DOI: 10.1016/j.epsl.2020.116075
论文题名: Estimating the 3D shape of volcanic ash to better understand sedimentation processes and improve atmospheric dispersion modelling
作者: Saxby J. ; Rust A. ; Beckett F. ; Cashman K. ; Rodger H.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2020
卷: 534 语种: 英语
中文关键词: atmospheric dispersion
; morphology
; sedimentation
; tephra
; X-ray tomography
英文关键词: Computerized tomography
; Drag
; Morphology
; Particle size
; Sedimentation
; Surface roughness
; Volcanoes
; X rays
; Atmospheric dispersion
; Atmospheric dispersion modelling
; Atmospheric dispersion models
; Sedimentation process
; Small-scale surface roughness
; tephra
; X-ray computed tomography
; X-ray tomography
; Atmospheric movements
; atmospheric modeling
; sedimentation rate
; tephra
; tomography
; volcanic ash
; volcanic eruption
; X-ray analysis
英文摘要: The sedimentation rate of volcanic ash through the atmosphere influences its travel distance, with important implications for aviation and health. The fall velocity of a particle depends on its size and density, but also shape, and volcanic ash is not spherical. To capture the sedimentation of ash, atmospheric dispersion models use empirical drag equations calibrated using geometric shape descriptors. However, particle shape data are scarce and there is no standard method of shape measurement. In addition, shape measurements are not always available during an eruption, when dispersion models are used operationally to forecast ash hazard. We assess the variability in the shape of volcanic ash from Icelandic eruptions using X-ray computed tomography. To consider how good different drag equations and shape descriptors are at representing the sedimentation of volcanic ash we compare calculated fall velocities to measured fall velocities of volcanic ash in air in a settling column. We then suggest the best drag equations and shape descriptors for use in atmospheric dispersion models. We find that shape-dependent drag equations produce more accurate results than a spherical approximation. However, accurate drag calculations based on the shape descriptor sphericity, which is a function of surface area, require the imaging resolution to be within the range of 102 - 105 voxels per particle (where a voxel is a volumetric pixel) as surface area is sensitive to imaging resolution. We suggest that the large-scale form of the particle impacts sedimentation more than small-scale surface roughness. Shape descriptors based on ratios between principal axis lengths are more practical as they are less variable among particle size classes and much less sensitive to imaging resolution. Finally, we use particle shape data from this study and literature sources to make recommendations on default values for use with atmospheric dispersion models where no shape data are available. © 2020 Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/165256
Appears in Collections: 气候变化与战略
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作者单位: Dept. Earth Sciences, University of Bristol, Wills Memorial Building, Queen's Road, Bristol, BS8 1RJ, United Kingdom; Met Office, FitzRoy Road, Exeter, EX1 3PB, United Kingdom
Recommended Citation:
Saxby J.,Rust A.,Beckett F.,et al. Estimating the 3D shape of volcanic ash to better understand sedimentation processes and improve atmospheric dispersion modelling[J]. Earth and Planetary Science Letters,2020-01-01,534