Atmospheric stability and lapse rate

On Tue, 8 Feb 2005 12:25:34 -0500, "Icebound"
wrote:

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.

Can you give me a realistic example of how knowing exactly what the
definition of lapse rate is would help a pilot flying from point A to
point B?

Forgive me, I'm just trying to understand why the FAA considers this
so important that it is put on the written. I've never heard of
anyone calculating the lapse rate for a flight. Even if they did, it
seems to me that this rate could easily be different from one point to
the next throughout the flight.

I understand the need to be thorough when flight planning but I don't
get how to use this particular knowledge.

Thanks, Corky Scott

Nicely done guys. This thread is the Usenet we all enjoy.

A Chinook is the classic demonstration of lapse rate in action. You can
even see it on the satellite feeds.

From a pilots perspective there are only three kinds of weather.
Getting better
Getting worse
Staying the same
All of our studying and experience are drawn on to make this judgment, and I
think it is true to say that you can't have too much weather knowledge.
Ultimately weather and running out of fuel seem to be the biggest cause of
aviation fatalities.

The internet is a wonderful resource for students of life as there is a huge
amount of very good material available for free and the access to aviation
weather maps and data lets us practice our skills by constantly watching the
sky and asking yourself, if you were flying today
is it getting better or worse?
and where is the hidden weather killer hiding?

I make it a point to check the aviation weather daily and find that my
forecasts are usually as good as the very good TV weather (CFCN) I also
find this practice useful for forecasting powder snow and use my knowledge
of lapse rates and winds aloft to estimate whether it is likely to be heavy
or light and its effect on the avalanche hazard or if the high chairlift
will be closed for wind..

Weather newsgroup sci.gen.meteorology Most of the guys on
this group know way more than me, but then that's true here too.

The following is a repost, my appologies to the usenet purists.

When the local FSS were closed NavCan recognized that the briefers in the
centers may lack the local knowledge that the local FSS had provided. A
project to gather this local knowledge for briefer training lead to the
production of weather manuals for each of the weather regions. These
manuals are available on their website. The general weather chapter seems
to be common to each manual and is as good as any of the pilot weather books
I have read, with the possible exception of the TC Air Command Weather
Manual CFACM 2-700 ( TC. TP9352E)

http://www.navcanada.ca/NavCanada.as...Definition Fi
les\Publications\LAK\default.xml

My favorite weather source is

http://www.flightplanning.navcanada....gue=anglais&No
Session=NS_Inconnu&Page=rb&TypeDoc=html

Blue skies to all





"Icebound" wrote in message
...

"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.



and many previous posters

"Corky Scott" wrote in message
...
On Tue, 8 Feb 2005 12:25:34 -0500, "Icebound"
wrote:

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.

Can you give me a realistic example of how knowing exactly what the
definition of lapse rate is would help a pilot flying from point A to
point B?

....


If a pilot does not know the definition of lapse rate, then it is pretty
difficult for him to recognize the conditions which lead to atmospheric
buoyancy or to atmospheric stability.

I get to the airport on a clear summer morning. 7 AM. Sun is up. Not a
cloud in the sky. Temperature is 20C, dewpoint is 15. TAF for my airport
for later is PROB30 TSRA. TAF For airport 40 mi south for a similar time
period is TEMPO TSRA. Okay, only a risk of thunderstorms for me, more
definite for the guy down south.

As a pilot, I am interest in the possibilities of the TAF being "wrong". I
take off, fly up through the early-morning inversion and find the
temperature starts to fall off at about 4000 feet, peaking there at, say,
about 20 to 22 C.

*If I know* (maybe get a PIREP) that the 10,000 foot temperature in my area
is rather warm, say 14-15... that's maybe 1.5 degrees per 1000, pretty
stable in that mid layer and I'm pretty confident that even with good summer
heating only a few are likely to pop and I pretty much trust the TAF. I
know that it is "pretty stable" because I understand the concept of
adiabatic lapse rates and therefore know more-or-less how much colder a
rising air parcel will be than its environment.... and hence not buoyant.

But if I find out that the 10,000 foot temperature is closer to, say 6 or 8,
that's becoming 2.5 per 1000, and I am starting to consider the possibility
that my airmass maybe just as unstable as the guy down south and
Thunderstorms are a distinct possibility and something more than a "risk".

Am I likely to do exactly that kind of calculation in flight?

