Boreal Summer Intraseasonal Oscillation and Its Possible Impact on Precipitation over Southern China in 2019

Based on daily precipitation observation data in China, the intraseasonal oscillation (ISO) features of summer precipitation over southern China in 2019 have been investigated by wavelet and band-pass filtering analyses. The results show that enhanced (suppressed) precipitation occurred over southern China during early (late) boreal summer 2019. The signals of both 10–20- and 30–60-day ISO in southern China are remarkable, with the amplitude of the 10–20-day ISO larger than the 30–60-day ISO in boreal summer 2019. The synergistic effect of the 10–20- and 30–60-day ISO wet phases was found to exert a tremendous influence on persistent heavy precipitation in July 2019, when the amount of precipitation reached its maximum in southern China since 1981. The atmospheric circulation and convection evolution characteristics of both 10–20- and 30–60-day ISO are further investigated. An anomalous low-level anticyclone over the South China Sea is prominently linked to the wet phase of the 10–20-day ISO, wher-eas an anomalous low-level cyclone over southern China is dominantly associated with the wet phase of the 30–60-day ISO. Both events enhance the water vapor convergence and ascending motion over southern China. Thus, the atmospheric circulation that accompanied the synergism of the wet phases of the 10–20- and 30–60-day ISO resulted in persistent heavy precipitation over southern China in July 2019.