CERN explores link between cosmic rays and clouds

Brussels, 30 October 2006

Scientists at CERN, the European Organisation for Nuclear Research, have started a new experiment to investigate the possible influence of galactic cosmic rays on the Earth's clouds and climate. This is the first time that a high energy physics accelerator has been used for atmospheric and climate science.

Cosmic rays are high energy charged particles, originating in outer space, that travel at near light speed and collide with particles in the Earth's atmosphere to produce a cascade of secondary particle collisions and a characteristic ultraviolet burst of light.

Recent research has suggested a possible link between cosmic rays and climate change. In 1997 Henrik Svensmark and Eigil Friss-Christensen of the Danish Space Research Institute proposed that high fluxes of cosmic rays could lead to more clouds and a cooler climate, and vice versa. The Danish scientists proposed that changes in the strength of the solar wind - the stream of charged particles that flows from the Sun - could lead to changes in the cosmic ray flux.

The so-called CLOUD (Cosmics Leaving OUtdoor Droplets) experiment at CERN will put the hypothesis that cosmic rays influence climate to the test for the first time within controlled laboratory conditions. Scientists will send a beam of particles - the 'cosmic rays' - from CERN's Proton Synchrotron into a reactor chamber and an advanced cloud chamber.

The chambers are equipped with a wide range of external instrumentation and are designed to recreate, then monitor and analyse the temperature and pressure conditions anywhere in the atmosphere. Specifically, they will focus on analysing conditions such as the nucleation and growth of aerosols, formation of cloud droplets, production of condensable vapours, creation of ice nuclei, and dynamics of stratospheric clouds.

The experiment brings together an interdisciplinary team from 18 institutes and nine countries in Europe, the US and Russia, including atmospheric physicists, solar physicists, and cosmic ray and particle physicists. 'The experiment has attracted the leading aerosol, cloud and solar-terrestrial physicists from Europe; Austria, Denmark, Finland, Germany, Switzerland and the United Kingdom are especially strong in this area,' says the CLOUD spokesperson, Jasper Kirkby of CERN.

'CERN is a unique environment for this experiment. As well as our accelerators, we bring the specialist technologies, experimental techniques and experience in the integration of large, complex detectors that are required for CLOUD.'

An example in the present CLOUD prototype is the gas system, designed by CERN engineers, which produces ultra-pure air from the evaporation of liquid oxygen and liquid nitrogen. 'It's probably the cleanest air anywhere in the world,' says Mr Kirkby.

The first results from the CLOUD prototype are expected by the summer of 2007.

For more information, please visit: CERN.ch/cloud/"> http://cloud.web.CERN.ch/cloud/