Aerosol-Cloud Interactions - A Directed Programme to Reduce Uncertainty in Forcing through a Targeted Laboratory and Modelling Programme

Lead Research Organisation: University of Manchester
Department Name: Earth Atmospheric and Env Sciences

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

10 25 50

publication icon
Connolly PJ (2014) Factors determining the most efficient spray distribution for marine cloud brightening. in Philosophical transactions. Series A, Mathematical, physical, and engineering sciences

publication icon
Davies JF (2012) Bulk, surface, and gas-phase limited water transport in aerosol. in The journal of physical chemistry. A

 
Description The Aerosol-Cloud Interactions - A Directed Programme to Reduce Uncertainty in Forcing (ACID-PRUF) project comprised a series of laboratory and numerical modelling activities at a range of scales aiming to increase our quantitative understanding of the importance of aerosol particles on climate through the formation of clouds.

Measurement results:

i) Large-scale experiments, uniquely coupling aerosol and cloud chambers, were conducted with international collaborators, enabling investigation of warm and cold cloud formation on mixtures of man-made and natural particles: we studied the formation of particles from man-made pollutants, naturally-emitted "ingredients" and mixtures of the two in an aerosol chamber. We injected these particles into a cloud chamber to reproduce the conditions for "warm" (low level) and "cold" (higher) cloud formation. The way they formed clouds and their properties has enabled us to understand the differences between clouds formed under clean and polluted conditions and the effect these clouds will likely have on reflecting sunlight and affecting climate.

ii) Published water uptake and molecular diffusion rate measurements by consortium partners allow direct interpretation of warm cloud formation for model inclusion: to accurately calculate the formation of cloud droplets and hence to accurately reproduce clouds in weather and climate models, these physical constants (which determine the rate of condensation of water) must be known. We accurately made these measurements and hence will be able to better describe water condensation and warm cloud formation.

iii) An active ingredient enabling mineral dust to form ice has been identified, enabling process interpretation: it is important to know how many ice crystals there are in "cold" (upper level) clouds to be able to predict how much sunlight they reflect. In order to know how many ice crystals are formed, it is important to know how efficiently the particles that get sufficiently high will act as seeds for ice formation. We therefore need to identify the important ingredients of atmospheric dust that will act as efficient ice seeds.

Measurement Highlights:

Measurements of key fundamental physical and chemical properties related to both liquid droplets and ice crystals have been made. To better represent real atmospheric droplet behaviour, the evaporation coefficient of water from aqueous droplets with mixed organic film coatings has been quantitatively related to the single component film evaporation coefficients, in turn determined by the aqueous solubility of the film species. Measured water uptake by aerosol particles has been shown to depend on both the vapour pressure and the solubility of the compounds of which they are made. This supports the recent high profile theoretical calculations of the effects of semi-volatile vapours. Contact nucleation of ice on dust was investigated using a new experimental setup (EDB) that was extensively tested on pollen and water droplets. Immersion mode ice chamber studies of minerals suggest that ice nucleation efficiency may be underestimated at high temperatures by other techniques with implications for explaining high temperature ice nucleation in models. This continued rapid progress is allowing significant advances to be made in quantitative understanding of cloud processes.

Modelling results:

i) Results in press show uncertainty reduction in cirrus ice crystal concentrations from ice nucleation by several orders of magnitude indicating that elevated measured concentrations may not be real, possibly explaining high measured supersaturation.

ii) Inverse modelling has reduced discrepancy between field and laboratory derived water uptake and model and

iii) aircraft observations have been used to parameterise fine-scale updraft variability for weather models.

iv) Work modelling effects on clouds of condensing organic vapours has been published and

v) design of global and cloud model experiments for the large-scale uncertainty analysis is complete.

