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My point was that to an oceanographer, the atmosphere
does look like a heat engine in the sense that the atmosphere
takes in low entropy short-wave radiation, exports high entropy
long-wave radiation and in the process does work on the ocean
via the wind stress.
Francois says:
For the atmosphere there is a net input of radiative energy in thetropics and a net loss at high latitudes.
My conceptual objection here is that this is simply convection. If there
is a hot object at one side of a room (eg a radiator or wood stove) and a
cool object at the other side (eg a window) then I will set up exactly the
same sort of convective circulation, with a net source of thermal energy in
one place and a net sink of thermal energy in another place. Is this empty
room a "heat engine"?
John says:
However, in a very practical sense, you can stick a windmill into theatmosphere ...
I would say you have made a fundamental change here.
* If water just flows down a river, it is not an 'engine'. If I add a
waterwheel to extract energy, then I have an 'engine'.
* If I have a hot object touching a cold object, that is not an 'engine'.
If I add a thermopile between the objects to extract energy, then it is a
'heat engine'.
* The atmosphere is not an engine. When I add a wind turbine to extract
energy, THEN it is an engine.
John says:
but it is not entirely crazy.I agree. People who know about thermodynamics can navigate these ideas
easily and get to the core of the issue. (Much like people who understand
thermodynamics can deal with people using "heat" when they are discussing
"internal energy".)
I have also heard people call the atmosphere a "heat pump" because it
pumps heat from the tropics toward the pole. But the atmosphere is
certainly now a 'heat pump" in the sense HVAC people/engineers/physicists
would understand.
It is probably just another case of letting go in colloquial discussion
and educating in non-colloquial discussion.
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