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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