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In SLF’s cold laboratory, researchers experiment with snow from all over the world. This sometimes tests the ability not only of their instruments and materials to function in the cold, but also their own.
Matthias Jaggi is suffering. He is standing in the warm corridor in front of the cold chambers and trying to breathe life back into his bloodless hands. Slowly the stabbing sensation gives way to a tingling feeling and his stiff fingers thaw. “I’ve never had such bad frostnip before,” says the 34-year-old mechanical engineer. He had briefly taken off his gloves because they got in the way while handling the equipment. He is actually quite used to spending several hours working in the cold. During the past few days, however, he has had to brave particularly tough conditions: in Chamber No. 4 in SLF’s cold laboratory it is an icy –40 °C.
The cold laboratory enables the snow researchers to experiment with snow at any time of year under controlled ambient temperatures – regardless of how warm or cold it is outside. It consists of six chambers, each around 20 m2 large and reminiscent of a walk-in freezer. The temperatures inside them can be adjusted as required. Most of the time they are between –25 and 0 °C. There is a good reason for Chamber No. 4 to be as cold as –40 °C: Matthias Jaggi is simulating polar temperatures.
The experiments that Matthias is carrying out in the laboratory are in preparation for his expedition to Antarctica. He will spend around three months at the Italian-French research station Concordia (Dome C), which is almost 1000 kilometres away from the coast and about 3200 metres above sea level. The temperatures there are certain to be cold: air temperatures in the central regions of the Antarctic are on average –54 °C. It will be Matthias’ first time in Antarctica. “I am delighted to have this opportunity, and curious about what awaits me at the research
station,” he says.
Snow the whole year round
Matthias Jaggi has been working as a member of the technical staff in the Group ‘Snow Physics’ at SLF for nine years. He supports researchers in their projects and makes sure that, among other things, everything in the cold laboratory runs smoothly. Take, for example, Chamber No. 6, which is in operation all summer and winter. The refrigerator-shaped box seems at first sight unspectacular. But its appearance is misleading. Inside the apparatus, delicate snow crystals are hanging like ornaments on thin nylon threads. The ‘Snowmaker’ produces snow that is practically identical to that occurring naturally because, in principle, the same processes take place inside the machine as those in nature. Thanks to the ‘Snowmaker’, snow physicists are no longer dependent on snowfall for their experiments. They can, moreover, produce differently shaped crystals by varying the temperature and humidity. The machine can make about seven kilograms of snow per day – research material for studying, for example, physical processes in snow.
The cold chambers can also be used to store snow from all over the world. Researchers bring back snow samples from their various expeditions to analyse later. When storing these samples, the most important thing is to keep the temperature at around –25 °C. Under such conditions, the snow structures change slowly and the samples remain more-or-less intact in their original states. This is how they can be stored until the experiment proper starts.
One indispensable piece of equipment in the cold laboratory is the computed tomography scanner, which is well-known from human medicine. With such devices, researchers can scan the snow samples and reconstruct them in three dimensions to observe the so-called snow metamorphism (see page 13). During this transformation, the snow changes its structure and thus also its physical properties. In the laboratory, researchers can reproduce this process, which takes places naturally, under controlled conditions. Their findings help them understand the structure of snow cover and the formation of avalanches better.
Snow metamorphism is also the focus of the experiments in Antarctica. The expedition is part of the SLF’s joint project ‘Snow properties evolution in a changing climate in Antarctica’ with the Institute of Géosciences de l'Environnement in Grenoble and the French Polar Institute IPEV. The Antarctic serves as an important climate archive for the Earth. The analyses of ice cores allow conclusions about temperatures in the past to be drawn. Here snow metamorphosis is a factor that may well need to be taken into account when reconstructing earlier temperatures. In order to understand the interrelationships better, SLF’s Research Group ‘Snow Physics’ wants to study the metamorphosis processes in polar snow cover under extreme temperature conditions.
Specially developed boxes
Matthias’ break in the corridor to warm up is over. He slips back into his full-body down suit, puts on his lined hat and thick gloves and goes back into the cold chamber. On the laboratory bench is a block of snow. Matthias picks up a saw and, with just a few cuts, transforms it into the required shape. Franziska Roth, who is on work placement in the Snow Physics Group, joins him. Carefully, they together lift the roughly 40-centimetre thick block and lay it on silvery aluminium foil. It is vapour-tight and should prevent an exchange of the air in the snow block with the atmosphere. Later analyses should find out what effect this has on the snow structure and the isotopes in snow. Franziska and Matthias wrap the snow block up in the foil with practised hands. With experiments in the cold, it is sometimes the details that are decisive. For example, normal adhesive tapes only hold at temperatures above –10 °C. That’s why Matthias uses a special tape that sticks even under Antarctic conditions. He and Franziska then carefully place the packet inside a specially developed box.
After tests in the laboratory, the box will also be used in Antarctica. Inside, snow metamorphosis can take place under controlled conditions as both the lid and floor temperatures can be regulated. This enables Matthias to create a temperature gradient in the box between the top and the bottom. The larger the temperature difference, the faster the metamorphosis of the snow. In the Antarctic, Matthias will take snow blocks from a zone with untouched snow out in the open and then pack it into the metamorphosis boxes. He will also measure the temperature gradient in the natural snow cover in the field every day. He will then set the temperatures in the boxes to the same as those in the polar snow profiles – which means typically at about –45 °C at the bottom and –30 °C at the top. The boxes will be stored in an ice cave with a temperature of –50 °C. The snow in the boxes differs from the snow samples in the field only in being packed airtight so that no exchange with the atmosphere can take place.
Antarctic snow comes to Davos
In the meantime Matthias and Franziska are not at all unhappy to have almost finished the work. The cold has long made itself felt again: Matthias’ nose is dripping and his glasses are misted over. Franziska’s hair and eyelashes are covered with white frost. They quickly pack up all the material. Now the tests, which have taken several weeks, and the preparation in the laboratory are almost completed. Matthias considers them to have been successful: “The chances are good that the experiments will also work in Antarctica.” Now the metamorphosis boxes just need to be shipped so that they can get to Dome C before Matthias.
Matthias will only be able to take a few personal things with him for his three-month stay in Antarctica. Thick jackets, gloves and over-trousers all take up a lot of space. Nevertheless, he can’t do without his running shoes. They have to go with him. He’s already decided what he wants to do in his spare time: he plans to learn the programming language Python.
Once the expedition has been completed, the snow samples are shipped from Antarctica to Europe. Some of them will be sent to Paris, where French researchers will carry out isotope analyses. The rest will come to Davos. It is when Matthias gets back that his work will really start. He will use computer tomography to study the samples and analyse the snow structure. And where will he do it? Where it all started: in the cold laboratory at SLF. (Sara Niedermann, Diagonal 1/18)