9:30 AM - 9:45 AM
[HTT15-03] Heavy rainfall and vapor transport in Aomori Prefecture on August 3-10, 2022
Keywords:Heavy precipitation, isotope of water vapor
Landslides caused by heavy rainfall occurred in Aomori Prefecture on August 3, 2022, and a flood event caused by heavy rainfall occurred in western Aomori Prefecture on August 9-10, 2022. The causes of the maximum precipitation were analyzed from a global (e.g., La Nina, etc.) and mesoscale scale perspective, however, the forecasting of senjo-kousui-tai (a kind of meso-scale convective cloud) is still in the development stage, so it is important to clarify the elementary processes of extreme precipitation events in order to improve the forecasting and disaster prevention in the future.
Here, we report on some analyses in terms of water vapor transport, which is a necessary condition for heavy rainfall. In addition, continuous observation of water vapor isotope ratios has been conducted using Picarro-SDM since September 2021, and data during the heavy rainfall described above have also been obtained. Since water isotope ratios change with phase change and mixing, continuous observation of water vapor isotope ratios may provide insight into the origin of water in heavy rainfall events.
Hourly precipitation data from JMA's AMeDAS was used for precipitation analyses. For regional water vapor flux data, hourly total precipitation and vertically integrated zonal and meridional water vapor fluxes from the ERA5 reanalysis data (0.25 degree) are used.
Isotopes of water vapor were observed by Picarro-SDM at three locations: the main unit was installed in a room on the 5th floor of the university, and tubes were installed on the roof of the 6th floor (ground altitude: 20 m), the roof of the 4th floor (ground altitude: 15 m), and outside the room on the 1st floor (1.2 m). The time required for one cycle was about 6 hours. Isotope ratios (oxygen, hydrogen) were obtained approximately every 2 seconds, and the one-minute averages were corrected with the measurements of the standard sample and then averaged over one hour (δ18O, δD).
Observations showed that δ18O was low during the heavy rainfall events on 8/3 and 8/9. This can be attributed to the quantitative effect that the isotopic ratio of water, or water vapor, in the atmosphere gradually decreases due to condensation of heavier water molecules first. The peak δ18O was lower during the heavy rainfall event on 8/3 than on 8/9 when the Iwaki River was in danger of flooding, and Iso-RSM calculations generally reproduced the trend in isotope ratios and d-excess at Hirosaki.
The ERA5 analysis reproduces the precipitation time series extremely well, especially the peak at 0 UTC (= 9 JST) on 8/3 and the temporal variation of precipitation from 8/9 to 8/10. However, the total amount of precipitation is underestimated. Quantitative precipitation reproducibility will be verified based on grid precipitation generation and radar AMeDAS rainfall analysis.
According to the vertical-integrated water vapor flux, divergence and precipitation distribution by ERA5 on both days near the time of peak precipitation in Hirosaki, precipitation on 8/3 was caused by a low pressure system with a front, but a significant water vapor divergence area was observed over the northern Sea of Japan compared to 8/9, indicating a water vapor source from western Aomori to Akita Pref. The source of the water vapor is from western Aomori to Akita Prefectures. The Aomori District Meteorological Observatory (2022a) indicated that warm, moist air originating from Typhoon No. 6 flowed in as the source of the water vapor for the heavy rainfall on 8/3, but a water vapor contribution from the water vapor divergence off the western coast of Aomori is also possible, and detailed analysis is a future issue.
The precipitation on 8/9-10 was reported to be warm and moist air flowing toward a front that extended from northern China through the Sea of Japan to northern Japan, and the ERA5 precipitation distribution and the existence of weak convergence areas are also close to this view. The water vapor flux and precipitation distribution show a precipitation zone from the Oga Peninsula to the Shimokita Peninsula with a precipitation peak near Fukaura and water vapor convergence in that area, as well as a divergence peak slightly northwest of the divergence peak on 8/3. The contribution of water vapor from this area and the Japan Sea will be discussed in the future.
