A Comparison of AgI and CO2Seeding Effects in Alberta Cumulus Clouds

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Abstract
Three convective clouds extending above a stratocumulus layer were identified as being seedable on one day and were then seeded in a random sequence with CO2 pellets, a placebo and droppable AgI flares. The radar and microphysical seeding effects were observed with the Alberta Hail Project S-band radar and with the University of Wyoming Queen Air aircraft. Distinct seeding effects were observed in both seeded clouds by both data systems. The CO2 seeded cloud developed a single curtain of precipitation particles 18 min after seeding which reached the ground 20 min after seeding and ceased precipitating 10 min later. The placebo cloud failed to develop any precipitation-sized particles or radar echo and dissipated after ∼30 min. The AgI seeded cloud developed its first echo 8 min after seeding near the threshold temperature for AgI (−7°C), produced precipitation at the ground 20 min after seeding, and continued to develop a new echo near the −7°C level and precipitate for ∼1 h. A natural echoing st... Abstract Three convective clouds extending above a stratocumulus layer were identified as being seedable on one day and were then seeded in a random sequence with CO2 pellets, a placebo and droppable AgI flares. The radar and microphysical seeding effects were observed with the Alberta Hail Project S-band radar and with the University of Wyoming Queen Air aircraft. Distinct seeding effects were observed in both seeded clouds by both data systems. The CO2 seeded cloud developed a single curtain of precipitation particles 18 min after seeding which reached the ground 20 min after seeding and ceased precipitating 10 min later. The placebo cloud failed to develop any precipitation-sized particles or radar echo and dissipated after ∼30 min. The AgI seeded cloud developed its first echo 8 min after seeding near the threshold temperature for AgI (−7°C), produced precipitation at the ground 20 min after seeding, and continued to develop a new echo near the −7°C level and precipitate for ∼1 h. A natural echoing st...

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