The Earth's upper atmosphere has had a record breaking collapse, one that has scientists both puzzled and worried, NASA announced Thursday.
The collapse occurred during a period of low solar activity known as a "solar minimum." During a solar minimum, sunspots and solar flare activity heavily diminish. Since the date range of a solar minimum expands over a 12-month period, it can take up to 6 months to identify one.
This collapse occurred during the 2008-2009 solar minimum. While these minimums are known to cool and contract the thermosphere, this collapse was 3-times greater than low solar activity could explain.
"This is the biggest contraction of the thermosphere in at least 43 years," said John Emmert of the Naval Research Lab, lead author of a paper announcing the finding in the June 19 issue of the journal Geophysical Research Letters. "It's a Space Age record. Something is going on that we do not understand."
Earth's thermosphere ranges in altitude from 55 miles to 370 miles above ground, so it is heavily affected by solar activity. This layer is responsible for intercepting extreme ultraviolet light (EUV) before it hits the Earth's surface.
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When solar activity is high--known as a solar maximum--solar EUV warms the thermosphere causing it to expand--a lot! It's like sticking a marshmallow peep in the microwave. When it is low, the opposite happens. While the 2008-2009 solar minimum was an extreme low for solar activity, the collapse was bigger than the sun's activity alone could explain.
It's worth noting that during a solar maximum, power outages, satellite function and communication disruption, and GPS malfunctions are all very common. For solar maximums and minimums are the two extremes of the sun's 11-year cycle.
Emmert suggests high carbon dioxide (CO2) levels might play a role. As you know, CO2 acts as a coolant, shedding heat through infrared radiation. He speculates that the CO2 could magnify the cooling period during a solar minimum.
But if it is CO2, wouldn't solar maximums also be affected?
"But the numbers don't quite add up," notes Emmert. "Even when we take CO2 into account using our best understanding of how it operates as a coolant, we cannot fully explain the thermosphere's collapse."