Different Modulations of Arctic Oscillation on Wintertime Sea Surface Temperature Anomalies in the Northeast Pacific

Abstract

Persistent positive sea surface temperature anomalies (SSTAs) in the mid-latitude Northeast Pacific (NEP), also known as “warm blob” or “marine heatwave,” have substantial ecological and climate effects. This study delves into the spatiotemporal connection between Arctic Oscillation (AO) and SSTAs in the NEP. First, we conduct the lead-lag correlation and maximum covariance analyses to disentangle the closest temporal relationship between October AO and wintertime SSTAs in the NEP. Then, we categorize the years in positive AO (pAO) phase into two groups: positive AO with warm anomaly (pAO&Blob) group and positive AO without warm anomaly (pAO&noBlob) group based on the October AO index and wintertime blob index. Results show that the positive phase of AO in October strongly influences the wintertime warm SSTAs in the NEP through local and remote pathways. The local pathway is contingent upon the longitudinal positioning of AO-related high-pressure anomaly (i.e., anomalous ridge) in the North Pacific. When easterly anomalies prevail at the southern flank of the anomalous ridge over the NEP, they foster warm SSTAs in the NEP. However, different locations of the high-pressure anomalies may impede the NEP warming. Remote pathways indicate the teleconnections triggered by AO-related precipitation increase in Greenland and decrease in East Asia, sustaining the high-pressure anomaly and promoting the anomalous NEP warming. Hence, this study presents new evidence on polar and mid-latitude climate connections, which may provide potential predictability for the warm SSTAs in the NEP.