基于拉格朗日方法的中国东部雨季水汽输送垂直特征

Vertical Characteristics of Water Vapor Transport during the Rainy Season in Eastern China Based on the Lagrangian Method

利用基于拉格朗日轨迹追踪模式(HYSPLIT),结合区域源汇归属法,追踪1961~2010年中国东部地区雨带推进过程中各雨季后向轨迹,定量确定各雨季不同垂直层上的水汽输送路径与水汽贡献。结果表明在南海夏季风爆发前的华南前汛期,低层最主要水汽通道为太平洋通道,轨迹占比达到52.3%,中高层最主要的水汽通道为印度洋通道,占比超过37%;水汽主要源自低层的西太平洋和中国东部地区,水汽贡献均在20%以上。南海季风爆发后的华南前汛期,低层到高层最强水汽通道均为印度洋通道,特别是中层,轨迹数量达到了65.6%;印度洋源地的贡献明显增加,中高层水汽主要源自印度洋,低层最主要的水汽源地为中国东部和南海。江淮梅雨时低层最主要通道为太平洋通道,中高层最主要通道为印度洋通道,相比华南前汛期,在中高层印度洋通道减弱,而西风通道增强。华北雨季中,低层最主要水汽通道为太平洋通道,而中高层最主要的水汽通道为欧亚大陆中纬西风通道。江淮梅雨和华北雨季中,最主要的源地为中低层的中国东部地区和西太平洋地区,特别是华北雨季中,来自中国东部局地低层的水汽达到了43.1%,表明低层局地蒸发对华北雨季降水起到至关重要的作用。

The Hybrid Single-Particle Lagrangian Integrated Trajectory(HYSPLIT) platform, which was enhanced with the areal source–receptor attribution method, was used to simulate the Lagrangian trajectories of air parcels in eastern China during the summer monsoons from 1961 to 2010 at different vertical levels. At these levels, water vapor transport pathways and moisture contributions in each rainy season were quantitatively determined. During the pre-monsoon season in South China(SC), the dominant water vapor transport channel at the lower level(below 1500 m) was the West Pacific Ocean channel, with the proportion of trajectories reaching 52.3%, whereas at the middle level(1500-5000 m), the Indian Ocean channel was found to be dominant, with the proportion of trajectories exceeding 37%. The most important moisture source was the land area of East China and the West Pacific Ocean at the lower level;their contribution rate for each of the two sources exceeded 20%. After the onset of the South China Sea summer monsoon and during the entire monsoon season in SC, the Indian Ocean channel was the strongest moisture channel at the lower, middle, and upper levels(>5000 m),and the proportion of trajectories at the middle level was 65.6%. Further, the moisture contribution from the Indian Ocean showed a significant increase, and it was the most important moisture source at the middle and upper levels. However, the most important moisture source at the lower level was East China and the South China Sea. During the Meiyu season, the West Pacific and Indian Ocean channels were the dominant channels at the lower level and at the middle and upper levels,respectively. Compared with the monsoon season in SC, the Indian Ocean channel was weaker at the middle and upper levels, whereas the mid-latitude westerly channel was stronger. During the rainy season in North China, the West Pacific and mid-latitude westerly channels were the dominant water vapor channels at the lower level and at the middle and upper levels, respectively. During the Meiyu and North China rainy season, the main source areas were eastern China and the West Pacific regions. In particularly, during the rainy season in North China, the water vapor from East China at the lower level reached 43.1%, which indicates that the local evaporation at the low level plays a crucial role during the rainy season precipitation in North China.