Effect of the representation of mountains on the Asian monsoon in a global warming world

Abstract:

Previous studies show that the evolution of the Asian monsoon is sensitive on the height of the large-scale mountains such as the Tibetan Plateau, in which monsoon rain areas move inland and northward with stronger Meiyu-Baiu rain bands as mountains become higher. These studies suggest that the future projections of the Asian monsoon under the global warming may be sensitive to the imposed topography used in the model. Here, we investigate the effects of the representation of large-scale mountains on the Asian monsoon by global warming. We have varied the mountain height every 25% from 0 to 150% of the present value with the 120-km mesh MRI-AGCM for the present and the future climate. The latter experiment is performed by adding the CMIP5 model ensemble mean sea surface temperature changes under the RCP8.5 scenario at the end of the 21st century to the present (end of the 20th century) values. It is found that the Asian summer monsoon rainfall increases by global warming with relatively similar rates regardless of mountain height, but the change of the Meiyu-Baiu rainfall is sensitive to mountain height. Northward moisture flux into the Meiyu-Baiu region at the present climate increases with mountain height as the Pacific subtropical anticyclone becomes stronger. Under the global warming, weakened lower troposphere convergence over the western Pacific results in westward extent of the Pacific subtropical anticyclone. As mountain becomes higher, northward moisture flux over the western Pacific increases more, resulting in more intensified rainfall in the Meiyu-Baiu region from China to western Japan.