Precipitation 17O‐Excess Altered During Tropical Convection: Evidence From Monsoon Cold Surges in Singapore

Abstract

AbstractDespite the recent recognition of 17O‐excess as a promising new tracer for hydrological processes, our knowledge of the control mechanisms underlying 17O‐excess in tropical regions remains limited. To understand how microphysical processes during tropical convection affect precipitation isotope ratios, particularly 17O‐excess, in Singapore, we collected precipitation samples at minute intervals from six rain events associated with cold surges during the Northeast Monsoon seasons and analyzed their triple oxygen isotopes. Our results show that precipitation δ18O decreases in the convective zones and then gradually increases in the stratiform zones, while d‐excess exhibits an inverse trend. This correlation between δ18O and d‐excess indicates that rain evaporation plays a crucial role in regulating precipitation isotopes. Moreover, the rain events with a higher upstream rainout amount have lower δ18O and higher 17O‐excess values, suggesting that precipitation δ18O and 17O‐excess likely reflect the integrated upstream convective activity. Microphysical processes associated with upstream convection, such as rain evaporation and vapor recycling, are potential mechanisms that increase 17O‐excess values along moisture transport pathways for a rain event, and hence, undermine the effectiveness of 17O‐excess as a tracer of moisture source humidity. Contrary to the negative correlation observed in monthly precipitation, there is generally a positive correlation between d‐excess and 17O‐excess at the event scale. However, this correlation weakens as convective rain intensifies, suggesting that stronger convection can attenuate the positive correlation between d‐excess and 17O‐excess. Therefore, it is crucial to consider how tropical convection alters 17O‐excess when utilizing this tracer to interpret atmospheric dynamics and hydrological processes.