Observed and Simulated Dynamic Responses to Glaciogenic Seeding in Wintertime Mixed-Phase Clouds

Observations from recent field campaigns investigating glaciogenic cloud seeding demonstrate the process of silver iodide (AgI) dispersion through ice nucleation, crystal growth, then enhanced snowfall at the surface. These observations, combined with numerical simulations, were used to quantify seeding’s impact on enhancing precipitation in targeted regions. With the microphysical chain of events established, fundamental knowledge gaps remain on the mechanisms by which seeding modifies the cloud dynamics, structure, and precipitation enhancement. This study presents the first direct observational evidence that glaciogenic seeding generates buoyant forces in wintertime orographic clouds that elevate cloud tops and secondary circulations that alter the cloud structure. 

 

In this study, we analyze dynamic responses induced from seeding in the Seeded and Natural Orographic Wintertime Clouds: The Idaho Experiment (SNOWIE) and CLOUDLAB field campaigns. The SNOWIE cases occurred in the Payette mountains in presence of widespread supercooled liquid conditions and low natural ice number concentrations. Ground-based X-band radars tracked the development and evolution of cloud and precipitation from five seeding legs. Distinct cells, directly attributable to airborne seeding, developed from smaller weaker echoes (10 dBZ) at the natural cloud top and rapidly intensified to produce precipitation with echoes >30 dBZ. The key observed processes were dynamic responses induced by the latent heat released from seeding that led to enhancing cloud top by 350 m compared to the natural cloud. An airborne W-band Dual-Doppler cross-section illustrates the detailed dynamic structure for one cell consisting of a central updraft, divergence near cloud top, and toroidal circulations along its periphery in an observed moist-neutral environment. In situ measurements show distinct microphysical regimes in the elevated cloud top, with seeding generated ice number concentrations up to 580 L-1. A WRF-WxMod ensemble shows the evolution of dynamic responses, the microphysical characteristics, and precipitation enhancement up to 200 km downwind of release.

 

We combine these results with preliminary observations from the 2025-2026 CLOUDLAB field campaign that further investigate the roles each step in a dynamic response has on seeded cloud microphysical properties. We show the evolution of seeded cloud from Ka-band cloud radars, combined with in-situ measurements from a holographic imager, to show dynamic response impact on microphysical structure and cloud properties.