How high is that cloud?

On 24 Nov 2004 21:38:35 -0800, (Andrew
Sarangan) wrote:

"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.



Adiabatic lapse rate never changes. It is not a useful indicator of
stability. It tells you nothing about stability until you know the
actual lapse rate of the air mass in question.



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

wrote:

On 24 Nov 2004 21:38:35 -0800, (Andrew
Sarangan) wrote:


"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.




Adiabatic lapse rate never changes. It is not a useful indicator of
stability. It tells you nothing about stability until you know the
actual lapse rate of the air mass in question.

It depends on which adiabatic lapse rate is being considered. The dry
adiabatic lapse rate is basically constant, but the moist/wet rates are not.

Matt

wrote in
:

On 24 Nov 2004 21:38:35 -0800, (Andrew
Sarangan) wrote:



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.



Adiabatic lapse rate never changes. It is not a useful indicator of
stability. It tells you nothing about stability until you know the
actual lapse rate of the air mass in question.


You should read up on lapse rates. There is dry adiabatic lapse rate, moist
(saturated) adiabatic lapse rate, average adiabatic lapse rate and even
more obscure ones like superadiabatic lapse rate and autoconvective lapse
rate. It is definitely not a constant, but the commonly accepted average
lapse rate is 2C/1000ft.

"Andrew Sarangan" wrote in message
om...

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.

No, moist but unsaturated air has an adiabatic lapse rate of 3 degC (i.e.
the unsaturated adiabatic lapse rate). The difference between that and
saturated comes not from the amount of water vapor in the air as a mixing of
properties, but from the latent heat produced when the water vapor
condenses, which only happens when the air becomes saturated. It's not a
progression, but a sharp difference when the water vapor starts to condense.

Julian Scarfe

That's interesting, but I find it strange that moisture content does not
change the adiabatic lapse rate. Moist air has a higher heat capacity than
dry air, so I would expect the adiabatic lapse rate of moist air (but
unsaturated) to be lower than dry air.




"Julian Scarfe" wrote in
:

"Andrew Sarangan" wrote in message
om...

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.

No, moist but unsaturated air has an adiabatic lapse rate of 3 degC
(i.e. the unsaturated adiabatic lapse rate). The difference between
that and saturated comes not from the amount of water vapor in the air
as a mixing of properties, but from the latent heat produced when the
water vapor condenses, which only happens when the air becomes
saturated. It's not a progression, but a sharp difference when the
water vapor starts to condense.

Julian Scarfe

"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

Mike Rapoport wrote:

"Andrew Sarangan" wrote in message
om...

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'.

Last I knew C was a unit of temperature, not pressure.

Matt