Microphysical Characteristics of Winter and Summer Precipitation on the Southeastern Tibetan Plateau

Abstract

The special topography of the southeastern Tibetan Plateau (SETP) provides sufficient moisture for the precipitation in this area. An accurate description of the microphysical characteristics of precipitation is critical for accurate estimation of precipitation rates in the region. In 2022, we used two-dimensional video disdrometer (2DVD) and micro rain radar (MRR) to study the microphysical characteristics and vertical structures of winter (January-March) and summer (May-October) precipitation on the SETP. There were nine snowfall events observed, consisting of weak snowfall processes. The particle number concentration on the SETP is lower than that reported in the low-altitude areas of eastern China. We infer that this may be related to the altitude. The ambient temperature in high-altitude areas is lower than that in low-altitude areas, which affects the collision-coalescence efficiency of snowfall particles. As the snowfall rate increases, the efficiency of collision-coalescence between snowfall particles increases, so that the number concentration of small particles decreases and the number concentration of large particles increases. The shape parameters and slope parameters of the Gamma distribution model of snowfall particles on the SETP are higher than those in low altitude areas. A negative correlation between aspect ratio and diameter of snowfall particles is exhibited. There were 133 rainfall events observed. Compared with the falling speed of raindrops in low-altitude areas, that on the SETP is high. The raindrop diameter corresponding to the peak raindrop number concentration is 0.35 mm. On the SETP, the concentration of raindrops and the maximum raindrop diameter are smaller than those in the low-altitude region in southern China. The frequency distribution histogram of the Dm and log10Nw of stratiform rainfall is unimodal, while that of convective rainfall is bimodal. The average Dm and log10Nw values of stratiform rainfall (Dm=1.02 mm, log10Nw=3.81 mm-1m-3) are smaller than those of convective rainfall (Dm =1.40 mm, log10Nw =3.95 mm-1m-3). The convective rainfall on the SETP is more continental. Compared with stratiform rainfall in low-altitude regions of China, the average Dm value is the smallest and the average log10Nw value is the largest on the SETP. However, the average Dm-log10Nw value of the convective rainfall on the SETP is close to that in southern China. The number concentrations of small raindrops for stratiform and convective rainfall on the SETP are higher than those in low-altitude areas. The Dm and log10Nw of the two types of rainfall increase as the rainfall rate increases. Compared with low-altitude areas, the Dm on the SETP is small and the log10Nw is large. The log10Nw of stratiform rainfall is balanced at a low rainfall rate, while the log10Nw of convective rainfall is balanced at a high rainfall rate. Compared with other regions in China, for a given μ value, the λ value is the highest on the SETP.