Atmospheric stability and lapse rate

"jim rosinski" wrote in message
oups.com...

....
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".


Ooops, Jim. Just when you had them on your side :-) :-)

On 7 Feb 2005 20:06:38 -0800, "jim rosinski"
wrote:

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

Jim, to me this is kind of the point regarding this subject and the
FAA's insistance on it being a part of the written examination. How
does knowing this information help the average pilot in his task of
flying safely from one point to another.

Does any pilot (besides yourself) actually think about this while
flying? If so when? Under what circumstances?

After a while don't pilots kind of get to understand when clouds begin
forming due to warming? And when the clouds do form, don't we (VHF
guys) normally just avoid them?

Thanks, Corky Scott

Andrew Sarangan wrote:
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.

There is an excellent explanation of all this stuff (including how to
predict cloud bases, the presence of vertical air currents, and the
likelihood of T-storms) in Reichmann's "Streckensegelflug" (man I hope
I got that right) which is translated into English (the whole book -
you need not speak German) as "Cross Country Soaring." It includes the
use of the Stuve diagram to predict what the atmosphere is going to do.

I would bet you any money that if you took a survey of CFI's
most would not know this fact.

Sure, as long as you limit to power-only CFI's. I can't think of any
glider CFI's who have not read Reichmann, though of course anything is
possible.

Michael

"Corky Scott" wrote in message
...

Does any pilot (besides yourself) actually think about this while
flying? If so when? Under what circumstances?

After a while don't pilots kind of get to understand when clouds begin
forming due to warming? And when the clouds do form, don't we (VHF
guys) normally just avoid them?


Perhaps there are parts of the country where that is true, but in the
4-seasons part of the world....
yes, you should be thinking about these things BEFORE flying, not just WHILE
flying.

Now I DO agree that knowing the "fact" that the
dry-adiabatic-lapse-rate-is-3-degrees-Celsius-per-thousand-feet and being
able to check off the correct multiple-choice-box on the FAA or
Transport-Canada exam... is somewhat irrelevant if we do not take that fact
and understand it within the context of the rest of our weather environment.

And I have this belief that some of our instructors are concentrating on
ensuring we pass the exam by knowing these "facts", just as they did,
without really understanding nor properly communicating the broader subject
of aviation meteorology to us.
Therefore, it is left to US to obtain that understanding somehow. We should
not cancel our willingness, hell, our *obligation* to learn, once we walk
out of that ground-school session.


As has been often recorded in these newsgroups, TAFs are often "wrong".
Sometimes even METAR observations are less than perfect, especially from
AUTO sites.

If we had a real good understanding of all aspects of meteorology, we could
recognize the situations in which forecasting should be relatively "easy",
and the situation is which it is more "difficult".... therefore the
situation in which we can take the TAF as gospel, and the situation in which
it is likely to be suspect.

We would recognize not only the "actual" forecast for your area, but also
the "potential" of what the other possibilities were. This works both
ways.... we would recognize the potential for good weather when the TAF said
no, and we would recognize the potential for bad weather when the TAF said
go.

We would recognize whether the formation of an unexpected cloud bank is
potentially dangerous or benign. We would recognize whether an unexpected
clearing is real (and may be bad timing on the part of the TAF), or just a
sucker-hole.

We would understand the "thinking behind the TAF" and we would be in a
position to do our own "now-casting" if the
underlying-conditions-to-that-thinking have changed.... because we would
understand what "underlying conditions" to look for, and what their
implications are.

Knowing more about the underlying meteorology of your current situation will
not only help us avoid current BAD weather... it will help us understand
when GOOD-weather-going-bad is a possibility, and it will help us to
understand the difference between MARGINAL-weather-getting-good and
marginal-weather-getting-bad.

I have a real fear that the new generation of in-cockpit tools to
"upload-the-weather" will further deteriorate our desire to learn. If we
are going to use those tools only to "avoid the bright spots on the map",
then I am afraid that they will not increase our safety factor one bit.

