Glaciogenic seeding-induced hole-punch clouds and their sensitivity to the clouds' background state

Hole-punch clouds are a visual representation of ice crystal formation and growth as well as their interactions with the liquid phase via the Wegener–Bergeron–Findeisen process. Their appearance is usually associated with an aircraft passing through a liquid cloud layer. However, they can also appear upon glaciogenic seeding of a supercooled low-level stratus cloud, as we showcase in this study. The observations of a hole-punch cloud prompted an investigation into the sensitivity of these clouds to the clouds' background state. We employ high-resolution large-eddy simulations with the weather model ICON and simulate one seeding experiment with different initial liquid water paths. The ensemble of 9 simulations helps us to quantify how the properties of a hole-punch cloud, i.e., strong reductions in the liquid water contents, depends on the cloud liquid water paths. Moreover, we perturb the turbulent mixing length, i.e., the Smagorinsky constant, to evaluate the impact of the intensity of mixing on hole-punch clouds. Generally, larger liquid water paths lead to a delay in the strongest reductions of liquid water content through the Wegener–Bergeron–Findeisen process. Interestingly, the turbulent mixing length does not appear to have a significant impact on the hole-punch cloud properties. These findings improve our understanding of the Wegener–Bergeron–Findeisen process and of the effectiveness of glaciogenic cloud seeding.