“Fête de la Science” is a national event that promotes French science to the general public and gives access to research institutes and laboratories, including hands-on experiments, activities for the whole family and screening of movies. LÉGI is an important contributor for the region Isère and welcomed many important French people at the opening of the event on Thursday.

Here you can see the big crowd squeezed onto the surrounding platforms gazing at the rotating Coriolis tank, while Samuel and the director of the laboratory explained what kind of experiments they conduct in the lab. Unfortunately the tank was not filled with water yet, but the topography for our experiments that will start next week was mounted in the tank.

Among the visitors there were also journalists that interviewed Céline afterwards. It was screened on the local TV channel France3 and is available online: http://france3-regions.francetvinfo.fr/auvergne-rhone-alpes/emissions/jt-1920-alpes.

A short translation of what the journalists says in the beginning and what Céline explains about the background of the experiment:

Journalist: It looks like a big merry-go-round. Its name is Coriolis. With 13-m diameter, it’s the largest platform of its kind in the world. People come from all around the world to use it. Here, Swedish scientists are preparing their experiments that they will perform with a lot of instrumentation and nearly 1m of water height. They are studying the melting of Antarctic glaciers.

Céline: « Once the glaciers have melted, and have produced a relatively fresh water, what does this freshwater do ? To which depth does it sink, where does it go to, how does it mix with the rest of the water column, and which consequences does that have on the whole global ocean circulation ? »

 

Yesterday was the last day of experiments with the shelf break setup, before we will continue ice front experiments next week. To celebrate a (hopefully) successful series of many experiments without any big troubles (we’ve heard stories about a leaking tank, shut off electricity etc), we just couldn’t resist to go swimming in the rotating pool! Here you see how we were having fun!

Apparently, we are the first people that went swimming in the tank! It was not only fun, but we also got our personal experience of the Coriolis force that deflected us to the left while swimming. In addition, the water was mixed up for the following last two experiments, in which we induced fluorescent dye to get shiny pretty pictures of the current. Those photos will be coming next week…

Similarly to last Friday’s Kelvin-Helmholtz instabilities, observing swirls and eddies made from green fairy dust is not really what we are in Grenoble for. But are they pretty!

And it is actually very interesting to observe the formation of eddies. If you look at the picture above and focus on the sharp edge “downstream” of the canyon, you see that there are some small instabilities forming there that detach as eddies. And in the picture below you see that there are more, and larger ones, a little while later.

And below you see how they have grown into larger eddies.

And in the gif below you see that the structures of those eddies inside the canyon are actually coherent throughout the uppermost three layers (which are the only ones in which the shelf is lit, for the lower three layers we can just observe what’s going on deeper than the depth of the canyon). So a nice and barotropic flow, just like we had hoped!

Don’t those eddies look just like phytoplankton patches observed from a satellite?

This is really not the focus of our experiments here in Grenoble, but they are too nice not to show: Kelvin-Helmholtz instabilities!

They showed up really nicely in our first experiment, when we only had neutrally-buoyant particles in our source water (and not yet in the ambient water). The water that shows up as the lighter green here is thus water that originally came from the source (and at this point has recirculated out of the canyon again).

I get so fascinated with this kind of things. How can anyone possibly not be interested in fluid dynamics? 🙂

Watch the movie below to see them in motion! The scanning works as explained here.