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Updated: May 13, 2026
13:27
Exploring the Effects of Atmospheric Forcings on Evaporation: Experimental Integration of the Atmospheric Boundary Layer and Shallow Subsurface
Published on: June 8, 2015
Worldwide data sets constrain the water vapor uptake coefficient in cloud formation
Tomi Raatikainen1, Athanasios Nenes, John H Seinfeld
1Earth & Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USA.
Summary
Cloud droplet formation relies on water vapor condensing on aerosols. This study finds rapid water uptake kinetics (condensation coefficient, αc > 0.1) are common, reducing uncertainty in climate models.
Area of Science:
- Atmospheric Science
- Cloud Physics
- Climate Science
Background:
- Cloud droplet formation is initiated by water vapor condensation on atmospheric aerosols.
- The rate of condensation is governed by the condensation coefficient (αc), a key factor in cloud microphysics.
- Previous estimates of αc for ambient aerosols have varied significantly, creating uncertainty in climate models.
Purpose of the Study:
- To constrain the value of the condensation coefficient (αc) for ambient aerosols using global cloud condensation nuclei data.
- To reduce uncertainty in climate change projections related to aerosol indirect forcing.
Main Methods:
- Analysis of 10 globally relevant datasets of cloud condensation nuclei (CCN).
- Statistical evaluation of CCN data to determine the prevalence of different water uptake kinetics.
Main Results:
- Rapid activation kinetics, with αc > 0.1, were found to be uniformly prevalent across the analyzed datasets.
- This indicates consistent and fast water vapor uptake by ambient aerosols.
Conclusions:
- The uncertainty in water vapor accommodation kinetics on cloud droplets is significantly less than previously estimated.
- This finding resolves a long-standing issue in cloud physics and improves the reliability of climate models.
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