Change in the Relationship between Winter Monsoon and Jet Stream in East Asia across the 1998–99 Regime Shift

The East Asian winter monsoon (EAWM) is one of the most important Asian circulation systems with pronounced variability on the interannual and interdecadal scales. Previous studies showed that the relationship between East Asian jet stream (EAJS) and winter monsoon is significantly correlated for the period 1968-2000. When the EAJS is strong (weak), the anomalous cyclonic vorticity is strong (weak), the East Asian trough is deep (shallow), the Siberian high is strong (weak), and anomalous northerly (southerly) wind prevails over East Asian, and the regional temperature decreases (increases). Meanwhile, the North Pacific climate regime shift exhibited a significant interdecadal change across the late 1990s. We examined the relationship between the EAJS and EAWM before and after the late-1990s. After the late 1990s, it is found that the relationship between the EAJS and EAWM becomes to weaken due to the northward shift of the EAJS. We suggest that the northward shift of the EAJS is associated with the changes in the western tropical Pacific convective activity and Arctic warming after the late 1990s.