The Role of Nonlinear Energy Advection in Forming Asymmetric Structure of ENSO Teleconnections Over the North Pacific and North America

Abstract

In boreal winter, the El Niño/Southern Oscillation (ENSO)-induced Pacific-North American (PNA) teleconnection pattern is farther westward during La Niña relative to that in El Niño, causing discernible distinct climate implications. However, there has been a lack of consensus regarding the underlying mechanism driving this asymmetric structure. This study highlights the contribution of nonlinear kinetic energy advection (nKA) to this asymmetry. The zonally symmetric responses to ENSO, specifically the anomalies in zonal mean zonal flow, generate opposing nKA patterns by advecting anomalous eddy kinetic energy in the North Pacific, which leads to the shift of the PNA teleconnection pattern. In addition to nKA, transient eddy activities responded to changes of baroclinicity help maintain the asymmetry through a feedback effect. These findings underscore the importance of considering extratropical factors, such as nonlinear energy processes and synoptic-scale transient eddies, in understanding the mechanism responsible for the asymmetric structure of the PNA teleconnection pattern.