Conditional impact of boreal autumn North Atlantic SST anomaly on winter tropospheric Asian polar vortex

Abstract

This study investigates the relationship between the North Atlantic sea surface temperature (NASST) in autumn (September–October–November, SON) and the tropospheric Asian polar vortex (APV) in the following winter (December–January–February, DJF). The results show that the SON SST anomaly over the mid-latitude North Atlantic conditionally provides a valuable source for the prediction of the DJF APV’s interannual variability. When the SON NASST anomaly can persist into DJF, there is a practical prediction of the DJF APV. Physical diagnosis indicates that the presence/absence of an active air–sea interaction determines whether the SON SST anomaly signals could be maintained to DJF. During the years when the SON NASST anomaly is well sustained, the SST anomaly could efficiently heat the air column above. The resultant atmospheric circulation anomalies, in turn, change the low-level climatological winds and induce anomalous turbulent heat flux, which further exerts impacts on the NASST anomaly, resulting in a similar SST anomaly pattern with the pronounced NASST anomaly. Therefore, the resultant atmospheric circulation anomalies provide positive feedback to the anomalous SST and favor the persistence of the SST anomaly. In DJF, the NASST anomaly can excite a wave train pattern to influence the APV. However, during the poorly sustained years, the air–sea interaction over the North Atlantic is weak, and the SST anomaly can hardly influence the overlying air column. Without the positive air–sea feedback, the SON NASST anomaly cannot persist into DJF and cannot affect the DJF APV.