Abstract
This study investigates the roles of water vapor transport and sea surface temperature (SST) warming in the tropical Indian Ocean (TIO) on the heavy rainfall in central China during the boreal early summer (May–June–July). In the past four decades, four significant rainfall events, in 1983, 1998, 2016, and 2020, occurred in central China and caused severe floods, and the year 2020 has the most extreme event. All four events are associated with significant TIO SST warming and a strong anomalous anticyclone on the western North Pacific (WNPAC). The anomalous winds in the northwestern flank of the WNPAC bring excess water vapor into central China. The water vapor, mainly carried from the western tropical Pacific, converges in central China and result in heavy rainfall. A theory of regional ocean–atmosphere interaction can well explain the processes, called the Indo-Western Pacific Ocean Capacitor (IPOC) effect. The WNPAC is usually associated with strong El Niño-Southern Oscillation (ENSO), except for the 2020 case. The 2020 event is extraordinary without a significant El Niño occurred in the previous winter. In 2020, the significant TIO warming sustained the anomalous WNPAC, inducing the most significant extreme rainfall event in central China. This study reveals that the IPOC effect can dramatically influence the East Asian climate even without involving the ENSO in the Pacific.
Highlights
Boreal summer is the rainy season for China
This study mainly reveals that the extreme rainfall of 2020 MJJ is attributed to the Indo-Western Pacific Ocean Capacitor (IPOC) effect even without involving the El Niño-Southern Oscillation (ENSO) in the Pacific
This study investigated the cause for the 2020 extreme rainfall from water vapor transport and tropical Indian Ocean (TIO) sea surface temperature (SST) warming
Summary
Boreal summer is the rainy season for China. During early summer (May–June–July, MJJ), warm and moist southwesterly winds, originated from the Indian Ocean, the South China Sea, and the Western Pacific, supply abundant water vapor to central China (Fig. 1a; Sampe and Xie 2010), one of the most populated regions in China, ranged from 106.25° E–121.25° E, 26.25° N–33.75° N in this study Many factors may contribute to the 2020 extreme rainfall in central China (e.g., Takaya et al 2020; Chen et al 2021; Ding et al 2021; Wang et al 2021a, b; Zhang et al 2021a, b; Zhou et al 2021; Zheng and Wang 2021). The atmospheric circulation pattern in the middle to high latitudes facilitated the cold air intrusions to the central China region, making an extraordinary contribution (Ding et al 2021) Some studies ascribed this unexpected extreme rainfall event to mid-latitude factors, for example, the negative upper-level relative vorticity over North China in June (Zheng and Wang 2021) and the phase transition of the North Atlantic Oscillation (NAO) (Liu et al 2020).
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