National Geographic News
Earth's upper atmosphere "breathes," expanding and contracting due to previously unnoticed influences from the sun, say scientists who have measured the phenomenon for the first time.
The steady rhythm of "breaths" is linked to the ebb and flow of geomagnetic activity that is driven by intense solar winds—charged particles streaming outward from the sun—according to recent satellite data.
The breathing cycle seems to reach its peak when solar features called coronal holes are facing Earth. These dark spots in the sun's corona—a sort of solar atmosphere—are areas where the sun's magnetic field has been blown open by pressurized solar wind, sending the "winds" toward Earth at high speed.
As the fast winds streaming from coronal holes approach Earth, they cause gases in our upper atmosphere to heat up and expand, then cool down and contract, changing the upper atmosphere's density.
(Related: "Sun's Mysterious Waves Found; May Be Solar Wind Source" [December 6, 2007].)
A Drag on Satellites Flying through the resulting "hills and valleys of density," orbiting satellites experience more or less drag, respectively, noted research team member Jeff Thayer of the University of Colorado, Boulder, during a meeting of the American Geophysical Union in San Francisco.
Like runners trying to sprint through a lake, satellites faced with denser atmosphere will slow down and need more energy to keep moving in a given orbit.
The changes in drag affect a satellite's ability to stay on course, requiring more fuel and complicated orbital adjustments to keep on a predictable and safe path.
Better understanding of the Earth's breathing effect is therefore crucial, because the upper atmosphere is heavily populated with spacecraft and debris, Thayer said.
The region includes the orbits of the space shuttle, the International Space Station, more than 800 working probes, and about 10,000 pieces of space junk.
Outer Gaseous Shell
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