DCMEX -- Deep Convective Microphysics EXperiment

Lead Research Organisation: University of Leeds
Department Name: National Centre for Atmospheric Science


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 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.

Planned Impact

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.