Southern European rainfall reshapes the early-summer circumglobal teleconnection after the late 1970s

摘要

The summer circumglobal teleconnection (CGT), which crucially affects mid-latitude climate in the Northern Hemisphere, is generally characterized by a mid-latitude wave train along the strong upper-tropospheric westerly jet. In this study a significant change is identified in the spatial pattern of the early-summer CGT after the late 1970s: An additional high-latitude wave train has occurred over northern Eurasia. Based on observational evidences and simulation results with a linear baroclinic model, it is proposed that the post-1970s CGT change is induced by enhanced impact of rainfall over southern Europe (SE) after the late 1970s. Specifically, the mid-latitude wave train of CGT in early summer is dominated by Indian rainfall before the late 1970s but by both rainfall over India and SE after the late 1970s; the high-latitude wave train of CGT occurring after the late 1970s, however, is induced only by the SE rainfall. The coupled Indian and SE rainfall after the late 1970s, which is probably due to the basic flow change over the North Atlantic, induce both mid-latitude and high-latitude wave trains of the CGT.