Accelerated impact of airborne glaciogenic seeding of stratiform clouds by turbulence

Abstract

Several recent studies have reported complete cloud glaciation induced by airborne-based glaciogenic cloud seeding over plains. Since turbulence is an important factor controlling mixed-phase clouds, including ice initiation, snow growth, and cloud longevity, it is hypothesized that turbulence may have an impact on the seeding effect. To understand the role of turbulence in seeded clouds, idealized Weather Research and Forecasting (WRF) large eddy simulations over flat terrain were conducted for a shallow stratiform cloud in which complete glaciation was observed. The results show that the model can reasonably capture the magnitude and spatial distributions of radar echoes in seeded areas. Sensitivity tests suggest that, for this case, stronger turbulence enhanced the particle dispersion, the nucleation of silver iodide (AgI) particles, and the growth of ice crystals, which accelerated cloud glaciation, even though the condensation of droplets was also enhanced. The faster cloud glaciation intensified precipitation within a short time after seeding, while the liquid water was quickly consumed, leading to a decrease in precipitation rate in the further downwind areas. Such a transition from positive to negative seeding effect is more pronounced for seeding with a higher AgI release rate. This study provides strong evidence that turbulence plays a vital role in the physical chain of events associated with cloud seeding.