Two-year statistics of columnar-ice production in stratiform clouds over Hyytiälä, Finland : environmental conditions and the relevance to secondary ice production

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http://hdl.handle.net/10138/335472

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Li , H , Möhler , O , Petäjä , T & Moisseev , D 2021 , ' Two-year statistics of columnar-ice production in stratiform clouds over Hyytiälä, Finland : environmental conditions and the relevance to secondary ice production ' , Atmospheric Chemistry and Physics , vol. 21 , no. 19 , pp. 14671-14686 . https://doi.org/10.5194/acp-21-14671-2021

Title: Two-year statistics of columnar-ice production in stratiform clouds over Hyytiälä, Finland : environmental conditions and the relevance to secondary ice production
Author: Li, Haoran; Möhler, Ottmar; Petäjä, Tuukka; Moisseev, Dmitri
Other contributor: University of Helsinki, Institute for Atmospheric and Earth System Research (INAR)
University of Helsinki, Institute for Atmospheric and Earth System Research (INAR)
University of Helsinki, Institute for Atmospheric and Earth System Research (INAR)

Date: 2021-10-05
Language: eng
Number of pages: 16
Belongs to series: Atmospheric Chemistry and Physics
ISSN: 1680-7316
DOI: https://doi.org/10.5194/acp-21-14671-2021
URI: http://hdl.handle.net/10138/335472
Abstract: Formation of ice particles in clouds at temperatures of 10 ffiC or warmer was documented by using ground-based radar observations. At these temperatures, the number concentration of ice-nucleating particles (INPs) is not only expected to be small, but this number is also highly uncertain. In addition, there are a number of studies reporting that the observed number concentration of ice particles exceeds expected INP concentrations, indicating that other ice generation mechanisms, such as secondary ice production (SIP), may play an important role in such clouds. To identify formation of ice crystals and report conditions in which they are generated, W-band cloud radar Doppler spectra observations collected at the Hyytiala station for more than 2 years were used. Given that at these temperatures ice crystals grow mainly as columns, which have distinct linear depolarization ratio (LDR) values, the spectral LDR was utilized to identify newly formed ice particles. It is found that in 5 %-13% of clouds, where cloud top temperatures are 12 degrees C or warmer, production of columnar ice is detected. For colder clouds, this percentage can be as high as 33 %; 40 %-50% of columnar-ice-producing events last less than 1 h, while 5 %-15% can persist for more than 6 h. By comparing clouds where columnar crystals are produced and to the ones where these crystals are absent, the columnar-ice-producing clouds tend to have larger values of liquid water path and precipitation intensity. The columnarice-producing clouds were subdivided into three categories, using the temperature difference, Delta T, between the altitudes where columns are first detected and cloud top. The cases where Delta T is less than 2K are typically single-layer shallow clouds where needles are produced at the cloud top. In multilayered clouds where 2K
Subject: 114 Physical sciences
1171 Geosciences
MIXED-PHASE CLOUD
MELTING LAYER
PARTICLE CONCENTRATIONS
MICROPHYSICAL PROPERTIES
DEPOLARIZATION RATIOS
RADAR OBSERVATIONS
LIQUID-WATER
W-BANDS
DOPPLER
PRECIPITATION
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