Microphysical Responses to Catalysis During a Stratocumulus Aircraft Seeding Experiment over the Sanjiangyuan Region of China

This study explores the microphysical responses to a cloud seeding operation in the Sanjiangyuan re-gion, China. The cloud seeding was performed using a zigzag flight pattern, while the detection phase was accomplished using a back-and-forth flight pattern through the top of a stratocumulus layer. Global Position System (GPS) and Particle Measuring System (PMS) data obtained during the operation are used to determine the effective cloud area before and after the operation, differentiate the phase states of cloud particles, and analyze changes in the concentrations of liquid cloud particles and ice crystals, the evolution of the cloud particle spectrum, and the content of supercooled water. The median diameter of liquid cloud particles in the area of the cloud-seeding operation was 3.5-18.5 μm, most cloud particles observed in the 21.5-45.5-μm size regime were ice crystals, while all particles of size 50μm and above were in the ice phase. Changes in the concentration and typical diameter of cloud particles within 36 km downwind of the cloudseeding operation did not exceed natural fluctuations in the cloud area before the operation; however, the concentration of liquid cloud particles decreased substantially in areas with high concentrations of supercooled water (concentrations of supercooled water exceeding 0.01 g m-3). The concentration of ice crystals within the measuring range of the Forward Scattering Spectrometer Probe (FSSP) increased substantially, the water content of ice-phase particles increased, and the average supercooled water content in the cloud decreased from (68.3±23.1)% before the operation to (34.2±12.4)%. The effects of cloud seeding were more pronounced in parts of the cloud where the content of supercooled water was higher. Little to no effects were observed in parts of the cloud with low concentrations of supercooled water.