In the ice clouds

The weather couldn¡¯t be worse. Nothing but a sea of grey. Not a trace of the Aletsch Glacier. Instead of a glorious alpine panorama, today all the Jungfraujoch can offer its guests are thick clouds. But that hasn¡¯t deterred a handful of tourists from venturing onto the Sphinx observation terrace. The wind is lashing against their faces, and snowflakes are swirling through the air. It is bitterly cold. The visitors from all over the world just about manage to muster a brave smile for the camera. Two storeys further up ¨C and inside, where it¡¯s warm ¨C Ulrike Lohmann and Larissa Lacher are gazing through the window at the clouds and they¡¯re tickled pink. But this is no schadenfreude, it¡¯s the enthusiasm typical of scientists who have a burning passion for their subject.

Lohmann is an atmospheric physicist and a professor at the Institute for Atmospheric and Climate Science at ETH Zurich. She is visiting Lacher, her doctoral student, at the external page High Altitude Research Station Jungfraujoch. This young scientist is spending four weeks here at the Sphinx Observatory, 3,571 metres above sea level, in order to make climate measurements. She is interested in particles in the air that aid cloud formation. And if today¡¯s weather is anything to go by, they are hardly in short supply up on the mountain.

Desert sand meets glacial ice

The blanket of clouds briefly opens to offer a glimpse of the snow fields outside the window. It¡¯s not much, but enough for Lacher to be able to show her boss the reddish deposits in the snow. The two women dart from one window to the next before the clouds swallow everything up again. What has set the researchers¡¯ pulses racing looks just like dirty snow to visitors from the city. But it¡¯s actually dust from the Sahara. It comes from the last Sahara dust event, which carried sand northwards from Africa in May. The two scientists are interested in how the Saharan sand affects the formation of clouds on the Jungfraujoch. Because fine particles like Saharan dust in the air ¨C known as aerosols ¨C act as condensation nuclei upon which water or ice can accumulate, depending on the temperature and relative humidity. This is how cloud droplets or ice crystals are formed, which eventually combine to make entire clouds. These ¡°warm clouds¡± mostly consist of relatively small water droplets and are recognisable from their sharp outlines. Ice clouds, on the other hand, are composed of ice crystals that fall out of the cloud more readily on account of their size, which is why they typically have blurred outlines. 

Lacher completed her Master¡¯s thesis in Lohmann¡¯s lab, and back then she was already studying Sahara dust events and their impact on the formation of clouds. She did this on Tenerife in the Canary Islands, which lies only 250 kilometres from the Sahara Desert. ¡°Measuring the same Sahara dust event during two parallel measuring campaigns ¨C initially in Tenerife and now here on the Jungfraujoch ¨C that would be a great success¡±, says Lacher, and her blue eyes light up. Because this would enable her to study the ageing process of the aerosol particles and their influence on the formation of clouds.

Other kinds of fine particles can also contribute towards the formation of clouds, such as sulphates from volcanoes and salts from the sea, not to mention fine particles from exhaust gases and industry. Lacher made the journey up here just over a week ago to study their impact on cloud formation, bringing a chamber with her in which she can simulate cloud formation under controlled conditions. The cloud chamber has now been installed in the Jungfraujoch lab and connected up to all manner of pipes, wires and sensors. The chamber sucks in atmospheric air through an inlet pipe that starts outside on the roof. Depending on the air sample and the conditions in the chamber, ice crystals of different shapes and sizes form. These are then detected at the other end of the chamber and evaluated later on.

Measuring well into the night

The measuring device was only constructed by Lohmann¡¯s research group a few months ago, based on a piece of equipment from the University of Toronto. There aren¡¯t any commercial products as yet; the field is still far too young. ¡°I find my research exciting because engineers are also on board¡±, says Lohmann. She had already come up with the idea of building a cloud chamber herself, albeit for an aircraft rather than a research station in the mountains. Gathering cloud data in a plane, however, is highly complex and expensive. What¡¯s more, the measurements are limited to the duration of the flight. The Jungfraujoch is more practical as it is enshrouded in clouds 30 to 40 percent of the time ¨C and these are the perfect prerequisites for Lohmann¡¯s doctoral student to collect suitable data. Lacher begins her first measurements every day at noon and usually keeps on going until way after midnight. ¡°Throughout the measuring campaign, I¡¯m completely detached from normal life, so I soon got used to the new rhythm. And besides, it means it can have a lie-in¡±, says Lacher with a grin.

Her room up here on the Jungfraujoch is modest. A hut-caretaker couple runs the accommodation side of things, and Lacher has high praise for them. And what the Jungfraujoch can¡¯t offer can always be ordered online from a supermarket down in the valley. The shopping bags are brought up to Europe¡¯s highest railway station by train, where Lacher can collect them. Even though it is challenging to work at this altitude, she has settled in well. When there are technical challenges ¨C like yesterday, when the cloud chamber iced up unexpectedly ¨C Lacher needs to know how to fix them herself. But she likes it. ¡°My work is very varied¡±, she says. ¡°The time just flies by up here.¡± 

Unpredictable clouds

Although Lacher has only been here for a week, she can already draw some initial conclusions about her measurements. In the afternoon, the air contains many more aerosol particles than at night. In the daytime, air close to the ground can sometimes be transported onto the Jungfraujoch by the upcurrent. It is polluted and contains far more man-made aerosol particles, but also biogenic particles such as pollen, which can sometimes cause increased ice formation in the chamber. At night, however, the air is much cleaner as the research station is in the free troposphere during this period and there are only very few aerosols for ice crystals to form upon. 

This spatial and temporal variability of the aerosol particles renders the formation of clouds difficult to predict. As a result, clouds are one of the main sources of uncertainty in climate models. The influence of clouds on climate change is also the subject of debate. During the daytime the clouds have a cooling effect because they reflect radiation. But at night, clouds have the opposite impact as they keep in the earth¡¯s heat like a greenhouse.  

For a long time, simulating clouds and aerosol particles in climate models was the main focus of Lohmann¡¯s group. Meanwhile, they have taken things a step further and gather the data for their models themselves. ¡°I¡¯m simply too impatient to wait for others to make the measurements I need for my models¡±, admits the spirited professor. That¡¯s why modelling, field work and lab work are all integral elements of her studies. Consequently, the data that Lacher is gathering up here will be channelled into the climate models of Lohmann¡¯s group. 

Dusk is beginning to descend on the Jungfraujoch. The mountain finally offers a glimpse of its more generous side: suddenly, the cloud layer bursts open and the Aletsch glacier appears in all its splendour. The sun and the shade dance on its ice. Despite her deep fascination with clouds, Lacher is delighted with this sudden change in weather that has unveiled the true beauty of the alpine world. ¡°I¡¯m very fond of my temporary workplace up here¡±, she says. ¡°Above all, it is a great opportunity to gather some extraordinary measurement data.¡± And as the sun gradually sinks behind the mountain tops, Larissa Lacher settles in for another night in the lab.