台风“杜鹃”降水δ18O的云雨区效应初探

我国东南地区台风降水显著,但对这种强降水事件中的稳定同位素研究较少,限制了对短时间极端降水稳定同位素变化过程和影响因素的认识。论文根据2015年9月28日至29日第21号台风“杜鹃”两次登陆（台湾宜兰、福建莆田）前后台北、福州两地气象数据和降水稳定同位素数据,分析了此次台风的降水稳定同位素变化特征及影响因素。台风期间,两地降水δ¹⁸O波动范围为-3.4‰~-15.0‰,变化幅度达11.6‰。台风前端和尾端两地降水同位素值相对偏正,平均值为-4‰~-6‰而台风中端两地降水同位素值极其偏负,平均值分别为-12.4‰和 -13.2‰。台风前端与尾端降水同位素值偏正,水汽受蒸发效应影响明显;而台风中端降水δ¹⁸O值极端偏负主要受“云雨区效应”的影响,即云雨区气流急剧上升,水汽在过饱和环境中快速凝结降落,受动力分馏作用小,降水δ¹⁸O极端偏负。结合降水δ¹⁸O变化特征、过量氘及模拟水汽轨迹,得到台风“杜鹃”降水主要的水汽来源为西太平洋海域。

A Tentative Study of “Cloudy and Rainy Area Effect” of the δ18O in the Precipitation of Typhoon “Dujuan”

Typhoon precipitation is conspicuous in southeastern China, but little is known about the characteristics of the stable isotopes in these heavy rainfall events. It is thus highly needed to study the variation and controlling factors of the stable isotopes in extreme precipitation events. According to the meteorological data and stable isotope compositions of precipitation in Taipei and Fuzhou, the No. 21 Typhoon “Dujuan” led to landfall twice in Yilan County, Taiwan Province and Putian City, Fujian Province respectively, from September 28th to 29th, 2015. This paper analyzed the characteristic of stable isotopes in the precipitation of Typhoon “Dujuan” and the influence factors. During the period of Typhoon “Dujuan”, the δ¹⁸O varied from -3.4‰ to -15.0‰ with a fluctuation range of 11.6‰. The stable isotope compositions in the precipitation at the front and back in these two places are relative positive, and the average values vary from -4‰ to -6‰. The stable isotope composition of precipitation in the central area of these two places are most negative, and the average values are -12.4‰ and -13.2‰, respectively. The stable isotope compositions of front-end and back-end precipitation in two places are relative positive and the water vapor is obviously affected by “evaporation effect”. The stable isotope composition of middle-end precipitation is mainly influenced by “cloudy and rainy area effect”, which has the most negative values. In the sharp rise process of the airflow in cloudy and rainy area of Typhoon, water vapor rapidly condensed and fell in supersaturated environment, and the effect of kinetic fractionation is small, so the δ¹⁸O is most negative. Characteristics of δ¹⁸O, deuterium excess and simulated vapor transport trajectories suggest that the water vapor source of precipitation with Typhoon “Dujuan” is the western Pacific Ocean.