资源环境科技发展态势分析平台

The connection between November Arctic Oscillation (AO) and the following spring-summer tropical Pacific sea surface temperature (SST) experienced a pronounced enhancement around the late-1970s. The connection was weak before, but strong after the late-1970s. The present study investigates the plausible reasons for the connection change. After the late-1970s, significant anomalous cyclone appears over subtropical North Pacific and pronounced anomalous westerly winds occur over tropical western Pacific in the positive phase of November AO. As such, November AO could exert a significant influence on the subsequent spring-summer tropical Pacific SST variation. By contrast, before the late-1970s, anomalous cyclone and associated anomalous westerly winds to its south are weak and shift northward. Thereby, the connection between November AO and tropical Pacific SST is weak. Further analyses suggest that the interdecadal change in the anomalous cyclone over the subtropical North Pacific may be related to the change in the November AO's Pacific component and the strength of feedback of synoptic-scale eddy to mean flow. Specifically, after the late-1970s, November AO's Pacific component displays a zonally elongated structure, which is favorable for the formation of easterly wind anomalies over the mid-latitude North Pacific and related wave-mean flow interaction. In addition, feedback of synoptic eddy to mean flow is enhanced after the late-1970s, which is partly related to the intensification of the North Pacific storm track. This may also contribute to enhancement of the anomalous cyclone over the subtropical Pacific.