EUREC4A-UK: Elucidating the role of cloud-circulation coupling in climate

EUREC4A-UK is a programme of observational and modelling research which aims
to study the detailed aerosol and cloud processes in the life cycle of shallow trade
cumulus clouds and the two-way interactions between the cloud processes and the
large-scale dynamics. The different responses of these clouds to warming in global
climate models (GCM) explain most of the inter-model differences, yet the physics
of these responses remains poorly constrained. The programme is focussed on
the participation of UK scientists and the BAS Twin Otter aircraft in EUREC4A
(Elucidating the Role of Clouds-Circulation Coupling in Climate). EUREC4A is
a coordinated international campaign that aims to address the current lack of understanding of
the processes controlling the response of trade-wind cumulus clouds to changing environmental
conditions in a warmer climate. The goal of EUREC4A is to examine the interplay between the
clouds, atmospheric circulations and climate sensitivity. EUREC4A-UK will make a unique and self-
contained contribution to the international programme by: (i) providing observational facilities which
are needed as part of the coordinated field campaign; (ii) conducting and leading the analysis of
the aerosols, cloud microphysics and boundary-layer processes in the life cycle of shallow trade
cumulus clouds; (iii) placing the analysis in the context of the EUREC4A problems by modelling the
two-way interactions between the cloud processes and the large-scale dynamics; and (iv) applying
the results by testing the new convection scheme in the UM and using the improved model to determine
the dominant processes controlling the cloud fields. International partners will complement the re-
search with a focus on observing and modelling the macrophysical properties and the environment
of trade-cumulus clouds in order to determine: (i) what controls the convective mass flux, mesoscale
organization and depth of shallow-cumulus clouds; (ii) how the trade-cumulus cloud fraction varies
with turbulence, convective mixing and large-scale circulations; and (iii) the impact this variation has
on atmospheric radiation.

Governments and businesses world wide, 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. Specifically, EUREC4A will help to reduce the uncertainty in climate sensitivity, or estimates of aerosol-radiative forcing by advancing our understanding of cloud processes and their feedbacks. Improved planning for climate change will deliver major economic benefits. Advancing understanding and modelling of clouds and circulation in the trade-wind regions is also very important for improving Numerical Weather Prediction models.

The UK addition would also contribute to the goals of the NCAS-led project the North Atlantic Climate System Integrated Study (ACSIS). Furthermore, the Global Energy and Water Cycle Exchanges Project (GEWEX) Aerosols, Clouds, Precipitation and Climate (ACPC) programme want to include EUREC4A since the cloud systems and circulation will be measured so well. This proposal provides a unique opportunity to add urgently needed measurements of aerosol and cloud processes