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Abstract

Mêdog, with its mountain and valley terrain, 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. As part of the Second Tibetan Plateau Scientific Expedition and Research (STEP) field campaign, raindrop size distribution (DSD) measurements were conducted with a disdrometer and a micro rain radar (MRR) in Mêdog. Based on the measurements, the seasonal and diurnal variations of DSD and vertical evolution were investigated. In addition, DSD characteristics in Mêdog were compared with those in Nagqu, which is located in the center of the TP with different geographical locations and climate regimes. The results can be summarized as: (1) The convective rainfall in the monsoon and postmonsoon periods is characterized by a high concentration of limited-size drops and can be classified as maritime-like. The premonsoon convective rainfall has a larger mean <em>D</em>_m and a lower mean <em>N</em>_w and could be considered a transition between maritime- and continental-like conditions. (2) Although heavier rainfall appears in the evening and at night, the DSD of convective cluster has a negligible diurnal variation. (3) Summer convective clusters in Nagqu are characterized by the lower concentrations of larger drops, and could be identified as continental-like, while may be attributed to the dominant cold rain process, whereas warm rain prevails in Mêdog, producing abundant small drops.