Abstract:

A low trough cold front precipitation process occurred on January 6, 2018, in Hebei province.Based on two sets of aircraft detection data, macro and micro cloud structure and cloud development process were analyzed, and the catalytic condition and seeding opportunity for the stratiform cloud in low trough cold front system in winter were investigated.The results show that when the wind center of southwest wind occurred at an altitude of 6500 m at the beginning of the weather system, the wind speed was discontinuously distributed with the height, the cloud top temperature of stratiform cloud was around-29.2℃, and the low and middle clouds were thin.At the same time, cloud particles above 3000 m were glaciated, the supercooled water content in the cloud was less than 0.05 g·m^-3, and the solid water content was about 0.1 g·m^-3.Meanwhile, there were a lot of natural ice crystals in the cloud below 3000 m, and the supercooled water content was less than 0.15 g·m^-3, which was not available for seeding.At the height of 700-3000 m, the southwesterly wind was strengthened, the supercooled water content in the cloud was generally larger than 0.1 g·m^-3, and the wind speed at the wind center at 2200 m was 16 m·s^-1, and the maximum liquid water content at this height was 0.38 g·m^-3, and ice crystal concentration was 6 L^-1, and the temperature was-9℃, which was suitable for seeding.The structure characteristics and seeding conditions of stratiform clouds in this low cold front weather system were affected by the intensity of the southwest wind ahead of the trough and the height of the wind center.Because the top of the stratiform cloud was too high and the temperature was too low in the early stage of the weather system, this cloud system was not in favor of seeding.As the trough line moved eastward, the wind center height decreased and the southwesterly wind below 3000 m was intensified, this stratiform cloud was transformed into the cloud available for seeding.

Key words: Stratiform clouds, Cloud structure characteristics, Seeding possibility