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[U11-01] Factors behind the development of the quasi-stationary precipitation band that caused record-breaking rainfall around northern Noto Peninsula in September 2024
★Invited Papers
Keywords:quasi-stationary precipitation band, convective system, low-pressure system along the front, water vapor supply from the sea surface
From September 21 to 22, 2024, record-breaking rainfall occurred mainly over the northern Noto Peninsula in Ishikawa Prefecture, owing to a low-pressure system moving eastward along the stationary front, and an extratropical cyclone changed from Typhoon Pulasan. A quasi-stationary precipitation band developed on the morning of the 21st, and the maximum 1-hour rainfall of 121 mm and 3-hour rainfall of 220 mm at the Wajima observation site broke the record for the largest amount in the observation history. Because the area where heavy rainfall occurred also coincided with the Noto Peninsula Earthquake that occurred on January 1, 2024, extensive damage occurred due to landslides, debris flows, and river floodings.
On the 21st, when the quasi-stationary precipitation band developed, the stationary front lay across the Sea of Japan, with warm and moist southwesterly flowing south of the front, cool northeasterly flowing north of the front, and wind convergence near the front was strengthened. A low-pressure system that originated near the Korean Peninsula on the afternoon of the 20th moved eastward along the front and approached the Noto Peninsula on the morning of the 21st. The low-pressure system along the front enhanced the warm and moist southwesterly near the Noto Peninsula, resulting in a large amount of moisture inflow to the Noto Peninsula. This continuously generated well-developed convective clouds, resulting in the development of the quasi-stationary precipitation band. When the quasi-stationary precipitation band occurred, the sea surface temperature (SST) from the Tsushima Strait to the Noto Peninsula was approximately 5°C higher than the climatology, and the air flowing into the Noto Peninsula received a large amount of water vapor from the sea surface. Numerical experiments using a non-hydrostatic atmospheric model to replace the high SST of the Sea of Japan with climatological values revealed that the development of the low-pressure system moving eastward along the front was suppressed, and rainfall associated with the quasi-stationary precipitation band was reduced compared with a simulation using the actual SST distribution. Higher SST increased the sensible and latent heat fluxes from the sea surface to the atmosphere, making the atmosphere highly unstable. The enhanced development of the low-pressure system along the front further increased the moisture inflow, resulting in an increase in the rainfall associated with the quasi-stationary precipitation band.
On the 21st, when the quasi-stationary precipitation band developed, the stationary front lay across the Sea of Japan, with warm and moist southwesterly flowing south of the front, cool northeasterly flowing north of the front, and wind convergence near the front was strengthened. A low-pressure system that originated near the Korean Peninsula on the afternoon of the 20th moved eastward along the front and approached the Noto Peninsula on the morning of the 21st. The low-pressure system along the front enhanced the warm and moist southwesterly near the Noto Peninsula, resulting in a large amount of moisture inflow to the Noto Peninsula. This continuously generated well-developed convective clouds, resulting in the development of the quasi-stationary precipitation band. When the quasi-stationary precipitation band occurred, the sea surface temperature (SST) from the Tsushima Strait to the Noto Peninsula was approximately 5°C higher than the climatology, and the air flowing into the Noto Peninsula received a large amount of water vapor from the sea surface. Numerical experiments using a non-hydrostatic atmospheric model to replace the high SST of the Sea of Japan with climatological values revealed that the development of the low-pressure system moving eastward along the front was suppressed, and rainfall associated with the quasi-stationary precipitation band was reduced compared with a simulation using the actual SST distribution. Higher SST increased the sensible and latent heat fluxes from the sea surface to the atmosphere, making the atmosphere highly unstable. The enhanced development of the low-pressure system along the front further increased the moisture inflow, resulting in an increase in the rainfall associated with the quasi-stationary precipitation band.