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

Lead Research Organisation: University of Leeds
Department Name: School of Earth and Environment

Abstract

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.

The radiative properties of the trade-wind cumulus clouds that are ubiquitous over the tropical oceans have a major influence on the Earth's radiation budget. The response to global warming of these clouds is therefore critical for global mean cloud feedbacks. It is the differing response to warming that explains most of the spread of climate sensitivity in climate models. Hence, a better understanding is required of the mechanisms that control the low-level cloud fraction. The urgency of the research is made clear by the fact that the World Climate Research Programme endorses the EUREC4A field project which supports the Grand Challenge on Clouds, Circulation and Climate Sensitivity.

There is a clear need for EUREC4A-UK because the aerosol,
cloud and precipitation processes influence the macrophysical properties of the clouds in different
environments. For example, the vertical distribution of rain
can affect the concentration and size of cloud drops in the upper detrainment layers, which influ-
ences cloud radiative properties. The intensity of rain and evaporation of raindrops influences the
strength of gust fronts and hence secondary cloud-production. However, model calculations of the
rate of production of rain and hence the quantity of rain are uncertain due to the complex interactions
of aerosols, entrainment, turbulence and giant cloud condensation nuclei (GCCN). These processes
depend on the environment conditions, controlled by the large-scale dynamics. Equally, the aerosol-
cloud-precipitation processes can influence the larger-scale dynamics, for example through radiative
transfer. Indeed there are many interactions between processes on a range of scales that need to be
understood and represented in models.

Planned Impact

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.

Publications

10 25 50
 
Description Bjorn Stevens and his group in Germany 
Organisation Max Planck Society
Department Max Planck Institute for Meterology
Country Germany 
Sector Charity/Non Profit 
PI Contribution Data gathered by the BAS Twin Otter aircraft during the field campaign and the analysis of that data. The cloud physics data is of particular interest. Also contributions to the successful preparations of the field campaign.
Collaborator Contribution Bjorn Stevens and Sandrine Bony are responsible for EUREC4A. The partners provided platforms for the field campaign and the operation of the instruments on those platforms, as well as analysis of the data gathered.
Impact Successful preparation and execution of the EUREC4A field campaign.
Start Year 2019
 
Description Met Office involvement in EUREC4A 
Organisation Meteorological Office UK
Country United Kingdom 
Sector Academic/University 
PI Contribution Provision of BAS Twin Otter data gathered in the EUREC4A field campaign and analysis of data. Organisation of forecast meetings and logistics for the field campaign
Collaborator Contribution Staff time setting up model runs and providing output leading up to the field campaign and during it. Participation in WP work doing and helping with model runs and interpretation of model results. Comparisons with observations. Staff time during the workshop and testbed. Staff time as a mission scientist during the field campaign.
Impact Successful workshop and testbed. Successful preparations for the field campaign. Successful field campaign.
Start Year 2019
 
Description Sandrine Bony and her group in France 
Organisation National Center for Scientific Research (Centre National de la Recherche Scientifique CNRS)
Country France 
Sector Academic/University 
PI Contribution Provision of data from the BAS Twin Otter aircraft gathered during the field campaign and analysis of the data. The cloud physics data in particular is of great interest.
Collaborator Contribution Dr Bony is the PI of EUREC4A and as such is responsible along with Prof Bjorn Steven for making the project possible. Contributions of whole EUREC4A project, in particular data from the French aircraft gathered during the field campaign.
Impact Successful preparation and completion of the EUREC4A field campaign.
Start Year 2019
 
Description Caribbean Weather Forecasting Initiative Workshop I 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Study participants or study members
Results and Impact Through a partnership between the Caribbean Meteorological Organization (CMO) and the
EUREC4A-UK project, led by the University of Leeds, the Caribbean Weather Forecasting
Initiative has been leveraged to support the Severe Weather Forecast Programme (SWFP) in the
Eastern Caribbean. The workshops and forecast testbed support the SWFP by developing
collaboration practice among regional forecasters and helping forecasters to understand the
capabilities and limitations of high-resolution NWP models and global ensemble systems.
National Meteorological Services in the Caribbean have gained enhanced capability of
forecasters in understanding local weather, such as localized storms, through the training
workshop and forecast test-bed. The project supported capability development within the
Caribbean through forecasting activities linked to the field campaign and through lectures and
exercises on the underpinning science needed for model development.
Year(s) Of Engagement Activity 2019
URL http://www.cmo.org.tt/eurec4a.html
 
Description Caribbean Weather Forecasting Initiative Forecast Testbed 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Study participants or study members
Results and Impact During the testbed, the same forecasters that participated in the workshop held in 2019 worked in dispersed teams, collaborating
via the CMO-licensed web-conferencing system, to deliver weather forecasts to the scientists involved in the field campaign of the EUREC4A project. The scientists needed forecasts in order to plan their flights. The local expertise from these forecasters was an important part of the planning. The testbed participants evaluated the forecasts using information gathered during the project.
Year(s) Of Engagement Activity 2020
URL https://eurec4a.uk/forecast_testbed/