气候变化领域集成服务门户(CCPortal): Rapid ice aggregation process revealed through triple-wavelength Doppler spectrum radar analysis

CCPortal

DOI	10.5194/acp-19-5753-2019
	Rapid ice aggregation process revealed through triple-wavelength Doppler spectrum radar analysis
	Barrett A.I.; Westbrook C.D.; Nicol J.C.; Stein T.H.M.
发表日期	2019
ISSN	16807316
起始页码	5753
结束页码	5769
卷号	19 期号:8
英文摘要	We have identified a region of an ice cloud where a sharp transition of dual-wavelength ratio occurs at a fixed height for longer than 20 min. In this paper we provide evidence that rapid aggregation of ice particles occurred in this region, creating large particles. This evidence comes from triple-wavelength Doppler spectrum radar data that were fortuitously being collected. Through quantitative comparison of the Doppler spectra from the three radars we are able to estimate the ice particle size distribution (of particles larger than 0.75 mm) at different heights in the cloud. This allows us to investigate the evolution of the ice particle size distribution and determine whether the evolution is consistent with aggregation, riming or vapour deposition. The newly developed method allows us to isolate the signal from the larger (non-Rayleigh scattering) particles in the distribution. Therefore, a particle size distribution retrieval is possible in areas of the cloud where the dual-wavelength ratio method would fail because the bulk dual-wavelength ratio value is too close to zero. The ice particles grow rapidly from a maximum size of 0.75 to 5mm while falling less than 500m in under 10 min. This rapid growth is shown to agree well with theoretical estimates of aggregation, with aggregation efficiency being approximately 0.7, and is inconsistent with other growth processes, e.g. growth by vapour deposition or riming. The aggregation occurs in the middle of the cloud and is not present throughout the entire lifetime of the cloud. However, the layer of rapid aggregation is very well defined at a constant height, where the temperature is 15-C and lasts for at least 20 min (approximate horizontal distance: 24 km). Immediately above this layer, the radar Doppler spectrum is bimodal, which signals the formation of new small ice particles at that height.We suggest that these newly formed particles, at approximately-15-C, grow dendritic arms, enabling them to easily interlock and accelerate the aggregation process. The large estimated aggregation efficiency in this cloud is consistent with recent laboratory studies for dendrites at this temperature. © Author(s) 2019.
语种	英语
scopus关键词	aggregation; cloud; Doppler radar; ice cover; particle size; size distribution; wavelength
来源期刊	Atmospheric Chemistry and Physics
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/144447
作者单位	Department of Meteorology, University of Reading, Reading, RG6 6BB, United Kingdom; Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology, Karlsruhe, 76131, Germany
推荐引用方式 GB/T 7714	Barrett A.I.,Westbrook C.D.,Nicol J.C.,et al. Rapid ice aggregation process revealed through triple-wavelength Doppler spectrum radar analysis[J],2019,19(8).
APA	Barrett A.I.,Westbrook C.D.,Nicol J.C.,&Stein T.H.M..(2019).Rapid ice aggregation process revealed through triple-wavelength Doppler spectrum radar analysis.Atmospheric Chemistry and Physics,19(8).
MLA	Barrett A.I.,et al."Rapid ice aggregation process revealed through triple-wavelength Doppler spectrum radar analysis".Atmospheric Chemistry and Physics 19.8(2019).