EcoAlert: Earth’s Shrinking Atmosphere

Spacecraft-re-entry-4 The shrinking of the Earth's high outer atmospheric layer has been linked to a sharp drop in the sun's ultraviolet radiation levels. The research, led by scientists at the National Center for Atmospheric Research in Boulder, Colo., and the University of Colorado at Boulder, 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 NCAR's High Altitude Observatory. "All solar minima are not equal."

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 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. "With lower thermospheric density, our satellites will have a longer life in orbit," says CU professor Thomas Woods, a co-author. "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 thermosphere, which ranges in altitude from about 55 to more than 300 miles (90 to 500 kilometers), is a rarified layer of gas at the edge of space where the sun's radiation first makes contact with Earth's atmosphere. It typically cools and becomes less dense during low solar activity. But the magnitude of the density change during the recent solar minimum appeared to be about 30 percent greater than would have been expected by low solar activity.

The study team used computer modeling to analyze two possible factors implicated in the mystery of the shrinking thermosphere. They simulated both the impacts of solar output and the role of carbon dioxide, a potent greenhouse gas that, according to past estimates, is reducing the density of the outer atmosphere by about 2 percent to 5 percent per decade.

Jason McManus via the National Science Foundation

error

"The Galaxy" in Your Inbox, Free, Daily