Earth Atmosphere "Breathes," Thanks to Solar Winds

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The Earth's upper atmosphere, also called the thermosphere, "is the outer gaseous shell of the planet's atmosphere that exchanges energy with the space-plasma environment," Thayer said.

In other words, it's the region that has direct interactions with the sun's atmosphere.

"From Earth's perspective, we're embedded in the sun's upper atmosphere," he said.

Starting at about 5 miles (85 kilometers) above Earth's surface, the thermosphere has been known to experience expansion and contraction every 27 days, the time it takes the sun to rotate on its axis.

But until now few scientists had looked at shorter-term changes in atmospheric density.

Thayer and colleagues found fluctuations in density roughly every five, seven, or nine days that correspond to changes in geomagnetic activity, atmospheric composition, and infrared radiation—all signs that extreme solar weather is at work.

The team thinks coronal holes help explain the pattern of the breaths.

"Think about a searchlight" that takes 27 days to complete a rotation, Thayer said. "If you have one searchlight … and you mark down every time you saw brightness, you'd see it every 27 days.

"Now if you had three searchlights [set up] so they're all evenly distributed and you rotate those at 27 days, you would see … a bright light every 9 days."

Similarly, four lights would equal bright sweeps every 6.75 days, while five lights would yield passes every 5.4 days—the periods found in the new study.

Thayer and colleagues' data was published earlier this year in the journal Geophysical Research Letters.

Ringing Atmosphere

David Klumpar, a solar physicist at Montana State University in Bozeman, said that activity from the sun is constantly and randomly "tapping" Earth, creating oscillations in the our planet's natural frequencies like a spoon tapping on a glass of water.

"I would imagine that Thayer [and colleagues] are finding some of those natural frequencies," said Klumpar, who was not involved in the work.

"The atmosphere is ringing, like a water glass when 'tapped' by solar eruptions."

David Hathaway, a solar physicist at NASA's Marshall Space Flight Center, said that, without having seen the actual data, "I'm a little surprised."

He noted that solar scientists have long known about the 27-day cycles of geomagnetic activity related to the sun's rotation.

"But on a nine-day cycle, I'm not sure what it would be."

He added that the last two years would indeed have seen most of the atmospheric disturbances coming from coronal holes.

The real question with the shorter-term bumps noticed by Thayer's team would be how significant they are above the "noise"—expected and random variations in atmospheric conditions.

For now, he said, the idea raises more questions than it does answers.

Study co-author Thayer agrees that more work needs to be done, including getting solar physicists involved in analyzing the data.

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