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Mêdog is located at the entrance of the water vapor channel of the Yarlung Tsangpo Great Canyon on the southeastern Tibetan Plateau (TP). In this study, the seasonal variation in the microphysical vertical structure of stratiform precipitation at the Mêdog site in 2022 was investigated using micro rain radar (MRR) observations, as there is a lack of similar studies in this region. The average melting layer height is the lowest in February, after which it gradually increases, reaches its peak in August, and then gradually decreases. For lower rain categories, the vertical distribution of small drops remains uniform in winter below the melting layer. The medium-sized drops show slight increases, leading to negative gradients in the microphysical profiles. Slight or evident decreases in concentrations of small drops are observed with decreasing height in the premonsoon, monsoon, and postmonsoon seasons, likely due to significant evaporation. The radar reflectivity, rain rate, and liquid water content profiles decrease with decreasing height according to the decrease in concentrations of small drops. With increasing rain rate, the drop size distribution (DSD) displays significant variations in winter, and the fall velocity decreases rapidly with decreasing height. In the premonsoon, monsoon, and postmonsoon seasons, the concentrations of large drops significantly decrease below the melting layer because of the breakup mechanism, leading to the decreases in the fall velocity profiles with decreasing height during these seasons. Raindrops with sizes ranging from 0.3–0.5 mm are predominant in terms of the total drop number concentration in all seasons. Precipitation in winter and postmonsoon seasons is mainly characterized by small raindrops, while that in premonsoon and monsoon seasons mainly comprises medium-sized raindrops. Understanding the seasonal variation in the vertical structure of precipitation in Mêdog will improve the radar quantitative estimation and the use of microphysical parameterization schemes in numerical weather forecast models over the TP. [ABSTRACT FROM AUTHOR]

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Mêdog is located at the entrance of the water vapor channel in the Yarlung Zangbo Grand Canyon (YGC). This area has the largest annual accumulated rainfall totals and precipitation frequency on the Tibetan Plateau (TP). This paper investigates the seasonal variation in raindrop size distribution (DSD) characteristics in Mêdog based on disdrometer observations from 1 July 2019 to 30 June 2020. The DSD characteristics are examined under six rain rate classes and two rainfall types (stratiform and convective) in the winter, premonsoon, monsoon and postmonsoon periods. The highest (lowest) concentration of small raindrops is observed in monsoon (winter) precipitation, whereas large raindrops predominate in premonsoon precipitation. For stratiform rainfall, the mean mass-weighted mean diameter (Dm) exhibits overlooked differences in the four periods, while the mean normalized intercept parameter (Nw) is significantly higher in the monsoon period than in the other three periods. 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. This is probably attributed to abundant warm and humid airflow transported by the Indian Ocean monsoon into Mêdog. The westerly winds prevail over the TP during the premonsoon period, and thereby the premonsoon convective rainfall in Mêdog has a larger mean Dm and a lower mean Nw. In addition, the relationships of radar reflectivity Z and rain rate R for different precipitation types in different periods are also derived. A better understanding of the seasonal variation in the microphysical characteristics of precipitation in Mêdog is important for improving the microphysical parameterization scheme and the precipitation forecast of models on the TP. [ABSTRACT FROM AUTHOR]

As part of the Second Tibetan Plateau Scientific Expedition and Research (STEP) field campaign, raindrop size distribution (DSD) measurements were conducted with a laser optical particle size velocity disdrometer in Motuo on the Tibetan Plateau (TP). The DSD characteristics of five different rain rate classes and convective and stratiform precipitation types were studied using the DSD data from July to September 2019, comprising a total of 47,774 1-min raindrop spectra. The average raindrop spectral width and number concentration of large drops increased with the rainfall intensity. Furthermore, the combination of small- and midsize drops dominated the precipitation in Motuo, and their contributions exceeded 99% of the number concentration. The convective precipitation in Motuo was identified as maritime-like precipitation and was characterized by a large normalized intercept parameter log 10 N w = 4.0–4.4 and small mass-weighted mean diameter D m = 1.1–1.4 mm. Empirical relations among the three parameters (intercept N 0 , shape μ , and slope Λ) of the gamma distribution model, N w and D m of the normalized gamma distribution were derived. We also obtained power-law relationships of Z = AR b for the stratiform and convective precipitation in Motuo, and the empirical relation of Z = 300R 1.4 significantly underestimated the convective precipitation in Motuo. When the precipitation type transitioned from stratiform into convective precipitation, coefficient A decreased and exponent b increased. Finally, empirical relations between D m and the radar equivalent reflectivity factor at the Ku and Ka bands were obtained to improve the rainfall retrieval algorithms of the dual-frequency precipitation radar on the southeast TP. • As part of the Second Tibetan Plateau Scientific Expedition and Research (STEP) field campaign, raindrop size distribution (DSD) measurements were conducted with a laser optical particle size velocity disdrometer in Motuo on the Tibetan Plateau (TP). DSD characteristics in main entrance to the water vapor channel of the Yarlung Zangbo Grand Canyon was studied for the first time. • The combination of small- and midsize drops dominated the precipitation in Motuo, and their contributions exceeded 99% of the number concentration. The convective precipitation in Motuo was identified as maritime-like precipitation and was characterized by a large normalized intercept parameter log 10 N w = 4.0–4.4 and small mass-weighted mean diameter D m = 1.1–1.4 mm. [ABSTRACT FROM AUTHOR]