When Planes Punch “Holes” in the Sky

This post also appears at Climate Central, a content partner of Climate Watch.

By Michael D. Lemonick

Hole-punch clouds, such as this one, can result when aircraft fly through clouds  containing supercooled water droplets.  Photo credit: Alan Sealls, chief meteorologist, WKRG-TV

Hole-punch clouds such as this one can result when aircraft fly through clouds containing supercooled water droplets. (Photo: Alan Sealls, WKRG-TV)

How did this happen? The crazy-looking cloud formation in the photo above isn’t a still from a sci-fi movie. It’s not “Photoshopped.” It’s quite real.

It’s also totally artificial, which requires a bit of an explanation.

Since at least as early as the 1940s, meteorologists have been noticing formations like this, and it wasn’t long before they figured out that aircraft were probably involved somehow–perhaps by creating a pressure wave as they passed through, or by heating the clouds and evaporating them.

By the 1980s, says Andrew Heymsfield, a scientist with the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, the holes had become more common and the explanation clearer: as planes punch through cloud decks that have particular characteristics, the air is compressed, then expands and cools, just like the coolant in an air conditioner. The cooling forces water droplets to freeze into tiny ice particles; these in turn act as seeds around which raindrops or snowflakes can form. The clouds then “rain out” or “snow out,” leaving a hole in their wake.

That’s the theory, anyway, though the phenomenon also makes great fodder for tabloids. But now Heymsfield has the smoking gun (outlined in a press release from NCAR), so to speak. Back in 2007, he and some colleagues flew their research aircraft through a snow squall west of Denver. They checked later with ground radar and learned that the band of precipitation was oddly shaped–about 20 miles long–but only about 2½ miles wide. It had appeared and disappeared quite abruptly, leaving a couple of inches of snow in its wake. Then they checked the cameras on their plane and discovered a hole in the clouds. Sandwiched between solid cloud decks, it wasn’t visible from the ground.

You might not have seen it from a satellite either; such holes are often hidden entirely. But that’s not the case in this image (below) from space, centered over the Texas-Louisiana border. Nearly all of the spots, big or small, are holes punched by ascending or descending aircraft. Some of the lines are also caused by planes traveling through the clouds at a constant altitude. “You can probably see around 50 of these artifacts in the image,” Heymsfield said.


This image, captured by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite, shows shows up to 50 hole-punch features in clouds above Oklahoma, Arkansas, Louisiana, and Texas. (Photo: NASA)

The holes don’t just close up right away, either. “We’ve tracked some of them (by satellite) for up to five hours,” said Heymsfield.

If this phenomenon were just an example of gee-whiz science, the paper Heymsfield and four co-authors published about it in the Bulletin of the American Meteorological Society would be fascinating enough. But it turns out that it has military implications as well. Heymsfield has consulted with Boeing on how to fly jets so as not to leave their calling cards in the sky. “Military aircraft,” he notes, “really don’t want to be visible. (On the day the satellite image was taken) we saw a fantastic trail from a B-52.”

The study also underscores how one of our most natural instincts is simply wrong; that the Earth is so enormous, it seems impossible that human activity could alter the planet in any significant way. Unfortunately, there’s no lack of evidence showing how wrong our instincts can be. Oil spewing into the Gulf, another set of record warm temperatures, and endangered species wherever we look are just a few examples. Holes punched in clouds can now be added to the list of human modifications of the environment around us, even if the results do look like science fiction.

NCAR researcher Andrew Heymsfield discusses his aircraft-induced cloud modification study. (Video: NCAR)

Seeding Clouds for Hydropower

PG&E cloud seeders located near Burney Falls, CA.  Photo: PG&E

PG&E cloud seeders located near Burney Falls, CA. Photo: PG&E

Christina Aanestad’s radio feature for Climate Watch airs Monday morning on The California Report.

Wringing Hydropower Out of the Clouds

By Christina Aanestad

When cloud seeding began in the 1950’s there were no laws governing weather modification. According to Maurice Roos, Chief Hydrologist with the state Department of Water Resources (DWR), it wasn’t until the late 1970’s when a storm in a seeded area near Los Angeles flooded, that regulations governing weather modification were included in the state’s water code. In the West, “Most of the states have legislation that governs the conduct of weather modification activity,” says Brant Foote, director of the Research Applications Lab at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado.

Government oversight has changed over the years. Today in California, state regulations have slackened. “As for the State’s role, it is mainly informational. There are no permits or licenses,” said Roos. According to Roos, all cloud-seeding projects required permits until the law was reformed. “The old law required licenses and permits but it was repealed in the 1980’s. There was a general move toward deregulation in the government–mainly to reduce costs.” Today, according to Roos, Sponsors of cloud-seeding projects must notify DWR and county governments of the project, “This can be a letter or, for DWR, an e-mail notice,” he said. “They also have to publish a Notice of Intention in the county or counties affected by their proposed operations.”

Most of what this reporter learned was from Roos’ institutional memory, and going directly to sponsors of cloud-seeding operations–about 15 intermittent projects around the state. Data on cloud seeding at the state level is scattered, according to Roos. “We used to have an annual report that was published. Last time I tried to find it, it was in an archived box and nobody knew where it was,” said Roos, who added that budget cuts and deregulation mostly gutted the oversight program.

Despite lax oversight, the State of California wants to use weather modification as part of its 2009 Water Plan, which states:

“Cloud seeding has advantages over many other strategies for providing water. A project can be developed and implemented relatively quickly…it could offset some of the loss in snow pack expected from global warming.”

According to the plan, some regulation remains: weather modification sponsors need to comply with the California Environmental Quality Act [CEQA]. But not all seeding has to comply with environmental regulations. PG&E contends that an environmental impact report is not required for its Pit-McCloud River project because it is privately funded, with equipment on private lands,” said Roos.

That has locals groups near Mount Shasta concerned with PG&E’s proposed project in the Pit and McCloud River watersheds. “It’s a clear unequal treatment between public agencies and private entities,” said Angelina Cook with the Climate Council and the Mount Shasta Community Rights Project. “Private corporations require more government oversight and regulation to ensure accountability for the their practices.” But compiling all cloud-seeding data in California into one reference source today would be “a labor of love,” says Roos. “There’s no funds for it,” he said.

Cook says she is working on a cloud-seeding ban in Mount Shasta City, which may include a chemical trespass for silver iodide, the common chemical used in cloud seeding. “If silver iodide is found in the area, PG&E would be liable,” said Cook.
But Roos, who says cloud seeding is mostly benign, asks where one would draw the line. “There’s all kinds of influences on the air like people driving their cars, diesel trucks running around,” said Roos. Just as California has increased its regulations on air emissions in the state, some like Cook would like to see tougher regulations for weather modification as well.

Meanwhile, the state’s 2009 water plan also urges more research and development into cloud-seeding. Research could include cloud seeding’s impact on global climate change, and it’s effectiveness. The plan also identifies areas that could provide optimal results from cloud seeding, mostly in Northern California, along the Sacramento, Trinity and Russian Rivers.

Cloud Seeding Projects in California

View Cloud Seeding Projects in California in a larger map

To find references to cloud-seeding in the state’s water plan, look under Volume 3, then for “Precipitation Enhancement.”