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The sky is shrinking

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Geplaatst op 21 juli 2010 - 16:22

The sky is not falling, but it is shrinking

Scientists have discovered yet another enigma about our planet: the thermosphere has undergone serious shrinkage. The thermosphere is the largest portion of the Earth's atmosphere and is the next-to-last region before you reach the vacuum of outer space. The fact that it has contracted is not surprising; the thermosphere absorbs extreme ultraviolet (EUV) photons from the sun and warms and cools—expanding and contracting—in a pattern that follows the 11-year solar cycle. While we are coming out of one of the longer periods of low solar activity in a century, scientists have found that the thermosphere has shrunk some 28 percent. That's the largest drop in recorded history, and they cannot explain why.

Solar cycle 23 (the previous one) was unusually long—12.4 years—and the minimum between it and cycle 24 had the most days without sunspots since 1933, both of which will result in a cooled thermosphere. CO2 in the lower thermosphere is the dominant cooling agent, so increased concentration of CO2 will lead to a cooler, more contracted thermosphere. The cooling process is accelerated during a solar minimum as well, causing the entire system to be very complex and difficult to fully describe.


Lees verder: http://arstechnica.c...tm_campaign=rss

Bron: Ars Technica

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