Injecting silver iodide into clouds has been helping boost precipitation since the 1940s. But while the process obviously works based on models and statistics, no one is sure exactly how well it works, or where the seeded snow ends up.
To answer that question, geosciences professor Shawn Benner and graduate student James Fisher are teaming up with Idaho Power to measure the amount and location of cloud-seeded snow by looking for silver iodide in Idaho’s mountain snowpack.
Finding and measuring the silver is very challenging because the cloud-seeded silver is present at very low concentrations and is often obscured by silver from other, often natural, sources. To avoid contamination, the team wears clean room “bunny suits,” masks and gloves when collecting cylinders of snow from areas of the Lost River Range so remote they require a helicopter or snowmobile to reach.
That’s because it only takes one gram of silver iodide to produce about 100 trillion snowflakes. This means the resulting silver concentrations in the snow are very low, and even the little bit of natural dust in the snow may hide the cloud seeding signature. Contamination is also lurking on their clothing and equipment. Even the tiniest variation in the actual silver iodide count could skew the results.
And that data is important, because accurately targeting cloud seeding to produce even a 10 percent increase in snowpack could translate to enough hydropower for about 15,000 homes for a year. Water also is critical for healthy rivers, for fish, irrigation and recreation, and especially our ski areas throughout the state. Diminishing snowpacks due to climate change is making cloud seeding efforts increasingly important.
“Water can exist at temperatures between 0 and negative 39 degrees centigrade in the atmosphere, called super-cooled liquid water. But to become a snowflake, there first has to be a particle in the air,” explained Fisher. Without particles to help make snowflakes, little precipitation occurs. This is especially true for short-lived clouds in mountainous terrain. Silver iodide provides the particle to promote precipitation.
Even under the best circumstances, many storms are deemed less than optimal for seeding. Currently, Idaho Power’s forecasting teams monitor storms 24/7 to identify conditions that offer the best chance of success. Last season there were only a handful of successful seeding events. This year there were many more opportunities.
“This is a great partnership for both Boise State and Idaho Power,” Benner said. “We get to do interesting research and provide training opportunities for our students, and Idaho Power gets information that helps their operations. It is very rewarding to work on a problem that has such relevance to our state’s future.”
“Boise State was asked to get involved because of our unique facilities and expertise,” he said. “In this case, you need the right instrumentation and you’ve got to be very precise. James, and our laboratory team, have done an amazing job of developing these techniques.”
Some of those techniques can take months. Because the vials used to collect snow samples are contaminated by the metal in the manufacturing process, they need to be carefully purified. In a clean room, Fisher first wipes them with ethyl alcohol, then alternates rinsing them in ultrapure water and then in an acid bath with super-clean acid. After doing this three times he leaves them in an acid bath for up to six months until there is no trace of metals.
In the field, samples are stored in dry ice until they can be returned to the lab, where measurements must be taken quickly. “If you let the snow melt, the silver is sucked into the walls of the vial,” Fisher said.
Partnering with Idaho Power to improve cloud seeding has the potential of saving tens of millions of dollars in energy costs, while also expanding our knowledge of the environmental factors that influence the project. And in an arid state like Idaho, that’s a definite silver lining.