flying into snow showers without deice

Matt Whiting wrote:

So, part of the flake is still below freezing and
part is above.

Is that really possible?

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Peter







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So, part of the flake is still below freezing and
part is above.

Is that really possible?

Of course it is. It just doesn't represent a snowflake at
equilibrium. I don't think snowflakes that are beginning to melt, and
then get rammed by an airplane wing and blasted by hundred mile an
hour freezing cold air can be expected to be at equilibrium.

Do that to me and I will =certainly= lose my equilibrium!

Jose
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Peter R. wrote:

Matt Whiting wrote:


So, part of the flake is still below freezing and
part is above.


Is that really possible?


Sure, just as it is possible for water to be below 32F and not frozen.


Matt

It goes the other way. You would have to take quite a bit of energy out of
the partially melted snowflake to refreeze it. Snow is fully crystalized.
If it is melting than the temp has to be above freezing. It the temp is
above freezing then nothing can stick. It is impossible for snow freeze
onto an airplane above 0C SAT. The temp must be below freezing and the
stuff sticking to your wing is almost certainly supercolled water from cloud
droplets.

By the time snow is melting the energy is above that required to refreeze it
and if the temp is above 0C then the energy of the snow flake is increasing
and it continues to melt.

Mike
MU-2


"Matt Whiting" wrote in message
...
Mike Rapoport wrote:
From a strictly theoretical viewpoint it is diffucult to see how snow can
be both melting (implying temp0C) and freezing to the wing (implying
temp 0C) at the same time. NASA studies have never be able to create
icing above 0C.

I can't explain it, but I've seen it happen enough to know that it does.
I'll venture a guess that it is due to the fact that not all of the
snowflake is melted. So, part of the flake is still below freezing and
part is above. Mash it against the wing at 150 MPH and the energy may
well equalize fairly quickly causing freezing of what was water a moment
before. Could well be similar to the way super cooled droplets work. They
are below freezing, but still liquid. Yet the slightest impact and they
freeze instantly.


Matt

"Matt Whiting" wrote in message
...
Peter R. wrote:

Matt Whiting wrote:


So, part of the flake is still below freezing and part is above.


Is that really possible?

Sure, just as it is possible for water to be below 32F and not frozen.


Matt

No. The difference is that the snowflake is *melting*. If you cool water,
it will go below 0C before freezing but ice will *not* melt below 0C (at
normal pressures).

Mike
MU-2

No. The difference is that the snowflake is *melting*.

Well, suppose the snowflake passed through some warmer air and then
some cooler air. It would start to melt, then start to refreeze. The
outer portion of the snowflake might be freezing while the inner part
is still melting. Then this aluminum thing whips into it at a hundred
knots, and the gentle breeze it was falling through becomes a gale.

Jose
--
Nothing is more powerful than a commercial interest.
for Email, make the obvious change in the address.

He said that the snow was melting. Anyway once crystalization is started
you don't have supercooled water. The supercooled water rapidly crystalizes
which releases heat and the temp reaches 0C.

Mike
MU-2


"Jose" wrote in message
. com...
No. The difference is that the snowflake is *melting*.

Well, suppose the snowflake passed through some warmer air and then some
cooler air. It would start to melt, then start to refreeze. The outer
portion of the snowflake might be freezing while the inner part is still
melting. Then this aluminum thing whips into it at a hundred knots, and
the gentle breeze it was falling through becomes a gale.

Jose
--
Nothing is more powerful than a commercial interest.
for Email, make the obvious change in the address.

Mike Rapoport wrote:

It goes the other way. You would have to take quite a bit of energy out of
the partially melted snowflake to refreeze it. Snow is fully crystalized.
If it is melting than the temp has to be above freezing. It the temp is
above freezing then nothing can stick. It is impossible for snow freeze
onto an airplane above 0C SAT. The temp must be below freezing and the
stuff sticking to your wing is almost certainly supercolled water from cloud
droplets.

Yes, I agree and didn't say anything different. My point was it may be
possible that the frozen part of the flake could absorb enough energy
from the liquid part to partially refreeze it.

I don't agree that nothing can stick above freezing. Snow will stick to
a wet surface much easier than a dry surface. If the wing is damp from
the wet snow, it may well attract "dry" snow that is impinging.

As I said earlier, I make no claim to have an explanation for this.
I've simply observed it many times in winter in PA. You can believe it
or not, your choice.


Matt

Mike Rapoport wrote:

"Matt Whiting" wrote in message
...

Peter R. wrote:


Matt Whiting wrote:



So, part of the flake is still below freezing and part is above.


Is that really possible?

Sure, just as it is possible for water to be below 32F and not frozen.


Matt


No. The difference is that the snowflake is *melting*. If you cool water,
it will go below 0C before freezing but ice will *not* melt below 0C (at
normal pressures).

I never said it would melt below 0C. I said it is possible that the
frozen part of the flake could absorb enough energy from the liquid part
to refreeze it.

Did you ever put ice in a glass and then add some water and have the ice
cubes bond together? Same idea. If you don't believe that ice can
extract enough energy from water to refreeze it, how do you explain this?

Keep in mind that ice doesn't have to be at 0C. The temperature of ice
can be much lower than 0C and thus it can absorb a fair bit of energy
from its surroundings before melting.


Matt

Mike Rapoport wrote:

He said that the snow was melting. Anyway once crystalization is started
you don't have supercooled water. The supercooled water rapidly crystalizes
which releases heat and the temp reaches 0C.

I never said there was supercooled water in the snowflake. Read again
what I wrote. I only mentioned supercooling as an example of things
happening that aren't always intuitive. Something happens in wet snow
that causes it to occasionally stick to the airfame. This isn't
intuitive, but it happens. That was the point.


Matt