Chemical characteristics of ice residual nuclei in anvil cirrus clouds: evidence for homogeneous and heterogeneous ice formation C. H. Twohy1 and M. R. Poellot2 1College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331-5503, USA 2Dept. of Atmospheric Sciences, University of North Dakota, Grand Forks, North Dakota, 58202-9006, USA
Abstract. A counterflow virtual impactor was used to collect residual particles larger
than about 0.1 μm diameter from anvil cirrus clouds generated over
Florida in the southern United States. A wide variety of particle types were
found. About one-third of the nuclei were salts, with varying amounts of
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, evidently
reflecting the transition from primarily heterogeneous to primarily
homogeneous freezing as a source of anvil ice.
Citation: Twohy, C. H. and Poellot, M. R.: Chemical characteristics of ice residual nuclei in anvil cirrus clouds: evidence for homogeneous and heterogeneous ice formation, Atmos. Chem. Phys., 5, 2289-2297, doi:10.5194/acp-5-2289-2005, 2005.