A Puzzling Collapse of Earth's Upper Atmosphere

[BridgeTheGap]

July 15, 2010: NASA-funded researchers are monitoring a big event in our planet's atmosphere. High above Earth's surface where the atmosphere meets space, a rarefied layer of gas called "the thermosphere" recently collapsed and now is rebounding again.


Layers of Earth's upper atmosphere. Credit: John Emmert/NRL. "This is the biggest contraction of the thermosphere in at least 43 years," says John Emmert of the Naval Research Lab, lead author of a paper announcing the finding in the June 19th issue of the Geophysical Research Letters (GRL). "It's a Space Age record."

The collapse happened during the deep solar minimum of 2008-2009—a fact which comes as little surprise to researchers. The thermosphere always cools and contracts when solar activity is low. In this case, however, the magnitude of the collapse was two to three times greater than low solar activity could explain.

"Something is going on that we do not understand," says Emmert.

The thermosphere ranges in altitude from 90 km to 600+ km. It is a realm of meteors, auroras and satellites, which skim through the thermosphere as they circle Earth. It is also where solar radiation makes first contact with our planet. The thermosphere intercepts extreme ultraviolet (EUV) photons from the sun before they can reach the ground. When solar activity is high, solar EUV warms the thermosphere, causing it to puff up like a marshmallow held over a camp fire. (This heating can raise temperatures as high as 1400 K—hence the name thermosphere.) When solar activity is low, the opposite happens.

http://science.nasa.gov/science-news/science-at-nasa/2010/15jul_thermosphere/

[ananda]

1. They seem to be trying very hard to minimize the CO2 and warming connection..

.. but I'm not.

[Jim__]

2. Why do you say that. The information in the paper sounds like legitimate analysis.

They may even go a little the other way by saying that the changes in the atmospheric chemical content may have reached a tipping point where it now causing some unanticipated effect - although they are not sure.

[meow mix]

3. massive sub-zero "air thermoclines" to commence tomorrow

or maybe the day after

[Jim__]

4. Does anyone know why CO2 in the thermosphere acts as a coolant?

From the article:

When carbon dioxide gets into the thermosphere, it acts as a coolant, shedding heat via infrared radiation. It is widely-known that CO2 levels have been increasing in Earth's atmosphere. Extra CO2 in the thermosphere could have magnified the cooling action of solar minimum.

"But the numbers don't quite add up," says 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."

According to Emmert and colleagues, low solar EUV accounts for about 30% of the collapse. Extra CO2 accounts for at least another 10%. That leaves as much as 60% unaccounted for.

In their GRL paper, the authors acknowledge that the situation is complicated. There's more to it than just solar EUV and terrestrial CO2. For instance, trends in global climate could alter the composition of the thermosphere, changing its thermal properties and the way it responds to external stimuli. The overall sensitivity of the thermosphere to solar radiation could actually be increasing.

I thought I understood how it acts to heat up the lower atmosphere, but I don't understand why it would act as a coolant in the upper atmosphere.

[Birthmark]

5. It prevents heat from near the surface...

...to escape upward into the upper atmosphere.

[Jim__]

8. That could be, but that not what it says.

The implication is that the cooling is a direct result of CO2 in the thermosphere: When carbon dioxide gets into the thermosphere, it acts as a coolant, shedding heat via infrared radiation.

If they actually are talking about CO2 in the lower atmosphere, that statement is misleading.

[nilram]

9. this flash movie explains it in about a minute

http://www.ucar.edu/news/releases/2006/thermospherevisuals.shtml

(I didn't bother to look at the quicktime movies it references.)

In the upper atmosphere, CO2 absorbs heat from other molecules and radiates it into space.

I just skimmed through the paper (time to get to work), it doesn't seem to mention methane. I wonder if that is part of the unaccounted-for 60%.

[Jim__]

10. Thanks.

[pscot]

6. A most excellent post

:thumbsup:

[obxhead]

7. off to the greatest for you. nt