Dry ice is shown to be an attractive agent for on-top seeding of convective clouds. A modest payload of small dry ice pellets can effectively seed dozens of clouds, depending on cloud volumes encountered and crystal concentrations desired. A dry ice pellet size of about 7 mm diameter is suggested for efficient use of seeding agent when dropped from the −10°C level.
Supercooled convective clouds that were seeded on-top with dry ice were investigated to determine empirical nucleation effectiveness values. The clouds were repeatedly penetrated to measure the resulting ice crystal concentrations. The experiments gave conservative effectiveness values of 2 to 5 × 1011 crystals per gram of dry ice, but with possible error bars extending an order of magnitude to each side of those values. A well-documented experiment giving effectiveness values twice as large is discussed in detail.