Record-breaking northward shift of the western north pacific subtropical high in July 2018

Abstract

The northward shift of the estern orth Pacific Subtropical High (PSH) in July 2018 broke the historical record since 1958 and resulted in extreme heat waves and casualties across ortheast sia (E). n the present work, we associated this extreme PSH anomaly with the anomalies of barotropic anticyclone above E originating from the strongest positive tripole pattern of sea surface temperature anomaly (SS) in the orth tlantic in July. Both data analysis and numerical experiments indicated that the positive tripole SS pattern could produce an upper-tropospheric wave source over Europe, which stimulated an eastward propagating wave train along the subpolar westerly jet over the Eurasian Continent. hen its anticyclonic node reached E, the PSH started to shift northward. fter the cyclonic node in the circulation anomaly encountered the ibetan Plateau (P), atmospheric diabatic heating was enhanced over the eastern P, initiating another subtropical wave train, which furthered the northward shift of the PSH. herefore, the wave source over Europe was critical for the northward shift of the PSH in July, connecting the tripole SS pattern in the orth tlantic with the PSH anomaly and maintaining the downstream effects of thermal forcing over the eastern P on the East sian summer monsoon.