Interannual Variability of Springtime Extreme Heat Events over the Southeastern Edge of the Tibetan Plateau: Role of A Spring-type Circum-global Teleconnection Pattern

Abstract

AbstractDue to the high mountains to the west and north of the plateau, and the control by westerly mean flow in spring, hot and dry conditions are often observed over the southeastern edge of the Tibetan Plateau (SETP), and hence favoring occurrences of extreme heat events there. Indeed, maximum centers and remarkable increasing trends of extreme heat (EH) days in spring are found over the region. Springtime EH events over the SETP also exhibit strong interannual variability and are closely linked to a spring-type circum-global teleconnection (SCGT) pattern, which is the second leading mode of 200-hPa meridional wind over the North Hemisphere in spring. This SCGT shows distinctive features from the traditional circum-global teleconnection patterns found in boreal summer and winter. It is revealed by a circum-globally navigated Rossby wave train along the mid-high latitudes, which splits to a north branch along the polar jet and a south branch along the subtropical jet over Eurasia after propagating through the North Atlantic. The two branches eventually reach the SETP, forming an anomalous anticyclonic circulation over the region. Hence, conditions in the SETP are controlled by significant anomalous subsidence and a clearer sky, resulting in below-normal rainfall and above-normal air temperature, in favor of more EH events in the region. The SETP EH events are also closely linked to the spring-type CGT-like pattern in April and May, but not in March. In addition, the influence of the foehn effect on the SETP EH is discussed.