Joint Effect of West Pacific Warming and the Arctic Oscillation on the Bidecadal Variation and Trend of the East Asian Trough

This study investigates bidecadal variation and trends in the winter East Asian trough (EAT) intensity for the period from 1958 to 2020. The EAT intensity index, calculated with the JRA55 reanalysis, demonstrates bidecadal variation, which is closely related to the intensity of cold advection in East Asia that affects northeast China, the Korean Peninsula, and Japan. In addition, it is noted that the positive phase of the Arctic Oscillation (AO) plays an important role in suppressing EAT intensity, particularly on a bidecadal time scale. On the other hand, a warm anomaly in the west Pacific can enhance the intensity of the EAT, which is also reproduced by numerical simulation. The influence of a significant warming trend in the west Pacific and a weak positive trend in the AO on the EAT intensity and the East Asian winter monsoon is investigated. Warming in the west Pacific supports a strengthening of EAT intensity, cooling in northeast Asia, and enhancement of easterly wind in the subtropical west Pacific. A weak positive AO trend plays an insignificant role in affecting the trend of EAT intensity, but it supports warming in northeast Asia.