Droplet accretion during rime growth and the formation of secondary ice crystals
作者:
Ya Yi Dong,
John Hallett,
期刊:
Quarterly Journal of the Royal Meteorological Society
(WILEY Available online 1989)
卷期:
Volume 115,
issue 485
页码: 127-142
ISSN:0035-9009
年代: 1989
DOI:10.1002/qj.49711548507
出版商: John Wiley&Sons, Ltd
数据来源: WILEY
摘要:
AbstractLaboratory experiments have been performed to study rime growth and its relation to secondary ice crystal production (the Hallett‐Mossop process). The rime was grown in a wind tunnel on a fixed vertical fibre 0.5 mm in diameter. The range of conditions extended from −1.0°C to −13°C in temperature, from 20cms−1to 200cms−1in air speed, and liquid water content up to 1.5 gm−3. The droplet size distributions were 5 to 25 μm and 8 to 50 μm, peaking at diameters of 9 and 22 μm respectively. Under conditions favourable for secondary ice production, the accreting droplets spread out on the ice surface; individual frozen droplets formed only at the lower temperatures. A separate experiment showed that supercooled water droplets froze as cones on a flat surface above −10.°C. At temperatures between −1. and −4.°C the spreading ratio of supercooled droplets on the basal surface of ice was less than on other faces, with lower molecular packing density. It is hypothesized that spreading takes place in a quasi‐liquid layer which is thinner on the basal surface. Splinter formation by pressure build‐up inside individual frozen droplets is therefore unlikely to be responsible for shatter; a new model is suggested in which thermal gradients give stresses leading to
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