Maybe, maybe not..... If I did, would it affect my go-nogo decision? Maybe,
maybe not. But if I *did* go, I know what I would be looking out for, and I
would treat the first appearance of a Towering Cumulus quite differently in
those two situations. In the first case, I'm not panicking until I see a
few more.... in the second, I'm thinking seriously about heading for an
airport.

My rant was about knowledge of meteorological concepts in general, not lapse
rates in particular. Lapse rates were an easy target example because of the
obvious misunderstanding of adiabatic lapse rates in that particular post.
I agree that in a great many cases, knowing the actual lapse rate may not
help you much. You might not have the information, or it may be a situation
where it is not important. (And FAA or TC exams that test "knowledge" are a
whole other issue :-) )

But knowing the complete concept... how adiabatic lapse rates affect the
temperature of rising parcels... how that relates to the difference in
temperature between the environment and a rising air bubble... how that
difference in temperature affects buoyancy... how the degree of buoyancy
affects convection....

Knowledge of these concepts may just help you to understand the TAF, your
own observations, and how to reconcile a busted forecast.

On Wed, 9 Feb 2005 18:29:52 -0500, "Icebound"
wrote:

If a pilot does not know the definition of lapse rate, then it is pretty
difficult for him to recognize the conditions which lead to atmospheric
buoyancy or to atmospheric stability.

You really think so? You feel that people would not/do not understand
how and when clouds might form if they do not have an understanding of
what lapse rate is?

When I flew out to Oshkosh in '95 in the front seat of a Waco UPF-7,
we encountered a LOT of thunderstorms along our route. The plan was
to fly from Vermont due west staying south of the Great Lakes until we
reached Chicago, then turn right. Known as the "Northeast Corridor"
it's home to a lot of thunderstorm activity during the summer.
Typically, we'd fly along our route for as long as possible, and when
the sky filled with thunderstorms that we could no longer fly around,
we landed and waited them out. We ended up waiting more than we'd
planned due to the amount of storms we encountered. By the time we
turned north past Chicago, the storms were individually extremely
violent but isolated and we could and did just detour around them.

How would the pilot who truly understood lapse rate have flown it any
differently?

Thanks, Corky Scott

"Corky Scott" wrote in message
news
On Wed, 9 Feb 2005 18:29:52 -0500, "Icebound"
wrote:

If a pilot does not know the definition of lapse rate, then it is pretty
difficult for him to recognize the conditions which lead to atmospheric
buoyancy or to atmospheric stability.

You really think so? You feel that people would not/do not understand
how and when clouds might form if they do not have an understanding of
what lapse rate is?

Well, no, pretty much by definition they would not.

Many sunny days clouds form. Many other sunny days they do not. Should we
just be *surprised* by the formation of cloud on this day, or *surprised* by
the absence of cloud on another?

If you know that on sunny days clouds form because bubbles of air move
upward and cool to the point of condensation, you already know something
about environmental and adiabatic lapse rates, even if you will not admit
it. Otherwise, why would you expect clouds to form even if these bubbles do
float upward?


When I flew out to Oshkosh in '95 in the front seat of a Waco UPF-7,
we encountered a LOT of thunderstorms along our route. The plan was
to fly from Vermont due west staying south of the Great Lakes until we
reached Chicago, then turn right. Known as the "Northeast Corridor"
it's home to a lot of thunderstorm activity during the summer.
Typically, we'd fly along our route for as long as possible, and when
the sky filled with thunderstorms that we could no longer fly around,
we landed and waited them out. We ended up waiting more than we'd
planned due to the amount of storms we encountered. By the time we
turned north past Chicago, the storms were individually extremely
violent but isolated and we could and did just detour around them.

How would the pilot who truly understood lapse rate have flown it any
differently?


You asked for a practical situation and I gave you one.

Maybe he would fly your situation no differently at all... As I said before,
lots of situations when the pilot will not have sufficient information
beyond what he sees out the window.

But he *would* be flying with the subtle difference that he is pressing on
because he understands what is happening here and can *anticipate any
changes*, rather than just *react to changes*. And he would also be more
comfortable *in advance* about the probability of his
success-without-diversion.

On Thu, 10 Feb 2005 14:19:44 -0500, "Icebound"
wrote:

Maybe he would fly your situation no differently at all... As I said before,
lots of situations when the pilot will not have sufficient information
beyond what he sees out the window.

