[A-HW23] 同位体水文学2023

[AHW23-07] Characteristics of short-term fluctuation of stable isotope ratios in precipitation using automatic water samplers

*大串 湧二¹、一柳 錦平²、壁谷 直記³ (1.熊本大学理学部、2.熊本大学自然科学研究科、3.森林総合研究所九州支所)

キーワード：熊本、降水の安定同位体、短時間変動

Short-time fluctuation of stable isotopes (δ¹⁸O and δ²H) in precipitation was observed at Kumamoto using two types of self-made automatic water sampler. Although precipitation sampling for stable isotopes is often 1 day to 1month intervals, and few studies have observed short-term fluctuations during precipitation events. In this study, the stable isotope ratio of precipitation was measured with a high temporal resolution of 1 hour. Precipitation samples were collected on the rooftop of Kumamoto University from May to December 2022, and also precipitation amount was observed. Samples from Typhoons No. 11 and No. 14 were also collected. δ¹⁸O and δ²H in precipitation were measured using Water Isotope Analyzer (Picarro L2120-i) at Kumamoto University. By using the rain cloud radar of Japan Meteorological Agency and the wind profiler at the Kumamoto District Meteorological Observatory, factors controlling short-term fluctuations in stable isotope ratios of precipitation were considered. A total of 235 samples were collected from 25 precipitation events. As a result, short-term fluctuations for stable isotope ratios in precipitation could be divided into two patterns. The first pattern is low fluctuation in stable isotope ratios with low precipitation. In this situation, Rayleigh process is unlikely to occur. The second pattern is a gradual decrease in stable isotope ratios, recovering to values near the beginning of the event. It is considered that the Rayleigh distillation process occurred during the isotope ratio decrease. Precipitation amount is often low during the isotopic ratio increase. According to the wind profiler, the altitudes of raindrops descending were about 4km for both patterns of most precipitation events except during the stable isotope ratio increase.