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

EUREC4A-UK is a programme of observational and modelling research that is focussed around the participation of UK scientists and the BAS Twin Otter research aircraft to study sub-cloud coherent structures that occur in the boundary layer, aerosol and cumulus cloud processes, and the links to the larger scales (from Barbados to Africa) in the international project, EUREC4A (Elucidating the Role of Clouds-Circulation Coupling in Climate). The French-German led EUREC4A funded project aims to address the current lacking in understanding of the response of clouds to a changing climate, the urgency of which is evidenced by inclusion of this problem as a Grand Science Challenge of the World Climate Research Programme. The UK scientists and BAS Twin Otter have been invited to participate to uniquely provide observations and analysis of clouds and their environment that are necessary to understand and model this coupling in a changing climate.

The EUREC4A field campaign will take place between 20 January and 20 February 2020 in the lower Atlantic trades, over the ocean to the east of Barbados. It will involve several aircraft, including the German HALO (for upper-level sampling) and French ATR-42 aircraft, four research vessels, radars and lidars and other ground-based instruments on Barbados. The project will exploit new methods that have been developed for constraining the large-scale factors influencing cloudiness. Field operations will be coordinated with overpasses of several satellites: including the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), as well as a number of satellites from flagship space missions that are expected to be in orbit by the time of the campaign: e.g. ADM-Aeolus.

There is a missing component in EUREC4A, however. There is no plan to study the details of the sub-cloud structures and aerosols, cloud processes, dynamics involved in the life cycle of trade-wind cumulus clouds and the importance in climate models. EUREC4A-UK will fill this gap and provide new knowledge of these processes and allow both for the use of state-of-the-art parametrisations of convection and cloud processes to aid the understanding, but also to be challenged. The BAS Twin Otter aircraft will be integrated into the above project plan in coordination with the other aircraft and facilities.

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.