"Andrew Sarangan" wrote in message
om...
"Mike Rapoport" wrote in message
link.net...
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

Adiabatic lapse rate is 1C/1"Hg for moist air (depending on moisture
content) and 3C/1"Hg for dry air. 2C/1"Hg is a representative average
for somewhat moist but unsaturated air. It is still a useful indicator
of stability. I would not discount is as a completely meaningless
number. It is a useful reference, just like 29.92" and 15C.

How can 2C/1000' tell you anything about stability? If the air is saturated
then 2C/1000 is unstable, absoluteley totally unstable. 2C/1000 in
saturated air is likely to be the inside of a thunderstorm. If the air is
unsaturated and the lapse rate is 3C/1000, the air is stable, totally stable
and smooth. 2C/1000 tells you nothing about stability unless you know
whether the air is saturated or not. The only numbers that tell you about
stability without knowing the vapor content are lapse rates above 3C/1000
(termed absolutely unstable) or below 1C/1000 (absolutely stable). Any
lapse rate between 1C and 3C/1000 is termed "conditionally stable".

Please explain how 2C/1000 is used in altimeter calibration. I did not
know altimeters had any temperature corrections.

Altimeters are preasure guages with a scale in feet. They assume a pressure
lapse rate with altitude and the pressure lapse rate that they use is ISA
whch assumes 15C at SL and 2C/1000'.

Mike
MU-2