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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 113, D09206, doi:10.1029/2007JD009064, 2008

Ice nucleation and overseeding of ice in volcanic clouds

A. J. Durant

Department of Geological and Mining Engineering and Sciences, Michigan Technological University, Houghton, Michigan, USA
School of Geographical Sciences/Department of Earth Sciences, University of Bristol, Bristol, UK


R. A. Shaw

Department of Physics, Michigan Technological University, Houghton, Michigan, USA


W. I. Rose

Department of Geological and Mining Engineering and Sciences, Michigan Technological University, Houghton, Michigan, USA


Y. Mi

Department of Physics, Michigan Technological University, Houghton, Michigan, USA


G. G. J. Ernst

Mercator and Ortelius Research Centre for Eruption Dynamics, Geology Department, University of Ghent, Ghent, Belgium


Abstract

Water is the dominant component of volcanic gas emissions, and water phase transformations, including the formation of ice, can be significant in the dynamics of volcanic clouds. The effectiveness of volcanic ash particles as ice-forming nuclei (IN) is poorly understood and the sparse data that exist for volcanic ash IN have been interpreted in the context of meteorological, rather than volcanic clouds. In this study, single-particle freezing experiments were carried out to investigate the effect of ash particle composition and surface area on water drop freezing temperature. Measured freezing temperatures show only weak correlations with ash IN composition and surface area. Our measurements, together with a review of previous volcanic ash IN measurements, suggest that fine-ash particles (equivalent diameters between approximately 1 and 1000 μm) from the majority of volcanoes will exhibit an onset of freezing between ∼250–260 K. In the context of explosive eruptions where super-micron particles are plentiful, this result implies that volcanic clouds are IN-rich relative to meteorological clouds, which typically are IN-limited, and therefore should exhibit distinct microphysics. We can expect that such “overseeded” volcanic clouds will exhibit enhanced ice crystal concentrations and smaller average ice crystal size, relative to dynamically similar meteorological clouds, and that glaciation will tend to occur over a relatively narrow altitude range.

Received 11 June 2007; accepted 27 December 2007; published 15 May 2008.

Keywords: Volcanic clouds; volcanic ash; heterogeneous ice nucleation; ice nuclei.

Index Terms: 0320 Atmospheric Composition and Structure: Cloud physics and chemistry; 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801, 4906); 0370 Atmospheric Composition and Structure: Volcanic effects (8409); 3311 Atmospheric Processes: Clouds and aerosols; 3354 Atmospheric Processes: Precipitation (1854).

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Citation: Durant, A. J., R. A. Shaw, W. I. Rose, Y. Mi, and G. G. J. Ernst (2008), Ice nucleation and overseeding of ice in volcanic clouds, J. Geophys. Res., 113, D09206, doi:10.1029/2007JD009064.