Process Model Highlights:
Intense precipitation from deep convective clouds has been studied using new modelling techniques enabling combined effects of all important model uncertainties to be studied using a small number of simulations. These clouds are responsible for a large fraction of the UK's extreme rainfall. The most important cloud processes that determine the intensity of rain are found to be related to the way that ice particles and droplets interact in the cloud. In our studies, under normal continental aerosol conditions the maximum rain rate varied between less than 100 mm/hr to nearly 200 mm/hr, with three-quarters of the uncertainty attributable to the rate at which graupel particles (ice pellets) and droplets combine to form larger particles. These rain intensities are sufficient to cause flooding in localised areas, and are typical of some intense rain events over the UK. Aerosols contribute a maximum of about 20% of the uncertainty in maximum precipitation rate, except at very high concentrations of aerosols typical of smoke plumes. Accurate simulation of intense precipitation from deep convective clouds largely depends on poorly defined microphysical processes. Our results suggest that the influence of aerosols is substantially less than other more important uncertainties and our ability to predict cloud response to changes in aerosols (from air pollution) will very much depend on how well we can accurately specify the complex cloud microphysical processes going on in the cloud.

Large-Scale Model Highlights:
Our studies have led to improved capability to describe clouds in large-scale models. Bridging the gap between the cloud scale and the global scale to capture complex aerosol cloud interactions (ACI), use of high-resolution large-scale models such as those from operational numerical weather prediction has been explored. Malavelle et al. (2014) describes a way to include missing subgrid scale (or unresolved) contribution to vertical velocity variability in such models operating with horizontal grid sizes up to ~2 km and highlights the importance of representing the subgrid scale updraft in kilometer-scale simulations of ACI. The high profile finding that semi-volatile organic vapours affect the efficiency of cloud condensation nuclei (CCN) with potential large radiative effect in specific geographical locations has been efficiently and accurately parameterised for use in large-scale models (Connolly et al., 2014). We have found that the best CCN activation parameterisations tend to overestimate the number of cloud drops. Simpson et al. (2014) points out reasons for this discrepancy and areas for parameterisation improvements. The research from ACID-PRUF has continued to lead to high profile findings and publications, most recently leading to strong constraint on the aerosol-cloud interactions from volcanic eruptions, published in Nature in 2017 (Malavelle et al., 2017)
Exploitation Route The primary external impact that will continue to occur was achieved through the complete integration of the Met Office in the work programme activities as project partners. Met Office personnel were involved directly in the CRM work package 3 and in the activity linking the cloud resolving and large-scale modelling (investigating sub-grid scale vertical velocity parameterisation). The improved physical processes incorporated in the Hadley Centre's Unified model suite including numerical weather prediction (NWP) and global climate models (HadGEM) allows assessment of impacts of improved parameterisations for both short timescale operational weather forecasting and longer timescale climate scenarios.

Development of the parameterisations via the UKCA chemistry and aerosol module will lead to climate projections with aerosol-cloud processes traceable from the laboratory studies through the cloud resolving model studies to the regional and global scales. Implementation in such models will allow both the impact of improved indirect radiative forcing estimates and the impacts upon weather and climate via complex feedback mechanisms.

Policy will be directly influenced by improved climate projections and it is necessary to engage policymakers within the ACID_PRUF programme. The Department of Energy and Climate Change (DECC) are direct potential beneficiaries. A DECC representative attended programme meetings ensuring that the science directly feeds through to policymaking. The Department of the Environment, Food and Regional Affairs (Defra) will also benefit from the increased realism associated with the improved parameterisations in global and regional projections of climate change. Such improvements will inform policy.

Programme Delivery: All work was presented at the annual programme meeting with participation of the international advisor. Draw-through from measurements to models ensured the programme met its target to reduce uncertainty in radiative forcing resulting from aerosol-cloud interactions - the exploitation activities will continue beyond the programme.
Sectors Environment

URL http://www.cas.manchester.ac.uk/resprojects/acidpruf/
 
Description The findings related to improved treatments of aerosol and cloud processes continue to make their way through into the Met Office models. They are being adopted in the appropriate levels of operational weather forecating and ESM models through the Met Office's standard procedures on the timescale dictated by these processes. The first year of materialisation has been selected as 2014, though the process is ongoing. Since the findings relate to improved weather and climate forecasting, they are of public service and societal benefit. Since the forecasts are used in a range of the Met Office products, they will eventually influence multiple sectors, though the first generation influence is on the Environment sector and so has been selected.
First Year Of Impact 2014
Sector Environment
Impact Types Societal

