ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-5-3723-2005 Chemical characteristics of ice residual nuclei in anvil cirrus clouds: evidence for homogeneous and heterogeneous ice formation Twohy C. H. 1 Poellot M. R. 2 College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon, 97331-5503, USA Dept. of Atmospheric Sciences, University of North Dakota, Grand Forks, North Dakota, 58202-9006, USA 07 06 2005 5 3 3723 3745 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys-discuss.net/5/3723/2005/acpd-5-3723-2005.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/5/3723/2005/acpd-5-3723-2005.pdf

A counterflow virtual impactor was used to collect and analyze residual particles from anvil cirrus clouds generated over the state of Florida in the southern United States. A wide variety of particle types were found, including salts, crustal material, industrial metals, carbonaceous particles, and sulfates. Ambient aerosol particles near the anvils were found to have similar compositions, indicating that anvils act to redistribute particles over large regions of the atmosphere. Sampling occurred at a range of altitudes spanning temperatures from –21 to –56°C. More insoluble (crustal and metallic) particles typical of heterogeneous ice nuclei were found in ice crystals at warmer temperatures, while more soluble salts and sulfates were present at cold temperatures. At temperatures below about –35 to –40°C, soluble nuclei outnumbered insoluble nuclei, reflecting the transition from primarily heterogeneous to primarily homogeneous freezing as a source of anvil ice.