Session 6 Aerosol Impacts on Cirrus Clouds

Wednesday, 13 January 2016: 10:30 AM-12:00 PM
Room 357 ( New Orleans Ernest N. Morial Convention Center)
Host: Eighth Symposium on Aerosol–Cloud–Climate Interactions
Andreas Muhlbauer, JISAO/Univ. of Washington, Atmospheric Sciences, Seattle, WA
Trude Storelvmo, Yale University, Department of Geology and Geophysics, New Haven, CT and Eric Jensen, NASA/Ames Research Center, Earth Sciences Division, Moffett Field, CA

Aerosol effects on cirrus clouds are highly uncertain both in terms of magnitude and sign of the effective radiative forcing (IPCC, 2013). The key uncertainties of aerosol effects on cirrus clouds are tied to the limited understanding of the properties (e. g., size distribution, chemical composition) of ice nucleating aerosols in the upper troposphere as well as limited knowledge of the environmental conditions (e. g., ice supersaturation, vertical velocity) leading to the formation of cirrus clouds through homogeneous or heterogeneous ice nucleation and affecting their evolution and life cycle. Recent observational studies indicate that heterogeneous ice nucleation could be the dominant freezing mechanism operating in cirrus clouds because heterogeneous ice nucleation requires lower values of ice supersaturation whereas recent GCM simulations find aerosol effects on cirrus clouds smaller than previously estimated and of opposite sign. This session will discuss results from new observational and modeling studies relevant to aerosol effects on cirrus clouds, including laboratory studies on ice nucleation, observations from recent field campaigns (e. g., ATTREX, DC3, SEAC4RS, AIRTOSS, ML-CIRRUS), remote sensing (ground-based and space-borne), process-oriented modeling, and geoengineering of cirrus clouds. Specific topics of interest are (but not limited to) the formation, life cycle, microphysical and radiative properties of cirrus clouds as well as the physiochemical properties of ice nucleating aerosols in the upper troposphere.

11:00 AM
On the Susceptibility of Cold Tropical Cirrus to Ice Nuclei Abundance
Eric Jensen, NASA, Moffett Field, CA; and R. Ueyama, L. Pfister, T. V. Bui, R. P. Lawson, S. Woods, T. Thornberry, A. W. Rollins, G. S. Diskin, and M. A. Avery
11:15 AM
11:45 AM
Cirrus Clouds Radiative Effects in the Present Day Climate and in Response to Cirrus Seeding
Blaz Gasparini, ETH Zurich, Zurich, Switzerland; and T. Schaer, A. Meyer, and U. Lohmann
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