Space/Science — HabitableZone

Space/Science » in reply to re: the H and K lines of ionized calcium

Well, if you're appealing to Wiki...I won't be outdone.
ER — (archived)

"Quantum mechanics provides the basis for computing the interactions between molecules and radiation. Most of this interaction occurs when the frequency of the radiation closely matches that of the spectral lines of the molecule, determined by the quantization of the modes of vibration and rotation of the molecule. (The electronic excitations are generally not relevant for infrared radiation, as they require energy larger than that in an infrared photon.)?"

http://en.wikipedia.org/wiki/Greenhouse_effect

My background is astronomy, all the stuff I've looked at is highly ionized, extremely hot, and very far away. But it turns out the physics is remarkably similar. The reason the surface of the sun appears as a sharp and distinct edge is because at that point the opacity of the gas suddenly drops as certain species of ion change ionization state, and it becomes transparent to electromagnetic radiation. But this effect varies for different wavelengths, so by looking at different frequencies you are looking at deeper and deeper layers of the photosphere, like peeling away the layers of an onion.

At high altitudes an analogous effect occurs on earth, the planet appears bright in the infrared as it radiates its excess heat into space. The absorbing effect of molecular species in the upper atmosphere keeps the energy trapped, but sooner or later it has to work its way out and radiate away. But very minute changes in this surface opacity can have a great effect on this radiation. And I believe relatively modest changes in concentrations of greenhouse gases can result in substantial changes in this flux. If the upper atmosphere becomes more opaque to IR, the earth has to heat up in order to get the temperature high enough to radiate enough energy to maintain thermal equilibrium.

The "greenhouse effect" is misleadingly named because the true warming at the surface is only obliquely related to the alleged effects of CO2 and the rest of the usual suspects. The surface is warm mostly because of water vapor, it IS a damp greenhouse. But changing the CO2 in the upper atmosphere is like opening and closing a window.

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