5:15 PM - 7:15 PM
[ACG49-P04] Impact of sea surface temperature increase off the east coast of Japan due to extreme northward meandered Kuroshio Extension on snowfall in Tokyo -Case study of February 5, 2024-
Keywords:Kuroshio Large Meander, Air-Sea Interaction, snowfall
Snowfall in Tokyo causes transportation disruptions and has a significant impact on social activities. A low pressure that passed along the southern coast of Honshu, Japan from January 22 to 23, 2018, induced 23 cm of snow depth in Tokyo, causing highway closures and train delays and cancellations. Therefore, elucidating the mechanism of snowfall in Tokyo is an important issue in considering adaptation measures and stabilizing social life. Recent study has pointed out a tendency of snowfall in Tokyo to increase when the ocean off the east coast of Japan is cold (Takahashi et al. 2020).
Since the spring of 2023, the Kuroshio Extension has been an extremely northward meandering path, resulting in an increase of sea surface temperature (SST) off the east coast of Japan by about 6℃ above normal (Sugimoto et al. 2025). However, even with this extreme warming, snowfall was observed in Tokyo in the winter of 2023-2024. One possible cause of this is the increase in the atmospheric water vapor due to the extreme warming off the east coast of Japan. In this study, we try to evaluate the impact of the extreme warming off the east coast of Japan on snowfall in Tokyo using the snowfall case on February 5, 2024. In particular, we attempt to clarify whether or not the extreme warming enhanced or suppressed snowfall.
In this study, we used the regional meteorological model, the weather research and forecasting (WRF). We used OISST data for SST, and NCEP-FNL data for the atmospheric initial and lateral boundary conditions. We conducted two experiments: the control experiment with the actual SST and the non-warming experiments, in which the SST off the east coast of Japan (36°N–41°N, 141°E–146°E) was replaced with the SST on corresponding days from 1982 to 2020. For the atmospheric condition, data for the year of 2024 were used. The outer region covering Japan and seas near Japan has a horizontal resolution of 16 km, and the region covering the Kanto district and off the east coast of Japan has a horizontal resolution of 4 km, and the two regions are connected by two-way nesting.
The experiment showed that the snowfall in Tokyo was the least in 2024, when the ocean off the east coast of Japan experienced an anomalous warming. The result of ensemble experiments indicated that the higher SST off the east coast of Japan, the less snowfall was in Tokyo. Surprisingly, when the ocean off the east coast of Japan was about 4°C cooler than normal, as in 1988, snowfall in Tokyo was about three times higher than the control experiment. Furthermore, when the SST off the east coast of Japan was high, precipitation increased instead of snowfall. This was attributed to the increase in the water vapor transport to Tokyo due to the extreme warming off the east coast of Japan, and the increase in the lower atmosphere temperature in Tokyo due to the enhancement of warm air advection. Based on these results, we concluded that the increase in SST off the east coast of Japan due to the extreme northward meandered Kuroshio Extension acted to suppress snowfall in Tokyo.
Since the spring of 2023, the Kuroshio Extension has been an extremely northward meandering path, resulting in an increase of sea surface temperature (SST) off the east coast of Japan by about 6℃ above normal (Sugimoto et al. 2025). However, even with this extreme warming, snowfall was observed in Tokyo in the winter of 2023-2024. One possible cause of this is the increase in the atmospheric water vapor due to the extreme warming off the east coast of Japan. In this study, we try to evaluate the impact of the extreme warming off the east coast of Japan on snowfall in Tokyo using the snowfall case on February 5, 2024. In particular, we attempt to clarify whether or not the extreme warming enhanced or suppressed snowfall.
In this study, we used the regional meteorological model, the weather research and forecasting (WRF). We used OISST data for SST, and NCEP-FNL data for the atmospheric initial and lateral boundary conditions. We conducted two experiments: the control experiment with the actual SST and the non-warming experiments, in which the SST off the east coast of Japan (36°N–41°N, 141°E–146°E) was replaced with the SST on corresponding days from 1982 to 2020. For the atmospheric condition, data for the year of 2024 were used. The outer region covering Japan and seas near Japan has a horizontal resolution of 16 km, and the region covering the Kanto district and off the east coast of Japan has a horizontal resolution of 4 km, and the two regions are connected by two-way nesting.
The experiment showed that the snowfall in Tokyo was the least in 2024, when the ocean off the east coast of Japan experienced an anomalous warming. The result of ensemble experiments indicated that the higher SST off the east coast of Japan, the less snowfall was in Tokyo. Surprisingly, when the ocean off the east coast of Japan was about 4°C cooler than normal, as in 1988, snowfall in Tokyo was about three times higher than the control experiment. Furthermore, when the SST off the east coast of Japan was high, precipitation increased instead of snowfall. This was attributed to the increase in the water vapor transport to Tokyo due to the extreme warming off the east coast of Japan, and the increase in the lower atmosphere temperature in Tokyo due to the enhancement of warm air advection. Based on these results, we concluded that the increase in SST off the east coast of Japan due to the extreme northward meandered Kuroshio Extension acted to suppress snowfall in Tokyo.