The use of Potential Vorticity on understanding of the Tibetan Plateau Surface Thermodynamic Forcing in Climate Dynamics and Climate Modeling

In this study, a new index based on the potential vorticity (PV) framework is proposed for the quantification of the Tibetan Plateau (TP) surface thermodynamic and dynamic forcing. The results show that the derived TP surface PV (SPV) includes the topographical effect, near-surface absolute vorticity, and land–air potential temperature differences. The climatological annual cycle of the SPV suggests that the TP transitions from a cooling to a heating source in April. The SPV reaches a maximum from June to August, which is consistent with the evolution of the Asian summer monsoon precipitation. Further analysis suggests that the intensified SPV in the boreal summer results in a low-level cyclonic circulation anomaly associated with increased precipitation over the southeastern slope of the TP and South China and decreased precipitation over the Indian Ocean. The surface potential vorticity (SPV) is also used to quantify the surface thermodynamic forcing on the TP in the FGOALS-f2 climate model for both the standard Atmospheric Model Intercomparison Project (AMIP) and Coupled Model Intercomparison Project (CMIP) experiments with a modified orography, and various aspects of the ASM responses in the model are also examined, finally their relationships with TP-SPV changes are quantitively estimated. The results indicate that TP-SPV is substantially reduced in the AMIP runs, while it is reduced by two-thirds of the original intensity in the CMIP runs when large-scale Asian mountains are removed. Overall, the responses of the monsoon system are more sensitive when air-sea interactions are considered.