Comparative Analysis of the Characteristics of Rainy Season Raindrop Size Distributions in Two Typical Regions of the Tibetan Plateau

Medog and Nagqu are two typical regions of the Tibetan Plateau with different geographical locations and climate regimes. These differences may lead to discrepancies in the raindrop size distributions (DSDs) and precipitation microphysical processes between the two regions. This paper investigates discrepancies in the DSDs using disdrometer data obtained during the rainy season in Medog and Nagqu. The DSD characteristics are studied under five different rainfall rate categories and two precipitation types (stratiform and convective). For the total datasets, the number concentrations of drops with diameters D > 0.6 (D < 0.6) mm are higher (lower) in Nagqu than in Medog. The fitted normalized gamma distributions of the averaged DSDs for the five rainfall rate categories show that Nagqu has a larger (lower) mass-weighted mean diameter D-m (normalized intercept parameter, lgN(w)) than does Medog. The difference in D-m between Nagqu and Medog increases with the rainfall rate. Convective clusters in Nagqu could be identified as continental-like, while convective precipitation in Medog could be classified as maritime-like. The relationships between the shape factor mu and slope parameter ? of the gamma distribution model, the radar reflectivity Z, and the rainfall rate R are also derived. Furthermore, the possible causative mechanism for the notable DSD variation between the two regions during the rainy season is illustrated using reanalysis data and automated weather station observations. Cold rain processes are mainly responsible for the lower concentrations of larger drops observed in Nagqu, whereas warm rain prevails in Medog, producing abundant small drops.