I am certain (well okay: hopeful, anyway) that a very large segment of the
pilot population was well taught, understand meteorology very well and are
doing all they can to learn more and learn correctly. I do fear, however,
that some of us were not only poorly taught, but have accepted that as the
"norm" to be passed on to the next generation. And we now treat meteorology
as just one more check-mark on the exam to be forgotten-about, once passed.

(Pardon me for cross-posting to r.a.s, where this really belongs.)

Whoops. Typing error. the last entry should read "the average is 2°.

--

Darrell R. Schmidt
B-58 Hustler History: http://members.cox.net/dschmidt1/
-

"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°

--

Darrell R. Schmidt
B-58 Hustler History: http://members.cox.net/dschmidt1/
-

"Andrew Sarangan" wrote in message 1...
Instability produces cumulus clouds and stability produces stratus clouds.
We know that. However, since the saturated and unsaturated lapse rates are
significantly different (1C/1000' compared to 3C/1000'), it seems quite
possible to get cumulus clouds even when the atmosphere below is stable.
For instance, if the environmental lapse rate is 2C/1000', the unsaturated
air is stable. Once clouds form (how they form without vertical currents is
a different matter), the air inside the clouds will become unstable. Does
this seem reasonable?

On a related question, where does the concept of 'average' lapse rate
(2C/1000') come from? I always took this to mean 50% RH air, but it took me
a long time to learn that that was not the case. The air is saturated or it
is unsaturated. How can there be an average between saturated and
unsaturated? The standard lapse rate and standard temperature at
different elevations are all based on this 2C/1000' concept. What's the
deal with this?

Corky Scott wrote:

Jim, to me this is kind of the point regarding this subject and the
FAA's insistance on it being a part of the written examination. How
does knowing this information help the average pilot in his task of
flying safely from one point to another.

I agree the lapse rate stuff and implications for stability/instability
aren't of much practical value while flying. The main things are being
able to look at the sky and make some assessment of whether flying is a
good idea, and knowing what aspects of meteorological data might
warrant alarm. For example:

o Lenticulars over the mountains = won't be flying in the mountains
today (high winds).
o Smog over Denver = inversion, might be some bumps at the inversion
but no reason not to go flying.
o Temperature-dewpoint spread dropping toward zero = uh-oh, fog might
form. Don't stray too far.
o Low clouds forming east of the Rockies = upslope, bad weather moving
in. Maybe IMC soon.

Most pilots know these things, which I think are more important for
safe flying than some of the more esoteric aspects of atmospheric
science. And layman-level understanding of local meteorological warning
signs (I've given a few for the Denver area above) is really money in
the bank.

Jim Rosinski

"Michael" wrote in message
ups.com...
Andrew Sarangan wrote:
....
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.
....snipped...
I would bet you any money that if you took a survey of CFI's
most would not know this fact.

Sure, as long as you limit to power-only CFI's. ...

I have no doubt that this is absolutely correct.

Not being a soarer, but I expect he/she not only knows the "conditions" that
give rise to good thermal lift, but also the meteorological situations to
look for which are conducive.

Power pilots as a group seem less interested in the meteorological
situation. Give them the ceiling and visibility numbers from the TAF and
METAR and they go on that. Nobody seems to ask WHY does the TAF lower the
ceiling after 2100Z... If the ceiling should lower two hours early at 1900Z
instead of 2100Z, many are totally lost and simply consider this a "bad
forecast".

Power pilots as a group seem less interested in the meteorological
situation. Give them the ceiling and visibility numbers from the TAF
and
METAR and they go on that. Nobody seems to ask WHY does the TAF
lower the
ceiling after 2100Z... If the ceiling should lower two hours early at
1900Z
instead of 2100Z, many are totally lost and simply consider this a
"bad
forecast".

