Abstract
Binary tropical cyclones (BTC) often bring disastrous rainfall to China. From the viewpoint of the extreme of the BTC maximum daily rainfall, the characteristics of BTC extreme rainfall (BTCER) during 1960–2018 are analyzed, using daily rainfall data; and some representative large-scale mean flows, in which the associated BTCs are embedded, are analyzed. Results show that the frequency of BTCER shows a decreasing trend [−0.49 (10 yr)−1] and is mainly distributed within the BTC heavy rainstorm interval (100 mm ≤ BTCER <250 mm). BTCER occurs mostly from July to September with a peak in August. Three BTCER typical regions— Minbei, the Pearl River Delta (PRD), and Taiwan—are identified according to the clustering of stations with high BTCER frequency and large BTCER. A further analysis of the 850-hPa BTC composite horizontal wind and water vapor flux over the PRD region shows the existence of two water vapor transport channels, which transport water vapor to the western tropical cyclone. In the first of these channels, the transport takes place via the southwest monsoon, which accounts for 58% of the total moisture, and an easterly flow associated with eastern tropical cyclone accounts for the remaining 42%.
Highlights
Tropical cyclones (TCs) produced numerous disastrous rainfall events over the coastal regions of the Northwest Pacific Ocean (NWP)
During 1960–2018, 427 pairs of Binary tropical cyclones (BTC) formed in the NWP, 258 of which had an impact on China (Fig. 1)
A total of 106 BTCs produced the daily rainfall amounts that fell into the range of a BTC heavy rainstorm (i.e., 100 mm ≤ BTC extreme rainfall (BTCER)
Summary
Tropical cyclones (TCs) produced numerous disastrous rainfall events over the coastal regions of the Northwest Pacific Ocean (NWP). Numerous previous studies have examined devastating typhoons like those mentioned above, and found that the anomalous tracks and extreme rainstorms of TCs can be caused by the interaction of two typhoons, together referred to as a binary tropical cyclone (BTC) (Wu et al 2012; Zhou et al 2014; Fan et al 2014; Xu and Du 2015; Yu et al 2015; Xie et al 2016; Yu and Su-brahmanyam 2017; Moon and Ha 2019). Numerical model simulations have been used in recent years to study the water vapor and energy transport between BTCs. For instance, Xu et al (2011) and Wu et al (2012) pointed out that the existence of Typhoon Goni (2009)‘s water vapor transport played an important role in Typhoon Morakot causing heavy rainfall over Taiwan.
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