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气象:2020,46(8):1015-1025
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一次局地暴雪过程低层降温机制分析
彭霞云,刘汉华,李文娟,赵放,孔照林
(浙江省气象台,杭州 310017)
Analysis of Low-Level Temperature Cooling Mechanism of a Local Snowstorm Process
PENG Xiayun,LIU Hanhua,LI Wenjuan,ZHAO Fang,KONG Zhaolin
(Zhejiang Meteorological Observatory, Hangzhou 310017)
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投稿时间:2019-04-24    修订日期:2020-05-15
中文摘要: 2015年12月5日在强西南暖湿气流和弱冷空气配合之下,浙江杭州到安徽黄山一带出现了局地大到暴雪,此次过程预报偏差较大。通过对水汽、动力和温度条件分析表明:强西南暖湿气流和冷暖空气的辐合为大量地面降水的产生提供了水汽和动力条件;深厚的湿层和合适的中层温、湿条件有利于生成大量可供降落的冰雪晶;转雪前杭州站低层异常降温是形成降雪的关键原因。通过对降温机制的分析表明:引起杭州站低层降温的原因主要是水物质相变相关的非绝热加热,冷平流的作用很弱。5日08时之前低层降温主要是降水粒子蒸发吸热引起的;5日白天低层降温主要是由大量冰(雪)晶融化吸收环境潜热导致,冷平流和垂直输送项也有部分贡献。预报中对降温机制分析不足,可能是导致预报偏差的主要原因。该个例中平流等降温机制较弱,冰晶融化吸热作用导致中低层形成0℃的均温层,从而使冰晶顺利到达地面。中低层温度与常用的预报相态的温度阈值相差较大,说明预报中不能机械依赖温度指标,而应全面分析降雪形成的物理机制。当降水量大时,融化吸热可以成为降温的主要机制,预报中应予以充分考虑。
Abstract:On 5 December 2015, with strong southwest warm and humid air and weak cold air, a heavy snowstorm occurred in the area from Hangzhou of Zhejiang Province to Huangshan of Anhui Province. The forecast for this process was quite inaccurate. The analyses of water vapor, power and temperature conditions in this paper show that the strong southwest warm and humid airflow, the convergence of cold and warm air provided abundant water vapor and dynamic conditions for the generation of a large amount of surface precipitation. The deep wet layer, suitable intermediate temperature and humidity conditions were favorable for the generation of a large number of snow and ice crystals for landing. The abnormal temperature drop at the lower level of Hangzhou Station before the snowfall was the key cause for snowfall. The analysis of the cooling mechanism shows that the cause of the low-level temperature drop at Hangzhou Station was mainly non-adiabatic heating related to water vapor phase transition, and the effect of cold advection was weak. The low-level cooling before 08:00 BT on 5 December was mainly caused by the evaporation of precipitation particles; the low-level cooling during the day was mainly caused by a large amount of ice (snow) crystal melting to absorb the latent heat of the environment, and the cold advection and vertical transport items also contributed. The main reason for the failure of the forecast was the dependence on temperature index and the insufficient analysis of the cooling mechanism. In this case, the cooling mechanism such as advection was weak, and the melting and heat absorption of ice crystals caused the middle and lower layers to form a uniform temperature layer of 0℃, so that the ice crystals reached the ground. The middle and lower temperature was quite different from the temperature index commonly used in discerning precipitation type, which indicates that the temperature index can not be applied mechanically, and the physical mechanism of snowfall formation should be comprehensively analyzed. When precipitation amount is large, melting heat absorption can become the main mechanism of cooling, which should be fully considered in the forecasting operation.
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基金项目:浙江省科技厅重点项目(2017C03035)资助
引用文本:
彭霞云,刘汉华,李文娟,赵放,孔照林,2020.一次局地暴雪过程低层降温机制分析[J].气象,46(8):1015-1025.
PENG Xiayun,LIU Hanhua,LI Wenjuan,ZHAO Fang,KONG Zhaolin,2020.Analysis of Low-Level Temperature Cooling Mechanism of a Local Snowstorm Process[J].Meteor Mon,46(8):1015-1025.