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Open AccessArticle

Falling Mixed-Phase Ice Virga and their Liquid Parent Cloud Layers as Observed by Ground-Based Lidars

by Chong Cheng 1,2,3 and Fan Yi 1,2,3,*
1
School of Electronic Information, Wuhan University, Wuhan 430072, China
2
Key Laboratory of Geospace Environment and Geodesy, Ministry of Education, Wuhan 430072, China
3
State Observatory for Atmospheric Remote Sensing, Wuhan 430072, China
*
Author to whom correspondence should be addressed.
Remote Sens. 2020, 12(13), 2094; https://doi.org/10.3390/rs12132094
Received: 15 May 2020 / Revised: 24 June 2020 / Accepted: 24 June 2020 / Published: 30 June 2020
(This article belongs to the Special Issue Remote Sensing of Clouds)
Falling mixed-phase virga from a thin supercooled liquid layer cloud base were observed on 20 occasions at altitudes of 2.3–9.4 km with ground-based lidars at Wuhan (30.5 °N, 114.4 °E), China. Polarization lidar profile (3.75-m) analysis reveals some ubiquitous features of both falling mixed-phase virga and their liquid parent cloud layers. Each liquid parent cloud had a well-defined base height where the backscatter ratio R was ~7.0 and the R profile had a clear inflection point. At an altitude of ~34 m above the base height, the depolarization ratio reached its minimum value (~0.04), indicating a liquid-only level therein. The thin parent cloud layers tended to form on the top of a broad preexisting aerosol/liquid water layer. The falling virga below the base height showed firstly a significant depolarization ratio increase, suggesting that most supercooled liquid drops in the virga were rapidly frozen into ice crystals (via contact freezing). After reaching a local maximum value of the depolarization ratio, both the values of the backscatter ratio and depolarization ratio for the virga exhibited an overall decrease with decreasing height, indicating sublimated ice crystals. The diameters of the ice crystals in the virga were estimated based on an ice particle sublimation model along with the lidar and radiosonde observations. It was found that the ice crystal particles in these virga cases tended to have smaller mean diameters and narrower size distributions with increasing altitude. The mean diameter value is 350 ± 111 µm at altitudes of 4–8.5 km. View Full-Text
Keywords: ice virga; supercooled liquid layer; lidar observation; ice crystal diameter ice virga; supercooled liquid layer; lidar observation; ice crystal diameter
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MDPI and ACS Style

Cheng, C.; Yi, F. Falling Mixed-Phase Ice Virga and their Liquid Parent Cloud Layers as Observed by Ground-Based Lidars. Remote Sens. 2020, 12, 2094.

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