Interdecadal differences in the interannual variability of the winter monsoon over the South China Sea

We investigate interdecadal differences in the interannual variability of the South China Sea (SCS) Winter Monsoon (SCSWM) since 1950. The SCSWM is influenced by both the East Asian Winter Monsoon (EAWM) over the mid–high latitudes and the anomalous anticyclone over the western North Pacific (WNPAC). The EAWM tends to cause a positive linear correlation of wind speeds between the northern SCS (NSCS) and the southern SCS (SSCS). Because the cold surge of the EAWM can make wind speeds over the NSCS and SSCS increase simultaneously. While, the WNPAC tends to weaken this positive correlation (corNS) because anomalies associated with the WNPAC will decrease wind speeds over the NSCS but exert a small or even an opposite influence on wind speeds over the SSCS. The interannual variation of the EAWM before the late 1970s is greater than that after the early 1990s. And the WNPAC was weak and confined to the east of the SCS before the late 1970s but became strong and expanded towards the SCS after the early 1990s. As a result, the positive corNS was significant at the 95% confidence level before the late 1970s but became insignificant after the early 1990s.