A global warming projection was conducted by using a very high horizontal resolution atmospheric general circulation model with 20-km grid. The change of Asian summer monsoon season are selected as one of the main targets of this study, because the activity of Asian summer monsoon greatly affects the life and society of people living in the region. But so far the global climate models have not given reliable simulations and projections due to their insufficient resolutions.
Fig. 1a shows simulated July climatology by the model under the present-day climate condition. The model reproduces Baiu rain band reasonably well over Japan, Korea, China, although the model overestimates precipitation over Korea. Also the model well reproduces precipitation over Indian subcontinent, although the model overestimates precipitation over oceans. As for 850-hPa wind field, the model well reproduces clockwise circulation over the subtropical high, north-eastward flow from Indochina to Japan, and Somali jet.
Figure 1b show the change of precipitation and 850-hPa wind field projected by the model for July. Precipitation increases over the Yangtze river valley, the East China Sea and ocean to the south of Japan. Clockwise circulation change of 850-hPa wind over the subtropical high means the intensification of subtropical high. Strengthening of clockwise circulation together with increase of water vapour amount due to the warming of atmosphere leads to the increase of water vapour transport from tropics to the East China Sea. In contrast, precipitation decreases over Korea and Northern Japan. In spite of the weakening of Somali jet, precipitation over Indian subcontinent increases. This is because the water vapour transport decrease due to the weakening of Somali jet is compensated by the increases of water vapour amount due to the warming of atmosphere.