Alastair wrote:
> On Nov 27, 3:11�am, "Raymond W. Arritt"
> <[EMAIL PROTECTED]> wrote:
> > Alastair wrote:
> > > I (and Newton) say that warming is caused by absorption. �After WWII
> > > they found that the lines were narrower at high altitude, but the
> > > radiation has all been absorbed well before it reaches that height.
> > > In fact it is nearly all absorbed in the first 30m. �John Tyndall
> > > reckoned that 10% was absorbed in the within the first 6 feet.
> > > There are two things happening. �There is the greenhouse warming at
> > > the surface of the atmosphere, and there is OLR at the top of the
> > > atmosphere. The OLR has to balance the ISR but it cannot change
> > > because it is coming from the mesosphere which does not respond to the
> > > surface temperature. (I am leaving a lot out, but you should be able
> > > to see the picture.)
> >
> > Where does the OLR come from, if (as you state) all the outgoing
> > radiation from the surface is absorbed in the lowest few tens of meters?
>
> A good point! My previous description was an over simplification.
> Greenhouse gases both absorb and emit. Both are quantum mechanical
> effects and so are not simple but I will try to explain without
> writing a text book. So I will ignore water vapour which complicates
> things by condensing.
>
> In the middle atmosphere all the CO2 molecules are at the same
> temperature so on average they are all radiating with the same
> strength. And thus you have a situation where Kirchoff's Law is obeyed
> and absorption equals emission. At the TOA there are no molecules in
> space radiating in so there is a net loss of radiation out to space
> and this is where OLR is generated. (Of course you knew that already.)
>
> At the base of the atmosphere, the surface radiates blackbody
> radiation, and the intensity in the CO2 bands depends on the surface
> temperature through Planck's blackbody function B(T). Einstein showed
> that the greenhouse gas will also emit radiation according to B(T) so
> it would seem that once the air equals the surface temperature then
> all absorption will cease. So de Saussure's hot box should not work.
> http://www.solarcooking.org/saussure.htm
>
> But the T for the CO2 vibrational emission is the vibrational
> temperature not the kinetic temperature. Tvib is much lower than T for
> CO2 because its vibrations are "frozen out". So it is all of the net
> radiation which is absorbed in the first 30 m, not all of the all
> outgoing radiation :-)
>
I think you are missing the basic fact that convection carries most of
the energy from the lowest levels up to the Tropopause. In addition,
you seem to think that "surface temperature" means that of the solid
land or ocean, when it actually means the air just above each as far
as climate is concerned . Also, the emissions by the CO2 molecules
tend to go in all directions, with half going up and the other half
going down. Thus, the upward radiation from one layer which is
absorbed in the next higher layer will be split on emission, with only
half going in the upward direction. In the Stratosphere, increasing
CO2 results in more downward emissions as well as more upward
emissions and the Stratosphere cools, AIUI.
You might take another look at the AIP site again, reading the section
on "Simple Models"
http://www.aip.org/history/climate/simple.htm
Then study the section on Basic Radiation Calculations:
http://www.aip.org/history/climate/Radmath.htm
Or, there are examples of so-called one dimensional radiative-
convective models, such as those by Ramanathan:
Ramanathan, V., and James A. Coakley, Jr. (1978). "Climate Modeling
through Radiative Convective Models." Reviews of Geophysics and Space
Physics 16: 465-89.
I'm certainly no expert on all of this. The Bibliography associated
with the AIP site is loaded with references.
E. S.
---
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
Global Change ("globalchange") newsgroup. Global Change is a public, moderated
venue for discussion of science, technology, economics and policy dimensions of
global environmental change.
Posts will be admitted to the list if and only if any moderator finds the
submission to be constructive and/or interesting, on topic, and not
gratuitously rude.
To post to this group, send email to [email protected]
To unsubscribe from this group, send email to [EMAIL PROTECTED]
For more options, visit this group at
http://groups.google.com/group/globalchange
-~----------~----~----~----~------~----~------~--~---
