A multiscale analysis of the formation mechanisms of an extreme rainstorm event over the northeastern Tibetan Plateau

Using the Qinghai Analysis Data (QHA), together with surface observations, Himawari-8 satellite data, and ERA5 reanalysis data, a multi-scale comprehensive analysis was conducted for an extreme rainstorm event that occurred on the northeastern side of the Tibetan Plateau during August 13-14, 2022. The results show that this rainstorm occurred under a favorable large-scale circulation background. Cold air masses from the north and warm air masses from the south converged on the northeastern side of the plateau, forming an upper-level divergence and lower-level convergence vertical configuration. Precipitation was distributed in a banded pattern along the Huangshui and Yellow River Valleys, exhibiting significant topographic constraints and nocturnal enhancement. A meso-β-scale convective system was the direct influencing weather system for the heavy rainfall. It underwent a complete life cycle of development, maturation, and dissipation, and its evolution corresponded well with variations in precipitation intensity, with the heaviest rainfall occurring during the mature stage of convection. The easterly shear line at 600 hPa and low-level easterly flow were the key dynamic factors triggering the convection. Under the forcing of the trumpet-shaped valley topography, warm and moist air continuously converged, ascended, and extended westward, triggering severe convection in the presence of deep unstable stratification and a highly humid environment. During the mature stage of convection, dynamic lifting, latent heat release, and ice-phase microphysical processes formed a positive feedback mechanism. Melting near the 0℃ level and raindrop collision-coalescence significantly enhanced precipitation efficiency. The QHA successfully captured the mesoscale structural characteristics of this rainstorm event, providing an important basis for the monitoring and early warning of heavy precipitation in the complex terrain on the northeastern side of the Tibetan Plateau.