Cosmics Leaving Outdoor Droplets (CLOUD)CLOUD official website
/ref> is an experiment being run at CERN by a group of researchers led by Jasper Kirkby to investigate the microphysics between

galactic cosmic rays Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...

(GCRs) and aerosols under controlled conditions. This is a

fixed-target experiment A fixed-target experiment in particle physics is an experiment in which a beam of accelerated particles is collided with a stationary target. The moving beam (also known as a projectile) consists of charged particles such as electrons or protons a ...

that began operation in November 2009,CLOUD experiment provides unprecedented insight into cloud formation
CERN though it was originally proposed in 2000. The primary goal is to understand the influence of galactic cosmic rays (GCRs) on aerosols and clouds, and their implications for climate. Although its design is optimised to address the possibility of cosmic rays nucleating cloud particles, (as posed by, for example,

Henrik Svensmark Henrik Svensmark (born 1958) is a physicist and professor in the Division of Solar System Physics at the Danish National Space Institute (DTU Space) in Copenhagen. He is known for his work on the hypothesis that fewer cosmic rays are an indirect c ...

and colleagues) CLOUD allows as well to measure aerosol nucleation and growth under controlled laboratory conditions. Atmospheric aerosols and their effect on clouds are recognised by the IPCC as the main source of uncertainty in present radiative forcing and climate models, since an increase in cloud cover reduces global warming.

Setup

The core of the experiment is a stainless steel chamber of 26m³ volume filled with synthetic air made from liquid nitrogen and liquid oxygen. The chamber atmosphere and pressure is being measured and regulated by various instrumentations. The aerosol chamber can be exposed to an adjustable particle beam simulating GCRs at various altitude or latitude. UV illumination allows photolytic reaction. The chamber contains an electric field cage to control the drift of small ions and charged aerosols. The ionisation produced by cosmic rays can be removed with a strong electric field. Besides, humidity and temperature inside the chamber can be regulated, allowing for fast adiabatic expansion for artificial clouds (compare

cloud chamber A cloud chamber, also known as a Wilson cloud chamber, is a particle detector used for visualizing the passage of ionizing radiation. A cloud chamber consists of a sealed environment containing a supersaturated vapour of water or alcohol. A ...

) or experiments on ice microphysics. According to Kirkby "the level of cleanliness and control in a laboratory experiment is at the limit of current technology, and CERN know-how has been crucial for CLOUD being the first experiment to achieve this performance."

Results

CERN posted a 2009 progress report on the CLOUD project. J. Kirkby (2009) reviews developments in the CERN CLOUD project and planned tests. He describes cloud nucleation mechanisms which appear energetically favourable and depend on GCRs.Cosmic Rays and Climate Video
Jasper Kirkby, CERN Colloquium, 4 June 2009Cosmic Rays and Climate Presentation
Jasper Kirkby, CERN Colloquium, 4 June 2009 On 24 August 2011, preliminary research published in the journal ''

Nature Nature, in the broadest sense, is the physical world or universe. "Nature" can refer to the phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. Although humans ar ...

'' showed there was a connection between Cosmic Rays and aerosol nucleation. Kirkby went on to say in the definitive CERN press Release "Ion-enhancement is particularly pronounced in the cool temperatures of the mid-troposphere and above, where CLOUD has found that sulphuric acid and water vapour can nucleate without the need for additional vapours. The first CLOUD experiments showed that sulphuric acid (derived from sulphur dioxide, for which fossil fuels are the predominant source) as such has a much smaller effect than had been assumed. In 2014, CLOUD researchers presented newer experimental results showing an interaction between oxidised biogenic vapours (e.g., alpha-pinene emitted by trees) and sulphuric acid. Ions produced in the atmosphere by galactic cosmic rays enhance the formation rate of these particles significantly, provided the concentrations of sulphuric acid and oxidised organic vapours are quite low. This new process may account for seasonal variations in atmospheric aerosol particles, which are being related to higher global tree emissions in the northern hemisphere summer. Besides biogenic vapours produced by plants, another class of trace vapours,

amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent su ...

s have been shown by CLOUD to cluster with sulphuric acid to produce new aerosol particles in the atmosphere. These are found close to their primary sources, e.g.

animal husbandry Animal husbandry is the branch of agriculture concerned with animals that are raised for meat, fibre, milk, or other products. It includes day-to-day care, selective breeding, and the raising of livestock. Husbandry has a long history, star ...

, while

alpha-pinene α-Pinene is an organic compound of the terpene class, one of two isomers of pinene. It is an alkene and it contains a reactive four-membered ring. It is found in the oils of many species of many coniferous trees, notably the pine. It is als ...

is generally found over landmasses. The experiments show that sulfuric acid and oxidized organic vapors at low concentrations reproduce suitable particle nucleation rates. The nucleation mechanism used on global aerosol models yields a photochemically and biologically driven seasonal cycle of particle concentrations and cloud formation in good agreement with observations. CLOUD insofar allows to explain a large fraction of cloud seeds in the lower atmosphere involving sulphuric acid and biogenic aerosols. CLOUD researchers note that cosmic rays have little influence on the formation of sulphuric acid–amine particle formation: "The ion-induced contribution is generally small, reflecting the high stability of sulphuric acid–dimethylamine clusters and indicating that galactic cosmic rays exert only a small influence on their formation, except at low overall formation rates." This result does not support the hypothesis that cosmic rays significantly affect climate, although a CERN press release states that neither does it "rule out a role for cosmic radiation" in climate. Dunne ''et al.'' (2016) have presented the main outcomes of 10 years of results obtained at the CLOUD experiment performed at CERN. They have studied in detail the physico-chemical mechanisms and the

kinetics Kinetics ( grc, κίνησις, , kinesis, ''movement'' or ''to move'') may refer to: Science and medicine * Kinetics (physics), the study of motion and its causes ** Rigid body kinetics, the study of the motion of rigid bodies * Chemical k ...

of aerosols formation. The

nucleation In thermodynamics, nucleation is the first step in the formation of either a new thermodynamic phase or structure via self-assembly or self-organization within a substance or mixture. Nucleation is typically defined to be the process that de ...

process of water droplets/ice micro-crystals from water vapor reproduced in the CLOUD experiment and also directly observed in the Earth atmosphere do not only involve

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...

s formation due to cosmic rays but also a range of complex chemical reactions with sulfuric acid,

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogeno ...

and organic compounds emitted in the air by human activities and by organisms living on land or in the oceans (

plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a cr ...

). Although they observe that a fraction of cloud nuclei is effectively produced by ionisation due to the interaction of cosmic rays with the constituents of Earth atmosphere, this process is insufficient to attribute all of the present climate modifications to the fluctuations of the cosmic rays intensity modulated by changes in the solar activity and Earth magnetosphere.

References

External links

TED@CERN

Project websiteCLOUD experiment
record on

INSPIRE-HEP INSPIRE-HEP is an open access digital library for the field of high energy physics (HEP). It is the successor of the Stanford Physics Information Retrieval System (SPIRES) database, the main literature database for high energy physics since the 1970 ...

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