Midlatitude atmospheric transient eddy feedbacks influenced ENSO-associated wintertime Pacific teleconnection patterns in two PDO phases

Abstract

The El Nino-Southern Oscillation (ENSO)-associated wintertime atmospheric teleconnection patterns in two Pacific decadal oscillation (PDO) phases are investigated using ERA-20C reanalysis data for 1950–2010. A strengthened ENSO-associated Pacific-North American (PNA) teleconnection pattern presents in PDO positive phase, while a West Pacific (WP) pattern over Northwestern Pacific and a squeezed PNA pattern coexist when ENSO occurs in PDO negative phase. The dynamical role of atmospheric transient eddy feedbacks to the teleconnection patterns are highlighted in the present study. When ENSO occurs in PDO positive phase, the uniform strengthened westerly jet anomalies downstream of the climatological main body of jet accompany with energetic transient eddy anomalies over Northeastern Pacific. The transient eddy feedbacks largely enhance and favor the strengthened PNA pattern. When ENSO occurs in PDO negative phase, the strengthened westerly jet anomalies appear to separate into two parts, one locating north of the climatological main body of jet and the other at the downstream. The accompanied transient eddy anomalies also split into two parts. Under such conditions, the transient eddy feedbacks are limited over Northeastern Pacific and favor a weak PNA pattern. However, the transient eddy anomalies over Northwestern Pacific strengthen, and the feedbacks also strengthen and largely contribute to the WP pattern. Moreover, the transient eddy anomalies over Northwestern Pacific seem to be anchored along the anomalously poleward strengthened oceanic subarctic frontal zone (SAFZ) in PDO negative phase. The enhanced atmospheric baroclinicity anomalies, coupled with the strengthened SAFZ, energize atmospheric transient eddy anomalies, and work as the potential maintenance in shaping the WP pattern.