Decent into Cleveland

This is an interesting discussion. I wonder if there might be some mixing
of terms that is adding to the confusion. Let's see if we can agree on a
few basics and take it from there.

The dominant part of the sun's emissions that supplies heating to the earth
is in the infrared end of the spectrum. While there are materials that
approach being 100% IR transmissive, water is not one of them. IR is
quickly absorbed in water. This is evidenced by the spectrum of light
present as water thickness is increased. For example, the deeper part of a
swimming pool appears bluer than the shallow part because the sun's light
has transition through more water, 2 x the depth, before reaching our eyes.
The deeper the water, the bluer and darker it looks (provided the water is
clear).

Does a cloud absorb IR radiation? Well, it's made up of water and water
absorbs IR. The answer is yes, clouds absorb IR radiation. If you have any
doubt, think of being outside on a hot day and what happens to the heat you
feel from the sun when a cloud passes overhead. The heat on your skin from
the sun drops significantly if the there is any thickness to the cloud.

This does not refute the thermal satellite imagery in any way. The
satellite imagery shows IR emissions. The earth's surface is much warmer
than the cloud tops and the earth has pretty high IR emissivity. It
registers as warmer due to its higher IR emissions.

Temperature vs altitude within clouds is a different matter and is affected
by several factors, some of which, like convective cooling, may overwhelm
the others.

Just another 2 cents into the discussion.

JimC

"Bob Gardner" wrote in message
news:54Ihb.536556$cF.207547@rwcrnsc53...
Here's another picture to look at:

http://www.nws.noaa.gov/sat_tab.html

Bob Gardner

"john cop" wrote in message
om...
"Bob Gardner" wrote in message
news:GwAhb.535167$cF.206989@rwcrnsc53...
Look at any text on the atmosphere and you will learn that temperature
decreases with altitude, cloud cover not withstanding (absent an
inversion).
The sun does not heat clouds.

Look, I am no atmospheric expert, but the above is just a plain silly
statement (less charitable types might say stupid). What do you think
happens to all that energy? It ALL get reflected back into space?

Clouds, which you should know even from just from watching the weather
on TV, are insulators of sorts. This means that the sun's energy (the
part that doesn't get reflected) get absorbed by the cloud as it is
transmitted through it. If were an ideal insulating situation, the
temp gradation would be linear, but, obviously, its not (gas laws and
all that), but the principle is the same. My bet is the energy
transfer to the clouds is greatest at the tops and reduces with
altitude according to some unknowable (too many variables) function.
If your statement were correct, the temp at the tops would be the same
during the day as during the night which is, I think, silly. This
does not mean the temp is going to rise as you climb (gas laws again).
What is does mean is that the cloud's capacity to absorb moisture (or
supper cooled stuff) very near the tops could be substantially greater
than near the bottoms.

Thank you. Makes sense.

In my little experience, the icing was ferocious within, in seemed,
the top 10 ft of the cloud (it was probably more like 100 to 500 but
who knows – it was 20 years ago and I wasn't taking notes at the
time). I always assumed that it was the sun heating the vapor,
droplets, whatever, and forcing them to a higher altitude so they were
a very nearly at their super cooled limit. The dividing line between
ferocious and minimal icing conditions was sharp and very pronounced
during the decent which suggested to me, that sun heating (energy
transfer, if you prefer) was the cause or at least a significant
contributing factor.

In your description of the weather it sounds as though the tops were
increasing in altitude. That suggests lifting agents, e.g. a front or
convective activity, were present. With air movement of that variety it
isn't likely that IR radiation absorption would be able to generate a
stratified effect like you describe. It's more likely that the moisture
near the top was the coldest from convective cooling and was therefore able
to generate the most ice. As you descended you probably encountered
increasing temps, resulting in reduced icing.

Just an educated guess.

JimC

"john cop" wrote in message
om...
Thank you. Makes sense.

In my little experience, the icing was ferocious within, in seemed,
the top 10 ft of the cloud (it was probably more like 100 to 500 but
who knows - it was 20 years ago and I wasn't taking notes at the
time). I always assumed that it was the sun heating the vapor,
droplets, whatever, and forcing them to a higher altitude so they were
a very nearly at their super cooled limit. The dividing line between
ferocious and minimal icing conditions was sharp and very pronounced
during the decent which suggested to me, that sun heating (energy
transfer, if you prefer) was the cause or at least a significant
contributing factor.

I don't have "little experience" flying in icing conditions...I have a lot
of experience flying pistons, turboprops, and jets in an area of the country
so prone to icing (on the west slopes of the Cascades) that the Concorde was
sent out here for icing certification...I flew media folks to Grant County
airport for the occasion.

A good source of information would be Dr. Marcia Politovich at the National
Center for Atmospheric Research in Boulder, Colorado ).
She is known in the aviation meteorology community as the Ice Queen, and has
lots of experience flying in icing research airplanes....but then again you
are not impressed by credentials.

Bob Gardner

"john cop" wrote in message
om...
Thank you. Makes sense.

In my little experience, the icing was ferocious within, in seemed,
the top 10 ft of the cloud (it was probably more like 100 to 500 but
who knows - it was 20 years ago and I wasn't taking notes at the
time). I always assumed that it was the sun heating the vapor,
droplets, whatever, and forcing them to a higher altitude so they were
a very nearly at their super cooled limit. The dividing line between
ferocious and minimal icing conditions was sharp and very pronounced
during the decent which suggested to me, that sun heating (energy
transfer, if you prefer) was the cause or at least a significant
contributing factor.

john cop wrote:
Thank you. Makes sense.

In my little experience, the icing was ferocious within, in seemed,
the top 10 ft of the cloud (it was probably more like 100 to 500 but
who knows – it was 20 years ago and I wasn't taking notes at the
time). I always assumed that it was the sun heating the vapor,
droplets, whatever, and forcing them to a higher altitude so they were
a very nearly at their super cooled limit. The dividing line between
ferocious and minimal icing conditions was sharp and very pronounced
during the decent which suggested to me, that sun heating (energy
transfer, if you prefer) was the cause or at least a significant
contributing factor.

The reason that the top portion of a cloud may produce the most icing...
is that the cloud's formation process has resulted in the most liquid
water near the top.

The formation of most clouds is the result of lift, and as air lifts it
cools at a very substantial rate. When the dewpoint is reached, the
condensation occurs. As the air lifts more, the air becomes colder and
has less capability to support water vapour... hence more
condensation. If the air near the top of the cloud was lifted the
furthest, then that is the air where the most liquid has been condensed.

The fact that the sun may heat the top of the cloud a little, actually
works against icing. By raising the temperature slightly, the air can
support more vapour, and some of the liquid will evaporate.



--
God grant me the serenity to accept the things I cannot change, the
courage to change the things I can, and the wisdom to know the difference.
--- Serenity Prayer

"Icebound" wrote in message
ble.rogers.com...

snip
The fact that the sun may heat the top of the cloud a little, actually
works against icing. By raising the temperature slightly, the air can
support more vapour, and some of the liquid will evaporate.

Liquid evaporating making cold.

A cloud can absorb energy without gaining temperature.