[TML] A new tourist ship design

[Timothy Little]

On Sun, Jan 13, 2008 at 03:38:55PM +0100, Knapp wrote:
> So what does keep the atmosphere warm?  As I understood it, it was
> the sun shining on the land and that turns the sunlight into heat
> that keeps the Earth warm.

Yes, this is pretty much it.  Some sunlight on Earth is absorbed
directly by the atmosphere, but not much.  The great majority is as
you describe.

However, a 500m ball has very very little "land" to absorb heat
compared with the 30km or so ball of the atmosphere that is radiating
heat away.  A negligible amount, in fact.


> On the other side I have read that the upper atmosphere is very hot.

The thermosphere is, yes.  Of course, for "upper atmosphere" read
"very good vacuum".  The ISS orbits *within* the upper thermosphere.


> Then you have the fact that heat rises.

Air that is hotter than the surrounding air rises, yes.  It also mixes
somewhat with the surrounding air and cools.  Also, if it rises over
greater heights it cools as the pressure decreases (adiabatic
cooling).


> If it is the land that heats the air then why is it could on the top
> of a mountain?

In the troposphere (i.e. less than about 10 km altitude), atmospheric
heat flows are dominated by convection.  Adiabatic cooling then means
that lower-pressure air tends to be colder, so the troposphere usually
has decreasing temperature with height.  This is known as adiabatic
lapse rate, which for dry air is about 10 K/km.


- Tim