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Previous studies indicated that El Niño–Southern Oscillation (ENSO) significantly impacts the zonal shift of the South Asian High (SAH) in boreal summer. This analysis reveals that the influence of ENSO on the zonal shift of the SAH has experienced a significant interdecadal weakening around the early 1980s. Specifically, ENSO has a significant relation with the SAH's zonal shift before the early 1980s. However, after the early 1980s, the impact of the ENSO on the SAH is weak. We further examined the physical processes for the interdecadal change of the ENSO–SAH relation. It is indicated that interdecadal change of relationship between ENSO and SAH zonal shift is attributable to change in the connection between ENSO and Indian summer monsoon (ISM). Before the early 1980s, ENSO could exert significant impacts on the ISM and lead to significant condensational latent heating anomalies around the northern Indian Peninsula. The atmospheric heating anomalies around the northern Indian Peninsula trigger an atmospheric wave train extending eastward from North Africa toward the Iranian Plateau (IP), which further leads to changes in the zonal location of the SAH. Hence, the ENSO exerts significant impacts on the summer SAH zonal shift. By contrast, after the early 1980s, ENSO had a weak impact on the ISM and could not lead to apparent atmospheric heating anomalies over IP. As such, ENSO has a weak effect on the SAH zonal shift. Further analysis indicates that interannual variation of the SAH zonal shift is related to an atmospheric wave train over mid–high latitudes of Eurasia after the early 1980s. [ABSTRACT FROM AUTHOR]

The East Asian winter monsoon (EAWM) exhibits long-term variations in intensity and spatial pattern, though the latter one is less understood. To investigate the long-term spatial variations of the EAWM and their possible causes, we propose a new position index of the EAWM by quantifying the low-level East Asian stream (EAS) of cold airmass in the Lagrangian sense. Based on the new-defined index, we find that the EAS undergoes an evident zonal shift between two channels over the land and coast. At interdecadal timescale, the peak location of the EAS is displaced eastward, with an increasing southward cold airmass flux at the coast since the mid-1960s. The interannual shift of the EAS presents not only the zonal oscillation of peak location between two channels but also the width changes of coastal channel over the northwestern Pacific. These shifts in the EAS are related to the strength changes of two source cold airmass streams from Siberia or Bering Sea, which are associated with the phase changes in the upper-tropospheric atmospheric teleconnections. At interdecadal timescale, the phase change in the North Atlantic Oscillation modulates the zonal shift in the EAS via the East Atlantic-West Russia teleconnection. At interannual timescale, the Pacific/North American teleconnection becomes the dominant factor altering the zonal shift and width change of the EAS.