A145-0008
Isotope constraints on moisture exchange processes from EUREC4A and ATOMIC
Monday, 14 December 2020
Poster
David Noone1, Franziska Aemisegger2, Adriana Raudzens Bailey3, Peter N Blossey4, Simon P de Szoeke5, Marina Duetsch6, Joseph Galewsky7, Dean Henze5, Sebastian A Los7, Estefania Quinones-Melendez8, Gilles P Reverdin9 and Leonie Villiger10, (1)University of Auckland, Department of Physics, Auckland, New Zealand, (2)ETH Zurich, Institute for Atmospheric and Climate Science, Zurich, Switzerland, (3)National Center for Atmospheric Research, Boulder, CO, United States, (4)University of Washington, Seattle, WA, United States, (5)Oregon State University, Corvallis, OR, United States, (6)University of Washington, Earth and Space Sciences, Seattle, WA, United States, (7)University of New Mexico, Albuquerque, NM, United States, (8)Oregon State University, College of Earth, Ocean and Atmospheric Sciences, Corvallis, OR, United States, (9)Sorbonne Université - CNRS/IRD/MNHN, LOCEAN, Paris, France, (10)ETH, Institute for Atmospheric and Climate Science, Zürich, Switzerland
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.
