Isotope constraints on moisture exchange processes from EUREC4A and ATOMIC
Abstract
The EUREC4A and ATOMIC field campaigns were undertaken in early 2020 near Barbados to advance our understanding of the role of shallow cumulus clouds in climate. The studies seek to evaluate how these low-level clouds respond to local moistening and drying within the context of varying large-scale conditions and mesoscale circulations. Fair-weather cumulus clouds form relatively close to the Earth's surface and are ubiquitous across the trade wind regions of the globe. These boundary layer clouds are part of an organized thermodynamic system which entails vertical mixing of water vapor between the boundary layer and the free troposphere. The balance between convective drying of the boundary layer by updrafts of moist air and downward exchange of dry air from the free troposphere and turbulent moistening by ocean and rainfall evaporation is a central element in the process chain of shallow cumulus cloud formation. General circulation models and large-eddy simulations show large disagreement in how sensitive shallow cumuli are to temperature perturbations. This is a problem that results in large uncertainties in projections of future climate, and an issue which prompts the need for new observational approaches to improve understanding of the underlying exchange processes.
EUREC4A-iso is an international coordinated program that leverages advances in measurement and modeling of the stable isotopic composition of water vapor to support the broader goals of EUREC4A. Stable isotopes of water vapor, precipitation and sea water were observed from aircraft, ship and the Barbados Cloud Observatory. Because the stable isotope ratios reflect the history of condensation and precipitation experienced by air masses, the measurements can be used to deduce moisture transport characteristics, including rapid dynamical exchanges associated with sub-cloud boundary layer activity, cold pools, convective detrainment, and large-scale advection. Combining the integrated isotopic measurements with model simulations provides an unprecedented opportunity to ensure that process-level simulations optimally represent the true shallow cumulus system. We summarize the breadth of the coordinated effort, and highlight examples of isotopic measurements from ship and aircraft profiles that illustrate the moistening and drying fluxes that regulate the humidity of the sub-cloud layer.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMA145.0008N
- Keywords:
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- 3311 Clouds and aerosols;
- ATMOSPHERIC PROCESSES;
- 3339 Ocean/atmosphere interactions;
- ATMOSPHERIC PROCESSES;
- 3373 Tropical dynamics;
- ATMOSPHERIC PROCESSES