Abstract In order to assess how the Bonin high af- fects interannual variability of the East Asian summer monsoon (EASM) around the Korean Peninsula, the pulsation of the Bonin high and its association with teleconnection patterns was examined. The major factor for the interannual intensity of the EASM is the center position of the Bonin high rather than its center pressure. Up to 12 harmonics over time can be used to reconstruct the Bonin high, demonstrating its intraseasonal variation. The interannual variability of the Bonin high correlates with the Tibet high. This correlation is dominant for the EASM onset time, though not its retreat. The primary teleconnection pattern, reliant up on the interannual variability of the Bonin high, is the Western Pacific oscillation (WPO) in April. In relation to long-term variability, the correlation between the WPO and the Bonin high appears to contribute to the retreat stage of the EASM, which has itself increased since the mid-1970s. Furthermore, the WPO in May and the Tibet corre- lation has marked the onset rather than the retreat of the EASM since the 1970s. This highly correlated pattern since the mid-1970s may be the result of El Nin ˜ o. 1 Introduction In recent years, the Korean Peninsula has suffered from an extra-ordinarily heavy rainfall during the East Asian summer monsoon (EASM). Nevertheless the definition of rainfall intensity associated with the EASM and the mechanisms that affect its interannual variability are unclear. The East Asian summer mon- soon rain over the Korean Peninsula, which is also called ‘Changma’, has been defined by approximately forty days of precipitation from late June to late July (Lu 2002; Ho et al. 2003; Ha et al. 2005). The most important aspect of the EASM is its large interannual variability. Therefore, predicting the interannual vari- ability (IAV) of regional rainfalls over the East Asian monsoon region is an imperative task. Most studies on the IAV of the EASM have noted that summer rainfall in East Asian regions is statistically associated with the Eurasian snow cover (Yang and Xu 1994) and SST anomalies (Yang and Yuan 1996) in the equatorial Pacific and Indian Oceans. Even though the relationship between snow cover/ SST and EASM is statistically correlated, many scien- tists (Wang et al. 2004; Kang et al. 2002; Sumi et al. 2004) have suggested that simulations of the East Asian monsoon are less than conclusive. Instead of using the levels of precipitation as an indicator of the IAV of the EASM, the characteristic large-scale cir- culations have been investigated. Several circulation- based indices have been produced for predicting the monsoon. In addition, invaluable efforts have been made to create an index using circulation for the pre- diction of monsoons such as WYI (Webster and Yang 1992), East Asian/Pacific index (EAPI, Huang 2003), and the Changma index (Ha et al. 2005). They suggest K.-J. Ha (&) Æ S.-S. Lee Department of Atmospheric Sciences, Pusan National University, Busan, South Korea e-mail: kjha@pusan.ac.kr Clim Dyn (2007) 28:67–83 DOI 10.1007/s00382-006-0169-x 123 On the interannual variability of the Bonin high associated with the East Asian summer monsoon rain Kyung-Ja Ha Æ Sun-Seon Lee Received: 22 February 2006 / Accepted: 13 June 2006 / Published online: 21 July 2006 Ó Springer-Verlag 2006