The systematic analysis of isotopes in precipitation provides basic data for the use of isotope-specific tools in hydrological and meteorological investigations. The Global Network of Isotopes in Precipitation (GNIP) observation project, initiated by the International Atomic Energy Agency (IAEA) and the World Meteorological Organization (WMO), is the largest endeavor of its type.

The climatological isotope patterns obtained from these measurements, recorded on an almost monthly basis, have typically been interpreted in terms of different isotope effects. Instead of being related to isolated physical processes, these effects have generally been found to reflect a complex sequence of fractionation during the phase transitions of water from evaporation to precipitation. However, variations in the stable isotopes of event-based precipitation generally offer more information concerning potential synoptic controls upon isotopic content, and thus yield information about the circulation and structure of the atmosphere. These data are particularly significant for the study of mid-latitude regions, where water cycle processes are more complex. Furthermore, better explanations of fluctuations in isotope ratios could result from an analysis that includes both the isotopic variations associated with changes in water vapor origins and the meteorological conditions attendant to particular transport paths (e.g. temperature, precipitation amount, and processes involving evaporation of rain drops falling into the dry atmosphere beneath the cloud base).

Dr. LIU Jiangrong, Prof. SONG Xiangfang and his colleagues, Institute of Geographic Sciences and Natural Resources Research (IGSNRR), have engaged in multi-isotope tracers to understanding precipitation water vapor sources and transport pathways in the water cycle. The researchers found that comparison of stable isotopes in continental and island precipitation events can reveal climatic controls upon isotopic content and yield information about patterns of atmospheric circulation. The overall deuterium (D) and oxygen-18 (18O) characteristics of 64 precipitation events observed in continental Beijing, China, and 109 precipitation events observed at Seongsan (Jeju Island, Republic of Korea) were investigated. To trace moisture origins and transport paths for all precipitation events, the 96 h backward trajectories of air masses arriving at 3000 m above ground level were calculated and categorized using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model.

The results indicate that during the Asian monsoon period, the air mass categories represented at Seongsan were principally from the southeast, southwest, and continental vicinity (CV). Those observed for Beijing were more varied (northwest, west, north, marine vicinity, south, and CV). Additionally, the meteorological controlling factors of each air mass category were identified using non-linear stepwise regression. The precipitation amount was the main predictor for ¹⁸O in precipitation in Seongsan, while the controlling factors involved in Beijing were more complicated.

This study has been published in Climate Research (Liu J, X Song, G Fu, X Liu, Y Zhang, and D Han (2011). Precipitation isotope characteristics and climatic controls at a continental and an island site in Northeast Asia, Clim Res, 49:29-44, doi: 10.3354/cr01013).