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.

Ah, I see what you are getting at. But I never said stability is only
determined by adiabatic lapse rate. The difference between the
environmental lapse rate and the adiabatic lapse rate is what determines
the stability. The average adiabatic lapse rate is 2C/1000' but can vary
based on moisture. Therefore, if the environmental lapse rate is higher
than 2C/1000' that atmosphere can be considered to be unstable. For a
moist parcel of air 2C/1000 environmental lapse rate will be unstable,
but for a dry parcel of air it will be stable.



wrote in
:



Adiabatic lapse rates (there are more than one) are theoretical and
calculated.

The calculations do not change from day to day.

The dry adiabatic lapse rate witll be calculated tomorrow the same way
it is today. It measures a physical process, i.e., the amount of heat
given up as air rises and expands,

Therefore it does not, as you suggest, indicate stability or
instability, since it will be the same in unstable air as it is in
stable air.

It is the ;lapse rate of the surrounding air that determines
stability, not the lapse rate of the rising air, which is the same
every day, day in and day out.

On 25 Nov 2004 12:02:42 -0600, Andrew Sarangan
wrote:

The difference between the
environmental lapse rate and the adiabatic lapse rate is what determines
the stability


Like I said...

wrote:

On Thu, 25 Nov 2004 09:14:32 -0500, Matt Whiting
wrote:


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



Not true as far as I know, but irrelevant nevertheless.

You need to do some research then and learn.


Adiabatic lapse rates, by themselves, tell nothing about stability.
It's the air mass that is either stable or unstable, and one needs to
know what the actual lapse rate of the air mass is in order to
predict stbility or instability.

The "actual" lapse rate is an adiabatic lapse rate. The lifted index is
determined by raising a parcel of air adiabatically.


Matt

"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

"Andrew Sarangan" wrote in message
1...
Ah, I see what you are getting at. But I never said stability is only
determined by adiabatic lapse rate. The difference between the
environmental lapse rate and the adiabatic lapse rate is what determines
the stability. The average adiabatic lapse rate is 2C/1000' but can vary
based on moisture. Therefore, if the environmental lapse rate is higher
than 2C/1000' that atmosphere can be considered to be unstable.

Absolutely not! If the air is unsaturated and the lapse rate is 2C/1000 but
below 3C/1000, then the air is absolutely, totally stable! No "ifs",
"ands", or "buts", it is stable. It cannot be considered to be unstable.

For a
moist parcel of air 2C/1000 environmental lapse rate will be unstable,
but for a dry parcel of air it will be stable.

Yes! but this is in direct contradiction to your above statement
"Therefore, if the environmental lapse rate is higher
than 2C/1000' that atmosphere can be considered to be unstable."

Mike
MU-2

wrote in
:



Adiabatic lapse rates (there are more than one) are theoretical and
calculated.

The calculations do not change from day to day.

The dry adiabatic lapse rate witll be calculated tomorrow the same way
it is today. It measures a physical process, i.e., the amount of heat
given up as air rises and expands,

Therefore it does not, as you suggest, indicate stability or
instability, since it will be the same in unstable air as it is in
stable air.

It is the ;lapse rate of the surrounding air that determines
stability, not the lapse rate of the rising air, which is the same
every day, day in and day out.