气候变化领域集成服务门户(CCPortal): Estimating the 3D shape of volcanic ash to better understand sedimentation processes and improve atmospheric dispersion modelling

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DOI	10.1016/j.epsl.2020.116075
	Estimating the 3D shape of volcanic ash to better understand sedimentation processes and improve atmospheric dispersion modelling
	Saxby J.; Rust A.; Beckett F.; Cashman K.; Rodger H.
发表日期	2020
ISSN	0012821X
卷号	534
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
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
语种	英语
来源期刊	Earth and Planetary Science Letters
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/202878
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
推荐引用方式 GB/T 7714	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],2020,534.
APA	Saxby J.,Rust A.,Beckett F.,Cashman K.,&Rodger H..(2020).Estimating the 3D shape of volcanic ash to better understand sedimentation processes and improve atmospheric dispersion modelling.Earth and Planetary Science Letters,534.
MLA	Saxby J.,et al."Estimating the 3D shape of volcanic ash to better understand sedimentation processes and improve atmospheric dispersion modelling".Earth and Planetary Science Letters 534(2020).