Adiabatic lapse rate

Does the lapse rate equation hold in all cases? I was recently
wondering what kind of temperature would be reached at 35 Kft
over Arctic Canada in January. It seemed that the lapse rate
equation would lead you to expect temperatures that would be
causing nitrogen and carbon dioxide to be condensing which
doesn't seem likely.

Everett M. Greene wrote:
Does the lapse rate equation hold in all cases? I was recently
wondering what kind of temperature would be reached at 35 Kft
over Arctic Canada in January. It seemed that the lapse rate
equation would lead you to expect temperatures that would be
causing nitrogen and carbon dioxide to be condensing which
doesn't seem likely.


The equation breaks at tropopause, and
your requested altitude is quite near it,
if not above.

AFAIK, you need measurements for the
temperature, as the equation cannot handle it.

--

Tauno Voipio (CPL(A))
tauno voipio (at) iki fi

On 10/21/2007 11:44 AM, Everett M. Greene wrote the following:
Does the lapse rate equation hold in all cases?
Don't count on it in the real world. I was once in the clear at 6,000 feet, 0
degrees C, and confidently told my wife that Approach would soon drop us into
the clouds at 4,000 feet but that we didn't have to worry about ice because it
would be +4 degrees. When we got there it was -- ta da -- 0 degrees! We
immediately started picking up some light ice, requested and got a descent to
3,000, and all was well.

Lapse rate is dependent on humidity. The dry rate is rapid,
the wet rate can be anything, even a temperature rise as the
condensation raises the temperature [makes
thunderstorms-hurricanes], the average lapse rate is just
that, a mathematical average.


"Mitty" wrote in message
...
|
|
| On 10/21/2007 11:44 AM, Everett M. Greene wrote the
following:
| Does the lapse rate equation hold in all cases?
| Don't count on it in the real world. I was once in the
clear at 6,000 feet, 0
| degrees C, and confidently told my wife that Approach
would soon drop us into
| the clouds at 4,000 feet but that we didn't have to worry
about ice because it
| would be +4 degrees. When we got there it was -- ta da --
0 degrees! We
| immediately started picking up some light ice, requested
and got a descent to
| 3,000, and all was well.

On Oct 21, 2:29 pm, Mitty wrote:
On 10/21/2007 11:44 AM, Everett M. Greene wrote the following: Does the lapse rate equation hold in all cases?

Don't count on it in the real world. I was once in the clear at 6,000 feet, 0
degrees C, and confidently told my wife that Approach would soon drop us into
the clouds at 4,000 feet but that we didn't have to worry about ice because it
would be +4 degrees. When we got there it was -- ta da -- 0 degrees! We
immediately started picking up some light ice, requested and got a descent to
3,000, and all was well.

In fact I've noticed when there is ice about and the temp is near
freezing that
it tends to stay that way -- no rate at all!!

It's as if the model is more like the ice-water mix where the temp is
constrained
at 32F until all the ice is melted or all the water frozen.

Look out, huh! It's an interesting question on the instrument written
but the real world is a lot different.

Bill Hale

Bill wrote:

In fact I've noticed when there is ice about and the temp is near
freezing that
it tends to stay that way -- no rate at all!!

I've noticed that too, and always assumed its because of the ice
buildup on the thermometer.

Latent heat. That is why they spray water on the oranges to
reduce frost damage.

After a day or two at below freezing, but near freezing
temperatures in stable air, there will be little airframe
ice because the water has finally frozen.
But with unstable air, more fresh and liquid water is being
cooled into the supercooled range and that makes structural
ice.


wrote in message
ups.com...
|
| Bill wrote:
|
| In fact I've noticed when there is ice about and the
temp is near
| freezing that
| it tends to stay that way -- no rate at all!!
|
| I've noticed that too, and always assumed its because of
the ice
| buildup on the thermometer.
|

On Oct 21, 12:44 pm, (Everett M.
Greene) wrote:
Does the lapse rate equation hold in all cases? I was recently
wondering what kind of temperature would be reached at 35 Kft
over Arctic Canada in January. It seemed that the lapse rate
equation would lead you to expect temperatures that would be
causing nitrogen and carbon dioxide to be condensing which
doesn't seem likely.

The adiabatic lapse rate only holds true in the troposphere. The
troposphere is heated from below by convective air currents, and this
is where the 3C/1000' comes from. In contrast, the stratosphere
absorbes solar radiation directly, and hence has a negative lapse
rate. In the polar regions the troposphere is thinner, about 20kft
high (also depends on season). So you cannot apply the tropospheric
lapse rate up to 35 Kft.

"Everett M. Greene" wrote in message
...
Does the lapse rate equation hold in all cases? I was recently
wondering what kind of temperature would be reached at 35 Kft
over Arctic Canada in January. It seemed that the lapse rate
equation would lead you to expect temperatures that would be
causing nitrogen and carbon dioxide to be condensing which
doesn't seem likely.

As you pass through the tropopause at approx 36,000 and -56 C the
temperature rises in the stratosphere as solar radiation is bounced back up
through the stratosphere by ozone (O3).

As you get right on the fringes of the atmosphere the temperature rise is
enormous.

The main issue in the troposphere is that well known greenhouse gas water
vapour. The adiabatic lapse rate is entirely dependent on the amount of
water in the air and you can calculate that using the wet and dry bulb
thermometers.

In article ,
S Green wrote:

"Everett M. Greene" wrote in message
...
Does the lapse rate equation hold in all cases? I was recently
wondering what kind of temperature would be reached at 35 Kft
over Arctic Canada in January. It seemed that the lapse rate
equation would lead you to expect temperatures that would be
causing nitrogen and carbon dioxide to be condensing which
doesn't seem likely.

A few years back, my (then) 4th grade son did his science fair project on how
temperature changes with altitude. Over the course of a year, and
probably a dozen or more family flights, he measured the OAT as a function
of altitude during our climb-outs and descents. He got data from sea level
up to 14,000. Amazingly enough, it averaged out to almost exactly
2 deg C/1000'. He noted that the greatest deviations from that occurred
very close to the ground (within 2000' AGL) and when we were in clouds (IMC).

Now, our Cherokee 6 can't climb up to FL 350, so I have no personal
experience with how high the standard lapse rate holds. However, my son
will tell you that for a clear day, above 2000' AGL, it seems to hold
very very well.

Oh....and he got first place for his science project. I couldn't be a
prouder pilot-papa.

-- Dane