Characteristics of Clouds and Raindrop Size Distribution in Xinjiang, Using Cloud Radar Datasets and a Disdrometer

Abstract

Observation data from March to May 2020 of the Ka-band millimeter-wave cloud radar and disdrometer, located in Xinjiang, a typical arid region of China, were used to study the diurnal variation of clouds and precipitation, raindrop size distribution (DSD), and the physical parameters of raindrops. The results showed that there are conspicuous diurnal changes in clouds and precipitation. There is a decreasing trend of the cloud base height (CBH) from 05:00 to 19:00 CST (China Standard Time, UTC +8) and a rising trend of CBHs from 20:00 to 04:00 CST. The cloud top height (CTH) and the cloud thickness show a rising trend from 03:00 to 05:00 CST, 12:00 to 14:00 CST, and 20:00 to 01:00 CST. The diurnal variation of clouds is mainly driven by wind and temperature closely related to the topography of the study area. There are three apparent precipitation periods during the day, namely, 02:00–09:00 CST, 12:00 CST, and 17:00–21:00 CST. The changes in the physical parameters of raindrops are more drastic and evident with a lower CBH, lower CTH, and higher number of cloud layers from 12:00 to 21:00 CST than other times, which are closely related to day-to-day variations of systems moving through, and incoming solar radiation and the mountain–valley wind circulation caused by the trumpet-shaped topography that opens to the west played a secondary role. The DSD is in agreement with a normalized gamma distribution, and the value of the shape factor μ is significantly different from the fixed μ value in the Weather Research and Forecasting (WRF) Model. The rain in arid Xinjiang had a higher concentration of raindrops and a smaller average raindrop diameter than the rain in other humid regions of the Central and Southeast Asian continent. In the Z−R (radar reflectivity–rain rate) relationship, Z=249R1.20 is derived for stratiform rain, and it is significantly different from humid regions. Using Z/Dm (mass–weighted mean diameter) and R, a new empirical relationship Z/Dm=214R1.20 is established, and improvement is obtained in rain retrieval by using the Z/Dm−R relation relative to the conventional Z−R relation. Additionally, the Nt−R, Dm−R, Nw−R, and Nt−Nw relationships with larger differences from humid regions are established by fitting the power-law equations. These results are useful for improving the data parameters of microphysical processes of WRF and the accuracy of quantitative precipitation estimation in arid regions.

Macro- and microphysical characteristics of snowfall and non-snowfall clouds in the West Tianshan Mountains of China based on cloud radar

“…1) has an important influence on airflow through the Tianshan mountains. Mountain valley wind circulation (Zeng et al 2020b), formed by a westerly wind blowing from the valley to the mountains during the daytime and an easterly wind blowing from the mountains to the valley during the nighttime, may also play an important role. Under the influence of westerly winds during the daytime, the lowlevel airflow has climbing and ascending motion, and the heating effect of solar radiation increases the instability of the low-level atmosphere, thereby making the exchange of matter and energy in the boundary layer more active.…”

“…Therefore, millimeter-wave cloud radar is a powerful tool for studying the macro-and microproperties of clouds. (Kollias et al, 2011;Zeng et al 2020b). In China, researchers have conducted research only in central and eastern China and the Qinghai-Tibet Plateau (Zhao et al 2016;Li et al 2017).…”

Fine vertical structures of cloud from a ground‐based cloud radar over the western Tianshan mountains

“…Thus, the regional topography‐forced thermal circulation in Xinyuan station needs to be analysed. As can be seen in Figure 8c, at night, the cooling rate of mountains is faster than that of the valley, causing an easterly mountain wind to blow from mountain to valley and tending to initiate precipitation clouds in the valley (Bhatt & Nakamura, 2006; Zeng et al, 2020). During the daytime, the heating rate of the mountains is faster than that of the valley, causing a westerly wind to blow from valley to mountain.…”

“…In addition, the MMCR is located inside the trumpet‐shaped terrain formed by the Tianshan Mountains in Xinjiang Province. Previous studies indicate that on an annual average, large‐scale dynamic processes may be weakened, and regional topography‐forced thermal circulation (e.g., mountain‐valley breezes) probably plays a dominant role in the cloud diurnal cycle (Zeng et al, 2020; Zhou et al, 2019). Thus, the regional topography‐forced thermal circulation in Xinyuan station needs to be analysed.…”

A Survey of Rain Fade Models for Earth–Space Telecommunication Links—Taxonomy, Methods, and Comparative Study

“…The drop size is one of the factors that affect the polarization. In the literature there are various types of raindrop size distribution, such as the normalized gamma model [80], seasonal variations in raindrop size [81], clouds and raindrop size distribution [82], vertical raindrop size distribution [83], exponential distribution [84], gamma distribution [85], log-normal distribution [86], and Weibull raindrop-size distribution [87].…”