CERN Accelerating science

Cloud(y) climate studies at CERN

by Stefan Weber

Continuous improvements to the CLOUD facility as well as to the instruments combined with the state of the art know-how available at CERN have enabled a steady increase in the measurement capabilities and resulted in numerous high impact publications. This combination reflects CLOUD's world leading role in experimental laboratory studies of atmospheric aerosol nucleation and growth.

Cloud studies under tightly controlled conditions the numerous different parameters as well as a great number of processes, happening in the atmosphere that lead to cloud formation and therefore significantly influence earth’s climate. The understanding of the interplay and the influence of the different parameters is fundamentally important to understand climate change and further improve climate predictions.

The constant evolution of the Cloud experimental area from 2009 to nowadays is shown in fig. 1. Cloud's chamber is hosted at T11 in the PS Easthall (building 157) and this adds another outstanding feature as the 3.5 GeV π-beam can be used to simulate the impact of galactic cosmic rays. Furthermore it allows to study the effect of ionizing radiation on aerosol and cloud formation.


Figure 1. Evolution of the CLOUD experimental area from CLOUD01 in 2009 (left) to CLOUD11 in 2016 (right). As the photos show, safety aspects (e.g. wearing of helmets) have evolved, too.

In recent years, the focus was twofold and driven by a great interest in pristine and urban environments. The former typically investigates processes happening in boreal forests and marine environments, while the latter is concerned with more polluted and purely anthropogenic causes. A detailed physics overview was already given by the spokesperson of Cloud, Jasper Kirkby, in an issue of the EP newsletter in 2016.

CLOUD’s first measurement campaign in 2018 is now in June-July. This is a technical run and devoted to the sharpening of our understanding of the measurement facility itself. This year's main campaign will start in autumn and has a similar goal as previous campaigns, namely to study the precursors responsible for clouds. On the contrary, in the following Cloudy campaign in 2019 we will change our focus towards the microphysical processes during cloud formation itself.

The achievements of the CLOUD collaboration, its unique scientific possibilities and focus made possible to receive a grant for a third Marie Curie Innovative Training Network, financed by the European Commission. The Cloud-MOTION ITN is a multi-site network of 15 Ph.D. students distributed over 10 institutes across Europe with two fo them located at CERN. 

Using the excellent capabilities of the CLOUD facility, researches will be able to perform detailed and high-precision studies on the role of atmospheric aerosols in cloud formation and consequently in climate change as members of a distributed network of collaborators. They will gather data from a wide range of instruments and by combining and analysing them will try to answer some of the key questions related to aerosol formation and its potential impact in climate change. Furthermore, their research also focuses on the formation of aerosol nucleus and growth both in pristine and urban environments, significantly adding to our knowledge on the role that a growing urban environment might play. Last but not least, another important aspect is the formation of ice on glassy Secondary Organic Aerosol that can act as Ice Nucleating Particles.

Due to the wide variety of instruments using different software and data formats a particularly delicate issue is the inclusion of all instruments into the same Data Acquisition System. Another complication is added by the need for ‘quasi’ real-time on-line monitoring and data analysis. This is required, since the exact parameter choice for the next measurements is decided on a day to day basis and based on the most recent data taken.

Besides that, a better understanding of the chamber characteristics is required to increase the precision of the aerosol physics measurements. Effort is now being put to measure the mixing time and possible non-uniformities of gases and ions inside the chamber. 

The CLOUD collaboration aims to maintain and strengthen its leading role in experimental laboratory studies on atmospheric aerosol and cloud formation, and ultimately to improve understanding of the climate change. The CLOUD facility at CERN has proven to be an excellent platform for this task while continue training the next generation of scientists to tackle these questions.