 
Description European network for studying atmospheric processes in simulation chambers 
Organisation Centre for Environmental Studies of the Mediterranean (Centro de Estudios Ambientales del Mediterráneo)
Country Spain 
Sector Public 
PI Contribution Operation of the Manchester photochemical chamber facility and participation in joint experimental programme in the European network. Leading the development of modelling capability in support of the network.
Collaborator Contribution Integration of a wide range of atmospheric simulation chamber facilities, hosting a joint database for experimental results, coordinating scientific goals and infrastructural support activities and serving as a focus for delivery of large-scale International collaborations in atmospheric science.
Impact Very many peer-reviewed outputs facilitated by being part of the chamber network.
Start Year 2009
 
Description European network for studying atmospheric processes in simulation chambers 
Organisation Julich Research Centre
Country Germany 
Sector Public 
PI Contribution Operation of the Manchester photochemical chamber facility and participation in joint experimental programme in the European network. Leading the development of modelling capability in support of the network.
Collaborator Contribution Integration of a wide range of atmospheric simulation chamber facilities, hosting a joint database for experimental results, coordinating scientific goals and infrastructural support activities and serving as a focus for delivery of large-scale International collaborations in atmospheric science.
Impact Very many peer-reviewed outputs facilitated by being part of the chamber network.
Start Year 2009
 
Description European network for studying atmospheric processes in simulation chambers 
Organisation Karlsruhe Institute of Technology
Country Germany 
Sector Academic/University 
PI Contribution Operation of the Manchester photochemical chamber facility and participation in joint experimental programme in the European network. Leading the development of modelling capability in support of the network.
Collaborator Contribution Integration of a wide range of atmospheric simulation chamber facilities, hosting a joint database for experimental results, coordinating scientific goals and infrastructural support activities and serving as a focus for delivery of large-scale International collaborations in atmospheric science.
Impact Very many peer-reviewed outputs facilitated by being part of the chamber network.
Start Year 2009
 
Description European network for studying atmospheric processes in simulation chambers 
Organisation Leibniz Association
Department Leibniz Institute for Tropospheric Research
Country Germany 
Sector Charity/Non Profit 
PI Contribution Operation of the Manchester photochemical chamber facility and participation in joint experimental programme in the European network. Leading the development of modelling capability in support of the network.
Collaborator Contribution Integration of a wide range of atmospheric simulation chamber facilities, hosting a joint database for experimental results, coordinating scientific goals and infrastructural support activities and serving as a focus for delivery of large-scale International collaborations in atmospheric science.
Impact Very many peer-reviewed outputs facilitated by being part of the chamber network.
Start Year 2009
 
Description European network for studying atmospheric processes in simulation chambers 
Organisation National Center for Scientific Research (Centre National de la Recherche Scientifique CNRS)
Country France 
Sector Public 
PI Contribution Operation of the Manchester photochemical chamber facility and participation in joint experimental programme in the European network. Leading the development of modelling capability in support of the network.
Collaborator Contribution Integration of a wide range of atmospheric simulation chamber facilities, hosting a joint database for experimental results, coordinating scientific goals and infrastructural support activities and serving as a focus for delivery of large-scale International collaborations in atmospheric science.
Impact Very many peer-reviewed outputs facilitated by being part of the chamber network.
Start Year 2009
 
Description European network for studying atmospheric processes in simulation chambers 
Organisation Paul Scherrer Institute
Country Switzerland 
Sector Public 
PI Contribution Operation of the Manchester photochemical chamber facility and participation in joint experimental programme in the European network. Leading the development of modelling capability in support of the network.
Collaborator Contribution Integration of a wide range of atmospheric simulation chamber facilities, hosting a joint database for experimental results, coordinating scientific goals and infrastructural support activities and serving as a focus for delivery of large-scale International collaborations in atmospheric science.
Impact Very many peer-reviewed outputs facilitated by being part of the chamber network.
Start Year 2009
 
