HR: 0800h
AN: V41B-0594    [Abstracts]
TI: Ice in volcanic clouds and the implications for halogen transport to the stratosphere
AU: * Rose, W I
EM: raman@mtu.edu
AF: Michigan Technological University, Geological Eng & Sciences, Houghton, MI 49931, United States
AU: Durant, A J
EM: ajdurant@mtu.edu
AF: Michigan Technological University, Geological Eng & Sciences, Houghton, MI 49931, United States
AB: Observations of ice in volcanic clouds and new understanding of the role of ice in the fallout of fine ash has led to a view of volcanic clouds with abundant ice nuclei, a feature that contrasts with pure water "meteorological" clouds. Mixed phase meteorological clouds in the temperature range -10°C to -30°C contain few ice nuclei (IN). This is significant because the saturation vapor pressure of water is greater than the saturation vapor pressure of ice: the few ice crystals that form on scarce IN experience rapid growth, and can subsequently trigger the precipitation formation process (Bergeron process). Volcanic ash is a highly effective at initiating ice nucleation in the liquid phase at temperatures below about -20°C. Abundant ash ice nuclei lead to a cloud with high ice particle numbers and competition for water vapor in the cloud is high. Consequently, hydrometeor growth is slowed, particles remain small and precipitation is inhibited. Thus volcanic clouds are unlikely to experience early washout of Cl and other halide volcanic gases. Observations of complete ozone destruction in the 26 March 2000 Hekla volcanic cloud strongly support these assumptions. It may be possible to test this hypothesis more extensively by modifying the TOMS ozone algorithm to correct for SO₂ effects.
DE: 0370 Volcanic effects (8409)
DE: 8408 Volcano/climate interactions (1605, 3309)
DE: 8485 Remote sensing of volcanoes
DE: 8488 Volcanic hazards and risks
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting