Vehicle-based in situ observations of the water vapor isotopic composition across China: spatial and seasonal distributions and controls

Abstract. Stable water isotopes are natural tracers in the hydrological cycle and have been applied hydrology, atmospheric science, ecology, paleoclimatology. However, factors controlling isotopic distribution, both at spatial temporal scales, debated low middle latitude regions, due to significant influence of large-scale circulation complex sources vapor. For first time, we made situ observations near-surface vapor over a large region (over 10 000 km) across China pre-monsoon monsoon seasons, using newly designed vehicle-based isotope monitoring system. Combined with daily multiyear monthly mean outputs from isotope-incorporated global spectral model (Iso-GSM) infrared sounding interferometer (IASI) satellite calculate relative contribution, found that observed variations periods represent mainly seasonal variations, but influenced by more synoptic-scale during period. The δ18O controlled Rayleigh distillation along air mass trajectories period, significantly different moisture sources, continental recycling processes, convection transport Thus, North–South gradient period is counteracted variation reflects summer convective precipitation southern dependence on temperature North. d-excess reflect recycling. Iso-GSM successfully captures distribution performance weaker maybe underestimation local or short-term high-frequency synoptic variations. These results provide an overview variability composition East Asia their factors, they emphasize need interpret proxy records context regional