Cloud Cluster Patterns of Tropical Cyclones over the Bay of Bengal and Their Influences on Precipitation in China

Activities of tropical cyclones (TCs) over the Bay of Bengal (BoB) often exert appreciable influences on precipitation in China, but how and to what extent these influences operate remain unclear. This study utilizes the International Best Track Archive for Climate Stewardship (IBTrACS) dataset and infrared satellite images from Japan during 1996–2021 to analyze the cloud system structure patterns associated with BoB TCs (excluding tropical depressions) and their impact on China rainfall. A fuzzy c–means clustering method was applied to classify TC cloud clusters into three morphological types: type “6”, abbreviated as T6, (type “9” as T9), with cloud distributions predominantly located north (south) of the TC center, and type “symmetry” (TSM), with relatively balanced cloud distributions on both sides. The results indicate that T6 (41.3%) occurs most frequently in autumn, T9 (31.2%) peaks in early summer, and TSM (27.5%) also shows a slight preference for autumn. Distinct circulation features are associated with each type. At 500 hPa over the Qinghai-Xizang Plateau (QXP), T6 is associated with the southern branch trough, T9 with straight westerlies, and TSM with a ridge. At 200 hPa, both centers of T6 and TSM are located at the periphery of the South Asian high (SAH), with an enhanced upper-level divergence outflows, resulting in northward extension of cloud clusters under the influence of the westerly jet. In contrast, T9 TCs are embedded within the SAH, where weaker divergence outflow restricts northward cloud development. All three types are characterized by a column-integrated water vapor channel extending from the BoB to southern China, with T9 exhibiting the strongest moisture transport to China. Precipitation analyses reveal that three types contribute to rainfall in Yunnan Province and the Guangxi Zhuangzu Zizhiqu. Moreover, T6 produces heavier rainfall in southern Xizang Zizhiqu, T9 in Yunnan Province, and TSM in Sichuan Province and Xizang Zizhiqu. Remote precipitation induced by TC long-distance moisture transport also exhibits distinct patterns: under T6, high-rainfall areas are widely distributed across southwestern China and parts of southern China; under T9, heavy rainfall is concentrated in southern China; and under TSM, heavy rainfall is mainly confined to Guangdong and Jiangxi provinces. These results provide helpful clues for forecasting precipitation in China based on the cloud cluster patterns of the BoB TCs.