This study investigates the interdecadal changes in the intensity of tropical cyclones (TCs) formed within or entered the South China Sea (SCS) in the TC season (June to November) during 1977–2018. Based on change-point detection in five TC datasets, two high-intensity periods [period 1 (P1): 1977–1993; and period 3 (P3): 2006–2018] and a low-intensity period [period 2 (P2): 1994–2002] were identified. Genesis location and vertical moisture advection dominate the interdecadal changes in TC intensity. TC genesis locations in P1 and P3 shift more eastward than in P2. Statistical analysis shows that the farther east the genesis is located, the longer the intensification duration and the higher the intensity the TC can reach. It is also found that environmental factors around the TC tracks are the other reason for the TC intensity. TCs in P2 pass through the region with adverse environmental conditions more frequently. Mid-level relative humidity and vertical motion are key environmental factors for TC intensity. Genesis location is regulated by the Pacific decadal oscillation, the north Indian Ocean SST and the Atlantic multidecadal oscillation. Atmospheric circulations in the tropical Indian Ocean and SCS affect vertical motion. The results provide some helpful insights into the variation of SCS TC intensity.

南海热带气旋强度的年代际变化

中文摘要：本研究调查了1977~2018年台风季（6~11月）南海（South China Sea，SCS）生成或进入南海的热带气旋（TCs）强度的年代际变化。根据5个TC数据集的气候突变点检测，确定了南海热带气旋强度的两个高强度期[时期1(P1):1977~1993；时期3(P3):2006~2018]和1个低强度期[时期2(P2):1994~2002] 。TC强度年代际变化主要受生成位置和垂直水汽输送的影响。与P2时期相比，P1和P3时期热带气旋的生成位置偏东。统计结果表明，热带气旋生成位置越偏东，其强化持续时间越长，TC强度越强。研究还表明，TC移动路径周围的环境因子也影响着TC的强度。P2时期的TC更频繁地经过不利于热带气旋发展的区域。中层相对湿度和垂向运动是影响TC强度发展的关键环境因子。热带气旋生成位置受太平洋年代际振荡、北印度洋SST和大西洋年代际振荡的影响。热带印度洋和SCS的大气环流影响着垂向运动。本研究为研究SCS TC强度的变化有一定的帮助。