Teleconnection between Summer NAO and East China Rainfall Variations: A Bridge Effect of the Tibetan Plateau

Abstract

Although the impact of the North Atlantic Oscillation (NAO), especially the antecedent NAO in winter and spring, on East Asian summer climate has been studied extensively, the possible connection from the summer NAO (SNAO) and then the Tibetan Plateau (TP) to East China summer rainfall remains unclear. This study reveals that on interannual time scales the SNAO is significantly correlated with the variations of East China summer rainfall and the thermal forcing of the TP provides an intermediate bridge effect in this Eurasian teleconnection. The SNAO primarily regulates the rainfall variability over the TP through large-scale wave trains and the TP rainfall anomalies in turn lead to a change in local diabatic heating, which excites Rossby waves to the downstream regions. To the northeast of the TP, an anomalous barotropic cyclone is formed in the nearly entire troposphere, generating low-level northerly flow anomalies over northern China. Meanwhile, the TP heating also induces low-level southerly flow anomalies over southern China. The anomalous northerly and southerly winds converge in the lower troposphere, enhancing the summer rainfall over central East China. Compared to the SNAO, the TP thermal forcing exerts a more direct impact on the variations of East China summer rainfall in the Eurasian teleconnection discussed.