5:15 PM - 7:15 PM
[ACG49-P03] Impact of the Sea Surface Temperature of the Japan Sea on the Heavy Rainfall in the Noto Region on September 21, 2024
Keywords:Meso Low, Air-Sea Interaction
From September 20 to 22, 2024, heavy rainfall occurred over a wide area from the Tohoku region to western Japan due to the eastward movement of a low pressure and the influence of the autumn rain front. In particular, on the 21st, heavy rainfall was observed in the northern part of the Noto Peninsula in Ishikawa Prefecture, where meteorological observation stations in Wajima City and Suzu City recorded their highest-ever hourly and three-hourly precipitation. This heavy rainfall caused river floods and landslides, mainly in the Noto region.
During the heavy rainfall, the sea surface temperature in the southern Japan Sea was about 5°C higher than the climatological mean (1982–2011 average). We try to clarify the impact of this high sea surface temperature on the heavy rainfall in the Noto region through numerical experiments.
In this study, the Weather Research and Forecasting (WRF) model was used. The sea surface temperature was from OISST data, and the atmosphere initial and lateral boundary conditions were taken from NCEP-FNL data. The experiment covered a region that sufficiently included Japan and the surrounding seas, with a horizontal resolution of 5 km. Two experiments were conducted: a control experiment using the actual sea surface temperature and a non-warming experiment in which the sea surface temperature of the Japan Sea was replaced with the climatological mean. The impact of high sea surface temperatures was evaluated by comparing the results of these two experiments.
In the control experiment, the 24-hour precipitation in Wajima City, Ishikawa Prefecture, reached 380 mm, which was almost consistent with the observed values, and therefore we concluded that this experiment realistically reproduced the event. In the non-warming experiment, the accumulated precipitation at the same location decreased by approximately 40%. This result suggests that the high sea surface temperature in the Japan Sea contributed to the heavy rainfall. The formation of a meso low off the western coast of the Noto Peninsula played a role in this heavy rainfall event. In the control experiment, the central pressure of this meso low was about 2 hPa lower than that in the non-warming experiment. In other words, the high sea surface temperature in the Japan Sea intensified the meso low, strengthening the southwesterly winds on its eastern side and increasing moisture supply, thereby enhancing the autumn rain front and contributing to the heavy rainfall.
Our presentation will also introduce the impact of the extreme warming off the Sanriku coast caused by the extreme northward meandered Kuroshio Extension on the heavy rainfall in the Noto region.
During the heavy rainfall, the sea surface temperature in the southern Japan Sea was about 5°C higher than the climatological mean (1982–2011 average). We try to clarify the impact of this high sea surface temperature on the heavy rainfall in the Noto region through numerical experiments.
In this study, the Weather Research and Forecasting (WRF) model was used. The sea surface temperature was from OISST data, and the atmosphere initial and lateral boundary conditions were taken from NCEP-FNL data. The experiment covered a region that sufficiently included Japan and the surrounding seas, with a horizontal resolution of 5 km. Two experiments were conducted: a control experiment using the actual sea surface temperature and a non-warming experiment in which the sea surface temperature of the Japan Sea was replaced with the climatological mean. The impact of high sea surface temperatures was evaluated by comparing the results of these two experiments.
In the control experiment, the 24-hour precipitation in Wajima City, Ishikawa Prefecture, reached 380 mm, which was almost consistent with the observed values, and therefore we concluded that this experiment realistically reproduced the event. In the non-warming experiment, the accumulated precipitation at the same location decreased by approximately 40%. This result suggests that the high sea surface temperature in the Japan Sea contributed to the heavy rainfall. The formation of a meso low off the western coast of the Noto Peninsula played a role in this heavy rainfall event. In the control experiment, the central pressure of this meso low was about 2 hPa lower than that in the non-warming experiment. In other words, the high sea surface temperature in the Japan Sea intensified the meso low, strengthening the southwesterly winds on its eastern side and increasing moisture supply, thereby enhancing the autumn rain front and contributing to the heavy rainfall.
Our presentation will also introduce the impact of the extreme warming off the Sanriku coast caused by the extreme northward meandered Kuroshio Extension on the heavy rainfall in the Noto region.