Distribution characteristics of summer precipitation raindrop spectrum in Qinghai−Tibet Plateau

Abstract. To enhance the precision of precipitation forecasting in the Qinghai−Tibet Plateau region, a comprehensive study of both macro− and micro−characteristics of local precipitation is imperative. In this study, we investigated the particle size distribution, droplet velocity, droplet number density, Z (Radar reflectivity) − I (Rainfall intensity) relationship, and Gamma distribution of precipitation droplet spectra with a single precipitation duration of at least 20 minutes and precipitation of 5 mm or more at four stations (Nyalam, Lhasa, Shigatse, and Naqu) in Tibet during the recent years from June to August. The results are as follows: (1) In the fitting relationship curve between precipitation raindrop spectral particle size and falling speed at the four stations in Tibet, when the particle size was less than 1.5 mm, the four lines essentially coincided. When the particle size exceeded 1.5 mm, the speed in Shigatse was the highest, followed by Lhasa, and the speed in Naqu was the lowest. The falling speed of particles correlated with altitude. (2) The diameter of the six microphysical features at the four stations increased with altitude. (3) The Z−I relationships at the four stations exhibited variations. Owing to the proximity in altitude between Lhasa and Shigatse, as well as between Nyalam and Nagqu, the coefficients a and index b in the Z−I relationships of the two groups of sites were relatively similar. (4) The fitting curves of the M−P and Gamma distributions of the precipitation particle size at the aforementioned four stations are largely comparable. The M−P distribution fitting exhibits a slightly better effect. The parameter μ in Gamma distribution decreases with the increase of altitude, while N₀ and λ in M−P distribution show a clear upward trend with altitude.