川西高原持续性暴雨特征和水汽输送

利用常规资料、NCEP FNL分析资料和HYSPLIT模式,对2008—2017年川西高原持续性暴雨过程的时空分布、环流分型、水汽源地和输送路径进行分析。结果表明:①2008—2017年川西高原单站持续性暴雨的总频次为337次,在21次区域持续性暴雨中,位于高原与盆地过渡区的泸定、康定、汶川出现持续性暴雨次数最多;②7月发生频率最高,持续时间多为3～4天;③将影响川西高原暴雨的环流分型为两槽一脊型、一脊一槽型、西风槽型和偏西气流型,其中孟加拉湾气旋影响有16例,6—7月个例都有孟加拉湾气旋的存在;④川西高原上空气团主要通过4条路径进入,源自北大西洋、地中海和伊朗中北部的西北路径占比29%,源自里海到咸海之间地区的东北路径占比17%,源自热带印度洋洋面的西南和东南路径各占比43%和11%,偏北路径的空气质点起始高度比偏南路径的高,相应的温度和水汽含量也偏低;⑤将水汽输送分为"S"型、偏西气流型和偏南气流型3个类型。

Characteristics of Persistent Heavy Rainfall and Water Vapor Transport in Western Sichuan Plateau

Based on the routine observational data, NCEP FNL data and the HYSPLIT model, the spatio temporal distribution, circulation situation, water vapor source and transport path of the persistent heavy rainfall events in the western Sichuan Plateau from 2008 to 2017 are analyzed. The main results are as follows: The total frequency of persistent heavy rainfall events in all observation stations of the western Sichuan Plateau is 337, and the frequency of regional heavy rainfall episodes is 21, in which the transition areas between plateau and basin including Luding, Kangding and Wenchuan have the highest frequency of persistent heavy rainfall. The longest duration of heavy rainfall events is about 3 to 4 days. In this study, the influencing circulation situations contains two troughs and one ridge, one trough and one ridge, and westerly trough. The cyclone over the Bay of Bengal is found to be a crucial weather system, which appears in 16 of the 21 regional persistent heavy rainfall cases. Moreover, all the regional cases in June and July are affected by the Bay of Bengal cyclone. The air masses on the western Sichuan Plateau are mainly accessed through four paths. The southwest and southeast routes originating from the tropical Indian Ocean are 43% and 11%, respectively, and the northwestern routes originating from the North Atlantic, the Mediterranean and the north central Iran account for 29%. The northeast path from the Caspian Sea to the Aral Sea accounts for 17%. The initial altitude of air particles of the northerly path is higher than that of the southerly path, and the corresponding temperature and water vapor content are lower. After analyzing the water vapor flux and water vapor flux divergence, the water vapor transport in regional persistent heavy rainfall in the western Sichuan Plateau is classified as three types, namely the S type, the westerly airflow type and the southerly airflow type.