DOI:10.2151/jmsj.87.139 Relationship between High-Impact Weather Events in Japan and Propagation of Rossby Waves along the Asian Jet in July 2004

In July 2004, torrential rainfalls caused significant damages in parts of Japan, followed by heat waves. Our data analysis shows that both rainfall and heat wave events in late Baiu season were caused by the intensification of the subtropical anticyclone near Japan (Bonin high) and that intensity of the Bonin high was significantly in-fluenced by propagation of Rossby waves along the subtropical jet. Hindcast experiments from 15 July were conducted to study the mechanisms and predictability of these high-impact weather events. On 17–18 July, local-ized rainfalls at a few locations along the coast of the Sea of Japan including Sakata and Fukui were successfully simulated in a high-resolution (21-km mesh) global hindcast simulation. These rainfall events were found to occur near the leading edge of a filament of moist and warm air advected clockwise. On 20 July, anomalously high tem-perature was reproduced in the high-resolution hindcast simulation. With a moderate resolution of 83 km, the intensification of the subtropical anticyclone was reproduced although the föhn was much weaker. This result in-dicates that temperature distribution associated with föhn requires a resolution high enough to resolve major mountains. In order to investigate the predictability of propagation of Rossby waves and intensification of the Bonin high, 25-member ensemble experiments from 1 July 2004 were conducted using the moderate-resolution model. It is shown that the region along the Asian jet has twice as long predictability as the entire Norther