DCMEX -- Deep Convective Microphysics EXperiment

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The goal of the DCMEX project is to ultimately reduce the uncertainty in equilibrium climate sensi-tivity by improving the representation of microphysical processes in global models. It is the anvilsproduced by tropical systems in particular that contribute significantly to cloud feedbacks. The anvilradiative properties, lifetimes and areal extent are the key parameters. DCMEX will determine theextent to which these are influenced, or even controlled by the cloud microphysics including thehabits, concentrations and sizes of the ice particles that make up the anvils, which in turn dependon the microphysical processes in the mixed-phase region of the cloud as well as those occurring inthe anvil itself.There has been a rapid advancement in the sophistication of global climate models in recentyears. Yet some of the equations used to represent microphysics processes are based on a poorerphysical understanding than desired. Gettelman and Sherwood (2016), for example pointed outthat there is significant spread in determining cloud feedbacks across different global models dueto 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 modelsremains challenging partly due to the difficulty in representing the cloud microphysics, as well as theinteractions 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 modelsand then apply them globally to tropical deep convective systems. We propose to deploy the FAAMaircraft along with two dual-polarisation, Doppler radars and airborne and ground-based aerosolmeasurements to study the deep convective clouds that form over an isolated mountain range inNew Mexico. The focus will be on the formation of ice from ice nucleating particles (INPs) (primaryice 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 ofice 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 thereforea 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 accurateestimates 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 ofexisting in-situ data and satellite observations of anvils in tropical deep convection to validate themodel; and use of the knowledge gained to improve and test the representation of microphysicsin climate models. In particular, DCMEX will build on the experience of our groups in improvingmicrophysical representation. A seamless suite of Met Office models will be used for convection-resolving simulations and global simulations with parametrised convection. Finally, simplified climatechange (imposed warmer environment) experiments will be carried out to understand the role of thedifferent microphysical processes on cloud feedbacks.