On Wed, 24 Nov 2004 15:33:59 GMT, "Mike Rapoport"
wrote:

2C per thousand has nothing to do with stability. In unsaturated air,
2C/1000 is stable. In saturated air 2C/1000 is unstable. 2C/1000 is the
standard for calibrating altimeters, it has nothing to do with the real
atmosphere or stability.

Mike
MU-2




Exactly.

Stability is a function of the actual lapse rate and the dry (or
moist) adiabatic lapse rate.

The dry adiabatic lapse rate is 1C per 100 meters or 5 1/2deg F per
1000 feet.

If the actual lapse rate is more than this, the air is unstable.

In other words, a parcel of air will rise as long as the air around it
is cooler than the parcel. The parcel will be 5 1/2 degrees F cooler
after rising 1000 ft. If the surrounding air at 1000 feet is still
cooler than the cooled parcel, the parcel keeps on rising. It will
keep on rising (and cooling) until the parcel is the same
temperature as the surrounding air, which has its own (different)
lapse rate.

That's why its smoother above cumulus clouds. The clouds mark the top
of the column of rising air.