[A-HW19] 水循環・水環境

[AHW19-11] Stable isotopes of precipitation and moisture source determination using IsoGSM and backwards trajectory at Bandung, Indonesia

*Ilyas Nurfadhil Basuki¹、Kimpei Ichiyanagi¹、Rusmawan Suwarman²、Masahiro Tanoue³ (1.Kumamoto University、2.Bandung Institute of Technology 、3.Japan Meteorological Agency)

キーワード：Precipitation, Stable isotopes, Moisture, Backwards trajectory

A useful tracer for the atmospheric water cycle is stable water isotopes. Precipitation was collected at the Bandung Institute of Technology from late 2015 to mid-2016 and the stable isotopic ratios were analyzed at Kumamoto University. The analysis using the Water Isotope Analyzer (Picarro, L2020-i) gave results of stable oxygen isotope ratios between -18.4‰ and -2.0‰, stable hydrogen isotope ratios between -134.6‰ and -3.6‰, and d-excess values between 6.5‰ and 19.0‰. Oxygen isotope ratios were generally higher during the months of January, February, May, and June, and lower in March and April. In order to further analyze the results, the global 3D isotope-based IsoGSM model was used in this study. Simulated daily averaged stable isotope results had a decent fit with observations in the study area, with an R² of 0.53. Backwards trajectory simulations were run to determine the possible moisture sources of Bandung precipitation, with the assumption that a trajectory represents the movement of moisture in the atmosphere. Based on the preliminary results of the simulations, there are multiple possible sources during different months. Most months had trajectories originating from the Indian Ocean and the South China Sea, while the months of December, January, and June also had trajectories originating from around Australia. Horizontal winds at 850 hPa level and cloud cover data were then used to determine the impact of monsoon winds and the Inter-Tropical Convergence Zone (ITCZ) on moisture movement, respectively. Westerly wind vector was quite strong near the study area from March to May, and cloud cover was high in the study area from March to May, and lower during other months. It was concluded that the wet monsoon season and the ITCZ generally cause a decrease in isotope values. Further analysis will be needed to determine the isotope characteristics at each moisture source, as well as the contribution amount of each source.