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PLATEAU METEOROLOGY 2013, Vol. 32 Issue (2) :501-    DOI: 10.7522/j.issn.1000-0534.2012.00048
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Characteristics of Atmospheric Stratification and Cloud Physics
of Different Types of Freezing Rain over Southern China
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Abstract 

Three classical freezing rain processes over southern China were simulated by observation data and CAMS mesoscale cloud model. Characteristics of atmospheric stratification and cloud physics of the freezing rain and mechanism of freezing rain formation are analyzed. The results show that: (1) a necessary condition for exist freezing rain was the presence of the temperature inversion layer. The inversion layer with high humidity in lower atmosphere often associated with freezing rain. (2) Formation of freezing rain needed to meet three main conditions: freeze layer existed in the upper troposphere, a warm layer and temperature inversion layer existed blow the freeze layer, and cooling layer (temperature below 0 ℃) with high humidity existed near the surface. (3) Two different types of temperature stratification were existed during freezing rain, which are ‘cold-warm-cold’ and ‘warm-cold’ stratification. Corresponding to two types of stratification, two different clouds microphysical structures were existed and two different mechanism of freezing rain formation. Consideration of stratification (‘cold-warm-cold’ layer), the cloud thickness was deeper over Hunan Province on 28 January 2008 and Jiangxi Province on 5 January 2010, and cloud has large amount of ice-phase particles. So clouds belonged to mixed-phase cloud. Freezing rain over Hunan and Jiangxi Provinces  was formed by ice-crystal mechanisms (the melting process). That is, freezing rain developed as falling snow encountered a layer of warm air then the snow completely melted and became rain. As the rain continued to fall, it passes through a thin layer of cold air just above the surface and cools to a temperature below freezing and formed supercooled drops. When the supercooled drops strike ground, or anything else below 0 ℃, they instantly freeze, forming freezing rain. Clouds above freezing rain area over Hunan and Jiangxi Provinces belonged to mixed-phase cloud. However, clouds above freezing rain area over Guizhou Province on 28 January and 9 February 2008 belonged to warm cloud: the cloud thickness was thinner, cloud top temperature was higher, and clouds have little ice-phase particles. Consideration of stratification (‘warm-cold’ layer), freezing rain over Guizhou Province was formed by supercooled warm-rain processes (collision-coalescence process). Supercooled raindrops developed as microscopic cloud droplets collect one another as they fall. Ice processes were not involved in the formation of these raindrops. (4) Over the different freezing rain zone in the same weather systems, the different temperature stratification, cloud microphysical structure and formation mechanism of freezing rain can exist in different types of cloud. The freezing rain zone with same feature can also exist in different weather systems, namely temperature stratification of freezing rain formation, cloud microphysical structure and the mechanism of freezing rain formation are same.

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KeywordsFreezing rain   Cloud microphysical characteristics   Stratification structure     
Abstract

Three classical freezing rain processes over southern China were simulated by observation data and CAMS mesoscale cloud model. Characteristics of atmospheric stratification and cloud physics of the freezing rain and mechanism of freezing rain formation are analyzed. The results show that: (1) a necessary condition for exist freezing rain was the presence of the temperature inversion layer. The inversion layer with high humidity in lower atmosphere often associated with freezing rain. (2) Formation of freezing rain needed to meet three main conditions: freeze layer existed in the upper troposphere, a warm layer and temperature inversion layer existed blow the freeze layer, and cooling layer (temperature below 0 ℃) with high humidity existed near the surface. (3) Two different types of temperature stratification were existed during freezing rain, which are ‘cold-warm-cold’ and ‘warm-cold’ stratification. Corresponding to two types of stratification, two different clouds microphysical structures were existed and two different mechanism of freezing rain formation. Consideration of stratification (‘cold-warm-cold’ layer), the cloud thickness was deeper over Hunan Province on 28 January 2008 and Jiangxi Province on 5 January 2010, and cloud has large amount of ice-phase particles. So clouds belonged to mixed-phase cloud. Freezing rain over Hunan and Jiangxi Provinces  was formed by ice-crystal mechanisms (the melting process). That is, freezing rain developed as falling snow encountered a layer of warm air then the snow completely melted and became rain. As the rain continued to fall, it passes through a thin layer of cold air just above the surface and cools to a temperature below freezing and formed supercooled drops. When the supercooled drops strike ground, or anything else below 0 ℃, they instantly freeze, forming freezing rain. Clouds above freezing rain area over Hunan and Jiangxi Provinces belonged to mixed-phase cloud. However, clouds above freezing rain area over Guizhou Province on 28 January and 9 February 2008 belonged to warm cloud: the cloud thickness was thinner, cloud top temperature was higher, and clouds have little ice-phase particles. Consideration of stratification (‘warm-cold’ layer), freezing rain over Guizhou Province was formed by supercooled warm-rain processes (collision-coalescence process). Supercooled raindrops developed as microscopic cloud droplets collect one another as they fall. Ice processes were not involved in the formation of these raindrops. (4) Over the different freezing rain zone in the same weather systems, the different temperature stratification, cloud microphysical structure and formation mechanism of freezing rain can exist in different types of cloud. The freezing rain zone with same feature can also exist in different weather systems, namely temperature stratification of freezing rain formation, cloud microphysical structure and the mechanism of freezing rain formation are same.

KeywordsFreezing rain,   Cloud microphysical characteristics,   Stratification structure     
Cite this article:   
$author.xingMing_EN, $author.xingMing_EN, $author.xingMing_EN .Characteristics of Atmospheric Stratification and Cloud Physics
of Different Types of Freezing Rain over Southern China[J]  PLATEAU METEOROLOGY, 2013,V32(2): 501-
URL:  
http://210.72.80.159/jweb_gyqx/EN/10.7522/j.issn.1000-0534.2012.00048     或     http://210.72.80.159/jweb_gyqx/EN/Y2013/V32/I2/501
 
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