Comprehensive observations and preliminary statistical analysis of clouds and precipitation characteristics in Motuo of Tibet Plateau

In order to better understand the three-dimensional structure and microphysical characteristics of clouds and precipitation at the entrance of the water vapor transport channel in Yarlung Zangbo Grand Canyon, the Chinese Academy of Meteorological Sciences established a field campaign base in Motuo in 2019 under the support of the Second Tibetan Plateau Scientific Expedition and Research Program and the National (Key) Basic Research and Development Program of China. Motuo is located at the southeastern Tibet Plateau (TP). Advanced X-band dual polarization phased array radars, Ka band cloud radars, K band micro radars, precipitation phenomenometers, and microwave radiometers are used to carry out comprehensive observations of water vapor, clouds and precipitation. One of the specific scientific goals of the campaign is to obtain a better understanding of cloud and precipitation microphysical processes and improve the parameterization scheme of the cloud-precipitation microphysical processes in numerical models. Based on cloud radar data collected for the period from January to December 2019 and precipitation phenomenometer data for the period from June 2019 to June 2020, the macroscopic characteristics of clouds and raindrop spectrum characteristics are statistically analyzed. The macroscopic characteristics of clouds indicate that the occurrence frequency of clouds in this area is relatively high, accounting for 67% of cloud radar profiles in 2019, and precipitation clouds account for 45% of the cloud cover. Occurrence frequency of cloud base height (CBHs) in both dry and rainy seasons experienced two peaks corresponding to heights of 0–1 km and 2–3 km, respectively. One striking feature is that more than 40% of the CBHs are lower than 1 km probably due to high occurrence frequency of precipitation clouds. Nearly 60% of the cloud top heights (CTHs) are between 4 and 7 km. In general, the vertical frequency distributions of CBHs and CTHs indicate that low- and mid-level clouds prevailed in Motuo during the observational period. Clouds tended to form most frequently from the afternoon to the evening and slowly dissipate from the morning to the noon time. In terms of the raindrop spectrum characteristics, the average raindrop spectral width and number concentration of large drops increased with rainfall intensity. The combination of small- and mid-size drops dominated precipitation in Motuo, and their contributions exceeded 99% of the number concentration. Convective precipitation in Motuo is identified to be maritime-like precipitation and characterized by a large normalized intercept parameter lgN_w = 3.6–4.5 (with a mean value of 4.01) and small mass-weighted mean diameter D_m = 1.0–1.6 mm (with a mean value of 1.38 mm). Furthermore, the characteristic bimodality of lgN_w was observed in Motuo, corresponding to convective and stratiform precipitation.