Surface Air Temperature Variation over the Eastern Tibetan Plateau from 1979 to 2018: The Role of AMO and PDO

Using the observational and reanalysis datasets during the period of 1979-2018, this study examines the modulation effects of the Atlantic multidecadal oscillation (AMO) and Pacific decadal oscillation (PDO) on the interdecadal change in summer surface air temperature (SAT) over the eastern Tibetan Plateau (TP). The results show that the eastern TP has experienced a remarkable warming in boreal summer since 1997. In addition, the warming is associated with simultaneously enhanced westward water vapor transport and the northward shift of the subtropical westerly jet (SWJ) over the northeast of the TP. Further research indicates that both water vapor transport and the SWJ are modulated by the PDO and AMO on interdecadal time scales. Since the late 1990s, the PDO has changed from the positive to negative phase, while the AMO has changed from the negative to positive phase. The change in the out-of-phase combination of the PDO and AMO has resulted in a northward shift of the SWJ at 200 hPa near the northeast of the TP through the Rossby wave train originating from the northwestern Atlantic. In addition, the PDO and AMO could both affect the Rossby wave train. From the northwestern Atlantic to Eurasia, the wave train may be dominated by the PDO, while the wave train near the TP is dominated by the AMO. The anomalous anticyclone over the northeastern TP is part of the Rossby wave train, causing the northward shift of the SWJ, favoring the intrusion of the water vapor from the eastern China into the eastern TP, thus leading to the TP warming. SIGNIFICANCE STATEMENT: It is understood that the Tibetan Plateau (TP) may be among the most sensitive regions to the global climate change. In addition, this region has warmed very rapidly in the latter half of the twentieth century. Based on the statistical analysis and dynamic diagnostics, the influences of interdecadal variations of atmospheric circulations on summer surface air temperature (SAT) over the eastern TP were analyzed for the years 1979 to 2018. We found that the eastern TP experienced an increase in summer SAT. In addition, the interdecadal change in SAT over the eastern TP is strongly affected by the water vapor transport and the subtropical westerly jet. Further analyses show that the PDO and AMO were the key factors influencing summer SAT over the eastern TP on the interdecadal time scales. The PDO and AMO could both affect the Rossby wave train. From the northwest Atlantic to Eurasia, the wave train may be dominated by the PDO, while the wave train near the TP is dominated by the AMO. In addition, the northwest Atlantic SSTs, which are dominated by the AMO, could also affect the SAT over the eastern TP by the Rossby wave train.