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atmosphere seeds

The experiment includes an advanced cloud chamber equipped with a wide range of external instrumentation to monitor and analyse its contents. The temperature conditions anywhere in the atmosphere can be recreated within the chamber. All experimental conditions can be controlled and measured, including the “cosmic ray” intensity and the trace atmospheric vapours in the chamber, which are set to levels of only a few molecules per trillion.

CERN Accelerating science

CLOUD

Could there be a link between galactic cosmic rays and cloud formation? An experiment at CERN is using the cleanest box in the world to find out

The Cosmics Leaving Outdoor Droplets (CLOUD) experiment uses a special cloud chamber to study the possible link between galactic cosmic rays and cloud formation. Based at the Proton Synchrotron (PS) at CERN, this is the first time a high-energy physics accelerator has been used to study atmospheric and climate science. The results should contribute much to our fundamental understanding of aerosols and clouds, and their affect on climate.

What can cosmic rays tell us about climate?

Cosmic rays are charged particles that bombard the Earth’s atmosphere from outer space. Studies suggest they may influence cloud cover either through the formation of new aerosols (tiny particles suspended in the air that can grow to form seeds for cloud droplets) or by directly affecting clouds themselves. Clouds exert a strong influence on the Earth’s energy balance; changes of only a few per cent have an important effect on the climate. However, despite its importance for climate, aerosol formation is poorly understood. Measuring the underlying microphysics in controlled laboratory conditions is important for a better understanding of atmospheric aerosol and is the key to unravelling the possible connection between cosmic rays and clouds.

What does the CLOUD experiment do?

The CLOUD experiment involves an interdisciplinary team of scientists from 17 institutes in nine countries, comprising atmospheric physicists and chemists, and cosmic-ray and particle physicists. The Proton Synchrotron provides an artificial source of “cosmic rays” that simulates natural conditions between ground level and the stratosphere. A beam of particles is passed through the cloud chamber and its effects on aerosol production or on liquid or ice clouds inside the chamber are recorded and analysed.

The experiment includes an advanced cloud chamber equipped with a wide range of external instrumentation to monitor and analyse its contents. The temperature conditions anywhere in the atmosphere can be recreated within the chamber. All experimental conditions can be controlled and measured, including the “cosmic ray” intensity and the trace atmospheric vapours in the chamber, which are set to levels of only a few molecules per trillion.

What has CLOUD shown us about our world?

In 2014 CERN’s CLOUD experiment made a huge discovery when it showed that biogenic vapours emitted by trees and oxidised in the atmosphere have a significant impact on the formation of clouds, thus helping to cool the planet.

As the Earth’s surface temperature gradually rises, it has become vital for us to predict the rate of this increase with as much precision as possible. In order to do that, scientists need to understand more about aerosols and clouds. Jasper Kirkby details an experiment at CERN that aims to do just that. (Video: TED)

In an effort to understand exactly how the cloud micro- and macro-properties interact with atmospheric particles, a collaborative research team conducted a modeling study analyzing three well-documented weather systems that occurred in March of 2000 over the southern Great Plains in the United States.

The complexities of clouds and the seeds that make them

Clouds are complicated. Each cloud formation depends on the timing of the water cycle, in which water evaporates from Earth’s surface, condensates in the atmosphere and falls back down, as well as the types of aerosols in the atmosphere.

In an effort to understand exactly how the cloud micro- and macro-properties interact with atmospheric particles, a collaborative research team conducted a modeling study analyzing three well-documented weather systems that occurred in March of 2000 over the southern Great Plains in the United States.

The results were published in Advances of Atmospheric Sciences, and included in a special issue on aerosols, clouds, radiation, precipitation, and their interactions. Scientists from the California Institute of Technology, Texas A&M University, Brookhaven National Laboratory, University of Arizona and McGill University contributed to the study.

“The results from this modeling study highlight the complexity of the aerosol-cloud-precipitation-radiation interactions that vary on a case-by-case basis,” said Yuan Wang, first author on the paper and a research scientist in the division of geological and planetary sciences at the California Institute of Technology. “Aerosols are so small and mutable, so it’s hard to quantify their impact.”

Aerosols, commonly known as cloud seeds, are tiny particles of things such as sea salt or pollution in Earth’s atmosphere.

Researchers found that different simulated aerosols had significant influence in each of the three systems, but other factors, such as solar radiation changes due to aerosol pertubations, also greatly contributed to cloud formation and development.

“This study has shown that studying the aerosol microphysical effect alone is insufficient to assess the changes of clouds in the real atmosphere, as the aerosol radiative effects can also produce profound impacts on cloud development and precipitation processes,” Wang said.

In climate predictions, computer program can model global climates based on observational data or theoretical information. According to Wang, the global climate model is a good tool, but it doesn’t fully appreciate the influence of aerosols. Its scale eclipses the microphysical properties of aerosols and their impact.

“We are still seeking the right way to represent aerosols and their effects in global climate models,” Wang said. “We’re interested in the interactions between the microscale model and the global climate model, and we’re working to bridge the scales between the two.”

Global climate models are used to assess the Earth’s future climate, but they may not provide the full picture.

“The impact of aerosols needs to be fully assessed,” Wang sa >

More information: Yuan Wang et al, Aerosol microphysical and radiative effects on continental cloud ensembles, Advances in Atmospheric Sciences (2018). DOI: 10.1007/s00376-017-7091-5