Constraining marine boundary layer cloud properties in climate models: (CLOSURE)

Lead Research Organisation: University of Exeter
Department Name: Engineering Computer Science and Maths

Abstract

Concentrations of both greenhouse gases (GHG) and aerosols (tiny particles suspended in the atmosphere) have increased considerably since pre-industrial time. Whilst anthropogenic emissions of GHG warm the planet, aerosol emissions exert a significant, yet poorly quantified cooling that acts to offset a significant fraction of global warming from GHG. Despite decades of research, the Intergovernmental Panel on Climate Change Assessment Report continues to highlight the climate sensitivity and aerosol-cloud-interactions (ACI) as the two key uncertainties limiting our understanding of climate change. Improving model estimates of climate change sensitivity (global temperature change per unit climate forcing) to greenhouse gas emissions is primarily driven by inter-model differences how climate models represent the impacts of feedbacks between low-level clouds and the climate system as temperature increases. Reducing these inter-model differences is severely hampered by the accuracy by which low level marine boundary layer (MBL) clouds, key modulators of the net radiation budget, are represented in the Earth System Models (ESMs) we use to provide estimates of future climate scenarios. Due to computational limitations these ESMs cannot explicitly represent small-scale atmospheric processes key for the formation of MBL at the scale at which they occur in nature (down to the size of aerosols). Instead, atmospheric physical processes related to cloud formation have to be parameterised (a simplified form of the complex process). Creating simplified representations of complex cloud processes that occur over a wide range of temporal/spatial scales is a challenging undertaking for climate scientists. Uncertainties in these parameterisations propagates through to our ability to accurately represent MBL in ESMs.

The focus of this project will be to improve understanding of small-scale MBL processes by addressing current deficiencies in ESM parameterisations of cloud droplet formation, the direct microphysical link between aerosols and clouds. This will be achieved by using new modelling frameworks to capitalise on detailed flight measurements of MBL clouds from the NASA Earth Venture Suborbital mission called ACTIVATE (Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment). ACTIVATE represents a novel measurement campaign of unprecedented scope for understanding MBL clouds as it will involve the deployment of two aircraft with well-matched groundspeeds. This strategy will allow for co-location of radiative properties of clouds from an aircraft flying above the MBL with an aircraft performing in-situ aerosol and cloud measurements within the MBL. This will provide a unique dataset with which we can constrain both process-scale cloud models, and large-scale ESMs to improve current small-scale ACI parameterisations, and subsequently the accuracy by which MBL clouds are represented in ESMs. To reach these goals the CLOSURE will use a new modelling framework in which a computationally fast cloud model known as a cloud parcel model (CPM). has been embedded in an ESM for the first time. These types of cloud models can accurately simulate the growth of a population of aerosol particles into cloud droplets in an ascending parcel of air. This embedded CPM framework will crucially allow for a detailed investigation of ACI in ESMs against measurements from ACTIVATE by providing additional model information for evaluation, e.g. droplet spectra. Furthermore, it will provide an efficient and seamless integration of process knowledge gained at the process scale from offline simulation to the large-scale when embedded in the ESM. This will be used to provide better understanding on the role of key small-scale processes involved in ACI for the representation of MBL clouds. The resulting improved theoretical descriptions of MBL cloud processes will reduce current uncertainties in future climate scenarios estimates.

Publications

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Title Cloud Parcel Model: PARSEC 
Description We have rewritten an existing cloud parcel model (ICPM) and further developed its functionality and useability to create a new cloud parcel model (PARSEC) for use in the grant CLOSURE. 
Type Of Material Computer model/algorithm 
Year Produced 2023 
Provided To Others? No  
Impact The new model PARSEC has just been completed, and we are currently performing final stability testing of the model before making it available to other researchers via a GitHub repository. The new model has additional functionality and a new user interface for inputs/outputs to make it easier to use for the CLOSURE team and collaborators. The impacts will follow as part of the CLOSURE grant once we embed PARSEC into the UK Met Office Climate model. We also plan to create an interactive website that will allow anyone to run the model online an learn about cloud physics. We envisage that this will become a widely used teaching tool in the future once complete. 
 
Title Software package for processing aircraft observations 
Description We have developed a generic software package (in Python) which can be easily adapted to automatically process aircraft observations of aerosol and cloud microhysical properties from any aircraft research campaign. 
Type Of Material Data analysis technique 
Year Produced 2023 
Provided To Others? No  
Impact This package has only recently been completed and we are performing final testing. Once that is complete it will be made available to other researchers via GitHub. Impact: significant increase in efficiency by which we can process complex data from aircraft observations of aerosols and clouds for analysis and model evaluation. 
 
Description EPFL droplet activation parameterisations 
Organisation Swiss Federal Institute of Technology in Lausanne (EPFL)
Country Switzerland 
Sector Public 
PI Contribution Planning research visit of Prof Thanos Nenes at the University of Exeter for knowledge exchange on future development of droplet activation parameterisations.
Collaborator Contribution Prof Thanos Nenes has agreed to visit the University of Exeter for knowledge exchange on development of droplet activation parameterisations for climate models.
Impact Arranged a research visit for knowledge exchange and provided advice on strategies to speed up computation for droplet activation parameterisation to be used in the Met Office climate model.
Start Year 2023
 
Description NASA ACTIVATE aircraft observations 
Organisation National Aeronautics and Space Administration (NASA)
Department NASA Langley Research Centre
Country United States 
Sector Public 
PI Contribution Provision of observations from NASA ACTIVATE campaign: https://activate.larc.nasa.gov/?doing_wp_cron=1678714421.9450941085815429687500 Provision of technical support on instruments used during the measurement campaign. Provision of webinars providing an overview of the initial results from the measurement campaign.
Collaborator Contribution Analysisng measurements performed in campaign in preparation for evaluation of cloud and climate models. Ongoing.
Impact Developed a software package that can automate the processing of observations for ACTIVATE for comparison against a cloud model. Performed forward modelling closure study of 1 flight from the ACTIVATE measurements in preparation for performing inverse modelling simulations to a larger cohort of flights.
Start Year 2022
 
Description UK Met Office aircraft observation analysis 
Organisation Meteorological Office UK
Country United Kingdom 
Sector Academic/University 
PI Contribution To date we have developed a software package for processing measurements from aircraft observations of aerosols and clouds for efficient evaluation of cloud models. Contributions involve sharing strategies for processing the observations into the required format. Have demonstrated the new software package at two meetings at the UK Met Office where it was presented personally to the leads of the Cloud and Aerosol research group within Observation Based Research, as well as at a group meeting of the Cloud and Aerosol research group.
Collaborator Contribution UK Met Office partner has shared their existing processing scripts for aircraft data. This has led to improvements of our software package in some areas (and vice-versa to the UK Met Office). They have also provided expert advice via e-mail and during the in-person meetings on optimum strategies to process the aircraft observations.
Impact Development of a software package for automated analysis of observations of aerosol and cloud properties from aircraft observations for evaluation of models.
Start Year 2022
 
Description UK Met Office climate model simulation 
Organisation Meteorological Office UK
Country United Kingdom 
Sector Academic/University 
PI Contribution Started initial training process for PDRA in running the UM climate model in preparation for model development and evaluation.
Collaborator Contribution Implemented new droplet activation scheme into UKESM1 which is now being implemented into the UM vn13 as part of the CLOSURE grant.
Impact Identified version of UK Met Office climate model to implement new parameterisations. To date these parameterisations have been developed offline in preparation.
Start Year 2023