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Author:  AstroPhool Number:  44805 of 75007

This entire thread is a prime example of the old maxim about a little knowledge being a dangerous thing. Let me go through this mishmash of pseudoscience piece-by-piece. But before I start, be aware that this "research article" came from "Principia Scientific International". Thsi isn't a real professional organization -- it appears to exist solely to discredit the idea that greenhouse gases warm the earth. Its first Chair was Tim Ball, who had a pivotal role in establishing PSI.

Now to the science ...




This statement describing SABER is correct, although I haven't confirmed the energy values quoted. There is no contradiction between the paragraph above and greenhouse theory. The "harmful solar rays" being referred to are high-energy electrons from the solar wind. These electrons *never* reach the Earth's surface, whether the solar wind is active or not. Electrons are charged particles and they are mostly deflected away from the Earth by the Earth's magnetic field. A small number get trapped in the Earth's magnetic field and spiral down toward the Earth's magnetic poles. They end up exciting oxygen and nitrogen molecules high in the upper atmosphere (the very tenuous mesosphere), which causes the aurora. These electrons never reach the earth's surface or into the denser parts of the atmosphere responsible for weather. The energy contribution to the heating of the Earth by this "leakage" from the solar wind is negligible. Think about it! -- do you really believe that the aurora are a significant source of heating, enough to significantly affect the Earth's energy balance? Have you ever spent a winter in the Yukon?

The way the aurora forms is simple: solar wind electrons collide with atoms in the Earth's atmosphere and in doing so occasionally excite one of these atoms to an excited energy level or state. Atoms or molecules don't like to stay in an excited state for long, and try to get rid of this excitation energy anyway possible. Typically then atoms/molecules will decay to a lower state be emitting a photon, or equivalently, by radiating a quantum of light energy. It turns out that the dominant gases in the Earth's atmosphere (oxygen & nitrogen) can not easily do this (for reasons of symmetry). So these molecules interact extremely weakly and reluctantly with optical radiation (and a good thing too or the atmosphere would be completely opaque to solar radiation!). Most of these excited oxygen and nitrogen molecules eventually collide with other molecules and redistribute their excess energy -- in radiative transfer we say that the photons that originally excited these molecules are "thermalized", which means they are destroyed and their energy goes into heating the gas. A few oxygen and nitrogen do manage to radiate away their energy by means of extremely low-probability radiative decays called forbidden transitions. It is these rare decays that cause the aurora borealis (or australis), with their characteristic ghostly green (forbidden nitrogen decays) and/or red (forbidden oxygen decays) colors.

But there are a few molecules that can efficiently radiate away their excitation energy -- these are heteronuclear molecules that do not have the symmetry of molecular oxygen and nitrogen. One of the most abundant is these species is CO2, and that is why it is considered a coolant in this context (and the context is really important here). CO2 absorbs energetic electrons which would otherwise warm the far upper atmosphere (nothing to do with weather) and efficiently radiates this energy away to space. CO2 molecules do not block incoming solar radiation (except for a little bit in the infrared). Instead these CO2 molecules are blocking energetic electrons from the solar wind and reradiating that energy back to space.

I repeat -- there is no contradiction with greenhouse gas theory here. The same CO2 molecules, which interact so readily with infrared radiation (this is the very definition of a greenhouse gas = an infrared active gas) result in a completely opaque atmosphere in the CO2 infrared band in the dense lower atmosphere (troposphere), where essentially all weather occurs. In this context, these CO2 molecules hinder the transport of energy, which here is mainly flowing from the warm surface of the Earth out to space. The result is that the surface of the Earth warms until the larger temperature gradient is able to "force" enough radiation through the opaque CO2 (and water) bands and bring this outgoing longwave (infrared) energy into balance with solar (light or shortwave) radiation absorbed by the Earth's surface.

These concepts are not really hard to understand but there is a lot of understorey to learn first, and that is where people who really want to comment meaningfully on these processes really need to learn some physics. Unfortunately that is work, and not particularly rewarding work, and most people don't have the time or inclination to put in the necessary work to become "fluent" in basic physics.
