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.
Highlights
Cloudiness is one of the key factors affecting climate change, and it plays an important role in the radiation budget, energy balance, and water cycle of the Earth’s atmosphere [1,2,3,4]
The diurnal variation of clouds and precipitation were investigated in detail
The detection and study of diurnal variation of clouds and precipitation are valuable for improving our understanding of the related physical and dynamic issues of clouds [21]
Summary
Cloudiness is one of the key factors affecting climate change, and it plays an important role in the radiation budget, energy balance, and water cycle of the Earth’s atmosphere [1,2,3,4]. Atmosphere 2020, 11, 1382 cloud radiation strongly depends on the macro- and microphysical properties of the cloud. The observation, inversion, and research on the macroscopic and microscopic physical properties of clouds are important for improving the parameterization processing of clouds in the Weather Research and Forecasting (WRF) Model and to understand the feedback effect of clouds in climate change [5,6,7]. Aircraft can obtain the vertical characteristics of clouds by completing multiple passes at different altitudes [11,12]. It is expensive, and clouds can only be observed for a brief time and at a specific location [13]
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