Doubling frequency of summer cold surges in recent decades and their impact on East Asian extreme precipitation

Abstract

This research highlights the role of the summertime southward intrusion of the Siberian air mass in intensifying extreme precipitation over East Asia. We identify a recurrent cold-core anticyclone over Siberia termed the Summer Siberian High (SSH) and define its southward expansion as the Summer Cold Surge (SCS). Our analysis reveals that the frequency of SCS events has nearly doubled since the early 2000s. This increase is attributed to a regime shift in the precursor circulation, characterized by the intensification of thermally enhanced, quasi-stationary anticyclones over the Ural Mountains. Dynamically analogous to the winter cold surge, the SCS transports cold and dry air into East Asia. The interaction between this cold intrusion and the warm, moist flow from the Western North Pacific Subtropical High enhances low-level baroclinicity and frontal convergence, thereby intensifying heavy rainfall. These findings underscore the growing climatological importance of high-latitude systems during summer and suggest that understanding SCS dynamics is crucial for predicting extreme precipitation in a warming climate.