[1] The impact of the Atlantic Multidecadal Oscillation (AMO) on the Asian summer monsoon is investigated using a coupled atmosphere-ocean global general circulation model by imposing the AMO-associated sea surface temperature anomalies in the Atlantic as boundary forcing, and allowing atmosphere-ocean interactions outside the Atlantic. The positive AMO phase, characterized by anomalous warm North Atlantic and cold South Atlantic, leads to strong Southeast and east Asian summer monsoons, and late withdrawal of the Indian summer monsoon. These changes of monsoons are mainly through coupled atmosphere-ocean feedbacks in the western Pacific and Indian Oceans and tropospheric temperature changes over Eurasia in response to the imposed forcing in the Atlantic. The results are in agreement with the observed climate changes in China corresponded to the AMO phases. They suggest a non-local mechanism for the Asian summer monsoon variability and provide an alternative view to understanding its interdecadal variation during the twentieth century.

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The East Asian summer monsoon is characterized by strong interactions among its components in the meridional direction. The atmospheric convection over the Philippine Sea (PSAC), the western North Pacific subtropical high (WNPSH) and the East Asian westerly jet stream (EAJ) are all closely related to the summer rainfall in East Asia. In this study, we examined the relationship on the interannual timescale among these factors, by using the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Re-analysis data and satellite-observed outgoing long-wave radiation (OLR) data for the 20-year period from 1979 to 1998.It is found that the PSAC-EAJ relation is weak in June, but strong in July and August. Similar difference exists in the relationship between the PSAC and convective activity along the East Asian summer rainy belt. Corresponding to enhanced PSAC, the EAJ is weakened in July and strengthened in August, and tends to exhibit a slight poleward displacement in both months. All these variations in the EAJ intensity and meridional displacement, on the other hand, correspond to suppressed convection along the East Asian summer rainy belt. Finally, the monthly difference in the PSAC-EAJ relation is interpreted by the role of vertical shear of zonal wind. The easterly shear in July and August over the Philippine Sea excites external modes, which are necessary for the tropical-extratropical teleconnection mechanism according to previous numerical studies, but the neutral shear in June is inefficient in exciting external modes.

One-point correlation analysis on upper-level meridional wind identified the existence of a teleconnection pattern in July, which emerges from North Africa to East Asia along the westerly jet in the middle latitudes. We examined the spatial and temporal structures of this teleconnection pattern, and found the unique characteristics rather different from the patterns in other elements such as geopotential height, streamfunction and vorticity. We also investigated the relationship between this teleconnection and precipitation, and suggested that the teleconnection is a possible linkage of the EASM to the Indian monsoon, and even to subtropical heating anomalies over Atlantic. * Corresponding author. elements are zonally elongated at the upper tropo-Address: Institute of Atmospheric Physics, Chinese sphere, because of great seasonal and interannual Academy of Sciences, PO Box 2718, Beijing 100080, variabilities in meridional position of the westerly China.

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The meridional teleconnection patterns over the western North Pacific and East Asia (WNP–EA) during summer have a predominant role in affecting East Asian climate on the interannual time scale. A well-known seesaw pattern of tropical–subtropical precipitation is associated with the meridional teleconnection, and the subtropical precipitation anomaly has been previously viewed as a result of anomalous circulations associated with the teleconnection. In this study, however, the authors suggest that subtropical precipitation anomalies, in turn, can significantly affect large-scale circulations and may be crucial for maintenance of the meridional teleconnection. Diagnosis by using observational and reanalysis data indicates that the meridional teleconnection patterns are clearer in summers when the subtropical rainfall anomalies are greater. The simulated results by a linear baroclinic model indicate that a subtropical heat source, which is equivalent to the diagnosed positive subtropical precipitation anomaly, induces zonally elongated zonal wind anomalies that resemble the diagnosed ones in both the upper and lower troposphere over the extratropical WNP–EA. The simulated results also indicate that the horizontal and vertical structures of circulation responses are insensitive to the locations and shapes of imposed subtropical heat anomalies, which implies the important role of basic flow in circulation responses. This study suggests that, for confidential dynamical seasonal forecasting in East Asia, general circulation models should be required to capture the features of interannual subtropical rainfall variability and basic-state flows in WNP–EA.

Regional temperature changes are a crucial factor in affecting agriculture, ecosystems and societies, which depend greatly on local temperatures. We identify a nonuniform warming pattern in summer around the mid-1990s over the Eurasian continent, with a predominant amplified warming over Europe–West Asia and Northeast Asia but much weaker warming over Central Asia. It is found that the nonuniform warming concurs with both the phase shift of the Atlantic Multi-decadal Oscillation (AMO) and the decadal change in the Silk Road Pattern (SRP), which is an upper-tropospheric teleconnection pattern over the Eurasian continent during summer. We suggest that the AMO may modulate the decadal change in SRP and then induce the zonal asymmetry in temperature changes. Our results have important implications for decadal prediction of regional warming pattern in Eurasia based on the predictable AMO.

The Silk Road pattern (SRP), which depicts the teleconnection pattern along the Asian jet, has been extensively investigated and commonly described as the leading mode of upper-tropospheric meridional wind anomalies in summer. In this study, the SRP is identified as having a significant relationship with the meridional displacement of the Asian jet (JMD), which manifests as the leading mode of upper-tropospheric zonal wind anomalies. This significant relationship is confirmed by the correlation coefficient between the indices for JMD and SRP, which is 0.39 and reaches statistical significance at the 0.01 level. When the Asian jet is in a northward (southward) displacement, the phase of SRP tends to be shown as anticyclonic (cyclonic) anomalies over western Asia and East Asia and cyclonic (anticyclonic) anomalies over Europe and central Asia. The authors propose an internal atmospheric mechanism for this relationship. In addition, it is found that the JMD is significantly affected by the tropical surface temperature anomalies. In particular, the negative (positive) SST anomalies in the tropical central and eastern Pacific of the preceding spring lead to significant cooler (warmer) tropical tropospheric temperatures in summer and may induce the northward (southward) displacement of the Asian jet through modifying the meridional gradient of tropospheric temperatures. The tropical tropospheric temperature anomalies may also affect the SRP through the JMD.