Re: Hot air rising and automobile thermometers

[brian whatcott <inet@INTELLISYS.NET>]

At 17:04 7/23/99 +0100, you wrote:
> I wrote:
>
> > The anabatic and katabatic winds up and down hillsides
> > take something away from the vivid cooling often noticed
> > when climbing an airplane on a hot day.
>
> What are "anabatic winds" and why are they called that
> way? How do they differ from common winds?
> Same questions about the "katabatic winds".


We could visualise an ordinary wind as flowing nearly parallel to
lines of equal atmospheric pressure ('isobars') across a plane surface
and motivated by the pressure gradient between them.

 An anabatic wind may arise on an otherwise still day on an insolated
 slope of a mountain - particularly its south slope in the Northern
hemisphere.
 The warmed surface air rises in an uphill wind, carying
less dense relatively warmer air than the surrounds.

This is not a major effect: most noticeable when reinforcing a
 valley wind (funnel effect) and near coastlines where mountains
probably reinforce the sea breeze effect.

A katabatic wind derives from cooled air flowing downhill during
an otherwise slack wind.
The mountain cooling is radiative, and so is noticed at night.

The katabatic wind is cold, in contrast to the Fohn or Chinook,
where the wind is pushed up a mountain, cooling at the saturated
adiabatic lapse rate (SALR), shedding precipitation and descending
on the other side at the dry adiabatic lapse rate, giving a marked
temperature increase on the lee side at comparable elevations.

As to the reason for naming the temperature-driven winds (as opposed
 to the pressure-driven common wind) I suppose one should consult
Xenophon's description of the uphill march of Cyrus' son into Asia.
It was the prototype anabasis. Katabasis was the Greek word
for going down.

(From IR notes)


brian whatcott <inet@intellisys.net>
Altus OK