Quasi-Biweekly Oscillation of the Tibetan Plateau Surface Forcing during Summer: Spatiotemporal Propagation and Impact Monitoring

Abstract Quasi-biweekly oscillation (QBWO) of the surface forcing over the Tibetan Plateau (TP) in boreal summer plays a pivotal role in regulating downstream weather and climate, but it remains preliminarily understood and lacks operational monitoring. Using surface potential vorticity (SPV), a novel metric integrating surface thermal and dynamical forcing, we identified the dominant modes of summer TP surface forcing associated with the QBWO and further developed robust real-time monitoring metrics. The first two leading spatiotemporal modes derived from extended empirical orthogonal function analysis jointly characterize a southeastward propagation of anomalous TP surface forcing (termed SPV QBWO TP ). This propagation is driven by the tendency of land–air potential temperature (PT) difference. Near-surface air PT variations are governed by the advection of upstream atmospheric PT and vorticity perturbations via background westerlies, while surface PT is modulated by the combined effects of upstream wave train and TP thermal forcing on local cloud–radiation feedback and precipitation variation. The first two leading principal components can serve as effective metrics for monitoring the SPV QBWO TP activities. Real-time metrics developed by a running-mean method exhibit outstanding operational potential, including monitoring the onset timing of the South China Sea summer monsoon and changes in monsoon rainfall over eastern China. The SPV QBWO TP thus plays a bridge role in connecting the upstream extratropical variabilities and downstream weather and climate. This study deepens understanding of the spatiotemporal propagating features and dynamics of quasi-biweekly TP surface forcing and further highlights the importance of its real-time monitoring and potential applications in subseasonal prediction. Significance Statement Quasi-biweekly oscillation (QBWO) is the dominant intraseasonal mode of the surface forcing over the Tibetan Plateau (TP) in summer. It significantly influences local and surrounding meteorological conditions and ecological environment. Enhancing our understanding of the dynamic mechanisms of TP surface forcing and its impact monitoring is of great significance. Using surface potential vorticity that effectively represents TP’s combined surface thermal and dynamical forcing, this study reveals the dominant southeastward-propagating mode of the QBWO in the TP area. The propagation is driven by the interactions between upstream atmospheric wave train and local TP thermal forcing. More importantly, we develop real-time monitoring metrics for monitoring the TP surface forcing that shows considerable operational potential. These metrics can effectively capture the onset timing of the South China Sea summer monsoon and the subseasonal rainfall variations in eastern China.