2024年初湖南两次区域性低温雨雪冰冻天气的成因对比  

Comparison of causes of two regional rainfall/snowfall and freezing events with low temperatures in Hunan in early 2024

作　　者：胡燕 叶成志 赵恩榕 陈红专[4] 刘红武 HU Yan;YE Chengzhi;ZHAO Enrong;CHEN Hongzhuan;LIU Hongwu(Hunan Key Laboratory of Meteorological Disaster Prevention and Reduction,Changsha 410118;Hunan Meteorological Observatory,Changsha 410118;Institute of Meteorological Sciences of Hunan Province,Changsha 410118;Huaihua Meteorological Office of Hunan Province,Huaihua 418000)

机构地区：[1]气象防灾减灾湖南省重点实验室,长沙410118 [2]湖南省气象台,长沙410118 [3]湖南省气象科学研究所,长沙410118 [4]湖南省怀化市气象局,怀化418000

出　　处：《暴雨灾害》2024年第6期680-692,共13页Torrential Rain and Disasters

基　　金：湖南省自然科学基金重大项目(2021JC0009);国家重点研发计划项目(2023YFC3007804);湖南省气象局重点项目(XQKJ22A004);湖南省创新发展专项(CXFZ2023-ZDZX07)。

摘　　要：2024年2月湖南省出现2次区域性低温雨雪冰冻天气过程,即2—6日湘北低温雨雪冰冻过程(简称“2.02”过程)和21—26日全省性大范围雨雪冰冻过程(简称“2.21”过程)。使用常规地面高空观测资料、加密自动站资料与NCEP再分析资料,从环流形势、降温机制、水汽输送特征等方面,对上述两次过程的物理成因进行对比分析。结果表明:(1)两次过程环流背景存在明显差异,“2.02”过程发生在南支槽和西风槽同位相叠加东移的大尺度背景下,而“2.21”过程则发生在阻塞高压崩溃导致寒潮爆发的背景下,受南支槽上小波动影响反复出现雨雪相态转换。(2)两次过程均存在低层强锋区,而“2.21”过程还出现了少见的大于26℃南北温差梯度,这可能是此次极端寒潮天气发生的重要原因。(3)温度平流对雨雪演变起重要作用,其中“2.02”过程主要受西风槽带动中层强冷平流入侵,整层气温下降,而“2.21”过程超低空强冷平流持续输入是导致持续冰冻天气的重要降温机制之一。另外,暖平流最强输送层对应垂直速度负值中心,对流层中低层垂直风切变更大,导致雨雪强度更强。(4)两次过程主要水汽源地均为阿拉伯海,对流层中层西南暖湿空气随500 hPa低槽或其分裂出的小槽移动,且比湿和水汽贡献率最大,低槽既为冬季雨雪过程提供了有利的动力条件,也提供了充沛的水汽。其中“2.21”过程,来自南海和阿拉伯海洋面、低纬内陆的三条通道叠加传输暖湿气流,为湘南冰冻区提供了水汽和暖层条件,这也是造成该地强冰冻的重要原因。In February 2024,Hunan encountered two regional rainfall/snowfall and freezing events with low temperatures,one in northern Hunan from February 2 to 6(hereinafter referred to as the“2.02”event),and the other across the whole province from February 21 to 26(hereinafter referred to as the“2.21”event).Using conventional upper-air and surface weather observations,regional automatic weather station data,and NCEP reanalysis data,we conducted a comparative analysis of the circulation background,cooling mechanism,and water vapor transport characteristics of the two events.The results are as follows.(1)There are obvious differences in the circulation background between the two events.The“2.02”event occurred in the background with eastward movement of both the southern branch trough and westerly trough overlapping in phase.However,the“2.21”event occurred under the cold wave caused by the collapse of the blocking high,with the transition of rain and snow phases appearing multiple times due to the small influence on the southern branch trough.(2)There were the strong low-level frontal zone in both events.A rare north-south temperature gradient greater than 26°C was observed in the“2.21”event,which may be an important indication of this extreme cold wave weather.(3)Temperature advection played an important role in the transition of rain and snow phases.In the“2.02”event,the strong cold advection intrusion in the middle level was driven by the westerly trough,causing a temperature decrease across the whole layer.In the“2.21”event,the continuous input of the ultra-low-level strong cold advection was one of the important cooling mechanisms.In addition,the strongest transport layer of warm advection corresponded to the negative center of vertical velocity,and the stronger vertical wind shear in the middle and lower troposphere resulted in stronger rain and snow intensity.(4)The Arabian Sea was the main source of water vapor for both events.Southwest warm and wet airflow in the middle troposphere moved

关 键 词：雨雪冰冻天气 环流背景 温度平流 水汽特征 物理成因 

分 类 号：P458.3[天文地球—大气科学及气象学]