Weakening trend of Tibetan Plateau winter surface cold source driven by anthropogenic forcing in a warming climate

It is well known that the Tibetan Plateau (TP) has experienced a pronounced and spatially coherent surface warming during boreal winter, second only to that over the Arctic. However, how the thermodynamic forcing of the TP has changed remains poorly understood. In this study, the TP surface potential vorticity forcing (TP-SPV*) is used to quantify changes in TP forcing. The long-term trends and associated attribution analysis of TP surface forcing during the past 70 years are investigated. Our results demonstrate that wintertime thermodynamic forcing over the TP exhibits a significant quasi-dipole trend, with negative anomalies in the western TP and positive anomalies in the central-eastern TP. This pattern is mainly driven by snow-related and cloud-related radiative processes: over the central-eastern (western) TP, the increase in net shortwave radiation induced by rapid (slow) snow cover depletion through the snow-albedo feedback is stronger (weaker) than the reduction in the longwave cloud radiative effect, which generates positive (negative) TP-SPV* anomalies by altering the ground-air potential temperature difference. Moreover, increased atmospheric static stability and absolute vorticity can generate positive atmospheric PV anomalies, which further reinforce TP-SPV* in the central-eastern TP via the PV−θ mechanism. Attribution analysis indicates that the decrease in TP-SPV* over the western TP is primarily driven by anthropogenic aerosol forcing, while the increase in TP-SPV* over the central-eastern TP and the positive atmospheric PV anomalies are dominated by greenhouse gas forcing. The results suggest a generally weakening TP cold source during boreal winter in a warming climate.