The Water Vapor Source and Transport Characteristic of Rainy Seasons in Eastern China Based on Lagrangian Method

The Hybrid Single-Particle Lagrangian Integrated Trajectory platform is employed in this study to simulate trajectories of air parcels in the different rainy seasons in East China from 1961 to 2010, with the purpose of investigating general and specific characteristics of moisture sources and the eventual relationship with precipitation in each rainy season. The moisture transport and source-sink characteristics of different rainy seasons have evident differences. The results show that the frontal pre-rainy season is mainly influenced by winter monsoon system, and the precipitation is strongly affected by water vapor from Pacific Ocean (PO) and East China (EC). After the onset of South China Sea Summer Monsoon (SCSMS), the moisture from Pacific Ocean decreases and from Indian Ocean monsoon area increases. Afterwards, with the northward of the rain belt, the parcels from Southwest region (South China Sea (SCS), Indian Ocean (IO) and Indo-China Peninsula and Indian Peninsula (IP)) decrease and from North region (EC, Eurasia (EA) and PO) increase. Besides, most of the land areas are water vapor sink region and most of sea areas are water vapor source region. Before the onset of SCSMS, EC and PO are two main water vapor source areas. After the onset of SCSMS, the source from PO decreases and Indian monsoon area becomes the main vapor source region. IP is the main water vapor sink area for all four rainy seasons. As for moisture circulation characteristics, the results of vertical structure of water vapor transport indicate that the maximum water vapor transport in west and east boundaries is located in mid-troposphere and in south and north boundaries is at low-troposphere. The spatiotemporal analysis of moisture trajectory based on multivariate empirical orthogonal function (MVEOF) indicates that the first mode has close relationship with the precipitation in North China and PDO pattern; the second mode is closely related with the precipitation in Yangtze-Huaihe river basin and EAP pattern.