Description European network for studying atmospheric processes in simulation chambers 
Organisation SP Sveriges Tekniska Forskningsinstitut AB
Country Sweden 
Sector Private 
PI Contribution Operation of the Manchester photochemical chamber facility and participation in joint experimental programme in the European network. Leading the development of modelling capability in support of the network.
Collaborator Contribution Integration of a wide range of atmospheric simulation chamber facilities, hosting a joint database for experimental results, coordinating scientific goals and infrastructural support activities and serving as a focus for delivery of large-scale International collaborations in atmospheric science.
Impact Very many peer-reviewed outputs facilitated by being part of the chamber network.
Start Year 2009
 
Description European network for studying atmospheric processes in simulation chambers 
Organisation University College Cork
Country Ireland 
Sector Academic/University 
PI Contribution Operation of the Manchester photochemical chamber facility and participation in joint experimental programme in the European network. Leading the development of modelling capability in support of the network.
Collaborator Contribution Integration of a wide range of atmospheric simulation chamber facilities, hosting a joint database for experimental results, coordinating scientific goals and infrastructural support activities and serving as a focus for delivery of large-scale International collaborations in atmospheric science.
Impact Very many peer-reviewed outputs facilitated by being part of the chamber network.
Start Year 2009
 
Description European network for studying atmospheric processes in simulation chambers 
Organisation University of Bayreuth
Country Germany 
Sector Academic/University 
PI Contribution Operation of the Manchester photochemical chamber facility and participation in joint experimental programme in the European network. Leading the development of modelling capability in support of the network.
Collaborator Contribution Integration of a wide range of atmospheric simulation chamber facilities, hosting a joint database for experimental results, coordinating scientific goals and infrastructural support activities and serving as a focus for delivery of large-scale International collaborations in atmospheric science.
Impact Very many peer-reviewed outputs facilitated by being part of the chamber network.
Start Year 2009
 
Description European network for studying atmospheric processes in simulation chambers 
Organisation University of Copenhagen
Country Denmark 
Sector Academic/University 
PI Contribution Operation of the Manchester photochemical chamber facility and participation in joint experimental programme in the European network. Leading the development of modelling capability in support of the network.
Collaborator Contribution Integration of a wide range of atmospheric simulation chamber facilities, hosting a joint database for experimental results, coordinating scientific goals and infrastructural support activities and serving as a focus for delivery of large-scale International collaborations in atmospheric science.
Impact Very many peer-reviewed outputs facilitated by being part of the chamber network.
Start Year 2009
 
Description European network for studying atmospheric processes in simulation chambers 
Organisation University of Leeds
Country United Kingdom 
Sector Academic/University 
PI Contribution Operation of the Manchester photochemical chamber facility and participation in joint experimental programme in the European network. Leading the development of modelling capability in support of the network.
Collaborator Contribution Integration of a wide range of atmospheric simulation chamber facilities, hosting a joint database for experimental results, coordinating scientific goals and infrastructural support activities and serving as a focus for delivery of large-scale International collaborations in atmospheric science.
Impact Very many peer-reviewed outputs facilitated by being part of the chamber network.
Start Year 2009
 
Description European network for studying atmospheric processes in simulation chambers 
Organisation University of Paris XII: Paris-Val-de-Marne
Country France 
Sector Academic/University 
PI Contribution Operation of the Manchester photochemical chamber facility and participation in joint experimental programme in the European network. Leading the development of modelling capability in support of the network.
Collaborator Contribution Integration of a wide range of atmospheric simulation chamber facilities, hosting a joint database for experimental results, coordinating scientific goals and infrastructural support activities and serving as a focus for delivery of large-scale International collaborations in atmospheric science.
Impact Very many peer-reviewed outputs facilitated by being part of the chamber network.
Start Year 2009
 
Description European network for studying atmospheric processes in simulation chambers 
Organisation University of Wuppertal
Country Germany 
Sector Academic/University 
PI Contribution Operation of the Manchester photochemical chamber facility and participation in joint experimental programme in the European network. Leading the development of modelling capability in support of the network.
Collaborator Contribution Integration of a wide range of atmospheric simulation chamber facilities, hosting a joint database for experimental results, coordinating scientific goals and infrastructural support activities and serving as a focus for delivery of large-scale International collaborations in atmospheric science.
Impact Very many peer-reviewed outputs facilitated by being part of the chamber network.
Start Year 2009
 
