Earth’s upper atmosphere ’shrinking’

WASHINGTON - The upper layer of Earth’s atmosphere is shrinking due to large changes in the Sun’s energy output, new research indicates.

The study links a recent, temporary shrinking of a high atmospheric layer with a sharp drop in the Sun’s ultraviolet radiation levels.

The research indicates that the Sun’s magnetic cycle, which produces differing numbers of sunspots over an approximately 11-year cycle, may vary more than previously thought.

“Our work demonstrates that the solar cycle not only varies on the typical 11-year time scale, but also can vary from one solar minimum to another,” says lead author Stanley Solomon, a scientist at the National Center for Atmospheric Research’s High Altitude Observatory.

“All solar minima are not equal.” Researchers from the University of Colorado at Boulder (CU) also contributed to the project.

The findings may have implications for orbiting satellites, as well as for the International Space Station.

The fact that the layer in the upper atmosphere known as the thermosphere is shrunken and less dense means that satellites can more easily maintain their orbits. But it also indicates that space debris and other objects that pose hazards may persist longer in the thermosphere.

CU professor Thomas Woods, a co-author, says: “With lower thermospheric density, our satellites will have a longer life in orbit. This is good news for those satellites that are actually operating, but it is also bad because of the thousands of non-operating objects remaining in space that could potentially have collisions with our working satellites.”

The Sun’s energy output declined to unusually low levels from 2007 to 2009, a particularly prolonged solar minimum during which there were virtually no sunspots or solar storms.

During that same period of low solar activity, Earth’s thermosphere shrank more than at any time in the 43-year era of space exploration.

The study has been published in Geophysical Research Letters. (ANI)