The bottom line is that the temperature structure of the atmosphere is determined by
series of processes that we talked about in various lessons
that all come together and fit together into this picture.
The temperature profile from radiation-only is much steeper than observed
although this is what we assumed implicitly in the layer model to start with.
And then if
we add convection it's not as strong
a temperature difference between high and low, and
then adding water vapor pretty much brings
our ideas into sync with reality.
This is what is really governing the temperature of the atmosphere.
The sunlight puts in energy at the ground, which drives convection,
which is the buoyant fluid rising from below.
The gas expands because it's a compressible medium,
and therefore it cools, which tends to make it cool down as it rises up.
But cooling makes water vapor condense,
because water doesn't like to be vapor if it's really cold.
It would prefer to be in a condensed state like fluid, like liquid.
So the water condenses,
but when the rain falls out, it leaves behind the
heat that was with the water vapor to start with.
The process overall, that looks like
the real thing, is what's called moist convection.
This is what sets the intensity of the greenhouse effect on Earth.
And if there were anything that could change this, like a change in
the amount of water vapor in the
atmosphere or something like that, it could
feed back and change the climate of the Earth.
So it's something we have to think about.