Abstract:

In order to deeply understand the water vapor characteristics and sources of persistent rainstorms in the Sichuan Basin and improve the rainstorm forecast capability in this region, the meteorological observation data from 4 955 national and regional automatic meteorological stations in Sichuan Province, the global data assimilation system (GDAS) data, the fifth-generation atmospheric reanalysis (ERA5) from the European Centre for Medium-Range Weather Forecasts (ECMWF) are used to analyze the water vapor transport characteristics of a continuous rainstorm process in August 2020 in the Sichuan Basin by using the Lagrangian method. The results show that the characteristics of water vapor transport at different initial height layers are different before and during the heavy precipitation process. In the middle and high level (from 5 500 to 10 000 m), the low latitude ocean is main source of air mass trajectory before the heavy precipitation occurring, while the southern coast of the Mediterranean is main source of air mass trajectory during the heavy precipitation process and dry and cold air in the middle and high latitude westerlies is brought to the basin. In the middle and lower level (from 1 500 to 5 500 m), during the heavy precipitation process, the source of water vapor trajectory adjusts from the southern coast of the Mediterranean to the low latitude ocean surface and warm and humid air on the low latitude ocean surface is brought to the basin. In the lower level (from ground to 1 500 m), the source of water vapor trajectory first adjusts to the low latitude ocean surface before the heavy precipitation occurring, and warmer and wetter air flow is delivered to the basin compared with the middle and lower level. Quantitative analysis of the water vapor contribution rates of different sources shows that the water vapor from the Bay of Bengal to the Gulf of Thailand is the dominant (66.6%), followed by the Arabian Sea (23.9%), and the South China Sea is the lowest (9.5%).

Key words: Lagrangian, Sichuan, water vapor transport, rainstorm, water vapor path

摘要：

为深入认识四川盆地持续性暴雨的水汽特征及来源，提高该地区暴雨预报能力，利用四川省4 955个国家级及区域级自动气象站资料、全球资料同化系统（Global Data Assimilation System， GDAS）资料、欧洲中期天气预报中心（European Centre for Medium-Range Weather Forecasts，ECMWF）第五代大气再分析资料（ERA5），基于拉格朗日方法对四川盆地2020年8月的一次持续性暴雨过程的水汽输送特征进行了分析。结果表明：强降水开始前和强降水过程中，不同起始高度层水汽输送特征有所不同。中高层起始高度（5 500~10 000 m），强降水开始前气团轨迹源地主要为低纬洋面，而在强降水过程中调整为地中海南岸并为盆地带来中高纬西风带干冷空气;中低层起始高度（1 500~5 500 m），降水过程中气团轨迹源地由地中海南岸逐渐调整为低纬洋面并为盆地带来低纬洋面暖湿空气;低层起始高度（地面至1 500 m），强降水开始前轨迹源地率先调整为低纬洋面并为盆地输送比中低层更为暖湿的气流。统计不同源地水汽贡献率可知，孟加拉湾—泰国湾的水汽占主导（66.6%）、阿拉伯海次之（23.9%）、中国南海最低（9.5%）。

关键词: 拉格朗日, 四川, 水汽输送, 暴雨, 水汽路径