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气象:2021,47(1):36-48
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华北地区雪密度不同的两次降雪过程对比分析
陈双,符娇兰
(国家气象中心,北京 100081; 中国气象局-河海大学水文气象研究联合实验室,北京 100081)
Comparative Analysis of Two Snow Events with Different Snow Density in North China
CHEN Shuang,FU Jiaolan
(National Meteorological Centre, Beijing 100081; CMA-HHU Joint Laboratory for Hydrometeorological Studies, Beijing 100081)
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投稿时间:2019-08-01    修订日期:2020-06-16
中文摘要: 利用加密降雪观测资料、地面常规观测、FY-2E卫星观测及ERA5再分析资料对华北地区两次融化比存在显著差异的降雪过程其降雪特征、云内垂直热动力结构、降水粒子垂直分布、地面气温和地表温度等进行了对比分析,揭示了热动力垂直结构和水汽条件对降雪过程的雪密度影响。结果表明:融化比较大降雪过程(简称“0103”过程)整层温度偏低,位于对流层低层的-18~-12℃温度层较为深厚,与最大上升运动中心、水汽饱和区相重合,有利于树枝状雪花的形成进而产生较大融化比,其云中粒子以冰相粒子为主;融化比较小降雪过程(简称“1129”过程)整层温度偏高,前述温度层位于对流层高层,较为浅薄,且位于最大上升运动中心下方,其云层下部存在较多过冷水滴,有利于凇附作用进而产生较小融化比; “0103”过程短波槽较浅,导致最大动力抬升层次低,-18~-12℃温度层位于暖锋锋区附近,锋前暖平流有利于深厚温度层的建立和维持,水汽主要来自低层偏东气流输送,导致其水汽含量偏小;“1129”过程主要由高空槽前暖湿气团沿冷锋锋面爬升所引起,动力抬升位于中高层,-18~-12℃温度层位于冷锋锋区上部,温度直减率大,导致-18~-12℃温度层较为浅薄,中层西南风水汽输送提供了有利水汽条件。
Abstract:By using densely-observed snowfall, surface conventional observation, FY-2E satellite TBB and ERA5 reanalysis data, comparative analysis is carried out for two snowfall events with significantly different snow to liquid ratios (SLR) in North China. Based on the analysis of difference of the snowfall characteristics, vertical thermodynamic structure in clouds, verticaldistribution of precipitation particles and surface temperature, the effect of vertical thermodynamic structure and water vapor conditions on snow density is revealed. The results show that the event with higher SLR (hereinafter referred to the 3rd January Case) occurs in a colder condition from surface to upper atmosphere, and the vertical layer with temperature between -18℃ to -12℃ is much thicker, which almost coincides with the level of maximum ascending motion in the cloud. The perfect match of temperature and vertical motion in the cloud leads to the formation of dendritic snowflake and a higher SLR. In addition, the precipitation particles are mainly ice-phase particles in the 3rd January Case. The case with lower SLR (hereinafter referred to the 29th November Case) appears in a warmer condition. The vertical layer with 〖JP2〗temperature between -18℃ to -12℃ is rela-〖JP〗tively thinner, which is located below the level of its maximum ascending motion. This kind of profiles of temperature and vertical motion in the cloud would result in a low SLR snowfall. Besides this, there are large amounts of super-cooled water droplets in the lower level of the cloud, thus the riming process may occur, which would cause a lower SLR further. The 3rd January Case is mainly caused by a short-wave trough, thus its accent motion is relatively weaker with its peak in 〖JP2〗low-level layer. The layer with tempera-〖JP〗ture between -18℃ to -12℃ is located near the frontal zone of a warm front, where there is a strong warm advection and a small temperature lapse rate. This is the main reason why the -18℃ to -12℃ layer for the 3rd January Case is thick. While the 29th November Case is mainly caused by a deep upper trough, which generates a strong updraft with its peak in upper-level layer. The layer with temperature between -18℃ to -12℃ is located over the frontal zone of a cold front, where the temperature lapse rate is much larger, thus -18℃ to -12℃ layer is shallow. Meanwhile, water vapor provided by easterly over boundary layer, which is the primary source for the 3rd January Case, is generally less; while the southwesterly in front of the upper trough brings a plenty of water vapor for the 29th November Case.
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基金项目:国家重点研发计划(2018YFF0300104)资助
引用文本:
陈双,符娇兰,2021.华北地区雪密度不同的两次降雪过程对比分析[J].气象,47(1):36-48.
CHEN Shuang,FU Jiaolan,2021.Comparative Analysis of Two Snow Events with Different Snow Density in North China[J].Meteor Mon,47(1):36-48.