Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: atmospheric blanket / greenhouse effect



I had written:

The assumptions of absorption are certainly
dependent on
the thickness of the atmosphere. A very thin atmosphere
won't absorb
100% of the outgoing IR, for example. However, if you can meet my
assumptions (or close to it - say, 80%), then in a sense it is
independent of the thickness of the atmosphere.

To which John Denker responded:

I disagree.

For a thick atmosphere, if you want a self-consistent
theory, you need to divide the atmosphere into layers
and iterate your argument. The Nth layer shields the
N-1 lower layers as surely as the first layer shields
the surface. The effect is cumulative. The radiation
is _diffusing_ outwards.

It would be quite a coincidence if the atmosphere's
thickness just happened to exactly equal one mean-free-path.

Yes, I agree with you, yet somehow I don't think I disagree with myself.

Yes, it is better to divide the atmosphere into layers. My argument
assumed a single layer which, as you point out, may not be a good
approximation to the earth's atmosphere although I'd argue it is roughly
correct. I'd also argue it is not even close to being correct for
Venus. For Venus, one definitely needs to subdivide into layers in
order to get such a hot surface temperature.

Or, are you saying that even by subdividing and using the appropriate
absorptivity, the approach is still flawed?

____________________________________________________
Robert Cohen; 570-422-3428; www.esu.edu/~bbq
East Stroudsburg University; E. Stroudsburg, PA 18301