Subseasonal to Seasonal Potential Predictability of the East Asian Monsoon Onsets

Abstract:

East Asian monsoons greatly affect the livelihoods, economic activities, and water resource management in East Asia, where lives more than one-fifth of the global population. The subseasonal to seasonal prediction of monsoon onset timing is crucial for early warning of floods and agricultural management, whereas the research progress is still limited due to its complexity of East Asian monsoon system. Instead of involving ad hoc criteria to define monsoon stages, this study introduces a novel neural network based approach to systematically redefine monsoon stages all year round over the EAM region. The results of monsoon stages are found in good agreement with the literature during the warm season, with interesting new features of each stage identified as well. In line with the derived monsoon onsets, we explore the potential predictability of the arrival and withdrawal timings of the Meiyu, which is known as the peak rainy period in the Yangtze River Basin, around 10 to 90 days ahead with reasonable prediction skills. Circulation systems triggering the monsoon stages are also identified, including the Aleutian Low, the North Pacific Subtropical High, and the dipole of pressure anomaly over East Asia. This study provides considerable implications for weather diagnosis, monsoon onset forecast on the subseasonal to seasonal time scale.