Influence of the Scandinavian Pattern on Summer Extreme Precipitation over the Eastern Slopes of the Tibetan Plateau

The Scandinavian(SCA) pattern is an important climate signal in regulating the variability of summer extreme precipitation(SEP) over the eastern slopes of the Tibetan Plateau(ESTP). There is a strong negative correlation between the SCA pattern and SEP over the ESTP, with a correlation coefficient of -0.57. Moisture budget analysis showed that the dynamic component anomalies of both the zonal and vertical moisture advection induced by the SCA pattern play the dominant roles in extreme precipitation variability over the ESTP. These anomalies are solely linked to variations in zonal wind and vertical velocity. The anomalies of the SCA pattern propagate downstream through Rossby waves, leading to the formation of cyclonic circulations over northern East Asia and the Iranian Plateau. The westerlies on the southern side of these cyclonic circulations play a crucial role in influencing the development of significant anomalous westerlies over the ESTP. The anomalous westerlies bring climatologically moist air from the Tibetan Plateau(TP) to the ESTP, resulting in positive zonal moisture advection anomalies over the area. Furthermore, these anomalous westerlies transport climatologically warm air from the TP to the ESTP, leading to significant warm advection anomalies and vertical upward motion anomalies over the ESTP. The upward motion carries lower-tropospheric moisture upward, resulting in positive vertical moisture advection anomalies over the ESTP. The combination of these positive zonal and vertical moisture advection anomalies eventually leads to excessive SEP.