Dual Synoptic Pathways of Winter Extreme Precipitation over the Tibetan Plateau: Classification, Moisture Origin, and Rossby Wave Activity

Abstract This study investigates the spatiotemporal characteristics and governing mechanisms of winter extreme precipitation over the Tibetan Plateau (TP), identifying two distinct synoptic categories through spectral clustering analysis. Based on 192 regional extreme precipitation events (REPEs) during 1980–2020, we classify these events into Type 1 (68.23%, 131 events) characterized by precipitation centers over the western and eastern parts of the southern slope of the TP, and Type 2 (31.77%, 61 events) featuring precipitation centers located in the western TP. These types exhibit contrasting dynamic origins and long-term trend changes, with Type 2 REPEs showing a significant increase in occurrence frequency in recent decades, while Type 1 REPEs have declined. Type 1 REPEs are driven by a Rossby wave train originating over western North America, which propagates southeastward to induce equivalently barotropic cyclonic anomalies over the TP. This configuration enhances ascending motions and convective activity along the southern TP slopes, further supported by anomalous moisture convergence along the southern slope of the TP. In contrast, Type 2 REPEs are governed by a mid-latitude Rossby wave train along 40°N, generating an anomalous cyclonic-anticyclonic dipole southwest and southeast of the TP. This structure triggers ascent and convection over the western TP, with moisture concentrated over the western TP. These findings advance the understanding of TP extreme precipitation variability and its teleconnection drivers, highlighting the role of hemispheric-scale wave trains in modulating regional climate extremes.