Testing the efficacy of cloud-seeding

Cloud-seeding graphic via Science Matters

Here’s an in-depth report from Sarah Scoles writing for Popular Science. Click through and read the whole article. Here’s an excerpt:

TTHE GROUP SET UP ITS BASE IN IDAHO FROM JANUARY 7 TO MARCH 17, with the resources to do around 20 seeding sessions. Every day they would determine, via their own ­weather balloons and outside forecasts, whether the clouds saturated with super-cooled ­water would form at the right temperature and height over the mountains.

Josh Aikins, Friedrich’s graduate student, was a key member of the mountain radar group. He’d snowmobiled only once before, when he was a teenager on vacation in Vermont. But he quickly got the hang of sliding up to the Packer John Mountain radar site, at 7,000 feet of elevation—even when the snow was so new and light that the machine meant to float atop it instead sank down and needed to be dug out. Aikins had fallen in love with snow as a kid when the Blizzard of ’96 blanketed the Mid-Atlantic. The snow drifted into banks that reached over the roof of his family’s York, Pennsylvania, home. He graduated from Penn State with a degree in meteorology but knew he didn’t want to be a weatherman. “I’m a T-shirt and shorts guy,” he says.

When the SNOWIE team decided to try for a seeding run, Aikins and the other radar-runners packed up a week’s worth of food and clothes into the vehicles; ­given that they were purposefully driving up the mountain during storms, they never knew how soon they’d be able to get back down. One time the 10-mile ride was so challenging, it required seven professional snowmobilers to help them out.

Each time they arrived at their site—a mountaintop with a radar system atop a big truck and an old camper as their luxury accommodations—Aikins would fire up the generator, warming up the radar and the camper. “We had a bunch of computers that we didn’t want to start up cold,” he says, because some electronic components won’t function well in that condition. They’d stash their clothes and food in the camper and dig out the drift-covered porta-potties.

Then they would scan with the radar and watch what the weather was doing. When the seeding started, they’d search for changes in reflectivity that suggested the electromagnetic waves were bouncing off an area of newly formed ice particles.

Aikins remembers well the day of the first signal. “We saw these linear bands coming through the area,” he says, referring to the radar readout. “It didn’t look natural.” He sent an email to the command center, asking if the planes were out. They were. “We could see the seeding in real time. We could see the path of the flares.”

In his public field report of that flight, principal investigator Geerts wrote ­impassively of their finding: “Possible seeding signature…two bands of higher reflectivity aligned with the seeding aircraft, drifting with the wind and dispersing over time.”

Put simply: They got it.

AIKIS AND GEERTS SOUND PRETTY STOIC ABOUT THAT FIRST FINDING, considering it was exactly the gold they’d gone West seeking. But that’s probably because, as Friedrich says, everyone was —and still is—suspicious. They haven’t fully analyzed the data. Their results haven’t undergone peer review and been published in an academic journal.

But their online reports note three instances where snow formation could be linked to their activity. The second time, Rauber wrote, “The seeding signatures were unmistakable and distinct, with the lines mimicking the seeder flight track.” They started to believe maybe the signatures weren’t a coincidence—and they wanted more. Soon enough, they were rewarded.

“The remarkable thing was not that we saw it,” says Friedrich, “but that we were able to repeat it multiple times.”

Rauber, who’s worked in seeding without certain results for decades, cops to his excitement. “Honestly, the first time we saw this, I was giddy,” he says. “I was almost dancing around in the room.” Think of it from “the perspective of an old cloud seeder,” he implores. He labored throughout the ’70s and ’80s, trying to see a signal those Coke-bottle glasses just couldn’t bring into focus. And now it’s like he’d had Lasik surgery.

Of SNOWIE’s data, Derek Blestrud—a meteorologist with Idaho Power and president of the North American Weather Modification Council—said, “What we got was well above and beyond what anybody imagined.”
Even though the team captured those zigzags, they still have a lot of work to do before they can tell the world exactly how—and how well—cloud seeding might work. Depending on who you ask, they’ll be ­digging into data for four to six years, although they aim to get the ­whiz-bang results out within 12 months. “We have more data than any of us ever dreamed of being able to collect,” French says.

The plane alone scooped up 25 gigabytes of data on each of its 18 flights, gleaned from the radar and laser systems, as well as from its direct temperature, pressure, and water-vapor probes. The scientists will sort through that and ground-based research, and do some interpretation and analysis on local machines at their universities and at the Center for Severe Weather Research in Boulder, Colorado. That will give them a rudimentary understanding of what the gigabytes signify: the physics of how snow forms and falls naturally in the mountains, how burning bits of inorganics alter them, the impact on weather as a whole. As French puts it, they’ll have 100 pieces of a 5,000-piece jigsaw puzzle.

To get the complete picture, they’re gonna need a bigger box—a supercomputer. The National Center for Atmospheric Research has a new one named Cheyenne, with 5.34 petaflops of capacity. It’s the 20th-fastest calculator on the planet. Cheyenne will show how well the physical observations—from the planes, the radars, and the real world—match up with the predictions. And based on how well they do or don’t, the SNOWIE team and other scientists can then tweak the predictors to better see which weather is the most fertile for modification.

This isn’t just about Idaho. SNOWIE will figure out the underlying mechanisms that determine how clouds come to form, evolve, and drop snow—whether seeded or not—down to Earth. “It should apply anywhere,” says Geerts. After all, physics is physics, on Earth as it is in heaven, as it is where the two meet.

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