我国南方两次低温雨雪事件天气成因对比分析

2018年和2021年末我国南方分别发生了一次大范围的低温雨雪天气，对生活、生产造成了严重影响，因此对比分析这两次低温雨雪天气成因具有重要意义。结果表明：两次过程期间，对流层中层中高纬阻塞流场显著，阻高位于贝加尔湖西侧，脊前偏北气流在下游横槽后部堆积，使得西伯利亚高压强度增强。东传的Rossby波在阻高区域发生能量频散，利于阻高减弱、崩溃，横槽转竖引导槽后冷空气南下，导致地面强烈降温，同时在西伯利亚高压东侧和南侧，低频风温度平流是造成强降温的主要原因。低纬南支槽活跃，向北的暖湿空气与中高纬南下的冷空气汇合，造成我国南方大范围的低温雨雪、冻雨天气。与2018年过程相比，2021年过程持续时间较短，降水范围小，关键区降温幅度更大，是因为2021年过程期间Rossby波能量频散更快，阻高维持时间较短，冷空气从中高纬地区直接南下侵袭我国，而2018年冷空气在贝加尔湖附近发生堆积、西折，向南渗透时势力减弱。

Comparison of formation causes of two low temperature rain and snow events in south China

A large-scale low temperature rain and snow occurred in southern China at the end of 2018 and 2021 respectively, which had made a severe damage to the life and production. As a result, it is of great significance to compare the formation factors of the two low temperature rain and snow weathers. The results show the northerly airflow in front of high pressure ridge lying the west side of the Lake Baikal accumulates at the rear of the downstream transverse trough which makes the Siberian high become stronger. The Rossby wave originating from the North Atlantic has energy dispersion in the blocking high regions, which is conducive to the weakening and collapse of blocking high. The cold air sweeps across China after the transverse trough turns to a meridional trough, resulting in strong cooling of the ground. At this time, the related strong cooling on the east and south sides of the Siberian high is controlled by the cold advection by low-frequency wind. The south branch trough in the low latitude is active, and the warm and wet air northward merges with the cold air from mid-high latitude, causing a wide range of rain, snow and freezing rain in southern China. However, compared with 2018 process, the 2021 process has shorter duration, smaller precipitation range and greater cooling amplitude in key regions. The reason is Rossby wave energy disperses faster and the blocking high weakens more quickly which makes the cold air directly intrude China from mid-high latitude. While the cold air accumulates and transports westward near Lake Baikal, and then becomes weak when it penetrates southward in 2018 process.