[A-CG49] Kuroshio Large Meander

[ACG49-P05] Impact of coastal warming induced by the Kuroshio large meander on extremely hot and humid events in the Kanto region, Japan

*Hidetaka Hirata¹, Atsuhiro Suzuki¹ (1.Rissho University)

Keywords:Kuroshio, extreme weather, coastal climate

Recent research has indicated that the Kuroshio large meander (LM) caused a warming of the sea surface temperature (SST) off the Tokai region, leading to an increase in water vapor and temperature in the Kanto region during summer. However, it has not been investigated whether the Kuroshio LM affects the occurrence of extremely hot and humid events. In this study, we examine the relationship between the Kuroshio LM and extremely hot and humid events in the Kanto region region during summer (July-August) using the Japan Meteorological Agency's ground observation data and the fifth generation ECMWF reanalysis data (ERA5) for the period 1990-2024. First, we extracted extremely hot and humid days (extreme events) based on the maximum daily discomfort index calculated from the observation data, and investigated the interannual variation in the number of the days. The results showed that the number of extreme events increased rapidly after 2018. This was confirmed not only in the coastal area, but also in the inland area. These results suggest that the Kuroshio LM, which is occurring from August 2017 to the present, contributed to the increase in the extreme events. Next, we investigate how the LM-induced coastal warming affects the occurrence of extreme events using the reanalysis data. In the coastal warming region, positive anomalies in surface latent heat flux were evident, while anomalies in sensible heat flux were very small. This is consistent with previous studies, and it is possible that the coastal warming affects the extremely hot and humid conditions in the Kanto region by increasing the water vapor content and the associated enhancement of the greenhouse effect. In fact, clear positive anomalies in water vapor were observed in the Kanto region, and these were accompanied by positive anomalies in temperature and the discomfort index. On the days when extreme events occurred, we found the surface pressure pattern associated with the near-surface air flows from the coastal warming area to the Kanto region. This pressure pattern seems to trigger the occurrence of extreme events by increasing the inflow of water vapor from the coastal warming region to the Kanto region.