Long-lead ENSO control of the boreal summer intraseasonal oscillation in the East Asian-western North Pacific region

Abstract

The boreal summer 30–60-day intraseasonal oscillation (ISO) in the East Asian-western North Pacific (EAWNP) region strongly influences persistent heavy rainfall in East Asia and tropical cyclone activities in the tropical western Pacific. In this study, we show that there exists a significant interannual south-north shift of the EAWNP-ISO activity between the equatorial eastern Indian Ocean—Maritime continent region and the subtropical South China Sea—western Pacific. This is reflected by the year-to-year changes in the occurrence frequency of individual ISO phases that correspond to different latitudinal locations of the convection anomaly. This interannual shift is largely controlled by the El Niño—Southern Oscillation (ENSO) in the preceding winter and spring. Following an El Niño event, the ISO convective activity tends to occur in the equatorial eastern Indian Ocean—Maritime continents, whereas after a La Niña, frequent ISO-related precipitation occurs in the region of south China and the subtropical South China Sea—western Pacific. This result implies long-lead predictability for the occurrence of the summertime EAWNP-ISO activity and its associated weather.