Decadal change in relationship between east Asian and WNP summer monsoons

It has been recognized that the intensity of the east Asian (EA) summer monsoon has a negative correlation with that of the western North Pacific (WNP) summer monsoon. Here we show that this relationship is much stronger in the recent decade (1994-2004) than in the epoch before 1994 (1979-1993). The first two leading modes of summer-mean precipitation over the large region of the WNP and EA region are shown to be associated with two factors: the ENSO development and the WNP summer monsoon fluctuation. The leading mode has changed from an ENSO-related mode in 1979-1993 to a WNP summer monsoon-related mode in the recent decade (1994-2004). The summer-mean mid-tropospheric geopotential heights that are correlated with the WNP monsoon index also show a marked change in the teleconnection (wave-train) pattern between 1994-2004 and 1979-1993. All together this evidence suggests that the relationship between the EA and the WNP summer monsoons has experienced a significant decadal change around 1993-1994.