17Aerosol Winter Orographic Cloud Seeding in SNOWIE: Insights from Ensemble Simulation

The SNOWIE (Seeded and Natural Orographic Wintertime Clouds: The Idaho Experiment) campaign, conducted in January and February 2017 over the Payette River Basin in Idaho, represents a significant milestone in the study of winter orographic cloud seeding. With a total of 24 intensive observation periods (IOPs), including 20 that involved cloud seeding via ground-based generators, burn-in-place flares, and ejectable seeding, SNOWIE has provided an unparalleled dataset for understanding cloud and precipitation processes in complex terrain. Previous numerical studies by Xue et al. (2022) and Chen et al. (2023) focusing on one or a few seeding events emphasize the need for systematic, observation-constrained ensemble approaches to accurately determine the effects of cloud seeding on winter precipitation in complex terrains.

This work presents the most comprehensive ensemble simulation dataset to date for SNOWIE's winter orographic seeding operations. Each IOP is represented by 32 ensemble members, with each member containing both seeded and unseeded simulations—resulting in 64 simulations per IOP. Over 2000 high resolution simulations were conducted to achieve this dataset. These simulations, conducted at various grid spacings, driven by different reanalysis datasets, and including different model physics, were designed to address the model uncertainties.

By validating the simulations against the observational data and comparison among the members and across IOPs, the dataset can provide insights on how seeding impacts are influenced by different factors, such as large-scale weather patterns, initialization datasets, model physics, and seeding methods (ground-based versus airborne).