3:45 PM - 4:00 PM
[HTT16-02] Moisture source of rainfall in Hirosaki associated with an explosive cyclone in Feb.15-16, 2021
Keywords:Precipitation, Water Vapor, isotope, meteorological model
Hirosaki is a heavy snowfall area located on the Japan Sea side of Aomori Prefecture. We continued isotopic analysis of precipitation and water vapor for the winter since 2019 (water vapor is from 2021). Ueno et al. (2021) analyzed the case, 15-16 February, which showed the lowest isotopic ratio of precipitation during the winter of 2020/2021. This precipitation event was associated with a rapidly developing low pressure system that moved northward off Sanriku, and sometimes referred to as an explosive cyclone. The JMA AMeDAS recorded daily precipitation of 21 mm in Aomori, 13.5 mm in Hirosaki, and 31.5 mm in Mutsu on the February 15th. A record breaking daily maximum wind speed for February was recorded at Oma, Kuroishi, and Sanno in Aomori Prefecture. Hirosaki experienced heavy rainfall, not snowfall, from 15 to 23 JST on 15 February, and then, intermittent precipitation (snowfall) was observed thereafter.
Yamaguchi (2021) conducted a dynamical and thermodynamical analysis of the cyclone development, and found that latent heat release from the sea surface off the Ogasawara Islands, development of baroclinic instability, and interaction with upper level potential vorticity contributed significantly to the rapid development of the cyclone.
The numerical experiment reported here is an extension of that of Ueno et al. (2021), we newly set a domain of considering water source over the Pacific Ocean. Namely, in addition to the Japan Sea (120-140E/35-50N) and the East China Sea (120-140E/20-35N), which are also conventionally considered as water evaporation sources of winter precipitation along the Japan Sea side, this experiment assesses the contribution of water evaporation from the four ocean areas, including Pacific Ocean (North: 140-160E/35-50N; South: 140-160E/20-35N). For this experiment, the isotopic atmospheric general circulation model IsoGSM (T248) driven by ERA5 was utilized as the initial boundary condition, and IsoRSM (Yoshimura et al., 2011) executed at 30 km resolution.
During the first half of the period of the lowest isotopic ratio measurements (2/15 3UTC - 2/16 3UTC), until 2/15 12UTC when rainfall was observed in Hirosaki, the contribution of evaporation from the south Pacific to precipitation in Hirosaki was significant (60% at the peak), followed by the north Pacific origin (20%). From 12 UTC to 18 UTC, which is defined as term-2 (T2) by Ueno (2022), evaporation from the Sea of Japan (~30%), the East China Sea, and the southern Pacific Ocean were mixed, with the proportion of the Sea of Japan origin gradually increasing during T2. After 20 UTC when snowfall was observed in Hirosaki (T3 in Ueno 2022), the contribution of evaporation from the Pacific Ocean southeast of Japan decreased, and from February 16th 00 UTC, the contribution was almost completely replaced by the evaporation from the Japan Sea.
Yamaguchi (2021) conducted a dynamical and thermodynamical analysis of the cyclone development, and found that latent heat release from the sea surface off the Ogasawara Islands, development of baroclinic instability, and interaction with upper level potential vorticity contributed significantly to the rapid development of the cyclone.
The numerical experiment reported here is an extension of that of Ueno et al. (2021), we newly set a domain of considering water source over the Pacific Ocean. Namely, in addition to the Japan Sea (120-140E/35-50N) and the East China Sea (120-140E/20-35N), which are also conventionally considered as water evaporation sources of winter precipitation along the Japan Sea side, this experiment assesses the contribution of water evaporation from the four ocean areas, including Pacific Ocean (North: 140-160E/35-50N; South: 140-160E/20-35N). For this experiment, the isotopic atmospheric general circulation model IsoGSM (T248) driven by ERA5 was utilized as the initial boundary condition, and IsoRSM (Yoshimura et al., 2011) executed at 30 km resolution.
During the first half of the period of the lowest isotopic ratio measurements (2/15 3UTC - 2/16 3UTC), until 2/15 12UTC when rainfall was observed in Hirosaki, the contribution of evaporation from the south Pacific to precipitation in Hirosaki was significant (60% at the peak), followed by the north Pacific origin (20%). From 12 UTC to 18 UTC, which is defined as term-2 (T2) by Ueno (2022), evaporation from the Sea of Japan (~30%), the East China Sea, and the southern Pacific Ocean were mixed, with the proportion of the Sea of Japan origin gradually increasing during T2. After 20 UTC when snowfall was observed in Hirosaki (T3 in Ueno 2022), the contribution of evaporation from the Pacific Ocean southeast of Japan decreased, and from February 16th 00 UTC, the contribution was almost completely replaced by the evaporation from the Japan Sea.