Atmospheric stability and lapse rate

"jim rosinski" wrote in message
ups.com...
Icebound's post is well-written and almost exactly accurate. Just one
quibble:

Icebound wrote:

"dry adiabatic" mean no heat
added and no condensation occurring. This number has been
experimentally determined... it is an almost straight line
value of approximately 3 degrees C per 1000 feet.

The dry adiabatic lapse rate is not an experimentally determined
number.

I simply meant that it is a number which, one way or another, is
more-or-less known. It was a bit of a typo... "experimentally" should not
have been there, but I didn't want to say "theoretically", because I worried
pilots might think that the number is some kind of guess and not really
known.

Saying "Experimentally" didn't alter the gist of the post for pilots... only
for research-meteorologists! :-)

I wrote:

remarkably simple expression: g/Cp, where g is gravity (9.8 m/s)

This should have read 9.8 m/s^2, not 9.8 m/s, for those who care.

Jim Rosinski

"Darrell S" wrote in message
news:bdUNd.46622$bu.24635@fed1read06...
2°/1000' is "average" since air at different levels may be saturated
or unsaturated and can change from one to the other
at different levels. Lifted air would cool at 3°/1000' while
lifting through dry air and at 1°/1000' lifting through moist air levels.
So.... the average is 1°


no, No, NO!!!

The 2 degrees per 1000 feet comes from a "determined" average lapse rate of
real atmospheres averaged around the globe and averaged throughout time....
determined within reason. It has nothing, NOTHING, to do with saturated or
unsaturated or dry adiabatic or saturated adiabatic. Dry and Saturated
adiabatic lapse rates are a law-of-physics-rates-of-cooling, not actual
temperatures in the real nor in the "standard" atmosphere.

Please divorce those two concepts:

First concept:
Environmental lapse rate: temperature structure of the real atmosphere
right now. Usually, but not necessarily, cools with height. How much per
1000 feet? Depends on the structure TODAY, THIS INSTANT. Not constant
throughout. May be several degrees per 1000 feet in some layers, zero in
others, and even an inversion in still others.

.... and Standard Atmosphere Lapse Rate: defined at "lowering 1.98 degrees
per 1000 feet" within the troposphere (lowest 11 kilometres).

Second concept:
Dry Adiabatic lapse rate: a RATE-OF-COOLING (or heating) of a parcel of air
should it be displaced from its present level and rise (or descend) through
the atmosphere, with the consequent pressure change on it. The
"dry-adiabatic" rate of cooling will occur as long as no moisture is being
condensed. About 3 degrees per 1000 feet, reasonably linear with height.

.... and Saturated Adiabatic lapse rate: a RATE-OF-COOLING (or heating) of a
parcel of air should it be displaced from its present level and rise (or
descend) through the atmosphere, with the consequent pressure change on it.
The "wet-adiabatic" rate of cooling (or heating) will occur as long as the
relative humidity of the parcel is 100 percent and moisture is being
condensed (or evaporated if descending). This rate is less than the
dry-adiabatic rate, because the condensation of moisture releases heat which
slows the cooling of the air. Not linear with height. Varies from about 1
degrees per 1000 feet at very high dewpoints, to almost 3 degrees per 1000
feet at very low dewpoints.

Two different concepts!

Icebound wrote:

Saying "Experimentally" didn't alter the gist of the post for
pilots... only
for research-meteorologists! :-)

Agreed. I really am pleased to see this much interest, and frankly
knowledge, displayed by pilots for a subject I've spent a good part of
my life studying.

Jim Rosinski

What you described is exactly the point many people (including myself)
have been confused about. The 2C/1000' is the average environmental
lapse rate. Adiabatic lapse rate is never 2C/1000'. It is 1C/1000' or
3C/1000'. Many FAA texts do not explain this point clearly. Since most
pilots get their meterology knowledge from FAA texts, and are not
formally educated on the subject, it is not surprising this confusion
exists. I would bet you any money that if you took a survey of CFI's
most would not know this fact.


"Icebound" wrote in
:




"Darrell S" wrote in message
news:bdUNd.46622$bu.24635@fed1read06...
2°/1000' is "average" since air at different levels may be saturated
or unsaturated and can change from one to the other
at different levels. Lifted air would cool at 3°/1000' while
lifting through dry air and at 1°/1000' lifting through moist air
levels. So.... the average is 1°


no, No, NO!!!

The 2 degrees per 1000 feet comes from a "determined" average lapse
rate of real atmospheres averaged around the globe and averaged
throughout time.... determined within reason. It has nothing,
NOTHING, to do with saturated or unsaturated or dry adiabatic or
saturated adiabatic. Dry and Saturated adiabatic lapse rates are a
law-of-physics-rates-of-cooling, not actual temperatures in the real
nor in the "standard" atmosphere.

Please divorce those two concepts:

First concept:
Environmental lapse rate: temperature structure of the real
atmosphere right now. Usually, but not necessarily, cools with
height. How much per 1000 feet? Depends on the structure TODAY, THIS
INSTANT. Not constant throughout. May be several degrees per 1000
feet in some layers, zero in others, and even an inversion in still
others.

... and Standard Atmosphere Lapse Rate: defined at "lowering 1.98
degrees per 1000 feet" within the troposphere (lowest 11 kilometres).

Second concept:
Dry Adiabatic lapse rate: a RATE-OF-COOLING (or heating) of a parcel
of air should it be displaced from its present level and rise (or
descend) through the atmosphere, with the consequent pressure change
on it. The "dry-adiabatic" rate of cooling will occur as long as no
moisture is being condensed. About 3 degrees per 1000 feet,
reasonably linear with height.

