User talk:Jouni Valkonen

[I am almost a complete beginner in Wikipedia so this is something of a test run]
 * I'm sorry to have to start with negative comments but


 * Your account of time dependence provides no references and is not easy to follow. I have my doubts about it, but here are some thoughts. It would not be relevant to any simple discussion of the steady state. If relevant at all it would have to apply to the time dependent conditions near e.g. dusk.


 * The time variable does not enter explicitly into the Schwarzschilds equation so any time dependence would have to enter implicitly via the temperature which occurs in the Planck function.


 * Consider the downward emission at time t from a slice of the atmosphere at temperature T(t). This is proportional to the Planck function B(T(t). Having being emitted it will be partially absorbed on its way down by a lower layer at a time (t+t') where t' is composed of the traveling time (negligible) and absorption time (very short) and thermalisation time (probably also short). Where is there room for more physics involving hours? Perhaps in the convection mechanism but that is not the way you have described it, i.e. in terms of delays based on radiation transfer. Am I wrong?


 * Remember that all the physics is in the Schwarzschild equations and the boundary conditions. They agree with observation.


 * I'm afraid that I also don't agree with your comment about glass greenhouses. Obviously there is something in common between the two effects but at one time in the 19th century it was thought that the  mechanisms were completely analogous. At that time I believe they used to refer to the term hothouse.

Geoff Wexler (talk) 16:19, 12 April 2012 (UTC)

There are various methods. One of the most important method is that water is absorbing incoming visible solar radiation and then heat is stored into phase change. Then vapor is rising into upper atmosphere where it again goes for phase change due to cooling. As heat is released in higher altitude, it is more free to radiate directly into space.

I did not actually follow your ideas (it was not very clearly explained), but did you consider that when outgoing thermal radiation is absorbed by greenhouse gasses, it is again emitted back with longer wave length. That is, atmosphere is almost fully impermeable for the infrared radiation. Lower atmosphere must be heated quite significantly (ca. 33°C) in order for heat to get enough momentum that it can radiate heat back into space with the same power level as incoming radiation.

When CO2 is increased, atmosphere gets even more impermeable for the outgoing infrared radiation.

As only 25 % of incoming visible radiation is absorbed by atmosphere, incoming heat via radiation is much faster than outgoing heat via mostly convection. Hence the greenhouse effect. This is from thermodynamic perspective exactly the same phenomena that happens in the real greenhouse.

There is also to be considered that when hot air rises it is cooling down due to pressure decrease. --Jouni Valkonen (talk) 17:14, 12 April 2012 (UTC)


 * This discussion is in danger of diverging. Yes there are other modes of thermal transport and they may occur slowly. But I was most concerned about your opening sentence which asserts that the so-called re-radiation is subject to a delay. Lets just concentrate on your remark

"I think that it would be relevant to mention how many hours it takes from heat to re-radiate back into space when IR radiation is bouncing back and forwards from Greenhouse molecules."


 * I disagree. The term re-emission is just a popular term for emission and that is one of the terms in the Schwarzschild equation. The other main term is the absorption. If there was a memory term of the kind you describe it would have to be included in the equation and it isn't. It looks as if the absorption and emission terms are treated as being simultaneous. The justification for that is that the absorption and thermalisation are fast compared to the changes which you discuss elsewhere in your second comment.


 * Incidentally this is all at one wavelength. There is no need to talk about individual photons changing their wavelength.


 * The equation has been used for donkey's years and checked against observations. — Preceding unsigned comment added by Geoff Wexler (talk • contribs) 19:39, 12 April 2012 (UTC)

Ah, so here were your misunderstanding. The way you describe fast radiation is physically impossible, because photons are losing their energy in absorbtions and emissions. Thus energy is stored as kinetic energy of air molecules or into phase change of water. This process is fast dissipated via convection until heat has reached upper atmosphere (above Ozon layer) where it can freely radiate into space. Perhaps you are thinking too simplemindedly, because you are trying to reduce a complex phenomena into single equation. This is quite common misunderstanding of many, because they think that greenhouse effect should be simple in the terms of equations. --Jouni Valkonen (talk) 08:09, 13 April 2012 (UTC)