Combined impacts of sea surface temperature in tropical Pacific and North Atlantic Oceans on the winter rainfall in southern China under decadal background

The sea surface temperature anomalies (SSTAs) in the tropical Pacific (TP) and North Atlantic (NA) are both important factors regulating the winter rainfall over southern China (SC). Our results show the combined impact of SSTAs exhibits an offset effect before 1985, after a decadal transition period, the two SSTAs patterns form an additive effect on the interannual timescale after 1995. These distinct impacts of the TP and NA result in the southward shift of the winter rainfall variability, which is associated with the decadal change of the TP and NA. Both the background modes in TP and NA show a phase transition during the period 1985-1995, accompanied by the interannual variations of the SSTAs in two ocean basins before 1985 and after 1995. Before 1985, the canonical El Nino-related southerly winds of the anticyclone over the western North Pacific transport sufficient water vapour and enhance rainfall in SC. While the concurrent dipole NA SSTA-related wave train propagates to Eurasia, causing a cyclone and divergence of water vapour fluxes suppressing the local rainfall. After 1995, the El Nino-related warm SSTAs move westward and strengthen the rainfall anomalies in the Yangtze River basin. Meanwhile, a tripole mode of SSTAs replaces the dipole counterpart in NA, resulting in the anomalous cyclonic circulation over South Asia with more rainfall in the south edge of SC. The decadal changes of the TP and NA mode combination could affect the seasonal distribution and prediction of China winter rainfall.