Melting ice cubes experiment — observing the finer details

If you don’t know my favourite experiment for practically all purposes yet (Introduction to experimenting? Check! Thermohaline circulation? Check! Lab safety? Check! Scientific process? Check! And the list goes on and on…), check it out here. (Seriously, of you don’t recognize the experiment from the picture below, you need to read up on it, it’s awesome! :-))

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Susann and I got funding from PerLe (our university’s project to support teaching innovation) to add a couple of cool new features to Susann’s “intro to meteorology” lecture, and doing a hands-on experiment with 50 students in a lecture theatre in their second lecture was only one of the first of many more to come.

We used the experiment to introduce the students to oceanic circulation, and this experiment is, in my experience, very engaging and sparks curiosity, as well as being very nicely suited as a reminder that things are not as easy as they seem to be when you see those nice plots of the great conveyor belt and all the other simplified plots that you typically see in intro-level lectures. Especially understanding that there are many different processes at play simultaneously, and that they have different orders of magnitude and might act in different directions helps counteract the oversimplified views of the climate system that might otherwise be formed.

I usually use dye to make it easier to observe what’s going on in the experiment (either by freezing it directly into the ice cubes as shown in the picture on top of this blog post, or by dripping it onto the melting ice cubes when students have started to observe that — counter to their intuition — the ice cube in the fresh water cup is melting faster than the one in the salt water cup).  We had dye at hand, but I decided on the spur of the moment to not use it, because the students were already focussing on other, more subtle, aspects that the dye would only distract from:

The shape of the ice cubes

In many of the student groups, the most prominent observation was that the shape of the melting ice cubes was very different in the fresh water and salt water case. In the fresh water case, the ice cube melted from the sides inwards: as a cylindrical shape with a radius that was decreasing over time, but in any instance more or less constant for all depths. In the salt water case, however, the ice cube melted upwards: The top did not melt very much at all, but the deeper down you looked the more was melting away. Why?

Condensation on the sides of the cup

Another observation that I prompted was in what regions the cups showed condensation. In the fresh water case, there was a little condensation going on everywhere below the water line, and sometimes there were vertical streaks down from where the ice cube was touching the wall. In the salt water case, there was only a small band of intense condensation close to the water level.

This, not surprisingly, looks very similar to what a thermal imaging camera sees when observing the experiment (as described in this post).

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Taken together, those two observations are quite powerful in explaining what is going on, and it seemed to be a fun challenge for the students to figure out why there was condensation on the outside of the cups in the first place (does condensation occur in warmer or colder places?), what it meant that different places ended up being warmer or colder, and how all of that is connected to global ocean circulation. Definitely an experiment I would recommend you do! :-)

Fog and clouds in a bottle

A little bit of hands-on meteorology for a change.

This post is inspired by www.planet-science.com‘s “fog in a bottle” and “make a cloud in a bottle” posts. Inspired meaning that I had to try and recreate their experiments after I saw this when approaching Zurich airport recently:

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Clouds and fog somewhere close to Zurich airport.

So let’s start with fog in a bottle. I’m doing fog in a jar, because it is easier to balance a sieve with ice cubes on a wide-mouthed jar than on a bottle… There is about 2 cm of hot water in the jar and the sieve with ice cubes is put on top to cool the moist air enough for fog to form.

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And now the cloud in a bottle. This one is fun! And a lot more impressive in the flesh than in the movie, so try it out yourself! Suck some smoke into a bottle that contains a little water. Close the cap, press and release the bottle and see a cloud forming when you release it. The smoke acts as condensation nuclei here. And pressure changes, temperature changes, yada yada… Anyway, try it yourself!

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P.S.: Kristin – erkennst Du die Flasche? Die, die Deine Freundin Dir mitgegeben hatte, damit Du was zu trinken hast, die dann mit in Göteborg war und die ich dem Recycling zuführen sollte? Hat offensichtlich nicht geklappt, aber viele Grüße an Deine Freundin! :-)

Internal waves in the atmosphere

A photo of internal waves in the atmosphere.

Internal waves exist on the interface between fluids of different densities. In the ocean they are mostly observed through their surface imprint. In the tank, we could also observe them by looking in from the side, but this is hardly feasible in the ocean. But luckily vision is easier in the atmosphere than in the ocean.

On our research cruise on the RRS James Clark Ross in August 2012, we were lucky enough to observe atmospheric internal waves, and even breaking ones (see image above). This is quite a rare sight, and a very spectacular one, especially since, due to the low density contrast between the two layers, the waves break extremely slowly.

It is really hard to imagine what it looked like for real. This movie shows the view of Jan Mayen – the volcano, the rest of the island and then the atmospheric waves. Please excuse the wobbly camera – we were after all on a ship and I was too excited to stabilize properly.

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Heat capacity of air and water

Hands-on activity to better understand the concept and consequences of heat capacity. Also a great party trick.

Imagine you take a balloon. Any kind of normal balloon. You blow it up. You hold it over a candle flame. What do you think will happen?

Yes – it will burst pretty instantly.

Now imagine you are taking a new balloon. You fill it with water (or, in our case, you fill it about half with water and half with air). You hold it over the flame. What will happen now?

You wait.

And wait.

And wait.

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Balloon, filled with water, being heated above a candle. Note the remnants of the previous balloon (the one that was just filled with air) on the table.

You even take a second candle.

You wait some more.

What happens? Nothing.

And why not? Because water has a much higher heat capacity than air. Meaning you have to put a lot of energy into a small volume of water to warm it up, about 4 times more than you would have to add to a similar volume of air. So the balloon does not get hot quickly, hence the plastic doesn’t get weakened enough for the balloon to burst. In fact, it did not only not get hot quickly, it did not get hot enough at all within the attention span of a typical student or instructor. So, because my students asked nicely, I decided to demonstrate what happens when the balloon is half filled with water, but the flame is directed to an area of the balloon that is not in direct contact with the water. If you can’t imagine what happens, check it out here (if you CAN imagine what happens, I’m sure you will check it out, too…).

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