Breakdown of the Summertime Meridional Teleconnection Pattern over the Western North Pacific and East Asia since the Early 2000s

Abstract

The meridional teleconnection over the western North Pacific and East Asia (WNP–EA) plays a predominant role in affecting the interannual variability of East Asian climate in summer. This study identified a breakdown of the meridional teleconnection since the early 2000s. Before the early 2000s, there are close tropical–extratropical relationships in light of both circulation and rainfall anomalies. For instance, the westward extension of the western North Pacific subtropical high (WNPSH) is closely associated with the southward shift of the East Asian westerly jet (EAJ), and more rainfall in the tropical WNP closely corresponds to less rainfall in the subtropical WNP–EA. However, after the early 2000s, the tropical–extratropical relationships are absent. Particularly, the tropical WNP precipitation anomalies can induce WNPSH anomalies, but the WNPSH anomalies cannot induce subtropical precipitation in the latter period, due to the absence of EAJ-related extratropical circulation anomalies. Further results indicate that in the latter period, the westward extension of the WNPSH is associated with the decay of central Pacific-like El Niño, and simultaneous summer sea surface temperature (SST) anomalies in the central eastern Pacific favor the northward shift of the EAJ, resulting in the disruption of the WNPSH–EAJ relationship. This evolution of tropical SSTs is sharply different from the decay of canonical El Niño and simultaneous summer tropical Indian Ocean warming, which favor the WNPSH–EAJ correspondence in the former period.