Aircraft Observed Cloud Microphysics Variation Related to a Cloud Trough during Stratiform Cloud Seeding over Central China

Previous satellite observations have identified the appearance of “cloud trough” (or “cloud trench”), with cloud tops visually collapsed following airborne cloud seeding operation, demonstrating the effect of weather modification. However, refined observations of troughed clouds and associated cloud microphysics remain lacking, especially using in-situ observations from aircraft sensors. In this study, variations in cloud microphysics associated with and without troughed clouds along the airborne stratiform cloud seeding path over central China on 15 December 2019 are analyzed and compared based on aircraft measurements, ground-based radar observations, and FY-4A satellite imagery. The results show that (1) the troughed clouds were mainly formed to the northeast of the flight path and appeared only in some parts of the seeded stratiform clouds. The seeding tracks became visible starting from 60 minutes post-seeding and sustained for about 3 h, covering a maximum width of 30-40 km in FY-4A imagery. Radar echo enhancements observed by a ground-based radar can be seen at some parts of the seeding tracks. (2) The troughed clouds were observed only when the ambient air temperature (T) was ≤ －7°C, which favored high nucleation efficiency of silver iodide (AgI) aerosol particles, while no cloud troughs formed for T_a above that. (3) The troughed clouds with strong radar echoes (i.e., large precipitation) corresponded to regions with high values (＞0.1g m⁻³) of supercooled water content after cloud seeding, which facilitated the growth of precipitation particles. (4) Within the troughed clouds, the cloud optical thickness and cloud top height decreased, while the effective radii of cloud particles increased by nearly 10 μm. These results provide valuable guidance for optimizing cold cloud catalytic conditions in artificial rainfall enhancement. Meanwhile, the occurrence of high supercooled water content, particularly the threshold of supercooled water content, is a critical factor for strong precipitation, which necessitates further studies.