Abstract
Abstract. Investigating the synchrony and interdependency of heavy rainfall occurrences is crucial to understand the underlying physical mechanisms and reduce physical and economic damages by improved forecasting strategies. In this context, studies utilizing functional network representations have recently contributed to significant advances in the understanding and prediction of extreme weather events. To thoroughly expand on previous works employing the latter framework to the East Asian summer monsoon (EASM) system, we focus here on changes in the spatial organization of synchronous heavy precipitation events across the monsoon season (April to August) by studying the temporal evolution of corresponding network characteristics in terms of a sliding window approach. Specifically, we utilize functional climate networks together with event coincidence analysis for identifying and characterizing synchronous activity from daily rainfall estimates between 1998 and 2018. Our results demonstrate that the formation of the Baiu front as a main feature of the EASM is reflected by a double-band structure of synchronous heavy rainfall with two centers north and south of the front. Although the two separated bands are strongly related to either low- or high-level winds, which are commonly assumed to be independent, we provide evidence that it is rather their mutual interconnectivity that changes during the different phases of the EASM season in a characteristic way. Our findings shed some new light on the interplay between tropical and extratropical factors controlling the EASM intraseasonal evolution, which could potentially help to improve future forecasts of the Baiu onset in different regions of East Asia.
Highlights
The Asian summer monsoon dominates the rainfall pattern over South and East Asia, thereby impacting nearly a third of the world’s population
The main goal of this study is to understand the temporal evolution of heavy rainfall events in the East Asian summer monsoon (EASM) domain, we first analyze a static network accounting for the complete EASM season, which was studied in Ozturk et al (2019)
We observe a region of elevated degree and link distance in the southernmost part of the study area, which is associated with the intertropical convergence zone (ITCZ) that is gradually shifted northward during boreal spring
Summary
The Asian summer monsoon dominates the rainfall pattern over South and East Asia, thereby impacting nearly a third of the world’s population. Disregarding the western (Arabian Sea) branch of the Indian summer monsoon (ISM), this major weather system is mainly initiated over Southeast Asia and the maritime continent, from which one branch expands westward to the Bay of Bengal and eastern Indian Ocean, forming the eastern branch of the ISM (Yihui and Chan, 2005). A second branch, the East Asian summer monsoon (EASM), progressively moves northward along the western edge of the Northwest Pacific Subtropical High (NPSH) following the gradual northward migration of the upper-level jet (Suda and Asakura, 1955; Okada and Yamazaki, 2012). The main EASM-related frontal pattern largely contributes to the annual rainfall over the Philippines and China (as Meiyu), Korean peninsula (as Changma), and Japan (as Baiu) during. Wolf et al.: Synchronous heavy rainfall patterns during the Baiu season
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