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.