The capacity to make it snow lacks the cultural cachet of “rainmakers”, but demand is only going to grow in a warming world. Now, for the first time, we have watched the formation of human-induced snowflakes, hopefully taking much of the guesswork out of efforts to target snow production.
Those shoveling snow may wonder why anyone would want more of the stuff, but ski resort owners have a simple answer. As California heads ever closer to a reckoning with its lack of local water supplies, the decline of its snowpack, and that of inland states, is a much more widespread problem.
Dr Jeffrey French of the University of Wyoming led a team that scanned clouds in western Idaho with radar and aircraft-borne probes to observe the effects of cloud-seeding experiments. Since radar is sensitive to particle size, the work tracked the size and number of what eventually became snowflakes as they developed. The results have been published in the Proceedings of the National Academy of Sciences, allowing us for the first time to see aerosols be injected into a supercooled cloud, ice particles form around them, and these particles grow and eventually fall to the ground as snow.
For decades scientists have been trying to make it rain, or more precisely, make it rain where and when they want. Unfortunately, these efforts have been only slightly more successful than earlier generations of traveling scammers who promised precipitation for profit. The most popular technique has been “seeding” clouds with silver iodide to provide a nucleus for ice crystals, around which water droplets can grow until they are large enough to fall from the sky.
The same process has been used to induce snowfall in colder weather, but in both cases, the reliability is so low there has been dispute over whether it really works at all, or if cloud seeders are just claiming credit for what would have happened anyway. One possible explanation for this limited success is that, as the paper notes, the work has been done based on assumptions about how raindrops and snowflakes start and grow, but; “Despite numerous experiments spanning several decades, no direct observations of this process exist.”
The cloud-seeding planes release their silver iodide in a zig-zag pattern, so French and his co-authors could track the differences between seeded and unseeded clouds, with crystals appearing 30 minutes after release and reaching concentrations 100-1000 times those of unseeded clouds, indicating models of snow formation have been broadly accurate.
The measurements could help determine just how well existing cloud-seeding projects work, although this paper explicitly does not do that. They could also inform future attempts to induce snowfall that will fill strained reservoirs come the thaw.