Possible linkage between East Asian summer drought and North Pacific Oscillation

The May North Pacific Oscillation Index and the summer (May and June-July-August-JJA) Effective Drought Index have a strong negative correlation in the East Asian region, particularly in northern China, Korea, and the southwestern regions of Japan (here termed Northeast Asia); this signifies an intensification of the summer drought during positive North Pacific Index (NPI) phase in this region, and the presence of such a phenomenon has been observed in this study. The low-south/high-north anomalous pressure pattern forming in all layers of the troposphere in Northeast Asian region has been a cause of drought. This unusual pressure pattern gives rise to a cold northeasterly and intensifies downward flow and reduces relative humidity. In addition, this cold northeasterly hinders the northward movement of the western North Pacific high and reduces the frequency of tropical cyclones passing through this region, thereby further intensifying drought.