Earth's Atmosphere "Breathes" More Rapidly Than Thought

Earth?s atmosphere was known to "breathe" in a cycle lasting nearly a month. Now scientists say the planet takes a quick breath every few days.

The breathing-like activity is the result of high-speed solar wind disturbances that cause a recurrent expansion and contraction of Earth?s atmosphere every few days, satellite observations show. This atmospheric mode could affect radio communication, orbiting satellites and possibly the Earth's climate, researchers say.

The expansion and contraction happens way up in the Earth's thermosphere, the layer of the atmosphere that extends from about 60 to 300 miles (96.5 to 483 kilometers) above the planet's surface. The thermosphere is constantly interacting with the sun's upper atmosphere as it expands out into the solar system, said one of the researchers who made the discovery, Jeff Thayer of the University of Colorado in Boulder, during a press conference at the annual meeting of the American Geophysical Union in San Francisco yesterday.

This interaction causes an energy exchange that can change the density of the thermosphere (how closely the gas molecules within it are packed together). As its density changes, the thermosphere expands and contracts.

5, 7 and 9

Extreme ultraviolet (UV) radiation from the sun was known to cause a 27-day expansion-and-contraction cycle by changing the thermosphere's density through heating.

Thayer and his team analyzed data from the German Challenging Minisatellite Payload (CHAMP) and the NASA Advanced composition Explorer satellite and found that the thermosphere also appeared to breathe every five, seven and nine days, "which was unexpected," Thayer said.

The researchers determined that the cause of these shorter expansions and contractions was high-speed winds generated by relatively cool pockets on the sun's surface known as solar coronal holes, which periodically rotate around the solar surface.

Thayer said this finding could help improve satellite tracking, which was part of the aim of the study, which was funded in part by the U.S. Air Force. The thermosphere is heavily populated with spacecraft, including the International Space Station and more than 800 operational satellites.

Implications

Changes in the thermosphere's density can change the amount of drag on a satellite, slowing it down when the density is higher. This can throw off estimates of where a satellite's position should be at a given time, which can in turn lead to problems in avoiding collisions among spacecraft and space junk. Thayer and his colleague hope their discovery will lead to improved satellite tracking.

This breathing of the atmosphere can also lead to changes in the composition of the ionosphere, which ranges from the upper portions of the mesosphere (just below the thermosphere) to the exosphere. These changes have implications back on Earth's surface, because "the ionosphere affects all kinds of radio operations," said study team member Geoff Crowley, president and chief scientist at Atmospheric & Space Technology Research Associates (ASTRA) LLC in San Antonio, Texas.

The changes in heating that cause the breathing can also impact climate, by triggering the upper atmosphere's "thermostat," as study team member Martin Mlynczak of NASA's Langley Research Center, Hampton, Va., put it. The added UV radiation heats up the atmosphere, in turn causing gaseous molecules to radiate that heat away in the form of infrared radiation.

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