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 Oxford
Department Name: Oxford Physics
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'.
People |
ORCID iD |
Philip Stier (Principal Investigator) |
Publications
Booth B
(2018)
Comments on "Rethinking the Lower Bound on Aerosol Radiative Forcing"
in Journal of Climate
Carslaw K
(2017)
The Global Aerosol Synthesis and Science Project (GASSP): Measurements and Modeling to Reduce Uncertainty
in Bulletin of the American Meteorological Society
Ghan S
(2016)
Challenges in constraining anthropogenic aerosol effects on cloud radiative forcing using present-day spatiotemporal variability.
in Proceedings of the National Academy of Sciences of the United States of America
Gryspeerdt E
(2017)
Constraining the instantaneous aerosol influence on cloud albedo.
in Proceedings of the National Academy of Sciences of the United States of America
Koffi B
(2016)
Evaluation of the aerosol vertical distribution in global aerosol models through comparison against CALIOP measurements: AeroCom phase II results.
in Journal of geophysical research. Atmospheres : JGR
Lowe S
(2016)
Inverse modelling of Köhler theory - Part 1: A response surface analysis of CCN spectra with respect to surface-active organic species
in Atmospheric Chemistry and Physics
Malavelle F
(2017)
Strong constraints on aerosol-cloud interactions from volcanic eruptions
in Nature
Peters K
(2013)
Corrigendum to "Aerosol indirect effects from shipping emissions: sensitivity studies with the global aerosol-climate model ECHAM-HAM" published in Atmos. Chem. Phys., 12, 5985-6007, 2012
in Atmospheric Chemistry and Physics
Stier P (in Boucher Et Al.)
(2013)
Working Group I Contribution to the Intergovernmental Panel on Climate Change Firth Assessment Report
Description | In this work we have improved our understanding of how aerosols, small particles in the air, affect cloud droplet formation and ultimately climate. We have identified significant uncertainties in existing representations in the MetOffice Unified Model and further improved this model. |
Exploitation Route | The improvements to the MetOffice Unified Model have been implemented in the main model versions. |
Sectors | Environment Government Democracy and Justice |
URL | https://www2.physics.ox.ac.uk/research/climate-processes/projects/acid-pruf |
Description | Our work in ACID-PRUF focused on the representation of aerosol effects on clouds (a key uncertainty in climate change) in the UK climate model HadGEM. We have improved the aerosol activation scheme coupling the aerosol scheme UKCA to HadGEM. These model improvements are being included in the MetOffice Unified Model and also in the UK Earth System Model, participating in the next climate model inter-comparison project informing the Intergovernmental Panel on Climate Change. |
First Year Of Impact | 2013 |
Sector | Environment,Government, Democracy and Justice |
Impact Types | Societal |
Title | A novel inverse modelling framework to compare droplet activation parameterisations to cloud models |
Description | Undertaken by Dr. D. G. Partridge: Developed a new way to compare parametrization of cloud processes (e.g. droplet activation) to cloud models using Markov Chain Monte Carlo simulation. Framework is shown to work for cloud models but could could be applied to any field where it is necessary to identify weaknesses in parametrization of models. |
Type Of Material | Improvements to research infrastructure |
Provided To Others? | No |
Impact | This inverse tool allows for a much more robust assessment of the weaknesses inherent in any given parametrization by exploring the entire mufti-dimensional parameter space, differing from previous work which has typically undertaken parametrization-model inter-comparison by running the parametrization/model for a subset of the total parameter space using forward model simulations. By method is more efficient than brute force approaches (standard Monte Carlo) and quickly pinpoints input parameters that are causing the largest discrepancy between parametrization/model allowing for identification of key weaknesses and optimal improvement. |
Title | Updated aerosol activation scheme for UK HadGEM Earth System Model |
Description | ACID-PRUF work led to an improved aerosol activation scheme used in the UK HadGEM Earth System Model family, also used in the MetOffice Unified Model |
Type Of Material | Computer model/algorithm |
Year Produced | 2012 |
Provided To Others? | Yes |
Impact | Improved representation of aerosol-cloud interactions in current climate models |
URL | https://ukesm.ac.uk |
Description | A Parametric Response Surface Analysis of CCN Spectra |
Organisation | University of Manchester |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | Dr D. G. Partridge developed an new inverse modelling framework to compare CCN spectra measurements to models (Kohler theory) used to describe the hygroscopic growth of aerosols. A student, was supervised at Oxford University (Samuel Lowe) to undertake the work. Proof of concept of the framework with basic models was completed at Oxford University, and the advantages of using global parameter sensitivity methods to probe the uncertainty of the parameters describing the chemical properties of the aerosol was shown. |
Collaborator Contribution | Dr David Topping provided more advanced Kohler models which treat more robustly bulk to surface partitioning and surface tension depression affects for the inverse modelling framework to be applied to. Dr Topping provided assistance on how to initially run these models. |
Impact | A paper in preparation, to be submitted this year has been completed. This proof of concept study introduces such a framework by coupling a response surface analysis to traditional Kohler theory and synthetic measurement data. It is hoped this then acts as an exemplar for future studies using ambient data from aircraft campaigns of aerosol/cloud properties to help reduce the uncertainty in GCMs of the current representation of aerosol hygroscopic growth. The results highlight the importance of using robust statistical techniques that account for the entire range of atmospheric supersaturations when performing sensitivity analysis of Kohler models as well as the advantage as performing global sensitivity analysis over one-at-a-time studies (as performed previously in the literature). |
Start Year | 2013 |
Description | Aerosol Clouds Precipitation Climate initiative |
Organisation | Global Energy and Water Exchanges Project |
Country | United States |
Sector | Charity/Non Profit |
PI Contribution | I am on the steering committee of the international Aerosol Clouds Precipitation Climate initiative sponsored by iLeaps, GEWEX and IGAC. |
Collaborator Contribution | I am on the steering committee of the international Aerosol Clouds Precipitation Climate initiative sponsored by iLeaps, GEWEX and IGAC. |
Impact | Workshops and two intercomparison studies. |
Start Year | 2016 |
Description | Emulation of an adiabatic cloud parcel model |
Organisation | University of Leeds |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | By Dr D. G. Partridge Re-written adiabatic parcel model into a framework that can be coupled to a global climate model (GCM): This involved optimization of the model, changing the model framework so that the input/output matches that of the GCM, and simplifying the physics scheme. Provided model test data for emulation via Monte Carlo simulation of the modified model. |
Collaborator Contribution | By Jill Johnson Carried out the statistical emulation of the modified cloud parcel model. Dr D. G. Partridge will then insert the emulated version of the model into the GCM. |
Impact | The out comes to date from the study is that we have demonstrated that it is feasible to emulate adiabatic cloud parcel models. This is important as the method shows promise for application to even more complex cloud models in the future, thus improving climate model simulations of aerosol-cloud interactions. The emulated cloud parcel model is more efficient than current state of the art droplet activation parameterisations. |
Start Year | 2013 |
Description | GEWEX Aerosol Precipitation (GAP) initiative |
Organisation | Global Energy and Water Exchanges Project |
Country | United States |
Sector | Charity/Non Profit |
PI Contribution | I am co-chairing a new initiative on aerosol precipitation interactions as part of the international Global Energy and Water cycle Exchanges (GEWEX) project. |
Collaborator Contribution | Co-chairing new initiative. Currently writing white paper. |
Impact | GAP workshop in Oxford 2017 |
Start Year | 2016 |
Description | School science fair |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Schools |
Results and Impact | Participation in Science Fair at Wolvercote Primary School. |
Year(s) Of Engagement Activity | 2017 |