Lecture 6: Stability [in the atmosphere]

After much Googling, I have finally found somebody who looks at the bigger picture. From The University of California, Irvine (pdf), slide #5:

What Happens to the Temperature?

• Similarly when the air parcel descends, the potential energy of air molecules is converted back to kinetic energy.
=> Air temperature rises.

All the dime store explanations only give first three sentences and ignore the obvious questions:
- What happens to the heat aka kinetic energy of the legendary ‘parcel of air’ once it has risen?
- What happens to the temperature of the air that was higher up that is displaced and falls?

That kinetic energy isn’t “lost”, it is just converted to a different type of energy – potential energy. That is the missing figure you need to get the whole atmosphere to balance, despite being the easiest to calculate (mass x height x gravity).

Fr every parcel that rises, an equal and opposite amount of air must fall elsewhere, which causes it to warm up. Which is most of the reason that air is warmer at sea level. The dime store explanation that the sun hits the ground, warms it up and this warms up the air above it etc is only a small part of the picture (it ignores night time and the two-thirds of the Earth’s surface that is ocean and stays nearly the same temperature 24/7).
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If this seems far fetched, let me give a real life example:

How can use water to store electricity?

Clearly you can’t. But you can do the next best thing and use spare night time electricity to pump water up into a dam (convert electrical energy to potential energy), then at times of peak demand, you use the water in the dam to generate generate electricity (convert potential energy back into electrical energy).

The air in the atmosphere does exactly the same trade-off, only the trade-off is between heat aka kinetic energy and potential energy.