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Viewing Single Post From: The giant space ship example
Chris Ho-Stuart
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Dec 5 2011, 06:52 PM

Anyways, your statement: "With a transparent atmosphere (as you get with a mix of only O2 and N2) the heat loss from the atmosphere is zero."

Is interesting. One aspect of having a large atmosphere was the idea of reducing loss of heat from the surface. It would great to have full atmosphere, but that seemed to make too complicated on 1/10th gravity world [I think the sheer distance/height of atmosphere would bring into play the gravity difference as factor. Even with this dwarf planet I am uncertain the molecule speed will not exceed it's gravity- and more atmosphere makes it more uncertain.].
And be easier if smaller world, but wanted enough gravity to get as much atmosphere as possible. Btw, this world's atmosphere is unlikely to survive near the sun [earth distance]- or at least it adds a lot of more complications and unknowns- like when would atmosphere be blown away by the sun within a year or decades/centuries

So it's your contention that there little or no difference if one had 1/5th earth pressure
as compared to 1/3?

IF the atmosphere is transparent.... then yes. The pressure is irrelevant in this case.

Remember, the atmosphere is not itself a source of energy. It can only "insulate" somehow; moderate the flow of heat from the surface to space. If the atmosphere is transparent, the the thermal radiation from the surface just goes straight out to space without loss. That is what being transparent means.

There are other flows of energy -- convection, conduction, etc, but all that can do is bring the temperature of the atmosphere into equilibrium with the temperature of the surface. The atmosphere has no way of passing any energy on out in to space because it is transparent. It neither absorbs nor emits thermal radiation. So when the atmosphere is transparent, the convection in the atmosphere will be very sluggish. There can be no large sustained flow of energy into the atmosphere because the atmosphere can't get rid of it again.

You must have some way for the atmosphere to actually absorb some of that thermal radiation from the surface before it can have any impact at all on the surface temperature.

This is a really fundamental point, and it explains why I am going to have to add some CO2 (or any other greenhouse gas) into the atmosphere and calculate the transparency in order to make any difference to the calculation of 6.58e15 Watts.

If this point is at all confusing, then what I am going to do next will be hard to follow. It's important to grasp why I have to do this to answer your original question; or at least have that clearly identified as a point of dispute or question.

Cheers -- Chris

PS. I'm being a bit slow, because I am trying to fix up a few things in the operation of the board itself. Judy has offered to us a guest thread at Climate Etc, and I have suggested your problem as a useful aspect of such a thread. But I'd also like the board here to be in a good state to accept an influx. Might take me a week. When we get to that point, I'd be happy to have input from you or others on how the initial blog post is put together!
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The giant space ship example · Physical theory for climate