Cloud seeding — modifying the amount or type of precipitation a cloud produces — is not a new idea. But the first direct observation of the feat occurred about one year ago, thanks in part to a University of Wyoming scientist and UW’s King Air research aircraft.
Jeff French, assistant professor of atmospheric science, worked with a team of private and public researchers to measure the effects of cloud seeding, a notoriously difficult task which has never before produced conclusive results.
“We saw this happening before our eyes,” French said. “We could actually see it in the field. We could see this data coming in on the radars.
We could see it on the aircraft … and to put it mildly, we were all giddy when we saw this coming in.”
The team’s research was published Monday in the Proceedings of the National Academy of Sciences, “one of the world’s most prestigious multidisciplinary scientific journals, with coverage spanning the biological, physical and social sciences,” according to a UW news release.
The team’s observations — made in the winter months of 2017 — accomplished something researchers have been after for half-a-century, French said.
“Cloud seeding has been going on throughout the United States, throughout the world, since the 1960s — that was really kind of the heyday,” he said.
“And over the course of 20 or 30 years, really up through the 1980s, numerous experiments have been conducted, including throughout the western United States.”
Most research got shut down at the end of this period, French said, because it had failed to produce results.
“By the mid-1980s, people were beginning to realize that all of this research money was being spent on cloud seeding and they weren’t really any closer to the answer of whether cloud seeding worked or not,” he said.
“And in fact, even with all of that research, they were never even able to answer the basic question of whether — under any circumstances — a cloud could be modified in such a way that it could produce precipitation.”
Glaciogenic cloud seeding — the variety studied by French and his fellow researchers — involves injecting clouds with silver iodide in the hopes of increasing snowfall.
“It tries to add a material to the clouds that promotes the freezing of liquid water, of some of the liquid water, so you then have ice in the clouds which can grow more readily, more easily, to a larger part of a cloud,” he said. “This type of cloud seeding is the type of cloud seeding that is often used or studied for seeding wintertime clouds in mountains.”
Western states get the majority of their water from snowpack in the mountains, French said, and began to reconsider cloud seeding when water became scarcer and cloud seeding potentially offered a way to increase snowfall.
“Now fast forward another 10 or 15 years to droughts of the 1990s and the early 2000s throughout the intermountain west, and the ongoing droughts even today,” French said. “Numerous state agencies, water managers — state of Wyoming — began looking toward cloud seeding as a potential way to augment water supplies.”
Sarah Tessendorf, a National Center for Atmospheric Research project scientist who co-authored the research, was involved in Wyoming’s effort to investigate cloud seeding, dubbed the Wyoming Weather Modification Pilot Project.
“Even though that was a modern day statistical program, it still had some inconclusive results because the natural variability of the weather is so great that trying to tease out a very small change in precipitation due to cloud seeding is quite challenging,” Tessendorf said.
The ongoing effort to measure the effects of cloud seeding were plagued by the same difficulties which had made conclusive measurements elusive since the 60s.
“Over all that time, research projects that have been trying to quantify the impacts of cloud seeding have oftentimes failed or been inconclusive and part of the reason for that is once you seed a cloud, you’re never going to really know what it would have done otherwise.”
A new approach to the problem was required, French said.
“One of the things that was realized coming out of the Wyoming project was to really do this right — to really make measurements inside the cloud — we need to attach ourselves with a project that was doing cloud seeding from an aircraft,” he said. “And Idaho Power had this ongoing operational cloud seeding program.”
At the National Center for Atmospheric Research, Tessendorf and other researchers developed models to simulate the effects of cloud seeding, but needed detailed observations to improve those model simulations.
Unique instruments aboard UW’s King Air research aircraft — some of which were developed at UW — were able to produce these detailed observations.
“The experiment itself is not significantly different from some of the experiments that were run 30 years ago,” French said. “It’s just that we have much better instrumentation now. We have much better numerical models to be able to help guide us.”
He added the research represents a breakthrough in the study of cloud seeding.
“It was really beyond our wildest expectations that we would see such clear signals,” French said. “We knew very early on that we have something very special.”
The project itself — which required a consortium of researchers across the region and funding from the National Science Foundation — also represented a success outside the data it produced, Tessendorf said.
“We had professors from universities, a lot of students, folks on my team from NCAR and Idaho Power company,” she said. “It was a true public-private partnership that is kind of unique in science and it really made for a successful program.”