Original URL: http://www.theregister.co.uk/2006/10/24/rain_cloud/

Rainy day? Blame cosmic rays

Particle accelerators show us how

By Lucy Sherriff

Posted in Science, 24th October 2006 14:58 GMT

Scientists have speculated for some time that cosmic rays could have an effect on the weather, and now the experiment designed to test the idea has begun collecting data.

The CLOUD experiment (which contrives to be short for Cosmics Leaving OUtdoor Droplets) kicked off on Thursday last week, with a prototype detector in a particle beam at CERN. It is, you will be surprised to hear, the first time a particle detector has been used to investigate the links between space and Earth weather.

The experiment is designed to probe the tiny interactions between the clouds and cosmic rays. The working hypothesis is that cosmic rays can create seed particles, tiny aerosols around which cloud droplets form. This in turn can increase cloud cover, which is tremendously significant in determining our climate. Very small variations in the amount of cloud cover can make a big difference to the planet's energy balance.

So, scientists from a range of disciplines, including experts on cloud and solar physics, plan to send a high energy beam representing the cosmic rays into a closely monitored reaction chamber.

The chamber is filled with pure "air", evaporated oxygen and nitrogen produced by a gas system designed by CERN engineers. The scientists say it will be the cleanest air anywhere in the world, and therefore free of many of the other aerosols that are present in the atmosphere.

The beam's effect on aerosol production will be measured and analysed, and the first results are expected in the summer of 2007.

The full experiment will involve an advanced cloud chamber and reaction chamber capable of reproducing the temperature and pressure conditions anywhere in the atmosphere. The chambers will also be equipped with an array of instruments to detect the tiniest details of the physical interactions taking place. ®