Description National collaboration to reduce climate uncertainty resulting from aerosol-cloud interaction 
Organisation Meteorological Office UK
Country United Kingdom 
Sector Public 
PI Contribution Coordinator of major consortium investigating aerosol-cloud interactions in the climate system, informing climate models through systematic scale-up from detailed laboratory process studies.
Collaborator Contribution Extensive active participation in the consortium.
Impact Very many publications including Nature and Nature Geosciences. Ongoing extensive publication plan.
Start Year 2012
 
Description National collaboration to reduce climate uncertainty resulting from aerosol-cloud interaction 
Organisation University of Bristol
Country United Kingdom 
Sector Academic/University 
PI Contribution Coordinator of major consortium investigating aerosol-cloud interactions in the climate system, informing climate models through systematic scale-up from detailed laboratory process studies.
Collaborator Contribution Extensive active participation in the consortium.
Impact Very many publications including Nature and Nature Geosciences. Ongoing extensive publication plan.
Start Year 2012
 
Description National collaboration to reduce climate uncertainty resulting from aerosol-cloud interaction 
Organisation University of Cambridge
Country United Kingdom 
Sector Academic/University 
PI Contribution Coordinator of major consortium investigating aerosol-cloud interactions in the climate system, informing climate models through systematic scale-up from detailed laboratory process studies.
Collaborator Contribution Extensive active participation in the consortium.
Impact Very many publications including Nature and Nature Geosciences. Ongoing extensive publication plan.
Start Year 2012
 
Description National collaboration to reduce climate uncertainty resulting from aerosol-cloud interaction 
Organisation University of Exeter
Country United Kingdom 
Sector Academic/University 
PI Contribution Coordinator of major consortium investigating aerosol-cloud interactions in the climate system, informing climate models through systematic scale-up from detailed laboratory process studies.
Collaborator Contribution Extensive active participation in the consortium.
Impact Very many publications including Nature and Nature Geosciences. Ongoing extensive publication plan.
Start Year 2012
 
Description National collaboration to reduce climate uncertainty resulting from aerosol-cloud interaction 
Organisation University of Hertfordshire
Country United Kingdom 
Sector Academic/University 
PI Contribution Coordinator of major consortium investigating aerosol-cloud interactions in the climate system, informing climate models through systematic scale-up from detailed laboratory process studies.
Collaborator Contribution Extensive active participation in the consortium.
Impact Very many publications including Nature and Nature Geosciences. Ongoing extensive publication plan.
Start Year 2012
 
Description National collaboration to reduce climate uncertainty resulting from aerosol-cloud interaction 
Organisation University of Leeds
Country United Kingdom 
Sector Academic/University 
PI Contribution Coordinator of major consortium investigating aerosol-cloud interactions in the climate system, informing climate models through systematic scale-up from detailed laboratory process studies.
Collaborator Contribution Extensive active participation in the consortium.
Impact Very many publications including Nature and Nature Geosciences. Ongoing extensive publication plan.
Start Year 2012
 
Description National collaboration to reduce climate uncertainty resulting from aerosol-cloud interaction 
Organisation University of Oxford
Country United Kingdom 
Sector Academic/University 
PI Contribution Coordinator of major consortium investigating aerosol-cloud interactions in the climate system, informing climate models through systematic scale-up from detailed laboratory process studies.
Collaborator Contribution Extensive active participation in the consortium.
Impact Very many publications including Nature and Nature Geosciences. Ongoing extensive publication plan.
Start Year 2012
 
Description National collaboration to reduce climate uncertainty resulting from aerosol-cloud interaction 
Organisation University of York
Country United Kingdom 
Sector Academic/University 
PI Contribution Coordinator of major consortium investigating aerosol-cloud interactions in the climate system, informing climate models through systematic scale-up from detailed laboratory process studies.
Collaborator Contribution Extensive active participation in the consortium.
Impact Very many publications including Nature and Nature Geosciences. Ongoing extensive publication plan.
Start Year 2012