气候变化领域集成服务门户(CCPortal): Influence of low-level blocking and turbulence on the microphysics of a mixed-phase cloud in an inner-Alpine valley

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DOI	10.5194/acp-21-5151-2021
	Influence of low-level blocking and turbulence on the microphysics of a mixed-phase cloud in an inner-Alpine valley
	Ramelli F.; Henneberger J.; David R.O.; Lauber A.; Pasquier J.T.; Wieder J.; Bühl J.; Seifert P.; Engelmann R.; Hervo M.; Lohmann U.
发表日期	2021
ISSN	1680-7316
起始页码	5151
结束页码	5172
卷号	21 期号:6
英文摘要	Previous studies that investigated orographic precipitation have primarily focused on isolated mountain barriers. Here we investigate the influence of low-level blocking and shear-induced turbulence on the cloud microphysics and precipitation formation in a complex inner-Alpine valley. The analysis focuses on a mid-level cloud in a post-frontal environment and a low-level feeder cloud induced by an in-valley circulation. Observations were obtained from an extensive set of instruments including ground-based remote sensing instrumentation, in situ instrumentation on a tethered-balloon system and ground-based precipitation measurements. During this event, the boundary layer was characterized by a blocked low-level flow and enhanced turbulence in the region of strong vertical wind shear at the boundary between the blocked layer in the valley and the stronger cross-barrier flow aloft. Cloud radar observations indicated changes in the microphysical cloud properties within the turbulent shear layer including enhanced linear depolarization ratio (i.e., change in particle shape or density) and increased radar reflectivity (i.e., enhanced ice growth). Based on the ice particle habits observed at the surface, we suggest that riming, aggregation and needle growth occurred within the turbulent layer. Collisions of fragile ice crystals (e.g., dendrites, needles) and the Hallett-Mossop process might have contributed to secondary ice production. Additionally, in situ instrumentation on the tethered-balloon system observed the presence of a low-level feeder cloud above a small-scale topographic feature, which dissipated when the low-level flow turned from a blocked to an unblocked state. Our observations indicate that the low-level blocking (due to the downstream mountain barrier) created an in-valley circulation, which led to the production of local updrafts and the formation of a low-level feeder cloud. Although the feeder cloud did not enhance precipitation in this particular case (since the majority of the precipitation sublimated when falling through a subsaturated layer above), we propose that local flow effects such as low-level blocking can induce the formation of feeder clouds in mountain valleys and on the leeward slope of foothills upstream of the main mountain barrier, where they can act to enhance orographic precipitation through the seeder-feeder mechanism. © 2021 Copernicus GmbH. All rights reserved.
语种	英语
scopus关键词	alpine environment; atmospheric blocking; cloud microphysics; mountain region; precipitation (climatology); valley; Alps
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/246999
作者单位	Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland; Department of Geosciences, University of Oslo, Oslo, Norway; Leibniz Institute for Tropospheric Research, Leipzig, Germany; Federal Office of Meteorology and Climatology MeteoSwiss, Payerne, Switzerland
推荐引用方式 GB/T 7714	Ramelli F.,Henneberger J.,David R.O.,et al. Influence of low-level blocking and turbulence on the microphysics of a mixed-phase cloud in an inner-Alpine valley[J],2021,21(6).
APA	Ramelli F..,Henneberger J..,David R.O..,Lauber A..,Pasquier J.T..,...&Lohmann U..(2021).Influence of low-level blocking and turbulence on the microphysics of a mixed-phase cloud in an inner-Alpine valley.ATMOSPHERIC CHEMISTRY AND PHYSICS,21(6).
MLA	Ramelli F.,et al."Influence of low-level blocking and turbulence on the microphysics of a mixed-phase cloud in an inner-Alpine valley".ATMOSPHERIC CHEMISTRY AND PHYSICS 21.6(2021).