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Abstract
In this study, we employed a three-dimensional mesoscale cold-cloud seeding model to simulate the microphysical impacts of artificial ice crystals used as cloud seeding catalysts. Our objective was to elucidate the mechanism of snowfall enhancement in stratiform clouds in the Bayanbulak test area of Xinjiang, China. The results indicated that the optimal seeding time was the early stages of weather system development. In this case, the optimal seeding zone was identified as the northwest of the test area, especially near the cloud top (altitudes between 3500 and 4000 m, temperatures range −11 to −15°C), and the ideal concentration of catalyst was with ice crystal density of 1.0 ×ばつ 107 kg−1 within the target area. Under such conditions, the total precipitation rate in the seeding-affected area increased to 50.1 mm h−1. The results also showed that the favorable seeding region was featured by high content of supercooled water and low population of natural ice crystals, where artificial ice crystals could substantially increase the snowfall. This augmentation typically appeared in a unimodal pattern, with the peak formed within 2–3 h after seeding. Seeding in the ice–water mixed zone of a supercooled cloud facilitated rapid ice crystal growth to snowflake pieces via the Bergeron process, which in turn consumed more supercooled water via collision–coalescence with cloud water droplets. Simultaneously, the intensive consumption of supercooled water impeded the riming process and reduced the formation of graupel particles within the cloud. The dispersion of artificial ice crystals extended over tens of kilometers horizontally; however, in the vertical direction most particles remained approximately 1 km below the seeding layer, due to limited vertical ascent rate in the stratiform clouds restricting upward movement of artificial ice crystals. The above results help better understand the snowfall enhancement mechanism in stratiform clouds and facilitate related weather modification practice.
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