It is known that the d-excess of the oxygen/hydrogen isotope ratio of water is high in the case of repeated severe evaporation and re-evaporation. In this study, d-excess was high at both of the two δ18O minima. We will discuss the contribution of typhoon origin, large-scale moisture transport to fronts, and evaporation from the Japan Sea based on the isotopic results.
Here, we report on some analyses in terms of water vapor transport, which is a necessary condition for heavy rainfall. In addition, continuous observation of water vapor isotope ratios has been conducted using Picarro-SDM since September 2021, and data during the heavy rainfall described above have also been obtained. Since water isotope ratios change with phase change and mixing, continuous observation of water vapor isotope ratios may provide insight into the origin of water in heavy rainfall events.
Hourly precipitation data from JMA's AMeDAS was used for precipitation analyses. For regional water vapor flux data, hourly total precipitation and vertically integrated zonal and meridional water vapor fluxes from the ERA5 reanalysis data (0.25 degree) are used.
Isotopes of water vapor were observed by Picarro-SDM at three locations: the main unit was installed in a room on the 5th floor of the university, and tubes were installed on the roof of the 6th floor (ground altitude: 20 m), the roof of the 4th floor (ground altitude: 15 m), and outside the room on the 1st floor (1.2 m). The time required for one cycle was about 6 hours. Isotope ratios (oxygen, hydrogen) were obtained approximately every 2 seconds, and the one-minute averages were corrected with the measurements of the standard sample and then averaged over one hour (δ18O, δD).
Observations showed that δ18O was low during the heavy rainfall events on 8/3 and 8/9. This can be attributed to the quantitative effect that the isotopic ratio of water, or water vapor, in the atmosphere gradually decreases due to condensation of heavier water molecules first. The peak δ18O was lower during the heavy rainfall event on 8/3 than on 8/9 when the Iwaki River was in danger of flooding, and Iso-RSM calculations generally reproduced the trend in isotope ratios and d-excess at Hirosaki.
The ERA5 analysis reproduces the precipitation time series extremely well, especially the peak at 0 UTC (= 9 JST) on 8/3 and the temporal variation of precipitation from 8/9 to 8/10. However, the total amount of precipitation is underestimated. Quantitative precipitation reproducibility will be verified based on grid precipitation generation and radar AMeDAS rainfall analysis.
According to the vertical-integrated water vapor flux, divergence and precipitation distribution by ERA5 on both days near the time of peak precipitation in Hirosaki, precipitation on 8/3 was caused by a low pressure system with a front, but a significant water vapor divergence area was observed over the northern Sea of Japan compared to 8/9, indicating a water vapor source from western Aomori to Akita Pref. The source of the water vapor is from western Aomori to Akita Prefectures. The Aomori District Meteorological Observatory (2022a) indicated that warm, moist air originating from Typhoon No. 6 flowed in as the source of the water vapor for the heavy rainfall on 8/3, but a water vapor contribution from the water vapor divergence off the western coast of Aomori is also possible, and detailed analysis is a future issue.
The precipitation on 8/9-10 was reported to be warm and moist air flowing toward a front that extended from northern China through the Sea of Japan to northern Japan, and the ERA5 precipitation distribution and the existence of weak convergence areas are also close to this view. The water vapor flux and precipitation distribution show a precipitation zone from the Oga Peninsula to the Shimokita Peninsula with a precipitation peak near Fukaura and water vapor convergence in that area, as well as a divergence peak slightly northwest of the divergence peak on 8/3. The contribution of water vapor from this area and the Japan Sea will be discussed in the future.
It is known that the d-excess of the oxygen/hydrogen isotope ratio of water is high in the case of repeated severe evaporation and re-evaporation. In this study, d-excess was high at both of the two δ18O minima. We will discuss the contribution of typhoon origin, large-scale moisture transport to fronts, and evaporation from the Japan Sea based on the isotopic results.