you did not.
Thanks, Uta and Siska, for organizing this great field trip!
On my recent trips through the Port of Hamburg one thing has fascinated me a lot – the floating dry dock. It’s right there when you get off the tube and walk towards the port:
Dry docks in the Port of Hamburg. A classical dry dock “Elbe 17” on the left, and a floating dry dock on the right.
The floating dry dock basically has a u-shaped profile of water tanks that can be flooded or emptied to adjust the buoyancy of the whole structure. As the tanks are flooded, the dry dock sinks and a ship can drive in. Then the tanks are emptied, the dock floats up, carrying the ship out of the water so people can work on it above water. Voila.
In the picture above you see some kind of dark fabric blocking the view into he floating dry dock on the right. How disappointing. But when Jenny and I were there we got lucky:
As we went past, we got a glimpse of the stern of the ship inside. And a little while later, the front had been opened up, too.
Here we can even see the bow of the ship.
I think it is really cool to be able to see a ship propped up and out of the water like that.
And still cooler – a while later they started to flood the dock, so it was starting to sink and the ship was starting to float. (And don’t you just looooove this view of the port? No? Is it just me?)
When you compare the (obviously not heavily loaded) Cap San Diego in front of the dock with the ship inside, the ship in the dock seems to be almost floating already, too. Sadly we couldn’t continue watching until the ship sailed out of the dock. But we saw plenty of other cool ships and stuff, so I guess I shouldn’t complain :-)
I’ve been visiting the Port of Hamburg on all of my weekends recently. First when J&J&T came to visit and Torge described the huge thunderstorm, then more recently when Jenny came to visit. The Port of Hamburg is a tidal port with water levels changing approximately 3 meters between high- and low tide. Hence currents are pretty strong during ebb and flood and a lot is going on oceanographically speaking.
So Jenny and I were strolling along the water’s edge when suddenly we noticed a tug behaving strangely.
A tug in the Port of Hamburg.
It just sat in one place, but was producing a lot of turbulence for no obvious reason.
Tug pushing against the Cap San Diego in the Port of Hamburg.
Then, maybe 100 meters away, a second tug was behaving even more strangely: It sat flush against the museum ship Cap San Diego and pushed against it, producing again a lot of turbulence.
What was going on?
Anyway, clearly the tugs weren’t only producing turbulence, but also pretty strong currents. Watch the movie to see what kept us entertained there for quite some time:
Seeing the first boat being swung around so badly was pretty scary (and after that first one, the tug visibly tuned down the engine), but after having watched six or so little boats pass the tug, we lost interest and went on a boat ourselves to explore the harbor from a different point of view. So maybe 45 minutes later and a bit further downstream, we suddenly spotted the Cap San Diego!
The Cap San Diego on the Elbe river, downstream of the Port of Hamburg.
I wasn’t aware this ship was still sailing – I had only ever seen it as a museum ship, moored at Landungsbrücken. But I have since learned that it does indeed still sail. If you pay enough, that is. Apparently a while back it was rented by my university for a practical, where students of ship building measured the propulsion and engineering students something else. I will have to make sure I’ll be on board if that happens again!
Anyway, isn’t Hamburg beautiful?
After having finished our harbor tour, more sightseeing, lunch, and some more sightseeing, Jenny and I went up on St. Michael’s Church for its nice view over the whole city. And guess what we saw?
No thunderstorms this time, but Cap San Diego coming back into port!
Today I have the pleasure to announce a guest post by Torge Martin. Torge, together with J&J, came to visit Hamburg recently, and we got stuck in some pretty bad weather. Which, being the oceanographers and meteorologists we are, meant that we got very excited, took about 100 pictures each, and me talking Torge into writing about what actually happened there. Which he did! So without further ado – enter Torge!
The 5-minute warning of a summer’s day sudden end.
Guest post by Torge Martin
A week ago we spent a wonderful day with Mirjam in Hamburg touring the harbor and downtown – very touristy. It was sunny and pretty hot for the average northern German. In the early afternoon the thermometer hit 28˚C. Perfect conditions for eating a big cup of ice cream at the Binnenalster, jumping on a Barkasse (little boats that ship tourists around the harbor) to catch at least a slight breeze, and for … a gorgeous thunderstorm.
When we climbed the 429 steps of the Michel (St. Michael’s tower) later in the afternoon we didn’t know that this was perfect timing to witness an impressive natural spectacle: The sky darkened quickly in the West and Southwest and within minutes a dramatic cloud formation took over the scene.
Photo by Torge Martin.
Photo by Torge Martin.
The horizontal “roll” across the picture (below the bright stripes) is a so-called shelf cloud that marks the leading edge of the approaching thunderstorm. In German such a cloud is often called Böenkragen (“gust collar”) or Böenwalze (“gust roll”), which hints at its shape and the strong winds that it is accompanied by.
How does such a shelf cloud form? I won’t go into all details of thunderstorm formation. The high cumulonimbus clouds of typical summertime thunderstorms are formed by strong, thermally driven updraft. Updrafts can reach vertical velocities of 50 km/h. When the moist air is cooled at higher levels, say at 6-9 km, condensation starts, and water droplets or ice crystals form. The droplets begin to fall within the cumulus cloud simply due to their weight and pull the ambient air with them along their way. This forms a downdraft, which is typically found in the rear part of the cloud while updraft still dominates the front side of the cloud. The downdraft flow spreads out horizontally near the ground and often comes with strong gusts at surface level. Since downdraft air is much cooler than the surrounding warm summer air, its spreading is associated with a cold front. The latter rapidly pushes upward the warm, moist surrounding air. As the warm air is lifted condensation may occur, which we then observe as a shelf cloud marking the leading edge of the gust front. On the ground we typically feel the downdraft from a thunderstorm as a drop in temperature and strong winds—in our case the 10-minute averaged wind speed peaked at 44 km/h and temperature dropped by 5˚C—while a change in wind direction and increase in air pressure can also be observed.
The shelf cloud, however, is not only beautiful and fascinating to observe, it also is nature’s “5-minute” warning to stop playing and go home (or find another safe place) before strong gusts and downpour hit.
In our case rainfall was heavy enough to reduce visibility from about 15 km to a mere 2 km. The rain was pushed horizontally through the tower top hurting on the skin. The crowd remaining at the top huddled together on the lee side of the hut, which shields the staircase from the elements. The gusts picked up dust from a nearby construction site in the harbor
Photo by Torge Martin.
which probably helped the dramatic coloring of the lee side scenery. But that’s a different story …
I was going to take pictures for a specific blog post I wanted to write…
…but then life happened and I had to concentrate on other things. We were sailing with kids and it was quite windy…
Alster in Hamburg
Luckily they are all pretty skilled sailors already, and were sensible enough to accept the restrictions on sail area that we imposed without too much grumbling.
But the bad weather approaching when I took those pictures is nothing compared to the bad weather approaching when my friends J&J&T came to visit Hamburg a while back. But that’s a topic for another post.
In the end all we had to do that day was watch the kids sail into the sunset.