Abstract. Further verification about the circulation effect of stalagmite δ18O in East Asian monsoon region needs the quantitative description for the proportion of water vapor transport (WVT) from different source regions. WVT passageway intensities are defined as regionally averaged WVT flux modes in this paper. The ratio between two WVT passageways' intensities represents relative intensity of the two WVT passageways. Using the NCEP-NCAR reanalysis data for 1948–2011, the ratios of the intensities of three WVT passageways from low latitudes (the intensity of WVT from Bay of Bengal (IBOB), the intensity of WVT from South China Sea (ISCS) and the intensity of WVT from western North Pacific (IWNP) in summer are calculated. SB is for the ISCS-IBOB ratio, WB for the IWNP-IBOB ratio, and WS for the IWNP-ISCS ratio. The decadal increase occurs in the time series of WB and WS, with higher values in 1976–1995 and lower values in 1950–1975, probably resulting from the strengthening of WVT from WNP in the midterm of 1970s. East Asian atmospheric circulations, WVTs and previous SST characters corresponding to the ratios are analyzed. The result indicates that SB, WB and WS may properly reflect the relative intensities between ISCS and IBOB, between IWNP and IBOB, and between IWNP and ISCS, respectively. For high SB years, the Asian Low and the western Pacific subtropical high (WPSH) weaken. The southwesterly winds from BOB to the Yangtze River valley by the southeast of the Tibetan Plateau weaken and the WVT from BOB to East Asia weakens. The southwesterly winds from SCS to East Asia strengthen and the WVT from SCS to East Asia strengthens. In high WB years, the Asian Low weakens and the WPSH shifts westwards, enhances and enlarges. The WVT from WNP to East Asia increases because of the strengthening of the easterly winds on the south of the WPSH. The westerly winds from BOB to East Asia by Indo-China Peninsula decrease and the WVT from BOB to East Asia weakens. The atmospheric circulation and WVT associated with WS are similar with those associated with WB. There are close relationships between WB (and WS) and the WPSH area, position and intensity. In high WB (and WS) years, the WPSH shifts westwards, enlarges and enhances. There is no obvious anomalous previous SST signal in tropical Indian Ocean and equatorial central and eastern Pacific for anomalous SB years. WB and WS are closely related to previous SST signal. When the equatorial central and eastern Pacific is in El Niño phase, SST in the tropical Indian Ocean, BOB and SCS is high and SST at middle latitudes in North Pacific is low, WB and WS tend to be high. After the midterm of 1970s, the equatorial central and eastern Pacific is often in El Niño phase. It is in agreement with higher WB in 1976–1995 than that in 1950–1975. In light of circulation effect of stalagmite δ18O in East Asia, high WB implies high stalagmite δ18O. Therefore, the interdecadal increase of WB in 1976–1995 than in 1950–1975 provides the proof using the conception of circulation effect to explain the interdecadal change of stalagmite δ18O at most regions in East Asia.
Tropical Origins of the Record-breaking 2020 Summer Rainfall Extremes in East Asia
