西南地区冬季低温冰冻雨雪事件异常的大尺度环流特征

Large-Scale Circulation Characteristics of Anomalous Low-Temperature Freezing Rain and Snow Events in Winter in Southwest China

本文利用国家气象局气象信息中心提供的逐日最高、最低气温和日降水数据以及ERA5、NCEP/NCAR再分析资料,主要运用Mann-Kendall突变检验法及合成分析法对西南地区冬季低温冰冻雨雪事件的时空变化特征及其异常的大尺度环流特征进行了分析。结果表明:1) 西南地区低温冰冻雨雪事件存在一个“偏多–偏少”的年代际振荡特征,在1994年左右发生突变,从21世纪开始呈现显著下降趋势。2) 事件发生区域主要在川西高原至贵州中部一带,贵州中部一带在1月频次最多,到2月频次减少,同时川西高原发生频次增多。3) 在事件多发年,贝加尔湖到中国江淮地区为异常气旋式环流,我国南海到西南华南地区为异常西伸高压环流系统,沿异常气旋式环流西侧南下的冷空气与异常高压环流西北侧的暖湿空气在西南地区汇合,形成低温雨雪天气。相反,在少发年,大气环流场的变化特征与多发年呈相反变化态势,不利于低温冰冻雨雪事件的发生。

In this paper, the daily maximum and minimum temperature and daily precipitation data from the Meteorological Information Centre of the National Meteorological Service, as well as ERA5 and NCEP/NCAR reanalysis information are used, and Mann-Kendall mutation test and synthetic analysis method are mainly applied to analyze the spatial and temporal variability characteristics of low-temperature freezing rain and snow events in winter in Southwest China and anomalous large-scale circulation characteristics. The results show that: 1) Low-temperature freezing rain and snow events in winter in Southwest China have an inter-decadal oscillation characteristic of “more and less”, with an abrupt change around 1994 and a significant downward trend from the 21st century onwards. 2) The occurrence area was mainly from the western Sichuan Plateau to central Guizhou, with the highest frequency in central Guizhou in January and decreasing in February, while the frequency increases in the western Sichuan Plateau. 3) In years of high incidence, there is an abnormal cyclonic circulation from Lake Baikal to the Jianghuai region of China, and an abnormal westward extending high circulation system from the South China Sea to the South China Sea of Southwest China. The cold air moving southward along the west side of the abnormal cyclonic circulation converges with the warm and humid air on the northwest side of the abnormally high circulation in Southwest China, forming low-temperature rain and snow weather. On the contrary, in years of low incidence, the variation characteristics of atmospheric circulation field are opposite to those in years of low incidence, which is not conducive to the occurrence of low-temperature freezing rain and snow events.