Changes in the Relationship between ENSO and Asia-Pacific Midlatitude Winter Atmospheric Circulation

Interdecadal changes in the relationship between El Nino-Southern Oscillation (ENSO) and midlatitude atmospheric circulation are investigated in this study. Comparison of associations between ENSO and midlatitude atmospheric circulation anomalies between 1958-76 and 1977-2010 suggest that during 1958-76, ENSO exerted a strong impact on the East Asian winter monsoon (EAWM) and the associated atmospheric circulation pattern was similar to the positive North Pacific Oscillation (NPO). In contrast, during 1977-2010, the NPO-like atmospheric pattern disappeared. Instead, ENSO exerted a strong impact on the eastern North Pacific Ocean (NP) and North America, and the associated atmospheric circulation pattern resembled the Pacific-North America (PNA) teleconnection. Also, significant correlations between ENSO and sea surface temperature anomalies (SSTAs) over the western subtropical NP during 1958-76 became insignificant during 1977-2010, whereas negative correlations between ENSO and SSTAs in the central and northeastern subtropical NP became more significant since the mid-1970s. Further analyses suggest that the interdecadal shift of the Aleutian low, which occurred around the mid-1970s, might be responsible for the identified changes. Before the mid-1970s, warm ENSO events generated an anomalous anticyclone over the western NP, which is a key system bridging ENSO and EAWM-related atmospheric circulation. After the mid-1970s, the Aleutian low intensified and shifted eastward, leading to the impact of ENSO prevailing over the eastern NP. In addition, the weakened (strengthened) ENSO-NPO/ EAWM (ENSO-PNA) relationship likely contributed to the weakened (strengthened) relationship between ENSO and SSTAs over the western (central and eastern) subtropical NP.