Microphysical characteristics of seasonal rainfall observed by a Parsivel disdrometer in the Tianshan Mountains, China

Abstract

Raindrop size distribution (DSD) is critical for understanding rainfall microphysical processes. Correlated DSD relationships, including the radar reflectivity factor-rainfall rate (Z–R), shape factor-slope parameter (μ–∧), and the rainfall kinetic energy-R (mass-weighted average diameter) (KE–R (Dm)) are significant in many fields such as quantitative precipitation estimation, parameterization schemes in weather forecast models, and assessing rainfall kinetic energy; however, the collective scientific understanding of DSD in arid regions remains insufficient. Here, 2020–2021 DSD data from the Tianshan Mountains, China, were collected to assess various corresponding characteristics for a typical arid region in China across different seasons, rainfall types, and rainfall rate classes. Rainfall in the fall (summer) had the most (least) small raindrops (diameter < 1 mm), the least (most) mid-size raindrops (1 ≤ diameter ≤ 3 mm), and large raindrops (diameter > 3 mm). Mean Dm was the largest (smallest) in the summer (fall) at 1.059 mm (0.876 mm), while the mean generalized intercept parameter was the largest (smallest) in the fall (winter) at 3.738 (3.505). For stratiform rainfall, fall (summer) had the most (least) small raindrops, as well as the least (most) mid-size and large raindrops, whereas, for convective rainfall, summer displayed fewer small and mid-size raindrops compared to spring. Regarding the rainfall rate classes, the concentration of mid- and large-size raindrops in spring changed from a minimum at C1 (0.1 ≤ R < 0.5 mm·h−1; notably comparable to fall rates) to C4 (2 ≤ R < 5 mm·h−1; comparable to summer), before peaking beyond summer rates at C5 (R ≥ 5 mm·h−1). The localized Z-R, μ–∧, KEtime–R, and KEmm–Dm relationships also exhibited marked seasonal characteristics, which ultimately impact estimates of regional radar quantitative precipitation and rainfall kinetic energy, as well as efforts aimed at improving model parameterization schemes. Additionally, the more abundant water vapor, the more frequent cold rain process, and the stronger warm–dry atmospheric vertical environment in summer appeared as the most important influencing factors leading to the fewest small-, and greatest mid- and large-size raindrops.