Oceanic Feedback to the Atmosphere for Anomalous SST Events Peaking in Early Winter in the Northeast Pacific

Abstract

In the past decade, large-scale and persistent warm sea surface temperature anomalies (SSTA) occurred frequently in the mid-latitude Northeast Pacific (NEP), offering a valuable opportunity to further illuminate the oceanic feedback to the atmosphere, which has been a complex issue for mid-latitude ocean-atmosphere interaction. Previous studies reported that the prolonged warm SSTAs in the NEP are usually passively triggered by atmospheric high-pressure anomalies. In this study, results show that the early winter positive SSTAs can actively reverse the high-pressure anomalies into low-pressure anomalies within the whole troposphere through diabatic heating and transient eddy vorticity forcing. However, when the positive SSTAs appear in mid-winter, the atmospheric preconditioning of warm air temperature anomalies related to the high-pressure anomalies prevents oceanic thermodynamic and dynamics feedback onto the atmosphere, which results in no reversal of the high-pressure anomalies. Therefore, the atmospheric state is an important factor in initiating the mid-latitude oceanic feedback to the atmosphere.