Cooling thermosphere

The thin blanket of gases that surround our beautiful planet is changing. Our atmosphere has changed many times in the past but many independent measurements show that it is changing particularly quickly these days. These changes have quite a few effects and some of them you might not expect. For instance, whilst increases in carbon dioxide in the atmosphere are warming up things down here on the surface, measurements show that the upper layers of our atmosphere are actually cooling. The reason for this is that they are thin and the extra carbon dioxide present isn't at a high enough density to cause a warming effect in those regions. Instead, the CO2 actually absorbs heat from its surroundings and emits it into space (the net effect). According to the Institute of Physics news item, the mesosphere (50-80km altitude) is cooling at 3 degrees Celcius per decade (measured over more than 15 years).

So what does this mean? Cooling down a gas generally causes it to contract which will mean that our atmosphere hugs the planet more tightly. This seems to have been confirmed by measuring the drag experienced by satellites in low Earth orbit. The drag has been decreasing implying that the density has been dropping by around a couple of percent per decade. This is probably good news for the owners of low Earth orbit satellites (and the International Space Station) as they will need less fuel to provide boosts to their altitude. However, I'm not sure I like the idea that the sky is falling ;-)

Posted in astro blog by Stuart on Wednesday 29th Nov 2006 (12:06 CET) | Permalink
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