I think it's less a matter of disinterest and more a matter of
ignorance. Knowledge of meteorology isn't something that can
effectively be tested using a government-issue multiple choice test,
and it's not particularly easy to test in an oral exam either. For
that matter, it's not easy to teach, and it sure isn't easy to learn
from a textbook. I would have to say that of all the important
aviation topics, meteorology is the most poorly taught and the most
poorly understood. Power pilots as a group are simply not qualified to
speculate WHY the TAF lowers the ceiling after 2100Z. Quite a few
don't even understand that they should be asking why.

One thing I've noticed is this - when an inexperienced pilot cancels a
trip based on a forecast, very rarely is it a matter of good judgment -
meaning the weather is likely to be beyond the pilot's capabilities for
the reasons he believes to be true. Usually it's a matter of poor
understanding - he cancels because he doesn't understand what the
weather is actually doing, and this state of ignorance (quite properly)
scares him. Even when the weather is beyond his capabilities, very
rarely is it for the reasons he thinks it is.

By the same token, the decision by an inexperienced pilot to make the
trip in something other than good weather forecast to stay that way is
rarely a matter of properly understanding that the weather, while not
really good, is within the pilot's capability - it's usually more a
matter of rolling the dice. Even when the weather is within his
capabilities, his logic for coming to that conclusion is generally very
flawed.

This isn't a good situation, but I have to say that in power flying
that's basically the way it is - and that goes double for instrument
flying. I find it amazing that anyone can believe he is making
intelligent decisions with regard to his safety margins against
encountering icing and T-storms in IMC in any but the most clearcut
cases without an understnading of what lapse rates mean, yet here we
have quite a few instrument pilots and instrument instructors still
hashing out the topic. And I'm going to be honest - had I not had my
glider rating long before my instrument rating, and my CFI-G long
before my CFII, I would likely have been just as ignorant.

While I admit it's possible in theory to learn enough about meteorology
from books and classes to make competent go/no-go decisions, I have to
say that I've never actually seen it happen in practice. In reality,
the only people I know who have actually learned to understand what the
weather is doing sufficiently to realistically asess the flight risks
are those who have flown in the weather. Unfortunately, every one of
these people has scared himself more than once by having misunderstood
or ignored some seemingly minor but actually very important factor.
And lest you think that it's somehow different for gliders, every one
of those glider pilots who has become pretty good at knowing what the
weather is doing has stories of guessing wrong and making an
off-airport landing or escaping one only by the skin of one's teeth.

Michael

"Michael" wrote in message
oups.com...
.... many relevant observations snipped....

This isn't a good situation, but I have to say that in power flying
that's basically the way it is - and that goes double for instrument
flying.
....more relevant observations snipped....
And lest you think that it's somehow different for gliders, every one
of those glider pilots who has become pretty good at knowing what the
weather is doing has stories of guessing wrong and making an
off-airport landing or escaping one only by the skin of one's teeth.

I had been around the periphery of aviation for many years, but have only
had my very first peeks "inside" since mid-2004.

What you have said mirrors that meager experience perfectly. It surprised
me a little...maybe more than a little.

"Andrew Sarangan" wrote in message
1...
Instability produces cumulus clouds and stability produces stratus clouds.
We know that. However, since the saturated and unsaturated lapse rates are
significantly different (1C/1000' compared to 3C/1000'), it seems quite
possible to get cumulus clouds even when the atmosphere below is stable.
For instance, if the environmental lapse rate is 2C/1000', the unsaturated
air is stable. Once clouds form (how they form without vertical currents
is
a different matter), the air inside the clouds will become unstable. Does
this seem reasonable?

I think there's an aspect to this that hasn't been discussed. It *does*
require instability to produce cumulus cloud, but that instability can be
very local. So you may see an average environmental lapse rate of 2
degC/1000' through the lowest 3000' of the atmosphere, but actually you've
got at least patches of surface being heated by the sun, producing higher
temperatures and local instability. In that simple example, if you heat a
thin layer at the surface by just 3 degC, you've now got instability and the
makings of vertical convection.

That's not to say that stratiform clouds can't become unstable by the
mechanism you propose, but cu can form, particularly close to the surface,
in atmospheres that start off looking stable.

Julian Scarfe