Isotope Ratios of Rainfall and Water Vapor observed in Typhoon Shanshan

Isotope ratios of rainfall and water vapor during the passage of Typhoon Shanshan were observed in Ishigaki Island, southwestern part of Japan, on 15—16 September 2006. High-resolution samples of 1-mm rainfall allow a more quantitative understanding of detail water circulation of typhoon system. Observational results show that the isotope ratios of rainfall in rainband accompanying Shanshan decrease radially inward, but appear to be anomalously high in the eye wall. We speculate that the inward decrease in the isotope ratios of rainfall is due to the recycling process, diffusive isotope exchange between rainfall and converging vapor in the boundary layer. On the other hand, the anomalously high isotope ratios of the eye-wall rainfall is a consequence of their local cycling process which is a major source of the precipitating vapor for the typhoon's inner region. We also collected the water vapor in the eye of the typhoon where rainfall and storm ceased rapidly. The isotope ratios of water vapor in the eye are markedly higher than that of water vapor near the rainband. In addition, a quite decrease in the deuterium excess from the eye wall to eye (d = 37.8 to 10.9 per mil) appears, which is attributed to the difference in the water vapor source area. These findings indicate that the water circulation of the typhoon's core is significantly different from that in the outer region.