----- Original Message -----
From: "Eli Rabett" <[EMAIL PROTECTED]>
> This is the usual confusion.
!
> The saturaters somehow never come to the
> point that emission also increases.
Oh?
> The base idea is that if
> atmospheric absorption increases, then the temperature of any packet of
> air must increase until emission can match absorption.
But emission is independent of temperature. It depends on the number
of excited molecules which is a function of pressure not temperature. The
air temperature of the saturated layer will rise until it convects. It won't
wait around until the temperature rises to a level at which the radiation in
equals radiation out.
> Absorption is
> measured over a path length, so if it is saturated over 100 meters
> (reduced by exp(-2) for example), it is not saturated over 10 m. If
> you double the CO2 mixing ratio, the absorption will be saturated over
> 50 m, but not 5.
So if you double the concentration you will half the height of the
layer where the absorption is saturated. i.e. the absorption (greenhouse
effect) is proportional to the concentration, not the log of the
concentration.
> When a CO2 molecule absorbs an IR photon, the energy is transferred to
> other molecules, primarily O2 and N2 as translational and rotational
> energy.
Translational energy is kinetic energy i.e. heat. The O2 and N2 (air)
are heated.
> Thermal energy excites the bending vibration in other CO2
> molecules which radiate.
Yes, the collisions from the air molecules excite the CO2, but they
do not change because the air expands and the density falls as the
temperature rises. In other words collisions depend on pressure, and
are not affected by air temperature rise.
> The relevant distances are several times the
> mean free path for energy transfer between molecules and the average
> path length of the IR photon. You would be gasping for breath before
> they are comparable.
Perhaps you would like to state what the mean free path between two
molecules and the path length of a photon leaving the earth's surface are.
Cheers, Alastair.
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