Microphysical Properties of a Convection-Embedded Stratiform Cloud Event and Implications for Rain Enhancement Conditions in Shangqiu, Henan

Stratiform clouds with embedded convection are the primary targets for aircraft-based cloud seeding for rain enhancement in China. A thorough understanding of the microphysical properties in such clouds is essential not only for the scientific design of aircraft operations but also for improving the effectiveness of rain enhancement. Using aircraft observational data collected on 3 May 2023, over Shangqiu in eastern Henan Province, this study investigates the horizontal and vertical cloud microphysical characteristics of stratiform clouds with embedded convection and discusses the associated rain enhancement conditions. The results show that the cloud event formed under the passage of a weak, tilted westerly trough with relatively stable atmospheric stratification. The rainfall distribution was wide but nonhomogeneous, exhibiting the typical structure of large-scale stratiform echoes embedded with convective echoes. The aircraft measurements were conducted during a period of intense rainfall; therefore, the collected data are well-suited for examining the structural properties of stratiform clouds with embedded convection and their precipitation formation mechanisms. The observations show that the supercooled cloud water content (SLWC) was very low in the stratiform cloud regions and at the edges of convective regions, where pristine column ice crystals were dominant. In contrast, the upper, colder portions of convective regions exhibited high concentrations of supercooled cloud droplets with diameters less than 25 μm, with number concentrations of 10⁵–10⁶ L⁻¹. The maximum SLWC exceeded 0.7 g kg⁻¹. Rimed aggregates were the dominant particles in these regions, with number concentrations of 10⁰–10² L⁻¹. The presence of relatively high SLWC in regions with lower ice particle concentrations indicates suitable conditions for rain enhancement operations. However, because the regions of high SLWC were primarily located within convective areas at relatively high temperatures, they are not ideal for the nucleation temperature requirements of the silver iodide agent. Thus, in such cases, the use of cooling agents, such as liquid nitrogen and dry ice, would be more appropriate for effective cloud seeding.