Predicting global atmospheric ice nuclei distributions and their impacts on climate

TitlePredicting global atmospheric ice nuclei distributions and their impacts on climate
Publication TypeJournal Article
Year of Publication2010
AuthorsDeMott, P. J., A. J. Prenni, X. Liu, S. M. Kreidenweis, M. D. Petters, C. H. Twohy, M. S. Richardson, T. Eidhammer, and D. C. Rogers
JournalProceedings of the National Academy of Sciences of the United States of America
Pagination11217-11222
Keywordsaerosol indirect effects climate forcing ice nucleation MICROWAVE IMAGER SSM/I MIXED-PHASE CLOUDS AIRBORNE MEASUREMENTS NUCLEATING AEROSOLS LIQUID WATER MODEL DUST PARTICLES PARAMETERIZATION MICROPHYSICS
Abstract

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 degrees 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 mu m in diameter. This new relationship reduces unexplained variability in ice nuclei concentrations at a given temperature from similar to 10(3) 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 similar to 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.