A Lagrangian Analysis of Water Vapor Sources and Pathways for Precipitation in East China in Different Stages of the East Asian Summer Monsoon

International audienceThe Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) platform is used to simulate Lagrangian trajectories of air parcels in East China during the summer monsoon. The investigation includes four distinct stages of the East Asian Summer Monsoon (EASM) during its seasonal migration from south to north. Correspondingly, the main water vapor channel migrates from the West Pacific Ocean (PO) for the pre-monsoon in South China (SC) to the Indian Ocean (IO) for the monsoon in SC and in the Yangtze-Huaihe River Basin, and finally back to PO for the terminal stage of monsoon in North China. Further calculations permit to determine water vapor source regions and water vapor contribution to precipitations in East China. To a large extent, moisture leading to precipitation doesn't come from the strongest water vapor pathways. For example, the proportions of trajectories from IO are larger than 25% all the time, but moisture contributions to actual precipitations are smaller than 10%. This can be explained by the large amount of water vapor lost in the pathways across moisture-losing areas such as the Indian Peninsula and Indochina Peninsula. Local water vapor recycling inside East China (EC) contributes significantly to regional precipitations, with contributions mostly over 30%, although the trajectory proportions from sub-regions in EC are all under 10%. This contribution rate can even exceed 55% for the terminal stage of monsoon in North China. Such a result provides an important guidance to understand the role of land surface conditions in modulating rainfall in North China