4:15 PM - 4:30 PM
[AOS18-04] Increase in summer surface air temperature at the Kanto district attributable to Kuroshio large meander
Keywords:Kuroshio large meander, Hot summer, Kanto district, Greenhouse effect, Discomfort index
The summer climate in the Kanto district, Japan, including Tokyo, where has 40 million inhabitants, is characterized by high temperature and humidity. The Kuroshio that flows off the southern coast of Kanto district has taken a large meander (LM) path since the summer of 2017, which is still continuing after three and a half years. It has been recognized that the cool water pool is broadly distributed in the onshore region between the Kuroshio and the southern coast of Kanto-Tokai district during the LM path period. Recently-developed satellite observations detected marked coastal warming off the Kanto-Tokai district during the LM path period. In this study, we conducted regional atmospheric model experiments to quantitatively assess the influence of LM-induced coastal warming on the summer climate of Japan via atmospheric responses. Results indicated that summertime coastal warming increases water vapor in the low-level atmosphere through enhanced evaporation from the ocean and influences near-surface winds via the vertical mixing effect over the warming area. These two changes induce an increase in water vapor in Kanto district, leading to an increase in downward longwave radiation at the surface and then surface warming through a local greenhouse effect. Resultantly the summer in Kanto district becomes increasingly hot and humid in LM years, with double the number of discomfort days compared with non-LM years. Our simulations and supplementary observational studies reveal the significant impacts of the LM-induced coastal warming on the summertime climate in Japan, which can exceed previously identified atmospheric teleconnections and climate patterns. Our results could improve weather and seasonal climate forecasts in this region.