Re: hot air rising

[John Denker <jsd@MONMOUTH.COM>]

At 12:14 PM 7/21/99 -0400, Robert A Cohen wrote:
> As for point (b), this is what I was referring to in regard to the
> "mixing" theory.  I apologize for not being more specific.  As you say,
> there are many ways to force an air parcel upwards/downwards.  The key is
> that the air is moving up and down, which leads to a well-mixed atmosphere
> and a temperature profile that is adiabatic.

Mixing does occur, but IMHO it is not the main point and tends to distract
attention from the main point.  Suppose you had air parcels in floppy
plastic bags (to prevent mixing), going up and down on a Ferris wheel.  Any
given parcel would be cooler when on top and warmer when on the bottom.

> Point (b) by itself doesn't
> explain why the top floors of a house are the warmest, does it?

No, but it is part of the explanation.  The profile you described (warm on
top, cool on bottom) corresponds to what is called a temperature inversion
on those rare occasions where it occurs in the atmosphere.

We should not assume that all the heat sources are upstairs, nor all the
cool sources downstairs, so it would be better to assume that the hot air
upstairs typically came from somewhere else.  According to our newfound
understanding, such air parcels must have been EVEN HOTTER before they went
upstairs.  This is easy to believe.  Just think how hot the air is coming
out of the heating-system vents.  That air will cool a tiny bit on its way
upstairs (which is not after all a very great distance) but it will still
be warm enough to stay up there;  if it were not still warm it would be
cooler than the air already there, and would sink.