Recent intensification of the western Pacific subtropical high associated with East Asian summer monsoon

Thursday, 18 December 2014
Shinji Matsumura1, Shiori Sugimoto2 and Tomonori Sato1, (1)Hokkaido University, Sapporo, Japan, (2)Tokyo Metropolitan University, Tokyo, Japan
The summer western Pacific subtropical high (WPSH) has intensified during the past three decades. However, the underlying mechanism is not yet well understood. Here, we show that Baiu-rainband activity, which is part of the East Asian summer monsoon, plays an important role in recent intensification in the WPSH along the Baiu rainband. In contrast with the WPSH, the summer Okhotsk high, which is located to the north of the Baiu rainband, has weakened during the past three decades. The north-south contrasting changes between the two highs reflect a response to northward-moved and enhanced Baiu heating, which intensifies the upper-tropospheric ridge, resulting in the baroclinic intensification of the WPSH. Regional climate model experiments also support the observational analysis. The results here suggest that the mechanism intensifying the summer North Pacific subtropical high clearly differs between the western and eastern Pacific.