Heavy Rainfall Events in Southern China Associated with Tropical Cyclones in the Bay of Bengal: A Case Study

Abstract

We use a case study to show that a continuous heavy rainfall process in southern China was closely related to tropical cyclone activity in the Bay of Bengal. The continuous heavy rainfall that occurred in southern China on 11–13 May 2002 can be considered as two different processes. The first process, referred to as a predecessor rain event, occurred over southwestern China before landfall of the tropical cyclone. The second process occurred after dissipation of the tropical cyclone when its remnant caused heavy rainfall that expanded from southwestern China to the middle to lower reaches of the Yangtze–Huaihe river basin. Both of the heavy rainfall processes were closely related to the transport of warm, moist air associated with a tropical cyclone originating over the Bay of Bengal, but the mechanisms in the two processes were quite different. Low-level orographic forcing was the main contributor to the predecessor rain event, whereas baroclinic frontogenesis induced by thermal advection was the main contributor to the tropical cyclone remnant event. Both heavy rainfall events occurred beneath the equatorial entrance of the upper level East Asian subtropical jet.

Role of the subtropical westerly jet wave train in the eastward-moving heavy rainfall event over southern China in winter: A case study

“…The rainfall over southeastern China was mainly attributed to the baroclinic frontogenesis caused by strong warm, wet advection. Numerous previous studies also revealed that the local conditions favored for heavy rainfall occurrence over southwestern China and southeastern China were different, including the underlying surface conditions, the impact of weather systems and cold air activity (Yuan et al, 2018;Li and Li, 2019;Yuan et al, 2019;Chen and Li, 2022;Li et al, 2022), etc. These findings suggested that the characteristics of rainfall and its mechanisms may have regional differences in southern China.…”

“…The two-dimensional horizontal frontogenesis function was calculated to investigate the frontogenesis related to rainfall process (Ninomiya, 1984), which was also used in Yuan et al (2019) and shown good performance in diagnosing frontogenesis over southern China. Empirical orthogonal function (EOF) analysis was used to investigate the modes of SBT variation.…”

“…The topography of southwestern China is very complex (Yuan et al, 2019), which is higher in the northwest and lower in the southeast, and strong orographic gradient appears in the northwest-southeast direction (Figure 1). The southwesterly flow impinged almost perpendicularly on the windward slopes of the mountains in southwestern China.…”

“…The southwesterly flow in front of the SBT can transport large amounts of warm, moist water vapor from the Bay of Bengal to southern China, which favors the occurrence of heavy rainfall in this region (Wang et al, 2011;Li and Zhou, 2016). When the deepening SBT meets the westwardexpanding western Pacific subtropical high, widespread heavy rainfall can occur in southwestern China and also further downstream in southeastern China (Duan et al, 2012;Zong et al, 2014;Yuan et al, 2019).…”

“…Previous studies have mainly focused on the conditions favoring the large region of persistent heavy rainfall over the whole of southern China in winter. Numerous case studies have shown that persistent heavy rainfall events over southern China feature an eastward movement from the perspective of daily variations in the weather (Li and Sun, 2015;Li and Li, 2019;Yuan et al, 2019). Under the winter background of westerly flows over southern China, precipitation tends to occur first over southwestern China and then spreads eastward downstream to southeastern China.…”