Variations of stable isotope in Typhoon Lupit (2021) rainfall and its response to upstream convective processes

Typhoons produce a large amount of rainfall with a highly depleted isotopic composition. However, the mechanisms of isotope fractionation during typhoons remain poorly understood. Here, we present the hourly resolution isotope composition of rainfall during Typhoon Lupit (2021) in Fuzhou, on the southeast coast of China, to better understand these processes. Our results showed that the rainfall of Typhoon Lupit had significant fluctuations in delta O-18 values, ranging from -20.1 parts per thousand to -6.3 parts per thousand, and exhibited a three-stage variation with distinctly negative delta O-18 values in the second stage. In the first stage of Lupit, water vapour originated primarily from the nearby sea area, which did not undergo sustained convective activity, resulting in relatively enriched delta O-18 values. In the second stage, the delta O-18 values were extremely negative mainly because of the accumulated convective activity and continuous precipitation as they travelled towards the centre of the typhoon. In the third stage, the mixing of more localized and nearby sea water vapour caused an increase in the delta O-18 values. In summary, the three-stage characteristics of Typhoon Lupit were largely caused by the integration of accumulated convective activity and moisture sources. Our findings reveal how upstream rainout affects the isotopic behaviour of rainfall and may have implications for understanding the dynamics of typhoon rainfall isotopes.