Mechanistic Link Between Precipitation Types and Stable Isotope Evolution in Tropical Cyclones: A Case Study of Typhoon Rai (2021)

ABSTRACT The influence of precipitation types on isotopic composition has been extensively studied, with foci on the distinct isotopic signatures of convective and stratiform precipitation. The typhoon precipitation system is characterised by pronounced convective processes alongside stratiform influences. Such a system provides a unique opportunity to advance the mechanistic understanding of isotopic fractionation during Typhoon Rai (December 2021). In this study, we analysed hourly precipitation samples collected in Fuzhou, Southeastern China, during Typhoon Rai to elucidate stable isotope signatures associated with distinct precipitation types. Our results revealed significant fluctuations in δ 18 O values (−9.24‰ ± 3.80‰, mean ± SD; range: −2.75‰ to −13.29‰), exhibiting a typical two‐stage variation pattern. During the first stage, as the typhoon approached the sampling site, rainfall δ 18 O progressively decreased from −2.75‰ to −12.62‰, driven mainly by intense convective precipitation and subsequent rainout processes. During the second stage, isotopic values stabilised at −13.29‰, reflecting a shift to the stratiform‐dominated precipitation. This stabilisation was attributed to post‐convective stratiform development (i.e., anvil clouds), which had inherited an extremely depleted δ 18 O signature and was further modified by cloud microphysical fractionation processes. These findings highlight the critical role of precipitation types in governing isotopic variability during typhoon events, offering new insights into the complex interplay between dynamic and microphysical processes in future strong tropical cyclones.