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

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. Under rapid climate change, long-lasting warm sea surface temperature anomalies (SSTAs) in the mid-latitude Northeast Pacific (NEP) have attracted wide attention due to their substantial ecological and climate effects. Arctic Oscillation (AO) is the dominant mode of atmospheric circulation variability in mid-to-high latitudes of the Northern Hemisphere. Its positive phase is featured by a low-pressure center in the Arctic region and high-pressure centers in the mid-latitude regions. Our results reveal a robust connection between the positive phase of AO in October and warm SSTAs in the NEP during winter. We identify two primary pathways through which the October AO influences the wintertime sea surface temperature (SST) warming in the NEP. Locally, a high-pressure anomaly over the NEP is associated with easterly wind anomalies to its southern flank, which diminish oceanic latent heat loss to the atmosphere, thus fostering the SST warming in the NEP. However, other locations of the high-pressure anomaly related to AO may not be favorable for the warming of the NEP. From a remote view, AO can impact the NEP SST through teleconnections due to increased precipitation in Greenland and decreased precipitation in East Asia, sustaining the high-pressure anomaly over the NEP and further bolstering the NEP warming. Temporally, Arctic Oscillation (AO) in October is closely linked to wintertime sea surface temperature (SST) anomalies in the mid-latitude Northeast Pacific (NEP) The AO-related anomalous ridge located over the NEP is favorable for the warming of SST locally Remotely, enhanced rainfall in Greenland and decreased rainfall near East Asia sustain the anomalous ridge over the NEP via teleconnection