HR: 1330h
AN: A22A-1055    [PDF]
TI: The Statistical Nature of Heterogeneous Ice Nucleation: Laboratory Measurements with Volcanic Ash
AU: Mi, Y
EM: ymi@mtu.edu
AF: Department of Physics, Michigan Tech, 1400 Townsend Drive, Houghton, MI 49931 United States
AU: * Shaw, R A
EM: rashaw@mtu.edu
AF: Department of Physics, Michigan Tech, 1400 Townsend Drive, Houghton, MI 49931 United States
AB: Cirrus cloud processes (e.g., lifetime and radiative properties) are sensitive to the competing effects of heterogeneous and homogeneous ice nucleation. Tropical cirrus also may be affected by perturbations to the background aerosol, for example due to large volcanic eruptions. To this end, we have devised a laboratory experiment for studying the mechanisms of heterogeneous ice nucleation, with specific attention given to ice formation on volcanogenic particles. The statistical nature of heterogeneous ice nucleation can yield clues about the \emph{physical mechanisms} responsible for ice formation. Using a laboratory system capable of measuring the freezing temperature for a single ice nucleus hundreds of times we have obtained detailed estimates of the probability density functions for freezing time (or temperature). We compare these pdf's to the `idealized' case of an inhomogeneous Poisson process based on the classical model of heterogeneous ice nucleation. In addition, we are able to perform SEM analysis of each ice nucleus and thereby estimate the influence of properties such as surface area and morphology on the ice nucleation process. The laboratory measurements have implications for ice formation in volcanic clouds and volcanically-influenced cirrus clouds, as well as for the broader phenomenon of heterogeneous liquid-solid nucleation.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0320 Cloud physics and chemistry
DE: 0370 Volcanic effects (8409)
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting