Abstract:In winter 2015/2016, the Arctic Oscillation (AO) showed a remarkable subseasonal variation with the positive phase in December 2015 while strong negative phase in January 2016, which resulted in the southward invading of the super cold wave from the polar region to the mid latitudes in the Northern Hemisphere. The temperature in the Northern Hemisphere including China changed from positive anomaly in December to negative anomaly in January. The phase transition of the AO from positive to negative was mainly associated with the North Atlantic storm activity. At the end of December 2015, a strong cyclonic storm appeared over the North Atlantic. This storm conveyed huge quantities of warm air into the polar region, which quickly warmed the Arctic up. The geopotential height anomaly over the Arctic region changed from negative in December 2015 to positive in January 2016, eventually leading to the transition of the AO from positive phase to negative phase.