How Do Cloud-Top Generating Cells Impact the Agi Seeding Effect in Wintertime Precipitating Clouds?

Snowpack from the wintertime precipitation over the mountainous region is the main source of freshwater to human society. The formation of ice phase hydrometeors and their subsequent growth are critical to the amount and distribution of the snowpack in mountains. Understanding the mechanisms and conditions mixed-phase precipitation form and develop not only help us predict the natural precipitation but also provide knowledge on how to increase precipitation and water resources through artificial modifications of clouds or cloud seeding.

Among different ice forming regions in clouds, cloud-top generating cells (GCs) are small-scale structures featuring stronger turbulence than the surrounding areas, that produce drizzle drops or ice particles leading to precipitation fall streaks. Recent field observations during the Seeded and Natural Orographic Wintertime clouds: the Idaho Experiment (SNOWIE) field campaign showed that cloud-top GCs were very common in many Intensive Observed Periods (IOPs). Detailed analysis of high-resolution (grid spacing ranging from 20 to 300 m) WRF Large Eddy Simulations (LES) revealed that cloud-top GCs formed only when the radiative cooling is simulated. Cloud-top evaporation cooling is not sufficient to form GCs if radiative cooling is turned off. How do these commonly-observed ice forming GCs impact the AgI seeding effect is unknown and to be investigated in this work.

High-resolution real-case LES cloud seeding simulations (300 m and 100 m grid spacing) under GC and no GC conditions during one SNOWIE IOP are conducted to explore this question. The results will be presented at the meeting.