Modulation effects of the Tibetan-Mongolian Plateaus on East Asian winter air temperature associated with synoptic evolution of Siberian high

The Siberian High (SH) over central Asia can affect East Asian weather and climate, and its formation is primarily due to the uplift of the Tibetan and Mongolian Plateaus (TP and MP). However, it is unclear whether these plateaus can modulate the synoptic (2–7 days) evolution of the SH and the subsequent temperature over East Asia during the boreal winter. Using model simulations with and without the plateau topography north of the Himalaya, we show that the synoptic evolution of the winter SH is accompanied by an anomalous tropospheric transient wave train that migrates eastward to the MP over central Siberia before the SH intensification, which is then forced to propagate southeastward along the northeastern flank of the TP after the SH peaks. This results in subsequent cold anomalies from the north to the south of East Asia and thus increases synoptic variability of winter surface air temperature (Tas) over South China. However, the plateau uplift weakens this synoptic wave train due to the inefficiency of energy conversion from the mean flow to the transient flow, thus partly limiting the increase of the synoptic variability over South China. Further analyses showed that the synoptic evolution of the SH and its associated temperature anomalies is mainly caused and maintained by the anomalous cold advection due to the southeastward propagating northerly wind anomaly and the increased winter mean temperature gradient in the lower troposphere due to the northern plateau uplift. Our findings suggest that the TP and MP uplifts north of the Himalaya can affect both the winter mean state and synoptic-scale variability over East Asia and thus play a crucial role in the emergence of frequent cold air outbreaks from the higher latitudes toward South China.