Funny how that works. The Earth gets about 1.7E17 Watts from the Sun, or about a billion times more--but apparently most doesn't effect this layer of the atmosphere. Solar flares can change a lot of pictures, though.
Saturday, March 24, 2012
Toasty times in the thermosphere
I have to admit that I'd not heard of the thermosphere of Earth's atmosphere before. That's up with the auroras and the Space Station, with a lower end driven by atmospheric tides and middle and upper too thin to support bulk gas motion on this kind of distance scale. The last solar flare dumped 26 billion KWhr of energy into the atmosphere at that level. Which sounds kind of huge, though it turns out to be about 0.1Watt-hr per square meter. Over a three day period. But it is quite a bit more than usually gets absorbed at that level.
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I don't know about the thermosphere, but my husband's erstwhile work involved what he called weather forecasting for the Space Station. He focused almost entirely on radiative heat transfer. I was surprised to hear how much of a difference the station's orientation made to the equipment and the astronauts. It wasn't just whether they were in direct sunlight, but whether they were exposed to space, to the dark side of the Earth, or to the sunlit side of the Earth.
PS, he adds, upon reviewing the Wiki entry, that no one pays any attention to heat conduction in low earth orbit; it's all about the radiative transfer. Until they get to re-entry, there may be gas out there that has a high temperature, but it's too thin to impart noticeable heat to orbiting people and their tools, either by radiation or by conduction.
Heat conduction inside the pressurized space of the Station, of course, is another matter. They had big problems with cooling equipment, because they couldn't count on gravity-induced convection to spread the heat around effectively. There were little fans all over the place, which started to create a real noise-pollution problem.
That sounds like an interesting job.
There's a lot about the upper atmosphere that isn't very intuitive.
Does he want to fix the Wikipedia article? It said that the air was too thin for bulk motion, which is obviously oversimplified. I presume they mean that that the mean free path becomes comparable to that size of the layer of the atmosphere.
He would never do that. He's quite a hermit, even Internet-wise.
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