The impact of tropical intraseasonal oscillation on the summer rainfall increase over southern China around 1992/1993

A pronounced summer rainfall increase over southern China occurred around 1992/1993. In the present study, the impact of the boreal summer intraseasonal oscillation (BSISO) on this decadal increase is investigated through diagnostic analysis. It is found that the BSISO-induced rainfall increase accounts for approximately 17.4% of the observed decadal rainfall increase, with a primary part coming from changes in the rainfall pattern associated with phases 3-5 of the BSISO. A further analysis reveals that changes in rainfall pattern over southern China are mainly ascribed to changes in spatial structure of anomalous convection associated with interdecadal change in BSISO tracks. Apart from significant influence of changes in BSISO tracks, changes in the frequency of individual active BSISO phases also have considerable influence on the interdecadal change in summer rainfall over southern China. Based on our analysis, the increase in absolute and relative frequency of occurrence of phases 1 and 8, coupled with their corresponding rainfall pattern, makes a positive contribution to the increase in southern China summer rainfall. The interdecadal change in the BSISO tracks and the frequency of active BSISO phases is likely related to coherent changes in atmospheric circulation and sea surface temperature over the Indian Ocean and the western Pacific.