Effect of the Ise Bay SST on the summer air temperature of the Nagoya urban area

The sensitivity of the urban summer air temperature on the sea surface temperature (SST) of the bay near the urban area is investigated. The future climate projection on the urban area is often based on the downscaling simulation from the result of the coupled general circulation model (CGCM). However, due to the lack of the resolution, the CGCM used in the global climate projection cannot reproduce the SST distribution near the coastline. Since many large cities are located near the coast, it can lead to uncertainty of the future climate projection on the urban area. Regional climate simulations are carried out on the Nagoya area, the largest urban area in the Chubu region of Japan located north of the Ise Bay. In the control case (referred to as CTL hereafter), the surface boundary condition is generated from NCEP/NCAR reanalysis, whose resolution is similar to the typical CGCM of CMIP3 and CMIP5, and does not capture the SST distribution of Ise Bay. Another simulation with increased SST of 2K to the CTL in the Ise Bay (SST+2K), which is typical difference between the inside and outside of the bay, is carried out to estimate the sensitivity. In the monthly mean field, the temperature of SST+2K is larger at most 0.2 K on the land. The difference can be found in the area with the distance less than 10km from the Ise Bay, and hardly reaches to the Nagoya city center. However, in instantaneous fields of clear days, the difference of the temperature exceeds 0.6 K, and reaches far inland. The result suggests that the bay SST is crucial in the prediction of the maximum air temperature on the clear days, which gives the hottest temperature in the summer.