Pacific-East Asian teleconnections: how does ENSO affect East Asian climate?

Observational evidence is presented to show a teleconnection between the central Pacific and East Asia during the extreme phases of ENSO cycles. This Pacific-East Asian teleconnection is confined to the lower troposphere. The key system which bridges the warm (cold) events in the eastern Pacific and the weak (strong) East Asian winter monsoons is an anomalous lower tropospheric anticyclone (cyclone) located in the western North Pacific. The western North Pacific wind anomalies develop rapidly in late fall of the year when a strong warm or cold event matures. The anomalies persist until the following spring or early summer, causing anomalously wet (dry) conditions along the East Asian polar front stretching from southern China northeastward to east of Japan (Kuroshio extension).

Using atmospheric general circulation and intermediate models, we show that the anomalous Philippine Sea anticyclone results from a Rossby wave response to suppressed convective heating, which is induced by both the in situ ocean surface cooling and the subsidence forced remotely by the central Pacific warming. The development of the anticyclone is nearly concurrent with the enhancement of the local sea surface cooling. Both the anticyclone and the cooling region propagate slowly eastward. The development and persistence of the teleconnection is primarily attributed to a positive thermodynamic feedback between the anticyclone and the sea surface cooling in the presence of mean northeasterly trades. The rapid establishment of the Philippine Sea wind and SST anomalies implies the occurrence of extratropical-tropical interactions through cold surge-induced exchanges of surface buoyancy flux. The central Pacific warming plays an essential role in the development of the western Pacific cooling and the wind anomalies by setting up a favorable environment for the anticyclone-SST interaction and midlatitude-tropical interaction in the western North Pacific.