Search

In this study, we obtained the first leading mode and principal component 1 (PC1) of North Pacific sea surface temperature (SST). The PC1‐related SST anomalies, located relatively north/south, are referred to as North/South PC1 events. Model outputs, observations, reanalysis datasets and sensitivity experiments show that during the North PC1 events, an enhanced Aleutian low occurs and is located relatively north, favoring anomalous southerlies over western North America. The anomalous southerlies induce a strong warming anomaly over North America via warm advection of the anomalous southerlies and temperature advection of the climatological westerlies over North America. However, the Aleutian low anomaly and corresponding southerly anomaly associated with South PC1 events shift southward, favoring weakened effects of South PC1 events on atmospheric circulations and surface temperatures over North America. The meridional position of PC1 events deserves to be considered in the studies of the PC1 and its related climate changes. Plain Language Summary: Understanding of surface temperature variations is important since it largely affects human and society. This paper categorizes the North Pacific sea surface temperature anomaly events, which are associated with the first leading mode of North Pacific sea surface temperature, into North and South events according to their meridional positions. Using model outputs, observations, reanalysis datasets and sensitivity experiments, we found that the surface temperature anomalies over North America during the North events are quite different from those during the South events. During the North events, an enhanced Aleutian low occurs over high‐latitude North Pacific. The enhanced Aleutian low tends to induce anomalous southerlies over western North America. The anomalous southerlies favor warming anomalies over North America via the warm advection of anomalous southerlies and temperature advection of climatological westerly. However, the Aleutian low anomaly and meridional wind anomaly during the South events shift southward, leading to weakened effects of the South events on atmospheric circulations and surface temperatures over North America. Key Points: North American warming anomaly occurs during North Pacific sea surface temperature anomaly events located northThe warming anomaly is related to an enhanced Aleutian low anomaly located north and climatological westerlyDuring the events located south, North American surface temperature responses are weak due to a southward‐shift Aleutian low anomaly [ABSTRACT FROM AUTHOR]

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. Plain Language Summary: The El Niño/Southern Oscillation (ENSO)‐induced atmospheric anomalies over the North Pacific and North America (PNA region) are more westward during La Niña relative to that during El Niño in boreal winter. The disparity of atmospheric responses causes discernible distinct climate implications, and limits the seasonal prediction. The mechanism underlying this asymmetry, however, remains in disagreement. Some believe that it is due to variations in the location of tropical convective anomalies. Whereas others show that the climatological zonal flow could anchor the disturbance. Utilizing a more comprehensive energy diagnostic framework, we find that the nonlinear component, in particular, the nonlinear kinetic energy advection and the feedback effect of synoptic‐scale disturbances contribute to the asymmetric atmospheric responses. The study emphasizes the importance of nonlinear processes and multi‐scale interactions in the asymmetric structure of ENSO‐induced atmospheric anomalies in the PNA region, which are essential for understanding ENSO teleconnections, comprehending model biases, and improving seasonal predictions. Key Points: The El Niño/Southern Oscillation‐induced Pacific‐North American (PNA) teleconnection pattern is farther westward during La Niña relative to that in El NiñoThe nonlinear energy advection redistributes the kinetic energy, hence contributing to the asymmetric PNA teleconnectionsDifferent synoptic‐scale transient eddy activities help to maintain and amplify the asymmetry through a feedback effect [ABSTRACT FROM AUTHOR]