Main moisture sources affecting lower Yangtze River Basin in boreal summers during 2004-2009

摘要

This study presented a quantitative climatology of atmospheric moisture affecting the Yangtze River Basin (YRB) region in boreal summer season, as well as the spatial evolution of atmospheric moisture passage towards the target regions. A three-dimensional Lagrangian particle dispersion model FLEXPART was driven by the National Centers for Environmental Prediction Final Operational Global Analysis data combined with a backtracking scheme, and the transport contributions to the moisture budget over the YRB region was identified through the continuous calculation of changes in specific humidity along the FLEXPART back trajectories of all air masses residing over this region for a period of six summers of year 2004-2009. The back trajectory analysis revealed four major moisture sources contributed to the YRB summer water vapour with different transport timescales: the East China Sea (17.5%), South China Sea (26.6%), Indian peninsula and the Bay of Bengal (20.5%) and Arabian Sea (13.6%). The properties of moisture sources and its transport processes are dominated by the Asian Summer Monsoon regimes. The Tibetan Plateau also acts as an effective barrier for the meridional moisture transport, leading to distinct moisture sinks at the southern slope. In contrast to the previous results, the tropical western Pacific only plays a minor role in the water vapour contributors. The importance of the four source areas varies over the summer: East and South China Sea sources persist throughout the summer, whereas the Indian peninsula, the Bay of Bengal and Arabian Sea sources reach the strongest moisture supply to the YRB region only in high summer (July), showing a close association with the March of Asian monsoon. The further evaluation shows that the inter-annual variability of precipitation over YRB is strongly related to the moisture sources in the Bay of Bengal and Arabian Sea.