9:15 AM - 9:30 AM
[HTT16-02] Stable Isotope Variability in Winter Precipitation and Water Vapor in Hirosaki: Implications for Explosive Cyclone-Induced Hydrological Processes
Keywords:water isotope, snowfall, explosive cyclone
Stable isotope ratios in precipitation reflect fractionation during phase changes, allowing for the reconstruction of water cycle processes. This study analyzes winter precipitation and water vapor isotope in Hirosaki focusing on an explosive cyclone on February 15–16, 2021, using the isotope-enabled regional spectral model (IsoRSM).
Precipitation was collected using buckets, and water vapor was captured with a cold trap at Hirosaki University. IsoRSM was used to analyze water vapor origins, with tracer-mode experiments assessing contributions from the East China Sea, the Sea of Japan, the northern Pacific, and the southern Pacific. A previous study (Ueno et al., 2022) simulated November 26, 2020 – March 1, 2021, showing that the model reproduced δD variations well but struggled with d-excess variability. They identified three terms of the February 15–16, 2021, explosive cyclone case based on the simulated values:
T1 (Feb 15, 04–12 UTC): Sharp delta 18O decrease;
T2 (Feb 15, 12–19 UTC): Sharp delta 18O increase;
T3 (Feb 15, 19 UTC-Feb 16, 22 UTC): delta 18O decrease
The experiments showed that T1 was influenced by southern and northern Pacific moisture, T2 by the southern Pacific and the Sea of Japan, and T3 by the Sea of Japan. HIMSST analysis indicated a widespread positive sea surface temperature (SST) anomaly, particularly in the Pacific east of Kanto, with +3°C above normal. Model air temperatures closely matched SSTs, suggesting gradual evaporation. This suggests that the d-excess decline in T1 and T2 resulted from gradually evaporating Pacific moisture.
Additionally, we are analyzing a record-breaking snowfall event in northern Iwate on February 27, 2024. This explosive cyclone showed the lowest water vapor isotope ratios in Hirosaki. HIMSST analysis revealed a high SST anomaly off Iwate, similar to the February 2021 case.
Precipitation was collected using buckets, and water vapor was captured with a cold trap at Hirosaki University. IsoRSM was used to analyze water vapor origins, with tracer-mode experiments assessing contributions from the East China Sea, the Sea of Japan, the northern Pacific, and the southern Pacific. A previous study (Ueno et al., 2022) simulated November 26, 2020 – March 1, 2021, showing that the model reproduced δD variations well but struggled with d-excess variability. They identified three terms of the February 15–16, 2021, explosive cyclone case based on the simulated values:
T1 (Feb 15, 04–12 UTC): Sharp delta 18O decrease;
T2 (Feb 15, 12–19 UTC): Sharp delta 18O increase;
T3 (Feb 15, 19 UTC-Feb 16, 22 UTC): delta 18O decrease
The experiments showed that T1 was influenced by southern and northern Pacific moisture, T2 by the southern Pacific and the Sea of Japan, and T3 by the Sea of Japan. HIMSST analysis indicated a widespread positive sea surface temperature (SST) anomaly, particularly in the Pacific east of Kanto, with +3°C above normal. Model air temperatures closely matched SSTs, suggesting gradual evaporation. This suggests that the d-excess decline in T1 and T2 resulted from gradually evaporating Pacific moisture.
Additionally, we are analyzing a record-breaking snowfall event in northern Iwate on February 27, 2024. This explosive cyclone showed the lowest water vapor isotope ratios in Hirosaki. HIMSST analysis revealed a high SST anomaly off Iwate, similar to the February 2021 case.