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2024年2月初贵州东部及长江中下游低温雨雪冰冻天气的基本特征及成因

Characteristics and causes of low-temperature rainfall/snowfall and freezing weather event in eastern Guizhou and the middle and low reaches of the Yangtze River in early February 2024

  • 摘要: 2024年2月初贵州东部及长江中下游出现低温雨雪冰冻天气,恰逢春运高峰,给春运、能源保供及人民生活造成严重影响。为揭示此次低温雨雪冰冻天气的异常特征,利用国家气象信息中心实况观测资料、美国国家环境预报中心和国家大气研究中心(NCEP/NCAR)再分析资料以及怀化双偏振雷达资料对此次天气的基本特征和成因进行了分析。结果表明:(1) 2024年春节前贵州东部、湖南中北部、湖北东部南部及安徽西部北部出现4~6 d严重冰冻灾害,冰冻灾害主要由两轮低温雨雪天气造成,首轮低温雨雪出现在2月1—4日,降水相态具有多样性,尤其是3日雨雪最为明显,以强降雪及强冻雨为主,导致积雪和积冰快速增长。第二轮低温雨雪出现在5—6日,贵州东部、湖南中北部以冻雨为主,湖北等长江沿线以雨夹雪和降雪为主,积冰得以维持或继续增长。(2) 亚洲中高纬度位势高度距平呈西低东高分布,且南支槽活跃,为低温雨雪冰冻天气提供了重要天气背景。南支槽前强盛的西南急流沿锋面爬升形成倾斜上升气流,增强了锋后的降水强度,造成第一轮强低温雨雪天气;而后南支槽减弱,但南支锋区仍维持,中低层急流和地面静止锋均维持,造成了第二轮持续低温雨雪天气。(3) 受华南静止锋和云贵静止锋形成及维持的影响,锋后逆温范围宽广,且长江以南地区暖层显著,造成长江南北不同相态的降水。同时长江南北的温湿场在垂直方向上有较大差异,长江以北地区以强降雪为主时,温湿场上表现为深厚的冷湿特征,具有典型的冰相结构;长江以南地区以强冻雨为主时,温湿场上具有“强暖湿-冷湿”特征。(4) 2月3—4日长江南北地区均出现快速跃增的雨水、冰水和雪的混合比,形成了强湿雪和强冻雨;长江以南地区低层过冷水3日夜间以小雨滴和大雨滴方式共存、5日夜间则是由小雨滴构成。

     

    Abstract: In early February 2024, severe low-temperature rainfall/snowfall and freezing weather events occurred in the eastern parts of Guizhou and the middle and lower reaches of the Yangtze River. Coinciding with the travel period of the Spring Festival, the event caused serious impacts on travel, energy supply guarantees, and people's daily lives. To reveal the exceptional characteristics of the weather event, observation data from the National Meteorological Information Center, NCEP/NCAR reanalysis data, and Huaihua dual-polarization radar data were used to analyze the characteristics and causes of rainfall/snowfall and freezing weather events. The results are as follows: (1) Severe freezing disasters lasting 4-6 days occurred in eastern Guizhou, northern and central parts of Hunan, eastern and southern parts of Hubei, and northern and western parts of Anhui. These disasters were primarily caused by two rounds of low-temperature rain and snow weather. The first round occurred around February 1 to 4, with the most severe period appearing on the 3rd. It was characterized by heavy snowfall and freezing rain, leading to rapid accumulation of snow and ice. The second round occurred from February 5 to 6, with freezing rain predominating in eastern Guizhou and northern and central parts of Hunan, and sleet predominating along the Yangtze River in Hubei and other areas, which sustained or further increased the ice accumulation. (2) The geopotential height anomaly of the mid to high latitudes in Asia showed a distribution of low in the west and high in the east, and the southern trough was active. Both provided important weather conditions for the low-temperature rain and snow weather. The strong southwest jet stream climbs along the front to form a tilted upward airflow, enhancing the precipitation intensity behind the front, and leading to the first round of the weather event. The weakening of the southern trough and the maintenance of the southern front area, the mid-to-low low-level jet, and the surface stationary front resulted in the second round of the weather event. (3) Affected by the formation and maintenance of the South China stationary front and the Yunnan-Guizhou stationary front, the range of inversion was wide, with a significant warm layer in the southern region of the Yangtze River, resulting in different phases of precipitation on the south and north sides of the Yangtze River. Meanwhile, there were significant differences in the vertical direction of the temperature and humidity fields on the north and south sides of the Yangtze River. When heavy snowfall dominated north of the Yangtze River, the temperature and humidity fields exhibited deep cold-wet characteristics, with a typical ice-phrase structure. However, when heavy freezing rain dominated south of the Yangtze River, the temperature and humidity fields exhibited a"strong warm-wet and cold-wet"feature. (4) The rapidly increasing amount of rainwater, ice, and snow formed strong wet snow and severe freezing rain on February 3-4. The low-level supercooled water of both light and heavy rain droplets coexisted in the southern region of the Yangtze River on the night of the 3rd day, while it was dominated by light rain on the night of the 5th day.

     

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