[A-CG43] Science in the Arctic Region

[ACG43-04] Remote influences and long-term variation of the summer Siberian blocking

*Tetsu Nakamura¹, Tomonori Sato¹ (1.Faculty of Environmental Earth Science, Hokkaido University)

Keywords:blocking high, Meiyu/Baiu rainband, Global warming, Arctic warming, Remote influence

The Blocking high occurred in summer Siberia has been studied not only for frequent heat wave as a direct influence but also its remote influences. Through analyses of 2020 summer, it has been reported that Meiyu/Baiu rainfall is enhanced in association with development of the Siberian blocking. It has been also reported that the Siberian blocking enhances its frequency and magnitude due to the rapid warming over the Arctic region, and future projection of the Siberian blocking under the global warming condition has large uncertainty. In this study we investigate statistical relationship between the Siberian blocking and East Asian summer rainfall using 60-years reanalysis data. An empirical formula of blocking occurrence that is widely used was expanded to a horizontal two dimension, thereby area fraction of occurrence over Siberian region was defined as a magnitude of the blocking. Composite analysis shows increase of the Meiyu/Baiu rainfall in accordance with the increase of the blocking magnitude. Due to the transient eddy feedback, development of the blocking high is accompanied by the trough in its south. The summer Siberian blocking locates north of the climatological Meiyu/Baiu rainband, therefore the southern trough enhances rainfall in East Asia. Such the remote influence of the blocking high could not appear for the blocking high of the other longitudes, and thus a unique characteristic of the Siberian blocking. The long-term variation of the Siberian blocking has gently increased trend and marked decal variations, suggesting both of influences of the rapid Arctic warming and modulation by the tropical and mid-latitude ocean variations.