Abstract
At present, there is insufficient research on the refinement of the vertical structure of winter snowstorm systems in arid areas, and, compared with the central and eastern China, the observation sites in arid areas of northwestern China are scarce. To deepen the understanding of dynamics and microphysical processes and improve the level of forecasting and warning of snowstorms in northwestern China, the Institute of Desert Meteorology, China Meteorological Administration, Urumqi, carried out the Central Asia Extreme Precipitation Observation Test (CAEPOT) in Yili, Xinjiang, a typical arid region in China in February 2020. This paper uses multiple fine detection datasets obtained from the CAEPOT, including radar wind profiler, ground-based microwave radiometer, and millimeter-wave cloud radar to analyze macroscopic characteristics and microphysical changes of snowstorm system in Xinjiang. Studies have shown that the low trough with sufficient moisture, heat, power conditions, and weakening banded cloud system, which moved eastward from the Aral Sea to the west of Xinjiang during the snowstorm, were the key influencing system of this snowstorm. Before the snowstorm, the vertical shear of the horizontal wind field was severe, which aggravated the instability of the atmosphere, and there was upward motion in the lower atmosphere. A variety of physical quantities related to moisture showed a tendency to increase at the lower level and could be used as an early warning signal for snowstorm about 8 hours in advance, and the cloud and snow particles observed by millimeter-wave cloud radar were simultaneously developing upward and downward from 4 km, providing snowstorm warning 12 hours in advance. During the snowstorm, the horizontal wind speed and vertical speed were obviously enhanced, and the physical quantities related to moisture further increased, and, with the blocking and uplifting of the Tianshan Mountains, the snowstorm increased. The particles collided and grew while falling, resulting in a decrease in particle concentration and an increase in particle radius from high altitude to the ground, eventually resulting in near-ground reflectivity factor up to 30 dBz. In addition, reflectivity factor, physical quantities related to moisture, wind field, particle concentration, and particle radius all had a good correspondence with the beginning, end, and intensity of snowstorm, so when the physical quantities mentioned above weakened and stopped, snowstorm also weakened and stopped. In a word, this research is an important and meaningful work that provides more backgrounds and references for the forecast and warning of snowstorm in northwestern China.
Highlights
A radar wind profiler is a new wind measurement device that can provide a continuous distribution of data on meteorological elements such as the horizontal atmospheric wind field, the vertical airflow, and the atmospheric refractive index structure constant over the altitudinal profile. e type of the observed system can be determined from the change in the vertical profile over time, such as grooves, ridges, fronts, shear lines, and gravity waves [1,2,3,4,5]
Previous studies have shown that terrain plays an important role in snowstorms in Xinjiang, and the snowstorm centers in Xinjiang are all located near the mountains [41], and different atmospheric circulations divide Xinjiang snowstorms into warm front snowstorms in the Altay region and the Tacheng-Emin basin and cold front snowstorm in the Yili region and the region of northern Xinjiang along the Tianshan Mountains [40, 44, 45]
Some meaningful conclusions have been obtained from some case analysis, warm front snowstorm and cold front snowstorm are caused by warm front system and cold front system respectively [45], and warm front snowstorm occurs in the decompression and heating zone on the ground, while cold front snowstorm is the opposite
Summary
A radar wind profiler is a new wind measurement device that can provide a continuous distribution of data on meteorological elements such as the horizontal atmospheric wind field, the vertical airflow, and the atmospheric refractive index structure constant over the altitudinal profile. e type of the observed system can be determined from the change in the vertical profile over time, such as grooves, ridges, fronts, shear lines, and gravity waves [1,2,3,4,5]. The research on radar wind profiler data during snowstorms in arid regions of China is still lacking. The application of millimeter-wave cloud radar to evaluation of the snowstorm process in arid regions of China is still lacking. Wang et al [38, 39] used a vertically directed radar wind profiler and a microwave radiometer to conduct research on the snowstorm in Urumqi, Xinjiang. E observation instruments are located at the Xinyuan station in Yili, including a radar wind profiler, ground-based microwave radiometer, and millimeter-wave cloud radar (Figure 1(b)). 2. Data and Methods e data used in this research include hourly snowfall data from ground weather stations in the Yili region of Xinjiang, temperature of black body (TBB) data from FY-2G, radar wind profiler data, microwave radiometer data, and millimeter-wave cloud radar data. The Yili area was located to the left of a high-level jet outlet area, the intensity of the jet center exceeded 60 ms−1 (Figure 3(d)), studies have shown that high-level jets are beneficial to the formation of divergence in the upper atmosphere [42], and strong divergence was conducive to the formation of snowstorms
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