Contribution of Aloft Gravitational Sorting and Lower-Part Coalescence to Precipitation Over the Southeastern Tibetan Plateau

Observational constraints on the vertical microphysical evolution of mixed-phase precipitation across the melting layer over the high-altitude of southeastern Tibetan Plateau remain scarce. Using collocated two-dimensional video disdrometer and Micro Rain Radar measurements in rainy seasons of 2022–2025, we characterize the vertical microphysical evolution of mixed-phase precipitation across the melting layer. Contrary to many low-altitude regions where breakup dominates raindrop evolution, precipitation there exhibits a coalescence-dominated growth regime below the melting layer, while the influences of breakup and evaporation remain subordinate. Near-surface humidity primarily mitigates evaporative depletion of liquid water content, while stronger winds favor coalescence with limited influence on total water content. Above the melting layer, ice particles show clear height-dependent evolution governed mainly by gravitational sorting. These results identify a distinct high-altitude microphysical regime shaped by low air density and temperature, highlighting different controls on raindrop growth compared to precipitation systems over lower altitude regions.