Aerosol-Cloud Interactions - A Directed Programme to Reduce Uncertainty in Forcing (ACID-PRUF) through a Targeted Laboratory and Modelling Programme
Lead Research Organisation:
University of Leeds
Department Name: School of Earth and Environment
Abstract
Aerosol particles act as sites for cloud droplet and ice particle formation. Cloud properties can be perturbed through the addition of aerosol particles into the atmosphere from anthropogenic and natural processes. This addition influences cloud microphysical properties, and subsequently affects cloud dynamics and thermodynamics, and the way the cloud interacts with radiation. The Earth's radiation budget is very greatly affected by clouds, and human-induced changes to the particle loading affecting them, known as indirect effects, are large and highly uncertain. A large part of this uncertainty is the result of poor knowledge of the fundamental aerosol and cloud properties and processes, leading to their poor representation in models. A programme of research is proposed here to i) directly investigate these processes in the laboratory, ii) evaluate the sensitivity of climate relevant parameters to the studied processes, iii) interpret the laboratory studies with detailed model investigations and iv) to incorporate and test new descriptions of the studied processes in cloud-scale and, where possible, global scale models. The programme will thereby reduce the uncertainty in estimates of radiative forcing and climate feedbacks relating to aerosol and cloud processes. The studies are split into those affecting warm clouds (those containing only liquid droplets) and those affecting clouds containing ice particles. The programme brings together an interdisciplinary team of researchers with expertise in 'warm' and 'cold' cloud and aerosol processes combining laboratory and multiscale modelling activities to deliver the improved predictive capability. The 'warm' laboratory work focuses on two major aspects i) the rate at which water is taken up by growing aerosol particles as they become cloud droplets (or 'activate) and ii) the ability of aerosol particles of various compositions to act as seeds for cloud droplets. These studies use a number of techniques including single particle optical levitation and investigations in a large photochemical chamber coupled to a large number of chemical and physical probes of ensembles of particles formed in simulated atmospheric chemical processes. The 'cold' work uses a similar coupling of a large, well-instrumented cloud chamber experiments and single particle levitation studies. The chambers used in both aspects will be coupled to investigate the impacts of aerosol transformation conditions on warm and cold cloud formation, using the instrumental payload from both chambers. A range of detailed models will be used to explicitly describe the processes by which aerosol particles interact with increasing relative humidity and reducing temperature to form cloud droplet and ice crystals and to their properties. The processes and properties will be represented in dynamical frameworks to predict the interactions between aerosols and clouds and their radiative effects at cloud resolving scales and radiative forcing of some of the investigated properties on global radiative forcing and feedbacks. The sensitivity of climate relevant parameters to the fundamental parameters investigated in the laboratory programme and their improved quantification will be evaluated using a simplified model 'emulator'.
Organisations
Publications
Malkin TL
(2015)
Stacking disorder in ice I.
in Physical chemistry chemical physics : PCCP
Johnson J
(2020)
Robust observational constraint of uncertain aerosol processes and emissions in a climate model and the effect on aerosol radiative forcing
in Atmospheric Chemistry and Physics
Johnson J
(2015)
Evaluating uncertainty in convective cloud microphysics using statistical emulation
in Journal of Advances in Modeling Earth Systems
Johnson J
(2018)
The importance of comprehensive parameter sampling and multiple observations for robust constraint of aerosol radiative forcing
in Atmospheric Chemistry and Physics
Igel A
(2018)
Meteorological and Land Surface Properties Impacting Sea Breeze Extent and Aerosol Distribution in a Dry Environment
in Journal of Geophysical Research: Atmospheres
Hiranuma N
(2015)
A comprehensive laboratory study on the immersion freezing behavior of illite NX particles: a comparison of 17 ice nucleation measurement techniques
in Atmospheric Chemistry and Physics
Herbert RJ
(2015)
Sensitivity of liquid clouds to homogenous freezing parameterizations.
in Geophysical research letters
Herbert R
(2014)
Representing time-dependent freezing behaviour in immersion mode ice nucleation
in Atmospheric Chemistry and Physics
Description | A detailed model that calculates physical processes in clouds has been used to test whether barriers to the uptake of water vapour onto cloud droplets (described by the accomodation coefficient) makes any difference to the production and development of ice and precipitation particles. Values from the literature were used while waiting for laboratory results being produced in another part of the grant. It was found that the ice and precipitation production and growth was not sensitive to a wide range of values of the accomodation coefficient. |
Exploitation Route | Improved forecasts of all processes involving clouds and global climate models. The results will be used in numerical weather prediction models and global climate models. |
Sectors | Environment |