DCMEX: The Deep Convective Microphysics EXperiment

The goal of the DCMEX project is to ultimately reduce the uncertainty in equilibrium climate sensitivity by improving the representation of microphysical processes in global models. It is the anvils produced by tropical systems in particular that contribute significantly to cloud feedbacks. The anvil radiative properties, lifetimes and areal extent are the key parameters. DCMEX will determine the extent to which these are influenced, or even controlled by the cloud microphysics including the habits, concentrations and sizes of the ice particles that make up the anvils, which in turn depend on the microphysical processes in the mixed-phase region of the cloud as well as those occurring in the anvil itself.

There has been a rapid advancement in the sophistication of global climate models in recent years. Yet some of the equations used to represent microphysics processes are based on a poorer physical understanding than desired. Gettelman and Sherwood (2016), for example pointed out that there is significant spread in determining cloud feedbacks across different global models due to uncertainties in microphysical processes, such as the treatment of ice processes. Ceppi et al. (2017) also concluded that accurately representing clouds and their radiative effects in global models remains challenging partly due to the difficulty in representing the cloud microphysics, as well as the interactions between microphysics and dynamics. The microphysical and radiative processes and dynamics that control the opacity and areal coverage of tropical anvil clouds are not well represented in global climate models.

DCMEX will make novel measurements of cloud microphysics in a real-world laboratory convective cloud system - both the mixed-phase region and anvil - as well as improve and test models and then apply them globally to tropical deep convective systems. We propose to deploy the FAAM aircraft along with two dual-polarisation, Doppler radars and airborne and ground-based aerosol measurements to study the deep convective clouds that form over an isolated mountain range in New Mexico. The focus will be on the formation of ice from ice nucleating particles (INPs) (primary ice production) and by processes involving existing ice particles (secondary ice particle production), such as collisions. These observations will be used to test and further refine the representation of ice processes in climate models. Our approach recognises that in order to represent cloud feedbacks accurately a model needs to represent the individual processes within the system accurately. Demonstrating that the model is able reproduce the observed evolution of these clouds is therefore a necessary condition for the accurate prediction of cloud feedbacks.

The research in DCMEX will have a robust pathway from a novel field campaign to more accurate estimates of climate sensitivity. This pathway is built with four integrated parts: new observations; the use of these observations and process modelling to derive new parametrisations; the use of existing in-situ data and satellite observations of anvils in tropical deep convection to validate the model; and use of the knowledge gained to improve and test the representation of microphysics in climate models. In particular, DCMEX will build on the experience of our groups in improving microphysical representation. A seamless suite of Met Office models will be used for convection- resolving simulations and global simulations with parametrised convection. Finally, simplified climate change (imposed warmer environment) experiments will be carried out to understand the role of the different microphysical processes on cloud feedbacks.

DCMEX will seek to work with scientists in Leeds that are involved with the Intergovernmental Panel on Climate Change (IPCC) for example those working on CONSTRAIN. The IPCC which provides rigorous and balanced scientific information to decision makers in governments throughout the world. It will help to reduce the uncertainty in climate sensitivity, and estimates of aerosol-radiative forcing by advancing our understanding of cloud processes and cloud feedbacks. The IPCC has acknowledged that cloud-climate feedbacks are now the greatest uncertainty in the modelling of future climate, and our research will lead to reduction in those uncertainties. Specifically, DCMEX will pave the way to reducing the uncertainty in climate sensitivity by advancing our understanding of cloud microphysical processes which are currently poorly constrained, and making improvements to parametrisations in global climate models. Improved planning for climate change will deliver enormous economic benefits to society as a whole. The absence of such plans could lead to losses of billions of pounds. Improved planning for climate change will deliver enormous economic and societal benefits and will greatly help with mitigation strategies.

Governments and businesses worldwide, and the general public will benefit greatly from this research because of the greater accuracy (reduced uncertainty) in climate model predictions that will result from this research.

Advancing understanding and modelling of cloud processes, particularly the ice process, is also very important for improving Numerical Weather Prediction models. This will have the effect of improving forecasts of heavy precipitation and other severe weather. We specifically target deep convection, which is associated with heavy rainfall and hailstorms. The field campaign will take place in New Mexico, but ice processes are important for extreme rainfall throughout the tropics and mid-latitudes. Social and economic benefits are likely to be significant as a result. For example, improved Met Office forecasting of flash flooding will benefit the insurance industry (who can take measures to avoid losses), flood forecasting agencies (e.g. Environment Agency, Scottish Environmental Protection Agency who can issue warnings) and ultimately, the wider public affected by flooding episodes. This could even save lives in extreme circumstances.

This proposal provides a unique opportunity to add urgently-needed measurements of aerosol and cloud processes. The Global Energy and Water Cycle Exchanges Project (GEWEX) Aerosols, Clouds, Precipitation and Climate (ACPC) programme will benefit from the data and modelling in DCMEX since the aerosols and convective cloud systems will be measured with state-of-the-art new instruments and an excellent combination of radars and aircraft.

There is a growing public awareness and sense of urgency about climate change. The youth climate strikes and the change of language used by The Guardian newspaper to "climate emergency, crisis or breakdown'' are some evidence of this urgency. DCMEX scientists will work with existing networks and platforms at NCAS and the Universities of Leeds and Manchester (e.g. The Climate Press podcast) to communicate the results of the research to schools and the general public.