Influence of Potential Vorticity Generated by Diabatic Cooling over the Tibetan Plateau on the Surface Air Temperature of Eastern China during Boreal Winter

Abstract Using reanalysis and model data, this study investigates potential vorticity (PV) generated by diabatic cooling over the Tibetan Plateau (TP) and its associated climatic effects on adjacent regions. Results suggest that anomalous diabatic cooling over the TP exhibits a bottom-heavy vertical structure, which leads to the generated positive PV anomaly being confined within a shallow near-surface layer. The total PV generation anomaly within this layer is determined by the anomalous surface PV generation flux that is thermally driven by anomalous surface cooling. Further analysis revealed a significant interannual relationship linking stronger near-surface PV generation over the TP with anomalously warm winters in eastern China. The proposed mechanism involves PV generation by surface cooling, PV transport by katabatic flows, and an attendant weakened Siberian High. The surface cooling anomaly over the TP generates a positive PV anomaly within the near-surface layer, while simultaneously induces a form of anomalous katabatic flow down the slopes of the TP. This anomalous katabatic flow transports positive PV within the near-surface layer into the region of the Siberian High, increasing the local positive PV anomaly and weakening the Siberian High. A weaker Siberian High is associated with weaker winter monsoon flow and anomalous southerlies, leading to a warm surface air temperature anomaly over eastern China. The validity of the proposed mechanism was corroborated by numerical modeling. Relative to the well-studied winter blocking effect of the TP, this study offers and emphasizes new aspects of the TP’s climatic effects driven by its wintertime thermal conditions. Significance Statement The purpose of this study was to better understand the thermal effects of the Tibetan Plateau on surrounding regions during winter. We found that wintertime surface cooling over the Tibetan Plateau generates positive potential vorticity and induces downslope katabatic flows within the near-surface layer. The generated potential vorticity transported by these katabatic flows exerts substantial climatic impacts on surrounding areas. This result importantly reveals that the wintertime thermal effects of the Tibetan Plateau could be critical in driving the climate of eastern China. In addition to consideration of the blocking effect of the Tibetan Plateau, our results suggest that greater attention should be given to its thermal effects during wintertime.