Cloud environment controls the precipitation response to liquid propane (LP) seeding: an ice nucleation parameterization for LP seeding and idealized simulations

Abstract. This study presents a liquid propane (LP) seeding parameterization in the Weather Research and Forecasting (WRF) model. Two formulas derived from laboratory experiments express ice production as a function of temperature and LP release rate. The seeding impacts on clouds and precipitation are evaluated through idealized two-dimensional simulations spanning two mountain heights, four environmental soundings, and four seeding scenarios. The simulations reveal an environment-dependent microphysical response in which the ice conversion process near the seeding site varies with the natural rain efficiency, from a snow-dominated regime where riming is limited to a riming-dominated regime in efficient-rain conditions. The largest enhancement occurs in the low mountain, where supercooled liquid water (SLW) persists and natural precipitation remains weak. Seeding impacts in the high mountain are weaker, with a mild reduction in total precipitation in the case where natural rain process is the most efficient. Snow enhancement dominates the net total precipitation increase. Compared with AgI seeding in prior idealized studies, LP is weaker in both magnitude and spatial extent because LP-generated ice requires a continuous SLW cloud layer for dispersion from the surface to clouds. Nevertheless, LP is effective at temperatures warmer than -6 °C where AgI is less active, suggesting complementary roles of the two seeding agents. These simulations provide a physical basis for understanding LP seeding responses and for future three-dimensional real-case simulations, field evaluation, and direct comparison with AgI seeding simulations.