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New experiment to investigate cosmic connection to clouds
A novel experiment, known as CLOUD (Cosmics Leaving OUtdoor Droplets), begins taking its first data today with a prototype detector in a particle beam at CERN, the world's largest laboratory for particle physics. The goal of the experiment is to investigate the possible influence of galactic cosmic rays on Earth's clouds. This represents the first time a high energy physics accelerator has been used for atmospheric and climate science.
The CLOUD experiment is designed to explore the microphysical interactions between cosmic rays and clouds. Cosmic rays are charged particles that bombard the Earth's atmosphere from outer space. Studies suggest that cosmic rays may influence the amount of cloud cover through the formation of new aerosols (tiny particles suspended in the air that seed cloud droplets). Clouds exert a strong influence on the Earth's energy balance, and changes of only a few per cent have an important effect on the climate. The CLOUD prototype experiment aims to investigate the effect of cosmic rays on the formation of new aerosols.
Understanding the microphysics in controlled laboratory conditions is a key to unravelling the connection between cosmic rays and clouds. CLOUD will reproduce these interactions for the first time by sending a beam of particles - the "cosmic rays" - from CERN's Proton Synchrotron into a reaction chamber. The effect of the beam on aerosol production will be recorded and analysed.

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Cloudy grey weather is sometimes caused by cosmic rays.

New evidence that events in outer space affect the weather and climate of Earth has been revealed in a study by meteorologists at the University of Reading published in the Proceedings of the Royal Society on Wednesday 18 January, 2006.

In their paper ‘Empirical evidence for a non-linear effect of galactic cosmic rays on clouds’, Drs Giles Harrison and David Stephenson suggest that cosmic rays have a significant effect on the Earth’s lower atmosphere – particularly on levels of cloudiness.

The Reading meteorologists discovered that the chance of an overcast day decreases by 20% on days with low cosmic ray fluxes. The effect is strongest when low cosmic ray fluxes occur – this is often associated with solar flares, but may also result from changes outside the solar system.

"Back in 1959, Edward Ney suggested that variations in cosmic rays, which are charged particles mostly originating outside the solar system, could affect our weather. This research now provides strong evidence supporting Ney’s suggestion, which effectively links atmospheric and space science. As well as the influence of weather, our evidence shows a small yet statistically significant effect of cosmic rays on daily cloudiness. This suggests that cosmic rays are an additional external source of climate variability that should be considered when modelling past and future climate" - Dr Giles Harrison.

To detect changes in the atmosphere from cosmic rays, Harrison and Stephenson used solar radiation measurements made by meteorological stations. They conducted a careful analysis of the UK archives of daily solar radiation observations from 1951-2004 and compared them with neutron counter cosmic ray measurements taken at Climax, Colorado, between 1951 and 2000.

"The odds of a cloudy day increase by around 20 per cent when the cosmic ray flux is high" - Giles Harrison.

This amounts to a few extra days of cloudiness per year.

When cosmic rays hit the atmosphere they produce charged particles which seem encourage the growth of cloud droplets. Compared with greenhouse gases the effect of cosmic rays on climate is small. But it could help explain some of the more mysterious changes in climate Earth has experienced in the past.

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