Interdecadal variability of East Asian summer monsoon precipitation over 220 years (1777–1997)

In this study, long-term (1777–1997) precipitation data for Seoul, Korea, wetness indices from eastern China, and modern observations are used to identify the interdecadal variability in East Asian summer monsoon precipitation over the last 220 years. In the East Asian monsoon region, two long-term timescales of dry-wet transitions for the interdecadal variability and quasi-40- and quasi-60-year timescales are dominant in the 220-year precipitation data of Seoul, as well as in the wetness indices over China. The wet and dry spells between Seoul (southern China) and northern China are out-of-phase (out-of-phase) at the quasi-60-year timescale, and in-phase (out-of-phase by approximately 90° before 1900 and in-phase after 1900) at the quasi-40-year timescale. In particular, during the last century, the dominant long-term timescales over East Asia tend to decrease from the quasi-60-year to the quasi-40-year with increasing time. The dominant quasi-40-year and quasi-60-year timescales of the Seoul precipitation in Korea are strongly correlated with these timescales of the northern Pacific Ocean.