Winter Atmospheric Circulation Anomaly Associated with Recent Arctic Winter Warm Anomalies

The winter Arctic atmosphere in the middle and lower troposphere has shifted to a warmer stage since the winter of 2004/05 relative to the mean averaged from 1979/80 to 2003/04. Recent Arctic warm anomalies are concurrent with warm anomalies over the North Pacific, northern Africa, and the low latitudes of both the North American and Asian continents and with cold anomalies over the middle and high latitudes of Eurasia and North America. Meanwhile, strengthened winter SLP is observed in the middle and high latitudes of Eurasia, the Siberian marginal seas of the Arctic Ocean, and the North Pacific. Correspondingly, winter 500-hPa geopotential height anomalies exhibit wave train structures over Eurasia, the North Pacific, and North America. These major features frequently reappear since the winter of 2004/05. A regionally averaged winter SLP in 40°–65°N, 30°E–150°W can be regarded as the intensity index to characterize interannual variability of the atmospheric circulation anomaly associated with recent Arctic warm anomalies. This atmospheric circulation anomaly differs from the Arctic dipole anomaly and displays a closer association with atmospheric variability over the middle and low latitudes relative to the Arctic. It directly connects Arctic warm anomalies in the middle and lower troposphere to increased frequencies of extreme cold events in the middle and low latitudes of Eurasia and western North Pacific, and western North America. This study also implies that SST cooling in the tropical central and eastern Pacific may also contribute to recent Arctic warm anomalies, although its impact mechanism is not clear yet.