Predicting global atmospheric ice nuclei distributions and their impacts on climate

Knowledge of cloud and precipitation formation processes remains incomplete, yet global precipitation is predominantly produced by clouds containing the ice phase. Ice first forms in clouds warmer than —36 °C on particles termed ice nuclei. We combine observations from field studies over a 14-year p...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2010-06, Vol.107 (25), p.11217-11222
Main Authors: DeMott, P. J., Prenni, A. J., Liu, X., Kreidenweis, S. M., Petters, M. D., Twohy, C. H., Richardson, M. S., Eidhammer, T., Rogers, D. C., Tolbert, Margaret A.
Format: Article
Language:English
Subjects:
AEROSOLS
Atmosphere
Atmospherics
BOUNDARY LAYERS
Climate
CLIMATE MODELS
Climate science
CLIMATES
CLOUDS
Computer Simulation
Databases, Factual
ENVIRONMENTAL SCIENCES
Ice
Ice nuclei
Liquids
Models, Theoretical
Nucleation
Parameterization
Particle Size
Physical Sciences
Physics - methods
PRECIPITATION
Reproducibility of Results
SENSITIVITY
Simulation
Temperature
Water - chemistry
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Summary:Knowledge of cloud and precipitation formation processes remains incomplete, yet global precipitation is predominantly produced by clouds containing the ice phase. Ice first forms in clouds warmer than —36 °C on particles termed ice nuclei. We combine observations from field studies over a 14-year period, from a variety of locations around the globe, to show that the concentrations of ice nuclei active in mixed-phase cloud conditions can be related to temperature and the number concentrations of particles larger than 0.5 μm in diameter. This new relationship reduces unexplained variability in ice nuclei concentrations at a given temperature from ∼10³ to less than a factor of 10, with the remaining variability apparently due to variations in aerosol chemical composition or other factors. When implemented in a global climate model, the new parameterization strongly alters cloud liquid and ice water distributions compared to the simple, temperature-only parameterizations currently widely used. The revised treatment indicates a global net cloud radiative forcing increase of ∼1 W m⁻² for each order of magnitude increase in ice nuclei concentrations, demonstrating the strong sensitivity of climate simulations to assumptions regarding the initiation of cloud glaciation.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.0910818107