Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
doi:10.5194/acp-2016-1062
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
08 Dec 2016
Review status
This discussion paper is under review for the journal Atmospheric Chemistry and Physics (ACP).
CALIPSO observations of the dependence of homo- and heterogeneous ice nucleation in cirrus clouds on latitude, season and surface condition
David L. Mitchell1, Anne Garnier2, Melody Avery3, and Ehsan Erfani4 1Desert Research Institute, Reno, Nevada, USA
2Science Systems and Applications, Inc., Hampton, Virginia, USA
3NASA Langley Research Center, Hampton, Virginia, USA
4George Mason University, Fairfax, Virginia, USA
Abstract. There are two fundamental mechanisms through which cirrus clouds form; homo- and heterogeneous ice nucleation (henceforth hom and het). The relative contribution of each mechanism to ice crystal production often determines the microphysical and radiative properties of a cirrus cloud. A new satellite remote sensing method is described in this study to estimate cirrus cloud ice particle number concentration and the relative contribution of hom and het to cirrus cloud formation as a function of altitude, latitude, season and surface type (e.g. land vs. ocean). This method uses co-located observations from the Infrared Imaging Radiometer (IIR) and from the CALIOP (Cloud and Aerosol Lidar with Orthogonal Polarization) lidar aboard the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) polar orbiting satellite, employing IIR channels at 10.6 μm and 12.05 μm. The method is applied here to single-layered clouds of visible optical depth between about 0.3 and 3. Two years of Version 3 data have been analyzed for the years 2008 and 2013, with each season characterized in terms of 532 nm cirrus cloud centroid altitude and temperature, the cirrus cloud ice particle number concentration, effective diameter, layer-average ice water content and visible optical depth. Using a conservative criterion for hom cirrus, on average, the sampled cirrus clouds formed through hom occur about 43 % of the time in the Arctic and 50 % of the time in the Antarctic, and during winter at mid-latitudes in the Northern Hemisphere, hom cirrus occur 37 % of the time. Elsewhere (and during other seasons in the Northern Hemisphere mid-latitudes), this hom cirrus fraction is lower. Processes that could potentially explain these observations are discussed, as well as the potential relevancy of these results to ice nucleation studies, climate modeling and jet-stream dynamics.

Citation: Mitchell, D. L., Garnier, A., Avery, M., and Erfani, E.: CALIPSO observations of the dependence of homo- and heterogeneous ice nucleation in cirrus clouds on latitude, season and surface condition, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-1062, in review, 2016.
David L. Mitchell et al.
David L. Mitchell et al.
David L. Mitchell et al.

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Short summary
Although the main objective of our DOE/Atmospheric Systems Research project was to use aircraft measurements to determine the formation (i.e. ice nucleation) mechanism of cirrus clouds, it soon became evident that the formation mechanism will depend on latitude, season and surface topography. A new satellite remote sensing method was developed to discover this dependency, which shows that roughly half or more of the cirrus clouds at high latitudes form through homogeneous ice nucleation.
Although the main objective of our DOE/Atmospheric Systems Research project was to use aircraft...
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