... and Saturated Adiabatic lapse rate: a RATE-OF-COOLING (or heating)
of a parcel of air should it be displaced from its present level and
rise (or descend) through the atmosphere, with the consequent pressure
change on it. The "wet-adiabatic" rate of cooling (or heating) will
occur as long as the relative humidity of the parcel is 100 percent
and moisture is being condensed (or evaporated if descending). This
rate is less than the dry-adiabatic rate, because the condensation of
moisture releases heat which slows the cooling of the air. Not linear
with height. Varies from about 1 degrees per 1000 feet at very high
dewpoints, to almost 3 degrees per 1000 feet at very low dewpoints.

Two different concepts!

Andrew Sarangan wrote:

Adiabatic lapse rate is never 2C/1000'. It is 1C/1000' or
3C/1000'. Many FAA texts do not explain this point clearly. Since
most
pilots get their meterology knowledge from FAA texts, and are not
formally educated on the subject, it is not surprising this confusion
exists.

I don't want to re-confuse you, but there actually *is* a saturated
adiabatic lapse rate equal to 2C/1000'. Recall that warmer air can hold
more moisture than cold air. As a result, saturated adiabatic lapse
rates vary from nearly the same as the dry rate of 3C/1000' (cold air),
all the way up even beyond the 1C/1000' you quote (very warm air).

You're right about the ****-poor nature of FAA texts though. Not just
the bad meteorological explanations, even their basic physics is wrong.
They blather on about "centrifugal force", which doesn't even exist!
What does exist is centripetal acceleration, which acts in the opposite
direction of the mythical "centrifugal force".

Jim Rosinski

"jim rosinski" wrote in message
oups.com...
[...]
You're right about the ****-poor nature of FAA texts though. Not just
the bad meteorological explanations, even their basic physics is wrong.
They blather on about "centrifugal force", which doesn't even exist!

Well, except that unlike the whole lapse rate confusion, the idea of
"centrifugal force" is perfectly valid, depending only on one's frame of
reference, and complained about only by overly pedantic engineers and
laymen.

Pete

"Peter Duniho" writes:

"jim rosinski" wrote:
[...]
You're right about the ****-poor nature of FAA texts though. Not just
the bad meteorological explanations, even their basic physics is wrong.
They blather on about "centrifugal force", which doesn't even exist!

Well, except that unlike the whole lapse rate confusion, the idea of
"centrifugal force" is perfectly valid, depending only on one's frame of
reference, and complained about only by overly pedantic engineers and
laymen.

And physics instructors while grading test answers.

Joe Morris

"Joe Morris" wrote in message
...
"Peter Duniho" writes:

"jim rosinski" wrote:
[...]
You're right about the ****-poor nature of FAA texts though. Not just
the bad meteorological explanations, even their basic physics is wrong.
They blather on about "centrifugal force", which doesn't even exist!

Well, except that unlike the whole lapse rate confusion, the idea of
"centrifugal force" is perfectly valid, depending only on one's frame of
reference, and complained about only by overly pedantic engineers and
laymen.

And physics instructors while grading test answers.

I'd hope that physics instructors would realize that centrifugal force does
exist from the turning object's accelerated reference frame. It's just from
an inertial reference frame that centrifugal force is "fictitious". Either
reference frame is valid; you just have to be careful to specify which one
you're using.

Similarly, from the standpoint of curved spacetime, gravity is a
"fictitious" force. When you cruise near a planet, you just follow a
straight line (through curved spacetime), without being diverted by (or
feeling the influence of) any force. The pressure you feel on the seat of
your pants is analogous to centripetal force--it's the "real" force that
*opposes* the "fictitious" gravitational force.

Still, from our more familiar frame of reference, the force of gravity is
quite real, and we shouldn't object to the FAA's invocation of gravity, or
of centrifugal force.

--Gary

"Andrew Sarangan" wrote in message
1...
What you described is exactly the point many people (including myself)
have been confused about. The 2C/1000' is the average environmental
lapse rate. Adiabatic lapse rate is never 2C/1000'. It is 1C/1000' or
3C/1000'. Many FAA texts do not explain this point clearly. Since most
pilots get their meterology knowledge from FAA texts, and are not
formally educated on the subject, it is not surprising this confusion
exists. I would bet you any money that if you took a survey of CFI's
most would not know this fact.

As Jim pointed out, the moist (saturated) adiabatic rate is not constant,
but anything from about 1 to about 3 deg C per 1000. Because the amount of
condensing moisture is different at different dewpoints, and therefore the
amount of heat released is different in the different situations. If no
condensation is occurring, yes, then it is only 3/1000.

I have only recently sat through my first aviation ground school.
Meteorology was taught by a pilot, not a meteorologist. The pilot himself
had obvious lack of understanding of the subject. After his instruction, we
have 30 new potential pilots in a second generation with similar
misconceptions. Eventually one or more of them are going to become CFIs.
They may upgrade their meteorological education.... or NOT; the current
instructor didn't.

I have not checked this out in detail:

http://66.208.12.20/amsedu/online/info/

but it appears to be EXACTLY what pilots could use. The full one-time
course fee at $250 is a bargain in the context of your overall flying costs.
Even the no-license-fee "textbook-only" option would help us all.

By the way, the American Meteorological Society, in case you don't know, has
been around since 1919, and is THE organization for professional
meteorologists in the USA, so I am pretty confident that you will be getting
your money's worth.