But he *would* be flying with the subtle difference that he is pressing on
because he understands what is happening here and can *anticipate any
changes*, rather than just *react to changes*. And he would also be more
comfortable *in advance* about the probability of his
success-without-diversion.

Ok, my apologies once again for seeming so dense about this.

I had another bunch of scenario's all worked up for argument's sake,
but have decided to just let this go.

Thanks for your information

Corky Scott

Corky,

With knowledge of the surface temperature, dewpoint, and lapse rate a
pilot can make an educated guess at what altitude cloud bases are
likely to be. Also, with knowledge of the temperature at your altitude
and lapse rate you can estimate your proximity to the freezing level.
Granted, lapse rates vary greatly and these "calculations" are more
like ballpark guesses, but they're still valuable.

Regards,

Rob

On Tue, 08 Feb 2005 10:01:35 -0500, 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.

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

GA pilots might not use it much. For glider pilots it can be very
valuable, as a predictor of when and where thermals will form. Also
ultralights, since it's also a good predictor of how smooth the air
will be (thermic days can be uncomfortable if not downright dangerous
in the extreme low end of ultralights like powered paragliders).

-Dana
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If replying by email, please make the obvious changes.
-------------------------------------------------------------------------------Daddy, why doesn't this magnet pick up this floppy disk?

"Corky Scott" wrote in message
...
On Thu, 10 Feb 2005 14:19:44 -0500, "Icebound"
....
Ok, my apologies once again for seeming so dense about this.

.....

No need.

My instructors did not really have to tell me all the gory details about how
that big red knob next to the throttle works. All they really had to say
was "when you get above about 3000 feet, you'll get a little more power if
you pull it out a bit... but not too far or the RPM will drop... and on your
way down push it in a bit... and stick it right to the dash when landing or
taking off..." That would have probably been enough to get me by.

But knowing the relationships between air/gas mixtures and fuel consumption
and engine cooling and engine power, etc., helps me use that little knob a
little smarter.

I think you can look at knowing the underlying weather theory the same
way... it helps you use TAFs, area forecasts, radar imaging, and even your
own observations... just a little bit smarter.

All the best.

Lapse rate can also tell you what type of icing you are likely to get.
Unstable clouds are more likely to have clear ice (the bad kind), and
stable clouds are likely to be rime ice.



"Icebound" wrote in
:


"Corky Scott" wrote in message
news
On Wed, 9 Feb 2005 18:29:52 -0500, "Icebound"
wrote:

If a pilot does not know the definition of lapse rate, then it is
pretty difficult for him to recognize the conditions which lead to
atmospheric buoyancy or to atmospheric stability.

You really think so? You feel that people would not/do not
understand how and when clouds might form if they do not have an
understanding of what lapse rate is?

Well, no, pretty much by definition they would not.

Many sunny days clouds form. Many other sunny days they do not.
Should we just be *surprised* by the formation of cloud on this day,
or *surprised* by the absence of cloud on another?

If you know that on sunny days clouds form because bubbles of air move
upward and cool to the point of condensation, you already know
something about environmental and adiabatic lapse rates, even if you
will not admit it. Otherwise, why would you expect clouds to form
even if these bubbles do float upward?


When I flew out to Oshkosh in '95 in the front seat of a Waco UPF-7,
we encountered a LOT of thunderstorms along our route. The plan was
to fly from Vermont due west staying south of the Great Lakes until
we reached Chicago, then turn right. Known as the "Northeast
Corridor" it's home to a lot of thunderstorm activity during the
summer. Typically, we'd fly along our route for as long as possible,
and when the sky filled with thunderstorms that we could no longer
fly around, we landed and waited them out. We ended up waiting more
than we'd planned due to the amount of storms we encountered. By the
time we turned north past Chicago, the storms were individually
extremely violent but isolated and we could and did just detour
around them.

How would the pilot who truly understood lapse rate have flown it any
differently?


You asked for a practical situation and I gave you one.

Maybe he would fly your situation no differently at all... As I said
before, lots of situations when the pilot will not have sufficient
information beyond what he sees out the window.

But he *would* be flying with the subtle difference that he is
pressing on because he understands what is happening here and can
*anticipate any changes*, rather than just *react to changes*. And
he would also be more comfortable *in advance* about the probability
of his success-without-diversion.