Source-receptor network, governing circulations and predictability of monsoon rain belt events in the mid-lower Yangtze River basin

Abstract:

The atmospheric water cycle is crucial for the monsoon climate system, and closely links with land/ocean-atmospheric processes at different scales. Recently, there has been a growing interest in studying the source-receptor network related to the East Asian summer monsoon rainfall, which reveals important hydrological processes such as local and external water vapor recycling, moisture transports and rainfall formation. Despite strong and long-lived monsoon rain belts that lead to torrential rains and floods in regions like the mid-lower Yangtze River basin over the years, the factors affecting rain belts’ growth, including the evaporation source, water vapor channels and the attributable atmospheric circulations, are still poorly understood.

In light of this, the present study focuses on understanding the regional state of the atmospheric water cycle that links to rain belts during the summer monsoon season. Using the dynamical recycling model, a substantial fraction of precipitation occurred in rain belts over the mid-lower Yangtze River basin stems from the Indian subcontinent, Southwest China, Bay of Bengal, Arabian Sea and Indochina. By grouping the consecutive rain belts with similar source-receptor networks into an event, the atmospheric circulations governing the water cycle of the rain belt events are investigated. By clustering the rain belt events and the diagnosis of composite maps, three types of pronounced weather regimes are found attributable to the derived moisture channels and the source-receptor network. Signals from the weather regimes could be useful precursors in our statistical models to access the predictability of upcoming monsoon rain belts in the river basin. Results from this study may also advance the understanding of the monsoon rain belts’ evolution and shed light on uncertainties and bias in the numerical simulations.