When Planes Punch “Holes” in the Sky

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

By Michael D. Lemonick

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.

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)

When Planes Punch “Holes” in the Sky 2 February,2018Climate Central

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