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Cosmic rays and CLOUD | The Economist

The Economist
The Economist
Researchers at CERN are using fake cosmic rays to see how real ones help seed clouds in the world's cleanest chamber

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Cern, the world's leading high-energy physics laboratory near Geneva, is most famous for probing the universe's tiniest constituents however is also engaged in more macroscopic research.

One experiment called cosmics leaving outdoor droplets, or cloud for short, looks at the mechanisms of cloud formation. Clouds grow from small particulates known as cloud seeds. Half of these are emitted directly into the atmosphere from sea spray and alike.

the other half however, are nucleated - produced when trace molecules in the air cluster together. Atmospheric physicists have long suspected that nucleation may be triggered by cosmic
rays. High-energy particles bombarding the Earth's atmosphere from space.

If their hypothesis is true it could have consequences for the climate. Since more cloud seeds mean more clouds, and clouds
reflect sunlight, cosmic rays might have a cooling effect on the earth.

Just how big an effect that is though has remained a mystery.

As for studying cosmic rays, all scientists can do in the field is wait for the fluctuations in the sun's magnetism - which is tied to the Rays intensity - to complete their 11-year cycle. Dr. kirkby and his colleagues decided to recreate both the atmosphere and the rays in a laboratory.

CERN is home to the world's biggest and most powerful particle accelerator, the Large Hadron Collider. The cloud project however uses the beam from one of the smaller less powerful machines called the proton synchrotron.

It's also one of the only parts of the facility that directs it's beam through the open air. Inside the chamber Dr. Kirkby's team can recreate the pressure temperature and humidity of any atmospheric conditions on earth, from a tropical seaside to the Arctic sky. But first their experiment must be untainted by contaminants - no plastics are used inside the chamber. Clouds scientists even mix their own air from scratch.

The chamber contains trace molecules believed to be responsible for cloud seed nucleation. Molecules like sulphur dioxide.

Ultraviolet lights mimic the sun's beams, which are known to spur the nucleation process. During an experiment their model atmosphere is bombarded by model cosmic rays. Tubes extract gas samples and probes provide the reading of what is happening inside.

As ever in science more researchers needed to confirm these findings for instance the cloud seeds produced in the chamber are still too small for actual cloud droplets to coalesce around.

Dr. Kirkby and his team are now hard at work trying to get their
seeds to grow bigger. Given clouds important role in climate, a better understanding of how they form could lead to more accurate climate models. But they have already shown that serious atmospheric science can, paradoxically, be done indoors.

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