Isotopic Composition and Moisture Sources of Precipitation in Midlatitude Regions Characterized by Extratropical Cyclones’ Route

Isotopic composition and their corresponding moisture sources of precipitation are important for understanding water cycles and reconstructing paleoclimate. To clarify the isotopic composition and water origins, we sampled precipitation diurnally at Sapporo, Northern Japan, and simulated the isotopic composition and moisture sources by using an isotopic regional spectral model for the 2014/2015 winter period. During the period, ten intensified extratropical cyclones, approached Northern Japan, were classified as Sea of Japan cyclone and Pacific cyclone according to the cyclone route. For precipitation at Sapporo, the Sea of Japan cyclone induced higher delta H-2 with more moisture from the Kuroshio region, whereas the Pacific cyclone triggered precipitation to Sapporo with lower delta H-2 and more moisture from the North Pacific Ocean. Regarding moisture transport within the extratropical cyclone frontal system for both cyclone types, moisture transported by the warm conveyor belt from the Kuroshio region mainly condensed in the cold and eastern warm fronts with high delta H-2 and d-excess, resulting from a high sea surface temperature and low humidity during evaporation; in contrast, vapors transported by the cold conveyor belt from the North Pacific Ocean precipitated in the western warm front and cyclone center with low delta H-2 and d-excess, arising from a low sea surface temperature and high humidity. With respect to the cyclone route effect on the geographical distribution of isotopic characteristics around Japan, when the Sea of Japan cyclone occurred, condensation in the Pacific Ocean showed higher delta H-2 and d-excess with more moisture from the Kuroshio via the warm conveyor belt. In contrast, during passage of the Pacific cyclone, condensation in the Pacific Ocean exhibited lower delta H-2 and d-excess with more vapors from the North Pacific Ocean via the cold conveyor belt. These phenomena observed around Japan could be applied in other midlatitude regions and for hydrological, biogeochemical, and paleoclimate studies.