Observed Vertical Structure of Precipitation over the Southeastern Tibetan Plateau in Summer 2021

Mêdog County, with its mountains and valleys, is located in the southeastern Tibetan Plateau (TP) and at the lower reaches of the Yarlung Zangbo River. This area has the highest annual rainfall amount over the TP, and in situ measurements are very scarce due to frequent debris flows and transportation difficulties. A monitoring campaign focused on cloud and precipitation observations was established in Mêdog in 2019 as a part of the Second Tibetan Plateau Scientific Expedition and Research Program. This paper evaluates the accuracy of micro rain radar (MRR) measurements and investigates the variations in precipitation vertical structure in Mêdog using observations collected from the MRR, disdrometer, and rain gauges in summer 2021. The measurements from the three instruments show a strong consistency, with correlation coefficients exceeding 0.93. Although the profiles of integral rain parameters for different rain rate categories in Mêdog are similar to those in other regions, the vertical evolution of raindrop size distributions shows significant differences. For lightest rain, the evaporation of small raindrops and breakup of large raindrops are clear during their descent. For the rainfall rate category of 0.2–2.0 mm h⁻¹ (2.0–20.0 mm h⁻¹), concentrations of small and medium (large) drops show almost uniform vertical structures, while the large (medium) drop number displays a positive (negative) gradient. A disturbance at height of 1.5–2.0 km above ground level (AGL) is observed in the heavy rainfall due to strong updrafts. In general, the MRR measurements in Mêdog are robust. The raindrop breakup process is more apparent in Mêdog than in other regions, resulting in high concentration of size-limited raindrops. In addition, it is found that the interaction between steep terrain and Mêdog convective rain causes the strong updrafts between 1.5 and 2.0 km AGL.